A Liquid Desiccant System for Solar Cooling and Dehumidification

A Liquid Desiccant System for Solar Cooling and Dehumidification K. Gommed G. Grossman Faculty of Mechanical Engineering, Technion, Israel Institute of Technology, Haifa 32000, Israel The growing demand for air conditioning, particularly in hot and humid climates has caused a significant increase in demand for energy resources. A promising solar technology with potential to alleviate the problem is an open absorption system, where humidity is absorbed directly from the air to be treated by direct contact with the absorbent. The absorbent is then regenerated, again in direct contact with an external air stream, at relatively low temperatures of the heat source. The paper describes a study of a liquid desiccant cooling system designed to air-condition a group of offices on the top floor of a building in the Mediterranean city of Haifa, Israel. The system is capable of using as its source of power low-grade solar heat, of the type obtainable from low-cost flat plate collectors, and has a potential to provide both cooling and dehumidification in variable ratios, as required by the load. Several cycle variations have been considered, corresponding to different design options. A parametric study shows that entrance conditions of the ambient air significantly affect the heat and mass transfer occurring during the dehumidification process. The temperatures and flow rates of the heating and cooling water and the flow rates of solution through the dehumidifier and regenerator affect the humidity of the supply air delivered to the conditioned space, and show an optimum in certain cases. DOI: 10.1115/1.1690284 Keywords: Dehumidifier, Evaporator, Regenerator, Absorber, Cooling, Dehumidification, Air Conditioning Contributed by the Solar Energy Division of THE AMERICAN SOCIETY OF ME- CHANICAL ENGINEERS for publication in the ASME JOURNAL OF SOLAR ENERGY ENGINEERING. Manuscript received by the ASME Solar Energy Division May 2003; final revision, December 2003. Associate Editor: M. Krarti. Introduction The growing demand for air conditioning, particularly in hot and humid climates such as in Mediterranean countries, has caused a significant increase in demand for energy resources. Electric utilities have their peak loads in hot summer days, and are often barely capable of meeting the demand, with brown-out situations. With suitable technology, solar cooling can help alleviate, if not eliminate the problem. It is a good application for solar energy due to the fact that the greatest demand for air conditioning occurs during times of highest insolation 1,2. Conventional closed-cycle absorption chillers require heat source temperatures that are significantly higher than the temperatures of corresponding heat sinks. Thus, they have to be operated with high-grade heat extracted from natural gas, steam, concentrating solar collectors and the like. A promising alternative is the use of an open absorption system, where humidity is absorbed directly from the air to be treated by direct contact with the absorbent. The absorbent is then regenerated, again in direct contact with an external air stream, at relatively low temperatures of the heat source. The entire operation takes place at atmospheric pressure, thus eliminating vacuum vessels and the like. Earlier work has been conducted on liquid desiccant systems for cooling and dehumidification, using solar energy for regeneration. In several cases, direct regeneration of the solution in the sun has been considered, using a special type of collector. Wood and co-workers at Arizona State University 3 6 have constructed and tested a full-scale liquid desiccant system, employing aqueous LiCl as well as an aqueous mixture of LiCl and CaCl 2 as liquid sorbents. Kessling 7 studied a LiCl-water system operating at a large concentration difference between the strong and weak desiccant, to facilitate cold storage by means of a regenerated solution. Kababaev et al. 8 10 report on the operation of a large scale air-conditioning system employing LiCl-water, where both direct regeneration in open collectors and cold storage in the form of regenerated solution have been attempted. Noteworthy are also the liquid desiccant system analyses of Collier 11, Haim et al. 12, and Gandihdasan and Al-Farayedhi 13. This project is concerned with an open absorption solar air conditioning system based on controlled evaporation and dehumidification using liquid desiccants. It is designed to air-condition a group of offices in a typical building and will serve as a prototype for larger systems, to be constructed at a later stage. The system is capable of using as its source of power low-grade solar heat, of the type obtainable from low-cost flat plate collectors and has the potential to provide both cooling and dehumidification in variable ratios, as