Coolerado Cooler Helps to Save Cooling Energy and Dollars

Technology Installation Review A New Technology Demonstration Publication DOE/GO-102007-2325

Federal Energy Management Program

Leading by example, Coolerado Cooler Helps to Save saving energy and Cooling Energy and Dollars taxpayers dollars in federal facilities New cooling technology targets peak load reduction

Executive Summary

A new evaporative cooling technology can deliver cooler supply air temperatures than either direct or indirect evaporative cooling systems, without increasing humidity. The technology, known as the Coolerado Cooler™, has been described as an “ultra cooler” because of its performance capabilities relative to other evaporative cooling products.

The Coolerado Cooler evaporates water in a secondary (or working) airstream, which is discharged in multiple stages. No water or humidity is added to the primary (or product) airstream in the process. This approach takes advantage of the thermodynamic properties of air, and it applies both direct and indirect cooling technologies in an innovative cooling system that is drier than direct evaporative cooling and cooler than indirect cooling. The technology also uses much less energy than conventional vapor compression air- conditioning systems and therefore can be a cost- and energy-saving technology for many Federal facilities in the United States.

Performance tests have shown that the efficiency of the Coolerado Cooler is 1.5 to 4 times higher than that of conventional vapor compression cooling systems, while it provides the same amount of cooling. It is suitable for climates having low to average humidity, as is the case in much of the western half of the United States. This technology can also be used to precool air in conventional heating, ventilating, and air-conditioning systems in more humid climates because it can lower incoming air temperatures without adding moisture. Introduction

Air-conditioning systems are a major contributor to summer peak electrical demands in most of the United States. Both electric power generators and conventional vapor compression electric air-conditioning systems operate at lower efficiencies when ambient air temperatures are high, and this increases the peak demand on the grid even further. Moreover, peak demand charges are often billed at a utility’s highest rates. Because a significant portion of summer air-conditioning loads occur when electricity is the most expensive, cooling is often more costly than other electrical loads. Therefore, reducing cooling energy demand can offset energy costs at a proportionally greater rate than other load-reduction strategies and yield greater cost savings for a given amount of energy Bringing you a prosperous savings. fuure where energy is clean, abundant, reliable, This Technology Installation Review, prepared for the U.S. Department of Energy’s Federal and affordable Energy Management Program, describes the operating principles, measured performance,

U.S. Department of Energy Internet: www.eere.energy.gov/femp/ No portion of this publication may be altered in any form without Energy Efficiency prior written consent from the U.S. Department of Energy, Energy Efficiency and Renewable Energy and Renewable Energy, and the authoring national laboratory. Technology Installation Review

and energy savings potential of Types of Cooling Systems water vapor, the heat that goes into the Coolerado Cooler technology. the evaporation process is removed A wide variety of systems and Because this technology signifi- from the air, resulting in a cooler technologies are used for cooling cantly reduces electric demand for air temperature. commercial and residential build- cooling over the course of a cooling ings. The following short descrip- season, it can provide energy and Evaporative coolers are effective in tions of several system types cost savings and help Federal average- to low-humidity climates, provide a frame of reference for energy managers meet the energy- and they consume much less evaluating the Coolerado Cooler’s reduction goals stated in the energy than other types of air- performance. conditioning systems. Energy Policy Act (EPAct) of 2005.1 It can also help to reduce expen- Conventional Systems. Evaporative coolers can be either sive peak demand charges. Conventional HVAC systems direct or indirect. In direct evapo- condition supply air year-round rative cooling, water evaporates The technology uses a water- to deliver fresh, comfortable air directly into the supply airstream, fueled cooling system powered to building occupants. In summer, solely with fan energy to provide reducing the dry-bulb temperature conventional air-conditioning more cooling at a lower cost. of the air while raising its humid- systems cool the air and often Incorporating this concept with ity. The latent heat of the air is remove the moisture in it simulta- multiple purges of moist second- used to evaporate the water. neously by passing the air over a ary/working air creates a staged Evaporation cools the air while cold surface. When warm, moist indirect evaporative cooling increasing its moisture content or “inside” air is blown across the process. This process, known relative humidity. No heat is surface of a unit’s cooling coil, as the Maisotsenko Cycle, is added or taken out of the air; thus, the air temperature drops and the the innovation that led to the it is an adiabatic process. water vapor in it condenses. The Coolerado Cooler’s receipt of a conditioned air is both cooler and In direct evaporative coolers, often prestigious R&D 100 Award from drier and therefore more called swamp coolers, the supply R&D Magazine in 2004. comfortable. airstream is in direct contact with The Coolerado Cooler is modular water by means of an evaporative Typically, conventional air- in design; thus, multiple units medium or wetted pad (such as conditioning systems depend on can be stacked as high and wide fiberglass, fabricated paper, or a vapor-compression cycle to as needed to meet a building’s aspen pad) or a series of spray provide cooling. Common types of cooling requirements. Capacity misters. The supply airstream conventional vapor-compression configurations range from 1-ton gains a lot of moisture in this systems are self-contained, factory- residential window units to 500- process, so cool, moist air must be assembled packaged units, split ton commercial units. With modifi- exhausted from the cooled space units with outdoor compressor cations, the Coolerado Cooler can and not reused or reconditioned. and condenser units and indoor be integrated into a precooling air-handling units (AHUs), and Figure 1 illustrates a supply system for ventilation air in new chiller systems. Chiller systems airstream being blown across an or existing heating, ventilating, use mechanical chillers to cool evaporative medium. Figure 2 and air-conditioning (HVAC) water that is then distributed to diagrams a psychrometric (see systems. When used for precool- coils located in AHUs. With each Glossary of Terms for psychro ing, it is capable of providing of these systems, the cooled air metric terminology) analysis of energy and cost savings in virtu- is delivered via terminal devices this direct evaporative cooling ally any climate in the continental (e.g., supply diffusers) to the space process. The entering dry-bulb air United States. to be cooled. temperature (TDB) is 110°F (43.3°C), the relative humidity (RH) is 15%, Evaporative Cooling. When liquid and the thermodynamic wet-bulb water evaporates and becomes temperature (TWB) is 72°F (22.2°C).

