Desiccant Enhanced 

Evaporative Air-Conditioning 

(DEVap): Evaluation of a New 

Concept in Ultra Efficient Air 

Conditioning 

Eric Kozubal, Jason Woods, Jay Burch, 

Aaron Boranian, and Tim Merrigan 

NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC. 

Technical Report 

NREL/TP-5500-49722 

January 2011 

Contract No. DE-AC36-08GO28308 
 

 

Desiccant Enhanced 

Evaporative Air-Conditioning 

(DEVap): Evaluation of a New 

Concept in Ultra Efficient Air 

Conditioning 

Eric Kozubal, Jason Woods, Jay Burch, 

Aaron Boranian, and Tim Merrigan 

Prepared under Task No. ARRB2206 

NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC. 

National Renewable Energy Laboratory Technical Report 

1617 Cole Boulevard NREL/TP-5500-49722 

Golden, Colorado 80401 January 2011 303-275-3000 • www.nrel.gov 

Contract No. DE-AC36-08GO28308 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NOTICE 

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Executive Summary 

NREL has developed the novel concept of a desiccant enhanced evaporative air conditioner 

(DEVap) with the objective of combining the benefits of liquid desiccant and evaporative 

cooling technologies into an innovative “cooling core.” Liquid desiccant technologies have 

extraordinary dehumidification potential, but require an efficient cooling sink. Today’s 

advanced indirect evaporative coolers provide powerful and efficient cooling sinks, but are 

fundamentally limited by the moisture content in the air. Alone, these coolers can achieve 

temperatures that approach the dew point of the ambient air without adding humidity; however, 

they cannot dehumidify. Use of stand-alone indirect evaporative coolers is thus relegated to arid 

or semiarid geographical areas. 

Simply combining desiccant-based dehumidification and indirect evaporative cooling 

technologies is feasible, but has not shown promise because the equipment is too large and 

complex. Attempts have been made to apply liquid desiccant cooling to an indirect evaporative 

cooler core, but no viable design has been introduced to the market. DEVap attempts to clear 

this hurdle and combine, in a single cooling core, evaporative and desiccant cooling. DEVap’s 

crucial advantage is the intimate thermal contact between the dehumidification and the cooling 

heat sink, which makes dehumidification many times more potent. This leads to distinct 

optimization advantages, including cheaper desiccant materials and a small cooling core. The 

novel design uses membrane technology to contain liquid desiccant and water. When used to 

contain liquid desiccant, it eliminates desiccant entrainment into the airstream. When used to 

contain water, it eliminates wet surfaces, prevents bacterial growth and mineral buildup, and 

avoids cooling core degradation. 

DEVap’s thermodynamic potential overcomes many shortcomings of standard refrigerationbased direct expansion cooling. DEVap decouples cooling and dehumidification performance, 

which results in independent temperature and humidity control. The energy input is largely 

switched away from electricity to low-grade thermal energy that can be sourced from fuels such 

as natural gas, waste heat, solar, or biofuels. Thermal energy consumption correlates directly to 

the humidity level in the operating environment. Modeling at NREL has shown that the yearly 

combined source energy for the thermal and electrical energy required to operate DEVap is 

expected to be 30%–90% less than state-of-the-art direct expansion cooling (depending on 

whether it is applied in a humid or a dry climate). Furthermore, desiccant technology is a new 

science with unpracticed technology improvements that can reduce energy consumption an 

additional 50%. And unlike most heating, ventilation, and air-conditioning systems, DEVap uses 

no environmentally harmful fluids, hydrofluorocarbons, or chlorofluorocarbons; instead, it uses 

water and concentrated salt water. 

DEVap is novel and disruptive, so bringing it into the entrenched conventional air conditioner 

market will create some market risk. Designing and installing a new DEVap system requires 

retraining. DEVap has unknown longevity and reliability compared to standard A/C. The 

availability of natural gas or other thermal energy sources may be an issue in certain places. 

However, DEVap does not require a large outdoor condenser, but instead uses a much smaller 

desiccant regenerator that can be placed inside or outside, and can be integrated with solar and 

waste heat. If these risks can be properly addressed, the DEVap air conditioner concept has 

i 
 

strong potential to significantly reduce U.S. energy consumption and provide value to energy 

companies by reducing summertime electric power demand and resulting grid strain. 

NREL has applied for international patent protection for the DEVap concept (see 

www.wipo.int/pctdb/en/wo.jsp?WO=2009094032). 

ii 
 

 

Acronyms and Abbreviations 

AAHX air-to-air heat exchanger 

AILR AIL Research 

A/C air-conditioning 

CHP combined heat and power 

COP coefficient of performance 

DEVap desiccant-enhanced evaporative air conditioner 

DOE U.S. Department of Energy 

DX direct expansion air conditioner 

HMX heat and mass exchanger 

HVAC heating, ventilation, and air-conditioning 

IRR internal rate of return 

LCC life cycle cost 

LDAC liquid desiccant air conditioner 

NREL National Renewable Energy Laboratory 

RH relative humidity 

RTU rooftop unit 

SEER seasonal energy efficiency ratio 

SHR sensible heat ratio 

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Contents 

Executive Summary......................................................................................................................... i
 

Acronyms and Abbreviations ........................................................................................................iii
 

1.0 Introduction.......................................................................................................................... 1
 

1.1 Intention ........................................................................................................................... 1
 

1.2 Background ...................................................................................................................... 1
 

2.0 Research Goals..................................................................................................................... 3
 

2.1 Air-Conditioning Functional Goals.................................................................................. 3
 

2.2 How Direct Expansion Air-Conditioning Achieves Performance Goals......................... 5
 

2.3 The DEVap Process ......................................................................................................... 7
 

2.3.1 Commercial-Grade Liquid Desiccant Air Conditioner Technology......................... 7
 

2.3.2 DEVap Process: Air Flow Channel Using Membranes (NREL Patented Design) 12
 

2.4 DEVap Cooling Performance......................................................................................... 16
 

2.5 DEVap Implementation.................................................................................................. 17
 

2.5.1 New and Retrofit Residential.................................................................................. 17
 

2.5.2 New and Retrofit Commercial................................................................................ 19
 

3.0 Modeling............................................................................................................................ 21
 

3.1 Fundamental Modeling for the DEVap Cooling Core ................................................... 21
 

3.2 Building Energy Models ................................................................................................ 22
 

3.2.1 Residential New and Retrofit.................................................................................. 22
 

3.2.2 New and Retrofit Commercial – EnergyPlus-Generated Load Following ............. 24
 

3.3 Cost Model ..................................................................................................................... 24
 

3.3.1 Initial Cost Estimates .............................................................................................. 24
 

3.3.2 Economic Analysis Assumptions for New and Retrofit Residential...................... 25
 

3.3.3 Economic Analysis Assumptions for New and Retrofit Commercial .................... 26
 

3.4 Cooling Performance...................................................................................................... 26
 

3.4.1 New Residential...................................................................................................... 28
 

3.4.2 Retrofit Residential ................................................................................................. 30
 

3.4.3 New and Retrofit Commercial................................................................................ 31
 

3.5 Energy Performance....................................................................................................... 32
 

3.5.1 New Residential...................................................................................................... 32
 

3.5.2 Retrofit Residential ................................................................................................. 35
 

3.5.3 New and Retrofit Commercial................................................................................ 37
 

3.6 Residential Cost Performance ........................................................................................ 38
 

3.7 Commercial Cost Performance ...................................................................................... 41
 

4.0 Risk Assessment ................................................................................................................ 42
 

4.1 Technology Risks........................................................................................................... 42
 

4.2 Market and Implementation Risks ................................................................................. 43
 

4.3 Risk to Expected Benefits .............................................................................................. 44
 

5.0 Future Work....................................................................................................................... 46
 

5.1 Laboratory DEVap A/C Demonstration......................................................................... 46
 

5.2 Regeneration Improvements .......................................................................................... 46
 

5.3 Solar Thermal Integration .............................................................................................. 46
 

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6.0 Conclusions........................................................................................................................ 47
 

6.1 Residential Performance Comparison............................................................................ 47
 

6.2 Commercial Performance Comparison .......................................................................... 47
 

6.3 Residential Cost Comparison......................................................................................... 47
 

6.4 Commercial Cost Comparison ....................................................................................... 48
 

6.5 Risk Assessment............................................................................................................. 48
 

7.0 References.......................................................................................................................... 49
 

8.0 Resources Not Cited .......................................................................................................... 51
 

Appendix A Data Tables.......................................................................................................... 52
 

A.1 Detailed Specifications for Retrofit Residential Building.............................................. 52
 

A.2 Detailed Specifications for New Residential Building .................................................. 52
 

A.3 Energy Performance – New Residential ........................................................................ 53
 

A.4 Energy Performance – Retrofit Residential ................................................................... 55
 

A.5 Economics – New Residential........................................................................................ 57
 

A.6 Economics – Retrofit Residential................................................................................... 58
 

A.7 Cost Estimates................................................................................................................ 59
 

A.8 Utility Prices From Utility Tariffs for 2010................................................................... 60
 

v 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figures 

Figure 2-1 ASHRAE comfort zone and 60% RH limit for indoor air quality ............................................. 4
 

Figure 2-2 SHR lines plotted on a psychrometric chart with room air at 76°F and 60% RH...................... 5
 

Figure 2-3 Lennox DX A/C with Humiditrol condenser reheat coil (Lennox Commercial 2010).............. 6
 

Figure 2-4 Psychrometric chart showing the dehumidification process using desiccants ........................... 8
 

Figure 2-5 Desiccant reactivation using single-effect scavenging air regenerator ...................................... 9
 

Figure 2-6 Major components and packaging of the AILR LDAC (Photograph shows packaged 

HMXs, water heater and cooling tower) ............................................................................. 10
 

Figure 2-7 LDAC schematic...................................................................................................................... 11
 

Figure 2-8 Calculated two-stage regenerator moisture removal rate and efficiency performance ............ 12
 

Figure 2-9 Physical DEVap concept description ....................................................................................... 13
 

Figure 2-10 Scanning electron microscope photograph of a micro porous membrane (Patent Pending,
 

Celgard product literature) .................................................................................................. 14
 

Figure 2-11 DEVap HMX air flows .......................................................................................................... 15
 

Figure 2-12 DEVap enhancement for LDAC ............................................................................................ 16
 

Figure 2-13 DEVap cooling process in a typical Gulf Coast design condition ......................................... 17
 

Figure 2-14 Example diagram of a residential installation of DEVap A/C showing the solar option....... 18
 

Figure 2-15 Example diagram of a packaged DEVap A/C........................................................................ 19
 

Figure 2-16 Example diagram of a commercial installation of DEVap A/C showing the solar and
 

CHP options ........................................................................................................................ 20
 

Figure 3-1 Temperature and humidity profiles of DEVap process using the Engineering Equation 

Solver model........................................................................................................................ 21
 

Figure 3-2 DEVap cooling core design...................................................................................................... 22
 

Figure 3-3 Residential/new – Houston simulation showing the return air and supply air from the
 

DEVap A/C ......................................................................................................................... 27
 

Figure 3-4 Return and supply air from the DX A/C and dehumidifier (shown as “DH”) in a new
 

residential building in Houston ........................................................................................... 28
 

Figure 3-5 Effect of a whole-house dehumidifier when used with DX A/C in a new residential
 

building in Houston ............................................................................................................. 28
 

Figure 3-6 Indoor RH histograms for Houston throughout the year.......................................................... 29
 

Figure 3-7 Indoor RH histograms for Houston in June–August................................................................ 29
 

Figure 3-8 Houston DEVap A/C SHR bins for meeting cooling load....................................................... 30
 

Figure 3-9 Indoor RH histograms for Houston throughout the year.......................................................... 30
 

Figure 3-10 Indoor RH histograms for Houston in June–August .............................................................. 31
 

Figure 3-11 RH histogram for a small office benchmark in Houston........................................................ 31
 

Figure 3-12 Latent load comparison and resultant space RH in Houston.................................................. 32
 

Figure 3-13 A/C power comparison in Houston for residential new construction .................................... 33
 

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Figure 3-14 Peak power in all cities, residential new construction............................................................ 33
 

Figure 3-15 Source energy in all cities, residential new construction ....................................................... 34
 

Figure 3-16 Water use (evaporation) in all cities, residential new construction........................................ 34
 

Figure 3-17 A/C power comparison in Houston for residential retrofit case............................................. 35
 

Figure 3-18 Peak power in all cities for residential retrofit case ............................................................... 35
 

Figure 3-19 Source energy in all cities for residential retrofit case ........................................................... 36
 

Figure 3-20 Water use (evaporation) in all cities, residential retrofit construction ................................... 36
 

Figure 3-21 A/C power comparison for a small office benchmark in Phoenix ......................................... 37
 

Figure 3-22 A/C power comparison for a small office benchmark in Houston......................................... 37
 

Figure 3-23 Annualized cost comparison for residential new construction............................................... 39
 

Figure 3-24 LCCs for residential new construction for Phoenix (hot, dry) and Houston (hot, humid)..... 39
 

Figure 3-25 Cost comparison for residential retrofit.................................................................................. 40
 

Figure 3-26 LCC breakdown for retrofit for Phoenix (hot, dry) and Houston (hot, humid)...................... 41
 

Figure 4-1 U.S. water use profile............................................................................................................... 43
 

Figure 5-1 Vapor compression distillation regenerator latent COP using natural gas (AILR 2002).......... 46
 

Tables 

Table 2-1 SHRs of Typical Climate Zones (ASHRAE Zones Noted)......................................................... 5
 

Table 2-2 Technology Options for Residential and Commercial Buildings................................................ 6
 

Table 2-3 Source Energy Efficiency Comparison for Commercial Equipment........................................... 7
 

Table 2-4 Technology Options for Residential and Commercial Buildings.............................................. 10
 

Table 3-1 DEVap 1-Ton Prototype Dimensions........................................................................................ 22
 

Table 3-2 A/C System Capacity in Each City Simulated .......................................................................... 23
 

Table 3-3 Modeled Pressure Losses at Maximum Air Flow Rate in Pascals ............................................ 23
 

Table 3-4 DEVap Retail Cost Estimate, Immature Product ...................................................................... 25
 

Table 3-5 Initial DX A/C Cost Estimate.................................................................................................... 25
 

Table 3-6 Economic Analysis Assumptions .............................................................................................. 25
 

Table 3-7 Source Energy Conversion Factors (Deru et al, 2007).............................................................. 32
 

Table 3-8 Results Summary for Phoenix ................................................................................................... 38
 

Table 3-9 Results Summary for Houston................................................................................................... 38
 

Table 3-10 Economic Analysis for Houston.............................................................................................. 41
 

Table 3-11 Economic Analysis for Phoenix .............................................................................................. 41
 

Table 4-1 Technical Risk Matrix for DEVap A/C..................................................................................... 43
 

Table 4-2 Market and Implementation Risk Matrix for DEVap A/C ........................................................ 44
 

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1.0 Introduction 

1.1 Intention 

Our intent is to describe the desiccant enhanced evaporative air conditioner (DEVap A/C) 

concept. To do this, we must give background in A/C design and liquid desiccant technology. 

After which, we can describe the concept which consists of a novel A/C geometry and a resulting 

process. We do this by: 

•	 Discussing the goals of an air conditioner in comparison to expectations 

•	 Discussing the benefits of combining desiccant technology and indirect evaporative 

cooling 

•	 Describing the DEVap A/C process 

•	 Providing a physical description of the DEVap device 

•	 Discussing the energy savings potential 

•	 Assessing the risks of introducing this novel concept to the marketplace 

•	 Discussing future work to bring this concept to the marketplace. 

This information is intended for an audience with technical knowledge of heating, ventilating, 

and air-conditioning (HVAC) technologies and analysis. 

1.2 Background 

Today’s A/C is primarily based on the direct expansion (DX) or refrigeration process, which was 

invented by Willis Carrier more than 100 years ago. It is now so prevalent and entrenched in 

many societies that it is considered a necessity for maintaining efficient working and living 

environments. DX A/C has also had more than 100 years to be optimized for cost and 

thermodynamic efficiency, both of which are nearing their practical limits. However, the 

positive impact of improved comfort and productivity does not come without consequences. 

Each year, A/C uses approximately 4 out of 41 quadrillion Btu (quads) of the source energy used 

for electricity production in the United States alone, which results in the release of about 380 

MMT of carbon dioxide into the atmosphere (DOE 2009). 