required by the load. The objective of this work has been to perform an analysis in order to choose the best potential configuration of the solar air conditioning system. Desiccant systems are quite efficient in dealing with the latent load, but considerably less so with regard to the sensible load. A good solution is for the solar-powered desiccant cooling system to deal with the latent heat while an electricpowered heat pump deals with the remaining sensible heat. Under such conditions, the electric heat pump can operate at evaporator temperatures considerably higher than normal as it is not required to cool the air below its dew point in order to dehumidify it, and hence with greater efficiency. The significance of this work lies in the potential to provide solar-powered cooling, dehumidification and air conditioning for residential or commercial applications. The required low-grade heat can be obtained from low-cost flat plate solar collectors, which do not require sun tracking and in some cases can be incorporated in the roof structure of the building. The use of hygroscopic salts in direct contact with moist air provides an attractive alternative to conventional cooling systems employing ozone- Journal of Solar Energy Engineering Copyright 2004 by ASME AUGUST 2004, Vol. 126 Õ 879

depleting CFCs. The possibility of using low-grade energy goes a long way toward the elimination of pollution and utilizing renewable and environmentally-safe energy sources. Project Description The system under consideration is designed to air-condition a group of offices total floor area of 35 m 2 ) on the top floor of the Energy Research Center building at the Technion Israel Institute of Technology Haifa, Israel. The city of Haifa is an ideal site to test such a system. Located on the Mediterranean coast at 33 degrees north latitude, it has the typical climate of Mediterranean cities. Outside summer conditions typical for design are 30 C and 70% relative humidity. Room design conditions have been selected at 24 C and 50% relative humidity. A load calculation for the three typically staffed and equipped offices shows about 4.2 kw with a room sensible heat factor RSHF of 0.92. At 30 cfm (51 m 3 /hr) of fresh air per occupant ASHRAE air quality recommendations, the additional fresh air associated load is about 3.0 kw, most of which 2.4 kw is latent. Thus, the total cooling capacity required is 7.2 kw, with a grand sensible heat factor GSHF of 0.62. The total supply air circulation needed based on 12 air changes per hour is 0.4 kg/sec 720 cfm. The desired conditions of the supply air are 14.7 C and 86% relative humidity. In considering the liquid desiccant system for performing the air conditioning task, two cooling options are available. Under option A, ambient air mixed with return air is dried in the dehumidifier absorber, to be described in detail in the next section. Leaving the dehumidifier, the air is cooled first in a heat exchanger by cooling water or exhaust air, then cooled further in an auxiliary chiller e.g. electrically-powered vapor compression heat pump and still further in an evaporative cooler before being supplied to the conditioned space. In this option, the desiccant part of the system treats the total supply air the return air together with the fresh air and deals with the latent heat together with part of the sensible heat. The auxiliary chiller deals with the remaining part of the sensible load. In option B, the fresh make-up air, accounting for most of the latent load, is treated separately by the desiccant system while an auxiliary heat pump deals with the sensible load of the rest of the air. Under this option, the fresh air is dried in the dehumidifier, then cooled by heat exchange with the exhaust air in an air-to air heat exchanger, and supplied to the conditioned space. Calculations show that option A has a thermodynamic advantage only when exercising the option of employing an auxiliary chiller with an evaporator temperature considerably higher than normal not requiring to cool the air below its dew point for dehumidification and hence operating at a higher efficiency. Otherwise, option B is preferable, providing a simpler way for controlling the complete system and for incorporating the auxiliary heat pump. Option B also requires considerably less pumping and fan power in the desiccant system than option A. In the final system design, Option B of handling only the fresh air part by the desiccant system was chosen. The desiccant solution is regenerated by solar heat, supplied by flat-plate solar collectors of conventional design, of the type widely employed in Israel for domestic water heating, but with better than average quality to enable higher efficiency at high temperatures. Solar-heated water serves as the heat carrier. The option of heating the regenerated solution directly, by