National Renewable Energy Laboratory 

Innovation for Our Energy Future 

A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 

A Zero Carryover 

Liquid-Desiccant Air Conditioner 

for Solar Applications 

Preprint 

A. Lowenstein 

AIL Research, Inc. 

S. Slayzak and E. Kozubal 

National Renewable Energy Laboratory

To be presented at ASME International Solar Energy Conference 

(ISEC2006) 

Denver, Colorado 

July 8–13, 2006 

Conference Paper 

NREL/CP-550-39798 

July 2006 
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Proceedings of ISEC2006 

ASME International Solar Energy Conference 

July 8-13, 2006, Denver, CO 

ISEC2006-99079 

A ZERO CARRYOVER LIQUID-DESICCANT AIR CONDITIONER FOR SOLAR APPLICATIONS 

ANDREW LOWENSTEIN 

AIL RESEARCH, INC. 

PRINCETON, NJ 

ail@ailr.com 

STEVEN SLAYZAK AND ERIC KOZUBAL 

NATIONAL RENEWABLE ENERGY LABORATORY 

GOLDEN, CO 

ABSTRACT 

A novel liquid-desiccant air conditioner that dries and cools 

building supply air has been successfully designed, built, and 

tested. The new air conditioner will transform the use of directcontact liquid-desiccant systems in HVAC applications, 

improving comfort and indoor air quality, as well as providing 

energy-efficient humidity control 

Liquid-desiccant conditioners and regenerators are 

traditionally implemented as adiabatic beds of contact media 

that are highly flooded with desiccant. The possibility of 

droplet carryover into the supply air has limited the sale of 

these systems in most HVAC applications. The characteristic 

of the new conditioner and regenerator that distinguishes them 

from conventional ones is their very low flows of liquid 

desiccant. Whereas a conventional conditioner operates 

typically at between 10 and 15 gpm (630 and 946 ml/s) of 

desiccant per 1000 cfm (0.47 m3

/s) of process air, the new 

conditioner operates at 0.5 gpm (32 ml/s) per 1000 cfm (0.47 

m3

/s). At these low flooding rates, the supply air will not 

entrain droplets of liquid desiccant. This brings performance 

and maintenance for the new liquid-desiccant technology in 

line with HVAC market expectations. 

Low flooding rates are practical only if the liquid 

desiccant is continually cooled in the conditioner or continually 

heated in the regenerator as the mass exchange of water occurs. 

This simultaneous heat and mass exchange is accomplished by 

using the walls of a parallel-plate plastic heat exchanger as the 

air/desiccant contact surface. Compared to existing solid- and 

liquid-desiccant systems, the low-flow technology is more 

compact, has significantly lower pressure drops and does not 

“dump” heat back onto the building’s central air conditioner. 

Tests confirm the high sensible and latent effectiveness of the 

conditioner, the high COP of the regenerator, and the operation 

of both components without carryover. 

Keywords: Dehumidifier, Liquid Desiccant, Air Conditioner, 

HVAC, Solar Cooling 

INTRODUCTION 

The 20th century was a period during which the cooling and 

dehumidification of homes and commercial buildings switched 

from being a luxury to a necessity. In the U.S. alone, air 

conditioning is a $10 billion industry that uses over 4.3 quads 

(4.54 billion GJ) of primary energy, almost all of which comes 

from non-renewable sources. Perhaps equally as important as 

its energy use, air conditioning is often the single largest cause 

of overloaded electric transmission and distribution systems. 

Now, at the start of the 21st century, there is growing 

awareness that our approach to air conditioning must change if 

its benefits are to continue and even expand into the developing 

regions of the world. One obvious change is to design 

buildings so that comfortable conditions can be maintained 

with less active cooling and dehumidification. A second is to 

develop air conditioners that run on renewable energy sources. 

But these changes are not enough. Other challenges 

now face the industry that provides systems for heating, 

ventilation and air conditioning (HVAC). Indoor environments 

are often uncomfortable and unhealthy because humidity is too 

high. The fundamental problem is that a cold heat exchanger, 

whether it is a chilled-water coil or a DX evaporator, is a poor 

way to dehumidify air. A 45F (7.2C) heat exchanger will 

typically provide 70% of its total cooling as sensible cooling 

(i.e., temperature reduction) and 30% as latent cooling (i.e., 

dehumidification). In many applications, this latent/sensible 

split must be reversed if indoor humidity is to be adequately 

controlled. 

Desiccants—which are materials that have a high 

affinity for water vapor—can be part of a sustainable approach 

to maintaining healthy and comfortable indoor environments. 

Desiccants are unique in that they can dry air without first 

cooling the air below its dewpoint. Latent cooling can be more 

than twice sensible cooling. Once the desiccant is loaded with 

water, heat is used to return the desiccant to its “dry” state. The 

high electrical demand of the compressor in a conventional air 

1
conditioner is replaced by the need for thermal energy to 

regenerate the desiccant. This creates an important opportunity 

to use solar thermal energy for air conditioning. 

PAST WORK ON SOLAR DESICCANT COOLING 

There have been numerous attempts at capturing the benefits of 

desiccants in a solar air conditioner. In one of the earliest 

efforts, Löf proposed a solar air conditioner that used 

triethylene glycol (Löf, 1955). In the early 1980s, American 

Solar King manufactured and sold a residential solar cooling 

system that used a lithium-chloride solid-desiccant rotor 

(Coellner, 1986). When energy prices declined in the late 

1980s, American Solar King converted their product to a gasfired unit. Robison conducted a 2-year field test of a solar 

cooling system that used a calcium-chloride liquid-desiccant 

conditioner (Robison, 1983). The test demonstrated the 

technical feasibility of this solar cooling system, but there was 

no attempt to commercialize the technology. Schlepp and 

Schultz have summarized the experiences of many solar 

desiccant cooling activities that followed the energy crisis of 

the 1970s (Schlepp and Schultz, 1984). 

 In addition to AIL Research, there are now at least two 

companies that are commercializing liquid-desiccant 

technology that can be used for solar cooling. L-DCS 

Technology is now commissioning a 350-kW solar cooling 

system in Singapore (L-DCS, 2006). In 2005, Jilier 

Technology Development introduced the American Genius line 

of liquid-desiccant air conditioners at the International AirConditioning, Heating and Refrigeration Exposition (Jilier, 

2005). 