R-22 (also known as Freon) as a refrigerant for A/C is quickly being phased out because of its 

deleterious effects on the ozone layer. The most common remaining refrigerants used today (R410A and R-134A) are strong contributors to global warming. Their global warming potentials 

are 2000 and 1300, respectively (ASHRAE 2006). Finding data on air conditioner release rates 

is nearly impossible, as they are generally serviced only when broken and refrigerant recharge is 

not accurately accounted for. A typical residential size A/C unit may have as much as 13 pounds 

of R-410A, and a 10-ton commercial A/C has as much as 22 pounds. 

Water is not commonly considered to be a refrigerant, but the American Society of Heating, 

Refrigerating and Air-Conditioning Engineers (ASHRAE 2009) recognizes it as the refrigerant 

R-718. Evaporative cooling uses the refrigerant properties of water to remove heat the same way 

DX systems use the refrigeration cycle. Water evaporates and drives heat from a first heat 

reservoir, and then the vapor is condensed into a second reservoir. Evaporative cooling is so 

efficient because atmospheric processes in nature, rather than a compressor and condenser heat 

exchanger, perform the energy-intensive process of recondensing the refrigerant. Water is 

delivered to the building as a liquid via the domestic water supply. 

1
 
 

 

 

 

 

NREL’s thermally activated technology program has been developing, primarily with AIL 

Research (AILR) as our industry partner, liquid-desiccant-based A/C (LDAC) for more than 15 

years. The technology uses liquid desiccants to enable water as the refrigerant in lieu of 

chlorofluorocarbon-based refrigerants to drive the cooling process. The desiccants are strong 

salt water solutions. In high concentrations, desiccants can absorb water from air and drive 

dehumidification processes; thus, evaporative cooling devices can be used in novel ways in all 

climates. Thermal energy dries the desiccant solutions once the water is absorbed. LDACs 

substitute most electricity use with thermal energy, which can be powered by many types of 

energy sources, including natural gas, solar thermal, biofuels, and waste heat. The benefits 

include generally lower source energy use, much lower peak electricity demand, and lower 

carbon emissions, especially when a renewable fuel is used. 

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2.0 Research Goals 

2.1 Air-Conditioning Functional Goals 

In developing a novel air conditioner based on principles that are inherently different than 

traditional A/C, we must consider the design goals for a new conditioner to be successful. We 

first define what an air conditioning system does in building spaces only. 

Today’s A/C systems: 

•	 Maintain a healthy building environment. 

o	 In commercial and new residential, A/C provides ventilation air to maintain 

indoor air quality. 

o	 A/C maintains humidity to prevent mold growth, sick building syndrome, etc. 

•	 Maintain human comfort by providing 

o	 Temperature control (heat removal) 

o	 Humidity control (water removal) 

o	 Some air filtering (particulate removal). 

•	 Distribute air throughout the space to encourage thermal uniformity. 

• In commercial applications, provide make-up air to accommodate exhaust air (EA) flows. 

Today’s A/C systems have: 

•	 Reasonable operations and maintenance (O&M) costs: 

o	 Cost of energy to operate 

o	 Ease of maintenance (for which the expectation is maintain at failure) 

•	 Reasonable size and first cost 

o	 Must fit in an acceptable space 

o	 Must be cost effective compared to minimum efficiency A/C equipment. 

At a minimum, a new air conditioner must be capable of meeting or surpassing these 

expectations when designed into an A/C system. 

For human comfort and building health, A/C is commonly expected to maintain a humidity level 

of less than 60% and inside the ASHRAE comfort zone (ASHRAE Standard 55-2004) seen in 

Figure 2-1. The comfort zone is only a general requirement and may be strongly influenced by 

occupant activity and clothing level. The summer zone is primarily for sedentary activity with a 

t-shirt and trousers. Often, temperatures are set to lower set points because activity generally 

increases. The winter zone is for significantly heavier clothing, but still sedentary activity. The 

60% relative humidity (RH) line does intersect the comfort zones, and thus influences how the 

A/C must react to provide proper building indoor air quality despite human comfort concerns. 

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Psychrometric Chart at 0 ft Elevation (1.013 bar) Psychrometric Chart at 0 ft Elevation (14.7 p (14.7sia) psia)

160 

Comfort Zone (Summer) 

Comfort Zone (Winter) 

60% 

50 60 70 80 90 100
 

140
 

120
 

100 

ω (grains/lb) 

80 

60 

40 

20 

0 

Dry Bulb Temperature (°F) 

Figure 2-1 ASHRAE comfort zone and 60% RH limit for indoor air quality 

Two types of space loads affect building humidity and temperature: 

•	 Sensible load. This is the addition of heat to the building space and comes from a variety 

of sources (e.g., sunlight, envelope, people, lights, and equipment). 

•	 Latent load. This is the addition of moisture to the building space and comes from 

multiple sources (e.g., infiltration, mechanical ventilation, and occupant activities). 

Sensible and latent loads combined form the total load. The sensible load divided by the total 

load is the sensible heat ratio (SHR). A line of constant SHR is a straight line on a 

psychrometric chart, indicating simultaneous reduction in temperature and humidity. The 

building loads determine the SHR and an air conditioner must react to it accordingly to maintain 

temperature and humidity. To match the space load, an A/C system must provide air along a 

constant SHR originating from the space condition (76°F and varying RH). To meet an SHR of 

0.7, one must follow the SHR line of 0.7 to a delivery condition that is lower in temperature and 

humidity. Figure 2-2 and Figure 2–3 show the implications of space SHR on an A/C system by 

illustrating how 60% and 50% RH levels influence A/C performance. Humidity is typically 

removed by cooling the air below the room air dew point. Thus, the saturation condition (black 

line at 100% RH) is the potential to dehumidify. The intersection of the SHR lines and the 

saturation line gives the “apparatus dew point” at which the cooling coil will operate. Reducing 

RH from 60% to 50% requires that the apparatus dew point change from 56°F to 47°F at a 

constant SHR of 0.7. When the SHR drops below 0.6 (which is typical of summer nights and 

swing seasons when sensible gains are low), the humidity cannot be maintained below 60% RH 

with standard DX cooling alone. 

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Psychrometric Chart at 0 ft Elevation (1.013 bar) Psychrometric Chart at 0 ft Elevation (14.7 psia) 

150 

125 

100 

75 

50 

25 

0 

Dry Bulb Temperature (°F) 

Figure 2-2 SHR lines plotted on a psychrometric chart with room air at 76°F and 60% RH 

2.2 How Direct Expansion Air-Conditioning Achieves Performance Goals 

For most of the A/C market, refrigeration-based (DX) cooling is the standard, and provides a 

point of comparison for new technologies. To describe the benefits and improvements of 

DEVap A/C technology, we must discuss standard A/C. 

Standard A/C reacts to SHR by cooling the air sensibly and, if dehumidification is required, by 

cooling the air below the dew point. This removes water at a particular SHR. Maintaining a 

space at 76°F and 60% RH (see Figure 2-2) requires the A/C to deliver air along the relevant 

SHR line. If the SHR line does not intersect the saturation line (as in the case of SHR = 0.5), 

standard DX A/C cannot meet latent load, and the RH will increase. If humidity is maintained at 

50% RH (Figure 2–3), standard DX A/C cannot maintain RH when the space SHR reaches 

below about 0.7. 

Building simulation results provide insight into typical SHRs in residential and commercial 

buildings. Table 2–1 shows typical SHR ranges in a few U.S. climates. Humidity control with 

standard DX A/C becomes an issue in climate zones 1A–5A and 4C. Thus, humidity control 

must be added. Western climates in the hot/dry or hot/monsoon climates have sufficiently high 

SHR and generally do not require additional humidity control. 

Table 2-1 SHRs of Typical Climate Zones (ASHRAE Zones Noted) 

Return or Room Air 

40 50 60 70 80 90 100 

ω (grains/lb) 

Climate Typical SHR Range 

1A–3A. Hot/Humid (e.g., Houston) 0.0–0.9 

4A–5A. Hot/Humid/Cold (e.g., Chicago) 0.0–1.0 

2B. Hot/Monsoon (e.g., Phoenix) 0.7–1.0 

3B–5B: Hot/Dry (e.g., Las Vegas) 0.8–1.0 

4C. Marine (e.g., San Francisco) 0.5–1.0 

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In the A/C industry, common technologies for meeting lower SHRs are: 

1.	 DX + wrap-around heat exchanger or latent wheel 

o	 Trane CDQ (wrap-around active/desiccant wheel) (see Trane 2008) 

o	 Munters Wringer (wrap-around sensible wheel) (see Munters Web site 

www.munters.us/en/us/) 

2.	 DX + active wheel 

o	 Munters DryCool system using condenser reheat to reactivate an active desiccant 

wheel (see Munters Web site www.munters.us/en/us/) 

3.	 DX + reheat 

o	 Lennox Humiditrol with condenser reheat (see Figure 2-3) 

4.	 DX + ice or apparatus dewpoint < 45°F 

o	 Four Seasons 

o	 Ice Energy Ice Bear energy storage module (see Ice Energy 2010) 

5.	 DX + space dehumidifier 

Figure 2-3 Lennox DX A/C with Humiditrol condenser reheat coil (Lennox Commercial 2010) 

Humidity control options for various building types are shown in Table 2-2. 

Table 2-2 Technology Options for Residential and Commercial Buildings 

Building Type New and Retrofit 

Residential 3. DX + reheat 

5. DX + space dehumidifier 

Commercial 1. DX + wrap-around heat exchanger 

2. DX + active wheel 

3. DX + reheat 

4. DX + ice or apparatus dew point < 45°F 

5. DX + space dehumidifier 

Commercial buildings can, in most cases, use all technology options. Residential systems align 

with options 3 and 5. These technologies do not come without penalties, which are always 

increased energy use and added upfront costs. With options 1 and 2, the primary energy use 

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comes from significant increase in fan power to blow air through the various wheel types. 

Option 3, DX + reheat, is the most common, but essentially erases the cooling done by the DX 

circuit without significant DX cycle efficiency change. This creates an air conditioner rated at 3 

tons that delivers 30% less cooling (or about 2 tons) with the same energy use as the original 3-

ton system. DX + apparatus dew point < 45°F has reduced cycle efficiency because deep 

cooling is provided. DX + dehumidifier is much like DX + reheat, but the dehumidifier is a 

specialized DX system used to deeply dry the air before reheating. 

Options 1, 2, and 4 are usually chosen to pretreat outdoor air (OA) in a dedicated outdoor air 

system, which in all but a few special cases (commercial kitchens and supermarkets with large 

exhaust flows) will not control indoor humidity. However, these technologies do meet large load 

profiles and can reduce the latent load requirements on the smaller DX systems serving the same 

spaces. For space humidity control, most people choose DX + reheat for commercial spaces and 

DX + reheat or dehumidifier for residential spaces. In all cases, latent cooling follows sensible 

cooling. Thus, sensible cooling is often too high and must either be reheated or combined with a 

desiccant to lower the SHR. 

Table 2-3 Source Energy Efficiency Comparison for Commercial Equipment 

(Kozubal 2010) 

DX With Sensible DX With Desiccant DX With WrapHumidity Level Gas Reheat Rotor and Condenser Around Desiccant 

(dry bulb/wet bulb) (200 cfm/ton) Heat Regeneration Rotor 

High humidity (87°/77.3°F) 65% 75% N/A 

Medium humidity (80°/71°F) 55% 65% 85% 

Modest humidity (80°/68°F) 48% 46% 83% 

2.3 The DEVap Process 

2.3.1 Commercial-Grade Liquid Desiccant Air Conditioner Technology 

Desiccants reverse the paradigm of standard DX A/C by first dehumidifying, and then sensibly 

cooling to the necessary level. Desiccant at any given temperature has a water vapor pressure 

equilibrium that is roughly in line with constant RH lines on a psychrometric chart (Figure 2-4). 

The green lines show the potential for two common types of liquid desiccants, lithium chloride 

(LiCl) and calcium chloride (CaCl2). If the free surface of the desiccant is kept at a constant 

temperature, the air will be driven to that condition. If used with an evaporative heat sink at 55°– 

85°F, the air can be significantly dehumidified and dew points < 32°F are easily achieved. The 

blue arrow shows the ambient air being driven to equilibrium with LiCl with an evaporative heat 

sink. At this point, the air can be sensibly cooled to the proper temperature. This type of 

desiccant A/C system decouples the sensible and latent cooling, and controls each independently. 

During the dehumidification process, the liquid desiccant (about 43% concentration by weight 

salt in water solution) absorbs the water vapor and releases heat. The heat is carried away by a 

heat sink, usually chilled water from a cooling tower. As water vapor is absorbed from the 

ambient air, it dilutes the liquid desiccant and decreases its vapor pressure and its ability to 

absorb water vapor. Lower concentrations of desiccant come into equilibrium at higher ambient 

air RH levels. Dehumidification can be controlled by the desiccant concentration that is supplied 

to the device. The outlet humidity level can be controlled by controlling the supplied desiccant 

concentration or decreasing the flow of highly concentrated desiccant. The latter allows the 

7
 
 8

highly concentrated desiccant to quickly be diluted and thus “act” as a weaker desiccant solution 

in the device. 

Figure 2-4 Psychrometric chart showing the dehumidification process using desiccants 

Absorption will eventually weaken the desiccant solution and reduce its dehumidifying potential; 

the desiccant must then be regenerated to drive off the absorbed water. Thermal regeneration is 

the reverse: In this process, the desiccant is heated to a temperature at which the equilibrium 

vapor pressure is above ambient. The vapor desorbs from the desiccant and is carried away by 

an air stream (see Figure 2-5). Sensible heat is recovered by first preheating the ambient air 

using an air-to-air heat exchanger (AAHX). The air comes into heat and mass exchange with the 

hot desiccant (in this example at 190°F) and carries the desorbed water vapor away from the 

desiccant. Sensible heat is recovered by taking the hot humid air to preheat the incoming air 

through the AAHX. The change in enthalpy of the air stream represents the majority of the 

thermal input. Small heat loss mechanisms are not represented in the psychrometric process. 

The process uses hot water or steam to achieve a latent coefficient of performance (COP) of 0.8–

0.94 depending on ultimate desiccant concentration. Latent COP is defined as: 

ሻ݊݋݅ݐܽݖ݅ݎ݋݌ܸܽ ݂݋ ݐ݁ܽܪሺ כ ሻ݁ݐܴܽ ݈ܽݒ݋ܴ݁݉ ݁ݎݑݐݏ݅݋ܯሺ ൌ ௧௘௡௧௅௔ܱܲܥ

ሻ݁ݑܸ݈ܽ ݅݊݃ݐ݁ܽܪ ݎ݄݅݃݁ܪሺ ݁ݐܴܽ ݐ݁ܽܪ

COP is maximized by maximizing the regeneration temperature and change in concentration 

while minimizing the ultimate desiccant concentration. Including the COP of the water heater 

(about 0.82), a typical combined latent COP is 0.82 × 0.85 = 0.7. 

0

20

40

60

80

100

120

140

160

30 40 50 60 70 80 90 100 110 120

ω (grains/lb)

Dry Bulb Temperature (°F)

Psychrometric Chart at 0 ft Elevation (1.013 bar)

Room or Return Air

Psychrometric Chart at 0 ft Elevation (14.7 psia) (14.7 psia) 
 

 

 

 

 

 

 

 

 

 

 

Psychrometric Chart at 0 ft Elevation (1.013 bar)

 

 

 

Psychrometric Chart at 0 ft Elevation (14.7 psia) (14.7 psia)

1000 

30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 

Enthalpy = 45 BTU/lbm 

Enthalpy = 60.6 BTU/lbm 

Enthalpy = 192.5 BTU/lbm 

Ambient Air 

SR Exhaust Air 

Majority of 

Heat Input 

900
 

800
 

700
 

600 

500 

400 ω (grains/lb) 

300 

200 

100 

0 

Dry Bulb Temperature (°F) 

Figure 2-5 Desiccant reactivation using single-effect scavenging air regenerator 

The AILR LDAC technology uses novel heat and mass exchangers (HMXs) to perform these 

two processes (see Figure 2-6), which show the desiccant conditioner and scavenging air 

regenerator. The liquid desiccant is absorbed into the conditioner (absorber) where the inlet 

ambient air is dehumidified. The liquid desiccant is regenerated in the regenerator (desorber) 

where the water vapor desorbs into the EA stream. This technology is called low flow liquid 

desiccant A/C, because the desiccant flow is minimized in both HMXs to the flow rate needed to 

absorb the necessary moisture from the air stream. The HMXs must therefore have integral 

heating and cooling sources (55°–85°F cooling tower water is supplied to the conditioner). The 

regenerator uses hot water or hot steam at 160°–212°F. The cooling or heating water flows 

internal to the heat exchange plates shown. The desiccant flows on the external side of the HMX 

plates. The plates are flocked, which effectively spreads the desiccant. This creates direct 

contact surfaces between the air and desiccant flows. The air passes between the plates, which 

are spaced 0.25 in. apart. Figure also shows a 20-ton packaged version on a supermarket in 

Los Angeles, California. Lowenstein (2005) provides more detailed descriptions of these 

devices. 