exposing it to the sun and to ambient air simultaneously, had been explored but found to be somewhat problematic. The advantages of the current option are simpler construction technology, simpler storage capability, dirt control and simpler ability for using an air-toair heat exchanger for heat recovery. With the total latent heat load of 2.75 kw, the solar energy demand was calculated to be 4.77 kw. Assuming ten hours of continuous operation daily, and taking a small safety factor, the solar collector area was selected at 20 m 2. Solution storage in the amount of 120 liters of LiCl solution at 43% concentration and a 1000 liter hot water tank added to the system make it possible to operate for a total of four hours with no insolation a typical situation in the summer during the morning hours. Description of the Liquid Desiccant System The liquid desiccant system is designed to serve as an opencycle absorption system that can operate with low-grade solar heat. A detailed description of the desiccant cycle, design considerations that led to the various choices and an experimental investigation of this system is given elsewhere 14. A schematic description of the final design version of the system is given in Fig. 1. The system consists of six major components: an air dehumidifier or absorber, a solution regenerator or desorber, two water-tosolution heat exchangers, a solution-to-solution heat exchanger, and an air-to-air heat exchanger. Arabic numerals indicate working fluids state points at specific locations. Air flow is represented by thick solid lines, solution flow by thin solid lines and water flow by dashed lines. The dehumidifier absorber consists of a packed tower and operates in an adiabatic mode. Ambient air at state 14 entering the bottom of the absorber packed section is brought into contact with a concentrated absorbent solution entering the unit at state 11. Water vapor is removed from the air stream by being absorbed into the solution stream. The dehumidified warm air leaving the absorber at state 15 passes through the blower and leaves the system toward the air-conditioned space for some further treatment under options A or B see the previous section at state 16. The blower controls the flow of air, while raising its temperature slightly. Solution is pumped from the absorber pool at the bottom of the tower into the plate heat exchanger state 10, where it is cooled by water from a cooling tower. The solution leaving the heat exchanger state 11 then proceeds to the distributor at the top of the packing, from where it trickles down in counter-flow to the air stream and collects in the pool. A controlled solution stream is transferred from the absorber pool to the regenerator, as shown state 10c. The return pumped stream from the regenerator 1c goes directly into the pool. As evident, the regenerator desorber device is very similar to the dehumidifier, and so are the flow system and associated components. The solution is heated in the liquid-to-liquid heat exchanger by solar-heated water states 3-4. Ambient air at state 5 is pre-heated in the air-to-air heat exchanger by recovering heat from the exhaust air leaving the desorber state 8. After preheating, the air stream state 6 enters the desorber where it serves to re-concentrate the solution state 2. The exhaust air leaves the desorber state 7, passing through the blower, then pre-heats the entering air stream and is rejected to the environment. The solution-to-solution heat exchanger facilitates pre-heating of the weak solution leaving the dehumidifier states 10c to 10h and recovers heat from the hot strong solution leaving the regenerator states 1h to 1c. The above brief description of the system already reveals a number of advantages of this system over conventional absorption heat pump cycles: 1 The number of main components is reduced by one by transferring condensation of the refrigerant from a condenser to the environment. 2 Capital-intensive pressure-sealed units are avoided as the whole system operates at atmospheric pressure. 3 The amount of refrigerant water evaporated in the regenerator is independent of an evaporator, providing greater flexibility. 4 Efficient utilization of very low heat source temperatures is possible. In the overall setup, the liquid desiccant system is connected in a flow arrangement allowing storage of concentrated solution and a capability to work in three different modes. The first is a manual mode used for testing individual components of the system. The other two modes are automatic, as may be selected by the user. One automatic mode is for full operation of the system FOP and the second is for regeneration only REG. In the automatic FOP mode, all system components operate, including the solution stor- 880 Õ Vol. 126, AUGUST 2004 Transactions of the ASME