STATE OF THE ART OF DESICCANT TECHNOLOGY 

Desiccant systems are commonly categorized as either solid or 

liquid types. Solid-desiccant systems most commonly use a 

porous rotor with face seals that create two isolated air paths 

through the rotor. The process air moves through one sector of 

the rotor, while at the same time, hot regeneration air moves 

through other. The rotation of the rotor permits continuous 

dehumidification of the process air without any valves or 

dampers periodically redirecting the air flows. Because there is 

no active cooling within the rotor and the rotor itself transfers 

some heat from the regeneration air to the process air, the dry 

process air leaves the rotor at a higher enthalpy than it entered. 

In most HVAC applications, the process air leaving the 

desiccant rotor must be cooled before it is supplied to the 

building. 

Figure 1 shows the configuration of most liquiddesiccant systems now being sold for industrial applications. 

Both the conditioner and regenerator are porous, adiabatic beds 

that are flooded with desiccant. The desiccant is first cooled 

before it is sprayed onto the bed of the conditioner. The 

process air flows through this bed and is both cooled and dried 

by the desiccant. 

A slip stream of desiccant (typically an order of 

magnitude smaller than the flooding rate) is continually 

recirculated between the conditioner and a regenerator where 

the desiccant is re-concentrated using thermal energy. Again, 

the desiccant flows over a porous bed of contact media. 

However, the desiccant is now first heated, typically to between 

180F and 210F (82C and 99C), before it is sprayed onto the 

bed. Air flows through the bed, scavenges the water vapor that 

is desorbed from the desiccant, and rejects it to ambient. 

The flooding rate in both the conditioner and 

regenerator of a conventional liquid desiccant system is 

relatively high for two reasons: (1) the entire internal area of 

the contact bed must be well wetted, and (2) the desiccant flow 

must have sufficient thermal capacity to ensure that the 

temperature of the desiccant does not increase or decrease 

significantly as water is absorbed or desorbed. At the high 

flooding rates, small droplets of desiccant will be created as the 

desiccant cascades down through the bed. These small droplets 

are entrained by the air flowing through the bed. Consequently, 

a conventional liquid-desiccant system must use a droplet filter 

or demister to prevent carryover of desiccant out of the 

conditioner and regenerator. In well-maintained systems, the 

droplet filter/demister will essentially eliminate desiccant 

carryover. 

A LOW-FLOW ZERO-CARRYOVER LIQUID 

DESICCANT CONDITIONER AND REGENERATOR 

The present need for increased ventilation and better humidity 

control within residential and commercial buildings has spurred 

interest in desiccant systems. However, most sales have been 

solid-desiccant systems. While the sales of both systems are 

limited by their higher costs, liquid-desiccant systems are 

perceived as having more intensive maintenance requirements, 

which further depress sales.1

 

A new generation of liquid-desiccant conditioners and 

regenerators that meets the needs of HVAC applications has 

been developed and proven. The two most important 

improvements are (1) desiccant flooding rates have been 

decreased by a factor of 10 to 20, and (2) contact surfaces are 

no longer adiabatic, being continually cooled in the conditioner 

and continually heated in the regenerator. These two changes 

are related in that when the desiccant flooding rate is decreased, 

the thermal capacitance of the flow is proportionately 

2

 

1

 A dedicated outdoor air system based on vapor-compression 

technology will cost on the order of $6 per cfm ($12.70 per l/s), 

while one based on liquid or solid desiccants will cost closer to 

$10 per cfm ($21.20 per l/s). 

Figure 1 – Operation of conventional liquid-desiccant 

system 
decreased. If the contact surface was adiabatic, the desiccant’s 

temperature would either rapidly increase in the conditioner or 

rapidly decrease in the regenerator, and the driving potential for 

the exchange of water vapor would be lost. 

The preceding two improvements in liquid-desiccant 

technology lead to a much more competitive cooling system. 

Compared to the technology now in use, a low-flow liquiddesiccant air conditioner (LDAC) will 

• have much lower pressure drops 

• be more compact 

• produce a greater cooling effect (e.g., lower cfm/ton) 

• more deeply dry the process air, and 

• have a higher COP. 

Perhaps most importantly, both the low-flow conditioner and 

regenerator will operate without the entrainment of desiccant 

droplets by the air streams (i.e., zero desiccant carryover). 

As shown in Figure 2, a LDAC that uses the low-flow 

technology has three main components: (1) the conditioner, (2) 

the regenerator, and (3) the interchange heat exchanger. The 

conditioner is a parallel-plate heat exchanger in which the 

plates are water-cooled. Films of desiccant flow in thin wicks 

on the outer surfaces of the plates. The process air (horizontal 

arrows) flows through the gaps between the plates and comes in 

contact with the desiccant. The desiccant absorbs water vapor 

from the air, and the heat that is released is transferred to the 

cooling water. The air leaves the conditioner drier and at a 

lower enthalpy (i.e., cooling occurs, although most of the 

cooling may be latent rather than sensible). 

The water absorbed by the desiccant in the conditioner 

is desorbed in the regenerator. This component is again a 

parallel-plate heat exchanger, but now hot water (or other heattransfer fluid) flows within the plates. The hot desiccant films 

that flow on the outer surfaces of the plates desorb water to a 

flow of scavenging air (horizontal arrows) that rejects the water 

to ambient. 

The interchange heat exchanger, which transfers heat 

from the hot, strong desiccant leaving the regenerator to the 

cool, weak desiccant flowing to the regenerator, performs a 

dual function. It improves the efficiency of the regenerator by 

preheating the weak desiccant. It also increases the cooling 

provided by the conditioner by reducing the heat load imposed 

by the strong desiccant. 

THE IMPLEMENTATION OF LOW-FLOW 

TECHNOLOGY 

Although many liquids have desiccant properties, solutions of 

halide salts, particularly lithium chloride and calcium chloride, 

are the most viable liquid desiccants for solar applications. 

However, the high chloride concentrations in solutions of these 

salts eliminate even most stainless steels from service in 

contact with the desiccant. If maintenance is to be acceptable, 

all wetted surfaces of a LDAC should be a plastic with suitable 

properties. 

regenerator 

conditioner 

Figure 3 – A 6,000 cfm low-flow liquid-desiccant 

conditioner

 Figure 3 shows a plastic-plate heat exchanger that 

functions as a 6,000-cfm liquid-desiccant conditioner. The 

plates are made from a plastic extrusion. The cross-section of 

each plate, which is shown in Figure 4, is 0.1 in. by 12.0 in. 