9
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

cool, dry ventilation Regenerator delivered to building 

Cooling Tower 

Water heater 

Conditioner 

Economizer 

hot and 

humid air 

humid 

exhaust 

heating 

water 

chilled 

water 

Figure 2-6 Major components and packaging of the AILR LDAC (Photograph shows packaged 

HMXs, water heater and cooling tower)
 

(Photos used with permission from AIL Research) 

A double-effect regenerator expands on the scavenging air regenerator by first boiling the water 

out of the liquid desiccant solution (250°–280°F) and reusing the steam by sending it through the 

scavenging air regenerator. This two-stage regeneration system can achieve a latent COP of 1.1– 

1.4. NREL is working with AILR to develop this product. A typical solar regenerator would 

consist of either a hot water supply to a scavenging regenerator (which would result in a singleeffect device that would have about a 60% solar conversion efficiency based on absorber area). 

We are currently monitoring more advanced concepts that generate steam by boiling either water 

or liquid desiccant internal to a Dewar-style evacuated tube. If filled with water to create steam, 

efficiency up to 70% is possible. An advanced version would boil desiccant directly in the solar 

collector to create steam that is then used in the scavenging regenerator. This would increase 

solar conversion efficiency to 120%. This work is ongoing and results are not yet available. 

Table 2-4 Technology Options for Residential and Commercial Buildings 

(Based on NREL calculations and laboratory data, available on request) 

Regenerator COP 

Solar 60%–120% solar conversion 

Single effect* 0.7–0.8 

Double effect* 1.1–1.4 

* Based on the higher heating value of natural gas 

For the low-flow LDAC, the regenerator and conditioner systems are shown connected in Figure 

2-7, which illustrates the three basic ways to regenerate the desiccant system with a thermal 

source: solar, water heater, and a double effect. The water heater or boiler can be fueled by 

many sources, including natural gas, combined heat and power (CHP), or even biofuels. 

Also shown is the desiccant storage option that allows an A/C system to effectively bridge the 

time gap between thermal energy source availability and cooling load. Desiccant storage at 8% 

concentration differential will result in about 5 gal/latent ton·h. In comparison, ice storage is 

approximately 13–15 gal/ton·h (theoretically 10 gal/ton·h, but in practice only 67% of the 

10
 
 

 

 

 

 

 

 

volume is frozen (Ice Energy 2010). This storage can be useful to enable maximum thermal use 

from solar or on-site CHP. LDACs leverage the latent storage capacity by producing more total 

cooling than the stored latent cooling. For example, an LDAC may use 2 ton·h of latent storage, 

but deliver 4 ton·h of total cooling. This is derived from an additional 2 tons of sensible cooling 

accomplished by the evaporative cooling system. 

Figure 2-7 LDAC schematic 

The latent COP for DEVap is 1.2–1.4, because it requires only modest salt concentration to 

function properly (30%–38% LiCl). Figure 2-8 shows the calculated efficiency of a two-stage 

regenerator using natural gas as the heat source. Moisture removal rate is also shown where the 

nominal rate is 3 tons of latent removal. 

11
 
 

 

 

 

 

 

 

2 Stage Regenerator Performance 

(30 kbtu gas input, Tamb,wb = 78°F, ∆CLiCl = 8% )
 

4.00 

3.50 

3.00 

2.50 

2.00
 

MRR
 

1.50 COP_Latent 

1.00 

0.50 

0.00 

Inlet Desiccant Concentration (% by weight) 

Figure 2-8 Calculated two-stage regenerator moisture removal rate and efficiency performance 

2.3.2 DEVap Process: Air Flow Channel Using Membranes (NREL Patented 

Design) 

This section describes how the LDAC process is enhanced with NREL’s DEVap concept. The 

DEVap process follows: 

1.	 Ventilation air [1] and warm indoor air [2] are mixed into a single air stream. 

2.	 This mixed air stream (now the product air) is drawn through the top channel in the heat 

exchange pair. 

3.	 The product air stream is brought into intimate contact with the drying potential of the 

liquid desiccant [d] through a vapor-permeable membrane [e]. 

4.	 Dehumidification [ii] occurs as the desiccant absorbs water vapor from the product air. 

5.	 The product air stream is cooled and dehumidified, then supplied to the building space 

[3]. 

6.	 A portion of the product air, which has had its dew point reduced (dehumidified), is 

drawn through the bottom channel of the heat exchange pair and acts as the secondary air 

stream. 

7.	 The secondary air stream is brought into intimate contact with the water layer [c] through 

a vapor-permeable membrane [b]. 

8.	 The two air streams are structurally separated by thin plastic sheets [a] through which 

thermal energy flows, including the heat of absorption [i]. 

9.	 Water evaporates through the membranes and is transferred to the air stream [iii]. 

10. The secondary air stream is exhausted [4] to the outside as hot humid air. MRR (tons) and Latent COP (Site) 

20% 25% 30% 35% 40% 

12
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

d. Liquid

Desiccant i. Heat Transfer 

1. Ventilation Air 

2. Warm Indoor Air 

4. Humid Exhaust 

iii. Water 

Evaporation 

(Cooling Effect) 

3. Cool-Dry 

Supply Air 

b. Membrane 

c. Water 

ii. Dehumidification 

a. Plastic 

Sheets 

e. Membrane 

Figure 2-9 Physical DEVap concept description 

NREL has applied for international patent protection for the DEVap concept and variations 

(Alliance for Sustainable Energy LLC 2008). 

The water-side membrane implementation of DEVap is part of the original concept, but is not a 

necessary component. Its advantages are: 

•	 Complete water containment. It completely solves problems with sumps and water 

droplets entrained into the air stream. 

•	 Dry surfaces. The surface of the membrane becomes a “dry to the touch” surface that is 

made completely of plastic and resists biological growth. 

The water-side membrane may not be necessary in the DEVap configuration, according to strong 

evidence from companies (e.g., Coolerado Cooler, Speakman – OASys) that have used wicked 

surfaces to create successful evaporative coolers. Omitting this membrane would result in cost 

savings. 

The desiccant-side membrane is necessary to guarantee complete containment of the desiccant 

droplets and create a closed circuit to prevent desiccant leaks. It should have the following 

properties: 

•	 Complete desiccant containment. Breakthrough pressure (at which desiccant can be 

pushed through the micro-size pores) should be about 20 psi or greater. 

•	 Water vapor permeability. The membrane should be thin (~25 μm) and have a pore 

size of about 0.1 μm. Its open area should exceed 70% to promote vapor transport. 

Several membranes, such as a product from Celgard made from polypropylene, have been 

identified as possible candidates (see Figure 2-10). 

13
 
 

 

 

 

 

 

 

 

 

 

 

Figure 2-10 Scanning electron microscope photograph of a micro porous membrane (Patent
 

Pending, Celgard product literature)
 

(Photos used with permission from Celgard, LLC) 

The DEVap cooling core (Figure 2–11) is an idealized implementation of the air flows. A higher 

performing air flow configuration (Figure 2–12) shows the cooling device split into two distinct 

areas and depicts the air flow channels from the top vantage point. The mixed ventilation air and 

return air enter from the bottom and exit at the top. The location of the desiccant drying section 

is shown in green; the location of the evaporative post cooling is shown in blue. Using OA to 

cool the dehumidification section improves the design by enabling higher air flow rates to 

provide more cooling. Thus, the left half of the exhaust channel (Figure 2–11) is replaced by an 

OA stream that flows into the page (Exhaust Airflow #1). The deep cooling of the indirect 

evaporative cooler section requires a dry cooling sink; thus, some dry supply air is siphoned off 

(5%–30% under maximum cooling load) to provide this exhaust air stream (Exhaust Airflow #2). 

This section is placed in a counterflow arrangement to maximize the use of this air stream. This 

is essential because it has been dried with desiccant, and thus has a higher embodied energy than 

unconditioned air. The result is that the temperature of supply air is limited by its dew point and 

will come out between 55°–75°F depending on how much is siphoned off. Combined with the 

desiccant’s variable drying ability, the DEVap A/C system controls sensible and latent cooling 

independently and thus has a variable SHR between < 0 (latent cooling with some heating done) 

and 1.0. 

14
 
 

 

 

 

 

Mixed air flow 

Exhaust air flow 

OA at: 

Twb = 65°–80°F 

Exhaust 

air flow #1 

Exhaust 

air flow #2 

Desiccant 

Dehumidification 

Indirect 

Evaporative 

Post Cooling 

Supply air flow at: 

T dp = 50°–55°F 

Figure 2-11 DEVap HMX air flows 

The DEVap core is only half of a complete air conditioner. Figure 2-12 depicts how the DEVap 

cooling core enhances the already developed LDAC technology and converts it from a dedicated 

outdoor air system to an air conditioner that performs space temperature and humidity control 

and provides all the necessary ventilation air. In fact, DEVap can be configured to provide 30%– 

100% ventilation air. Furthermore, DEVap does not require a cooling tower, which reduces its 

maintenance requirements. 

15
 
 

 

 

 

 

 

 

Figure 2-12 DEVap enhancement for LDAC 

2.4 DEVap Cooling Performance 

Because the drying process creates sufficiently dry air, the evaporative process is no longer a 

function of climate. Therefore, DEVap will work in all climates, whether hot and humid or hot 

and dry. Its most challenging operational condition is at a peak Gulf Coast condition (Figure 

2-13) (typical of Tampa, Florida, and Houston, Texas). In this example, DEVap mixes 70% 

return air with 30% OA, resulting in a 30% ventilation rate. The mixed air stream is first 

dehumidified to 51°F dew point. Then the post-evaporative cooler decreases the temperature to 

59°F and uses 30% of the mixed air flow. The result is that the supply and return air flows are 

equal, as are as the OA and EA flows. The system provides 7 Btu/lb of total cooling and 11.5 

Btu/lb to the mixed air stream (7 Btu/lb of space cooling is equivalent to 380 cfm/ton). This is a 

critical design parameter that is acceptable in the HVAC industry to provide air that is of proper 

temperature and sufficiently low air volume delivery. This is all done while providing an SHR 

of 0.6 to the space. Simply by decreasing the post-cooling, the SHR can be lowered further to 

the necessary level. This is more critical when the ambient conditions impose a much lower 

16
 
 

 

 

 

 

 

 

Psychrometric Chart at 0 ft Elevation (1.013 bar) (14.7 psia)

SHR onto the building. An example of such a condition would be a cool April day when it is 

65°–70°F and raining. 

Psychrometric Chart at 0 ft Elevation (14.7 psia) 

30 40 50 60 70 80 90 100 110 120 

Twb = 81.3 deg F 

Twb = 70.2 deg F 

Twb = 64.5 deg F 

Twb = 62.7 deg F 

Twb = 54.1 deg F 

Enthalpy = 44.9 BTU/lbm 

Enthalpy = 34.1 BTU/lbm 

Enthalpy = 29.5 BTU/lbm 

Enthalpy = 28.2 BTU/lbm 

Enthalpy = 22.6 BTU/lbm 

Return Air 

Outdoor Air 

Mixed Air 

1st Stage Air 

Supply Air 

Space Cooling: 

7 BTU/lb 

380 CFM/ton 

175 

150 

125 

100 

75 

50 

25 

0 

ω (grains/lb) 

Dry Bulb Temperature (°F) 

Figure 2-13 DEVap cooling process in a typical Gulf Coast design condition 

At the condition shown, the combined energy DEVap uses results in a total cooling source level 

COP of 1.4. This assumes the 30% ventilation air can be credited toward the cooling load and 

the regenerator latent COP is 1.2, a conservative value. If no ventilation air can be credited, the 

source COP is 0.85. As OA humidity drops (shown at 77°F dew point), the source COP 

increases. At the point where the ambient dew point drops below about 55°F, the desiccant can 

be turned off and no further thermal energy is required. This simplistic explanation indicates that 

as the climate becomes dryer (regardless of OA temperature), DEVap efficiency improves. As 

the sensible load decreases, DEVap uses less EA to provide sensible cooling. The balanced EA 

and OA result in less OA and less moisture removal by the regeneration system. 

2.5 DEVap Implementation 

2.5.1 New and Retrofit Residential 

A 3-ton DEVap A/C cooling core is expected to be about 18 in. deep and have a 20-in. × 20-in. 

frontal area if made square (see Section 3.1). This imposes no significant packaging problems in 

a residential sized A/C system. DEVap air flow rate and cooling delivery are designed to match 

exactly DX A/C (at 7 Btu/lb), thus the return and supply air duct design will work well. 

However, DEVap conditions the space air and rejects heat to the atmosphere, so air to and from 

the ambient air must be brought to the DEVap device, either by placing the DEVap cooling cores 

close to the outside, or by ducting these air streams. This requirement makes implementing 

DEVap different than standard DX A/C. 

17
 
 18

The regenerator for a 3-ton DEVap A/C contains a 30-kBtu boiler (compared to today’s ondemand water heaters, which are about 200 kBtu) and a 50-cfm, 1-ft3

 HMX scavenging 

regenerator. These two main components comprise the bulk of the regenerator, so the packaging 

is very small and can be accommodated in many spaces, including: 

• Outside (the regenerator contains no freeze-prone liquids) 

• Next to the DEVap and furnace 

• Next to the domestic hot water tank. 

The regenerator uses natural gas or thermal heat and a standard 15 Amp, 120-V electrical 

connection. The DEVap core can be integrated with the furnace and air handler, if there is one. 

Figure 2-14 illustrates a possible configuration for a DEVap A/C installed in a typical U.S. home. 

The regenerator component is powered by thermal sources such as natural gas and solar thermal 

heat.

Figure 2-14 Example diagram of a residential installation of DEVap A/C showing the solar option 

(green lines represent desiccant flows) 

In a home application, DEVap performs the following functions: 

• Air conditioner with independent temperature and humidity control 

• Dedicated dehumidifier 

• Mechanical ventilator 

Ventilation air

Cool, dry air

DEVap A/C

Two stage 

Regenerator

DHW

Desiccant 

Storage

Return 

air

Exhaust air

Optional Solar Thermal Collectors
 

 

 

 

 

2.5.2 New and Retrofit Commercial 

In a commercial application, DEVap performs all the same functions of a DX A/C system. The 

most common commercial cooling implementation is the rooftop unit (RTU). Figure 2–15 

illustrates how a packaged DEVap RTU (which is expected to be smaller) may be implemented. 

The DEVap core is marginally bigger than a DX evaporator coil; however, the regenerator is 

compact. There is no large DX condenser section in a DEVap RTU. The DEVap RTU air flows 

will integrate with the building much like a standard RTU, and will impose no significant change 

in the installation and ducting process. As with the residential unit, the DEVap unit will supply 

air at 380 or less cfm/ton. 

Humid 

Two stage 

Regenerator 

DEVap A/C 

Desiccant 

Storage 

Exhaust Air 

Outdoor 

Ventilation Air 

Return Air 

Natural Gas 

Supply Air 

Figure 2-15 Example diagram of a packaged DEVap A/C 

Figure 2–16 illustrates how a DEVap RTU would be installed on a commercial building 

application. The thermal sources for regeneration could again come from natural gas or solar 

thermal heat. However, the commercial application also opens the door to use waste heat from a 

source such as on-site CHP. The figure illustrates many options for heat sources, with many 

possible scenarios. Three possibilities are: 

• Natural gas only 

• CHP with or without natural gas backup 

• Solar heat with or without natural gas backup. 