Fig. 1 Schematic description of the open-cycle desiccant system age circuit, if required. In this case, the absorber solution pump may supply the dehumidifier with solution from both the absorber pool and from the solution storage tank, in parallel. Thus, dehumidification can continue independent of regeneration. If the solar collectors cannot supply water at sufficiently high temperature, or if the concentration of the solution in the storage tank and/or the regenerator pool rises above a set limit, the regeneration side of the system will shut down for a certain time. In the REG mode, only the regenerator desorber side of the system operates. The system shuts down automatically when the concentration of the solution in the storage tank reaches a certain high value or when the temperature of the hot water drops below a certain limit. At the end of days of high insolation, when a large amount of solar heat has been collected, the user can set the system to operate in the automatic REG mode before leaving the site. Practical aspects pertaining to the design, construction and operation have been discussed in the paper by Gommed, Grossman and Ziegler 14, which describes an experimental investigation of the liquid desiccant system. One concern in this type of opencycle system is the prevention of solution carryover. Our experiments have shown that the LiCl solution should not be sprayed, but rather dripped over the packing, with the drops large enough not to be carried away by the air stream. In addition, mist eliminators were incorporated in each of the packed towers, above the solution distributors, as shown in Fig. 1. These two measures were found to eliminate carryover almost completely. It should be noted that LiCl, while somewhat corrosive, is not a toxic material, and does not pose any health hazards; in fact, it possesses bacteriostatic qualities. Anther issue is the cost of such a system; while still in the proof-of-concept stage, it is already clear that the ultimate cost will be dominated by the solar part collector and storage and the ability to employ low-cost flat plate collectors could make this system cost-competitive with other solar air conditioning systems. Parametric Study The lack of reliable data on heat and mass transfer coefficients in the absorption and desorption processes has been a serious impediment in earlier simulation studies to obtaining a good prediction of the system s performance. Particularly critical are the performances of the dehumidifier absorber and regenerator desorber, forming the two key components of the liquid desiccant system. Such data has now been obtained through the experimental work described by Gommed, Grossman and Ziegler, 14. This makes it possible to conduct an extensive parametric study of the overall system behavior. The computer code ABSIM 15,16, developed specifically for simulation of absorption systems in flexible and modular form, was employed in this study. The modular structure of ABSIM makes it possible to simulate a variety of absorption systems in varying cycle configurations and with different working fluids. The code is based on unit subroutines containing the governing equations for the system s components. The components are linked together by a main program, which calls the unit subroutines according to the user s specifications to form the complete cycle. When all the equations for the entire cycle have been established, a mathematical solver routine is employed to solve them simultaneously. Property subroutines contained in a separate database serve to provide thermodynamic properties of the differ- Journal of Solar Energy Engineering AUGUST 2004, Vol. 126 Õ 881

Table 1 System parameters for reference case Room air conditions: Temperature, T R 24 C Humidity ratio, R 9.5 g/kg Ambient air conditions: Temperature, T o 30 C Humidity ratio, o 19.0 g/kg Heating water temperature, T HW 65 C Heating water flow rate, F HW 0.25 kg/sec Cooling water temperature, T CW 29.5 C Cooling water flow rate, F CW 0.25 kg/sec Air flow rate through desorber, F DA 0.16 kg/sec Air flow rate through absorber, F AA 0.16 kg/sec Desorber solution pump flow rate, F DS 0.5 kg/sec Absorber solution pump flow rate, F AS 0.5 kg/sec Heat transfer coefficients: desorber heat exchanger, UA DS 1.3 kw/ C absorber heat exchanger, UA AS 1.3 kw/ C solution-solution heat exchanger, UA DAS 1.3 kw/ C desorber air-to-air heat exchanger, UA DA 0.5 kw/ C absorber air-to-air heat exchanger, UA AA 0.5 kw/ C Mass transfer coefficients: desorber solution-interface, KA DS 0.36 kg/sec desorber air-interface, KA DA 1.00 kg/sec absorber solution-interface, KA AS 0.36 kg/sec absorber air-interface, KA AA 1.00 kg/sec ent working fluids. The property subroutine for LiCl-water, the particular working fluid employed in this study, contains correlations derived from the work of Uemura 17. The computer simulation yields the temperature and humidity of