JBarrowNews

Electric Motor Primer

2011-06-29T08:09:00.000-07:00

Aaon has published an electric motor primer that discussed the differences between AC, DC and ECM motors. It is a useful resource for engineers who want to optimize their choice of motors in the products they select and specify.

This document can be found here.

Greening RTU's: Aaon High Efficiency Units

2010-08-25T06:04:00.000-07:00

Today's codes and customers are demanding higher and higher efficiencies from their units. And Aaon has been continually improving their product offering to stay one step ahead of the curve. Not only do they offer energy-saving features like heat recovery, foam core panel construction, digital scrolls and the best RTU economizers on the market, but they also offer industry-leading cooling efficiencies.

To help customers select the unit that is right for their project, Aaon has created this quick select guide that shows the available efficiency levels of their RTU products (Energy Star, ASHRAE 90.1, ASHRAE 189, CEE Tier 1 or CEE Tier II) for all of their units from 2 tons to 70 tons.

See what else Aaon is doing to revolutionize the efficiency of rooftop units at our Greening RTU's section of this blog!

Smardt Displaying at 28th West Coast EMC Show, June 15-16

2010-06-10T08:01:00.000-07:00

Smardt is bringing their high-efficiency chillers to Seattle to show in the upcoming 28th West Coast Energy Management Congress Expo. Come see the industry leading oil-free compressor chillers and chiller controls systems first hand!

Exposition Hours:

Tuesday, June 15, 2010: 10:00 AM to 4:00 PM
Wednesday, June 16, 2010: 10:00 AM to 2:00 PM

Free tickets to the expo are available here.

The show will highlight energy efficiency products and programs and is supported by local utilities, industry organizations and local industry. It should be a very informative and exciting show, and it is conveniently located at the Washington State Convention and Trade Center in downtown Seattle.

See you there!

Aaon Completes Conversion to Foam Core Construction with Announcement of New RQ

2010-04-30T05:39:00.001-07:00

A few years back, Aaon made a committment to convert all of their air handling products to high-performance foam core panels. With the introduction of the new RQ rooftop unit (1-6 tons) this conversion is complete!

We've mentioned the many benefits of the foam core technology before, but it is worthwhile to revisit the subject to understand how much better this R-13 double-wall cabinet is than the standard single wall R-1 to R-3 batt insulation cabinet design in the industry. This detailed report on the performance of the foam core panel shows that in Seattle's environment, as much as 20% energy savings can be realized just from the better thermal performance and low leakage of this design.

But the RQ is not just better because of its high-performance cabinet. This product also makes available all of the energy saving advantages of the larger AAON RN product, like:

Digital scroll compressors

True Variable-Air-Volume Performance

Integrated, high-reliability economizers

Heat Recovery

Heat Pump Operation

Ground Loop Operation

Direct Drive Plenum Fans

And offers a new energy savings feature: ECM Fans!

And while SEER's are of relatively small importance to the overall efficiency of a rooftop system in a heating dominated climate like Seattle's, the RQ boasts SEER's that are in line with CEE's Tier 1 and Tier 2 efficiency levels

With the introduction of the RQ, Aaon has set a completely new standard in energy efficient rooftop air conditioning systems.

Energy Labs Announces IBC 2006 Seismic Certification

2010-02-17T16:57:00.000-08:00

Energy Labs Air Handling units have received IBC 2000, 2003, 2006 and 2009 seismic certification.

The certificate of compliance qualifies the company’s Air Handling Units for use in building structures wherever seismically rated equipment should be considered.

Air Handling Units play a critical role in maintaining the building environment and making them functional. Seismically Certified Air Handling Unit equipment is required in the 50 states that have adopted the IBC code.

Air handling Units must not only survive earthquakes, the intent of the IBC is to encourage manufacturers to create equipment that remains online and functioning during and after a catastrophic event in order to provide critical life–safety support.

Applications where seismically certified equipment should be considered include hospitals, healthcare facilities; fire, rescue and police stations; emergency shelters; telecommunications centers; power plants; air traffic control centers; military and government buildings; and water treatment facilities.

To qualify for seismic certification, Energy Labs Air handling Units were tested by the VMC Group, an ICC–approved, independent approval agency. All tests were done in accordance with IBC 2000, 2003 and 2006 Section 1707.7.2 and Section 1708.5.
Energy labs certified equipment will have a certificate and label in a clear, viewable location to assure the customer that this equipment qualifies for seismic locations.

When should you specify this certification? Energy Labs has created a quick slideshow to help illustrate the requirements of the code.

How should you specify this requirement? These suggested specifications from Energy Labs should help.

Greening Small Rooftop Package Units: Foam Core Panels in Depth

2009-07-20T05:17:00.000-07:00

A while back, I summarized the benefits of foam core panels in comparison to the industry standard of fiberglass batt insulation.

Now Aaon has published an in-depth, seventeen page study of the benefits of the foam core panel.

Foam core panels have many advantages over standard insulation:

Superior R-value
No thermal breaks
Greater Rigidity
Lower leakage
Stronger damage resistance

This new study calculates the effect of these advantages over the course of a year, in heating and cooling, for buildings in Atlanta, Chicago, Houston, Los Angeles, Miami, Minneapolis, New York, Seattle and Tulsa.

This study quantifies the benefit of this advanced cabinet construction to assist engineers and owners asses the benefit of demanding higher performance out of their roof top systems.

White Rust: What it is, and How to Protect Your Project

2009-03-31T10:01:00.000-07:00

What is "white rust"? Well, while it is white, it really isn't 'rust' in the normal sense of iron-oxidization. White rust is instead a corrosion product of zinc oxidization that often strikes galvanized surfaces subjected to moisture. In our industry, the most common victims of this corrosion mechanism are cooling towers and fluid coolers. And in these products, white rust can cause thousands of dollars of damage in a relatively short period of time.

White rust damages equipment by allowing a rapid and localized corrosion of the protective zinc coating on galvanized surfaces. Normally, in a galvanized surface, the zinc protects the underlying steel by providing a sacrificial cathodic protection to small areas of exposed steel, and provides bulk protection by providing a durable protective inert zinc oxide coating to prevent exposure of the underlying steel.

In white rust, however, this normal oxidation of the zinc surface goes wrong, and instead of providing a durable dull-gray surface, a porous, powdery or waxy oxide is produced instead. This corrosion product allows a rapid removal of the protective zinc surface--made worse in that the corrosion is generally localized in 'cells' which cause a very quick penetration of the zinc surface, exposing the underlying steel in a pitting process.

In recent years, the incidence of white rust has increased dramatically, leading the industry to study the process in greater depth. The Association of Water Technologies has produced an informative paper (pdf) that investigates the reasons for this increase (essentially changes in the methods used to produce galvanized sheet metal and water treatment methods) and how to prevent its occurrence.

Generally, white rust is more prevalent in soft water areas, which makes it a big problem in the Pacific Northwest. Preventing it entails both design and operational considerations.

White Rust Cells in Basin of Tower

If galvanized surfaces are used in your tower, it is critical that the tower be subjected to a 'passivation' treatment. This is a temporary water treatment regimen in the first few weeks of tower operation that acts to ensure the development of a desirable zinc oxide surface. Evapco discusses this process in this engineering bulletin. If Evapco's non-chemical Pulse~Pure product is provided, passivation is be included in the first year service that is provided with all installations. It is critical that this be performed immediately upon filling the tower with water--if water is left in the tower untreated for a period of time before the passivation treatment begins, white rust cells can develop in the interim. This is a very common cause of white rust corrosion in otherwise well-treated towers.

The other method to avoid problems with white rust in your tower installations is simply to chose your materials of construction wisely. In cooling towers, the most critical portion of the system is the basin--white rust can cause a rapid pinhole leak through the basin of a galvanized basin that would require immediate refurbishment. Providing a 304 ss basin is a very economical way to avoid costly system renovation at a future date. For areas with high chlorides, or when using water treatment methods that operate at high cycles of concentration (thus increasing the low chloride content of the utility water to dangerous levels) 316 ss is also available. Of course, the entire tower can also be constructed from these corrosion-resistant materials if desired.

In fluid coolers, however, the coil is an additional problem area. White rust on this galvanized component can rapidly lead to perforation of the closed-loop side of the system causing loss of cooling water and/or glycol coolant into the open loop side of the system. This can be a triple-threat due to the economic loss of glycol and water, an increased threat of freeze up, and huge water-quality problems due to bacterial growth and plasticization due to glycol exposure in the open side of the cooler.

Plasticized Bacteria/Glycol Slime: Yuck

The coil in your fluid cooler is the single most expensive component in it, by a large margin. And replacing coils can be an extremely costly proposition, especially in coolers without easy access to the coil section.

Until recently, there hasn't been a lot of choice for protection of this critical component of the system. Other than selecting a tower, like Evapco's highly efficient ESWA fluid cooler, that provides easy coil access for coil replacement, the usual option was to ensure a thorough passivation program. However, Evapco has now introduced 304 SS fluid cooler coils to protect your project's investment in this costly and critical component.

White rust is a problem that can cause great economic losses for building owners and operators. Thus it is critical that designers and contractors are aware of the prudent requirements necessary to prevent this damage. But with simple precautions, namely requiring a passivation program or wisely selecting materials of construction, this problem can be avoided in your projects.

::::::::::::::

But what if it's too late, and you already have white rust on your tower? Well, there are an array of options, including attempting to re-passivate the galvanized surfaces or a full refurbishment of the basin using a polymer coating like Evapco's Evapliner. The helpful people at Fluid-Tek would be happy to help you determine the best course of action for your project.

Fan Matrix White Paper

2009-03-01T09:11:00.000-08:00

In a previous post I discussed the advantages of the Climate Craft Matrix fan array system.

Climate Craft has now published a white paper that explores these advantages in more depth.

This paper discusses applications and advantages of this system, including:

VFD Considerations and Electrical Requirements
Sound and Efficiency Considerations
Vibration
Space Considerations
Reliability
Serviceability
Fan Isolation (Backdraft Dampers)
Cost
Common Options

This white paper is well worth review and will help designers and owners evaluate the best applications and advantages of this fan innovation.

LEED™ and Pulsed-Power Water Treatment

2009-03-01T08:30:00.000-08:00

Pulsed-power water treatment offers many advantages to designers of sustainable systems.

First, it eliminates the use of industrially produced chemicals and their subsequent release into the environment. Secondly, it provides superior control of scale and biological growth, both of which negatively affect the efficiency of systems utilizing treated condenser water. Pulsed-power water treatment also allows safe operation at high cycles of concentration in the condenser water which acts to reduce the use of our limited water resources.

But there are other ways in which Pulsed-power water treatment can contribute to the sustainability of your project--and these can often lead to opportunities to gain LEED™ points.

Evapco has developed their Pulse~Pure pulsed-power water treatment system in an effort to minimize the impact of our engineered systems on the environment. They have also provided a handy guide to attaining credit for this reduced impact through attaining points through the LEED™ program:

If you are considering a sustainable project where condenser water systems are to be used, it is well worth the effort to see if pulsed-power water treatment fits into your goals.

Johnson-Barrow/Fluid-Tek support Leukemia Research

2009-02-23T13:56:00.000-08:00

Johnson-Barrow/Fluid-Tek are participating in this year's "Big Climb Seattle" on March 22nd, 2009.

This is a stair walk (or run) up 69 flights of stairs in the Columbia Center building. That's 1,311 steps total, with an elevation gain of 788 feet!

Our "Go Green" team is currently soliciting donations to meet our team goal. If you think this is a worthy cause, please click on the link above and click on the team member whose totals you wish to add to.

If you use this website and find it has useful information, I would consider a donation in the name of Rand Conger to be a fitting thank-you. If you think the whole idea is a good one, I might suggest donating in Angela Lambert's name, since she was the one who coerced all of us into this....

Please consider donating to this cause. Help the "Go Green" team reach their 'lofty' goals!

(Or, even better, JOIN team "Go Green"!)

That's a long way up (gulp!)

Ultra-Low Sound Air-Cooled Chillers

2009-01-15T05:15:00.000-08:00

Air-cooled chillers provide significant advantages for many facility operators and owners. The elimination of a cooling tower greatly reduces the complexity of the system and significantly eases the maintenance of the system. For smaller facilities without the resources of large institutional owners, this reduced maintenance can be critical.

Therefore it is very common to see air-cooled chillers on smaller facilities such as public schools and small office buildings. However, this suitability does carry with it some costs--Air-cooled chillers are usually significantly less efficient than water-cooled chillers and, now with the advent of super-low sound cooling towers, often much noisier. The noise problem can be very significant with this sort of equipment in that a large proportion of the facilities that utilize this technology are located near or in residential areas.

In an earlier post I discussed how the Smardt air-cooled Turbocor chillers significantly change the balance between water-cooled and air-cooled chillers with respect to efficiency and sound. However, it is worth investigating the sound issue in more depth.

Recently, manufacturers have spent some effort in addressing the sound issue on their air-cooled chillers. This has generally been approached by providing low sound fans and addressing the compressor noise. Two products that are currently being marketed as low-sound chillers approach compressor sound in different ways. One product utilizes screw compressors with a VSD to reduce compressor sound at low loads. Another utilizes scroll compressors with elaborate compressor sound enclosures. This approach yields published sound data which is excellent at all chiller load conditions. Until recently, this chiller has been considered by many engineers to be the quietest air-cooled chiller n the market.

The Smardt chiller, of course, uses the extremely low-sound Turbocor compressor, and variable-speed ultra-low sound fans. It is reasonable to believe that this combination would make for a very favorable comparisons with these other low-sound chiller options.

And this expectation is borne out by the data. Smardt air-cooled chillers compare extremely favorably against the variable speed screw chillers as this graph illustrates:

Two things should be noted: First, the comparison here is between a 177 ton screw and a 200 ton Smardt chiller, and second that even at 100% load, the Smardt chiller is far quieter than the screw at 25% load. The difference is even more significant in the lower octave bands that carry so well over distance.

Comparing the Smardt Chiller to the acoustically treated scroll chiller also yields an extremely favorable comparison:

This comparison of 120 ton chillers shows that while both approaches yield extremely low sound levels overall, the Smardt chiller beats the competitor in 5 of 8 octave bands. And the advantage for the competitor in two of the other bands is slight. It also shows the significant effect of A-weighting sound data. In this graph, the red line represents the published sound data from the manufacturer. Close reading of this data indicates that it is not bare sound power, but A-weighted sound power. This method of reporting sound data takes very significant credits into effect, especially in the lower octave bands:

Octave band center frequency (hz)	Weighting
31.5	-39
63	-26
125	-16
250	-9
500	-3
1k	0
2k	1
4k	1
8k	-1

The dark blue data show the raw, uncorrected sound data for this chiller.

If acoustics are a design consideration for your air-cooled chiller product, Smardt offers a solution that is unmatched in the industry.

Extra: Audio Comparison of compressor noise

85 dBA screw compressor
73 dBA Turbocor compressor

Both measured at 1.0 m away from compressor. Your speaker volume will affect the output, but the comparison should be clear if the volume is not adjusted between clips.

Extra extra:

This link has sound files that illustrate the amplitude of a decibel, to give perspective to the graphs above.

EPA proposes tighter R-22 Refrigerant Regulations

2009-01-13T16:05:00.000-08:00

In a move that could significantly affect the application of R-22 in the HVAC marketplace, the Environmental Protection Agency has proposed new rules on the Phase-out of R-22. These rules affect both the allocation of R-22 production and the installation of these products. According to an article in ACHR News:

The proposed “Adjustments to the Allowance System for Controlling HCFC Production, Import, and Export” appears to allow to EPA to go beyond the 75 percent target effective Jan. 1, 2010. The ruling also provides production allocations for various refrigerant manufacturers, ending some uncertainty in that matter.

The proposed “Ban on Sale or Distribution of Pre-Charged Appliances” says that as of Jan. 1, 2010 it will be illegal to import, produce, or sell R-22 for use in new equipment or pre-charged into such equipment. In effect, the ruling appears to say that if a contractor buys a product as of Jan. 1, 2010 that needs R-22, the charging would have to be done with existing recovered, recycled, and/or reclaimed R-22 — or R-22 alternatives — rather than virgin R-22.

These changes are significant and are detailed in depth in the AHRI summary comments of these changes.

There as a public comment period for each of these rules. EPA will accept comments until February 6, 2009 for the pre-charged rule and March 9, 2009 for the allocation rule.

Cautious owners and engineers would be wise to strongly consider making a complete switch to the HFC alternates readily available today, R-410a being the most likely option.

Tax Breaks for Ground Loop Systems

2009-01-12T16:36:00.000-08:00

With the signing of The Emergency Economic Stabilization Act of 2008, H.R. 1424, the Federal Government has put their money where their mouth is and have acted to make geothermal heat pump systems a more attractive HVAC alternative.

Commercial geothermal heat pump installations now qualify for a 10% tax credit, with no cap on the credited expenditures!

For commercial installations, an ITC is provided for geothermal heat pumps equal to 10 percent of the expenditures, including allocable labor costs for facilities placed in service after October 3, 2008. There is no cap on the amount of expenditures which can be used for the credit (and no cap on the credit itself). In addition, geothermal heat pumps are eligible for Modified Accelerated Cost-Recovery which provides for depreciation over 5 years. The credit is determined by the cost of the system. However, if the equipment is financed by any subsidy program (federal, state or local) or with tax-exempt bond, the basis of the equipment must be reduced by the amount of the subsidy. Contrary to the residential credit, on commercial applications the units do not need to be Energy Star rated to apply. To collect this credit, the taxpayer would need to complete IRS Form 3468. The form will need revision by the IRS to reflect the addition of geothermal heat pumps.

Every little bit helps to get these highly-efficient systems to pencil out. Uncle Sam has lent a hand to owners and designers who wish to utilize this exciting technology!

Aaon Fan Engineering White Paper

2008-12-26T12:07:00.000-08:00

Aaon has pushed the envelope of packaged rooftop unit design by providing a wide selection of fan types in their systems, including forward curved housed centrifugals, backward inclined un-housed centrifugals (plenum fans) and axial fans. And, for their larger units, they have generally moved towards direct-driven plenum fans for supply air in arrays as best fits the application. This move has not been random, but is based upon solid engineering reasoning based on the inherent stability and efficiency of these types of fans. The newly published Aaon white paper, Value in the Air provides a thorough justification for this emphasis on direct-drive plenum fans. But in doing so, it also provides an excellent primer on general fan engineering topics including overloading vs. non-overloading fan curves, fan stability in single and dual fan applications, fan control for VAV systems, and the overall energy impact of fans on our HVAC systems. It is an excellent resource and one that engineers should review to enhance their understanding of fan systems.

Greening Small Rooftop Units: Digital Scrolls

2008-12-24T07:53:00.000-08:00

Digital scroll compressors offer many benefits to compressorized HVAC equipment, as I have discussed in previous articles. Some of these advantages are obvious, and need little computational support--like the modulating capacity control.

Others, however, could use some numerical support to quantify the advantages they confer. The efficiency advantage these compressors confer is one of these sorts of advantages. While it is easy to conceptually understand how this technology can improve efficiency of compressorized units, how much of an advantage this is depends on a myriad of factors, including the capacity of the unit, the operating schedule of the system, the climactic conditions the system experiences and the application of the system.

The energy advantage will change depending on whether the system operates seven days a week or five, whether the system has multiple or single compressors, whether the system is in Atlanta or Seattle, whether the system is VAV or constant volume and whether the system has hot-gas bypass or not.

Aaon realized that the complexity of this calculation made it difficult to quantify the advantage of this advanced feature. To make it easier to see the energy advantage, Aaon added a simple energy calculation tool to the Engineering Toolkit that they provide with their ECAT32 selection software.

After using the simple drop-down windows to select geographic location (by city), Aaon model number, 5 or 7 day schedule, 12 or 24 hour operation, Constant or VAV fan control you then can select the variable and constant capacity units to compare against each other. Options available include assigning hot gas bypass or not to the lead and/or lag compressors and variable speed or cycling fan control to the condenser fans. Once these options have been selected for both units, you simply hit the "calculate" button and the energy performance summary is generated.

This gives you the energy improvement conferred by the digital scroll as a percentage, and also in a comparative EER the constant capacity compressor system would have to be rated at in order for the energy performance of the two systems to be equal.

Further graphs allow you to examine the bin hours at a given OADB for the geographic location and operating schedule you specified,

and the relative energy performances of both systems at a given OADB.

A little playing around with the system allows a user to quickly find where the energy benefits are greatest. In general, the digital scroll confers the most benefit to single-compressor systems, and systems that require HGBP for constant-capacity compressors, such as VAV systems. The system also highlights the point that HGBP is a very expensive way to to capacity control, since the compressor draws full amps whenever it is running. It is the unique modulating capacity of digital scrolls that really makes a difference in these sorts of applications.