19
 
 

 

 

Solar Thermal Collectors 

DEVap RTUs 

CHP with Desiccant 

Regeneration 

Figure 2-16 Example diagram of a commercial installation of DEVap A/C showing the solar and 

CHP options 

(green lines represent desiccant flows) 

DEVap can be installed in buildings that contain central air handlers, similarly to a residential 

installation. However, for commercial buildings, this type of installation would be highly 

variable in scope and heat sources for regeneration, and is not discussed in this report. The 

examples are intended to inform a knowledgeable A/C designer enough to extrapolate to 

different scenarios. 

20
 
 

 

 

 

 

 

 

 

 

14.7 psia

3.0 Modeling 

This section describes the building-energy models used to compare a DEVap A/C with a 

standard DX A/C. Simulations were completed for residential new construction and retrofit 

cases and for commercial new construction. 

3.1 Fundamental Modeling for the DEVap Cooling Core 

The design chosen for this analysis is represented in Figure 3-2 with no water-side membrane 

and LiCl as the desiccant. The detailed heat and mass transfer in the DEVap core is simulated 

using the Engineering Equation Solver framework. A two-dimensional, finite-difference model 

calculates each air stream’s temperature and humidity, and the desiccant concentration at each 

point along the different flow channels. The heat and vapor transport rates between each flow 

(mixed/supply air stream, exhaust air streams, desiccant flow, and water flow) are estimated at 

each point with a resistance-in-series network. Figure 3-1 shows the state of each finite 

difference node plotted on a psychrometric chart. The exiting enthalpy of the air from the 

second-stage exhaust stream is at nearly the same enthalpy as the entering first-stage EA (OA). 

The first-stage EA can be two to three times the flow rate as the second-stage stream and thus 

provide more cooling in the dehumidification stage. In this model, membrane resistances are 

estimated using standard practice from the membrane science field. The air-side convection 

coefficients and friction factors are based on experimentally measured data of the DAIS energy 

recovery ventilator, which uses a similar flow enhancement spacer as that planned for the 

DEVap prototype. 

Psychrometric Chart at 0 ft Elevation (14.7 psia) 

Figure 3-1 Temperature and humidity profiles of DEVap process using the Engineering Equation 

Solver model
 

21
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The design condition for determining the size and form factor of the DEVap device is shown in 

Figure 3-1. This represents a typical Gulf Coast design condition. The design criteria were to 

supply cooling to the building at 7 Btu/lb (380 cfm/ton) and an SHR of 0.6 while maintaining 

55% indoor RH. The preferred form factor, along with the required number of channels for a 1-

ton unit, is shown in Table 3-1 and illustrated in Figure 3-2. The model uses this design to create 

performance maps for all potential indoor and ambient conditions. These maps are used in the 

building energy model discussed in Section 3.2. 

Table 3-1 DEVap 1-Ton Prototype Dimensions 

Parameter Value 

Length, L 1.57 ft 

L1 (desiccant section) 0.40 ft 

L2 (indirect evaporative cooler section) 1.17 ft 

Height, H 2.0 ft 

Width, W 1.64 ft 

# of pairs of channels 100 

Supply channel 0.1 in. 

Membrane 3 mil 

Desiccant flow thickness 10 mil 

Plastic sheet 10 mil 

Water film 10 mil 

Exhaust channel 0.08 in. 

L 2 

L 1 

W 

H 

Figure 3-2 DEVap cooling core design 

3.2 Building Energy Models 

3.2.1 Residential New and Retrofit 

The residential building energy model is implemented in the Transient System Simulations 

(TRNSYS) program. Four simulations were performed for each of the eight cities representing 

various U.S. climates (Table 3-2). Sizes were incremented in increments of 1 ton in order to 

meet 100% sensible load using the TMY3 input weather file. 

22
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

• New construction, standard DX A/C 

• New construction, DEVap A/C 

• Retrofit, DX A/C 

• Retrofit, DEVap A/C. 

Table 3-2 A/C System Capacity in Each City Simulated 

Phoenix 

San 

Francisco 

Washington, 

DC Tampa Atlanta Chicago Boston Houston 

New construction 

DX 4 ton 3 ton 3 ton 3 ton 3 ton 3 ton 3 ton 3 ton 

DEVap 4 ton 3 ton 3 ton 3 ton 3 ton 3 ton 3 ton 3 ton 

Retrofit 

DX 4 ton 3 ton 3 ton 3 ton 4 ton 3 ton 3 ton 4 ton 

DEVap 4 ton 3 ton 3 ton 4 ton 4 ton 3 ton 3 ton 4 ton 

In the DEVap system, the DEVap conditioner provides cooling, dehumidification, and 

ventilation. The DEVap system uses a two-stage regenerator operating with a constant latent 

COP of 1.2 and variable-speed supply and exhaust fans with 50% efficiency. Table 3-3 shows 

modeled pressure losses for DEVap at full fan speed. The DX system consists of a seasonal 

energy efficiency ratio (SEER)-13 air conditioner and a stand-alone dehumidifier, with 

ventilation provided by a separate fan. For the DX system, we assume the fan uses energy at 

0.59 W/cfm, which includes fan efficiency and pressure losses from ducts, filters, the furnace, 

and the cooling coil. 

Table 3-3 Modeled Pressure Losses at Maximum Air Flow Rate in Pascals 

Component ΔP (Pa) 

DEVap A/C 

Cooling core, supply 125 

Cooling core, exhaust 1 125 

Cooling core, exhaust 2 10 

Balance of system* 250 

Two exhaust ducts (each) 125 

* Balance of system losses include losses from ducts, furnace (supply only) and filters. 

Each component mentioned in the previous paragraph is modeled with a performance map. The 

DEVap map is based on parametric runs from the model described in Section 3.1, the air 

conditioner map is based on the default map from TRNSYS, and the dehumidifier map is from 

NREL experimental data on an Ultra-Aire dehumidifier (Christensen 2009). The system sizes 

are shown in Table 3-2. The DX system in each city (except Phoenix) has a dehumidifier with a 

65 pints/day capacity. No dehumidifier is required in Phoenix. The simulated building is a 

2500-ft2 house with a 42-ft × 30-ft footprint. The building has an unconditioned basement in the 

cold climates and a slab-on-grade construction for mild climates. Slab and basement ground 

coupling are modeled using the simplified model found in ASHRAE (2009). The building 

envelope U-values (walls, windows, floors, ceilings, and roof), infiltration, and internal gains for 

23
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

the new building are from Hendron (2010); the retrofit case uses a mid-1990s home from 

Hendron (2008). The new construction home has mechanical ventilation per ASHRAE 62.2­

2007; the retrofit building has no mechanical ventilation. The weather for each location is 

simulated with TMY3 data (National Solar Radiation Data Base). The details of these houses are 

presented in Appendix A.1. 

The HVAC systems are controlled such that the building is maintained at 74°–76°F in the 

summer and 70°–72°F in the winter. Dehumidification is provided whenever the indoor RH 

exceeds 55%. An on/off controller with a deadband is used for the DX system; a proportional 

controller is used for the DEVap system. 

3.2.2 New and Retrofit Commercial – EnergyPlus-Generated Load Following 

The commercial analysis was based on a small office benchmark building (Deru et al, 2010) run 

in standard thermostat control with a DX A/C system. The new versus retrofit definitions for 

commercial groups are not yet clearly defined and are not discussed here. The difference in the 

analysis is not likely to have a large impact, because the cooling loads for commercial buildings 

are primarily dominated by ventilation and internal gains and not by differences in envelope and 

building construction. Thus for the modeling exercise, the commercial new and retrofit are 

considered equal. 

This modeling was done with EnergyPlus as the load generation engine in Phoenix, Arizona, and 

Houston, Texas. The loads were created using a standard 16 SEER A/C without humidity 

control, so the building had many hours when the conditions were 60%–90% RH. Implementing 

humidity control in EnergyPlus was problematic when these loads were developed (summer 

2008) and the issue was not resolved. New loads were not generated for this study because the 

benefits of higher accuracy modeling do not warrant the effort. Furthermore, because humidity 

is not controlled, comparisons to the estimated DX A/C energy use estimate will be conservative. 

The DEVap A/C model was set up to load follow the EnergyPlus results with the DX A/C. 

Although not ideal, this creates the situation where the DEVap device must meet the same SHR 

as the DX system. The result is that the DEVap system is run sub optimally with higher than 

normal air flow rates. DEVap will run more optimally if the space RH is reduced and air flow 

rate can be managed to a more reasonable cfm/ton. The preceding arguments lend to a 

conservative estimate for DEVap A/C energy savings. 

The small office benchmark A/C capacity is 10 tons in both the DEVap and DX A/C cases. The 

ventilation rate was a constant 12% of total air flow, which was set at 475 cfm/ton. 

3.3 Cost Model 

3.3.1 Initial Cost Estimates 

Costs for the DEVap A/C are uncertain, but several similar products can be used to estimate. 

Costs from the Coolerado heat and mass exchanger are used to estimate costs for the DEVap 

conditioner; a cost estimate from AILR is used for the regenerator. The Coolerado is estimated 

to contain 205 ft2 of heat exchanger area per cooling core, and we estimate the manufacturing 

cost to be $0.68/ft2

. We assume an additional cost of $1.02/ft2 ($0.93 for the membrane, $0.09 

for attaching the membrane) for the first section, which results in a total cost of $1119/ton. The 

other cost assumptions are listed in Appendix A.7. These estimates are predicated on costs of the 

system as built in similar fashion as the Coolerado Cooler and at modest entry-level volumes. 

We do not attempt to estimate future improvements in designs and cost that would allow the 

24
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

system to approach the volumes of the DX A/C market, and thus reduce costs further. (See 

Table 3–4.) 

Table 3-4 DEVap Retail Cost Estimate, Immature Product 

DEVap Model Retail Cost Estimate 

3-ton DEVap A/C $7,484 

4-ton DEVap A/C $8,680 

10-ton DEVap A/C RTU $20,461 

The conventional system costs are shown in Table 3-5. 

Table 3-5 Initial DX A/C Cost Estimate 

A/C System Retail Cost Estimate 

SEER-13 air conditioner ($/ton)* $1,160 

Dehumidifier $1,200 

3-ton A/C + dehumidifier retail cost $4,680 

4-ton system retail cost $5,840 

10-ton, SEER 15, DX A/C RTU at $1,520/ton** $15,200 

* Estimate for air conditioners (DOE 2002)
 

** Estimate for 5-ton SEER 15 packaged RTU (Trane quotation)
 

3.3.2 Economic Analysis Assumptions for New and Retrofit Residential 

To compare costs between conventional and DEVap systems, we calculate the annualized cost of 

cooling in dollars per year. This cost includes the annual cost of loan repayment and the annual 

operating costs (electricity, gas, and water). This analysis is based on the assumptions listed in 

Table 3-6. 

Table 3-6 Economic Analysis Assumptions 

Assumptions 

New 

Construction Retrofit 

Market discount rate 0.08 0.08 

Loan rate 0.05 0.07 

Inflation rate 0.02 0.02 

Analysis period 15 15 

Loan period 30 5 

Effective income tax rate 0.3 

Property tax rate 0.02 

Ratio of down payment to initial investment 0.1 

Ratio of assessed value to installed cost 0.7 

P1 (ratio of life cycle costs to first-year costs) 9.60 9.60 

P2 (ratio of life cycle costs to initial investment) 0.59 0.97 

PWF0 (present worth factor for given discount rate and analysis period) 8.56 8.56 

The life cycle cost (LCC) is calculated with: 

where Cinit is the initial cost of the system as described in Section 3.3.1 and Cyr,util is the annual 

cost of utilities (natural gas, electricity, water), which is calculated based on region-specific 

utility prices. The monthly gas and electricity prices were estimated with utility tariffs from each 

25
 
 

city for 2010 and are tabulated in Appendix A.8. This was done to estimate the marginal cost of 

energy (not including any fixed monthly charge). We also consider the case where gas prices are 

50% higher than 2010 prices. Water prices were estimated at $3/1000 gal for all locations. 

The annualized cost of cooling is then:

ܥܥܮ 

Annualized cost of cooling ൌ ܹܲܨ଴

where PWF0 is the present worth factor based on the market discount rate (d) and the analysis 

period (15 years): 

1 1 ଵହ

ܹܲܨ ൌ ቈ1 െ ቉൰൬ ݀ 1െ݀ ଴ 

3.3.3 Economic Analysis Assumptions for New and Retrofit Commercial 

For the commercial economic analysis, we first assume that the DEVap A/C costs more than DX 

SEER 16 A/C. Thus, the decision to implement DEVap A/C is based on return on investment. 

A simple internal rate of return (IRR) is calculated. The period of analysis is taken to be 15 

years due to the expected lifetime of commercial A/C equipment (DOE 2009). For this analysis, 

nonfuel-related O&M expenses are presumed to be equal. The expected return is calculated 

solely on the combined energy and water costs improvement that DEVap provides. The analysis 

uses monthly average rates for electricity and natural gas for the years of 2005–2009 (EIA 2010). 

Consideration for peak power reduction or utility incentives is not accounted for, resulting in a 

conservative economic estimate. 

3.4 Cooling Performance 

For residential performance assessment, DEVap and standard A/C are sized to meet 100% of the 

sensible load using TMY3 data in each city. Load sizes are chosen to have zero hours of 

temperature excursion over 78°F. The tops and bottoms of the deadbands in all cities are 76°F 

and 74°F (note exception from the Building America baseline). For standard A/C, an ENERGY 

STAR dehumidifier described in section 3.2 is used to control humidity with a deadband of 

50%–55% RH. 

For the residential analysis, DEVap cooling performance is based on controlling humidity via 

three modes of operation: 

•	 Standard cooling mode. The outlet humidity is set to 51°F dew point and the sensible 

cooling is modulated with the evaporative post cooler. 

•	 Sensible only cooling mode. The outlet humidity is allowed to float with no desiccant 

dehumidification. 

•	 Dehumidification only mode. The DEVap A/C is run in an “adiabatic” mode with the 

desiccant portion of the A/C performing near adiabatic dehumidification. This can be 

implemented by running DEVap with no first- and second-stage exhaust air flows. 

These modes are controlled by using proportional control logic: 

•	 Sensible cooling is proportionally increased by increasing the amount of purge air 

through the evaporative post cooler from the minimum OA ventilation rate to 30% of the 

mixed air flow as the room air increases from 74° to 76°F. 

26
 
 27

• Sensible only cooling mode is activated when the ambient dew point is below 56°F. 

• Dehumidification only mode is turned on when the indoor RH reaches 54%. The air flow 

through the device is modulated from 40% to 100% of max flow as humidity ranges from 

54% to 60%. (RH was not expected to rise above 55% in this scheme.) 

Figure 3-3 shows the typical outlet air conditions and resulting return air conditions during a new 

residential simulation using the DEVap A/C. The points plotted are only when the DEVap A/C 

is ON, which takes away all the floating and wintertime conditions when the furnace is ON. 

Where the supply air conditions align with the 51°F dew point, the DEVap A/C is in standard 

cooling mode. Sensible only mode is represented where the supply air conditions do not align 

with 51°F dew point and are cooler than the return air. Dehumidification mode is represented 

where the supply air conditions are warm (above 80°F) and at approximately 27% RH. The 

coincident indoor air conditions for the dehumidification points align where the indoor air is at 

approximately 54%–55% RH. 

Figure 3-3 Residential/new – Houston simulation showing the return air and supply air from the 

DEVap A/C 

Figure 3-4 shows the return and supply air conditions of the standard A/C with a dehumidifier 

when either of the two systems is ON. The A/C supply air conditions are largely indicative of 

380 cfm/ton operation. The dehumidifier outlet conditions are largely grouped around 20% RH 

and warm. 

0

10

20

30

40

50

60

70

80

90

100

40 50 60 70 80 90 100

ω (grains/lb)

Dry Bulb Temperature (°F)

Psychrometric Chart at 0 ft Elevation (1.013 bar)

DEVap Supply

Return

Psychrometric Chart at 0 ft Elevation (14.7 psia) (14.7 psia) 
 28

Figure 3-4 Return and supply air from the DX A/C and dehumidifier (shown as “DH”) in a new 

residential building in Houston 

Figure 3-5 shows the effects of having or not having a whole house dehumidifier for a new 

residential building in Houston. These results are consistent with the results found by Fang et al. 

(2010). Significant RH excursions above 60% and 70% are prevalent with the no dehumidifier 

case. 