the air at the system outlets as well as heat duties of the various system components as functions of the specified conditions at inlets and other operating conditions. The behavior is quite complex and depends on many input parameters. In conducting the simulation, a design reference case has been selected, and the values of the relevant parameters were varied around it. The values of the various parameters influencing the problem for the reference case are listed in Table 1. When conducting the following parametric study, only one parameter from those listed in Table 1 was varied at a time, while all others remained fixed at their design value. The reference condition is indicated on each curve by a dot. Figure 2 describes the humidity ratio water content of the supply air to the conditioned space, which has been dehumidified by the desiccant system state 16 in Fig. 1, as a function of the inlet conditions of the ambient air supplied to the dehumidifier state 14 in Fig. 1. Three curves are shown representing the temperature, humidity ratio and flow rate of the ambient air. As expected, the absorption rate dehumidification performance of the desiccant system increases as each of these quantities decreases. The slope of the flow rate curve tends to become flat at the higher air flow rates. A similar behavior is exhibited by the regenerator heat duty as a function of the flow rate of ambient air being dehumidified not shown here. This behavior is due to the limited heat and mass transfer capacity area and coefficient, causing the driving force to diminish at the high flow rates. A heat duty of 6.13 kw is found to be required for regeneration at the reference condition, where the flow rate of ambient air supplied is 0.16 kg/sec. Figure 2 further indicates that the water content and flow rate of the ambient air supplied to the absorber have a more significant effect on the system performance than the temperature. Figure 3 describes the effect of the temperature of the hot water produced by the solar collectors on the strong solution concentration reached at the regenerator outlet. Clearly, the higher the heating temperature-the higher the solution concentration. At a hot water temperature of 70 C the solution concentration is about 43%, which is the preferred working concentration. It is high enough to produce a good degree of dehumidification in the absorber, while staying safely away from the crystallization limit of the solution. Fig. 2 Humidity ratio of supply air as function of inlet conditions of ambient air to dehumidifier Figure 4 describes the humidity ratio water content of the supply air to the conditioned space as a function of the conditions of the heating and cooling water supplied to the two water/ solution heat exchangers state points 3 and 12, respectively, in Fig. 1. Four curves are shown representing the heating water and cooling water temperature and flow rate. It is evident that the higher the heating water temperature and the lower the cooling water temperature-the better the dehumidification. A cooling water temperature of 29.5 C, selected for the reference condition, is a high-probability upper limit for the weather conditions of Haifa. During many summer days, lower cooling water temperatures can be produced by the cooling tower and therefore better performance. The humidity ratio tends toward a constant value as the heating and cooling water flow rates increase. This is again due to the limited heat transfer capacity in the solution/water heat exchangers, resulting in diminishing driving force at the high water Fig. 3 Effect of heating water temperature on strong solution concentration at regenerator outlet 882 Õ Vol. 126, AUGUST 2004 Transactions of the ASME

Fig. 6 Humidity ratio of supply air as a function of solution flow rate in the dehumidifier and split ratio in the regenerator Fig. 4 Humidity ratio of supply air as a function of heating and cooling water conditions flow rates. Keeping pumping power in mind, it is preferable to select the heating and cooling water flow rates in the range between 0.2 to 0.4 kg/sec 0.25 kg/sec for the reference condition. Figure 5 describes the effect of desiccant solution flow rate in the regenerator on several performance parameters. Three curves are shown representing the solution concentration at the desorber outlet, the supply air humidity ratio and the desorber heat duty. Here an optimum humidity ratio is reached when the solution flow rate is in the range between 0.4 to 0.6 kg/sec 0.5 kg/sec is the reference condition. The explanation for this is as follows: When the solution flow rate in the regenerator is low, the flow rate of strong solution reaching the absorber is low too. Then, the resulting low solution concentration in the absorber causes a reduction in absorber performance, and leads to higher water content in the supply