Heat your showers for FREE

2008-12-19T06:40:00.000-08:00

Earlier in this series of articles, I discussed using the waste heat in available on-site water-based sources to heat water. Essentially, you just add a water-to-water heat pump system that allows you to move a lot of heat to a useful function with the expenditure of just a little energy.

Wouldn't it be nice if you could do this sort of transfer of heat from a waste source to a useful function without requiring the addition of a compressorized system?

Well, in existing refrigeration systems, there already exists a source of heat that is usually of a temperature that can provide useful heating for a domestic hot water application without need for additional compressors: The compressor superheat.

In a refrigeration process, where cooling is the desired function of the compressorized system, this compressor superheat is essentially waste heat, and serves no useful purpose. It is simply thrown away to the environment through whatever heat rejection process the system employs. But this compressor superheat was put into the system by the energy used to run the compressor, and therefore was paid for once by the operator of the equipment. Instead of paying for it again in the operation of the heat rejection fan or cooling tower, why not instead use it for something, saving the heat rejection costs and reaping a real benefit?

It was this sort of thinking that prompted Florida Heat Pump to develop their HRP Heat Recovery Package (pdf). This is an add-on heat exchanger that transfers the compressor superheat directly into a domestic hot-water source--using double-walled heat exchangers to protect the potable system.

The heat from the desuperheater system provides supplemental heat to the domestic hot water system any time the compressor operates--in heating or in cooling. This can greatly reduce the amount of electric or gas heat required for water heating--even completely displacing this direct heating during many times of the year, depending on the building loads and use of the space.

(Note, however, that the compressor superheat is lost to the heat pump space heating process and therefore the space heating capacity of the heat pump will be reduced by the capacity of the desuperheater. As long as this is taken into account in the sizing of the heat pump, this presents no problem to operation.)

But water-source heat pumps represent only a small part of the compressorized systems that are exisiting or installed every year. It seems there is an opportunity for taking advantage of this same heat source on many other systems and on existing equipment, too.

That is where the Heat Harvester Heat Recovery System can be used to great effect. This heat recovery system is a stand-alone desuperheating device that is pre-designed for various compressor system capacities and is available for retrofit on existing or new systems.

How much heating potential is there? Well, Heat Harvester has provided an interesting analysis of the desuperheat capacities of compressorized systems:

Size of Air Conditioning System tons	Gallons of Hot Water per Hour	Gallons of Hot Water per Day
3	15-to-25	180-to-300
5	25-to-40	300-to-480
10	50-to-80	600-to-960
20	100-to-160	1200-to-1800
30	150-to-240	1800-to-2880

These systems can be economically installed into just about any compressorized systems using positive displacement compressors: Scroll and Screw air-cooled chillers, Rooftop packaged units, Condensing units, CRAC units, you name it. Since the Heat Harvester heat recovery system consists of a package with a heat exchanger and a pump, the installation basically involves a little refrigerant and water piping. And in a cooling-only application, all of the heat recovered would have otherwise been lost to the environment.

Ultimate Florida Heat Pump Cheat Sheet

2008-12-03T06:54:00.000-08:00

One of the difficulties our customers have with Florida Heat Pump is that their product offering is so wide, that it can sometimes get confusing: Which models have ECM motors? Which have scroll compressors and which have recip? What sound packages are available for a given model, etc...

So, in the interest of clarity and ease of use, we've pulled together all of this information into one convenient place: The Ultimate Florida Heat Pump Cheat Sheet

Presentations from JB 2008 Open House

2008-11-04T10:28:00.000-08:00

Due to a slew of interest, we have made the following presentation slides available for review.

All of the links below go to pdf files of the presentation, except for the Aggressive Building Energy Performance presentation which goes to the NBI website where similar presentations can be found.

Aggressive Building Energy Performance: Getting to 50 and Beyond. Mark Frankel, New Buildings Institute
PSE/SCL Energy incentive updates
Introduction to Variable-Refrigerant Flow Systems. Kim Olson, Sanyo
Introduction to Active Chilled Beams. Rand Conger, Johnson-Barrow

Click on the underlined words to link to the documents.

Thanks again for your interest and your participation!

More photos from the event can be found here.

Energy Code and Relief air in Rooftop Units

2008-11-03T06:14:00.000-08:00

In a warm building served by rooftop units in a cold ambient condition, air wants to do an unfortunate thing. Warm, less dense air tends to rise through the colder, denser air. If unchecked, this causes an air migration up through the ductwork, to the RTU and out into the environment, while cold air is infiltrated into the building to make up the vacated volume. This causes a loss of heating energy detrimental to the energy performance of the building.

If the rooftop unit is operating, this stack effect is usually more than overcome by the pressures developed by the fans. But when the unit is off, often the only thing preventing warm air from working its way up through the ductwork is the action of the unit dampers. Most units installed under the Seattle Energy code have an automatic OA damper associated with the economizer that can be driven closed. But the relief air path is a different story. Often, this air path is controlled with a simple gravity damper configured to relieve air when the building is under positive pressure, but to prevent air from entering while under negative pressure.

The problem with this arrangement is that it does nothing to prevent a stack effect from occurring when the unit is not operating. The damper will act to let warm air out, which is exactly what is what we would hope to avoid. To address thisl, the 2006 Seattle Energy code has a section that requires a positive-closing damper on all air openings on building air systems:

1412.4.1 Dampers: Outside air intakes, exhaust outlets and relief outlets serving conditioned spaces shall be equipped with motorized dampers which close automatically when the system is off or upon power failure. Stair shaft and elevator shaft smoke relief openings shall be equipped with normally open (fails open upon loss of power) dampers. These dampers shall remain closed until activated by the fire alarm system or other approved smoke detection system.
EXCEPTIONS:
Systems serving areas which require continuous operation.
Combustion air intakes.
Gravity (non-motorized) dampers are acceptable in systems with a design outdoor air intake or exhaust capacity of 300 cfm or less ~~buildings less than 3 stories in height~~.
~~Gravity (non-motorized dampers are acceptable in exhaust and relief outlets in the first story and levels below the first story of buildings three or more stories in height.~~ Reserved
Type 1 grease hoods exhaust.
Dampers installed to comply with this section, including dampers integral to HVAC equipment, shall have a maximum leakage rate when tested in accordance with AMCA Standard 500 of:
Motorized dampers: 10 cfm/ft² of damper area at 1.0 in. w.g.
Non-motorized dampers: 20 cfm/ft² of damper area at 1.0 in. w.g., except that for non-motorized dampers smaller than 24 inches in either dimension: 40 cfm/ft² of damper area at 1.0 in. w.g.
Dampers used as a component of packaged HVAC equipment shall comply with the damper leakage requirements, unless it is the lowest leakage available as a factory option. Drawings shall indicate compliance with this section.

This has caused some disruption in the rootop packaged unit market, because the option of providing automatically closing motorized dampers on all air openings on these sorts of units is not one that is easily available from most manufacturers.

Johnson-Barrow has worked with Aaon to provide an engineered option on most configurations of the Aaon RM and RN rooftop packaged line to meet this requirement.

So if you have a project where a packaged RTU is the right solution, there is a code-compliant option likely available from Aaon.

Open House: Where, When and How

2008-10-07T05:21:00.001-07:00

THURSDAY, OCTOBER 16th!

Details:

Where: 2001 22nd Ave S, Seattle WA, 10:00 AM to 6:00 PM

The open house will be located just down the street from the JB offices, about 5 blocks south of I-90, just off of Rainier Avenue in Seattle.

(click for active map, or click HERE)

Directions: Directions from your location can be found by clicking on on the active map above, then right-clicking on the open house location, selecting "Directions to" and typing in your starting address in the box provided! Parking is available.

Transit: Plan your trip Here (Use "2001 22nd Ave S" as the destination)

What:

Schedule of Presentations:

10:30 AM: Non-Chemical Water Treatment Case Studies. John Junk, Fluid-Tek
12:30 PM: Aggressive Building Energy Performance: Getting to 50 and Beyond. Mark Frankel, New Buildings Institute
1:45 PM: PSE/SCL Energy incentive updates
2:30 PM: Introduction to Variable-Refrigerant Flow Systems. Kim Olson, Sanyo
3:30 PM: Introduction to Active Chilled Beams. Rand Conger, Johnson-Barrow

Lunch provided at 11:30 AM to 1:30 PM

Refreshments provided 4:00 PM to 6:00 PM

Featured Products on site for your inpsection:

Climate Craft Matrix Air Handler

Evapco AT cooling tower with Super Low Sound Fan

Evapco Pulse~Pure non-chemical water treatment

Sanyo Mini-Splits

Dadanco Active Chilled Beams

Cerus Starters

And even MORE!

How:

Come throughout the day. Visit for as long or as short as you like

If you do plan to come, we would appreciate some feedback on when you think you will be here.

Please visit HERE to give us a quick RSVP. Thanks! (We'll still let you in if you don't)

Save the Date: October 16 JB Open House

2008-10-02T04:44:00.000-07:00

Johnson Barrow is pleased to announce an Open House, Thursday, October 16. Come 'kick the tires' of our products and attend talks on high-efficiency technology and design. We'll also provide lunch at noon and adult refreshments in the evening!

ClimateCraft Air Handler

Highlights:

Featured Presentation: Mark Frankel from the New Buildings Institute; "Aggressive Building Energy Performance: Getting to 50 and Beyond" 12:30 pm
Updates on local Utility rebate programs.
A full scale Demo unit of the Climate Craft MATRIX air handler
Evapco Pulse~Pure non-chemical water treatment device.
New product introduction: Sanyo ECO-i VRF systems
New product introduction: Dadanco active chilled beams

More details to follow. Watch your inbox!

Introduction to VRF systems

2008-10-02T03:41:00.000-07:00

Recently, there has been an Asian invasion of America.

Asian variable-speed heat split heat pump systems, that is.

While most engineers and contractors are familiar with the now-common ductless mini-split systems, these systems have a bigger cousin which can match multiple outdoor condensers with multiple indoor fan coils using variable speed compressor technology to greatly improve efficiency and add significant zoning flexibility to building designs.

Davis Watkins, Vice President of Applied Systems, Sanyo HVAC Solutions, recently wrote an introductory article for HVAC insider describing these systems, their applications and installation. He also debunks several myths about these systems that have caused concern in the past. It is well worth a read to understand how these systems provide better comfort control with great energy savings. A copy is locate here: Ductless Split System Technology: From Bonus Rooms to Commercial Buildings

Personally, I think one very strong argument for these systems can be summed up in a single graph:

This is a chart of the heating performance of the Sanyo ECO-i VRF system at low ambient conditions. Note that at as low as -4 deg F, the ECO-i VRF system still provideds 60% of the rated heating capacity without supplemental strip heat. Keep in mind that in a heat pump system the rated heating capacity is usually about 30% or so greater than the rated cooling capacity. In other words, you will get nearly 12 tons of heating out of a 12 ton cooling unit even in sub-zero weather!

If you are interested in reducing your carbon footprint, moving to a fully electric heat pump system makes sense in a primarily hydroelectric utility market--and even more so if you don't have to size your electrical service to provide redundant electric strip heat! Or, for that matter, pay for the energy required to provide that strip heat.

Another feature that highly recommends these systems is the capability to provide heat recovery while operating in simultaneous heating and cooling mode. A three-way Sanyo ECO-i system can operate much like a water-source heat pump system, re-using heat rejected from warm interior zones at perimeter zones that require heating. This inherent energy recapture ability allows the compressor in the outdoor unit to only have to work hard enough to transfer the difference in capacity between the two modes. If, on a given system, you have 7 tons of heating load and 4 tons of cooling load (11 tons, total) the compressor actually only sees 3 tons of load!

These advantages are above and beyond the already impressive efficiencies gained by the use of variable-speed compressors, and transferring heat and cooling energy with efficient refrigerant transfer instead of much less efficient air transfer. And, of course, these systems can offer great architectural advantages too: Lower floor to ceiling height, smaller spaces with independent comfort zones, very easy reconfiguration, etc.

It's no wonder these systems are gaining traction in a big way in the North American market.

Greg Nickels vows to DOUBLE Seattle Conservation Programs

2008-08-21T08:55:00.001-07:00

A recent article in the Seattle times indicates that the City of Seattle is getting serious about conservation:

Overlooking the Seahawks' field, Seattle City Light officials and Mayor Greg Nickels announced a $185 million plan Wednesday to double the city's energy conservation over five years -- an amount equal to the annual energy use of 180,000 Seattle homes.

The program, which targets residential and commercial electricity use, could save customers $310 million over that time.

"We are putting our conservation program on steroids," Nickels said.

The plan is available online at http://www.seattle.gov/light/conserve/docs/Conservation_5_Year_Action_Plan.pdf, and focuses on Lighting, HVAC, Industrial Processes and Data Centers.

Learn more about what this means to you and your business at http://www.seattle.gov/light/conserve/

Information on rebates, including spreadsheets to calculate rebates for common measures (VFD's, chillers, heat pumps, etc) is available at http://www.seattle.gov/light/Conserve/Business/cv4_ess.asp

Don't miss out on a great opportunity to fund your project and lower your operating costs at the same time!

Fan Engineering: Spark Resistance Ratings

2008-07-22T06:05:00.000-07:00

Every once in a while we will see a specification for "explosion proof" fans. While this may be a desirable characteristic, "explosion proof" is not a specifiable option, and usually is included because of confusion with electrical component (i.e. motors, disconnects) specifications.

Instead, fans are generally classified by "spark resistance". AMCA has created a standard that defines three different levels of spark resistance, classes A, B and C.

These classes, listed in decreasing order of assurance, are generally concerned with the prevention of sparks caused by the rubbing together of spark-producing metallic components (generally ferrous materials). These classes only address spark risks due to an explosive airstream, and do not address explosive conditions outside the fan. A summary of the different levels of protection is found in this helpful engineering paper from Twin City Fans.

Type C: The fan is designed so that if the impeller or shaft comes loose and shifts during operation, two ferrous parts will not come into contact.

Type B: In general, this requires a nonferrous impeller and a nonferrous rubbing ring around the shaft hole. Also, extra locking systems are required to prevent the fan impeller, shaft, and bearings from shifting.

Type A: This requires a nonferrous airstream. Also, the extra locking systems are required as in Type B.

As with any engineering decision, the correct level of spark resistance to specify depends strongly upon the particulars of the project: The gasses or substances expected, the concentration of these contaminants, the location of the air-moving device, etc.

Smarter Starters

2008-07-01T06:35:00.000-07:00

As anyone who has specified or supplied them on projects knows, motor starters can be a big headache. And despite the growth in the use of VFD's in today's energy conscious designs, motor starters still are used on about 60-70% of the motors provided in the industry. Typical problems can range from the very basic to the more involved. Some of the problems our customers report are:

Incorrect overload protection provided or heaters incorrectly sized
Incorrect control signal available on the site
Not enough BAS points to provide needed damper or valve interlocks

For the most part, starters are old technology. Cerus Industrial re-examined starters and found that a lot of benefit can be gained from re-working these components to take advantage of today's technology.

Cerus BAS Starter

Protecting The Motor

Besides starting the motor, the main function of a motor starter is to provide a measure of protection to the motor in case of an electrical malfunction. Typically, this protection is provided by means of an overload protection in the starter that trips power in case the motor pulls more amps than it is safely rated for. Traditionally, this has been provided by means of small heater elements that are rated for the motor FLA. These are interchangeable and different motor operating conditions will require different heaters.

In practice, these heaters can be problematic--Essentially, they must be sized correctly for the operating amps of the motor, and this may or may not be known at the time they are purchased. Many things can change a motor duty point from the design to the installation: product substitution, air or water balancing, changes to the design, etc. And since these heaters have very small operating ranges, even a small change in any of these criteria can result in a heater change. In fact, replacing starter heaters are one of the most commonly reported change orders.

Adjustable thermal overloads have been developed to allow a greater amp range for a starter overload protection, but the biggest ranges available are provided via solid state overloads. Solid state overloads typically provide about a 5:1 amperage adjustment (from 1A to 5A, or 4.4A to 22A in two typical sizes). This essentially allows a single overload device to protect any motor that would reasonably be started by a given contactor, meaning that starters equipped with solid state overloads will always have the right overload protection for the motor they are starting. And solid state overloads add phase loss protection, giving your equipment even better security.

Cerus has standardized on solid state overloads for their HVAC starter line, to greatly simplify the process of selecting the correct starter and to avoid last-minute trips to the electrical supply house to get the right overload protection.

Communications

Almost all available starters use 120v relays to communicate with building controls. However, almost all available building operating systems use 24v power for their signals. This means that in order to provide a control signal to the starter from the BAS, interposing relays are required to convert the 24v signal to a 120v signal. These relays are usually field wired, and therefore add complexity and field labor costs to the installation of motor starters.

Cerus has greatly simplified the interface between the BAS and their starters.

All of their standard starters have a terminal strip that can accept a 120vac, 24vac or 24vdc signal directly. The terminal is self-calibrating, and will adjust to whatever signal is provided automatically, greatly simplifying field wiring. In addition, this terminal strip has a terminal that will accept a dry contact, if that is the preferred method of control.

But even greater communication flexibility is provided in Cerus' new line of BACnet enabled starters. Integrating BACnet allows direct communication with the BAS system via a single network connection. The BAS system can provide start/stop signals, interlocked damper control, receive proof of flow via current sensing, monitor the runtime and HOA position remotely, detect phase failure or phase loss, and enact fireman's overrides or emergency shutdowns. These starters provide unequaled ease of use and troubleshooting capabilities and require the absolute minimum in field labor to accomplish this.

BACnet points matrix

Simplified Interlocks

Many fan systems have control dampers that are intended to close when the fan is not operating. These dampers can serve to isolate a single fan in a multiple fan array, or may serve to prevent undesired airflow when the fan is not operating. However, these sorts of systems present a problem--The damper must be opened before the fan is turned on in order to prevent overpressurization of the ductwork. This is typically is handled by the BAS sending a signal to open the damper, having and endswitch on the damper send a signal back to the BAS to indicate that it is open, and then having the BAS send a signal to start the fan. This requires three control points on a BAS controller. Often, these control points are limited, and may or may not be available without a significant cost impact. Cerus has again simplified things by providing for a direct interlock between the fan motor and damper. In this system, the BAS sends a signal to start the fan, then the starter sends a signal to the damper and waits for a confirming end-switch signal before it will initiate the fan. This eliminates two control points from the BAS and greatly simplifies this critical interlock.

Additionally, the control terminal strip for the Cerus BAS starter has dedicated contacts for emergency shutdown and fireman's override.

And More to Come

Cerus is quickly adding functionality to their BAS starter line and upcoming features will include revenue-grade power metering and automatically calibrating motor overload protection.

Smarter starters use today's technology to reduce installation costs, minimize field problems and simplify troubleshooting.

Cerus BAS motor starter specification
Cerus BACnet motor starter specification

Seismic/Hurricane Certification for Air Handlers

2008-05-27T05:39:00.001-07:00

When the IBC was adopted by Washington State, it brought in some new requirements in air handler construction and certification. These new rules required that for some projects, non-structural building components had to be shown to withstand, and in some cases operate after, a catastrophic seismic event. The intent of these rules was to provide critical facilities (first responders, hospitals, etc.) with systems that would likely survive an earthquake that would cause widespread damage elsewhere.

Likewise, Dade County Florida has created requirements for hurricane resistance for various building components, including rooftop Air Handlers. Rooftop Air Handlers must pass a rigorous series of tests to show compliance, including pressurizing a test section of the cabinet to over 30" of static and firing a 2x4 at the cabinet to simulate hurricane-blown debris!

Climate Craft has been a leader in the industry in showing compliance with both of these standards. They were one of the first manufacturers to show compliance with the Dade County requirements, as these videos from the testing attest:

Missile Testing

Cyclic Pressure Testing
Pressures up to 30" wg cause deformations of the cabinet well-beyond normal operation

Showing compliance to the IBC seismic regulations is a bit more complicated, since the code does not accept testing on a sample unit, and each individual air handler must show compliance as constructed. This means that the designer must take into consideration the site's seismic hazard, the soil conditions at the site, the unit's location within the building and the unit design itself before a determination can be made whether or not the air handler meets the code. Climate Craft has published a white paper discussing the complexities of this process:

In both cases, Climate Craft benefits greatly from its industry-leading cabinet design with doubly-reinforced standing seam joints:

Climate Craft's superior cabinet design ensures a superior performance on site.

For Your Inner Math Geek

2008-05-26T09:21:00.001-07:00

I offer no apologies.