Figure 3-5 Effect of a whole-house dehumidifier when used with DX A/C in a new residential 

building in Houston 

3.4.1 New Residential 

When comparing the DEVap and DX systems the primary concern is the indoor humidity 

performance, because DEVap and the DX A/C systems meet indoor temperature set point and 

0

10

20

30

40

50

60

70

80

90

100

40 50 60 70 80 90 100

ω (grains/lb)

Dry Bulb Temperature (°F)

Psychrometric Chart at 0 ft Elevation (1.013 bar)

AC Supply

DH Supply

DH Return

AC Return

Both Return

Psychrometric Chart at 0 ft Elevation (14.7 psia) 
 

 

 

 

 

 

 

 

 

maintain temperature below 78°F for 100% of the hours. Figure 3-6 shows the performance of 

both systems in controlling RH in Houston. All 8,760 hours are shown and bins are labeled with 

the value at the top of the bin. DEVap has a larger percentage of bins below 50% than does the 

DX system modeled. The difference is more clearly seen by looking at summertime bins where 

cooling load is dominant. Figure 3-7 shows June – August indoor RH for both DX and DEVap 

A/C in Houston. As designed, DEVap lowers the humidity in the space to a lower RH during the 

peak cooling season due to DEVap’s ability to achieve lower SHR at peak. Because the DEVap 

device controls humidity to a level lower than DX A/C, the DEVap A/C uses more energy than 

necessary, thus further optimization of the DEVap control strategy is needed. During the swing 

season, there are many hours when the dehumidification only mode of the DEVap A/C controls 

to 55% RH. 

Figure 3-6 Indoor RH histograms for Houston throughout the year 

Figure 3-7 Indoor RH histograms for Houston in June–August 

Figure 3-8 shows the bins of SHR for Houston. The DEVap device is able to modulate its 

sensible heat ratio down to 0.2 to exactly meet the buildings load during those hours. Hours with 

SHR > 1 is indicative of dehumidification mode where total and sensible cooling are both 

negative. Not shown for the DX case is run-time for the dehumidifier. 

29
 
 

 

 

 

 

Figure 3-8 Houston DEVap A/C SHR bins for meeting cooling load 

3.4.2 Retrofit Residential 

Similar results for comfort as the new residential case are shown in Figure 3-9 and Figure 3-10. 

DEVap maintains a lower RH in the building than the standard DX A/C. In general the DEVap 

A/C maintains an RH of 2%–4% dryer than the DX A/C + dehumidifier in the humid climates. 

Again, further optimization of the control strategy of the DEVap device is required to prevent the 

space from over drying. 

Figure 3-9 Indoor RH histograms for Houston throughout the year 

30
 
 

 

 

 

 

 

Figure 3-10 Indoor RH histograms for Houston in June–August 

3.4.3 New and Retrofit Commercial 

The EnergyPlus model completed in 2008 experienced issues that prevented humidity control 

from being implemented for the load profile in EnergyPlus. As a result, the RH frequently went 

out of control (see Figure 3-11 and Figure 3-12). This generally happens when the building is 

empty and the air conditioner is shut down (nights and weekends). This results in high latent 

removal (generally in the morning), during the building warm-up period. The DEVap is driven 

to achieve the same load profile that the A/C provided, thus the DEVap building would have the 

same RH histogram. The DEVap and DX A/C latent removal are equal. 

Houston, TX 

0% 

25% 

50% 

75% 

100% 

0 

100 

200 

300 

400 

500 

600 

700 

Frequency (hours) 

Frequency 

Cumulative % 

4%

10%16%22%28%34%40%46%52%58%64%70%76%82%88%94%

100% 

RH Bins 

Figure 3-11 RH histogram for a small office benchmark in Houston 

31
 
 

 

 

 

 

 

 

 

 

 

 

Latent Comparison 

0% 

20% 

40% 

60% 

80% 

100% 

0 

20 

40 

60 

80 

100 

Latent Load (tons) 

Relative Humidity 

27-Jun 4-Jul 11-Jul 18-Jul 25-Jul 

DEVap A/C DX A/C Return Air RH 

Figure 3-12 Latent load comparison and resultant space RH in Houston 

(DEVap A/C and DX A/C latent load profiles overlap) 

3.5 Energy Performance 

For all energy performance calculations, the conversion factors in Table 3–7 are used. 

Table 3-7 Source Energy Conversion Factors (Deru et al, 2007) 

Source Factor 

Electric source energy 3.365 

Natural gas source energy 1.092 

For the new residential simulations, the total source energy was for the sum of all the electric and 

thermal source energy to run the A/C systems, mechanical ventilator, and dehumidifier. For 

retrofit residential simulations, no mechanical ventilation is required in the DX case. 

For commercial, the source energy for cooling is the sum of all the electrical energy to run the 

DX system, only when there is a call for cooling. Similarly for the DEVap A/C, electrical and 

thermal energy is summed only for periods when there is a call for cooling. 

Water use impacts for the DEVap and DX A/C are summed to include on-site and off-site water 

use. Electric power plants evaporate at 0.5–4.4 gal/kWh in the United States (Torcellini et al. 

2003). Including on-site and off-site water use on a per ton·h basis is a reasonable metric to 

determine water impact on a regional scale. 

3.5.1 New Residential 

Power comparison for Houston is shown in Figure 3-13; peak yearly power consumption is 

shown in Figure 3-14. From inspection, the peak electricity draw of the DEVap A/C is 

considerably less than the standard A/C. This is primarily because compressor power is 

eliminated and replaced with only fan power to push air through the DEVap cooling core. Most 

of an A/C’s energy use is switched from electricity to thermal energy when switching from DX 

to DEVap. In this analysis, natural gas is used as the thermal source. 

32
 
 

 

 

 

 

 

Standard DX A/C Power DEVap A/C Power 

16 16 

14 14 

12 12 

10 10 

0 2000 4000 6000 8000 0 2000 4000 6000 8000 

kW

kW

8 8 Source 

Source 6 6 Natural Gas 

Elecric 

4 4 Electric 

2 2 

0 0 

Hour of Year Hour of Year 

Figure 3-13 A/C power comparison in Houston for residential new construction 

Phoenix SF DC Tampa Atlanta Chicago Boston Houston 

Peak DEVap A/C 1.00 0.67 0.74 0.96 0.95 0.72 0.72 0.97 

Peak Standard A/C 5.09 3.22 4.31 4.06 5.01 4.15 4.02 5.21 

0.0 

1.0 

2.0 

3.0 

4.0 

5.0 

6.0 

Peak kW 

Peak Power (kW) 

Figure 3-14 Peak power in all cities, residential new construction 

Source energy use is shown in Figure 3-15. DEVap source energy savings are 29%–66% across 

all the cities modeled. Although significant savings are shown, DEVap has yet to be optimized 

for energy performance. The lower RH provided by the DEVap A/C comes with an energy 

penalty. Humidity control and energy use still require additional optimization for a more 

accurate comparison on an energy basis. 

Figure 3-16 shows the specific water use (gal/ton·h) for all the cities modeled in terms of site 

water use and water use at the power plant (off site). Off-site water is calculated using a 

conversion of 1 gal/kWh-electric. 

33
 
 

 

0 

5,000 

10,000 

15,000 

20,000 

25,000 

30,000 

35,000 

40,000 

kWh (source) 

DEVap A/C 

DX A/C 

Phoenix SF DC Tampa Atlanta Chicago Boston Houston 

Figure 3-15 Source energy in all cities, residential new construction 

7 

Site - DEVap A/C 

Gallons / Ton-h 

6 

5 

4 

3 

2 

1 

0 

Offsite, DEVap A/C 

Offsite - DX A/C 

Phoenix SF DC Tampa Atlanta Chicago Boston Houston 

Figure 3-16 Water use (evaporation) in all cities, residential new construction 

(assumes 1 gal/kWh for electric generation) 

34 
 

 

 

 

 

 

 

 

3.5.2 Retrofit Residential 

Power comparison for Houston is shown in Figure 3-17; peak power comparisons are shown in 

Figure 3-18. Similar to the new construction cases, the peak electricity draw of the DEVap A/C 

is considerably less than the standard A/C. 

Standard DX A/C Power DEVap A/C Power 

20
 20

18
 18

16
 16

14
 14

12
 12

6
 Electric 6 Electric 

4
 4

2
 2

0
 

0 2000 4000 6000 8000 0 2000 4000 6000 8000
 

0 

Hour of Year Hour of Year 

Figure 3-17 A/C power comparison in Houston for residential retrofit case 

kW10
 

kW10 Source 

8
 Source 8 Natural Gas 

Phoenix SF DC Tampa Atlanta Chicago Boston Houston 

Peak DEVap A/C 1.00 0.54 0.72 0.73 0.72 0.74 0.69 0.74 

Peak Standard A/C 5.11 2.09 4.30 4.21 4.21 4.18 4.15 4.25 

0.0 

1.0 

2.0 

3.0 

4.0 

5.0 

6.0 

Peak kW 

Peak Power (kW) 

Figure 3-18 Peak power in all cities for residential retrofit case 

Source energy use is shown in Figure 3-19. DEVap source energy savings range from 1% to 

67% across all the cities modeled. Performance in Tampa and Houston are noticeably different 

than in the new construction case. In these cases, the standard A/C system is able to provide 

most of the humidity control without the help of the stand-alone dehumidifier. The retrofit 

construction case magnifies that DEVap requires additional optimization for energy 

performance. Figure 3-20 shows the specific water use for all the cities modeled. 

35
 
 

 

 

0 

5,000 

10,000 

15,000 

20,000 

25,000 

30,000 

35,000 

kWh (source) 

DEVap A/C 

DX A/C 

Phoenix SF DC Tampa Atlanta Chicago Boston Houston 

Figure 3-19 Source energy in all cities for residential retrofit case 

4 

Site - DEVap A/C 

Offsite - DEVap A/C 

Offsite - DX A/C 

Phoenix SF DC Tampa Atlanta Chicago Boston Houston 

Gallons / Ton

3 

-

2 

1 

0 

Figure 3-20 Water use (evaporation) in all cities, residential retrofit construction 

(assumes 1 gal/kWh for electric generation) 

36 
 

 

 

 

 

 

 

 

40 

3.5.3 New and Retrofit Commercial 

Figure 3-21 and Figure 3-22 show the energy performance of the DX and DEVap A/C in an 

hourly plot in both Houston and Phoenix. The electricity use and switch to thermal energy (in 

this case, natural gas) is evident as with the residential cases. In both cities, the peak electricity 

is reduced by 80%. 

SEER 16 DX A/C Power DEVap A/C Power 

0 

10 

20 

30 

40 

50 

kW 

Source Energy [kwh] 

Electric Energy [kwh] 

0 

10 

20 

30 

40 

50 

kW 

Source Energy [kWh] 

Thermal Energy [kWh] 

Electric Energy [kWh] 

1-Jan 2-Mar 1-May 30-Jun 29-Aug 28-Oct 27-Dec 1-Jan 2-Mar 1-May 30-Jun 29-Aug 28-Oct 27-Dec 

Figure 3-21 A/C power comparison for a small office benchmark in Phoenix 

SEER 16 DX A/C Power DEVap A/C Power 

40 

0 

10 

20 

30 

Source Energy 

Electric Energy 

1-Jan 2-Mar 1-May 30-Jun 29-Aug 28-Oct 27-Dec 

0 

10 

20 

30 

kW 

Source Energy 

Thermal Energy 

Electric Energy 

1-Jan 2-Mar 1-May 30-Jun 29-Aug 28-Oct 27-Dec 

kW 

Figure 3-22 A/C power comparison for a small office benchmark in Houston 

Table 3-8 and Table 3-9 show the results of the simulation in the two cities. The peak electricity 

reduction and the total electricity reduction are about 80% and 90%, respectively. The cooling 

source energy reductions of 39% and 84% are primarily due to the efficiency gain of the DEVap 

A/C. The total energy reduction accounts for energy used to ventilate and distribute air 

throughout the year. For the DEVap case, the air flow is set back by 50% during times when 

there is no A/C or heating. The variable-speed fan in the DEVap A/C results in energy savings, 

because this mode of operation is easily implemented. DX can, however, also implement a 

variable-speed fan with added cost. Site water evaporation is 2.08–2.68 gal/ton·h for the two 

cities. This level of water consumption is similar to the water used by A/C when electric power 

plant water draw (off-site) is considered. For comparison, a modest 1.0 gal/kWh was assumed 

for off-site water consumption. Water use by electricity plants was not compared at the state 

level because electricity is not bound by state borders. Furthermore, a reliable database of perstate water use by utilities is not readily available. 

37
 
 

 

 

 

 

 

 

 

 

 

 

 

Table 3-8 Results Summary for Phoenix 

Simulation DX DEVap Units 

Difference 

(%) 

Total cooling 15,724 15,725 ton·h 0% 

Sensible cooling 14,915 14,909 ton·h 0% 

Latent cooling 809 816 ton·h 1% 

Cooling electric energy 18,609 1,717 kWh –91% 

Total electric energy 31255 1,891 kWh –94% 

Cooling thermal energy 0 3,707 kWh 

Cooling source energy 63,270 9,917 kWh –84% 

Total source energy 106,268 10,506 kWh –90% 

Cooling electric energy (specific) 1.18 0.11 kW/ton –91% 

Source cooling COP 0.87 5.58 – 538% 

Peak electric 11.63 2.33 kW –80% 

Total site water evaporation 0 42,224 gal 

Total site water evaporation 0.00 2.69 gal/ton·h 

Total off-site water use (1 gal/kWh) 31,255 1891 gal –94% 

Total off-site water use (1 gal/kWh) 1.99 0.12 gal/ton·h –94% 

Table 3-9 Results Summary for Houston 

Simulation DX DEVap Units 

Difference 

(%) 

Total cooling 14,819 14,695 ton·h –1% 

Sensible cooling 9,933 9,927 ton·h 0% 

Latent cooling 4,886 4,768 ton·h –2% 

Cooling electric energy 15,750 1,579 kWh –90% 

Total electric energy 27,166 1,747 kWh –94% 

Cooling thermal energy 0 24,931 kWh 

Cooling source energy 53,550 32,791 kWh –39% 

Total source energy 92,366 33,365 kWh –64% 

Cooling electric energy (specific) 1.06 0.11 kW/ton –90% 

Source cooling COP 0.97 1.58 – 62% 

Peak electric 10.26 2.18 kW –79% 

Total site water evaporation 0 30511 gal 

Total site water evaporation 0.00 2.08 gal/ton·h 

Total off-site water use (1 gal/kWh) 27,166 1,747 gal –94% 

Total off-site water use (1 gal/kWh) 1.83 0.12 gal/ton·h –94% 

3.6 Residential Cost Performance 

Figure 3-23 shows the annualized LCCs for DX and DEVap A/C in new construction. These 

include loan payments, electricity, natural gas, and water. Using 2010 natural gas prices, the 

LCCs for DEVap are less than for DX A/C in most cities. The costs of the two systems in many 

locations are approximately the same given uncertainties in this analysis. Assuming 50% higher 

gas prices has a larger effect in cities that require much dehumidification. 

38
 
 

 

 

 

 

 

$3,000 

$2,500 

$2,000 

DX A/C 

DEVap A/C, current gas prices 

DEVap A/C, 50% higher gas prices 

$/year $1,500 

$1,000 

$500 

$­

Phoenix SF DC Tampa Atlanta Chicago Boston Houston 

Figure 3-23 Annualized cost comparison for residential new construction 

Figure 3-24 illustrates the cost breakdown for Houston and Phoenix. The upfront costs for 

DEVap A/C are higher than for DX A/C, but the lower energy costs quickly compensate. Gas 

price uncertainty in places like Tampa and DC (not shown), may result in higher overall cost for 

DEVap A/C. 

Figure 3-24 LCCs for residential new construction for Phoenix (hot, dry) and Houston (hot, humid) 

(loan is the repayment of the loan due to the upfront cost of each system) 

39
 
 

 

 

 

 

 

 

 

 

 

 

 

Figure 3-25 shows the annualized LCCs for DX A/C and DEVap A/C for the retrofit case. Costs 

for DEVap are higher in Tampa and lower in Phoenix, but uncertainties prevent a distinct 

conclusion in other locations. In general, the relative cost of DEVap A/C compared to DX A/C 

is higher for the retrofit case than for the new construction case because: 

•	 The assumed financing for the retrofit case (5-year loan at 7%) is more sensitive than the 

new construction case (30-year mortgage at 5%) to upfront costs and DEVap has a higher 

upfront cost. This is also evident from Figure 3-26, which shows the cost breakdown for 

each system in Houston and Phoenix. 