(2.5 mm by 305 mm), with 110 cooling passages running the 

Interchange 

HX 

Figure 2 – Operation of a low-flow liquid-desiccant air 

conditioner

Figure 4 – Cross-section of plate extrusion

3
length of the extrusion. The plates have a thin—approximately 

0.020 mil (0.5 mm)—wick covering their surfaces to ensure 

even wetting by the desiccant. Each plate is bonded to an 

upper and lower end-piece. For the conditioner shown in 

Figure 3, 198 plate/end-piece assemblies are stacked and 

bonded together. When stacked and bonded, the upper endpieces form two isolated flow circuits: one for distributing 

desiccant onto the plate surfaces, and the other for circulating a 

cooling fluid within the plates. In a similar fashion, the lower 

end-pieces form a collection sump for the desiccant that flows 

off the plates. Additional features of the conditioner are 

described in U.S. Patent 6,745,826 and several pending foreign 

patents. 

The preceding conditioner can operate effectively at 

desiccant-to-air mass flow ratios 20 to 30 times less than those 

in a conventional liquid-desiccant conditioner. At these low 

desiccant flows, the liquid films on the plates of the conditioner 

are contained within the wicks that cover the plates. As 

described in a later section, this design for the conditioner has a 

large operating envelope within which the process air does not 

entrain droplets of desiccant. Furthermore, because droplets 

are not created when the desiccant is either delivered to or 

collected from the plates, droplet carryover is completely 

suppressed during normal operation. 

A low-flow regenerator functions similarly to a 

conditioner, the major difference being that now a hot fluid 

flows within the plates instead of a coolant. The high operating 

temperatures forces several design changes. 

As with the conditioner, polymers can best deal with 

the corrosiveness of the liquid desiccant. Because both the 

efficiency and water-removal capacity of a scavenging-air 

regenerator increase with operating temperature, a polymer 

should be selected that withstands high temperatures (e.g., 

temperatures on the order of 212F [100C]). Polymers in the 

polysulfone family can meet this temperature requirement. 

Thermal expansion is more of an issue in designing 

the regenerator. Polymers have coefficients of thermal 

expansion (CTE) that are an order of magnitude greater than 

metals. The design 

previously 

described for the 

conditioner would 

make a poor 

regenerator because 

it fixes both ends of 

the plates to 

common manifolds. 

A non-uniformity 

in temperature 

between 

neighboring plates 

will induce stresses 

that could break the 

adhesive seals 

within the structure. 

The design 

for the regenerator 

locates the inlet and 

outlet manifolds for 

the hot heat transfer fluid at the same end of the plates. The 

passages within the plates create a two-pass flow circuit 

between the inlet and outlet manifolds. With both fluid 

connections at the same end, the opposite ends of the plates are 

unconstrained. Each plate can expand independently of its 

neighbor. 

Figure 5 shows a low-flow scavenging-air regenerator 

with “hanging” plates. Each plate is 0.12 in. thick, 4.5 in. wide 

and 24 in. long. (3 mm x 11.4 cm x 61 cm) The 21 plates of the 

regenerator provide a design water-removal capacity of 18 lb/h 

(8.2 kg/h). 

A COMPARISON OF THE LOW-FLOW CONDITIONER 

WITH CONVENTIONAL DESICCANT TECHNOLOGY 

A unique feature of the low-flow liquid-desiccant conditioner is 

the integration of heat and mass transfer in one low pressuredrop component. In contrast to this dual-function 

configuration, the rotor of a solid-desiccant system does only 

adiabatic drying with the process air being cooled in a separate 

heat exchanger. For a conventional liquid-desiccant 

conditioner, the process air is both dried and cooled, but a 

separate heat exchanger must be used to cool the desiccant 

before it flows onto the contact bed. 

By combining heat and mass transfer into a single 

component, the low-flow liquid-desiccant conditioner will be 

more compact and have lower air-side pressure drops than 

existing desiccant technologies. The lower desiccant flow rate 

compared to a conventional liquid-desiccant conditioner also 

reduces pump power by close to an order of magnitude. 

The performance of a low-flow liquid-desiccant 

conditioner is next compared with that of conventional liquiddesiccant and solid-desiccant systems. Manufacturer’s data is 

used to predict the performance of the two conventional 

systems 

All three systems are designed to meet the following 

constraints: 

• 6,000 scfm (2.8 m3

/s) of outdoor air at 95F and 

118 gr/lb (35C and 16.9 g/kg) are processed 

• Cooling tower water supplied at 86F (30C) is used for 

cooling 

• Air velocities at the face of the rotor or conditioner are 

400 fpm (2 m/s). 

With the preceding constraints, the low-flow liquiddesiccant conditioner that has been described in the preceding 

section and which operates with 44% lithium chloride solution 

will supply air at 93.3F, 24.4% rh, and 57.0 gr/lb (34.1C and 

8.14 g/kg). The air-side pressure drop will be about 0.3 in. w.c. 

(75 Pa), and the water-side pressure drop will be less than 1 psi 

(6,900 Pa). If two conditioners are placed in series, air will be 

supplied at 92.6F, 18.3% rh, and 41.7 gr/lb (33.7C and 5.95 

g/kg), and the air-side pressure drop will be doubled. The 

desiccant circulator pump will have a 1/5th HP motor that will 

draw 200 W (one pump/motor per conditioner). 

For the conventional, high-flooding-rate conditioner, 

the cooling-tower water cools the liquid desiccant before it is 

sprayed onto the contact bed. Assuming a conditioner 

configuration in which the process air flows horizontally Figure 5 – A low-flow scavengingair regenerator

4
through the bed, a representative supply air condition will be 

97F, 20.3% rh, and 53.0 gr/lb (36C and 7.57 g/kg). The airside pressure drop through the conditioner will be 1.3 in. w.c. 

(324 Pa). The desiccant recirculator pump will have a 2 HP 

motor that will draw 1.5 kW. 

The conventional conditioner will also be larger than 

the low-flow conditioner. Not including inlet and outlet 

plenums, a conventional conditioner that processes a nominal 

7,500 cfm will be 61 in. x 60 in. x 92 in. (W x D x H; 1.55 m x 

1.52 m x 2.34 m). For the same air flow, the low-flow 

conditioner will be 65 in. x 40 in. x 77 in. (1.65 m x 1.02 m x 

1.96 m). 