Added Conversion Tables to Blog

2008-05-17T06:57:00.001-07:00

I've added a bunch of conversion tables like the one below to the blog.

They are all located right here.

POWER CONVERSIONS

Direct Drive, Evolved

2008-05-10T07:02:00.000-07:00

Previous articles on this site have discussed the advantages of direct-drive plug fans and the technical tricks required to apply them correctly. However, despite their many advantages, there are times that direct-drive fans just haven't made sense.

In large part, this is because direct-drive fans have been applied as if they were belt-drive fans. It turns out, however, that there is a better way to apply these fans.

See, the problem with direct-drive is that due to the peculiarities of motor performance (discussed in the links above) you usually want to select your fan at a design speed very close to a synchronous motor speed (900, 1200, 1800 rpm, nominally). This limitation can be made up for by varying the width of the fan wheel, but this can cause an unacceptable decrease in static efficiency, or an unacceptable increase in fan noise. Or it can lead to the use of an oversized, less readily available low-rpm motor.

Another strategy is to consider selections of multiple fans, which opens up more design possibilities. However, in standard HVAC designs, this option has practical limits in the number of fans that can be arranged in a cabinet. In the traditional belt-drive paradigm, one or two large fans are mounted on the air handler floor. In unusual situations, three or more fans can be arranged this way, but this requires unusual cabinet geometries that are not often appropriate. This limits the number of direct-drive solutions that can be brought to bear, limitations that are not present with the infinitely-variable fan speeds that are available with belt-drive equipment.

But with a deceptively simple re-thinking of a traditional fan mounting, it becomes possible to stack fans one above another in an air handler cabinet--and suddenly a whole new universe of design solutions present themselves.

It is this evolved fan mounting that is the basis of the ClimateCraft Matrix system.

Matrix is an array of direct-drive plug fans designed to allow maximum flexibility in the selection of fan performance to maximize the benefits of direct drive without the traditional tradeoffs that used to be required. Five fan wheels between 16 and 27 inches are available, with motor sizes between 3 and 30 hp. The fan wheels are AMCA-certified welded aluminum wheels. The wheels are ‘modified class II’ to cover up to 11” static, or class III for higher pressures. The motors are premium efficiency, VFD compatible, 1600V insulation, ODP or TEFC—off the shelf replaceable.

An obvious temptation when mounting multiple, small fans is to avoid the costs associated with isolation and to mount them rigidly to the air handler itself. This simplistic approach, however, can result in repercussions downstream. In fact, the ASHRAE Applications handbook, chapter 47 recommends spring isolators on fans operating above 500 rpm with brake HP below 40. The issue isn’t so much transmitted vibrations, although that certainly can be a problem, but instead bearing life. Strong vibrations can kill bearings, and when the fan bearing is also a motor bearing as is the case in direct-drive plug fans, a bearing failure can be awfully expensive. Climate Craft avoids this problem by isolating every fan from the air handler structure with a unique three-point, seismically-restrained spring isolation system to prevent developing harmonics and creating damaging vibrations. But they have taken the effort even further and used a finite-element analysis to ensure that no harmonic frequencies exist in their fan base anywhere in the operating RPM of their fan systems. This step essentially converts every individual fan base into an inertia base.

This measure ensures that no VFD frequency lock-outs are needed to prevent violent vibration at the fan—a step that is often overlooked in commissioning and can cause unacceptable rates of motor failure. The unique isolator design has the added benefit of preventing the fan base from contacting the seismic restraints and causing a short-circuiting of the fan vibration directly to the frame of the unit and thus the building. This sort of grounding out of the seismic isolation is common on variable airflow systems where the fan thrust changes depending on the fan speed required at any given service point.

The Matrix allows fans to be stacked in towers 1, 2 or three high inside an air handler cabinet. Multiple towers can be installed across the air handler air tunnel. Since the fan wheels are much smaller than typical for the air handler size, many such towers can fit horizontally where only one or two typically sized fans could fit before. These fan towers are designed so that only two different designs are required to support all five different fan wheels and any required motor frame. This greatly aids in construction, making this approach a very cost competitive approach to fan mounting. The towers also serve as a rigid support truss for the fan inlet wall to support the interior of the unit at a location where the pressure differences are often quite high.

Operator Benefits

This sort of a change in fan concept represents a significant advantage for the operator of these systems. This system enhances the air handler’s reliability and serviceability. Redundancy is almost total, since in multiple-fan arrays, the loss of a single fan can often be overcome by the remaining fans simply by ramping up the RPM slightly. Replacement of a failed motor is also much easier. First of all, Matrix uses off-the shelf motor sizes that are easily obtainable on short notice. So simply getting a replacement is easier. Additionally, a typical Matrix motor and wheel assembly might weigh 150 lbs and be easily maneuvered into place by a couple of men, while a typical large fan motor may weigh 1500 lbs or more, and require special rigging to get into place. This may require a significant facility shutdown or even crane work in some cases.

Additionally, the multiple fan array allows shorter air handlers, making a more efficient use of valuable facility square footage. The smaller, faster fans also shift the acoustical signature of the system into higher octave bands, making sound attenuation easier and less expensive.

And a maintenance person will never have to tighten or align a belt on a Matrix system.

Matrix is the next evolution in fan system design.

Labs 21 Highlights Benefits of Low Pressure Lab Ventilation Design

2008-04-07T17:49:00.001-07:00

Labs21 is the leading organization focusing on low-energy, sustainable laboratory design. Cosponsored by the EPA and the DOE, Labs21 has their sights set on these highly energy-intensive buildings and strives to find technically sound solutions to minimize the energy impact of these facilities without sacrificing their mission.

And Labs21 has set their sights on pressure drop.

Their document, Low Pressure Drop HVAC Design for Laboratories, identifies huge opportunities for savings by paying attention to this design criteria. They feel that 30-65% of the laboratory HVAC energy use could be saved by designing low pressure drop into these systems.

Tek-Air's inherently low-pressure drop air-valves can be an integral part of a low-pressure lab HVAC design, and one of the few identified that is essentially cost-neutral.

'Green' is where the lab market is going. Labs21 can help point your way there.

Aaon Helps Project Achieve LEED Platinum

2008-02-01T05:25:00.000-08:00

Signature Center, in Golden Colorado, recently received a LEED™ Platinum rating. This ambitious goal was realized with inspired design, and wise choice of mechanical systems.

The design featured:

Underfloor Air Distribution
Chilled Beams
Evaporatively Cooled Chillers with Variable Speed Pumping
Evaporatively Cooled Rooftop DX Air Handlers
Non-CFC R-410a Refrigerant

Aaon made a natural choice because of their commitment to efficient packaged equipment. This project utilized a packaged LL Chiller Plant as well as a penthouse-type RL air handler. Both units utilized Aaon's unique, water-saving evaporative condensing system. Major project savings were achieved not just in energy, but in this other increasingly scare resource.

Not only did this project reach LEED™ Platinum--It also received the 2007 top award in the institutional building category from the Colorado Renewable Energy Society (CRES).

You can read more about this notable project in this Aaon case study.

'Greening' Lab Design

2008-01-29T06:19:00.000-08:00

Laboratory fume hoods are energy intensive. In order to provide safety for their operator, they need to ensure a constant face velocity of air at the sash--air that must first be conditioned to keep the space temperature acceptable for comfort, moved via mechanical means to the lab, and then exhausted out of the building.

A common comparison used to highlight the energy costs of these systems is to compare the energy impact of a single fume hood with that of a typical US household. On average a single lab fume hood uses as much energy as three typical US houses. And when you consider that a given facility may have many lab hoods in a single laboratory space, you can see how these energy impacts quickly add up.

In order to minimize the wasted energy associated with these laboratories, high-precision VAV lab controls have been developed to ensure operator safety, and to only provide the minimum amount of air necessary--And great savings have been realized by this sort of measure. But the energy efficiency of these systems can be improved even more.

Once the airflow has been taken down to a minimum, the energy associated with conditioning that air has been greatly reduced. But the energy associated with moving that air still can be reduced further. ASHRAE 90.1 states:

ASHRAE Standard 90.1 - 6.5.3.2.3:
“For systems with direct digital control of individual zone boxes reporting to the central control panel, static pressure setpoint shall be reset based on the zone requiring the most pressure; i.e., the setpoint is reset lower until one zone damper is nearly wide open.”

This calls for static pressure reset for VAV systems to minimize fan energy--ensuring that only the minimum amount of static pressure is provided to move the air. And this strategy is perfectly applicable to laboratory VAV systems as well as commercial air conditioning--as long as the system components are selected appropriately.

Tek-Air has published a white paper entitled Demand Based Static Pressure Reset Control for Laboratories That explores the energy benefits of this type of control scheme.

This paper analyzes system component selection, including control valves and sensors and illustrates the impact of these decisions on the overall energy use of the VAV system. In an analysis of a 50,000 cfm exhaust system, the reduced static from a pressure reset strategy can result in nearly $9,000 per year savings in fan energy (based on 0.75" savings, and $0.06/kwh electric costs).

These sorts of static pressure savings are easily attainable with a wise selection of air valve components. The commonly specified venturi-type valve has a minimum operating pressure that prevents these savings from being realized, and this added pressure drop often creates objectionable noise, which requires even more pressure drop for the system in the form of sound attenuators. This pressure reset strategy requires valves that can operate accurately and safely at low pressures.

The Tek-Air PRD valve provides unmatched pressure performance, and a quick examination of a cross section of the valve shows why:

Each blade of the damper is a smooth airfoil, greatly reducing turbulence and keeping the pressure and acoustic profile of the valve to a minimum.

If pneumatic air is not available, Tek-Air's new Accuvalve provides very similar performance with the convenience of electronic actuation. (And it won an innovation award at the 2008 AHR expo!)

A peek at the cross section of this valve shows how it attains these low pressure drops:

The airfoil shape of the valve assembly assures minimal pressure drop and sound generation for great efficiency in the fan system.

Energy savings cannot come at the cost of safety, and it is imperative that systems utilizing this method of pressure reset have sensors that can operate accurately and effectively in a wide range of pressure regimes. Tek-Air uses vortex shedding flow sensor technology to ensure the most accurate and linear control on the market.

Energy conservation is only going to become a bigger and bigger issue for designers of all building systems, and fume hood systems are a large opportunity for savings. It is important that designers and owners consider all the impacts of their design decisions and their system selections.

(Don't forget about checking the fan for stability: See this article for a review on this issue.)

Rethinking Air-Cooled Chillers

2008-01-25T05:54:00.000-08:00

Air Cooled Advantages

Air cooled chillers offer many advantages to owners and designers. The first, and perhaps most compelling for many jobs is lower installed cost. Lower installed costs (compared to water cooled chillers) are driven by the following advantages:

No Cooling Tower, Tower pumps, Tower and Pump Starters
No equipment room required for the chillers
Mounted starters

They also are easier to maintain, since the systems are significantly simpler than water-cooled systems:

No on site Systems Engineer required
No water treatment or make up water required
No leaks on the roof
No cooling tower, condenser pumps, associated starters

Generally, however, these advantages have come with significant trade-offs: Efficiency and Sound performance.

However, the introduction of Variable Speed oil-free air-cooled chillers by Smardt changes the balance.

First off, the Smardt Chiller is efficient. With IPLV's as low as 0.65 kw/ton, these chillers rival water-cooled system when the parasitic loads of the condenser pumps and cooling tower are considered. These chillers gain their efficiencies both from the inherent efficiency of the Turbocor compressor and the elimination of oil return issues that prevent other air-cooled chillers from capitalizing on the reduced head pressures available at low ambients.

This means these chillers use about 60-65% energy of other air-cooled chillers for the same load, and can nearly eliminate the energy benefit typically provided by moving to water-cooled systems. When you consider the cost of water (nearly $15/1000 gallons in Seattle, including sewer charges) this means the yearly cost of operation of these units is unrivaled. And energy conservation rebates are extremely attractive for these chillers.

The other major traditional trade off with using air-cooled equipment is sound. Screw chillers especially are known for their unfavorable sound characteristics. In most municipalities, sound ordinances are driven by occupancy and time of day. The most stringent criteria must be met during evening hours, typically when the units are not at their peak load. However, with constant-speed systems, the compressor is either on or off. This means it is either putting out its full sound or none at all. At full speed, such compressors can often exceed the evening sound criteria--even if they are on only momentarily. And the staging between on and off can be objectionable in its own right, regardless of sound level.

The Smardt chiller minimizes the problems with compressor sound in two ways. First, the variable speed drive allows the compressor to ramp slowly up and down to match the required output, eliminating the objectionable switching between compressors that constant-speed chillers exhibit. And secondly, they are just extremely quiet to begin with. Since no moving mechanical part is in contact with the chiller casing, very little mechanical noise is transmitted. Ninety-ton Turbocor compressors have been tested at 72 dBa at one meter, compared to screw compressors that can be as high as 80 dBa or higher in the same test. Five of these compressors operating together yield a sound level of 75 dBa at 10’.

More Benefits

But efficiency and sound are not the only benefits from using the Turbocor technology on air-cooled chillers. Other, less obvious ones exist.

Turbocor compressors have only one moving part, yielding un-matched reliability.

Reliability is enhanced by the elimination of oil in the refrigerant system. And the frictionless bearing requires almost no maintenance.

Since Turbocor compressors are variable speed driven, they provide an inherent soft-start on the compressor. Instead of kicking the motor up to full speed when power is applied to the system, the VSD slowly ramps the compressor up to the required speed for the load sensed by the system. This reduces stress on the already greatly simplified system to reduce wear and tear on the components.

But this soft start has another, very important advantage over standard air-cooled chiler systems--the use of the VSD eliminates inrush amperage. When an electrical motor is at rest, there is very little inductive resistance to current flow through the windings. As the motor starts to turn, this inductive resistance increases with the increase in RPM. What this means is when power is applied across the line (or even with a reduced voltage starter) to a stopped motor, there is a spike of electrical current far greater in amplitude than the design amp draw of the motor:

(example graph of inrush on a well pump motor)

This temporary increased amp draw heats the motor beyond where it is designed to operate for extended periods. This forces the chiller designer to provided anti-recycle timers to prevent rapid re-starts that could fatally overheat the motor. In practice, this usually means constant speed compressors cannot be started more often than every half-hour or so.

Additionally, this increased amp draw has effects that need to be addressed electrically. This becomes even more significant if the chillers are being served by emergency power. The emergency generators that serve the chiller must be sized to handle the inrush amperage. This can be a very costly addition, especially since the added amperage is only required for the first 30 second of operation or so.

Generators = $$$

Turbocor compressors on the Smardt air-cooled chillers eliminate inrush and provides a soft-start. This both heightens reliability and reduces electrical costs. For jobs where reliability is a primary concern, like data centers, this technology makes a lot of sense. First, it eliminates the need for increased generator sizing, it is an inherently more reliable compressor, and it frees the cooling system from reliance on a water utility service that could be disrupted.

The Dark Side of Chiller oil

2008-01-18T05:05:00.000-08:00

Most compressorized systems operate with oil mixed in with the refrigerant. This oil is required for lubrication of the shaft bearing and, in positive displacement compressors like scrolls or screws, it actually provides the seal that is necessary to effect the compression of the refrigerant. The oil is miscible with the refrigerant, and travels with it throughout the system to provide lubrication and compression sealing. That means the oil is everywhere the refrigerant is—Which can lead to several operation problems that need to be addressed in the design and operation of the system.

The first issue is oil transport. The oil travels with the refrigerant whenever the velocity of the refrigerant is high enough to carry the oil with it. This means that the system must be designed to ensure adequate velocities are met at all times. The biggest obstacle to refrigerant flow occurs, however, at the expansion device between the condenser and the evaporator. This is by design a big restriction on refrigerant flow—the greater the restriction, the greater the pressure drop across it and therefore the larger the temperature difference between condenser and evaporator. Its function is similar to that of a flow restrictor in a shower head or an orifice plate in a commercial piping system. Therefore, in order to ensure an adequate flow rate for oil transport between the condenser and evaporator, the pressure between these components must be kept above a minimum. If the pressure difference falls below this minimum, oil starts stacking up in the condenser and the machine will trip out on low oil pressure.

While there are methods that can be used to minimize this problem, such as oil pumps and eductors that siphon the accumulated oil out of the condenser, these are usually only provided on larger tonnage centrifugal machines, and even then there is a practical limit to the operating environment the compressor is designed for. In practice, head pressure control is used where low condensing temperatures are expected, such as fan cycling on air-cooled condensers or bypass lines on water cooled compressors. And even then, oil transport problems are a major cause of chiller downtime, especially in cool climates.

These head-pressure control mechanisms ensure a minimum condensing pressure to assure oil transport—which is good, because this ensures trouble-free operation. But it does this at the cost of energy efficiency.

See, a compressor is very similar to a pump. The total mass flow of refrigerant can be thought of as analogous to the flow rate of the pump and the pressure difference between the evaporator and condenser is analogous to the static head of the pump. In order to reduce energy use on a pump, you can either reduce the flow rate through the pump, or you can reduce the static head. In a chiller system you have the same options, but remember that the refrigerant mass flow rate is what determines the cooling capacity of the chiller. If you want to reduce energy use, but still provide the same cooling capacity, your only option is to reduce condenser pressure. One of the great advantages of using the ambient air as a heat sink is that for over 99% of the year, you have access to air temperatures (wet bulb or dry bulb, depending on the heat rejection of the system) below your design condition. This is why part load ratings on chillers are so much better than peak load ratings.

Head pressure controls, however, artificially limit how low this head pressure can go. Just when you are really getting efficient, the system kicks in a mechanism to keep your system from getting any more efficient! Without the need to maintain oil flow, a compressor can take full advantage of the available head pressure relief and operate extremely efficiently.

The second major issue with oil in your system is that it actually inhibits heat transfer, reducing the overall efficiency of the refrigeration system. In fact, a nominal 3.5% charge of oil in a chiller system equates to about an 8% loss of efficiency from this insulating effect (from ASHRAE 601).

And this only gets worse with time. An ARI study found that this insulating effect increases for the first 5-6 years of operation reducing chiller efficiency by about 20% due to oil fouling of the heat transfer surfaces in the chiller.

These numbers assume a constant oil charge—which is a big assumption. In practice, chiller oil charges often exceed the recommended oil charge by very significant amounts—since a common method of correcting a ‘low oil pressure’ alarm is to add more oil—despite the fact that the usual cause of this alarm is the stacking of refrigerant in the condenser, not any loss of oil in the machine. The same ASHRAE study above sampled many machines in the field and found that the average charge of oil was nearly 13% which equates to a total efficiency loss of 21%!

The last major issue with oil in the compressor is the chance of motor burnout. If a refrigerant system experiences a small leak in a low pressure location, moisture and air can enter the refrigerant system. Enough moist air can react with the refrigerant and oil to form hydrochloric and hydrofluoric acids which then travel through the system to the motor windings and eat away the insulation, eventually causing massive arcing and a catastrophic failure of the compressor motor. This acidic residue will be deposited throughout they system, requiring extensive flushing of the chiller shells before the system can safely be brought back on line. This is not only very expensive, but amounts to a very long downtime in what may be a critical building component.

Developed in Australia in the mid-90’s, the Turbocor™ compressor was born out of a desire to avoid the energy penalty and maintenance headaches associated with oil in the refrigerant circuit of traditional compressorized cooling systems.

These centrifugal compressors utilize a unique magnetic bearing to completely avoid the need for oil in the refrigerant system. These systems require very little maintenance and provide excellent efficiency both initially and many years down the road.

Smardt manufacturers water-cooled and air-cooled chillers exclusively utilizing these innovative compressors. These chillers avoid all of the drawbacks of oil, and eliminate much of the cost of ownership that is commonly associated with chiller systems. Since the bearings do not wear, traditional scheduled stop-major chiller teardowns are unnecessary, and all of the downtime and cost associated with oil (around 50% of the maintenance cost on these systems) are avoided. Smardt chillers provide an owner with excellent efficiency, reliability and economy.

Aaon Goes 'Outside the Box' in HPAC article

2008-01-13T12:22:00.000-08:00

Aaon makes some news in the HPAC Magazine article 'Outside-the-Box' Thinking Produces Outside-the-Building Mechanical Room published in the December 2008 issue.

The article discusses the conversion of an old Apollo Mission facility into a modern printing facility. Great economies were realized by using Aaon LL chillers and air handlers. The LL chillers can be provided with pumps, boilers and accessories to create a full 'mechanical room in a box' that can be shipped to the site, pre-designed and pre-piped. As the article describes:

Recognizing that a different type of solution was called for, Ecogenia, a Montreal-based distributor of HVAC products and controls, specified two 335-ton LL Series chillers from AAON Inc. The LL Series integrates mechanical-room components into a single packaged outdoor unit that includes a heat exchanger, a pumping package, boilers, expansion tanks, controls, and an air-cooled or a high-efficiency evaporatively cooled condenser section. A cooling tower is not required.