______1 See www.eere.energy.gov/femp/about/legislation_epact_05.html, 2006.

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Figure 1. Direct evaporative cooling through a wetted medium. Source: www.energy.ca.gov/appliances/ 2003rulemaking/documents/case_ studies/CASE_Evaporative_Cooler.pdf

Up to 38°F (21.1°C) of cooling can theoretically be achieved (110°F Figure 2. Direct evaporative cooling process shown psychrometrically.

(43.3°C) – 72°F (22.2°C)) by simply Source: PsycPro software at www.Linric.com adding water to the supply airstream. In this case, the supply airstream was cooled to within 6°F (3.3°C) of the thermodynamic wet-bulb limit, so it was 84% effective as 32°F (17.8°C) of cooling was achieved out of 38°F (21.1°C) that was theoretically possible. Achieving 90% to 95% of the wet- bulb temperature is often the target for direct cooling performance.

A psychrometric chart can show why direct evaporative cooling works well in dry climates and not as well in humid ones. Using Figure 3, if we start with 95°F (35°C) TDB air (A) with relative humidity of 70%, that air can be directly cooled only 9°F (5°C) before it reaches saturation at a TWB of 86°F (30°C). Moving up and to the left on the short red line at A, the final air temperature can Figure 3. Comparison of the direct evaporative cooling possible when starting with TDB of 95°F (35°C) at 70% RH vs. at 10% RH. Source: PsycPro software at www. be read by following the vertical Linric.com lines to the dry-bulb temperature. Starting with 95°F (35°C) TDB air (B) at 10% relative humidity, that

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Figure 4. In an indirect evaporative cooling process, the primary airstream flows in a different channel than the secondary airstream. Source: Wang, Shan K., Handbook of Air Conditioning and Refrigeration (2nd Edition), McGraw-Hill, p. 5, 2001; www.knovel. Figure 5. In the indirect evaporative cooling process, no water is shown being added com/knovel2/Toc.jsp?BookID=568& to the primary airstream as it cools from A to B. Source: PsycPro software, www. VerticalID=0 Linric.com air can be cooled to 65°F (18.3°C) addition, the added moisture in • No chlorofluorocarbon (CFC) before condensing, for about 35°F the air can be a bonus. usage (19.4°C) of cooling. This is a • Reduced pollution-causing Direct evaporative coolers have significant increase in the amount emissions several energy and cost advantages of cooling that can be delivered over vapor compression systems. The indirect evaporative cooling than from humid air at the same Typically, they have lower process typically involves two temperature. It shows that there installed costs and consume much airstreams: one primary or product is greater cooling potential in air less energy than central air condi- airstream and one secondary or that is initially at a lower relative tioners. These are some additional working airstream (Figure 4). The humidity when a direct evapora- advantages: indirect cooling process evaporates tive cooling process is used. water and removes heat from the • Lower initial cost than The cooling effect from direct secondary/working airstream, alternatives evaporative coolers is a result of while not adding moisture to the amount of moisture added to • Lower delivery temperature than the primary/product air. A heat the air. Direct systems are not as indirect units exchange membrane is used effective or efficient in climates • Less water use per cubic foot between the working airstream in which the outside ambient air per minute (cfm) than that of and the supply airstream. The is typically humid (such as the indirect evaporative coolers membrane’s ability to transfer heat eastern half of the United States), • Substantial energy and energy out of the supply airstream and because little moisture can be cost savings compared with the air flow rate determine the added to the air and the cooling vapor compression systems effectiveness of the system. effect is minimized. In very dry • Reduced peak power demand Psychrometrically, the indirect climates (such as those in many • Wide variety of packaged cooling process moves left hori parts of New Mexico and Nevada), systems available zontally across the chart, since direct cooling is quite effective • Easy integration into built-up no moisture is added (Figure 5). at cooling dry ambient air. In systems Theoretically, the air can be cooled