•	 Although DEVap still provides mechanical ventilation, none is required for the retrofit 

case. This results in energy savings for the standard DX A/C, which brings no OA into 

the house. 

•	 The higher SHRs in the retrofit case compared to new construction result in a smaller 

energy penalty for DX A/C. As homes become tighter and latent loads comprise a larger 

portion of the total load, this energy penalty increases for DX A/C and makes DEVap 

A/C more competitive. 

These analyses do not include the effects of time-of-use pricing and potential peak demand 

charges that may soon come to bear in the residential energy market. Such pricing would 

inevitably improve the economics of the DEVap A/C because it effects reductions in electricity 

use. 

Figure 3-25 Cost comparison for residential retrofit 

40
 
 

 

 

 

 

 

 

 

Figure 3-26 LCC breakdown for retrofit for Phoenix (hot, dry) and Houston (hot, humid) 

(loan is the repayment of the loan due to the upfront cost of each system) 

3.7 Commercial Cost Performance 

Table 3-10 and Table 3-11 show the results of the economic analysis for the payback return rate 

or IRR for each city. Each rate is based on a 15-year product lifetime for each system. Rates for 

electricity and gas are monthly averages. Time-of-use electricity rates and peak reduction credit 

are not taken into account. Because A/C power draw drives commercial peak consumption, 

inclusion of these factors will increase electricity costs. This would inevitably improve the 

economics of the DEVap A/C. 

Table 3-10 Economic Analysis for Houston 

Costs DX DEVap Difference 

First cost $15,200 $20,461 35% 

Yearly electricity cost $2,676 $173 –94% 

Yearly natural gas cost $0 $874 

Yearly water cost (at $3/1000 gal) $0 $110 

Net yearly cost $2,676 $1,157 –57% 

IRR 28% 

Table 3-11 Economic Analysis for Phoenix 

Costs DX DEVap Difference 

First cost $15,200 $20,461 35% 

Yearly electricity cost $2,646 $164 –94% 

Yearly natural gas cost $0 $157 

Yearly water cost (at $5/1000 gal) $0 $253 

Net yearly cost $2,646 $575 –78% 

IRR 39% 

41
 
 

 

 

 

 

 

 

 

 

 

 

4.0 Risk Assessment 

4.1 Technology Risks 

A/C reliability generally means that commercial and residential A/C equipment lifespan is 

expected to be 15 years and 11 years, respectively (DOE 2009). Longevity of a new technology 

will always be in question, especially compared to tried-and-true refrigeration-based A/C. 

Answering all these concerns takes time, although accelerated testing is being devised for 

DEVap. Longevity of the device would include issues such as: 

• Degradation of performance over the lifetime of the equipment 

• Maintainability to sustain performance 

• Catastrophic failure reducing the expected lifetime 

o Material degradation 

o Inadequate manufacturing techniques 

o Fundamental design issue. 

The DEVap A/C will increase site water use by approximately 60 gal/day for a typical home (3-

ton air conditioner). This water use is most economical if sourced from the buildings municipal 

water supply. However, other options such as rainwater harvesting and gray water reuse are 

available. Despite this, regional water use is not likely to be significantly affected because the 

volume impact of evaporative cooling when compared to regional uses. DEVap uses 

approximately 2.5–3-gal/ton·h of regional water (one to two times that of DX A/C) if one 

assumes 1.0 gal/kWh to generate electricity. However, 1.0 gal/kWh is a “middle of the road” or 

possibly a conservative estimate of off-site water use by electricity generation stations. 

Electricity generation accounts for 3.3% of all water use in the United States (Torcellini 2003), 

and A/C consumes 10% of all electricity produced in the United States (4 of 41 quads) (DOE 

2009). Therefore, A/C accounts for approximately 0.3% of U.S. water use. A conservative 

estimate would thus conclude that DEVap A/C will not increase the aggregated U.S. water use 

by more than 0.3%. Some markets face localized water supply issues, however, so DEVap A/C 

in these locations may not be acceptable. 

42
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 4-1 U.S. water use profile 

(Torcellini et al. 2003) 

Table 4-1 Technical Risk Matrix for DEVap A/C 

Building Type New and Retrofit 

Residential 

1. Longevity/reliability 

2. On-site water use increase 

Commercial 

1. Longevity/reliability 

2. On-site water use increase 

4.2 Market and Implementation Risks 

Most technological risk from DEVap stems from its evaporative aspect. Evaporative devices 

eject heat from the building to the atmosphere in the same device that cools the building air. 

This means a second set of exhaust air ductwork must be routed to and from the DEVap A/C and 

the outside, and constitutes the greatest implementation risk for retrofits. It is also highly 

dependent on the building type, vintage, and design. For instance, many homes have air handlers 

in the attic spaces. Duct access to the outside is not difficult from this location; however, some 

homes have air handlers in internal spaces such as closets. This would likely require some 

ductwork to be redirected so the air handler (which houses the DEVap device) can be placed 

close to the outside. 

Integrating the DEVap cooling device with air handlers, furnaces, or even RTUs may pose a 

practical issue. For an RTU, the traditional condenser that takes up about 30%–40% of package 

volume will be replaced by the “equivalent” regenerator. This component, which has a 30-kBtu 

boiler and a 50-cfm heat exchanger will be approximately 2 ft high × 2 ft wide × 1 ft deep for a 

3–5 ton system. This is substantially smaller than the condenser section of a DX RTU. 

However, the DEVap conditioner component will be larger with an increase in face area. The 

net packaging will be smaller, but packaging configuration may be different. 

Evaporative cooling will also have the risk of freezing to the DEVap core or water lines. This is 

manageable through educated implementation. It is primarily a residential issue, as commercial 

buildings commonly have knowledgeable people to manage evaporative systems. In new 

43
 
 

 

 

 

 

 

 

 

 

 

construction, such issues can be designed into the building. Cross-linked polyethylene piping is 

also a possible solution, as it can be freeze-thaw cycled indefinitely without breaking (Burch 

2005). The piping would thaw out long before the first demands for cooling in the spring. 

Because DEVap switches energy consumption away from electricity to thermal (primarily 

natural gas), the availability of natural gas may present an impediment to implementing the 

technology. Other thermal sources, including renewable energy, may need further study. Solar 

may be able to provide 100% of the thermal energy required and warrants further study. The 

economics of a solar-driven air conditioner are improved when space and water heating are 

added to the loads met with the solar system. One study has shown that such “triple play” solar 

systems are close to parity with conventional energy on a cost of energy basis (Burch 2010). 

Low-cost collectors reducing costs three to five times relative to today’s collectors are plausible, 

and would put solar-driven DEVap on a par with natural gas regeneration. 

Installing the DEVap A/C will require running gas lines and small desiccant lines, which would 

not be significantly different from current practices. Thus, connecting components of the 

DEVap system is not likely to be a significant implementation risk. 

Water draining issues are not likely to cause implementation problems, as standard A/C also 

requires water drainage. The DEVap device will direct all excess water to the normal drain. 

DEVap will have a different O&M profile that will require new procedures. Such new 

requirements may place restrictions on where or how DEVap is installed. For instance, the 

DEVap A/C will have two air filters instead of one. This may require that the O&M personnel 

access the attic for one filter, and the other will be located indoors as usual. O&M changes to 

retrofit buildings are likely where issues arise. In new construction, these issues can be more 

readily addressed during building design. 

Desiccant systems primarily use plastics in the design and could pose issues to satisfy regional 

codes. Many similar products, namely the DAIS ConsERV ventilator, also use significant 

amounts of plastic and are listed with Underwriters Laboratories. This is possible through a 

novel way to stop flames and smoke from reaching the plastic components. Similar designs can 

be used in the DEVap A/C, but this topic is largely unexplored. 

Table 4-2 Market and Implementation Risk Matrix for DEVap A/C 

Building 

Type New Retrofit 

Residential 

1. Building design to accommodate new type of 

ductwork 

2. Potential water line freezing 

3. Natural gas availability (southeastern United 

States) 

4. Code compliance with plastic construction 

1. Ducting modification and addition 

2. Potential water line freezing 

3. Integration with air handler and furnace 

4. Natural gas availability (southeastern United States) 

5. Changes to O&M 

6. Code compliance with plastic construction 

Commercial 

1. Building design to accommodate new type of 

ductwork 

2. New RTU packaging. 

3. Natural gas availability (southeastern United 

States) 

4. Code compliance with plastic construction 

1. Ducting modification and addition (central air handler) 

2. Integration with air handler and furnace or RTU 

3. Natural gas availability (southeastern United States) 

4. Changes to O&M 

5. Code compliance with plastic construction 

4.3 Risk to Expected Benefits 

DEVap, as with any new technology, has unknown consequences in the marketplace. Good 

design and engineering can result in a product that performs well; however, poor implementation 

44 
 

 

 

of a good design can affect performance. One such effect is poor commissioning that results in 

poor energy and comfort performance. Although this risk can be mitigated with good design, it 

cannot be eliminated. This risk is already inherent in current A/C, as seen by numerous accounts 

of faulty RTU installations in commercial buildings (economizer and damper faults). However, 

typical faults such as a damper stuck open are less likely to be issues with a DEVap A/C. For 

DEVap to provide the necessary cooling, dampers must operate correctly. Thus, a DEVap air 

conditioner manufacturer has an incentive to properly install damper mechanisms. However, 

with any new technology, there will be new, as yet unidentified, ways to “mess it up.” These 

issues will become apparent once field prototypes are deployed. 

45
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5.0 Future Work 

5.1 Laboratory DEVap A/C Demonstration 

During FY 2011, NREL will work on a 1-ton “proof-of-performance” prototype in which we 

will build the DEVap device. The unit will be performance tested when it is connected in the 

NREL HVAC laboratory. NREL will obtain a complete performance map of the system to 

create a correlated performance model. This model will then be used in the building simulation 

models already developed to update results and make them available. 

5.2 Regeneration Improvements 

We have worked on high-efficiency, thermally powered desiccant regeneration. Other options 

for desiccant regeneration, which use electricity or modified CHP, are available. These energy 

sources can be used to run a vapor compression distillation regenerator that runs a “reverse 

Rankine” or refrigeration cycle with water vapor at modest pressures (about 6 psia). Such a 

system has already been analyzed and proposed as a project by AILR (2002). It vastly improves 

the latent COP of the regeneration process and thus the COP of a DEVap A/C. 

Because DEVap uses LiCl concentrations of 28%–38%, the resulting latent COP of regeneration 

could potentially be 2.2–3.5 using natural gas. This would reduce the source energy use of a 

DEVap A/C by more than 50%. Although this technology has not yet been proposed as a DOE 

project, it is introduced here to highlight that the DEVap technology is still in its infancy, and 

there is still significant upward potential. 

Figure 5-1 Vapor compression distillation regenerator latent COP using natural gas (AILR 2002) 

(shaded area shows operating range of the DEVap A/C) 

5.3 Solar Thermal Integration 

The solar thermal option has been investigated to a small degree. We are working with AILR to 

increase the integration between LDACs and solar thermal collector with the clear goals of 

improving system performance and lowering costs. We are developing designs that greatly 

reduce the cost of evacuated tubes and deliver steam to the regeneration process. These “steamgenerating” collectors remove much of the copper and copper/metal seals in today’s collectors 

and can use the lower cost Dewar style tubes. Future work includes a double-effect solar 

regenerator where desiccant can be boiled to release water vapor in the tubes and the steam heat 

used in the scavenging regenerator. 

46
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6.0 Conclusions 

6.1 Residential Performance Comparison 

Analyses of the new and retrofit residential benchmark buildings using DX and DEVap A/C 

generally show a clear advantage for the DEVap A/C. The DEVap A/C is designed around a 

single typical Gulf Coast condition (Houston). This is a relatively good design condition for 

producing a 3-ton DEVap system that has the same capacity as a 3-ton DX A/C system. The 

control scheme for the DEVap still requires optimization, however. In all cases, the DEVap A/C 

provided more than necessary humidity control. Allowing indoor humidity to rise above 50% 

RH would have significant energy improvement. In the summertime, when sensible loads are 

high (high SHR), the DEVap A/C continuously maintained the space at less than 50% RH. This 

level of humidity control can be reduced to create higher energy savings. However, this level of 

humidity control may be advantageous from the perspective of building and occupant health, 

although health science has not yet addressed the health impacts of such small changes in indoor 

humidity. 

In general, new construction with the added ventilation and tighter envelope resulted in the 

conditions where DEVap performed better, because SHR decreased (which DEVap was designed 

to accommodate). The new construction is taken to be 2010 IECC building code, which is not as 

tight as future home designs (Building America 50% homes). Thus, we expect the DEVap A/C 

to increase its advantage in tighter homes, or as retrofit homes become tighter and better 

insulated. Furthermore, as ventilation requirements increase, the DEVap advantage increases. 

DEVap already over ventilates any residential building space under high sensible load conditions 

(summer days); however, energy credit is not given for this. For DX, there would be an imposed 

higher load that would result in higher energy use. 

Regional water use (site + off-site) for the DEVap system was 2.0–3.0 gal/ton·h for new and 

retrofit cases, which we argue is similar to the regional impact that DX A/C imposes (off-site 

only). Proper comparison must include off-site water use (at the utilities’ electricity generation 

stations). The DEVap A/C does increase site water use, but in general, the regional impact is 

small, especially compared to sectors other than electricity generation (see Figure 4-1). 

6.2 Commercial Performance Comparison 

Commercial implementation of the DEVap A/C shows a higher energy savings level than do the 

residential cases, primarily because of the higher cooling loads of commercial buildings and their 

increased ventilation requirements. The small office building benchmark is taken as a “middle 

of the road” building type for commercial buildings. It also has minimal ventilation 

requirements as a percentage of cooling load. For buildings with higher ventilation rates (e.g., 

commercial retail space), the relative energy savings for the DEVap A/C will increase. DEVap 

A/C is conservatively estimated because the load-following model is used. 

DEVap regional water use is expected to be 2.0–3.0 gal/ton·h for commercial buildings. Similar 

to the residential case, the DEVap A/C has minimal impact on regional water use compared to 

DX A/C. 

6.3 Residential Cost Comparison 

The initial cost estimates for the DEVap A/C are preliminary and based on market entry with the 

design we have today. Improvements and design for manufacturing and innovation have not 

been considered. These factors could have significant impact on initial cost. The fundamental 

47
 
 

 

 

 

 

 

 

 

 

 

 

 

concept is simpler, perhaps presaging lower costs for DEVap than for conventional A/C once 

manufacturing volumes are comparable. Furthermore, the cost estimate does not include the 

possibility of utility incentives that may be offered because of the potentially high value that the 

DEVap A/C provides for the utility companies. Their incentive would be based on DEVap 

A/C’s ability to reduce peak electricity demand and thus stabilize the electricity grid. The ability 

to store cooling energy via desiccant could also be a major consideration. And natural gas prices 

may not be representative of future prices, especially if its use increases significantly during the 

summer in residential applications. 

In most cases, the cost comparison using the best available data today shows that the DEVap air 

conditioner is competitive with DX A/C. Retrofit cost is higher on an annualized basis, because, 

the cost of equipment is amortized into a 5-year home equity loan rather than a 30-year 

mortgage. 

6.4 Commercial Cost Comparison 

The upfront cost of a DEVap A/C has a significant return on investment compared to best 

available (SEER 16) DX A/C. The higher cooling load over residential construction makes the 

cost savings from the reduced energy consumption a much larger factor. Again, initial cost 

estimates are based on the best available knowledge for a DEVap A/C and do not include 

incentives and future design improvements. 

6.5 Risk Assessment 

The risks have been laid out for technology and market/implementation risks. As with any novel 

and disruptive technology, the risks are broad and somewhat unknown. Reliability and longevity 

are the greatest risks to a successful technology, and they must meet or surpass those of today’s 

A/C to have any real market penetration. Furthermore, the increase in site water use may be a 

technical problem in some places where delivery of site water is scrutinized or of extreme value. 

Regionally, the water impact of the DEVap A/C compared to DX A/C is minimal. 

Most market risks for the DEVap A/C result different system operations. Additional ductwork 

and system design may be difficult to handle in retrofit applications. New construction can 

accommodate the different system designs better. The O&M profile of the DEVap will also 

change and may impose additional burdens to a retrofit application. 