Aaon LL chillers can be laid out using the Ecat32 software in just a few minutes, and the installation of an entire mechanical room is a easy as a crane pick and utility connection. This may be just the solution for your next project!

Read more about LL chillers here (pdf).

Saving Water in Evaporatively Cooled Systems

2008-01-05T16:27:00.000-08:00

Water is a limited resource, just like energy. Engineers are very aware of the need to save energy in their designs, and one of the best ways to do this is to take advantage of evaporative heat rejection for their cooling systems. The traditional cooling tower is an extremely effective way to reduce energy use at the compressors in a traditional cooling system. But introducing a cooling tower introduces a need for water to the system. It would be advantageous if this water use could be kept to an absolute minimum.

Especially since, in Seattle, water is expensive. As of this posting, the water utility rate per thousand gallons is $4.48 (summer) and the Sewer costs tack on an additional $9.96. When you consider that a cooling tower consumes a minimum of 1.8gph/ton (evaporation required to reject that heat), you can see that over a 1900 hour cooling season, these costs can really add up for a reasonably-sized cooling tower.

Earlier, I posted an article that highlighted ways to reduce water use in traditional cooling tower systems. For the most part, these recommendations address keeping the actual water use as close to the theoretical 1.8gph/ton evaporation figure as possible. Reducing the water use any further requires reducing the load on the tower, since evaporation is the only way a cooling tower can reject heat.

There are two ways to reduce load on a cooling tower--Reducing the total building load, or rejecting heat through some other method other than the cooling tower. Assuming the first option has already been exhausted through good engineering practices, the only other option is the second.

This is the approach taken by Aaon in their evaporative condenser systems. They essentially use a dry finned coil as the first stage of cooling before the refrigerant is cooled by evaporative methods. This essentially allows the system to reject as much heat as possible through a non-evaporative method before water is used. Every btuh that is rejected in this manner means less water used in the system.

This idea could be borrowed and applied to an open cooling tower by the use of a dry-cooler as a pre-cooler before a cooling tower. This way, the system rejects as much heat as possible in a dry fashion, and only uses water for what the dry-cooler can't do. This system gets to take advantage of the strengths of both methods of heat rejection--the water conserving function of a dry-cooler, and the lower water temperatures and more efficient heat rejection provided by a cooling tower.

Evapco has capitalized on this approach by creating a new, water-saving fluid cooler called the WDW:

This unit is a hybrid between a dry-cooler and an evaporative fluid cooler. It is provided with a control panel that controls both wet and dry sides of the unit, varying fan speeds with a VFD and determining when to run the evaporative pumps to optimize both water efficiency and fan energy.

Cutaway of an Evapco WDW unit

In practice, the evaporative system is only used for a small portion of the year, only when the design condenser water temperatures cannot be met by the dry-cooler side alone. What you see is a major reduction in water use compared to the same system served by a fully evaporative system:

Other advantages of this approach besides reduced water use are reduced chance of tower plume (since there are far fewer hours in which water is being evaporated, and when this does occur, it occurs in warmer temperatures) and the ability to provide some cooling even if city water is lost due to a service disruption.

But since a dry-cooler uses more fan energy per ton of cooling than a cooling tower, this system will inevitably use more energy to save water. Does this approach pay off?

An example from a real project might help demonstrate the economies involved. Below are the utility cost calculations from a project utilizing a 240 ton WDW installed in Seattle on a heat pump system with a portion of the load serving a 24/7 cooling application:

Note that even with the reduced water cost (to approximate the effective cost of using a deduct meter to avoid being charged wastewater charges for evaporated water) the hybrid system saves about 18% of the annual operational utility costs compared to a fully evaporative system. This affords a relatively quick payback for the added equipment costs associated with the hybrid system.

Aaon Rolls Out 410a Digital Scrolls!

2007-12-19T15:25:00.000-08:00

Digital Scrolls offer great advantages over standard scroll compressors for rooftop packaged systems. Aaon was the first manufacturer to offer digital scrolls for their R-22 systems--but the phaseout of that refrigerant is looming.

The latest version of the Aaon Ecat32 software includes new offerings of digital scrolls for selected units using R-410a. These advanced compressors are available in the following units for the HFC refrigerant:

230/3/60 – RM-006; RM-013; RN-026
460/3/60 – RM-006; RM-007; RM-013; RM-015; RM-016; RN-026; RN-031

Stay tuned for more offerings as Copeland rolls out their R-401A digital scrolls!

Greening Small Rooftop Packaged Units: Heat Recovery

2007-12-14T05:32:00.000-08:00

This article on 'greening' rooftop packaged units is the third of the ‘Greening Small Packaged Units’ series and addresses the use of exhaust air heat recovery in these types of systems.

Heat recovery is a well-understood and accepted method of energy conservation. However, the energy saved comes at a cost. Generally, an air conditioning system that has heat recovery capabilities operates with higher pressure drops than a system without heat recovery, and there may be other parasitic loads that are required to run the heat recovery equipment.

Energy codes generally require heat recovery on systems that use a significant amount of outdoor air, since it is a reasonable assumption that on such systems, which have very large ventilation loads, the amount of energy saved will greatly outweigh the additional energy required to operate the heat recovery equipment. However, depending on the operating conditions, there usually are energy benefits for systems that operate with even very minimal outdoor air requirements.

For an owner or designer trying to decide whether heat recovery is right for a particular application, it is important to know what these benefits are in terms of energy cost reductions, payback or return on investment, and, more and more frequently, carbon emission reductions.

For rooftop packaged units, the heat recovery product of choice is the heat wheel. The industry has settled on this product for many reasons, including first cost, footprint, efficiency and layout considerations. Aaon uses the Airxchange wheel, which is an ARI 1060 certified heat recovery device.

As with their rooftop economizers, Aaon provides this efficiency option as an integrated, factory installed option. This greatly reduces on site labor, eases commissioning, and ensures the owner of the energy benefits of their investment.

(If field-installed RTU economizers have a high rate of failure, imagine how often field installed heat recovery wheels are a commissioning problem!)

To aid in the heat recovery analysis, Airxchange has provided a free software program (registration required) to calculate the energy and cost benefits of applying their heat wheels on air-handling systems. This makes it very easy for an engineer to do a bin-data analysis of the benefits of this option. Given a particular heat wheel and some basic information about the RTU it is serving, it will calculate the gross heat recovery for cooling and heating hours, as well as calculate the additional fan energy required to operate the wheel. It will also perform a simple economic analysis calculating a net dollar savings when using the heat wheel.

An analysis of a 16 ton Aaon RM unit (pdf) shows the net energy savings available using a wheel on this type of unit. In the above analysis, a 5,200 CFM supply air system is compared looking at conditions of 100% OA and 30% OA. In both cases the analysis (using Seattle bin data, a 5 day week and typical office hours of operation) shows net energy cost savings, about $500/year on the 30% OA case, and about $1,700/year on the 100% OA case. Almost all of those savings come from the heat required to offset the ventilation load during the winter—the cooling savings are small by comparison.

However, the effect of the wheel on cooling is important in one respect--the use of the heat wheel may allow the designer to reduce the cooling (and, of course, heating) capacity of the RTU. In this example, the wheel adds 1.4 tons and 84 MBH to the cooling and heating capacity of the 30% OA system, and 3.7 tons and 230 MBH to the 100% OA system.

These ‘free’ tons of capacity that you gain by using the heat wheel effectively allows your cooling system to operate at a higher actual IPLV than is calculated in the ARI rating of the unit. ARI has acknowledged this in the publication of ARI Guideline V (Calculating the Efficiency of Energy Recovery Ventilation and Its Effect on Efficiency and Sizing of Building HVAC Systems). This guideline basically defines an efficiency rating for the heat recovery system (RER) and a ‘combined efficiency’ rating (CEF) for the entire system, accounting for the EER of the RTU and the RER of the heat wheel. This CEF is calculated in the Airxchange software linked above

If the goal of a design is not just energy savings, but carbon emission reduction, the wheel’s advantage is obvious. Every btuh that is recovered from the exhaust air is less natural gas that would need to be burned in a gas burner (the most common form of heat for these units in this region). But there is one other powerful way in which wheels can leverage energy savings or reduce carbon emissions: they can be used to greatly increase the applicability of a heat pump cycle for heating operation. In an Aaon unit, the entering air into the refrigerant coil needs to be 45º F or higher for the heat pump system to provide any heat. In the example reviewed above (RM16) the mixed air at a design heating day in Seattle is pre-heated to nearly 50 º F for the 100% OA case—well above the minimum needed for HP operation! And although capacity drops off, an air-source Aaon heat pump will still operate at conditions as low as 17 º F ambient. Converting the system to a water-source HP greatly improves the heat capacity at even the coldest days—and by reducing the amount of heat required from the ground, the use of the heat wheel can help keep ground loop costs down, too!

Converting a system from gas heat to heat pump operation has a large energy and carbon reduction benefit. First, it transfers the heating energy source from a high embodied-carbon fuel to electricity, which in the Pacific Northwest is considered a nearly carbon-free energy source. And it provides an advantage over electricity because, even with heating COP’s on the order of 1.5*, it greatly reduces the amount of utility electricity required to do the same amount of heating.

*at extreme conditions—moderate conditions greatly improve this performance

Adding Mechanical Cooling to Indirect/Direct Evaporative Systems

2007-12-01T20:55:00.000-08:00

On this website, I have discussed indirect evaporative cooling, direct evaporative cooling and systems that combine the two into indirect/direct evaporative cooling. As we saw from the last article, however, there will likely be many applications where additional cooling beyond what can be attained by evaporative methods is necessary to keep a space comfortable. In these cases, we need to add mechanical cooling into the mix. But it is important to understand how to do this—there are tricks that can preserve most of the energy benefit of the evaporative cooling systems you have designed into your system.

The first trick is to determine where to put the mechanical cooling coil. The temptation might be to think it would be a mistake to put it in as the last component in the air flow. This is because it seems you would then simply be removing a lot of the latent effect that you are putting into the air in the direct evap portion of the system. However, inspection of psychrometric processes indicates that this is not the case. In fact, anytime the dew point of the air leaving the indirect evap is lower than the desired design air drybulb, you will see an advantage in running the direct evap section if it is located upstream of the cooling coil. A quick example will demonstrate this effect: Let's look at a 12,000 cfm system providing 60º supply air at an extreme sensible ambient weather condition in Seattle, WA. We will first look at this system with a standard mixed air (20% OA) arrangement with a traditional cooling coil. Then we will superimpose a three-stage indirect-mechanical cooling-direct system and compare the energy performance:

(click for larger image)

In the above image, the traditional mixed-air psychrometric process is indicated in red and the evaporative process in purple (with blue indicating the mechanical cooling portion). Both systems start at the ambient OA condition of 95º/68º. The standard cooling system then mixes the OA with return air in a 20%/80% proportion and then cools sensibly to a 60º leaving air temperature. (The cooling process in the traditional system is shown as purely sensible, but in reality, the system would likely use a return air bypass configuration to allow the portion of the supply air to be super-cooled to achieve latent cooling and thus prevent any latent load in the space from steadily building humidity through multiple passes through this pyschrometric process.) Note that the sensible cooling load in this system requires about 20 tons of mechanical cooling.

In the three-stage evaporative system, 100% OA is first indirectly cooled to to the condition at point I/D evap + R2. Then, mechanical cooling takes over to point I/D evap + R3, after which the direct evap section evaporatively cools to a 60º LAT condition at I/D evap + R4. I have then shown a sensible heating process from the LAT to represent the zone load to demonstrate that this will provide a very comfortable resultant air condition in the space at I/D evap + R5. Note that this is true even if there is a significant latent component to this load (The resultant room temperature is approximately centered in the pink zone that represents the ASHRAE summer comfort envelope). For this analysis, the direct evaporative system is operating at full capacity, and the cooling coil is modulating to provide the desired LAT DB. (Since this system is 100% OA, we are not concerned about humidity levels building up in the space as in the recirculating system.)

The first thing that should just jump out of this is that the evaporative system requires less than HALF the mechanical cooling of the traditional system--while providing the increased ventilation benefit of 100% OA! And this is neglecting the additional latent cooling load that would probably be needed to maintain humidity levels in the space with the traditional recirculating system. To add to the IEQ benefit, the direct evap section works as an air washer and effectively increases the filtration of the air to improve IEQ beyond that of a traditional 100% OA system.

Now lets compare the three-stage system we just examined (with a indirect/cooling coil/direct arrangement) to that of a three-stage system with an indirect/direct/cooling coil configuration:

(click for larger image)

Two things should be obvious in this example. First, the mechanical cooling load is even lower than in the previous example: down to under 5 tons! Thats about a quarter of the load for the traditional system, and a little more than half of the load of the evaporative system with the cooling coil before the evap section. Second, and this is the secret behind the reduction in mechanical load, the air leaving this system is significantly closer to saturation than the previous example. In other words, despite the fact the leaving dry bulb temperatures are the same in both cases, in the latter case there is more latent heat in the supply air. The evaporative cooling process before the coil allows the system air to hold more latent energy but yield the same sensible condition for conditioning the space. A quick inspection of the comfort zone indicates this air is perfectly suitable to provide an acceptable comfort condition, even with a reasonable latent load.

Earlier, I said there should be an advantage to running the direct evap upstream of the cooling coil if the dew point of the air entering the direct evap was colder than the design air DB. In this case the dew point of the entering air is 53 degrees--which is quite a bit cooler than the 60 degree design point we are looking for, so thus we gain the advantage seen. What about the case where the entering air is too moist? Let's look at a system where the entering air dew point is well above the supply air temperature:

(click for larger image)

In this case, the OA enters with a 62º dew point. It cools through an indirect section to about 72º/65º, and then directly to a cooling coil to reach the leaving air temperature of 60ºF db. Since the enthalpy and WB lines are nearly parallel, it seems there is very little advantage to using direct evaporation to get the air leaving the indirect evap section to saturation and then cooling it. But, importantly, there is certainly no disadvantage, (other than the electrical draw of the pump). Also notice that again, this system provides a significant load reduction compared to a standard system even while providing 100% OA!

Running through that process actually shows a slight advantage for using the direct evap section:

(click for larger image)

This cooling advantage should be confirmed for your specific system since it is highly dependent on the latent capacity of the cooling coil, and is offset by the pump energy and some small increase in system static pressure when the direct evap media is wet.

However, keeping the direct evap pump running even in these conditions provides several advantages besides energy savings:

Simplifies the control scheme
Provides IEQ benefit of air washing
Increases the life of the direct evap media by reducing cycling of the evap pump

Whether or not it makes sense to use the direct evap portion of your system in times of high ambient moisture is a decision that can change depending on the particulars on any given project. But if there is a net energy penalty for using this system when the OA dew point is high, one can see from this analysis that the penalty is slight and that it would only occur for very few hours a year.

Greening Small Rooftop Packaged Units: Variable Air Volume

2007-11-18T11:09:00.001-08:00

Second in the "Greening Small Rooftop Packaged Units" series.

Variable air volume systems are an accepted energy conservation strategy that has gained wide acceptance in the HVAC industry. And HVAC systems provide other benefits, too, including improved occupant comfort and flexibility.

The energy benefit of VAV systems comes primarily from the ability to reduce fan energy use when the full capacity is not needed. Since the fan system is typically sized at peak load, using a constant volume system means that you essentially waste fan energy for 95% of the operating hours of your system. Since fan power decreases with the cube of the speed (theoretically--motor amp draws at low speeds plateau, reducing savings in practice), the fan savings can be significant.

In fact, ASHRAE considers the potential for energy savings with variable volume systems so great, that they are considering revising standard 90.1 to require this feature on single-zone systems, in addition to the current requirement on multiple zone systems.

But there is a catch for designers using rooftop packaged DX units. Very few manufacturers provide VAV enabled units for smaller tonnages. Below about 20-50 tons, there is very little on the market to service this need. Aaon, on the other hand, offers a full line of VAV units down to capacities as low as 2 tons. And they configure their units to use either air-cooled DX refrigeration, water-cooled DX refrigeration, or chilled water cooling!

Part of the problem with using VAV at smaller tonnages is that for DX systems, the size of the smallest compressor in the system is a considerable portion of the entire cooling load--as much as 100% for single-compressor systems. This means that as you vary the leaving air volume, the capacity of the cooling system stays the same, greatly decreasing the leaving air temperature. In most cases, this will cause the DX coil to frost, which leads to all sorts of problems for the system. This drawback is generally dealt with by installing a hot gas bypass on the first cooling circuit. However, this strategy works against the energy conservation intent of using a VAV system in the first place, since the HGBP imposes a false load on the compressor system, and the compressor draws full amps even at partial load.

In the example below (click here for full pdf of selection), the compressor on a 5-ton VAV unit draws more energy than the supply and exhaust fans together--nearly twice as much!

(click image for larger view)

You can easily see that in some systems a VAV unit operating with a hot gas bypass could actually use more energy than a constant-volume system with simple on-off compressor control. Of course the latter system may cause some comfort problems that the VAV system would avoid, but it would cost you energy to gain the added comfort.

Aaon has elegantly addressed this drawback by their use of digital scroll compressors allowing you to vary compressor capacity linearly to match system load and avoid freezing your coils--and to do so in an extremely energy-efficient manner.

In 2004, the ASHRAE Journal published a study (pdf) that examined possible advances in energy efficiency in rooftop packaged DX units. In it the researchers created a high-efficiency 10 ton unit configuration:

Based on the initial energy and cost analyses, we developed a design configuration incorporating the best design options:
• Increased heat exchanger size to achieve an EER of at least 10.3, consistent with the ASHRAE 90.1-1999 requirement for 10-ton electric-heat rooftop units;
• Variable air volume using an induction motor and inverter;
• Energy recovery wheel (ERW); and
• Economizer.

This unit was also tested in a configuration that included a variable speed compressor similar to the Aaon digital scroll. The researchers concluded that the base unit, without the variable speed scroll, reduced energy costs by 25% compared to a constant-volume unit. The variable speed compressor was shown to further improve the part load performance.

The proposed unit configuration, significantly, is extremely similar to the example unit above. In other words, the 'future energy-efficient unit' of 2004 is available as an Aaon catalog unit today!

High Efficiency VAV Unit of the Future

Aaon High Efficiency VAV unit of Today

Customers LOVE their Aaon

2007-11-18T10:18:00.001-08:00

We know that people love their Aaon units, but this seems to be taking things a little too far!

Seriously, though, congratulations to Digital Forest and many happy years of cooling!

Read more about the installation here, including this time-lapse video of the installation and crane pick:

Greening Small Rooftop Packaged Units: Economizers

2007-10-29T14:31:00.000-07:00

Introduction: Small rooftop packaged air conditioning units are sold in staggering numbers in the United States. As such, they represent a very large portion of the installed and future energy use in the built environment. This article on 'greening' rooftop packaged units is the first of a series that will address opportunities to increase the efficiencies of these units, and highlight JB products that can address these opportunities. Each article will discuss a different facet of efficient rooftop packaged unit design. This first installment will discuss the impact of effective economizers for rooftop packaged units

It is well established that air-side economizers save energy in the Pacific Northwest. And this stands to reason when you look at a graph of where the bulk of Seattle weather bin data lies:

(click for larger image)

The majority of the bin hours per year lie to the left of the 55º line, indicating that an economizer system would eliminate the need for mechanical cooling altogether during these hours. And nearly all of the hours are located to the left of the 75º line, where ambient temperatures would be lower than return air temperatures in a cooling system--allowing the system to offset some mechanical cooling load by using outside air.

When you consider that the use of outside air also brings IAQ benefits, it is clear why air-side economizers are such a compelling strategy for Northwest mechanical systems.

But there is a problem with air economizers in small packaged units: Too many of them don't work properly in the field. The reason for this is that for most small rooftop packaged cooling units do not have factory installed economizers. The standard of the industry is a bolt-on option that is shipped as a separate assembly to the jobsite for installation by the installing contractor. In some cases, they may not even be available at all for some duct configurations.

Typical small packaged unit economizer instalation

In practice, these economizers have a high rate of failure. The issue of non-functional economizers for small rooftop packaged units is significant enough that Puget Sound Energy includes re-commissioning of these devices in their Commercial HVAC Rooftop Unit Premium Service Rebate (program developed with the assistance of NEEC). And the Califorina Public Interest Energy Research program (PIER) goes further, recommending to owners and designers:

Specify reliable, factory-installed and -tested economizers with direct-drive actuators and low-leakage dampers.

That's exactly what Aaon provides on all of their units down to 1 ton.