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to the same wet-bulb temperature through indirect evaporative cooling as it can be through direct evaporative cooling. In practice, the direct evaporative cooling process typically delivers cooler air than the indirect process because of heat exchanger inefficiencies in the indirect process. Because the secondary/working airstream has added moisture, it is eventually exhausted from the building and no moisture is added to the primary/product airstream. Figure 6. Two-stage indirect/direct evaporative cooling. Source:/www.energy.ca.gov/ The thermodynamic wet-bulb appliances/2003rulemaking/documents/case_studies/CASE_Evaporative_Cooler.pdf temperature is often the target temperature for both direct and indirect evaporative cooling technologies. It is considered to be the lowest temperature attainable through thermodynamic processes without the need for additional energy.

Combined Indirect/Direct Evaporative Cooling. Both indirect and direct cooling processes can be combined into a single piece of equipment in a two-stage process (Figure 6). In typical indirect/ direct systems, the secondary airstream sensibly cools the primary air in the first stage in an indirect process. The air is then directly cooled through evaporation to lower the temperature Figure 7. Two-stage indirect/direct evaporative cooling (indirect from A to B and then further (Figure 7). The primary or direct from B to C) yields a lower TDB than does direct-only from A to D. Source: supply air may actually exit below PsycPro software at www.Linric.com the initial wet-bulb temperature. This approach increases the tional vapor compression air Cooler is one such ultracooler. humidity of the primary or supply conditioning. It differs markedly from conven- air. However, it can operate tional indirect/direct systems effectively in a wider range of Ultracoolers because the direct evaporative climates than direct evaporative process does not involve the cooling, and related energy costs Several coolers are able to cool air supply air; rather, it involves the are lower than those of conven- below the thermodynamic wet- secondary or working airstream. bulb temperature associated with As a result, no moisture is added the dry-bulb temperature of the to the supply air throughout the outside ambient air. The Coolerado entire cooling process, while the

______2 Source: www.oasysairconditioner.com, 2005.

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effectiveness of the evaporative cooling process is notably increased. The Coolerado Cooler can cool below the wet-bulb temperature; the dew-point temperature is its cooling limit.

The OASys™ system2 is another example of an innovative dual- stream ultracooler that employs both direct and indirect cooling processes in a single unit. This ultracooler can also add a controlled amount of moisture to the primary airstream. Figure 8. Supply air temperatures from several different cooling technologies. The Coolerado Cooler uses both Source: Don Cameron, NREL, 2005. a direct and an indirect process operating in parallel and in stages to achieve cooler air than a direct or indirect system alone would achieve. Water is evaporated into air in one chamber within the cooler, and this cools the air flowing in an adjacent chamber. The cold air is used to cool the building while the water vapor holding the heat is exhausted. Coolerado Cooler Basics

Figure 8 shows typical supply air temperatures from several different types of cooling technologies, given ambient psychrometric Figure 9. Comparison of conventional indirect/direct air flow vs. the Maisotsenko conditions of 96°F (35.6°C) TDB, Cycle air flow. OA is outside air; RA is return air.Source: Steve Slayzak, NREL. 71°F (26.7°C) TWB, 58°F (14.4°C) dew point, and RH of 29% at effectiveness of both the direct M-Cycle), named for Dr. Valeriy an elevation of 2500 ft (762 m). and indirect stages of its cooling Maisotsenko (see Figure 9). The As shown, conventional air- process. The schematic in Figure 9 cycle works by cooling both the conditioning delivers the lowest illustrates fluid movement through primary/product air and the supply air temperature, but at a the patented Heat and Mass secondary/working air in stages— significant cost in terms of energy Exchanger™ (HMX). The HMX is 20 stages in all. Each stage contrib- and dollars. Indirect evaporative made of plastic-coated, cellulose utes to cooling by lowering the coolers typically deliver air near blend fiber in a geometric design wet-bulb temperature. The cumu- the comfort threshold—either that cools both the product and lative result is a lower primary/ slightly above or slightly below working airstreams without product air temperature than is it, depending on ambient outside mixing them. possible with conventional evapo- air conditions. rative cooling technology. The key The development of a system of difference between this and other How It Works. The Coolerado cascading incremental airflows direct/indirect processes is that Cooler has a unique design creates a thermodynamic cycle the secondary/working air that approach to maximizing the called the Maisotsenko Cycle (or is accumulating moisture is

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exhausted at each stage, enabling more cooling to take place.