For the solid desiccant system, the rotor is 400 mm 

deep and regenerated at 250F (121C). The hot, dry process air 

leaving the rotor is cooled in a 4-row finned tube heat 

exchanger that has an 80% effectiveness and is cooled with 

cooling tower water. At these operating conditions, the process 

air leaves the rotor at 151F and 55.0 gr/lb (66.1C and 

7.85 g/kg). The heat exchanger downstream of the rotor cools 

the supply air to 99F and 19.8% rh (37.2C) with no change in 

humidity. The pressure drop through the rotor is about 1.5 in. 

w.c. (373 Pa) and through the heat exchanger, 0.24 in. w.c. (60 

Pa). The drive motor for the rotor draws on the order of 200 W 

(at 6,000 cfm [2.83 m3

/s], each 1.0 in. w.c. [250 Pa] air-side 

pressure drop increases fan power by about 1.3 kW). 

The psychrometric performances of the preceding four 

systems are compared in Figure 6, in which the x-axis is 

absolute humidity expressed in mass of water per mass of dry 

air. The single low-flow liquid-desiccant conditioner, the soliddesiccant rotor, and the conventional liquid-desiccant 

conditioner all supply air at about the same humidity. The 

single low-flow liquid-desiccant conditioner does deliver air at 

a lower temperature and slightly lower enthalpy. A more 

important difference is that the low-flow liquid desiccant 

conditioner delivers this cooling with only a 0.3 in. w.c. (75 Pa) 

pressure drop, while the other two systems have pressure drops 

between 1.3 and 1.7 in. w.c. (324 and 423 Pa). The use of two 

low-flow conditioners in series increases latent cooling by 25% 

and total cooling by 14%, but still has a pressure drop that is 

less than one-half that of the alternative systems. 

A COMPARISON OF THE LOW-FLOW REGENERATOR WITH CONVENTIONAL DESICCANT 

TECHNOLOGY 

Both the solid-desiccant and liquid-desiccant systems can use 

solar thermal energy for regeneration. This thermal energy can 

be provided by either glazed, flat-plate collectors or evacuatedtube collectors. (A third type of collector—concentrating, 

tracking collectors—tend to be used in very large systems and 

are not compared here.) Flat-plate collectors are less 

expensive, but they supply thermal energy at a lower 

temperature: their installed cost will be on the order of $25 to 

$40 per square foot ($269 to $431 per square meter), and at 

peak summer conditions, they will deliver between 50% and 

60% of the incident solar radiation as hot water at 180F (82C). 

Evacuated-tube collectors will have an installed cost that is 1.5 

to two times that of a flat-plate collector, but they will achieve 

the same 50% to 60% collection efficiency when operating at 

250F (121C) or higher. 

The selection of the collectors for a solar cooling 

system is a trade-off between their cost and performance. In 

general, the Coefficient of Performance (COP) for desiccant 

regeneration—defined as the thermal energy needed to 

evaporate a unit mass of pure water divided by the thermal 

energy supplied to the regenerator to remove the same mass of 

water from the desiccant—increases at higher temperatures. 

For liquid-desiccant systems, the improvement in COP with 

increasing regeneration temperature is most dramatic when the 

desiccant is regenerated in two stages (similar to the doubleeffect generator of an absorption chiller). While gas-fired twostage desiccant regenerators have been developed, no 

comparable technology is available for solar applications. 

When used with a single-stage liquid-desiccant regenerator, 

such as the scavenging-air regenerator shown in Figure 5, the 

higher operating temperature of the evacuated-tube collector 

will not justify its higher cost. 

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.020

0.022

0.024

0.026

0.028

0.030

90 95 100 105 110 115 120 125 130 135 140 145 150 155 160

Temperature (F)

Humidity (lb/lbda)

SD Rotor with HX

Hi-Flow LD

Lo-Flow LD (one core)

Lo-Flow LD (two cores)

Figure 6 – Comparative performance of solid- and 

liquid-desiccant systems 

As discussed in a later section, the 44% lithiumchloride solution that produces the performance shown in 

Figure 6 for the low-flow liquid-desiccant systems can be 

regenerated at a thermal COP of 0.80 in a low-flow regenerator 

that operates at 180F (82C). On a peak summer day, a glazed, 

flat-plate collector can deliver between 50% and 60% of the 

incident solar energy to the regenerator at this temperature. 

Thus, based on incident solar energy, the regeneration COP for 

the liquid desiccant will be between 0.40 and 0.48. Assuming a 

collector installed cost of $32.50 per square foot ($350 per 

square meter) and a peak solar insolation of 317 Btu/hr-ft2

(1,000 W/m2

), the solar collectors cost $2,800 per peak ton 

($796 per peak kW) of latent cooling. 

A conventional packed-bed regenerator that operates 

at the same conditions as the preceding low-flow regenerator 

will have a thermal COP of 0.55. The flat-plate solar collectors 

that provide thermal energy to this regenerator will cost $4,070 

per peak ton ($1,158 per peak kW) of latent cooling. 

The performance for the solid-desiccant cooling 

system shown in Figure 6 assumes that the desiccant is 

regenerated at 250F. This relatively high temperature can be 

supplied by evacuated-tube collectors, but not the lower cost 

flat-plate collectors. At this temperature, the solid-desiccant 

regeneration COP will be 0.5, and the efficiency of the solar 

5
collectors on a peak summer day will be between 50% and 60% 

(i.e., percent of incident solar radiation delivered to the heater 

for the desiccant regenerator). Thus, based on incident solar 

energy, the regeneration COP for the solid desiccant will be 

between 0.25 and 0.30. Assuming a collector installed cost of 

$65.00 per square foot ($700 per square meter) and a peak solar 

insolation of 317 Btu/hr-ft2

 (1,000 W/m2), the solar collectors 

cost $9,000 per peak ton ($2,560 per peak kW) of latent 

cooling. 

ENERGY STORAGE WITH LIQUID DESICCANTS 

A competitive solar cooling system must store energy if it is to 

effectively use the thermal energy provided by its solar 

collectors. Peak solar insolation will occur mid-day, while 

cooling loads for the building peak in the afternoon and extend 

into the early evening. At a minimum, several hours of storage 

are needed to accommodate this mismatch. 

 A liquid-desiccant cooling system has an important 

advantage over all alternatives in solar applications because of 

the ease with which concentrated desiccant can be stored 

(Kessling et al., 1998). All PV-based cooling systems will be 

penalized for the expense and inefficiency of battery storage. 

Although these systems can store “cooling” as either chilled 

water or ice, both options impose additional economic 

penalties. Chilled-water storage requires very large, insulated 

storage tanks. Ice storage systems can be much smaller, but 

they are inefficient. (In conventional applications, ice can be 

made at night when electric rates are low, and the lower 

ambient temperatures compensate for the low evaporator 

temperatures needed to make ice. For a PV-based cooling 

system, ice storage would require making ice during the higher 

ambient temperatures of mid-day.) 