(click for larger image)

Aaon's rooftop unit design provides inherent energy advantages over the competition. And factory-installed economizers are just one of many.

Extra: PIER software to estimate economizer savings.
Want free psychrometric software? See our offering here.

The Importance of Cooling Tower Maintenance

2007-10-28T09:25:00.000-07:00

Cooling tower maintenance is not just critical for extending the life of your equipment, but it also can significantly improve the energy performance of your mechanical system.

BetterBricks, a non-profit venture of the Northwest Energy Efficiency Alliance has summarized the energy benefits of cooling tower maintenance in their article, Optimizing Cooling Tower Performance.

This article highlights the negative effects of:

Scale Deposits
Clogged Nozzles
Poor Airflow
Poor Pump Performance

If you own or maintain cooling towers, this article is well-worth reviewing. And remember that Johnson-Barrow's FluidTek tower service group is a certified Evapco Mr. Goodtower service center.

Introduction to Modular Chillers

2007-10-27T14:43:00.000-07:00

Modular chillers are a product innovation that has recently gained wide acceptance in the HVAC industry. But since they cost more than standard chillers on a per-ton basis, it might seem a unlikely that this equipment would be a very popular cooling solution. However, modular chillers offer advantages that are not available with standard chiller equipment.

These advantages can be summarized in a few points:

Ease of Installation
Compact footprint
Redundancy

Ease of Installation

Modular chillers were originally developed as replacement chillers for existing building chiller plants. Many chillers are located in the bowels of the buildings they serve. It is often far easier to remove the existing equipment in pieces than to find a rigging path suitable to take it out of the building in one piece. Of course, this only helps if it is also possible to move the new chilling capacity into the chiller room in pieces!

Modular chillers were designed to fit through standard doors and to have a small turning radius to negotiate internal corridors without requiring demolition of existing walls.

Additionally, since these modules are light enough to ride in a freight elevator, it is usually possible to avoid crane costs for the installation project. Further cost savings are realized once the modules are in the room. Since each module has very low refrigerant volumes, the retrofit usually does not trigger codes requiring refrigerant monitoring or emergency ventilation.

Compact Footprint

In order to fit through doors and down corridors, modular chillers are designed to be extremely compact. They use highly efficient brazed plate heat exchangers to minimize their size as much as possible:

The result is a chiller plant with the smallest footprint per ton of any current option available--even if you are installing the modules in a new project instead of a retrofit.

330 ton chiller plant comparison (click for larger image)

Redundancy

With multiple, independent modules, modular chillers provide unmatched redundancy. If a single circuit is down there are always multiple other circuits operating. And providing N+1 redundancy to a modular chiller plant is far less expensive in first costs and mechanical room space than for any other chiller type. This inherent modularity allows fantastic turndown capabilities, and the part-load efficiency of a modular chiller plant is comparable with that of a large constant speed centrifugal or screw chiller.

ClimaCool Advantages

ClimaCool modular chillers were designed to take full advantage of the modular chiller design. For example, some manufacturers design their chillers for modular installation, but not modular operation. These chillers are designed with an electrical bus bar system to power all of the modules from a single power source. This may mean a slight savings at installation, but significantly degrades the redundancy advantage of this type of chiller. With a bus bar system if one chiller needs to be worked on, the entire array needs to be powered off.

ClimaCool avoids this disadvantage by powering each module independently of all the others:

Similarly, ClimaCool offers full redundancy on the water side, too, by providing isolation valves for the heat exchangers as a standard feature. Some manufacturers offer these valves as a first-cost add and they may significantly affect the chiller's footprint dimensions if added. Providing these valves as standard provides for yet another ClimaCool advantage: Easy conversion to a variable primary flow system! Modular chillers have a tight flow envelope on the brazed plate heat exchangers--each heat exchanger should essentially be considered a constant-flow device. By providing electric actuators controlled by the chiller controller on these isolation valves, the modular chiller plant can easily adjust for variable primary flow.

Another way in which ClimaCool offers advantages over other modular designs is in heat exchanger protection. Brazed-plate heat exchangers are highly efficient and very compact, but they demand very clean water to prevent clogging. All manufacturers of modular chiller equipment require straining of the system water before it enters the exchanger. Some manufacturers provide large-mesh strainers that are mounted in the headers serving the heat exchangers at each module. This approach requires an annual back-flush of the heat exchangers to clean out the debris that inevitably passes through the mesh. It also discourages proper maintenance, since the strainers are hard to get to and are therefore often ignored until clogging causes flow problems. ClimaCool takes a different approach, using small-mesh basket-type strainers outside of the headers to prevent heat exchanger fouling. This eliminates the need for annual back-flushing, and greatly eases maintenance. They also offer a deluxe 80-mesh high-capacity strainer option for especially dirty water or for systems where maintenance man-hours are limited:

Additionally, ClimaCool provides, as standard, convenient back-flush hose-bibs to allow this sort of maintenance as needed without requiring disassembly of the chiller header or taking the other modules off-line.

And, of course, ClimaCool offers chillers that comfortably exceed minimum energy code requirments:

Efficiency, redundancy, compact size and ease of installation: All reasons to consider ClimaCool modular chillers for your next chiller project.

Your Next Energy Conservation Measure May be a Quiet Fan

2007-10-22T08:54:00.000-07:00

It might sound strange, but a super low sound axial cooling tower fan is an energy-saving device--But not because it uses less energy than the fan it replaces, because it doesn't. The reason is a little more complicated than that.

But first it makes sense to review a few basics about cooling towers.

The Basics

There are two major types of cooling towers and fluid coolers: Induced Draft and Forced Draft.

Forced-Draft towers utilize centrifugal fans to blow air through the tower. The air is forced into a pressurized plenum inside the tower and then through the fill. This means that access into these towers is limited, since doors must be able to resist pressure without leakage and tend to be small and difficult to use. This also makes it difficult to observe the basin of these towers while operating in order to troubleshoot problems if necessary.

Induced draft towers use an axial fan to pull air through the tower, creating a negative pressure within the tower. This allows the unit to be built in an open configuration, making access and observation far easier. In general, induced draft towers cost less, are easier to maintain and, importantly, require about half the fan horsepower to do the same cooling as a forced draft unit.

In fact, there are only a few reasons why you wouldn't use an induced draft tower in preference to a forced draft tower:
1. Height restrictions
2. Static pressure capacity for ducted installations
3. Noise Control

If you project requires an extremely short cooling tower or needs a tower to be installed indoors with ducted inlets and/or outlets, there is a good chance you will need to use the less efficient forced-draft tower. And, until recently, it used to be that the same was true of sound-critical installations. But not any more.

The acoustical benefit of forced draft units are twofold: First, they are quieter than induced draft units right out of the box. (Low-profile forced-draft units are especially quiet.) And, secondly, they can easily accept sound attenuators to make their already quiet performance even quieter. The price you pay, of course, is fan energy and dollars. Attenuators require that you expend even more money and fan energy than the already more expensive and less efficient bare forced draft unit.

Th super low sound fan (SLSF) changes the playing field. The addition of the SLSF on an Evapco induced draft cooling tower does not affect the efficiency at all--the performance is the same with and without the quieter fan. And since the fan knocks 9-15 dBa off of the sound power of the tower, suddenly induced draft fans are competitive in sound level with a forced-draft unit. Generally speaking (and each application is different) a SLSF induced draft unit is just about as quiet (if not quieter) than a forced-draft unit of the same capacity--and very competitive in first cost. And further sound abatement is available to shave a few more dB off of the sound level.

This development makes it very possible to meet demanding noise criteria and still retain the sizable energy benefits of the axial fan. And with innovative products like the Evapco ESWA, the lowest-sound option can even be the energy leader!

Hearing is believing, so Evapco has provided a few video clips to help you get an idea of how significant this sound improvement is [videos may require Internet Explorer to work properly]:

Video 1
Video 2

More information on low-sound options is also available here (pdf).

After 10 years, Johnson-Barrow and JCI/York Announce Split

2007-10-19T09:39:00.000-07:00

JCI Worldwide services has recently announced a new HVAC products distribution strategy and support for its Building Efficiency business division which includes York international and JCI controls. In an effort to integrate its marketing efforts towards owners, contractors and engineers, JCI will be reorganizing its go-to-market strategy in 15 plus major markets around the nation, including Washington State. The plan is for York to be more directly marketed through the JCI offices with the assistance of an independent rep organization as a support service to the controls division. This will also include the integration of the unitary (Consumer Products) division into their new business strategy.

Wayne Garret, Western Regional Sales Manager for JCI, says the move is designed to better integrate the three aspects of the company. “We needed to get a single face to the customer regarding who JCI is. Unitary, Controls, and Engineered products needed to be more closely tied than was presently the case. This will help our customers get a better understanding of the JCI depth.”

Mark Johnson NW sales manager was asked what things will happen as a result of these changes. “In Markets such as Seattle, major changes are already underway to integrate controls, engineered products, and unitary equipment. Air Cold, a division of Ferguson has discontinued its representation of the York Unitary products. Johnson Barrow will be terminating it’s relationship with the Engineered products division, and finally JCI in Bothell, WA will direct marketing strategies for the Washington and other Pacific NW markets.”

Patrick Hollister of Johnson-Barrow commented that this announcement did not surprise their organization. “For years we have been figuring that York would reposition itself to better integrate the unitary and controls division into a more uniform marketing organization. Thus, over the last couple of years we have been positioning ourselves to be more diversified in our product and service offering. Evidence of this can be seen with the addition of AAON, Smardt Chiller, and Climate Cool. We want to maintain our independence as a solutions oriented company focused on unique products that provide value for our customers”.

When asked to comment on the JCI announcement, Gary Bodenstab of Johnson-Barrow echoed Hollister’s observations. “Look at the magnitude of change around the country. US Air has replaced Air cold in the major SW markets, Ferguson has dropped York. The controls division is in flux trying to regain market share in the NW markets. We figured some major change was underway in the NW—it was only a matter of time. We wish the best for JCI and its new strategy. It’s now time for Johnson-Barrow to focus on our roots of independent companies dedicated to market innovation, energy conservation, and customer value.”

FREE Psychrometric Software

2007-10-09T13:02:00.001-07:00

If you like the charts that I created to show psychrometric processes (like here), you're in luck.

Johnson-Barrow has made a deal to make this software available to our customers. We've also made some major aesthetic changes that we feel are a huge improvement: We've changed the chart colors and added a dynamic new logo!:

Pretty spiffy, huh?

The free version of the software allows you to do some simple analysis and process charting--allowing you to create high quality psychrometric charts for presentations or personal use. Additionally, a copy of the free version gives you a sizable discount off of the full version that is available here (chose HDpsychchart Pro Edition OEM upgrade SKU# HD1001, select Johnson-Barrow as OEM company).

The full version allows you to do the following:

Model mixing, direct evaporative and humidification processes
Create charts at any elevation
Add climactic bin data
Create flow charts
Create detailed psychrometic process data points tables
Vary the limits and extents of the chart axes
Show ASHRAE winter and Summer comfort zones
Project constant condition lines for ease of analysis

And many more tasks that make psychrometric chart analysis easy. The software also comes with additional tools like fan law calculators and even a loan payment calculator!

The free software is available for direct download on the toolbar to the right, on our www.jbarrow.com main page or right here.

UPDATE:

Some users have reported a problem with the software that prevents proper registration of the file. A new file that does not have this problem will shortly be uploaded.

A Giant Golf Ball in Your Outside Air Opening

2007-10-05T14:04:00.000-07:00

"What the heck is that thing"

That's often what we hear when we introduce people to the Tek-Air IAQ-Tek outside air monitor.

Sometimes elegant solutions to difficult problems are a little surprising.

The Problem: Outside Air Measurement

Getting an accurate measurement of outdoor air flow is a vexing problem for HVAC professionals. It's about the most difficult airflow measurement situation around.

The air is often moist, dirty, and at extreme temperatures. Most air inlets, especially on packaged air handling units, are poorly designed for accurate flow measurement. The airflows in the inlets are usually highly turbulent, non-uniform and at very low velocities. Wind impinging on the inlets can cause large flow fluctuations. This is tough duty for any flow measurement system.

To make matters worse, the outdoor air flow is one of the more important measurements in an building HVAC system with big implications to the indoor environmental quality and energy use of the building. Understandably, LEED® guidelines encourage the use of outdoor air monitoring.

Generally, the air flow velocities available at an OA probe need to be slow enough to prevent moisture carryover--this makes traditional pressure measurements with pitot-type sensors very unreliable, because the signal from these probes varies with the square of the velocity. At low velocities, the noise from turbulence, wind and other sources simply drowns out the signal with a very low signal-to-noise ratio.

This has led to the use of hot-wire anemometers (thermistors) in this application. These products provide excellent low velocity air flow measurement, but this application provides challenges unique to this technology. In particular, dirt and moisture build-up on the sensors will cause the calibration to stray and upstream filters are usually recommended. Additionally, since the sensors measure the velocity at a discrete point in the air opening, a large number of sensors are required to adequately provide a representative flow measurement for large openings. And even with a large number of sensors, the turbulence and non-uniformity of the airflow in an outdoor air hood or behind a louver makes it very difficult to get a useful reading, no matter how accurate each sample measurement is.

A Different Way

Tek-Air saw the above difficulties and looked for a new solution. And that's why they developed this unique airflow sensing device.

Most flow sensors are designed to minimize the disturbance they create in the airflow. Tek-Air realized they needed to take a different approach for this difficult challenge:

The IAQ-Tek probe is large--really large. In fact each sensor body is about 8" in diameter and has over a dozen pressure ports in it. It dampens out the effect of localized turbulence on the airflow measurement by forcing a large-scale diversion of the airflow in the inlet. The measured variable is the average pressure difference between the ports on the front of the sensor body and the ports on the back of the sensor body. The 'golf-ball' dimples in the face of the sensor ensure stagnation of the airflow to significantly decrease the effect of localized turbulence and ensure a steady, accurate reading.

The unique design of this probe allows accurate readings at 6-8" behind an oudoor air louver, and directly in front of dampers. No prefilters, air straighteners or sections of straight duct are required.

So what does this give you?

Accurate and stable low velocity readings from 75 to 750 fpm
Immunity to signal noise
Great flexibility in application

These probes can get accurate measurements in places you wouldn't even consider other OA probes:

The units come with a temperature and density compensating transducer (-40º to 120º F), for accurate measurement in all conditions. And each system comes with a Nema 4x monitor with LCD readout for local observation. They are rugged devices that need no significant maintenance requirements and can even be hosed down, if needed, for cleaning.

Can they really be accurate in such tight conditions? A test with the unit installed 4" behind a louver outlet, with 18" between the louver and an OA damper yielded the following results:

That's from -6% to +4% (of full range) error at velocities of 100 to 700 fpm with damper positions from full open to 45º. That's fantastic accuracy in an extremely difficult measurement condition.

So maybe you do need a giant golf ball, after all.

Rethinking Air Handler Pressure Testing Specifications

2007-10-02T16:25:00.000-07:00

Pressure testing is one of the most important ways to ensure the quality of the cabinet of an air handler provided on your job. Leakage costs money and energy. Every CFM that leaks out of an air handler is air that energy has been expended on that is now lost. Likewise, every CFM of air that leaks into an air handler displaces air that has been conditioned, requiring more air volume to do the same duty. And air leakage can have other negative effects, like causing condensation on surfaces or allowing unfiltered air to enter the system.

So to prevent leaks as much as possible, an experienced engineer will specify leak testing on the air handlers provided on their jobs. This is accomplished by blocking off all openings into the unit and pressurizing it (positively or negatively) with a pressure blower and then measuring the airflow into (or out of) the unit to maintain a test pressure:

Several decisions have to be made when deciding how to test the unit:

When to test (At factory or at jobsite)
How many sections to test
Positive or negative test pressure
What pressure to test to
How to set the failure criteria

When to test the unit

There is a very strong argument to be made that the only pressure test that matters is the pressure test performed on the site. After all, it really matters little to the final built out project if the unit performed flawlessly on the factory floor. The actual performance in the field is all that anyone really cares about. If only a single pressure test can be fit into the budget, it stands to reason that the field test is the one most critical to the overall quality of the delivered project.

However, there is a case to be made for a factory test, too. The field pressure performance of an air handler is not only a function of the manufacturing process, but is also strongly dependent on site conditions, including the flatness of the support the air handler sits on and the rigging and mating procedures used by the contractor. Once a unit is on site, it is sometimes very difficult to determine where the failure lies if it doesn't meet the specified leakage rates. In a worst case, you might have the manufacturer, the shipper, the installing contractor and the general contractor all pointing fingers at each other. If the fault actually lies in a factory defect, the problem could be found and corrected in the most controlled environment possible with a factory test.

So the real answer? Both, if you can afford it. And if you catch a problem before it gets to the field, you might feel you couldn't afford not to do both.

How many sections to test?

Many pressure tests specifications treat the entire air handler as a single section, and require a single test for the whole unit. Some break the unit up into positive and negative pressure areas (upstream and downstream of fans, respectively) and call for them to be tested separately. Each method has its advantages and its disadvantages.
The first consideration is cost. Each test costs time and energy that will be reflected in the overall price for the job. Requiring multiple tests on a single unit will raise the cost of the air handlers to the owner. This will also require more time at the factory and on site, and could affect overall completion dates in some instances.
A second consideration is accuracy. Since multiple tests allow the unit to be tested to the actual pressure condition the sections will see, presumably this will give you a better idea of the leakage than a single test. However, there is an appreciable amount of leakage within the air handler at the internal wall that will be factored into this measurement (and double counted!) that will unrealistically penalize the performance of the unit. This is especially significant, since the internal openings within an air handler (at fan walls, usually) that need to be blocked off to perform the test are rarely built in a fashion that allows for an effective air seal to be created for these temporary tests. Even a small amount of leakage at these internal walls can mean the difference between passing or failing a tight leakage criteria.
Consider a single test for units unless special requirements drive a need for multiple positive and negative tests.

Positive or negative test pressure?

If you are making multiple tests on multiple sections of an air handler, the answer to this question is simple: Test to the conditions each section will see in operation. If you are performing a single test on the entire unit, then you may want to carefully consider how you wish to test the unit. In general, there are some leaks that will open up under one pressure condition and will close under the other. Generally it is accepted that leaks at panel seams tend to close under negative pressure and tend to open under positive. Doors that swing out tend to behave similarly, while doors that swing in behave in the opposite fashion. Seams at test closures can do either based upon the method of construction of the closure. So there is no easy rule of thumb that says one method is preferable to the other. In many cases it makes sense just to find the point of extreme pressure in the unit under normal operation, determine if this is positive of negative, and test to that condition. This condition is easy to find by simply calculating the pressure condition at each section in the unit by starting at the external static pressure and working towards the inlet, adding back pressure losses at each internal component, and subtracting the fan static pressure increase at the fan wall. Each open section of air tunnel will have a pressure associated with it, with the extremes usually falling at the inlet or discharge plenum of the supply fan. These are the maximum pressures the air handler will see in operation--and usually one will be significantly further from ambient pressure than the other.

What Pressure to test to and
How to set failure Criteria

The above two considerations go hand in hand, so I will deal with both of them together. Traditionally, specifications are written so that a certain percentage of the total air flow is allowed in leakage (usually around 1-2%) at a specific test pressure. How the leakage percentage and the test pressure are determined varies from engineer to engineer and job to job. Sometimes the test pressure is based on the total fan static, sometimes it is based on the actual cabinet pressure, and sometimes it is based on a nominal test pressure (like, say 10"). In either of the first two cases, there is usually a sizable safety factor applied.
The allowed leakage percentage varies, but it is usually in the low single digits.
While this has been the standard in the industry for many years, there are some significant weaknesses in this approach to testing. First, the actual leakage rate measured in the field is determined essentially by the total face area of all the leaks in the system--this is a function of cabinet size and construction quality, not of supply air flow. By tying success or failure of the test to the fan capacity of the system, you are favoring simpler, smaller air handlers over larger, more complicated air handlers.
Imagine a simple 10,000 CFM air handler operating at 8" of total static with just a fan, a heating coil, prefilters and a mixing box. Then imagine that same air handler, but with a cooling coil, high efficiency final filters, return fan and air blender:

(click for larger image)

In the example above, you have two 10,000 CFM air handlers, one with 297 square feet of cabinet area, the other with 630 square feet of cabinet area. The large air handler has more than double the cabinet area, and more leak points such as doors, dampers, coil penetrations and shipping splits--yet both would be required to meet the same leakage rate in a test--in this case, say, 200 cfm at a 2% leakage criteria.

