Reducing Ground-Loop First Costs

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

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

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

HVAC System Efficiency Tool

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

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

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

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

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

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

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

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

We Have Moved

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

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

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

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.