Monday, October 29, 2007

Greening Small Rooftop Packaged Units: Economizers

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.

Sunday, October 28, 2007

The Importance of Cooling Tower Maintenance



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:
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.

Saturday, October 27, 2007

Introduction to Modular Chillers


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.

Monday, October 22, 2007

Your Next Energy Conservation Measure May be a Quiet Fan

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).

Friday, October 19, 2007

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

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.”

Tuesday, October 9, 2007

FREE Psychrometric Software

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.

Friday, October 5, 2007

A Giant Golf Ball in Your Outside Air Opening


"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.

Tuesday, October 2, 2007

Rethinking Air Handler Pressure Testing Specifications

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:
  1. When to test (At factory or at jobsite)
  2. How many sections to test
  3. Positive or negative test pressure
  4. What pressure to test to
  5. 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.