A further complication would arise with the pressure selection. A common pressure test criteria is 1.5x the maximum fan static pressure--or in this case, 12". It is often difficult to find a pressure blower with a static capability in this range--It might be impossible to effectively provide this test in a timely manner on a job site. Additionally, many components (especially doors, when tested in a pressure condition opposite that they would see in operation) leak uncharacteristically at higher pressures. And the unit would never see pressures anywhere near 12" in real operation, anyway, since the fan will typically create an area of negative pressure in the inlet plenum, and positive at the discharge. The maximum amplitude of either pressure is, by necessity, less than the total static pressure capability of the fan. Thus the leakage rate measured in the test will be a very significant overestimate of the actual leakage that will be experienced in operation.

A different way of specifying pressure performance can address both of these complications--and that is to tie the performance to the cabinet itself, as opposed to the air flow. There is already a criteria to do exactly this. ClimateCraft recognized the difficulty with specifying pressure test criteria to arbitrary pressures and airflow percentages. They realized that SMACNA already had a pressure test criteria, the SMACNA leak class rating. The leak class of a pressure plenum (or air handler, in this case) is calculated using the following formula (from ANSI/ASHRAE 111-1988):

Leak Class	=	(leak CFM) x 100
		(Area sq.ft.) x (Test Pressure) ^ 0.65
OR
Leak CFM	=	(Leak Class) x (Area sq.ft.) x (Test Pressure) ^ 0.65
		100

ClimateCraft has adopted this method of rating pressure performance and builds their units to meet or exceed a leak class of 6. For the units above, that equates to about 146 CFM at 8" for the larger unit, and 69 cfm for the smaller (or 1.5% and 0.7% of the supply air volume, respectively).

In practice, we have found that a leak class of 6 represents excellent performance for high-quality custom air handling units of any of the manufacturers we represent and quite often can be met by the high-quality foam panel semi-custom air handlers by Aaon, too. This is, however, a very high bar for traditional commercial-grade batt-insulated air handlers.

Perhaps the biggest advantage of the leak class specification is that it encompasses both the allowable leakage critiera and the test pressure in a single number. A leak class 6 air handler will perform to the same leakage class whether it is tested at 4" or 10"--the test pressure can be chosen to meet realistic pressure conditions and to facilitate testing of the unit. It is purely determined by the design of the air handler cabinet and the execution of assembly.

Reducing Ground-Loop First Costs

2007-09-26T06:37:00.000-07:00

Ground-Loop heat pump systems perhaps have the greatest potential for reducing energy use in the built environment than any other space-conditioning technology now in use. This potential has been long recognized by the EPA and the DOE, and represents a great opportunity for owners and designers attempting to create systems that out-perform those that are commonly built in this region.

They also have a reputation for being expensive--very expensive.

And with drilling costs in this region historically being quoted as high as $15/lineal foot, this reputation is well deserved. These prices usually put this technology out of the range of economic justification for typical projects.

So what can a designer do to minimize costs, yet still provide the energy benefits of this technology?

Add a cooling tower.

Hybrid Systems

To understand how adding a cooling tower to a ground loop saves costs, first you have to understand a simple concept about closed ground-loop systems. While the ground loop is often referred to as a "heat exchanger", the ground-loop (and the ground it occupies) acts more as a leaky heat storage battery. Unless there is sufficient ground-water movement through the well-field, most of the heat that is rejected into the ground remains there throughout the year unless it is later removed by the ground loop itself.

That means that over time, if the heat added is not balanced by heat removed, the ground temperature will continually increase over the seasons, increasing loop temperatures and decreasing system efficiency.

(graph showing increase in temperature over time for imbalanced loop of differing bore hole numbers. From here)

The best situation for a designer is when the heat added to the ground over the course of the year (by the process of cooling the building) is balanced by the amount of heat removed from the loop (by the process of heating the building). But a heat-pump does not just move heat from one source to another. Because a compressor is needed to perform this work, a heat pump always adds the heat of compression to the equation. This is a benefit in heating, since the heat of compression is added to the amount of heat moved from the loop to the building. This is a hindrance in cooling, since this compressor heat is added to the heat moved from the building to the loop. In practice, about 1.2 to 1.8 tons of heating are needed to balance out 1 ton of cooling. This means that many ground loops will see an imbalance where more heat is rejected to the loop than is removed from the loop over the course of a year. This effect can be significantly compounded (or mitigated) by the configuration and use of the building served--buildings with significant yearly cooling loads will be more affected than by buildings dominated by heating loads.

A ground-loop designer typically combats this effect by increasing the volume of the well field by increasing the number wells to a point where the relatively small amount of heat-leakage out of the well-field and added volume is enough to account for the imbalance of the system and minimize the heat gain. Thus ground loop well-fields are often sized due to the minimum requirements of either heating or cooling demand for the building. Cooling-dominated well-fields are more common throughout the US, especially in the southern portion of the country.

If the designer could correct for this imbalance and build the loop to the smaller size required by the heating load of the building, then fewer wells would be needed, and thus the overall cost of the loop would come down. One of the most cost-effective ways to provide extra cooling to balance out the loop on such a system is by way of a cooling tower or fluid cooler. When a cooling tower is used in conjunction with a ground loop, you have what is called a hybrid system.

Hybrid systems can be extremely effective at bringing down first costs of ground loop systems. A study by Kevin Rafferty of the Oregon Institute of Technology found that hybrid systems can reduce the cost of a ground loop by as much as half for some systems:

But can we expect similar reductions in first cost for the Puget Sound region, where we have a generally cool climate and a long heating season? For some systems, it appears the answer is yes. A presentation by Scott Hackel of the University of Wisconsin at the ASHRAE 2007 summer meeting investigated the cost savings possible using hybrid systems throughout the country. His study showed very significant reductions in ground heat exchanger (GHX) loop lengths for school, retail and office applications in the Seattle region:

(Click for larger image)

Hybrid loops may just make the next ground loop you consider pencil out.

Digital Scroll Compressors: Just Plain Cool

2007-09-23T07:55:00.001-07:00

Copeland Compressors (now a Division of Emerson) has recently introduced their digital scroll compressor technology. This is one of the most interesting products to come out in a long time for the DX cooling market. But to understand why it is so cool, you first need to understand a little bit about scroll compressors in general.

Scroll compressors have essentially displaced the older reciprocating compressor designs for small-tonnage air conditioning systems. Which is much to the operator's benefit, because scrolls are inherently more reliable and require none of the maintenance that the piston-type reciprocating compressors required. But this advantage comes with a price: comprehension. Reciprocating compressors were so much easier to understand--since the compression stroke in a piston is easy to grasp and most people are familiar with this process from the similar function of pistons in gas engines.

Some smart guy had to come along and invent a highly efficient and low-maintenance compressor technology that no one can describe easily--even using curious arm gestures and words like "orbit"!

The secret to a scroll compressor is two high-precision spiral "scrolls" that are designed to mesh with each other to extremely close tolerances:

The upper scroll is stationary and the lower scroll 'orbits' in a rotary fashion:

Comparison of scroll to piston compressors showing relationship of upper and lower scroll (click for larger image)

The upper and lower scrolls continually 'pinch' off volumes of low pressure gas and move them towards the center of the scrolls, compressing the volume further and further as they work. This compression requires extremely close tolerances between the sides and ends of the scroll surfaces, since the only seal is the lubricating oil in the refrigerant circuit. If tolerances are to great, no seal is effected and the compression is lost.

Still hard to picture? This animation should make things a bit clearer:

So, great: We have a highly efficient compressor with two capacity settings: 'On' and 'Off'. If you are trying to meet a close control spec, this may not be close enough control. You would typically overshoot and then undershoot the required cooling capacity as the compressor kicks on and off. And since anti-recycle timers are required to prevent overheating the compressor motor, there is a limited number of times the cooling capacity can be switched on and off in an hour.

A new innovation allows two-step unloading to 66% capacity--but this can still be a pretty big step of control on a small refrigeration system--especially ones with only a single compressor. Wouldn't it be nice to get a fully modulating compressor with all of the advantages of the scroll compressor?

That's where the digital scroll comes in. Copeland's engineers were clever enough to realize that they could achieve this performance out of a scroll, not by modulating its capacity directly, but instead by modulating the time during which this capacity is provided. They found that if they quickly turn on and off the compression cycle, without having to turn off and on the compressor motor, they could modulate the output very closely to meet the needed capacity. The trick was finding a mechanism by which this rapid switching between active and inactive compression could be accomplished.

The solution they arrived at was elegant. They found that by merely moving the scrolls apart axially, they could defeat the oil seal between the scrolls, and turn off the compression. Then they simply needed to move the scrolls back together and compression would immediately restart.

The above graphic shows the scrolls separated to cancel out the compression cycle, and a visual representation of how the scroll would operate to provide 50% capacity--Operating 10 seconds on and then 10 seconds off in a repeating cycle.

What's the result? Very efficient operation down to 10% of full capacity:

(click for larger image)

See the savings noted above? That's compared to the commonly used DX modulation method of hot gas bypass (HGBP). It's important to note that the HGBP works by applying a false load to the compressor--it does not reduce compressor energy at all! As far as the compressor motor is concerned, it is doing just as much work as when the compressor is providing full output. In fact, the HGBP system is even more of an energy hog than is suggested by the graph above--since compressors with this device will operate at full load for extended periods of time, drawing full amps all the time, as opposed to a standard system where the compressor would turn on and off to match the load.

The digital scroll gives a DX system all the fine control capability of a chilled water system, without sacrificing energy performance like HGBP systems do. It allows effective operation of VAV airflow systems without frosting coils. It provides efficiencies unmatched in the DX market. For these reasons Aaon was quick to incorporate these compressors into their RM and RN rooftop packaged AHU lines. Unfortunately, digital scrolls are not available in all standard scroll compressor sizes and voltage ratings. And they are currently only available in R-22 compressors. This handy chart indicates where the digital scrolls are available in each RM/RN model size and for which voltages. This file is valid as of 9/22/07, and is definitely subject to change in if/when new digital scrolls are released. Additionally, R-410a compressors are expected out in the near future for 6, 7, 13, 15, 16 and 25 ton sizes in 460/3ph electrical services only. Stay tuned for the availability of those units!

Update: Aaon has rolled out units using R-410a digital scrolls, as well as new software to calculate the efficiency benefits of these compressors.

Aaaah...They're Just Jealous

2007-09-23T07:37:00.000-07:00

Admit it: Did your mother react this way, too?

HVAC System Efficiency Tool

2007-09-22T11:03:00.000-07:00

Designers and owners are continually bombarded by claims of equipment efficiencies. Industry groups such as ARI, AMCA or CTI have been set up to validate these equipment efficiencies to give these claims credence.

However, it isn't the equipment efficiency that drives the energy use of the building, but the overall efficiency of the system that the equipment is part of.

Steve Kavanaugh, University of Alabama Professor, ASHRAE fellow and author of the ASHRAE design guide for ground-loop heat pump systems (with Rafferty) stresses the importance of the system efficiency. He has also provided (free of charge) a handy tool to calculate the system efficiency of typical HVAC systems, given the efficiencies of their component equipment.

This tool (HVACSysEff06)is available at Steve's Geokiss website software download page.

Take a look around--there are some other interesting tools there, too.

Heating Your Showers with Your Cooling Tower

2007-09-21T19:26:00.001-07:00

Most large buildings are throwing heat away for many hours of the year. In a large facility, this is most often accomplished by way of a cooling tower. Commonly, the cooling tower cools water from about 95º to around 85º. Many hundreds of thousands of btuh's from lighting, solar loads, equipment and any of the myriad heat load sources in these facilities are rejected to the atmosphere in this cooling process. Wouldn't it be nice if you could reclaim some of that heat and use it for a something that always requires heat input, like domestic water heating?

Sure, you could take the cooling tower water and run it through a heat exchanger to preheat the makeup water from the city utility before it enters your hot water heater, but that would only offset part of the heating load. The highest temperature you could reach would be on the order of 93º--any higher would require artificially allowing the condenser water to heat up, penalizing the efficiency of the chiller it serves.

It would be a lot more convenient if there were some way to use the heat in the condenser water loop to create higher temperature water--water that could be directly used to heat domestic water. And that is exactly why Colmac developed their HPW series of water-to-water heat pumps, specifically designed for domestic service.

These heat pumps include a circulating hot water pump and a double-wall heat exchanger as required for domestic service. They can directly heat the domestic water to temperatures of 140º or higher, using water as cold as 55º. This means that they can actually be used to pre-cool chilled water to reduce load on a chiller, as well as take waste heat out of a condenser line.

Florida Heat Pump also has a full line of water-to-water heat pumps for similar heat recovery jobs. These are a competitive alternative when domestic water service is not required, or where an external heat exchanger can be provided to meet domestic service requirements. These are also very flexible alternatives to traditional central plant chillers, with the ability to reverse cycle and provide hot water or cold, and come in convenient modular sizes for ease of installation and efficient capacity staging.

And there is no reason to stop at considering condenser water systems for sources of heat. Using water-to-water heat pumps, any source of flow that carries waste heat can be utilized to provide usable energy for your system. Why not pump heat out of your sewer lines? Luckily for the creative energy engineer, smells aren't transfered by the refrigeration cycle!

Advanced Tower Nozzle Design Eliminates Clogging

2007-09-21T06:05:00.000-07:00

Anyone who has operated cooling towers for any significant amount of time knows that a common maintenance point is clearing clogged water distribution nozzles. This is especially a problem for gravity-fed cross-flow towers, where there is very little pressure to force debris through the nozzle orifice, and debris such as leaves, paper and ferrous 'throw' from the pipes can clog the nozzle. This reduces the effectiveness of the water distribution, and in turn the efficiency of the cooling tower.

Typical cross-flow tower gravity distribution pan

Pressurized distribution systems, as are found on Evapco counter-flow towers, eliminate a lot of clogging problems by utilizing pressurized large-orifice nozzles which use the force of the water pressure to keep the nozzles clear. But even these types of systems can clog periodically.

So that is why Evapco developed the Evapjet nozzle.

That's a nozzle?

Yes, it is, but probably the best way to appreciate it is by watching the video of it in action: Evapjet Video (may require Microsoft Internet Explorer to view).

(Pretty cool, huh?)

Importantly, this nozzle can pass a 1" ball, and reduces the total number of nozzles required for a tower by 66%! So you have a much reduced chance of clogging, and many fewer nozzles to maintain.

This nozzle is provided on new Evapco cooling towers, and is available for retrofit on many existing towers of most major manufacturers. If you are interested in retrofit, call Fluid-Tek for a quote!

UPDATE: 9/23/07

Don't be discouraged if you have a fluid cooler and not a cooling tower. Evapco offers their unique ZM (Zero Maintenance) nozzles (pdf) with similar anti-clogging properties as the Evapjet--they just don't make for as cool a video!

Read more about spray header and nozzle replacements here.

Saving Water With Evaporative Condensing

2007-09-20T06:25:00.000-07:00

Using evaporative cooling makes energy sense, not just in directly cooling the air, but also in cooling the heat rejection portion of a compressorized cooling system. This is because refrigerant compressors can be thought of, simplistically, as pumps. In a pump, two things govern energy use--the flow rate of fluid through the pump, and the head that pump needs to overcome to move the water. The same is essentially true for compressors.

In a compressor, the mass flow rate of the refrigerant essentially determines the cooling capacity it is providing. So for a given cooling load, we can't reduce the flow rate to increase our efficiency. All that is left is the compressor head. And that is something that we can effect.

In a refrigerant system, the condensing pressure of the refrigerant vapor is determined by the temperature of that refrigerant.

Let's look at this relationship for R-410a (from DuPont .pdf here):

We can see that the condensing pressure for 120º R-410a (which is around where an air-cooled condenser would operate) is about 450 psi. Compare that to a condensing pressure of about 280 psi or so at a temperature of 90º-which is an easily attainable condensing temperature in an evaporative condenser in the Pacific Northwest. When you consider that a reasonable suction temperature might be about 42º (or 150 psi) reducing your condensing temperature from 120º to 90º represents a head reduction of nearly 60%! In practice, moving to an evaporatively condensed piece of equipment from a comparable air-cooled piece of equipment can improve NPLV's by about 20% or so.

So, obviously, this makes sense from an energy conservation point of view. But what about water use? The obvious trade-off is that you are now using water where before, in the air-cooled case, you weren't. So how can we reduce the use of water while still benefitting from the reduced head pressure on the compressors?

To understand how how to improve water utilization in these systems, it is important to know what the state of the industry is for evaporative condensing. A typical system is illustrated below:

What you typically have is an induced draft evaporative unit that sprays water over a refrigerant coil. The water evaporates, and that evaporation cools the refrigerant in the coil. The remaining water falls into a basin where a pump then sprays the water back up over the coil again. All the while, a fan operates to draw air past the water and enhance the evaporative process. Importantly, every 1000 btu rejected by this system reflects about pound of water evaporated.

So what can we do to reduce water use? Well, the obvious thing is to reject less heat via evaporation. However, this might seem problematic because we want to maintain the low condensing temperatures that we can reach using evaporation. This is where it is important to understand a little about how refrigerant systems really work.

One of the main concerns with refrigerant compressors is they are designed to move gas--not liquid. A very effective way to break a compressor is to introduce liquid into it. So to be sure that no liquid enters the compressor, refrigeration systems are designe to operate with a few degrees of superheat. This takes the refrigerant safely away from the saturation line, and assures that the compressor will not see any liquid. However, this adds some extra heat into the system that then need to be rejected. Then, through the operation of the compressor, even more heat is added into the system, taking the system even further away from saturation.

However, the additive effect of the intentional pre-compressor superheat and the heat added by the compressor itself means that there is a significant amount of heat in the refrigerant that needs to be rejected before refrigerant condensing can even start. This de-superheat process is illustrated below:

(click for larger image)

If this heat can be removed without requiring evaporation, a significant amount of the water use can be eliminated. And this is exactly the approach that Aaon has taked with their evaporative condensing design. Their solution is illustrated below:

The main difference between the first system and this one is the addition of a finned desuperheater coil located above the spray system, in the cool, saturated air stream above the wetted portion of the condenser. This coil allow the system to reject the superheat without using any water--saving, on average, about 20% of the water use at peak load.

However, the benefits extend beyond there, since at about 70º ambient, this coil can reject about 50% of the total heat in the system, and it can reject 100% at about 30º ambient. So the true water savings range from about 20% to 100% depending on the operating profile and ambient conditions of the unit.

There are still other benefits: If chemical water treatment is being used on this system, the lower water use will translate to lower chemical use. And, since the tube surfaces in the wetted portions are at lower temperature in the Aaon system, there is a corresponding lower chance of creating scale--which is formed primarily from calcium carbonate which exhibits inverse solubility, depositing much more readily at higher temperatures. This lower fouling, in turn means the system will operated more efficiently for years to come, since less scale means better heat transfer at the tube surfaces which means lower head pressure on the compressor!

Introduction to Indirect-Direct Evaporative Cooling

2007-09-18T06:04:00.001-07:00

Now that we have covered the basics of the indirect and direct evaporative cooling processes, it's time to consider one more wrinkle--putting them together.

In the IDEC cooling discussion, I made the point that not only do we get a reduction in dry-bulb temperature as our airflow passes through the IDEC unit, but we get a reduction in wet-bulb temperature, also. And since we now have seen that the direct evaporative cooling process depends critically on the wet-bulb temperature of the air it is cooling, it seems we should get some advantage by running the air through the IDEC section, and then running it through the direct section. And we do:

(click for larger image)

As you can see, the resultant leaving dry bulb is on the order of 64º, which is better than the resultant of 72º from the indirect section alone, or 69º for the direct evaporative section alone. Now 64º degrees may not seem cool enough for typical cooling applications--and for most projects it probably isn't (although it is important to not that ASHRAE comfort conditions can be met with this leaving air condition in a predominantly sensible load application given enough air). But keep in mind that this is the performance on a design day. How many hours a year would you be able to meet the traditional supply air temperature of 55º? Lets look at psychrometric chart with Seattle bin data loaded into it:

(click for larger image)

A quick note of explanation: The vertical line at 55º is the economizer line--any climactic conditions to the left of that line can be used to create cooling air directly using OA alone (or mixing OA with RA) and thus require no additional cooling at all. The blue diagonal line along the 53º wet-bulb line is a conservative mapping of the direct evaporative regime. At any bin hours under this line, direct evaporative cooling can be applied to the ambient OA to achieve cooling air directly. And lastly, the red diagonal line above that is the indirect-direct evaporative cooling regime, where the application of both cooling techniques will provide acceptable supply air conditions (assuming about 70% effectiveness on the IDEC). And above that line, the indirect evaporative system can still be applied to greatly reduce the load on any supplemental mechanical cooling system, if used to meet the same 55º leaving air condition.