air. Increasing solution flow rate in the regenerator, on the other hand, increases the system circulation losses due to the transfer of solution from the hot desorber to the cold absorber through a non-ideal solution-to-solution heat exchanger. The same considerations explain the existence of a maximum in the solution concentration at the desorber outlet: The reduction of the concentration from the maximum value at high solution flow rates is due to increased circulation losses. At low flow rates, a low equilibrium temperature of the solution during adiabatic regeneration leads to low solution concentrations. The regenerator heat duty curve shows a rapid increase in slope at low flow rates due to intensive dehumidification in the absorber. Beyond a solution flow rate of 0.4 kg/sec, the desorber heat duty increases more gradually due to increasing circulation losses. Figure 6 describes the humidity ratio of the supply air to the conditioned space as a function of two parameters: The split ratio in the desorber and the solution flow rate in the absorber. At the desorber outlet the solution is split into two streams, as shown in Fig. 1. The main stream state point 1 flows to the desorber inlet at the top, passing through the hot water heat exchanger. The second, smaller stream state point 1h flows to the absorber, passing through the solution-to-solution heat exchanger. The Split ratio is defined as the flow rate of the main stream to the total desorber flow rate. Figure 6 shows a seemingly unexpected behavior of increasing water content in the supply air with increasing desiccant solution flow rate in the absorber. A high solution flow rate has the advan- Fig. 5 Effect of desiccant solution flow rate in the regenerator on supply air humidity, solution concentration at regenerator outlet and regenerator heat duty Journal of Solar Energy Engineering AUGUST 2004, Vol. 126 Õ 883

tage of reduced sensitivity to the temperature increase due to the heat of absorption released during the dehumidification process, together with good wetting of the transfer surfaces. However, lowering the temperature of this solution stream in the heat exchanger by the cooling water becomes increasingly difficult with increasing solution flow rate. A higher solution temperature at the absorber inlet leads to higher equilibrium water content of the supply air. Lowering the split ratio increases the amount of strong solution transferred from the desorber to absorber. On one hand this leads to increased solution concentration in the absorber and hence to improved dehumidification. On the other hand, increasing solution flow rate between desorber and absorber increases the associated circulation losses. These two mechanisms working against each other are responsible for the behavior shown in Fig. 6. Increased dehumidification together with increased circulation losses related to a higher split ratio, both lead to an increased desorber heat duty. Figure 7 describes the system s coefficient of performance COP as a function of the heating water temperature for three different cooling water temperatures. The COP is defined here as the ratio of the useful dehumidification energy to the heat spent in the desorber. The useful dehumidification energy is the product of the change in humidity ratio of the process air, times the mass flow rate of the process air, times the latent heat of evaporation of the water. It was mentioned already in connection with Fig. 3 that an operating temperature of 70 C yields regenerated solution at 43%, which gives it good hygroscopic behavior while staying safely away from crystallization. Figure 7 indicates that for steady state operation at higher temperatures the COP decreases; this is due to increased desorber heat duty, resulting from increased circulation losses associated with the imperfect heat transfer between the weak and strong solution streams and mixing losses associated with the increased solution concentration. On the other hand, at very low heating temperatures, close to that of the heat sink, the system continues to operate and the COP is high, approaching unity. However, under such conditions the dehumidification process is very weak and the change in humidity ratio of the process air is extremely low. These simulation results are obtained assuming steady state operation; in practice, one can operate for short periods of time in batch mode, without reaching steady state, or in regeneration mode where the regenerator operates alone, without circulation to the absorber. Under these conditions, the circulation and mixing losses can be reduced and a high overall COP around 0.8 can be achieved with high regeneration temperatures, when available. In fact, the regeneration mode is preferred and often used at times of high insolation, to concentrate and store regenerated solution for operation at times of no