To better understand the process, it can be helpful to examine what happens in a single stage of the 20-stage process. In a typical indirect/direct evaporative cooling system, the working air is purged once, at the end of the cycle, so the limits of performance are based on the thermodynamics of initial conditions of relative humidity, dry-bulb, wet-bulb, and dew-point temperatures.

Here, the technology used for the Coolerado Cooler enhances its ability to further reduce primary/ product air temperatures. It does so by taking the primary/product Figure 10. Conceptual psychrometric representation of the staged indirect cooling air at the ending conditions and process with continual purge of secondary/working air. Source: PsycPro software at starting the process over. That www.Linric.com product air is split into two airstreams again—the primary/ purge process, so it will mix with of this purging, the Coolerado product air and the secondary/ air at higher humidity but only in Cooler requires greater total working air—but now at a lower the working airstream that is airflow than other types of cooling dry-bulb temperature and a lower continuously exhausted. systems. However, because the thermodynamic wet-bulb tempera- supply air temperature is lower ture. The new starting point of the The advantage of the Maisotsenko than that possible with direct and primary/product air is to the left Cycle is that the working air is indirect evaporative cooing sys- of the original starting point on purged repeatedly so that the tems, less supply air is required the psychrometric chart, so it has a initial conditions are essentially to meet space conditioning needs. lower achievable thermodynamic reset, as lower dry-bulb and wet- Laboratory Testing Parameters. wet-bulb temperature (Figure 10). bulb temperatures are established Engineers at the National No moisture is added at this point with each purge cycle. This allows Renewable Energy Laboratory to either the primary/product air the eventual supply air tempera- (NREL) in Golden, Colorado, or this portion of the working/ ture to be below what the original operated a Coolerado Cooler unit secondary air, so significant initial conditions would indicate in the NREL Thermal Test Facility cooling capacity is available. possible—below the thermodynamic wet bulb temperature. This key (TTF) during the 2003-2004 time In Figure 10, the red arrows cycling feature is essentially what frame (Figure 12). NREL put the indicate the direct evaporative sets the Coolerado Cooler apart Coolerado Cooler through a range cooling taking place in the process from other indirect/direct evapo- of tests to establish its performance airstream exhausted at each of the rative cooling systems and enables capabilities and parameters. The 20 stages. The blue arrows repre- greater cooling performance. This system was equipped with a wide sent indirect cooling through the cycling continues in all 20 stages, variety of sensors to measure heat exchange membrane, which is and each contributes to lowering relative humidity, wet-bulb and taking place in the process/supply the temperature of the primary/ dry-bulb temperatures, pressure airstream with no moisture being product air. drops, and flow rates across the added. Note that this portion of the HMX. Researchers measured the working air does get mixed into Figures 10 and 11 illustrate the fan power directly from a power the existing working air during the continuous purge process. Because transducer. These conditions were

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1 Outside air is pushed into the Coolerado Cooler heat exchanger with a single fan. 10 but under variable ambient condi- 10 tions determined by Colorado’s 2 Product Air Channels. 5 6 weather. Figure 13 shows the 3 Working Air Channels. 6 calculated EER for a variety of 4 Heat from the Product Air is transferred temperature differences between through the thin plastic and into the Wet dry-bulb and wet-bulb Channels below. 8 temperatures. 5 Working Air is blocked from entering 4 7 the building. 9 The calculated EER values indi- 6 The Blocked Working Air is turned and cated a high degree of correlation passed through small holes into Wet between the difference between the Channels below the Product Air stream. dry-bulb and wet-bulb tempera- 7 The Working Air is now moving through ture and the EER (i.e., the greater Wet Channels perpendicular or cross 2 ﬂow above and below the Dry Channels. the temperature difference, the greater the calculated EER). The 8 The heat that is passed from the Dry 2 Channel is converted into water vapor. Coolerado Cooler unit operates more efficiently when the weather 9 Heat from the Product Air has been 3 converted into water vapor and is now is both hot and dry. rejected as exhaust to the outside air. 1 Given the operating characteristics 10 The Product Air which has now traveled the length of the heat exchanger, enters of the Coolerado Cooler and its the desired space, cold and dry. performance in Colorado, an Figure 11. How the staged indirect/direct evaporative cooling process flows. Source: extrapolation was done to estimate http://www.idalex.com/technology/how_it_works_-_technological_perspective.htm its potential performance in various cities in the western United measured in a real-world type ment states its EER under specific States. Along with the correlation of environment with the unit test conditions (see Glossary of from the test data, an estimated installed and providing cooling Terms for cooling terminology). EER value was calculated using to the TTF, rather than in a At NREL, the first test involved 1% design wet-bulb and dry-bulb controlled-test setup. determining how effective or temperatures from the American efficient the Coolerado Cooler Society of Heating, Refrigerating, The energy efficiency ratio (EER) was in providing cooling by and Air-Conditioning Engineers’ on the Energy Guide label found determining its EER. The EER (ASHRAE) design temperature on new air-conditioning equip- calculation was done repeatedly, data for several locations throughout the West.