Two things jump out of this analysis: First, the vast majority of the hours are satisfied without using mechanical cooling. In fact, in Seattle, most hours are met with simple economizers--which explains the emphasis in our local codes on this cooling technology. You can even think of evaporative cooling as simply an enhancement to the standard economizer. The second takeaway is that there are still quite a few hours that are not met. How can we address this?

Well, one way is to play around with the leaving air temperature. If we supply some more air to the zone, we can provide warmer cooling air. Let's look at that same chart, only this time lets use a supply air temperature of 60º:

(click for larger image)

By simply providing for a little more air to the zone, we meet a much higher percentage of the bin hours; so much so you that can now consider a system without mechanical cooling, as long as the occupants are willing to accept a few more hours outside of standard comfort conditions a year. Granted, this additional comfort comes at an energy cost--the cost of moving that additional quantity of air. This cost is, of course, offset by the avoidance of mechanical cooling. But, additionally, we know from the previous chart that this additional air is not needed all of the time. A variable speed control on the fans would naturally bring the air volumes down during periods where colder air is achievable.

One of the things that should be obvious is that this analysis is greatly dependent on the local climate and elevation of the project. To evaluate how effective this cooling method is, you need to create similar plots for each project locale. And where you are in the state has a great effect on how well you do. For example, a cool-wet climate like that on the Olympic Peninsula sounds like it might be a good candidate. So let's see how it compares to Seattle:

(click for larger image)

It looks pretty similar to Seattle, as we might guess. How about a hot, dry climate like Spokane?:

(click for larger image)

That's a real winner! There's only a small fringe of hours outside of the range where indirect/direct evap works alone. So if Spokane works, surely Yakima must also be a great candidate:

(click for larger image)

Hmmm... There's quite a few hours outside of the indirect/direct evap zone. Good thing we did this analysis before committing to a evaporative-only system!

Indirect-direct evaporative cooling, either as the main cooling technology or as an enhancement to the economizer cycle is a technology that has wide application in the Pacific Northwest, even in rainy Seattle. But it is a technology that requires careful analysis--it's not as simple as throwing compressor tons at a cooling problem. With today's emphasis on energy efficiency and sustainability, it is a technology that deserves a second look.

There is certainly more to talk about on the subject. Future topics will include integrating compressorized cooling with an evaporative system, indoor comfort conditions, water treatment and maintenance, control of evaporative systems. and the role of return air in these systems.

Resources you may find useful:

Energy Labs Indirect/Direct System Performance Calculator (Simply the direct and indirect calculators linked together
Energy Labs Direct/Indirect Evaporative Systems Engineering Guide (booklet format)

ECM Motors and Heat Pumps

2007-09-17T06:22:00.000-07:00

What are electronically commutated (ECM) motors?

These are single-phase motors running off of a DC power signal (rectified, if running off of an AC power source) that use an electronic method of switching power to alternating coils around the rotor in order to induce a rotating magnetic field. (More information available here).

They are much more efficient than traditional electro-mechanically commutated motors, and local utilities offer rebates for their use. But ECM's also provide additional benefits on heat pump applications.

Because the motor speed is controlled by the speed at which the magnetic field rotates around the shaft, and that speed is controlled by the electronic switching of the ECM, these motors are inherently variable speed devices. When applied in equipment, this variable speed capability is either used directly, providing a variable speed capability on the fan, or, more commonly on packaged refrigeration equipment, as a self-balancing mechanism to provide a fixed discharge airflow, independent of external static pressure.

Additionally, the electronic switching in these devices allows for more torque to be delivered to the rotor, allowing for greater static pressure capability on the fan it is driving.

Florida Heat Pump has capitalized on these advantages by offering ECM motors on their heat pump products. FHP ES and GS series heat pumps are supplied with ECM fan motors for efficiency, ease of air balancing, and unmatched static pressure capacity.

Let's consider those last two further. FHP uses the ECM to self-balance their units to a set leaving air flow (low, medium and high settings controlled by jumpers on the control board) regardless of external static on the fan (within a given range). Let's look at the fan table for these units (2 1/2 ton ES030 shown):

(click for larger image)

You either get 850, 1000 or 1150 CFM at anywhere from 0.10" to 1.2" of external static pressure. All you do is set the jumper to the flow rate you want to see and then the fan motor will automatically adjust itself to provide the airflow desired.

But look at that range of static pressure! Typical heat pump fans might only provide three tenths of an inch or so external static. Having over an inch available (smaller units offer about 0.80" external) is a game changer, making it very possible to have improved filtration (LEED® points) or air side economizers (energy code requirement) on these inherently efficient heat pump systems!

And these advantages are above and beyond the improved energy efficiency that is realized by using the more efficient fan technology.

ECM motors improve WSHP efficiency, reduce balancing labor and widen the applicability of these already efficient systems.

Advanced Airflow Measurement

2007-09-16T13:26:00.000-07:00

Airflow measurement is a tricky business. Getting an accurate reading is dependent on a host of factors, not the least of which is the inherent accuracy of the technology you are using to measure the flow velocity. Traditional airflow measurement has usually utilized either pitot-type probes or hot wire anemometers, but each technology has its own drawbacks. Pitots rely on the velocity pressure of the air to develop their signal, so at low speeds the noise-to-signal ratio makes readings unreliable. Hot wires are sensitive to moisture and require complicated signal conditioning to resolve their output. Both are susceptible to fouling and require periodic re-calibration.

Tek-Air has developed an advanced airflow measurement technology that eliminates many of these traditional weaknesses, and delivers highly accurate, robust air velocity measurement.

The VorTek air sensor uses the physical phenomenon known as vortex shedding to accomplish this remarkable performance. Vortex shedding is the creation of alternating spiral eddies off of the back side of a bluff body in a flow of any fluid. Examples are the eddies off of a rock in a stream, the ripples in a flag, or, as seen below, the clouds behind an island in the trade winds:

The VorTek sensor uses a simple trapezoidal bluff body that is positioned in the air flow to create these alternating vortices. Two small pressure ports on the back side of the sensor body measure the local air pressure, and the frequency with which a low pressure (due to the shedding vortex) is switches from one side of the body to the other is determined.

(vortex generation behind VorTek sensor body)

There are several reasons why this technology has advantages over traditional measurement methods. The first is calibration. The principle by which the air velocity is measured is simply a property of the geometry of the bluff body in the airflow. This is not a characteristic that will drift over time, so the calibration of the device when installed will be the same as the calibration of the device years downstream.

The second advantage is noise-to-signal ratio. Unlike other technologies where a analog signal amplitude depends on the velocity of the air, the output from the VorTek sensor is a digital signal that is insensitive to fluctuations in a pressure signal--the device simply counts the number of vortices shed off of the sensor and converts this number into an analog velocity output.

Another advantage is signal conditioning. The VorTek technology depends on a linear relationship between vortex shedding frequency and velocity. Creating a velocity output is as simple as applying a constant to the measured shedding frequency. Note how much simpler this is than either hot-wire or pitot technology.

And lastly, the VorTek sensor is extremely insensitive to particulate fouling, as this demonstration illustrates:

(errata: 25 is not the 'square root of 50', but 25% is the square of 50%)

The VorTek sensor was designed for demanding applications like fume hood service, but is applicable for any airflow measurement job. And with accuracies on the range of +/-2% of signal for its entire range of measurement, it will meet the most stringent specification requirement. Cutsheets for the Tek-Air air flow stations using this sensor can be found here and here.

Playing With Gas Density

2007-09-14T11:05:00.000-07:00

I wonder if this works with R-134a, too?

We Have Moved

2007-09-14T08:15:00.000-07:00

As many of you probably know, Johnson Barrow, Inc. & Fluid-Tek have decided to move to a larger and more convenient location. With this move, we are expanding our office space to accommodate recent employment opportunities and the ability to stock miscellaneous replacement parts.

We hope you take this opportunity to update your current mailing list and we plan to do business with you in the near future!

2203 23rd Ave South
Seattle, WA 98144

HCFC Phaseout Timeline

2007-09-11T06:38:00.000-07:00

It's Fall of 2007: Do you know when your HCFC phaseouts are?

In 1989, the United States entered into a international treaty agreement to limit the production of ozone depleting substances as originally agreed to in the Montreal Protocol. This treaty was an effort to curb and hopefully reverse the observed ozone depletion in the upper atmosphere.

As most in the HVAC field are aware, however, this means that many of the traditional refrigerants we are used to using have either been or will soon be phased out of production. All CFC's are currently phased out, but HCFC's are soon to leave the market, too. The two major HCFC's in use today are R-123 and R-22. R-22, additionally, has been accelerated in its phase-out schedule beyond the original Montreal agreement. The schedule can be found on the EPA webpage, but to summarize, all R-22 is scheduled to be phased out for new equipment in 2010, and all other HCFC's, including R-123, are scheduled to be phased out of new equipment by 2015. No production or importation for these products, for any use, will be allowed after 2020 and 2030, respectively

The R-22 phaseout schedule is depicted below:

(click for larger image)

Why should you be concerned about what refrigerant you specify today? You should be able to get R-22 for the next 13 years for replacement in existing equipment, and the next 23 years for R-123. So why worry?

Perhaps the main issue is less about the refrigerant itself, and more about the refrigeration components. For example, once the phaseout date for new products hits, compressor manufacturers are unlikely to continue making compressors to operate on the phased-out refrigerants. Thus, while R-22 may be available, the replacement compressor for an R-22 system may not. It just is not cost-effective for these manufacturers to keep production lines in operation building an obsolete product.

One manufacturer's projection of the R-22/R-407c/R-410A market share picture is described in the following graph:

(click for larger image)

You can see that by 2008, R-22 is expected to be about 60% of the market, and then precipitously drop off to 0% by 2010. R-407c is expected to follow R-22, as the HFC R-410a takes over the market. And a similar picture exists for R-123, with already three of the four major chiller manufacturers in the US having phased out this refrigerant in favor of R-134a--and European markets already closed to R-123.

The dual concern of parts and refrigerant availability should be considered when choosing a refrigerant for your project. This article from FacilitiesNet discusses the overall trends of the industry and summarizes the effect of the Montreal accords. It raises special concerns about R-123's future availability:

Though other HCFCs are in the mix, this policy proposal raises questions about the availability of R-123 in coming years. Since R-123 has been used in only one type of equipment — centrifugal chillers — and historically has been produced by two manufacturers — and only one manufacturer currently — the certain availability of this refrigerant in the near future comes into question.

Refrigerant choice impacts the cost of ownership of the capital investment in a facility. Be aware of the impacts of that choice up front, to maximize the economic benefit of your cooling system.

Updated: Sept. 12:

HPAC Engineering has just published an article entitled 20 Years of the Montreal Protocol.

Timely, Huh?

Introduction to Direct Evaporative Cooling

2007-09-07T12:06:00.000-07:00

Now that we have discussed Indirect evaporative cooling, let's move on to the next question: What is direct evaporative cooling?

Direct Evaporative Cooling is a process where air is sensibly cooled by the effect of the evaporation of water directly into the delivered air stream. This is typically accomplished by use of a wetted absorbent media in the air stream, most commonly Munters CelDek (pdf) or GlasDek (pdf).

Evaporative media in an Energy Labs Unit

This process has the advantage over IDEC systems in being much more efficient (with efficiencies in the range of 90% easily attainable), but with one major difference: Direct Evaporative cooling is an adiabatic process. This means that there is no energy added to or removed from the airstream. The enthalpy of the air is unchanged, even as the sensible temperature is cooled.

How is this possible? Well, essentially you trade sensible heat for latent heat. As you reduce the dry-bulb temperature of the air, you concurrently increase the humidity ratio of the air. What you lose in sensible heat, you make up in the heat embodied in the evaporative phase-change of the water.

What does this look like on a psychrometric chart? Take that Seattle design day* of 85º/67º db/wb. Let's bring in 22,000 CFM of 100% OA. If we select a direct evaporative system with an 89% efficiency, the leaving air temperature will be about 69º/67º. Note that the wet bulb is essentially unchanged. The chart of this process is below:

(click for larger image)

Essentially, for this service, you get about 32 tons of sensible cooling but and zero tons of total cooling. If you were to allow this supply air to warm sensibly to a room temperature of 75º, you would find that the space RH would be close to 70%, which would probably not be acceptable for standard comfort cooling applications. However, in high-sensible cooling applications, like, say, data centers, this method of cooling has great application.

Additionally, since the resultant indoor conditions depend greatly on the outdoor air conditions, Direct evaporative cooling can provide acceptable air conditions for much of the year in a cool, dry climate like Seattle. In fact, any time the ambient wet bulb temperature is 53º or less, the direct evaporative cooling can provide supply air almost identical to that off of a 55º cooling coil, with pressure drops at the media on the order of half that of a standard cooling coil! Direct evaporative cooling can used to essentially greatly extend the hours of economizer performance available on almost any cooling system.

But the benefits do not end there--because pre-cooling with direct evap systems upstream of a cooling coil can significantly decrease energy costs for sufficiently dry ambient conditions:

Resources you may find useful:
Energy Labs direct evaporative performance calculator
Energy Labs Direct/Indirect Evaporative Systems Engineering Guide (booklet format)

*Note: When applying evaporative systems, often it is necessary to consider the performance of the system at the ASHRAE evaporative design day conditions, in addition to the sensible design day conditions that we commonly use. And, additionally, it can use what would normally be unwanted space heat in the return air to provide beneficial humidification in times of low humidity.

Introduction to Indirect Evaporative Cooling

2007-09-05T06:02:00.000-07:00

What is indirect evaporative cooling?

Indirect Evaporative Cooling (IDEC) is a process where air is sensibly cooled by the effect of the evaporation of water across a heat exchanger. The advantage being that for most climactic conditions, there is a significant difference between the wet-bulb and the dry bulb temperatures at design conditions. This 'wet-bulb depression' allows the designer using indirect evaporative cooling to create supply air temperatures below the ambient dry-bulb temperature without using any refrigeration at all.

Take a Seattle design day of 85º/67º db/wb. If we bring in 100% OA (which is pretty common for IDEC systems) we will have, obviously, an OA condition of 85º/67º. If we have indoor air to exhaust and use as a heat sink in a traditional, dry air-to-air heat exchanger, we will have about 75º air to use to cool down the 85º OA. Assuming about a 70% efficiency for this type of heat exchanger, that means we can realistically drop the OA by about 70% of the difference from 85º to 75º or about 7 degrees. We should be able to get a resulting LAT from the HX of 78º. Note, however, that we will need some sort of refrigeration in our system to create the indoor environment of 75º from which we are taking conditioned air to cool the OA.

Now let's consider an IDEC system for the same service. This sort of system can take on many forms, including the exact same configuration as noted above, simply with the addition of a direct-evaporative media section in the exhaust air upstream of the air-to-air heat exchanger above. For this comparison, however, let's use a built-up Energy Labs IDEC system. This is essentially a closed-loop fluid cooler for air. An induced draft fan pulls OA upwards past water spray to encourage evaporation and the supply air is cooled across an internal heat exchanger without contacting the water.

Energy Labs IDEC Module

To make this realistic, let's give this service an actual CFM and pick a particular IDEC model. Let's say this is a 22K cfm service and let's pick the nominal I-220-48 IDEC unit. With 85º/67º OA conditions*, the effective temperature difference across the heat exchanger is not 10º (OA db of 85º-EA db of 75º) but actually 18º (OA db of 85º - OA WB of 67º). Note we did two things, we increased the overall temperature difference the heat exchanger sees, and we eliminated the need to have an available exhaust air stream exhausting pre-cooled air. Checking the performance of this particular IDEC unit, we see that it has an overall effectiveness of 69% at these conditions, and the LAT from this system is 72.5º/63.2. That's a 5.5 degree improvement in LAT, or, for this supply air quantity, nearly 11 additional tons of cooling. And we don't need to have any mechanical cooling anywhere in the building to achieve this leaving air condition.

Let's examine this cooling effect on a psychrometric chart:

(click for large image)

The first thing you should notice is that the cooling process is purely sensible--no humidification or dehumidification is performed. The other thing you should note is that the supply air wet bulb temperature is a few degrees cooler than the OA wet bulb temperature, 63º vs. 67º. This is of critical importance when applying direct evaporative cooling to these systems in an indirect/direct hybrid system.

In the end, however, you can see that about 25 tons of cooling was provided, at a mechanical cost of about 1" of static pressure drop and the operation of 3 3/4 HP of fan and pump energy for the IDEC unit.

This is very inexpensive and sustainable cooling. Of course, the delivery temperature is higher than typical for standard air-conditioning applications, but if viewed as a first stage of a multi-stage system, you can see that there is a compelling case to be made for using this sort of technology to at least partially offset cooling loads that would traditionally require compressorized cooling, and greatly expand the hours of available economizer function.

Resources you may find useful:
Energy Labs IDEC performance calculator
Energy Labs Direct/Indirect Evaporative Systems Engineering Guide (booklet format)

*Note: When applying evaporative systems, often it is necessary to consider the performance of the system at the ASHRAE evaporative design day conditions, in addition to the sensible design day conditions that we commonly use.

Chris Muller of Purafil Honored by ASHRAE

2007-08-31T11:40:00.000-07:00

Purafil's Chris Muller was honored with an ASHRAE distinguished service award. Muller, a 12 year ASHRAE member, serves as a Distinguished Lecturer (DL) for ASHRAE and as chair of the ASHRAE Standard Committee 145P, which was charged with the task of engineering the ASHRAE Standard 62.1. In addition to these ongoing responsibilities, Muller remains thoroughly involved within the organization as a voting member of several committees and as a co-author of the ASHRAE Standard 62.1-2004 User’s Manual.

Muller’s continued service and commitment to ASHRAE contributed to his DSA nomination. ASHRAE members’ involvement in key roles such as society president, chapter officers and committee chair are assessed on a tally system. Each role accounts for a specified number of points and DSA nominees must score at least 15 to be considered for the honor.

Muller is a seasoned 20-year Purafil veteran responsible for technical support services as well as specific research and development functions. He has also written and edited over 100 articles and technical papers, which have been published by leading industry print media on environmental air quality and gas-phase air filtration applications.

Read more here (pdf).

Foam-Core Air Handler Panels: A Coming Standard

2007-08-30T05:57:00.000-07:00

If you've been specifying or installing commercial modular or semi-custom air handlers recently, you've probably noticed that quite a few manufacturers have switched away from the traditional single (or double) wall fiberglass batt insulation design, to a newer double-wall injected foam core panel. What is driving this change in the industry?

In a word: Performance.

To examine this further let's look at a typical design:

What you have is a sandwich construction with thin gage sheet metal enclosing the rigid foam core. The foam actually acts as a structural component, adhering to the exterior sheet metal and causing the entire composite assembly to function as a single structural unit. This means that you can achieve much greater rigidity with 20 or 22 gage steel than can be attained in a traditional batt insulation design with 16 gage steel or thicker! In fact, panel deflections for this type of panel are generally around L/240 or less (1/240th of the longest panel dimension) when subjected to an 8" static pressure load. That's actually better than the deflection spec for most custom equipment.

So why do we care about deflection? Well, a minor advantage is that this type of construction resists dings and dents much better. A slightly more important criteria is that the panels, especially floor panels, are much less likely to 'oil-can' when under pressure or under the weight of foot traffic. Even more important is that these panels make the unit itself more rigid and less susceptible to deflection or deformation in shipping or rigging. But the real advantage of this construction comes in the realm of energy savings.

These panels in general just blow away the thermal performance of batt-type panels. The following table compares the R-value improvement of rigid foam insulation over that of batt insulation:

(click on image for larger view)

Generally speaking, you get twice the insulation from foam in the same depth. Note that this only takes into account the performance of the insulation itself--further advantage is gained by the thermal break that prevents heat conduction from occurring at the panel seams--which is almost impossible to prevent in a traditional batt-insulation panel.

What does this amount to? Well, for a rooftop unit operating in a heating climate, this difference in R-value could amount to as much as 2% of the total unit energy over the course of a year.

But let's talk about panel rigidity again--it is in thermal performance where this really becomes important. Because the overall thermal performance of an air handler casing is really a function of two things--Overall U-value (defined by the insulation and thermal break) and the leakage rate.

Think about it: Every cubic foot of air leaked out of a cabinet is a cubic foot that had system energy applied to it to condition it, but now will not reach the occupied space. Conversely, every cubic foot of unconditioned air that leaks into a cabinet is a cubic foot that needs to be compensated for by more work by the air conditioning system. And this is a criteria that is critically affected by better panel design.

Traditional batt-type commercial air handlers catalog leakage rates of about 3-5% at 4" of static pressure. But because foam-core panels flex much less, and therefore don't open up leaks at panel seams as much, they typically exhibit much smaller leakage rates. Aaon catalogs leakages of less than 1% of the design airflow at 8" of static pressure. (To make a true comparison with the batt panels described above, you have to remember that static pressure increases with the square of leakage).