 Solar thermal cooling systems that use absorption 

chillers, adsorption chillers, or solid-desiccant systems must 

store energy as hot water which can later be used to run the 

cooling system. For single-effect technologies, hot water must 

be stored at between 190F and 210F (88C and 99C). Because 

the COP for single-effect technologies will be on the order of 

0.6, approximately 60% more thermal energy must be stored 

than the cooling that is eventually provided. The higher COP 

of double-effect technologies (COPs closer to 1.0), greatly 

reduces the quantity of thermal energy that must be stored, but 

now the storage temperature must be over 320F (160C). 

 Compared to batteries, hot water, ice, and chilled 

water, the storage of concentrated desiccant imposes a 

relatively modest economic penalty and no efficiency penalty 

on the liquid-desiccant cooling system. Concentrated desiccant 

can be stored in uninsulated plastic tanks with no loss in 

cooling potential over time. For cooling systems that use a 

solution of lithium chloride that cycles between 38% and 44%, 

the density of storage will be 8.3 gallons per ton-hour latent 

cooling (2.48 liter/MJ). This is a lower volumetric requirement 

than the 10 gallons per ton hour (2.99 liter/MJ) that is typical of 

ice storage. At $2.50 per pound ($5.50 per kg) for anhydrous 

lithium chloride, the cost for storage will be about $80 per tonhour ($6.32 per MJ), a value that is comparable to ice storage. 

 A solar cooling system that uses liquid desiccants can 

dramatically reduce its cost for storage by replacing lithium 

chloride with calcium chloride. The change does reduce the 

cooling capacity for the system because calcium chloride is a 

significantly weaker desiccant than lithium chloride. At typical 

high-load conditions, the switch to a 44% calcium chloride 

solution will decrease the total cooling effect by between 25% 

and 30%. While this loss is significant, the switch will reduce 

storage costs to less than $15 per ton-hour ($1.19 per MJ). 

More storage can then be part of the solar cooling system, 

which will greatly improve the utilization of the solar 

collectors. 

PERFORMANCE TESTING OF THE LOW-FLOW 

CONDITIONER 

The pre-production prototype described in this section is the 

product of a 5-year development effort that has progressively 

improved the cooling performance, pressure drop, and 

carryover suppression of low-flow liquid-desiccant 

conditioners. The 1,200-cfm (0.566-m3

/s) prototype had 42 

plates, each plate 4 feet in length, and a 3.47-ft2

 (0.323-m2) face 

area. 

Testing was conducted at the Advanced Thermal 

Conversion Lab of the National Renewable Energy 

Laboratory’s (NREL) Center for Buildings and Thermal 

Systems. This research facility accelerates development of 

high efficiency HVAC concepts by rapidly and accurately 

evaluating the thermodynamic performance and design features 

of full-scale prototypes and comparing them to the state-of-theart. The lab’s current technical specifications and unique 

capabilities are detailed in Slayzak and Ryan (2004). Airflows 

in these experiments were measured to ±2%; drybulb and 

dewpoint temperatures to ±0.3oF (±0.2oC). Uncertainties for 

the resulting grain depressions are therefore approximately 

±2 gr/lb (0.3 g/kg) for dry inlet air and ±3 gr/lb (0.4 g/kg) at the 

most humid conditions examined. Desiccant concentrations 

were monitored manually throughout testing by a temperaturecompensated hydrometer with 0.1% concentration graduations 

and were controlled to within ±0.25 concentration points of 

reported values. 

The performance of a low-flow prototype and a 

conventional packed-bed conditioner were measured at this 

facility. The prototype was tested under the following 

conditions: 

• Desiccant – commercial lithium chloride and water 

solution 

• Inlet air to conditioner drybulb temperature – 86F (30C). 

• Cooling water inlet temperature and desiccant inlet 

temperature – set to provide an outlet drybulb temperature 

from the conditioner equal to the inlet drybulb temperature 

• Cooling water flowrate – 15 gpm (56.8 l/min) 

• Desiccant flowrate – 0.5 gpm (1.9 l/min). 

An important objective in developing the low-flow 

liquid-desiccant technology was to reduce the air-side pressure 

drop through the conditioner. The data in Figure 7 show that at 

the design face velocity of 400 fpm (2.0 m/s), the pressure drop 

for the prototype is approximately one-tenth that for the 

conventional conditioner: 0.3 in. w.c. versus 3.4 in. w.c. (75 Pa 

versus 846 Pa). 

Desiccant concentration has a negligible effect on 

pressure drop at the design face velocity. At twice the design 

6
flow rate of desiccant, an increase in desiccant concentration 

from 36% to 44% produced a 15% increase in air-side pressure. 

Figure 8 compares the dehumidification provided by 

the low-flow prototype with that of a conventional packed-bed 

conditioner. (The 100 and 150 grain/pound full scales of the xaxis and y-axis in Figure 8 correspond to 14.3 and 21.4 g/kg.) 

Both units operated at a face velocity of 400 sfpm (2.0 m/s). 

The temperatures of the cooling water to the low-flow 

prototype and the desiccant to the industrial unit were adjusted 

so that at each operating point, the supply air temperature was 

86F (30C). 

As shown in Figure 8, when processing air at 115 gr/lb 

and 86F (16.4 g/kg and 30C), the low-flow prototype provided 

57 gr/lb (8.1 g/kg) of dehumidification when the inlet desiccant 

concentration was 44%. The packed-bed unit provided almost 

the same dehumidification when the inlet desiccant 

concentration was 39%. 

The packed-bed conditioner matched the 

dehumidification of the low-flow prototype when supplied with 

weaker desiccant. Although this may appear to be an 

advantage for the packed-bed conditioner, the advantage 

disappears when considering the concentration that must be 

returned from the regenerator. The low-flow prototype 

operates in a “once through” mode: the conditioner is supplied 

with concentrated desiccant from the regenerator, and the entire 

flow of the weak desiccant leaving the conditioner is sent to the 

regenerator. The packed-bed conditioner operates with high 

recirculation. The concentration of the desiccant that floods the 

packed bed is close to that of the weak desiccant that drains off 

it. In the preceding comparison, there is a 5.5-point change in 

desiccant concentration across the low-flow conditioner. The 

regenerator, therefore, must supply 44.5% desiccant to the 

packed-bed conditioner if it is to match the performance of the 

low-flow conditioner operating with 44% desiccant. 