Figure 13. Energy efficiency rating versus wet-bulb temperature depression. Note: Different colors represent different air mixtures and dates. Source: Data collected at NREL’s Thermal Test Facility, 2003-2004.

Figure 12. Coolerado Cooler test unit at NREL’s Thermal Test Facility. Source: NREL

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Table 1 shows the estimated EER State City April May June July August Sept. values for cooling from April through September, averaged over TX El Paso 13.6 13.7 12.4 9.1 8.8 7.7 both the month and the day. Peak NM Albuquerque 15.7 13.7 13.0 12.7 11.1 10.0 temperature values with average CO Grand Junction 14.5 13.9 17.3 12.4 12.5 10.9 to low humidity would lead to higher EERs when cooling WY Cheyenne 12.1 9.3 10.2 9.4 8.2 8.7 demands are the highest. MO Billings 14.6 12.8 13.9 12.8 15.8 14.2 Another analysis performed using ID Boise 11.2 15.2 17.0 16.8 17.3 14.6 the collected data was to determine UT Salt Lake City 13.1 11.9 16.4 13.3 10.3 10.9 how effectively the system cooled AZ Phoenix 20.5 20.8 19.5 15.1 13.6 14.5 relative to the thermodynamic wet- bulb temperature. This measure NV Las Vegas 20.0 18.5 24.0 16.8 15.1 13.0 of efficiency, known as wet-bulb CA Bakersfield 14.8 19.4 21.4 19.5 15.2 13.3 efficiency, is defined as follows: WA Spokane 9.7 13.9 13.7 15.2 15.2 14.8 where OR Pendleton 9.9 11.9 15.4 19.2 19.4 15.8

TSI_DB – TSO_DB ______Table 1. Estimated average EER for the Coolerado Cooler based on test data correla- e wet-bulb = T – T tions. Calculated at NREL (2004) using 1% design wet-bulb temperatures from SI_DB SI_WB ASHRAE 2001, Chapter 273. where

TSI_DB = Drybulb_Temperature_Supply_Inlet

TSO_DB = Drybulb_Temperature_Supply_Outlet

TSI_WB = Wetbulb_Temperature_Supply_Inlet

A value of 1.0, or 100%, indicates that a cooling unit has achieved as much cooling as is theoretically possible, i.e., the thermodynamic wet-bulb temperature. Because the Coolerado Cooler efficiency increases on these units when the difference between dry- and wet- bulb temperatures is greater, a trend can be seen with the change in temperature (Figure 14). As the temperature differential increases beyond 12°-13°C (21°-23°F), efficiencies greater than 85% are regularly achieved. Figure 14. Wet-bulb efficiency rating versus wet-bulb temperature depressions. Applications for the Note: Different colors represent different air mixtures and dates. Source: Data collected at NREL’s Thermal Test Facility, 2003–2004. Coolerado Cooler

The performance of the Coolerado Cooler will vary, depending upon average outside ambient condi-

______3 Table 1B Cooling and Dehumidification Design Conditions, Chapter 27.7 – Climatic Design Information, 2001 ASHRAE Handbook Fundamentals.` FEDERAL ENERGY MANAGEMENT PROGRAM — Technology Installation Review

a conventional air conditioner. Reducing the amount of electrical energy consumed for cooling can thus also reduce the amount of water consumed, from the power plant to the cooled space.