Implementation of the DEVap A/C may have unforeseen consequences. Mechanisms that could 

affect the performance of the DEVap A/C include improper installation and commissioning. An 

air conditioner that is improperly installed may work counter to the design intent, and not control 

temperature and humidity efficiently. These risks can be managed through education. 

The availability of a thermal source such as natural gas is an issue in some instances, mostly in 

the southeastern United States and some residential locations. Other sources of energy to 

regenerate the desiccant would have to be explored. Solar thermal energy could supply much of 

the thermal energy required in these regions, particularly when integrated in a complete thermal 

system meeting space and water heating needs. Ongoing development of low-cost, evacuated 

tube, steam generating collectors will help the economics of solar driven A/C. 

48
 
 

 

 

 

 

 

 

 

 

 

 

7.0 References 

AIL Research, Inc. www.ailr.com. 

AIL Research, Inc. 2002. An Advanced Regenerator for Liquid Desiccants. Federal Grant No. 

DE-FG02-01ER83140. 

Alliance for Sustainable Energy, LLC. 2008. Indirect Evaporative Cooler Using MembraneContained, Liquid Desiccant for Dehumidification. WIPO publication WO/2009/094032. 

ASHRAE. 2006. ASHRAE Handbook: Refrigeration. American Society of Heating, 

Refrigerating and Air-Conditioning Engineers, Inc. 

ASHRAE, 2007. Standard 62.2-2007: Ventilation and Acceptable Indoor Air Quality in LowRise Residential Buildings. American Society of Heating, Refrigerating, and AirConditioning Engineers, Inc. 

ASHRAE. 2009. ASHRAE Handbook: Fundamentals. American Society of Heating, 

Refrigerating and Air-Conditioning Engineers, Inc. 

Celgard. 2010. Celgard Z-series Microporous Membranes. Product literature. 

www.celgard.com. 

Christensen, D.; Winkler, J. 2009. Laboratory Test Report for ThermaStor Ultra-Aire XT150H 

Dehumidifier. NREL Report No. TP-550-47215. 

Conde-Petit, M. 2007. “Liquid Desiccant-Based Air-Conditioning Systems – LDACS.” 

Proceedings of the 1st European Conference on Polygeneration, Tarragona, Spain, 

October 16–17, 2007. 

Coolerado Corporation. www.coolerado.com. 

Deru, M.; Torcellini, P. 2007. Source Energy and Emission Factors for Energy Use in Buildings 

(Revised). 39 pp.; NREL Report No. TP-550-38617. 

Deru, M., Field, K., Studer, D., Benne, K., Griffith, B., Torcellini, P., Liu, B., Halverson, M., 

Winiarski, D., Rosenberg, M., Yazdanian, M., Huang, J., Crawley, D., 2010. U.S. 

Department of Energy Commercial Reference Building Models of the National Building 

Stock - Technical Report. TP-550-46861. Golden, CO, National Renewable Energy 

Laboratory. 

DOE. 2002. Energy Efficiency Standards for Consumer Products: Residential Central Air 

Conditioners and Heat Pumps. DOE Technical Support Document. 

DOE. 2009. Buildings Energy Data Book. http://buildingsdatabook.eren.doe.gov/. 

EIA. 2010. Monthly Report of Natural Gas Purchases and Deliveries to Consumers, Form EIA857. Released August 30, 2010. U.S. Energy Information Administration. 

EIA. 2010. Electric Power Monthly, Table 5.6a. November 2009 through September 2010 

Editions. U.S. Energy Information Administration. 

Fang, X.; Winkler, J.; Christensen, D. 2010. Advanced Dehumidification Analysis on Building 

America Homes Using EnergyPlus. Preprint. NREL Report No. CP-550-48383. 

49
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

Hendron, R. 2008. Building America Research Benchmark Definition. NREL Report No. 

NREL/TP-550-44816. 

Hendron, R. 2010. Building America Research Benchmark Definition. NREL Report No. TP550-47246. 

Ice Energy. www.ice-energy.com/. 

Lennox Commercial. www.lennoxcommercial.com/. 

Lowenstein, A.; Slayzak, S.; Kozubal, E.; Ryan, J. 2005. “A Low-Flow, Zero Carryover Liquid 

Desiccant Conditioner.” International Sorption Heat Pump Conference, Denver, CO, 

June 22–24, 2005. 

Lowenstein, A.; Slayzak, S.; Kozubal, E. 2006. “A Zero-Carryover Liquid Desiccant Air 

Conditioner for Solar Applications.” ASME International Solar Energy Conference, 

Denver, CO, July 8–13, 2006. 

Lowenstein, A. 2008. “Review of Liquid Desiccant Technology for HVAC Applications.” 

ASHRAE HVAC&R Research 14(6). 

Laevemann, E.; Hauer, A.; Peltzer, M. 2003. Storage of Solar Thermal Energy in a Liquid 

Desiccant Cooling System. White paper. Bavarian Center for Applied Energy Research, 

ZAE Bayern e.V. , Dep. 4: Solarthermal and Biomass, Garching, Germany. 

Munters. www.munters.us/en/us/. 

NREL. National Solar Radiation Data Base. 1991- 2005 Update: Typical Meteorological Year 

3. http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/tmy3/ 

NREL. Residential Efficiency Measures Database. www.nrel.gov/ap/retrofits/index.cfm. 

Slayzak, S.; Kozubal, E. 2009. DEVap Comfort Conditioner. NREL Report No. NREL/TP550-45481. 

Slayzak, S.; Lowenstein, A.; Ryan, J.; Pesaran, A. 1998. Advanced Commercial Liquid 

Desiccant Technology Development Study. NREL Report No. NREL/TP-550-24688. 

Speakman. http://oasysairconditioner.com/. 

Torcellini, P.; Long, N.; Judkoff, R. 2003. Consumptive Water Use for U.S. Power Production. 

NREL Report No. NREL/TP-550-33905. 

Trane Corporation . www.trane.com/commercial/. 

50
 
 

 

 

 

 

 

 

 

 

 

 

8.0 Resources Not Cited 

Balaras, C.A.; Henning, H.-H.; Wiemken, E.; Grossman, G.; Podesser, E.; Infante Ferreira, C.A. 

2006. “Solar Cooling: An Overview of European Applications & Design Guidelines.” 

ASHRAE Journal 48:14–21. 

Chen, X.Y.; Jiang, Y.; Li, Z.; Qu, K.Y. 2005. “Field Study on Independent Dehumidification 

Air-Conditioning System – II: Performance of the Whole System.” ASHRAE 

Transactions 111(2):277–284. 

Daou, K.; Wang, R.Z.; Xia, Z.Z. 2006. “Desiccant Cooling Air Conditioning: A Review.” 

Renewable and Sustainable Energy Reviews 10:55–77. 

European Commission. 2005. SACE Project, “Solar Air Conditioning in Europe – An 

Overview.” Renewable & Sustainable Energy Reviews D.G. XII. 

Lowenstein, A. 2010. AIL Research. Interview by Eric Kozubal. 

Roth, K. W.; Westphalen, D.; Dieckmann, J.; Hamilton, S. D.; Goetzler, W. 2002. Energy 

Consumption Characteristics of Commercial Building HVAC Systems Volume III: Energy 

Savings Potential. Cambridge, MA: TIAX LLC. Ref. No. 68370-00. 

van Helden, W.; Bakker, M.; Hauer, A. 2008. Materials for Compact Thermal Energy Storage: 

a New IEA SHC/ECES Joint Task. The Netherlands. Energy Research Centre of the 

Netherlands. 

Willis, R.; Parsonnet, B. 2009. “Energy Efficient TES Design for Commercial DX Systems.” 

ASHRAE Transactions. 

51
 
Appendix A Data Tables 

A.1 Detailed Specifications for Retrofit Residential Building 

San Washington, 

Chicago Phoenix Francisco Tampa Atlanta Boston Houston DC 

Foundation 

type 

Basement Slab-ongrade Crawlspace Slab-ongrade Crawlspace Basement Slab-ongrade Basement 

Detached 

frame wall U 0.052 0.092 0.082 0.092 0.082 0.058 0.092 0.070 

Ceiling U 0.027 0.044 0.037 0.048 0.037 0.028 0.043 0.037 

Floor U 0.052 0.071 0.052 0.071 0.052 0.052 0.071 0.052 

Underground 

wall U 0.103 n/a 0.135 n/a 0.135 0.106 n/a 0.126 

Min R slab 

unheated 5.350 none n/a n/a n/a 4.760 n/a 4.000 

Slab 

insulation 

depth (ft) 

2.000 none n/a n/a n/a 2.000 n/a 2.000 

Window U 0.236 0.277 0.277 0.960 0.277 0.277 0.277 0.277 

Window 

SHGC 0.333 0.721 0.648 0.866 0.721 0.648 0.721 0.648 

A.2 Detailed Specifications for New Residential Building 

Slab 

insulation 

depth (ft) 

Foundation 

type 

Detached 

frame wall U 

Ceiling U 

Floor U 

Underground 

wall U 

Min R slab 

unheated 

Window U 

Window 

SHGC 

2.000 

Chicago Phoenix 

Basement Slab-ongrade 

0.052 0.070 

0.026 0.034 

0.050 0.071 

0.089 n/a 

10.000 n/a 

n/a 

0.294 0.665 

0.314 0.311 

n/a 

San 

Francisco Tampa 

Crawlspace Slab-ongrade 

0.070 0.070 

0.034 0.034 

0.050 0.071 

0.089 n/a 

n/a n/a 

n/a 

0.665 0.665 

0.311 0.311 

n/a 

Atlanta Boston 

Crawlspace Basement 

0.070 0.052 

0.034 0.026 

0.050 0.050 

0.089 0.089 

n/a 10.000 

2.000 

0.665 0.294 

0.311 0.314 

n/a 

Houston Washington, 

DC 

Slab-ongrade Basement 

0.070 0.070 

0.034 0.026 

0.071 0.050 

n/a 0.089 

n/a 10.000 

2.000 

0.665 0.294 

0.311 0.314 

Actual U-values in Btu/(h·ft2·°F) 

52
 
 

 

 

A.3 Energy Performance – New Residential 

Site 

Phoenix San Francisco Washington, DC 

DEVap DX A/C DEVap DX A/C DEVap DX A/C 

Cooling fan (kWh) 1425.09 1368.49 169.29 75.05 976.79 817.92 

Mechanical ventilation (kWh) 145.22 240.9 235.36 240.9 181.20 240.9 

Dehumidifier (kWh) 0 0.00 0 470.09 0 868.38 

A/C (compressor) (kWh) 0 5159.07 0 252.55 0 2854.76 

DEVap auxiliary (kWh) 96.96 0 15.85 0 91.99 0 

Total electric (kWh) 1667 6768 421 1039 1250 4782 

Regenerator (kWh) 1977 0 672 0 5710 0 

Source 

Phoenix San Francisco Washington, DC 

DEVap DX A/C DEVap DX A/C DEVap DX A/C 

Electric (kWh) 5610 22776 1415 3495 4206 16091 

Thermal, cooling (kWh) 2159 0 734 0 6236 0 

Total (kWh) 7769 22776 2149 3495 10442 16091 

Site 

Tampa Atlanta Chicago 

DEVap DX A/C DEVap DX A/C DEVap DX A/C 

Cooling fan (kWh) 2278.68 1891.83 1199.86 1009.19 619 543.09 

Mechanical ventilation (kWh) 105.62 240.9 169.29 240.9 200 240.9 

Dehumidifier (kWh) 0 2276.59 0 975.31 0 640.16 

A/C (compressor) (kWh) 0 6583.69 0 3496.18 0 1872.29 

DEVap auxiliary (kWh) 221.32 0 107.10 0 60 0 

Total electric (kWh) 2606 10993 1476 5722 880 3296 

Regenerator (kWh) 16177 0 6422 0 3280 0 

Source 

Tampa Atlanta Chicago 

DEVap DX A/C DEVap DX A/C DEVap DX A/C 

Electric (kWh) 8768 36991 4968 19253 2960 11093 

Thermal, cooling (kWh) 17665 0 7013 0 3582 0 

Total (kWh) 26433 36991 11981 19253 6542 11093 

53
 
 

Site 

Boston Houston 

DEVap DX A/C DEVap DX A/C 

Cooling fan (kWh) 524.77 439.08 1917 1604 

Mechanical ventilation (kWh) 207.47 240.9 128 241 

Dehumidifier (kWh) 0 603.92 0 1996 

A/C (compressor) (kWh) 0 1513.30 0 5636 

DEVap auxiliary (kWh) 51.17 0 184 0 

Total electric (kWh) 783 2797 2229 9477 

Regenerator (kWh) 2672 0 13361 0 

Source 

Boston Houston 

DEVap DX A/C DEVap DX A/C 

Electric (kWh) 2636 9413 7502 31889 

Thermal, cooling (kWh) 2918 0 14590 0 

Total (kWh) 5554 9413 22092 31889 

Water Evaporation 

Phoenix San Francisco Washington, DC 

DEVap DX A/C DEVap DX A/C DEVap DX A/C 

Site gal/ton·h 2.65 2.19 2.21 

Off-site gal/ton·h 0.26 1.31 1.38 6.26 0.40 1.53 

Water Evaporation 

Tampa Atlanta Chicago 

DEVap DX A/C DEVap DX A/C DEVap DX A/C 

Site gal/ton·h 2.20 2.06 2.00 

Off-site gal/ton·h 0.36 1.52 0.36 1.47 0.40 1.60 

Water Evaporation 

Boston Houston 

DEVap DX A/C DEVap DX A/C 

Site gal/ton·h 2.07 2.23 

Off-site gal/ton·h 0.45 1.71 0.37 1.56 

54
 
 

 

A.4 Energy Performance – Retrofit Residential 

Energy Site 

Phoenix San Francisco Washington, DC 

DEVap DX A/C DEVap DX A/C DEVap DX A/C 

Cooling fan (kWh) 1696.80 1617.07 321.47 374.41 1099.75 909.13 

Mechanical ventilation (kWh) 0.00 0 0.00 0 0.00 0 

Dehumidifier (kWh) 0 0.00 0 224.63 0 319.08 

A/C (compressor) (kWh) 0 6025.34 0 1255.25 0 3150.15 

DEVap auxiliary (kWh) 106.69 0 34.71 0 100.01 0 

Total electric (kWh) 1803 7642 356 1854 1200 4378 

Regenerator (kWh) 2135 0 670 0 6188 0 

Energy Source 

Phoenix SF DC 

DEVap DX A/C DEVap DX A/C DEVap DX A/C 

Electric (kWh) 6069 25717 1199 6240 4037 14733 

Thermal, cooling (kWh) 2332 0 732 0 6757 0 

Total (kWh) 8401 25717 1930 6240 10794 14733 

Energy Site 

Tampa Atlanta Chicago 

DEVap DX A/C DEVap DX A/C DEVap DX A/C 

Cooling fan (kWh) 2904.41 1965.64 1620.76 1031.08 611 490.76 

Mechanical ventilation (kWh) 0.00 0 0.00 0 0 0 

Dehumidifier (kWh) 0 588.36 0 243.69 0 395.88 

A/C (compressor) (kWh) 0 6791.90 0 5028.52 0 1690.45 

DEVap auxiliary (kWh) 239.26 0 118.49 0 60 0 

Total electric (kWh) 3144 9346 1739 6303 671 2577 

Regenerator (kWh) 18731 0 7520 0 3118 0 

Energy Source 

Tampa Atlanta Chicago 

DEVap DX A/C DEVap DX A/C DEVap DX A/C 

Electric (kWh) 10578 31449 5853 21211 2257 8672 

Thermal, cooling (kWh) 20454 0 8212 0 3405 0 

Total (kWh) 31032 31449 14064 21211 5662 8672 

55
 
 

 