At the 115 gr/lb (16.4 g/kg) operating point, the lowflow conditioner was supplied with cooling water at 79F 

(26.1C), and the industrial unit was supplied with desiccant at 

81F (27.2C). Assuming that the desiccant is cooled in a 67% 

effective heat exchanger, then this heat exchanger must be 

supplied with cooling water at 75F (23.9C). 

The laboratory tests illustrate the advantages offered 

by the low-flow desiccant technology. For two conditioners 

that provide identical cooling, the low-flow conditioner 

operates with weaker desiccant, higher temperature cooling 

water, and, most importantly, an air-side pressure drop that is 

about one-tenth that of the conventional flooded-bed 

conditioner and its mist eliminators. 

Additional performance data for the low-flow liquiddesiccant conditioner from tests at the Advanced Thermal 

Conversion Laboratory appear in the report by Lowenstein et 

al. (2005). 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

0 200 400 600 800 1000

Face Velocity (afpm)

Pressure Drop (inches w.c.)

Low-Flow Prototype

Industrial Flooded Packing

w/Demister

Figure 7. Comparison of the pressure-drop 

characteristics of a low-flow conditioner and a 

conventional conditioner

VERIFICATION OF THE ZERO-CARRYOVER 

OPERATION OF THE LOW-FLOW CONDITIONER 

Tests at the Advanced Thermal Conversion Lab verified that at 

design operating conditions droplets of desiccant are not 

entrained by the air flowing through the low-flow liquiddesiccant conditioner. Two approaches were used to map the 

operating envelope for the prototype: visual inspection for 

desiccant bridging between the plates and laser particle 

counting/sizing. 

Particle counting was accomplished using a single 

LasairII Model 310 laser particle counter capable of counting 

total airborne particle concentrations and grouping them in bins 

by aerodynamic diameter. The bins for this unit were 0.5-

0.7 microns, 0.7-1 microns, 1-2 microns, 2-5 microns, 5-10 

microns, and >10 microns. 

Outdoor air supplied to the prototype during testing 

was filtered through a 90% effective pleated box filter to 

establish a particle challenge that was well below the sensor’s 

saturation limit of >375,000 particles/ft3

 (1.3 x 107

particles/m3

). Two isokinetic sampling probes were positioned 

upstream and downstream from the prototype. They were 

attached via 6-foot (1.8-m) sampling tubes to the sensor so that 

inlet and outlet concentrations could be alternately measured. 

The sampling tubes were designed so that they did not trap 

particles. The pressure differential between the duct from 

which sample air was drawn and the room to which the sensor 

discharged sample air was managed to allow the sensor’s 

internal sampling fan to maintain its continuous sample flow of 

1 cfm (0.47 l/s). Each sample point was averaged over 

approximately 30 seconds. The sensor does not distinguish 

between solid particles expected in ambient air at the inlet and 

any liquid droplets entrained into the outlet airflow. The sensor 

0

25

50

75

100

30 50 70 90 110 130 150 170 190

Inlet Humidity (grains/lb)

Dehumidification (grains/lb) 

36% Concentration

40% Concentration

44% Concentration

35% Concentration

39% Concentration

42% Concentration

Solid line – low-flow conditioner

Dashed line – conventional conditioner

Figure 8 – A comparison of the dehumidification 

provided by the low-flow conditioner and a 

conventional conditioner as a function of inlet 

humidity and desiccant concentration

7
rarely indicated any particles greater than 10 microns; this is 

reasonable considering the filtration implemented, the air 

supply duct flow conditions, and the settling time for such large 

airborne particulates. 

Figure 9 shows the particle counts for steady-state 

operation at 400 sfpm (2.0 m/s) and 0.5 gpm (1.89 l/min) 

desiccant flow. (In Figure 9, the 5,000 per ft3

 that is the full 

scale of the x-axis equals 176,600 per m3

.) The outlet particle 

count closely tracks the inlet challenge. (Similar tests of a 

flooded packed bed showed that the air downstream of the mist 

eliminators contained tens to hundreds of thousands of droplets 

per cubic foot of air in the 0.5-0.7 micron size range.) Because 

negligible particle arrestance is expected within the prototype 

as a result of laminar airflow between the parallel plates, 

droplet generation is inferred to be zero. Because of the need to 

switch sampling tubes, purge them, reach steady state in the 

sensor, and then average a sample reading, the time between 

points in the figure varied from 2 to 3 minutes. 

The primary mechanism for droplet generation in the 

parallel-plate prototype is bridging of desiccant between the 

plates and subsequent shattering of the liquid bridge by the 

airflow. Other mechanisms include air bubbles in the desiccant 

feed line that sputter as they exit the distribution header onto 

the wicks and high air and/or desiccant flow rates that lead to 

thick desiccant films at the trailing edges of the plates that 

bridge the air gaps. These mechanisms, which can be visually 

detected, were not present during the particle counting tests. 

Figure 10 summarizes a rough operating envelope for 

zero desiccant carryover as determined by visual inspection. 

(In Figure 10, the 1.25-gpm and 800-fpm full scales of the xaxis and y-axis equal 4.72 l/min and 4.07 m/s.) Desiccant flow, 

desiccant concentration, and airflow were varied to see under 

what combinations the system was able to suppress carryover. 

At 44% concentration, the highest tested, and 400 afpm (2.0 

m/s) face velocity droplet generation was not observed below 

0.75 gpm (2.84 l/min). At 500 afpm (2.5 m/s), the operating 

envelope became more restricted with carryover suppressed at 

desiccant flows below 0.5 gpm (1.89 l/min). Pushing the 

conditioner to 750 afpm (3.8 m/s) required a further reduction 

to 0.25 gpm (0.95 l/min). The operating envelope for desiccant 

flow could be extended by 0.25 gpm (0.95 l/min) at all air flow 

when the concentration was reduced to 40%. A further 

0.25 gpm (0.95 l/min) increase was possible at 36% 

concentration. A 1.0-gpm (3.78 l/min) desiccant flow appeared 

to be the prototype’s limit under all operating conditions 

because at this rate, the desiccant flow was no longer 

completely contained within the wicks that cover the plate 

surfaces. Once the desiccant film is thicker than the wick, the 

fluid dynamic shear of even a low airflow can move desiccant 

to the plate trailing edges, causing bridging and carryover. 

These tests demonstrate an operating envelope for the 

low-flow conditioner that allow it to meet equipment size and 

performance requirements (e.g., nominal operation at 400 fpm 

[2.0 m/s] and 0.6 gpm [2.28 l/m] for the 1,200-cfm [0.56 m3

/s] 

prototype, while effectively suppressing droplet carryover). 