The exact amount of water consumed in generating electricity varies, depending on the fossil fuel used (natural gas-fired plants use less water than coal-fired plants) and the type of conversion tech nology employed (combined-cycle power plants use less water than steam plants do). Generating a kilowatt-hour (kWh) of electricity at a new coal plant in the Southwest uses about 0.67 gallons (gal) (2.5 liters [L]) of water, while a new natural-gas-fired plant Figure 15. Map of summer cooling load hours. Source: ARI Unitary Directory, August consumes about 0.33 gal (1.2 L) 1, 1992, to January 31, 1993, pp. 16-17; Air-Conditioning and Refrigeration Institute, 4 www.energyexperts.org/ac_calc/default.asp. of water per kWh generated. The national weighted average for tions during the cooling season. consumption if it is used to thermoelectric and hydroelectric The map in Figure 15 provides a precool the air entering conven- water use is 2.0 gal (7.6 L) of color-coded graphical indication tional vapor compression systems. evaporated water per kWh of of where and how a direct evapo- Direct evaporative systems cannot electricity consumed at the point 5 rative cooler will be most effective. be used in a similar manner in of use. The impact varies by the The Coolerado Cooler will work these conditions because they source—either surface water or as well or better as a direct evapo- provide little cooling to moist air. groundwater. Water diverted or rative cooler does in the same The Coolerado Cooler is suitable withdrawn is water removed from regions but also in other regions, for use throughout the country, streams, groundwater, or other because it does not add moisture to though different configurations sources. Much of this water is the supply air. The map also shows and energy savings are applicable consumed through use. The the average number of summer in different climates. remainder returns to the local cooling hours per year. surface or groundwater system Water Use Issues and is available for subsequent The purple area indicates regions use downstream of its discharge.6 in which this technology and direct Water is used in both evaporative A conventional residential air- evaporative coolers should work cooling and in ultracoolers such as conditioning system does not well in stand-alone applications. the Coolerado Cooler and OASys consume water at the place where The large green area indicates systems. A significant amount it delivers conditioned air if it has regions in which the Coolerado of water is also used in thermal an air-cooled condenser. Most Cooler has the potential to signi electric power plants to generate commercial HVAC systems include ficantly reduce cooling energy the electricity required to power a wet cooling tower, which evapo-

______4 The New Mother Lode: The Potential for More Efficient Electricity Use in the Southwest, SWEEP, 2002. 5 Torcellini, P., Long, N., and Judkoff, R. Consumptive Water Use for U.S. Power Production, National Renewable Energy Laboratory, U.S. Department of Energy, December 2003. 6 The Last Straw: Water Use by Power Plants in the Arid West, Clean Air Task Force, The Land and Water Fund of the Rockies, The Energy Foundation, and The Hewlett Foundation, April 2003.

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Cooling system Load determination Operating characteristics Cost parameters Conventional air • Based on all building thermal • Supply air can be heated or cooled to remove or add • installed cost per ton conditioning loads i.e., solar gains, moisture $900–$1,800/ton systems building materials, internal • Supply air made very cool then mixed with return air • Power per ton gains by people, machines, • Cycles on and off between set points 900–1,500 W/ton appliances, etc. • Low CFM • High power consumption Direct • Size to blow enough air • High CFM — delivers cool air with enough velocity to • Installed cost/ton evaporative across wetted medium to provide sensible cooling to building occupants $280-$670/ton coolers evaporate water into the air • Open system — windows or exhaust vents must be • Power per ton thereby cooling it open 250–400 W/ton • Based on square footage of • Runs continuously during occupied hours with a building and air changes per cooling load hour for occupancy type • Needs periodic bleed-off to avoid mineralization • Low power consumption Coolerado • Sized based on square • Delivers cool air at moderate CFM • Installed cost per ton Coolers footage, thermal load, • High volume of moist air exhaust $900–$1,100/ton ambient air conditions • Low power consumption • Power per ton • Sized to about twice the CFM • Constant low volume bleed-off 220–260 W/ton of air conditioning • Secondary/working air moisture (water) is exhausted from building

Table 2. Comparison of load, operating, and cost parameters for small office coolers. Source: Compilation from R.S. Means Mechanical Cost Data 2005 and manufacturers’ data sheets rates the water. However, water water through the evaporative Economic and associated with the generation of medium, are often used to mini- Performance Data electricity used for cooling also mize mineral build-up on the needs to be accounted for in order medium. The Coolerado Cooler Conventional air-conditioning to make a meaningful comparison employs a small continual flow, systems, direct evaporative cool- of cooling methods. For both a rather than bleed-off cycles, to ers, and ultracoolers all have direct evaporative cooler and prevent mineral build-up. It uses different sizing, operational, and ultracoolers, the electricity con- about 10 gal/hr (37.9 L/hr) during cost parameters (Table 2). sumed in providing cooled air peak operation and averages about Meaningful comparisons are needs to be accounted for as well 3.5 gal/hr (13.2 L/hr) during the difficult to make, because of the as on-site water consumed during entire cooling season.8 lack of conversion factors between the evaporation process. systems designed to operate on Chiller plants in larger commercial different principles and data. This A study of 46 residences in HVAC systems use water to is especially true for a technology Phoenix, Arizona, found that direct remove heat from air and equip- that is still fairly new evaporative coolers consumed ment. A general rule of thumb for and deployed in relatively small about 4.4 gallons per hour (gal/hr) water usage is 2 to 3 gal/ton (7.6 numbers in various locations (16.7 L/hr) of water during to 11.4 L per ton) of cooling.9 with different environments. One operation without bleed-off and cannot simply compare one system about 10.4 gal/hr (39.4 L/hr) with with another in a different loca- bleed-off7 for an average of about tion, or even in the same location 7.6 gal/hr (28.8 L/hr) for all sys- in different ambient conditions, tems. Bleed-off cycles, which flush because the sizing and operating

______7 Evaporative cooler water use, Karpiscak, M.; Marion, M.; Arizona Cooperative Extension, http://ag.arizona.edu/pubs/consumer/az9145.pdf; 1994. 8 Telephone conversation with R. Gillan, February 2006. 9 Evaluating and Improving Chiller Plant Efficiency, Trane Corporation, www.trane.com/commercial/issues/environmental/short.asp, 2006.