Energy Site 

Boston Houston 

DEVap DX A/C DEVap DX A/C 

Cooling fan (kWh) 620.07 557.90 2405 1262 

Mechanical ventilation (kWh) 0.00 0 0 0 

Dehumidifier (kWh) 0 263.14 0 406 

A/C (compressor) (kWh) 0 1907.57 0 6270 

DEVap auxiliary (kWh) 58.10 0 197 0 

Total electric (kWh) 678 2729 2602 7938 

Regenerator (kWh) 2846 0 14920 0 

Energy Source 

Boston Houston 

DEVap DX A/C DEVap DX A/C 

Electric (kWh) 2282 9182 8754 26713 

Thermal, cooling (kWh) 3108 0 16292 0 

Total (kWh) 5390 9182 25046 26713 

Water Evaporation 

Phoenix SF DC 

DEVap DX A/C DEVap DX A/C DEVap DX A/C 

Site gal/ton·h 2.75 1.89 2.43 

Off-site gal/ton·h 0.25 1.29 0.29 1.48 0.35 1.28 

Water Evaporation 

Tampa Atlanta Chicago 

DEVap DX A/C DEVap DX A/C DEVap DX A/C 

Site gal/ton·h 2.67 2.36 2.21 

Off-site gal/ton·h 0.41 1.22 0.34 1.25 0.34 1.48 

Water Evaporation 

Boston Houston 

DEVap DX A/C DEVap DX A/C 

Site gal/ton·h 2.16 2.69 

Off-site gal/ton·h 0.32 1.36 0.41 1.26 

56
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A.5 Economics – New Residential 

Cost Phoenix SF DC Tampa 

Utilities DEVap AC DEVap AC DEVap AC DEVap AC 

Electric $ 181 $ 922 $ 59 $ 145 $ 180 $ 715 $ 266 $ 1,219 

Gas $ 96 $ - $ 33 $ - $ 265 $ - $ 613 $ -

Water $ 67 $ - $ 3 $ - $ 28 $ - $ 63 $ -

Total $ 344 $ 922 $ 95 $ 145 $ 473 $ 715 $ 942 $ 1,219 

Levelized cost per tonh Phoenix SF DC Tampa 

DEVap AC DEVap AC DEVap AC DEVap AC 

capital $ 0.095 $ 0.062 $ 1.693 $ 1.949 $ 0.165 $ 0.104 $ 0.072 $ 0.045 

Electric $ 0.032 $ 0.199 $ 0.216 $ 0.983 $ 0.064 $ 0.257 $ 0.042 $ 0.189 

Gas $ 0.017 $ - $ 0.122 $ - $ 0.095 $ - $ 0.096 $ -

Water $ 0.012 $ - $ 0.010 $ - $ 0.010 $ - $ 0.010 $ -

Total $ 0.157 $ 0.261 $ 2.041 $ 2.932 $ 0.334 $ 0.360 $ 0.219 $ 0.234 

Levelized cost per year Phoenix SF DC Tampa 

DEVap AC DEVap AC DEVap AC DEVap AC 

capital $ 600 $ 320 $ 517 $ 323 $ 517 $ 323 $ 517 $ 323 

Electric $ 203 $ 1,034 $ 66 $ 163 $ 202 $ 801 $ 298 $ 1,367 

Gas $ 108 $ - $ 37 $ - $ 297 $ - $ 687 $ -

Gas_high $ 162 $ - $ 56 $ - $ 445 $ - $ 1,031 $ -

Water $ 75 $ - $ 3 $ - $ 31 $ - $ 71 $ -

Total $ 986 $ 1,354 $ 624 $ 486 $ 1,047 $ 1,124 $ 1,573 $ 1,690 

Total_high $ 1,040 $ - $ 642 $ - $ 1,196 $ - $ 1,917 $ -

Cost Atlanta Chicago Boston Houston 

Utilities DEVap AC DEVap AC DEVap AC DEVap AC 

Electric $ 152 $ 663 $ 96 $ 363 $ 108 $ 390 $ 245 $ 1,042 

Gas $ 178 $ - $ 72 $ - $ 127 $ - $ 340 $ -

Water $ 34 $ - $ 18 $ - $ 14 $ - $ 54 $ -

Total $ 363 $ 663 $ 185 $ 363 $ 249 $ 390 $ 640 $ 1,042 

Levelized cost per tonh Atlanta Chicago Boston Houston 

DEVap AC DEVap AC DEVap AC DEVap AC 

capital $ 0.127 $ 0.083 $ 0.237 $ 0.157 $ 0.300 $ 0.197 $ 0.085 $ 0.053 

Electric $ 0.042 $ 0.191 $ 0.049 $ 0.197 $ 0.070 $ 0.267 $ 0.045 $ 0.192 

Gas $ 0.049 $ - $ 0.037 $ - $ 0.083 $ - $ 0.063 $ -

Water $ 0.009 $ - $ 0.009 $ - $ 0.009 $ - $ 0.010 $ -

Total $ 0.227 $ 0.275 $ 0.332 $ 0.354 $ 0.462 $ 0.464 $ 0.203 $ 0.246 

Levelized cost per year Atlanta Chicago Boston Houston 

DEVap AC DEVap AC DEVap AC DEVap AC 

capital $ 517 $ 323 $ 517 $ 323 $ 517 $ 323 $ 517 $ 323 

Electric $ 170 $ 744 $ 107 $ 407 $ 121 $ 437 $ 275 $ 1,169 

Gas $ 199 $ - $ 81 $ - $ 143 $ - $ 382 $ -

Gas_high $ 299 $ - $ 121 $ - $ 214 $ - $ 572 $ -

Water $ 38 $ - $ 20 $ - $ 16 $ - $ 61 $ -

Total $ 924 $ 1,067 $ 725 $ 730 $ 797 $ 760 $ 1,234 $ 1,492 

Total_high $ 1,024 $ - $ 765 $ - $ 868 $ - $ 1,425 $ -

57
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A.6 Economics – Retrofit Residential 

Cost Phoenix SF DC Tampa 

Utilities DEVap AC DEVap AC DEVap AC DEVap AC 

Electric $ 196 $ 1,057 $ 50 $ 293 $ 173 $ 689 $ 321 $ 1,059 

Gas $ 104 $ - $ 33 $ - $ 287 $ - $ 710 $ -

Water $ 79 $ - $ 9 $ - $ 33 $ - $ 81 $ -

Total $ 379 $ 1,057 $ 92 $ 293 $ 493 $ 689 $ 1,112 $ 1,059 

Levelized cost per tonh Phoenix SF DC Tampa 

DEVap AC DEVap AC DEVap AC DEVap AC 

capital $ 0.138 $ 0.086 $ 0.700 $ 0.376 $ 0.250 $ 0.148 $ 0.112 $ 0.067 

Electric $ 0.031 $ 0.194 $ 0.046 $ 0.232 $ 0.057 $ 0.215 $ 0.047 $ 0.150 

Gas $ 0.016 $ - $ 0.031 $ - $ 0.094 $ - $ 0.104 $ -

Water $ 0.012 $ - $ 0.008 $ - $ 0.011 $ - $ 0.012 $ -

Total $ 0.197 $ 0.280 $ 0.785 $ 0.608 $ 0.412 $ 0.363 $ 0.275 $ 0.218 

Levelized cost per year Phoenix SF DC Tampa 

DEVap AC DEVap AC DEVap AC DEVap AC 

capital $ 988 $ 527 $ 851 $ 532 $ 851 $ 532 $ 851 $ 532 

Electric $ 220 $ 1,185 $ 56 $ 329 $ 194 $ 773 $ 359 $ 1,187 

Gas $ 117 $ - $ 37 $ - $ 322 $ - $ 796 $ -

Gas_high $ 175 $ - $ 56 $ - $ 483 $ - $ 1,193 $ -

Water $ 88 $ - $ 10 $ - $ 37 $ - $ 91 $ -

Total $ 1,412 $ 1,712 $ 955 $ 861 $ 1,405 $ 1,305 $ 2,098 $ 1,719 

Total_high $ 1,471 $ - $ 973 $ - $ 1,565 $ - $ 2,495 $ -

Cost Atlanta Chicago Boston Houston 

Utilities DEVap AC DEVap AC DEVap AC DEVap AC 

Electric $ 179 $ 750 $ 74 $ 310 $ 93 $ 414 $ 286 $ 900 

Gas $ 208 $ - $ 68 $ - $ 136 $ - $ 380 $ -

Water $ 48 $ - $ 18 $ - $ 18 $ - $ 68 $ -

Total $ 435 $ 750 $ 160 $ 310 $ 247 $ 414 $ 735 $ 900 

Levelized cost per tonh Atlanta Chicago Boston Houston 

DEVap AC DEVap AC DEVap AC DEVap AC 

capital $ 0.193 $ 0.127 $ 0.428 $ 0.279 $ 0.402 $ 0.243 $ 0.154 $ 0.102 

Electric $ 0.039 $ 0.161 $ 0.042 $ 0.182 $ 0.049 $ 0.212 $ 0.050 $ 0.155 

Gas $ 0.046 $ - $ 0.039 $ - $ 0.072 $ - $ 0.067 $ -

Water $ 0.011 $ - $ 0.010 $ - $ 0.010 $ - $ 0.012 $ -

Total $ 0.289 $ 0.288 $ 0.518 $ 0.461 $ 0.533 $ 0.455 $ 0.284 $ 0.258 

Levelized cost per year Atlanta Chicago Boston Houston 

DEVap AC DEVap AC DEVap AC DEVap AC 

capital $ 979 $ 664 $ 851 $ 532 $ 851 $ 532 $ 979 $ 664 

Electric $ 200 $ 840 $ 83 $ 348 $ 105 $ 464 $ 321 $ 1,009 

Gas $ 234 $ - $ 77 $ - $ 152 $ - $ 426 $ -

Gas_high $ 350 $ - $ 115 $ - $ 228 $ - $ 639 $ -

Water $ 54 $ - $ 20 $ - $ 21 $ - $ 77 $ -

Total $ 1,466 $ 1,504 $ 1,031 $ 880 $ 1,129 $ 996 $ 1,802 $ 1,672 

Total_high $ 1,583 $ - $ 1,069 $ - $ 1,205 $ - $ 2,015 $ -

58
 
 

 

 

 

 

 

 

 

 

A.7 Cost Estimates 

A/C Markups Markup 

1 - Manufacturer 1.23 

2 - Distributer 1.49 

3 - Retailer 1.28 

4 - Retail cost 1.00 

DEVap Cost Estimate 

Cost 

Estimate 

Price 

Level Markup Retail Cost 

$/ton, core $477 1 2.35 $1,119 Coolerado estimate 

$/kg LiCl $18 4 1.00 $18 $/kg anhydrous 

Total fixed costs $3,894 

2-stage regenerator $900 1 2.35 $2,111 

AILR Estimate - e-mail 

correspondence 

Tank $50 4 1.00 $50 10-15 gal tank 

Supply/mixed-air fan $180 4 1.00 $180 Based on AILR estimate 

Exhaust fan $150 4 1.00 $150 Based on AILR estimate 

Electronics $400 4 1.00 $400 Estimate based on Coolerado 

Packaging $600 3 1.28 $768 

Estimate based on Coolerado 

distribution cost 

2 desiccant pumps $60 4 1.00 $60 Pumps, 1 gpm each 

Solenoid $75 4 1.00 $75 Retail estimate 

Filters $25 4 1.00 $25 Retail estimate 

Pressure regulator $75 4 1.00 $75 Retail estimate 

System Size – 3 ton 3.0 Tons 

LiCl storage 7.3 kg/tonh_L 0.6 0.5 hours + 20% for pipe volumes 

13.1 kg $231 

System retail cost $7,484 3-ton system cost with 30-min storage 

Mark-up level to estimate cost 4 1.00 

Total system cost at level 

shown above $7,484 

System Size – 4 ton 4.0 Tons 

LiCl storage 7.3 kg/ton·h L 0.6 0.5 hours + 20% for pipe volumes 

17.5 kg $308 

System retail cost $680 4-ton system cost with 30-min storage 

Mark-up level to estimate cost 4 1.00 

Total system cost at level 

shown above $8,680 

System Size – 

Commercial 10-ton 10.0 Tons 

LiCl storage 7.3 kg/ton·h_L 0.6 0.5 hours + 20% for pipe volumes 

43.8 kg $771 

System retail cost $0,461 

10-ton system cost with 30-min 

storage 

Markup level to estimate cost 4 1.00 

Total system cost at level 

shown above $20,461 

Estimates 3X regenerator cost and 

2X fan costs 

59
 
A.8 Utility Prices From Utility Tariffs for 2010 

Electric ($/kWh) Natural gas ($/therm1) 

Electric utility Summer Winter Gas utility Summer Winter 

Atlanta 

 < 650 kWh 

 > 650 kWh 

Georgia Power 

$0.103 

$0.140 

$0.103

$0.095 

Gas South $0.81 $0.81

Boston 

 < 600 kWh 

 > 600 kWh 

National Grid 

$0.137 

$0.144 

$0.137

$0.144 

Yankee Gas $1.40 $1.24

Chicago ComEd $0.111 $0.101 People's Gas $0.64 $0.72 

Houston CenterPoint $0.110 $0.110 CenterPoint $0.75 $0.75 

Phoenix 

 < 400 kWh 

 400 - 800 kWh 

 > 800 kWh 

AZ Public Service 

$0.109 

$0.155

$0.183 

$0.106

Southwest Gas $1.43 $1.43

San Francisco 

 < 300 kWh 

 300-390 kWh 

 390-600 kWh 

 > 600 kWh 

PG&E 

$0.123 

$0.139 

$0.300 

$0.412 

$0.123

$0.139

$0.300

$0.412 

PG&E $1.45 $1.45

Tampa 

 < 1000 kWh 

 > 1000 kWh 

Tampa Electric 

$0.102 

$0.123 

$0.102

$0.123 

People's Gas $1.10 $1.30

Washington, D.C. 

 < 400 kWh 

 > 400 kWh 

Potomoc Electric 

$0.144

$0.157 

Washington Gas $1.36 $1.36

1 1 therm = 29.3 kWh 

60
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188 

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources,

gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this

collection of information, including suggestions for reducing the burden, to Department of Defense, Executive Services and Communications Directorate (0704-0188). Respondents

should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a 

currently valid OMB control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION. 

1. REPORT DATE (DD-MM-YYYY) 

January 2011 

2. REPORT TYPE 

Technical Report 

3. DATES COVERED (From - To) 

4. TITLE AND SUBTITLE 

Desiccant Enhanced Evaporative Air-Conditioning (DEVap): 

Evaluation of a New Concept in Ultra Efficient Air Conditioning 

5a. CONTRACT NUMBER 

DE-AC36-08GO28308 

5b. GRANT NUMBER 

5c. PROGRAM ELEMENT NUMBER 

6. AUTHOR(S) 

Eric Kozubal, Jason Woods, Jay Burch, Aaron Boranian, and 

Tim Merrigan 

5d. PROJECT NUMBER 

NREL/TP-5500-49722 

5e. TASK NUMBER 

ARRB2206 

5f. WORK UNIT NUMBER 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 

National Renewable Energy Laboratory 

1617 Cole Blvd. 

Golden, CO 80401-3393 

8. PERFORMING ORGANIZATION 

REPORT NUMBER 

NREL/TP-5500-49722 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S) 

NREL 

11. SPONSORING/MONITORING 

AGENCY REPORT NUMBER 

12. DISTRIBUTION AVAILABILITY STATEMENT 

National Technical Information Service 

U.S. Department of Commerce 

5285 Port Royal Road 

Springfield, VA 22161 

13. SUPPLEMENTARY NOTES 

14. ABSTRACT (Maximum 200 Words) 

NREL has developed the novel concept of a desiccant enhanced evaporative air conditioner (DEVap) with the 

objective of combining the benefits of liquid desiccant and evaporative cooling technologies into an innovative 

“cooling core.” Liquid desiccant technologies have extraordinary dehumidification potential, but require an efficient 

cooling sink. DEVap’s thermodynamic potential overcomes many shortcomings of standard refrigeration-based 

direct expansion cooling. DEVap decouples cooling and dehumidification performance, which results in independent 

temperature and humidity control. The energy input is largely switched away from electricity to low-grade thermal 

energy that can be sourced from fuels such as natural gas, waste heat, solar, or biofuels. 

15. SUBJECT TERMS 

desiccant enhanced evaporative air conditioner; devap; liquid dessicant; evaporative cooling; dehumidification 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION 

OF ABSTRACT 

UL 

18. NUMBER 

OF PAGES 

19a. NAME OF RESPONSIBLE PERSON 

a. REPORT 

Unclassified 

b. ABSTRACT 

Unclassified 

c. THIS PAGE 

Unclassified 19b. TELEPHONE NUMBER (Include area code) 

Standard Form 298 (Rev. 8/98) 

Prescribed by ANSI Std. Z39.18 

F1147-E(10/2008)