PERFORMANCE OF A LOW-FLOW LIQUIDDESICCANT REGENERATOR 

The low-flow technology that has been successfully applied to 

the liquid-desiccant conditioner will also improve the 

performance of the regenerator. In addition to eliminating 

desiccant carryover and reducing pressure drops, low-flow 

technology will increase the regenerator’s COP beyond that of 

conventional packed-bed regenerators. Furthermore, these 

efficiency improvements extend to lower regeneration 

temperatures, making the low-flow liquid-desiccant air 

conditioner attractive in distributed generation applications 

with both engines and PEM fuel cells, as well as solar thermal 

collectors. 

The 21-plate model of the low-flow regenerator that 

is shown in Figure 5 was operated under controlled conditions 

at NREL’s Advanced Thermal Conversion Lab. Its 

performance was mapped over a range of desiccant 

concentrations, operating temperatures, air velocities, and 

water flow rates. 

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 2 4 6 810 12

Chronology

Particles/ft3

Inlet

Outlet

0.5-0.7 microns

0.7-1 microns

1-2 microns

2-5 microns

5-10 microns

Figure 9 – Particle concentrations at inlet and outlet of lowflow liquid-desiccant conditioner 

0.00

0.25

0.50

0.75

1.00

1.25

300 400 500 600 700 800

Face Velocity (afpm)

Desiccant Flow Rate (gpm)

36% LiCl Conc

40% LiCl Conc

44% LiCl Conc

Figure 10 – Operating envelope for no carryover based 

on visual inspection

8
Figure 11 shows the water removal (WR) and the COP 

of the low-flow regenerator when concentrating a solution of 

lithium chloride from 36% to 40%. The air velocity at the face 

of the regenerator is 100 sfpm (0.51 m/s), and inlet air 

conditions are 86F, 0.01649 lb/lb and 12.1 psi (30C, 16.5g/kg, 

and 83.4 kPa). The test was conducted to simulate operation 

with an interchange heat exchanger that had an effectiveness 

between 65% and 80%. Also shown on this figure are the 

predictions of AILR’s computer model for the regenerator. 

The measured COP for the regenerator ranged from 

0.62 with 160F (71.1C) hot water to 0.73 with 200F (93.3C) 

hot water. Both the measured water removal rate, and the COP 

agreed well with the computer predictions. 

The operation of the regenerator with an air-to-air heat 

exchanger (AAHX) that recovers thermal energy from the 

regenerator exhaust air to preheat the incoming scavenging air 

was simulated by increasing the inlet air temperature to the 

regenerator without changing its humidity. As shown in Figure 

12, these tests show that a 50% effective AAHX would 

increase the regenerators COP from 0.73 to 0.79 when 

operating with 200F (93.3C) hot water and a 100-sfpm (0.51-

m/s) face velocity. (The 30 lb/hr that is the full scale for the xaxis in Figure 12 equals 13.6 kg/hr.) The data in this figure 

also show the effect of face velocities of 100, 130, and 160 

sfpm (0.51, 0.66, and 0.81 m/s) on both the rate of water 

removal (MRR, which is the same as the parameter WR that 

was used earlier) and COP. 

THE FIELD OPERATION OF A 6,000-CFM ROOFTOP 

LIQUID-DESICCANT AIR CONDITIONER 

Figure 13 shows a rooftop liquid-desiccant air conditioner that 

is designed to cool and dry 6,000-cfm (2.83 m3

/s) of ventilation 

air. The air conditioner includes a low-flow conditioner and 

regenerator. It also includes a 400,000-Btu/h (117.2-kW) gasfired hot-water heater that meets the thermal requirements of 

the regenerator at 250 lb/h (113.6 kg/h) of water removal. In 

solar applications, this hot-water heater may be retained as a 

back-up to the solar collectors or it may be eliminated. A 25-

ton (87.9-kW) cooling tower provides 75 gpm (4.73 l/s) of 

cooling water to the conditioner. 

The field operation of the rooftop liquid-desiccant air 

conditioner began in late September 2005 and continued for 4 

weeks at which time ambient conditions in New Jersey became 

too cold and dry to permit meaningful testing. During the test, 

the air conditioner operated completely under automatic 

control, including PID loops for ventilation airflow, boiler 

temperature, and desiccant concentration. The controller also 

sequenced all startup and shutdown procedures for the 

conditioner, regenerator, boiler and cooling tower. 

The liquid-desiccant air conditioner operated 

throughout the test with a one-half scale regenerator. When the 

air conditioner first operated in the fall of 2004, it included a 

first-generation regenerator that eventually proved not 

sufficiently reliable for a commercial product. The hangingplate regenerator that was described in an earlier section was 

developed to replace the older design. However, because the 

new regenerator was not ready until the fall of 2005, when 

cooling loads would be well below peak summer values, the 

process of retrofitting the air conditioner with the new 

regenerator was simplified by installing a unit with one-half the 

required water-removal capacity. 

 The highest latent cooling during the test, 141 lb/h 

(64.1 kg/h) of water removal, occurred on October 5. Table 1 

summarizes the air conditioner’s performance for a 43-minute 

period on that day when ambient conditions averaged 77.7F 

and 0.01229 lb/lb (25.4C and 12.29 g/kg). 

Performance With Heat Recuperation

15

20

25

30

0% 20% 40% 60% 80% 100%

AAHX Recuperator Effectiveness

MRR (lbm/hr)

0.70

0.80

0.90

1.00

COPThermal

MRR - 100 SFPM MRR - 130 SFPM MRR - 160 SFPM

COP - 100 SFPM COP - 130 SFPM COP - 160 SFPM

Figure 12 – Performance of the low-flow 

regenerator with heat recuperation 

0

5

10

15

20

25

150 160 170 180 190 200 210

Inlet Water Temperature (F)

Water Removal Rate (lb/h)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

COP

30

0.70

0.80

WR - Exp't 

WR - Model

COP - Exp't

COP - Model

Figure 11 – Water removal and COP of a low-flow 

regenerator 

Figure 13 – Prototype of a 6,000-cfm rooftop liquiddesiccant air conditioner 9
During this period, the latent and total cooling 

supplied by the conditioner were within 3% of the values 

predicted by the computer models that were used to design the 

unit. 

Both the efficiency of the boiler and the effectiveness 

of the interchange heat exchanger (IHX) were lower than 

expected. A possible cause of the IHX’s poor performance 

may have been that it was not completely purged of air. A new 

design for the IHX will be installed in the rooftop air 

conditioner before tests begin in 2006, and better 

performance is expected. 