FEDERAL ENERGY MANAGEMENT PROGRAM11 — 11 Technology Installation Review

parameters would yield different ants are used in the cooling change in water content [TDew results. Unlike other building process. measured in F°]. energy systems, ultracoolers are not yet readily modeled in terms The Coolerado Cooler can have the Dry-bulb temperature: The inside of their energy use using currently greatest impact on demand charges air temperature measured by a available tools. and cost and energy savings when thermometer. These temperatures peak demand is greatest. During are shown as vertical lines on the Because it is a relatively new the cooling season, these are the psychrometric chart [TDB measured technology, the Coolerado Cooler hottest times of the day; they are in °F]. has not been the subject of a also times when air-conditioning widespread study and has not loads are highest and power plant Humidity ratio: The ratio of the undergone significant independent efficiencies are lowest. It performs mass of water vapor to the mass review, except as discussed earlier best during those times and of dry air in a moist-air mixture in this report. Consequently, the provides the benefits of cool, fresh, [W is the symbol used, measured manufacturer has had to supply dry air at a much lower cost than as a decimal ratio]. some of the economic and perfor- that of a conventional air Psychrometrics is the study of the mance data. conditioner. thermodynamic properties of moisture content in atmospheric Both direct evaporative coolers Glossary of Terms and the Coolerado Cooler consume air. It is used in the design and analysis of performance for a wide 25% to 40% as much power as vapor Psychrometric Terms compression air-conditioning variety of processes that involve systems do. The installed cost for Dew-point temperature: The tem- warming or cooling air, which the Coolerado Cooler can be 2 to perature at which moisture in the always contains some moisture. 3 times higher than that of direct air will condense on surfaces; The amount of this moisture has evaporative coolers, but it is either HVAC designers work to avoid a direct effect on the health and less expensive than most vapor condensation on building surfaces comfort of occupants. HVAC compression air-conditioning and equipment. From a given system designers and operators use systems or cost-competitive with dry- or wet-bulb temperature, psychrometric analysis techniques them. move horizontally to the left on with thermodynamic properties and the psychrometric chart to find principles to optimize health and Summary and Conclusions the lower temperature at which comfort levels within occupied condensation will occur with no spaces. The Coolerado Cooler technology can reduce cooling energy. Like other energy efficiency strategies, it can help Federal agencies, reach the energy-use reduction goals of EPAct 2005, particularly in the western United States. This technology also has the potential to have a significant impact on an agency’s energy bills in terms of reducing both energy and demand costs. Widespread deployment of this technology in average to dry climates in the United States could have a significant positive impact on electric demand and ease the burden on the utility grid. An added benefit is that no refriger- Figure G-1. Key properties measured in a psychrometric chart. Source: http://www. sp.uconn.edu/~mdarre/NE-127/NewFiles/psychrometric_inset.html