sun. Results of measurements while operating in this mode, conducted during a five-months monitoring period over the summer of 2003, will be reported in a later paper 18. Fig. 7 Coefficient of performance COP as a function of heating water temperature for three different cooling water temperatures refä29.5 C, per Table 1 Conclusion Several cycle configurations of the desiccant cooling system have been considered. Option B was found to be the most suitable for the current application, as it utilizes best the strong points of the desiccant system. Under this option, the solar powered desiccant system deals with the latent heat load, due mainly to the fresh air, while an auxiliary electric-powered heat pump deals with the remaining sensible load. A parametric study was conducted to investigate the effect of the various design parameters on performance. It was shown that entrance conditions of the ambient air humidity and flow rate significantly affect the heat and mass transfer occurring during the dehumidification process. The effect of the ambient air temperature is rather low. The temperatures and flow rates of the heating and cooling water and the flow rates of solution through the dehumidifier and regenerator affect the humidity of the supply air delivered to the conditioned space, and show an optimum in certain cases. The computer simulation supported by experiments has affirmed the system s capability to produce a high degree of dehumidification. The system designed and simulated for the current application contains a margin for future applicability to other system loads or configurations. Acknowledgment The support provided for this work under EU contract NNE5-1999-00531 ASODECO is gratefully acknowledged. References 1 Grossman, G., and Johannsen, A., 1981, Solar Cooling and Air Conditioning, Prog. Energy Combust. Sci., 7, pp. 185 228. 2 Grossman, G., 2002, Solar-powered Systems for Cooling, Dehumidification and Air-conditioning, Sol. Energy, 72, pp. 53 62. 3 Ameel, T. A., Gee, K. G., and Wood, B. D., 1995, Performance Predictions of Alternative, Low Cost Absorbents for Open-Cycle Absorption Solar Cooling, Sol. Energy, 54, pp. 65 73. 4 Nelson, D. J., and Wood, B. D., 1989, Combined Heat and Mass Transfer Natural Convection Between Vertical Parallel Plates, Int. J. Heat Mass Transfer, 32, pp. 1779 1787. 5 Nelson, D. J., and Wood, B. D., 1989, Fully Developed Combined Heat and Mass Transfer Natural Convection Between Parallel Plates with Asymmetric Boundary, Int. J. Heat Mass Transfer, 32, pp. 1789 1792. 6 Nelson, D. J., and Wood, B. D., 1989, Evaporation Rate Model for a Natural Convection Glazed Collector/Regenerator, ASME J. Sol. Energy Eng., 112, pp. 51 57. 7 Kessling, W., 1997, Luftentfeuchtung und Energiespeicherung mit Salzlösungen in offenen Systemen, Fortschritt-Bericht 509, VDI Verlag, Düsseldorf, Germany. 8 Kakabaev, A., Khandurdyev, A., Klyshchaeva, O., and Kurbanov, N., 1976, A Large Scale Solar Air-Conditioning Pilot Plant and its Test Results, Int. Chem. Eng., 16, pp. 60 64. 9 Kakabaev, A., Klyshchaeva, O., Khandurdyev, A., and Kurbanov, N., 1977, Experience in Operation a Solar Absorption Cooling Plant with Open Solution Regenerator, Geliotekhika, 13, pp. 73 76. 10 Kakabaev, A., Kurbanov, N., Klyshchaeva, O., and Redzhepov, G., 1981, Storage of Cold in an Open-cycle Solar Absorption Cooling System, Geliotekhika, 17, pp. 64 66. 11 Collier, R. K., 1979, The Analysis and Simulation of an Open Cycle Absorption Refrigeration System, Sol. Energy, 23, pp. 357 366. 12 Haim, I., Grossman, G., and Shavit, A., 1992, Simulation and Analysis of Open Cycle Absorption Systems for Solar Cooling, Sol. Energy, 49, pp. 515 534. 13 Gandihdasan, P., and Al-Farayedhi, A., 1995, Thermal Performance Analysis of a Partly Closed-Open Solar Regenerator, ASME J. Sol. Energy Eng., 117, pp. 151 153. 14 Gommed, K., Grossman, G., and Ziegler, F., 2002, Experimental Investigation of a LiCl-Water Open Absorption System for Cooling and Dehumidification, Proceedings, the 7th International Sorption Heat Pump Conference, Shanghai, China, September 24 27, pp. 391 396. Also ASME Journal of Solar Energy Engineering, May 2004 In Press. 884 Õ Vol. 126, AUGUST 2004 Transactions of the ASME

15 Grossman, G., and Wilk, M., 1994, Advanced Modular Simulation of Absorption Systems, Int. J. Refrig., 17, pp. 231 244. 16 Grossman, G., and Zaltash, A., 2001, ABSIM Modular Simulation of Advanced Absorption Systems, Int. J. Refrig., 24, pp. 531 543. 17 Uemura, T., 1967, Studies on the LiCl-Water Absorption Refrigeration Machine, Technology Reports of the Kansai University, Osaka, Japan, 9, pp. 71 88. 18 Gommed, K., and Grossman, G., 2004, Experimental Study of a Liquid Desiccant System for Solar Cooling and Dehumidification, Presented at EuroSun 2004, Freiburg, Germany, June 22 25. Journal of Solar Energy Engineering AUGUST 2004, Vol. 126 Õ 885