The nominal efficiency of the boiler is 79% at full 

firing. During the period reported in Table 1, the boiler 

operated at about 50% of full firing. It is probable that at partload firing, the air-to-fuel ratio of the combustor is too lean, 

which is degrading efficiency. 

 The COP of the regenerator during the test period was 

0.699. This good COP was achieved despite the poor 

performance of the IHX. Also, the regenerator did not use an 

air-to-air heat exchanger to preheat the scavenging air using the 

warm, humid exhaust from the regenerator. 

 At full load, the parasitic power requirements for the 

roof-top air conditioner are 

 cooling tower fan 1,600 W 

 coolant pump 1,100 W 

 strong desiccant pump 200 W 

 weak desiccant pump 200 W 

 hot-water pump 700 W 

 process fan 2,200 W 

 (at 0.5 in. w.c. external pressure). 

Table 1. CONCLUSION 

Date 5 - October 

T Ambient F 77.7 

W Ambient lb/lb-d.a. 0.01229 

T Supply F 78.9 

W Supply lb/lb-d.a. 0.00572 

C Des Conditioner Inlet lb /lb 0.403 

C Des Conditioner Outlet lb /lb 0.377 

Conditioner Des Flow gpm 3.19 

Conditioner Air Flow cfm 4772 

Q Air Total Btu/h 143,190 

Q Air Latent Btu/h 149,574 

Q Coolant Btu/h 170,347 

Water Removal lb/h 141.2 

T Hot Water Regen Inlet F 210.1 

Regenerator Des Flow gpm 3.15 

Regenerator Thermal COP 0.699 

Boiler Efficiency 0.688 

IHX Effectiveness 0.557 

A new generation of liquid-desiccant cooling systems is now 

being commercialized that will greatly expand the market for 

solar cooling. The distinguishing characteristic of the new 

technology is a desiccant flooding rate that is a factor of 10 to 

20 lower than the rates now used in conventional packed-bed 

systems. 

Compared to the technology now in use, the low-flow 

liquid-desiccant air conditioner will: 

• have much lower pressure drops 

• be more compact 

• produce a greater cooling effect (e.g., lower cfm/ton) 

• more deeply dry the process air, and 

• have a higher COP. 

Perhaps most importantly, both the low-flow conditioner and 

regenerator will operate without the entrainment of desiccant 

droplets by the air streams (i.e., zero desiccant carryover, which 

greatly reduces maintenance). 

The advantages of low-flow liquid-desiccant 

technology have been demonstrated in laboratory and field 

operation. In a controlled laboratory test, a low-flow 

conditioner matched the dehumidification provided by a 

conventional packed-bed conditioner, but with less than onetenth the air-side pressure drop. 

The low-flow technology used by the new liquiddesiccant conditioner was proven effective at suppressing 

droplet carryover, without the use of separate droplet filters or 

demisters, over a wide range of operating conditions. For 

operation with a 44% solution of lithium chloride, a face 

velocity of 400 afpm (2.0 m/s), and a total air flow of 

1,388 acfm (0.656 m3

/s) droplet carryover was suppressed for 

all desiccant flows less than about 0.75 gpm (2.84 l/min). 

Tests of a scavenging-air regenerator that uses the 

low-flow technology showed that both water removal and COP 

were close to the predictions of the computer model that was 

used to design the regenerator. This regenerator could 

effectively run on heat provided by either glazed, flat-plate 

collectors, or evacuated-tube collectors. With an air-to-air heat 

exchanger that recovers thermal energy from the regenerator’s 

exhaust air, the regenerator will have a COP of 0.79 when 

concentrating a solution of lithium chloride from 36% to 40% 

and supplied with hot fluid at 200F (93.3C). 

Although not unique to the low-flow technology, the 

storage of concentrated liquid desiccant provides an effective 

means to match cooling loads with the availability of solar 

energy. The relatively low cost for desiccant storage, 

particularly systems that use calcium chloride, will ensure a 

high utilization of the thermal energy provided by the 

collectors, thereby improving the competitiveness the solar 

cooling system. 

ACKNOWLEDGEMENTS 

The authors wish to thank the U.S. Department of Energy’s 

Distributed Energy Program, which is headed by Ms. Patricia 

Hoffman. The support of this program was critical to the 

successful development of this technology for use in natural 

gas fired and distributed generator waste heat applications.

10
REFERENCES 

Coellner, James, “Energymaster—Desiccant Cooling in the 

Marketplace,” Proceedings of the Desiccant Cooling and 

Dehumidification Opportunities for Buildings Workshop, 

Chattanooga, TN; June 1986. 

Jilier Science and Technology, Product Brochure, Zhejiang, 

China, 2005. 

Kessling, Laevemann, and Peltzer, “Energy Storage for Solar 

Desiccant Cooling Systems,” Solar Energy, Vol. 64, Nos. 4-

6, pp 209-221, 1998. 

L-DCS Technology Website, http://www.l-dcs.com/ 

applications/solar.html, 2006. 

Löf, “House Heating and Cooling with Solar Energy,” Solar 

Energy Research, University of Wisconsin Press, Madison, 

pp. 33-46, 1955. 

Lowenstein, A., Slayzak, S., Kozubal, E., and Ryan, J., “A 

Low-Flow, Zero Carryover Liquid Desiccant Conditioner,” 

International Sorption Heat Pump Conference Proceedings, 

Interlocken, CO, 2005. 

Robison, H., “Operational Experience with a Liquid Desiccant 

Heating and Cooling System,” 18th IECEC, Orlando, FL, 

1983. 

Schlepp and Schultz, “High Performance Solar Desiccant 

Cooling System: Performance Evaluations and Research 

Recommendations,” SERI/TR-252-2497, 1984. 

Slayzak, S. and Ryan, J., NREL’s Advanced Thermal 

Conversion Laboratory,” NREL/BR-550-34928, 2004. 

11
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4. TITLE AND SUBTITLE

A Zero Carryover Liquid-Desiccant Air Conditioner for Solar 

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14. ABSTRACT (Maximum 200 Words)

A novel liquid-desiccant air conditioner that dries and cools building supply air will transform the use of direct-contact 

liquid-desiccant systems in HVAC applications, improving comfort, air quality, and providing energy-efficient humidity 

control. 

15. SUBJECT TERMS

Dehumidifier; Liquid Desiccant; Air Conditioner; HVAC 

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