12 — FEDERAL ENERGY MANAGEMENT PROGRAM Technology Installation Review

Relative humidity: The measure of the moisture content of a mixed Cooling calculation parameters: airstream (dry air and water vapor) • A ton of refrigeration is defined as the cooling power of one relative to the amount of moisture short ton (2000 lb or 907 kg) of ice melting in a 24-hour period. in saturated air at the same temperature. These curved lines are • 1 ton of cooling equals 12,000 Btu/hr, or 3510 W. bounded by the dew-point curve, • It takes 1 Btu to raise the temperature of 1 lb of water 1°F. which is also 100% relative humid- • It takes approximately 1000 Btu to evaporate 1 lb of water and ity [RH, often denoted by the approximately 8700 Btu to evaporate 1 gal of water. symbol φ, is measured in percent]. • It takes 0.24 Btu to raise the temperature of 1 lb of air 1°F. Wet-bulb temperature: An interme- 3 diate quantity that informs the • 1 lb of air occupies 13.7 ft of space at sea level when the HVAC designer about the mois- temperature is 75°F. ture content in air, it is measured with 50% RH by the power consumed consumed (kWh). The result, a thermometer with a wetted wick (in watts [W]) in order to meet in units of Btu/kWh, indicates and a specified airflow over that indoor requirements of 80°F and seasonal performance. Higher wick. It represents the maximum 50% RH. The resulting unit for EER SEERs are more efficient. A SEER thermodynamic cooling that can is Btu/hr/W. Higher EERs are of 13.0 or greater is required for be achieved before condensation. more efficient. The EER indicates Energy Star qualification. SEERs These are shown as diagonal lines peak performance on the hottest will always be higher than EERs moving up and to the left in a days.10 The minimum required for a given piece of cooling equip- psychrometric chart and decreas- Energy Star® EER rating for a ment because they are tested at ing in temperature (cooling) [T WB room air conditioner is 9.4 or less extreme or less rigorous measured in F°]. greater. For an 8,000 to 13,999 Btu/ conditions.11 Cooling Equipment Terms hr capacity air conditioner without louvers, the Energy Star require- Acknowledgments Cooling capacity: This is a measure ment specifies a minimum EER of of the amount of air (mass) being 10.8. Energy Star EER require- This publication was written cooled per unit time, its specific ments vary between 9.4 and 10.8 by Robi Robichaud of the NREL heat capacity, and the change in for other configurations and FEMP Technical Assistance Team. temperature achieved. Typical units capacity sizes. The author wishes to thank the are in tons of cooling provided; following for their valuable SEER (seasonal energy efficiency 1 ton of cooling is equivalent to contributions: Ben Barnes, Mike ratio): This is a measure of the 12,000 Btu/hr of heat removed Brandemuehl, Sheila Hayter, seasonal efficiency of an air condi- from a space. Erik Kozubal, Steve Slayzak, Vern tioner through the entire cooling Smith, Otto Van Geet, and Andy EER (energy efficiency ratio): This season at a specific outdoor Walker. This analysis was funded is a measure of the instantaneous temperature (82°F), accounting for by the U.S. Department of Energy, efficiency of a room air conditioner seasonal temperature variations. Office of Energy Efficiency and and is calculated by dividing the It is calculated by dividing the Renewable Energy, Federal Energy cooling capacity (Btu/hr) at an seasonal cooling energy (Btu) by Management Program. outdoor temperature of 95°F and the seasonal electrical energy

______10 Buying an Air Conditioner? Remember the EER. Pacific Gas and Electric, 2006,www.pge.com/docs/pdfs/res/rebates/central_air/ 03eer_tech_v3.pdf.

11 Buying an Air Conditioner? Remember the EER. Pacific Gas and Electric, 2006, www.pge.com/docs/pdfs/res/rebates/central_air/ 03eer_tech_v3.pdf.

FEDERAL ENERGY MANAGEMENT PROGRAM13 — 13 A Strong Energy Portfolio for a Strong America

Energy efficiency and clean, renewable Log on to FEMP’s Web site for information energy will mean a stronger economy, a cleaner environment, and greater energy about New Technology Demonstrations independence for America. Working with a wide array of state, community, industry, www.eere.energy.gov/femp/ and university partners, the U.S. Department of Energy’s Office of Energy Efficiency and You will find links to Renewable Energy invests in a diverse portfolio of energy technologies. • A New Technology Demonstration Overview • Information on technology demonstrations For More Information • Downloadable versions of publications in Adobe Portable EERE Information Center Document Format (pdf ) 1-877-EERE-INF or • A list of new technology projects under way (877-337-3463) www.eere.energy.gov/femp • Electronic access to a regular mailing list for new products when they become available General Contacts • How Federal agencies may submit requests to us to assess Will Lintner new and emerging technologies Team Lead, RSTT Federal Energy Management Program U.S. Department of Energy 1000 Independence Ave, SW, EE Washington, DC 20585 Phone: (202) 586-3120 Fax: (202) 586-3000 [email protected] Steven A. Parker Pacific Northwest National Laboratory P.O. Box 999, MSIN: K5-08 Richland, WA 99352 Phone: (509) 375-6366 Fax: (509) 375-3614 [email protected] Technical Contact Robi Robichaud National Renewable Energy Laboratory Disclaimer MS 1534 This report was sponsored by the United States Department of Energy, Energy Efficiency and 1617 Cole Boulevard Renewable Energy, Federal Energy Management Program. Neither the United States Government Golden, CO 80401 Phone: (303) 384-7553 nor any agency or contractor thereof, nor any of their employees, makes any warranty, express Fax: (303) 384-7411 or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or [email protected] usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial Produced for the U.S. Department product, process, or service by trade name, trademark, manufacturer, or otherwise does not of Energy, Energy Efficiency and necessarily constitute or imply its endorsement, recommendation, or favoring by the United Renewable Energy, by the National States Government or any agency or contractor thereof. The views and opinions of authors Renewable Energy Laboratory expressed herein do not necessarily state or reflect those of the United States Government or any agency or contractor thereof. DOE/GO-102007-2325 June 2007

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