If you assume that 4" is a typical pressure rating for a commercial air handler, you can see that you would typically waste about 3-5% more energy in leakage with a traditional design than you would with a newer foam-core panel design. And this is additive to the direct thermal losses due to conduction through the cabinet. (Check the cataloged leakage rating even of foam-core designs, details matter and the seal and fastening design can also affect these leakage numbers. Not all manufacturers meet the standards described here).

But what about custom equipment? While generally the design details of that class of equipment can reduce the conduction, deflections and leakages even with standard batt insulation, there are still some advantages to foam core design. Energy Labs has introduced a foam-core panel for jobs that demand this premium construction, if needed. The traditional batt panel design still affords more flexibility in layout and does not come at the premium price necessary for a fully custom foam core unit.

So, Why Use Direct-Drive, Anyway?

2007-08-29T16:55:00.000-07:00

Why indeed?

If you have read my posts on the Hollisterian and Florentine effects on direct-drive fans, you may be wondering if it is really worth the complication to chose this type of fan-drive system for your project.

But when you think about it, the lesson from those two effects is to strive to use fan selections that are at a synchronous speed when at design. And since you know you can vary the width of the wheel to get the CFM you need, this should be a simple trick that you (or any decent AHU provider) can do when laying out your equipment. And if this isn't possible, you know how to compensate for an asynchronous fan selection in your motor size and system design. The only question left is what do you gain for this effort?

Plenty.

Efficiency for one. Belts are a source of inefficiency. Friction between the belt and the pulleys causes heat and erosion of the belt which is exhibited in the system by a reduction in efficiency of the system. How much friction are we talking about? A sample chart might help quantify this:

That's right--About 4% of your motor energy is lost on systems with brake HP's around 50, and more than seven percent on systems less than two BHP. That's a lot of energy to just throw away.

Another reason is maintainability.

Guess how much belt maintenance needs to be done on a direct-drive system? Guess how many belts need to be stocked to replace broken belts? Guess how much time needs to be spent adjusting belt tension to spec? Guess how many times someone needs to be called in to correct a squealing belt?

A rule of maintenance is that if something is hard to do, it won't be done. A good corollary to that might be that if something doesn't need to be done at all, there's a good chance it won't cause a problem downstream because someone didn't do it.

A related advantage is the longevity of the system. For starters, A belt drive system requires at least four bearings, two at the motor and two at the fan. Since a direct drive fan only has the motor bearings, simple mathematics would indicate that you would have at least half the bearing failures. But, as is often the case, the real situation is a bit more complicated than simple math. In each system there is a force on the motor bearing perpendicular to the shaft. In the belt drive system, this force is from the belt tension, in the direct drive system it is from the fan wheel weight.

This is where real life makes things more complicated--because the belt tension is usually several times the weight of the fan wheel. This means that the bearings in the direct-drive fan motor see much lower stress than in the belted case. This translates to many times the expected life for these critical components.

Another advantage? No belt dust. This means that projects with critical air quality concerns may be able to avoid final filters

And let's not forget belt noise--Not just the squeaking that is caused by the slipping of an incorrectly tensioned or worn belt, but the inherent noise that is added to the system from the normal operation of the belt drive itself. (Which is not, by the way, accounted for in the fan sound data you get from the manufacturer. Those were measured on direct-drive fan wheels....)

So let's review:

(Some people might argue that changing pulleys to adjust speed is less of an advantage than a disadvantage)

Now, of course, there will always be applications for belt-drive fans. Sometimes they just make a better fit for the project than direct-drive. Since the motor on a belt-drive fan is supposed to be operating at its synchronous speed (by design) you don't need to oversize motors to reach operating points where a full wheel width is truly the most efficient or quietest solution possible. But direct-drive sure makes sense when it makes sense.

Fun With Mechanical Engineering

2007-08-28T18:18:00.000-07:00

At least I think that's what this is.

The Florentine Effect, Explained

2007-08-28T14:02:00.000-07:00

This post is a follow-on to my earlier posting on the "Hollisterian" effect and is a further explanation of the tricks involved in properly selecting direct-drive fans in air handlers.

By now, you should be familiar with the Hollisterian reduction in available horsepower that occurs when you select a design point at an asynchronous motor speed. And you know that if you ever do need to design such a case, you will also need to oversize your motor by a factor equal to the motor design RPM divided by the actual operating RPM. Thus, if you are laying out an 1800 RPM motor to operate at design at 1500 RPM (let's ignore the fact an 1800 RPM motor is actually 1775 RPM, for now), you will need to select a motor nameplate HP that exceeds the brake HP of the design point by a factor of 1.2 (1800/1500). And because you are such a careful engineer, you've thrown in a bypass around the VFD in order to allow fan operation even if the VFD burns out.

So you are ready to go, right? What else could possibly trip you up now?

This is where the Florentine effect can get you.

The Florentine Effect

Let's go back to that 13.5 HP selection at 1500 RPM we discussed in the last post. Turns out, that's pretty close to a 77% width 30" fan operating at 14,000 cfm and 4" of static. When I select an EPQN fan using the Twin City Fan software, I get a brake horsepower of 13.22 HP. You know that in order to account for the derate due to the RPM that you need to pick a motor that can provide a nominal HP at least 1.2X this brake, or 15.9 BHP. You select the next larger size, or the 20 HP motor. That's a full 50% bigger than the design brake, and at least 25% bigger than you need, when you account for Hollisterian effects.

So you install the fan, and everything works just fine. In fact, you might go several years before any trouble raises its head. But then, suddenly, one day it does.

Let's say the VFD serving the fan burns out, or is taken out of service for a short while. The owner, wanting to preserve function of his fan system, even if he has to operate it at constant speed, does the obvious thing and flips the fan to bypass...

Suddenly the fan kicks on, starts roaring, and then the motor burns out. A follow up inspection might even find that some of the duct fittings have blown apart. What happened?

Well, let's think about what happened. The fan normally operated at 1500 CFM at peak design. The bypass, which is essentially a standard motor starter wired in parallel to the VFD, kicked the motor on at the line power frequency of 60 HZ, or 1800 rpm. This means that you weren't supplying air at 14,000 CFM at 4", but something greater. Following the fan laws, you would ride the system curve up to about 17,000 CFM at 5.5"! And that is assuming that you are operating a constant volume system or a VAV system at peak cooling load. If you were in heating on a VAV system with the boxes choked back to their minimum flows, you might develop even higher pressures!

Let's look at what happened:

(click to see larger image)

The above is a fan curve plot of the two operating conditions of your fan: 1500 RPM and 1800 RPM. The HP curves are plotted for both cases also. They share a common system curve (this assumes an unchanging duct system--a bad assumption for a VAV system). I've highlighted the resulting flow rates and brake horsepowers at the two resultant operating points where the system curve intersects the fan curve.

The first thing that should jump out is that the brake horsepower for this fan operating at 1800 RPM jumps up to 22.9 HP*--even greater than the 20 HP that you picked to protect from the Hollisterian effect! The other thing you should notice is that if this is, in fact, a variable volume system, the system curve shown at design is not the system curve that would be seen by the fan unless the system was at full cooling. If the boxes neck back at part load or in a heating condition, the system curve shifts to the left, pushing the intersection between the fan curve and the system curve closer to the fan curve peak. This greatly increases the amount of static pressure the fan can develop at this higher speed--up to about 9" in the case shown here.

*this can be calculated by the fan law formula:

bhp₂=bhp₁(rpm₂/rpm₁)³

Thus in a VAV system, this can be a double whammy, kicking out your motor and damaging your duct system.

How to avoid this problem? Well, you could size the motor for the even larger size demanded by the Florentine effect--but that would still leave you with the possible problem of overpressurization of the ductwork in bypass. Probably the first thing to consider is whether or not you really need a bypass, anyway. With today's more reliable VFD's, putting in a bypass is far less of a necessity. Many drives can function for the life of the equipment with no failures at all. If redundancy is absolutely necessary, consider providing a second, parallel VFD instead of a standard starter. VFD prices have come down considerably since the parallel-starter bypass concept was developed. This is no longer the cost-prohibitive strategy that it was at one time.

The Hollisterian Effect, Explained

2007-08-27T15:10:00.000-07:00

One of the best things about working with seasoned experts is that you get to benefit from their previous, um, experiences. You don't always have to learn the hard way yourself.

Sometimes, these not-quite-the-way-I-planned it episodes are actually elegant illustrations of physical principles, and deserve something more fitting than being remembered as that one time someone screwed something up. Two particular examples certainly fit this bill, and, as it turns out, they both have to do with applying direct drive in custom air handlers. The principles that they illustrate have been christened the "Hollisterian" and "Florentine" effects by our own Jake Marley, in honor of certain colleagues who shall remain unidentified for the purposes of this post. I will discuss the Hollisterian effect here, and the Florentine effect in a future post.

And, instead of dredging up the actual events that gave rise to the discovery of these principles, the gist of which I am sure most readers could figure out, I will instead focus on the principles themselves.

The Hollisterian Effect

Direct Drive fans offer some great advantages to a system designer. There are no belts to maintain, no belt dust to foul the discharge air, no inefficiencies from the belt drive and far less vibration than a belted system. But they also do carry some design limitations that must be dealt with appropriately.

The first limitation? Direct drive fans are direct drive. In other words, they are directly coupled to the motor shaft, and therefore turn at the speed of the motor. Which is great, if you have a design condition where the fan needs to turn at 1800 or 1200 or 900 rpm. If you have a design condition that requires a fan selection at, say, 1500 RPM, then you need to do pick a motor/fan system at an 'asynchronous' design condition.

No big deal, right? We've got VFD's today, so this is a piece of cake.

This is exactly where the Hollisterian effect can get you. See, VFD's are not constant horsepower devices. They are, up to 60 Hz, constant torque devices.

Let's look at the equation for motor power:

hp = (Torque x Speed)/5250

If you have a constant-torque motor, this equation simplifies to"

hp=C x Speed

Where C is a constant equal to the torque constant divided by 5250.

So, what you have got is something like this:

(click on image for larger view)

Where the HP available (the blue line) increases linearly up to 60 Hz, at which point the HP then remains constant and the available torque drops away.

So what does this mean to a designer?

Well, let's say you selected a direct-drive fan to meet your design criteria at a 1500 rpm design condition. Let's say the brake horsepower of that fan selection is 13.5 HP. You select a 15 HP, 1800 RPM motor driven by a VFD. You're good, right?

Well, let's look back at our HP equation--Applying the math, you now have only 1500/1800 (or 5/6th) of the motor hp available at 1500 RPM, or, in this case, 11.7 HP. You really needed a 20 HP motor!

If you are working with low speed fans, and you are selecting in the 400-500 RPM range, you can see that you are going to be robbing about half of the nameplate HP from the selected motor, assuming you are going to select a reasonably available standard motor speed. In the above example, that would turn the 20 HP motor into a 30 HP motor!

So what do you do? Well, one way to attack this problem is to select the bigger motor (and VFD) and call it good. Other than some additional first costs, this might be the right solution. A more elegant solution might be to see if you can't select a fan wheel with slightly shorter blades to bring your design condition in closer to a synchronous speed. Energy Labs provides direct drive systems regularly, and thus will allow you to select plug fans from 50% to 105% of the standard AMCA wheel width to address these sorts of issues. Aaon's fan selection routine in their Ecat32 software allows for variable width wheels and actually takes into account any Hollisterian or Florentine effects (discussed later) in the sizing of their motors!

Variable-width wheel selections allow you to shift the whole fan curve leftwards on the page without losing height--reducing CFM to match your needs, but preserving peak static pressure. This means you could select a fan wheel at 1800 RPM, but reduce the total air delivered by providing a 80% wheel width so that you don't exceed your design flow at the faster speed.

Or, lastly, you could instead chose a 1200 RPM motor, and just select it for 72 Hz service. As long as the motor and drive manufacturer are happy with this selection, there is nothing preventing you from over-speeding your motor.

Too Much Seriousness

2007-08-25T16:08:00.001-07:00

Laughing babies needed.

Why You Can't Buy an NC 35 Air Handler

2007-08-25T14:38:00.000-07:00

No, it's not because we can't make quiet air handlers.

It's because NC isn't the right criteria to use to specify an air handler's sound level.

Why not? Well, to understand that, we have to discuss what NC is, exactly.

NC levels are defined by a series of curves that define the maximum sound level at a given frequency that an ambient sound can exhibit. Stated like this, it seems simple in the extreme to apply this rating to the sound level created by an air handler--but there is one important point missing: NC is a property of spaces, not equipment. Typically, allowable NC values are determined from charts like these:

It doesn't matter if the air handler whispers or is a screamer--if the sound levels in the space are below an acceptable NC curve, the sound level is acceptable. But this resultant sound level depends on a myriad of factors--the discharge sound level from the air handler, the duct layout, the selection of diffusers, attenuation devices, and, importantly, the room itself.

Hard surfaces and small volumes will tend to result in louder overall conditions, while large volumes and soft surfaces quiet a space. And, of course, sound generated in the space or from outdoor sources (traffic, etc.) will affect the overall NC level of a space.

How can you account for these effects? Well IAC has created a simple worksheet to determine the required insertion loss criteria needed in an attenuator array to meet a given target NC level. The SNAP sheet (Systemic Noise Analysis Procedure) is a simple method of calculating the resultant sound levels due to the HVAC system in a space. We've created a simple spreadsheet that helps keep the calculations straight here. Just simply copy the NC level you wish to meet from the green-tinted table at the bottom and paste those cells into the green bar at the top of the sheet. Then enter the discharge sound level from the air handler in the blue cells. If you follow the step-by step instructions on the SNAP form, you should be able to fill out the yellow cells with the sound attenuating characteristics of the system you are designing.

What you will have after putting in all this data is a required insertion loss criteria that should help you select a sound attenuator. Once you have picked one, just input its insertion loss performance into the first red bar, and the self-noise criteria in the next two bars. A successful selection will give you a sound attenuator that brings the sound level below the NC curve you are trying to hit, and does not generate enough self-noise to bring the sound levels back up above it!

This procedure only accounts for sound generated and transmitted by the HVAC system serving the space--You will need to account for other noise sources separately. But at least it takes care of the noise source you as an HVAC designer/contractor control!

How should you specify your air handler sound performance? By specifying the outlet, inlet and radiated sound power levels. As long as you have verified that the appropriate NC level in the space will not be exceeded with the specified values, you can be assured that any air handler meeting or beating your specification will be an appropriate fit.

Zero Pressure Drop Sound Traps?!

2007-08-25T09:16:00.000-07:00

There's an old adage in life: There ain't no such thing as a free lunch.

In the world of sound traps, the "lunch" is insertion loss (the amount of sound attenuation provided) and the "bill" is pressure drop. Generally speaking, the more insertion loss you get at a given air velocity, the more static pressure drop you pay. And, when you consider that these pressure drops are greatly increased if the sound attenuator is located close to duct fittings (see page 8-9 of this document for examples), this bill can be very high indeed for any project where duct space is at a premium.

You know, all of them.

Enter the ZAPD™ series silencer from Industrial Acoustics (Z12A series cutsheet linked).

These silencers eliminate added static pressure drop by eliminating the air constriction that typical silencers impose upon the airstream:

Traditional Silencer

This is done by keeping the fill out of the airstream, so that the airflow sees no disturbance, and thus experiences no pressure drop:

New ZAPD™ Silencers

This design can provide significant insertion loss performance, with up to 12-14 dB in the first band for some 10' models, and 35-50 dB in the center bands for some 10' models--all with negligible self-noise and no additional pressure drop!

The exterior-baffle design does create functional limits to the size of these silencers, but they are great for use in systems where energy efficiency is a high priority, or where there is very little static pressure available, such as in VAV terminal boxes or water-source heat pumps.

Your free lunch just arrived. And it will pay you in energy savings for the rest of its life.

Evapco ESWA: The Most Efficient Fluid Cooler on the Market

2007-08-25T08:08:00.000-07:00

Recently, Evapco introduced a new fluid cooler design that blows away other traditional units in efficiency and sound performance.

The secret? They re-thought how to design a fluid cooler.

In their testing, they found that the most efficient heat transfer occurred in a fluid cooler coil when the coil was completely flooded with water. However, in a traditional fluid cooler design, this condition could not be attained because air flow was needed over the coil in order to evaporate a portion of the spray water pouring over it.

Traditional Fluid Cooler Design

A little out-of-the box thinking led their engineers to realize that there were two heat transfer processes that really mattered in a fluid cooler:

1. The spray water cooling the fluid in the coil by conduction
2. The air cooling the spray water water by evaporation

Both of these processes were optimized in different conditions. So they decided to separate the two processes from each other:

New ESWA Design

The new ESWA cools the spray water with conventional cooling tower fill and then, only after the water is cool, floods the coil for optimal heat transfer.

The result? A fluid cooler that uses 30%-50% less energy than a traditional induced draft cooler, and up to 80% less than a forced draft tower!

And there are other benefits, too. Since the water basin is completely enclosed, the splash noise from the basin is attenuated, making the ESWA one of the quietest fluid coolers on the market. The basin is also accessible, making the ESWA coil extremely easy to inspect and clean. And since the air inlets are above the coil, very little 'stack' effect is created, making the heat loss from a standard ESWA in heating season less than that of a traditional fluid cooler equipped with positive closure dampers!

Evapco Hits the Big Time

2007-08-25T07:38:00.000-07:00

Funny things happen when you type "Evapco" in to the search box at Youtube:

No, I don't understand it either

HVAC Engineering Calculations Software

2007-08-25T07:08:00.000-07:00

Engineering Power Tools is a third party shareware program that some of us at Johnson-Barrow have found useful. It is an engineering program with an HVAC module that includes the following HVAC modules:

☆ Air Flow Thru Perforated Plate
☆ Blower Wheels
☆ Clean Room Standards**
☆ Control Valve Sizing**
☆ Convection Coefficients
☆ Duct Sizing**
☆ Fan Law Calculations
☆ Fluid Flow in Pipes
☆ Heat Index**
☆ Heat Loss From Insulated Pipes**
☆ Inert Gas Purge Rate**
☆ Orifice Flow
☆ Pipe Sizing Tables
Air
Natural Gas
Water
☆ Pressure & B.P. vs. Altitude**
☆ Properties of Air
☆ Psychrometrics
☆ Psychrometrics II**
☆ Refrigerant Vapor Pressure**
☆ Safety Ventilation
☆ Saturation Tables
☆ Solar Radiation
☆ Standard Atmosphere Data
Calculations**
Table (SI Units)**
Table (US Units)**
☆ Steam Pipe Sizing
☆ Temperature Conversions
☆ Water Hammer**
☆ Wind Chill Factor**

**Available in "Plus" version

If it looks useful to you, you can try before you buy.

Best Practices for Data Center Design

2007-08-23T12:51:00.000-07:00

A 2006 study published by Lawrence Berkley National Laboratory, Environmental Energies Technologies Division examines best practices for energy-efficient data center design. Some of the best practices highlighted include well-understood and accepted practices like ‘right-sizing’ central plants and using hot and cold aisles. However, the article makes a strong case for the use of air-side economizers for the minimization of energy-using refrigeration and direct evaporative cooling for humidification. Read more here:

Best Practices for Data Centers: Lessons Learned from Benchmarking 22 Data Centers

VAV Static Pressure Control

2007-08-23T12:41:00.000-07:00

Most VAV systems require that a minimum duct static pressure point be maintained to ensure operation of the air terminals. This means that even at very low flow rates, an elevated static pressure needs to be provided, above that expected by following the traditional system curve. As the fan speed drops to match the required flow, the intersection of the actual system curve and the fan curve moves the fan closer and closer to stall.

What is the effect of this interaction? And how can you select a fan to best deal with this problem? Energy Labs has done a valuable study of this effect and it can be found here.

Cool Ways to Conserve Water

2007-08-23T12:31:00.000-07:00

A few years back, I had an article published in the April 2005 issue of Plumbing Systems and Design Magazine that highlighted the many ways to optimize the water saving performance Cooling towers.

You can read that article right here.

Pressure Conversions

2007-05-17T07:08:00.000-07:00

Area Conversions

2007-05-17T06:52:00.000-07:00

Length Conversions

2007-05-17T06:48:00.000-07:00

Velocity Conversions

2007-05-17T06:46:00.000-07:00

Energy Conversions

2007-05-17T06:43:00.000-07:00

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power conversion factors provided by unitconversion.org

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© unitconversion.org

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area conversion factors provided by unitconversion.org

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length conversion factors provided by unitconversion.org

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© unitconversion.org