Abstract:
The solar-powered LiBr-water absorption air conditioning system using hybrid storage includes one or more solar collectors generating heat energy to drive the system. The solar collector communicates with a generator to heat an aqueous LiBr solution and release refrigerant through vaporization. The refrigerant feeds into a condenser to form a refrigerant condensate. The condensate feeds into an evaporator, which throttles the refrigerant and causes flash vaporization, resulting in cooling discharged into a load. The refrigerant from the evaporator feeds into an absorber containing a weak LiBr-water mixture from the generator to facilitate absorption of the refrigerant. A pump feeds the resultant aqueous LiBr solution back to the generator for another cycle. The hybrid storage includes a combination of heat storage tank, refrigerant storage tank, and/or a cold water tank coupled to the generator, condenser, and the evaporator to supplement driving or additional cooling during nighttime for continuous daily operation.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to air conditioning systems, and particularly to a solar-powered LiBr-water absorption, air-cooled, air conditioning system, which is a single-effect vapor absorption refrigeration system that includes hybrid storage to provide continuous 24-hour per day operation, without any interruption during the storage-maintenance process. 
         [0003]    2. Description of the Related Art 
         [0004]    Most conventional absorption cycle systems are categorized into single- and multi-circuit (or multi-effect) systems. In a typical absorption cycle system, a refrigerant, such as water vapor, is absorbed into an absorbent mixture, such as an aqueous LiBr (lithium bromide) solution, and released out of the absorbent mixture, creating a cooling effect. A heat source, such as solar energy, fossil fuel flame, waste heat from factories, and the like, provides the energy needed to drive the cooling process. A single-circuit system usually includes a generator, condenser, evaporator, and an absorber to process the refrigerant and absorbent mixture through the absorption cycle, whereas a multi-circuit system includes the necessary components to facilitate independent, multiple streams of refrigerants and absorbents. 
         [0005]    While these absorption cycle systems provide cooling more efficiently and with less operating cost compared to electric vapor compression systems, solar-powered absorption systems present unique challenges. Due to the heat source, solar-powered systems typically cannot operate continuously in a 24-hour daily period. Solar exposure and insolation is only available during daylight hours, and nighttime operation must resort to other sources of heat energy, such as the fossil fuel flame mentioned above. This situation is also exacerbated when maintenance is required on a failed or worn component of the system which can lead to interrupted operation and/or extended downtime. There is a need for some means to compensate for the lack of solar exposure and insolation during nighttime hours for continuous operation. Thus, a solar-powered LiBr-water absorption air conditioning system using hybrid storage solving the aforementioned problems is desired. 
       SUMMARY OF THE INVENTION 
       [0006]    The solar-powered LiBr-water absorption air conditioning system using hybrid storage includes one or more sets of solar collectors generating heat energy to drive the system. The solar collector communicates with a generator to heat an aqueous LiBr solution and release refrigerant through vaporization. The refrigerant feeds into a condenser to form a refrigerant condensate. The refrigerant condensate feeds into an evaporator, which throttles the refrigerant and causes flash vaporization, resulting in a cooling effect discharged into a load. The refrigerant from the evaporator feeds into an absorber containing a weak LiBr-water mixture to facilitate absorption of the refrigerant. A pump feeds the resultant aqueous LiBr solution back to the generator for another cycle. The hybrid storage includes a combination of heat storage tank, refrigerant storage tank, and/or a cold water tank coupled to the generator, condenser, and the evaporator to supplement driving or additional cooling during nighttime for continuous daily operation. 
         [0007]    These and other features of the present invention will become readily apparent upon further review of the following specification and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic diagram of a first embodiment of a solar-powered LiBr-water absorption air conditioning system using hybrid storage according to the present invention. 
           [0009]      FIG. 2  is a schematic diagram of a second embodiment of a solar-powered LiBr-water absorption air conditioning system using hybrid storage according to the present invention. 
           [0010]      FIG. 3  is a schematic diagram of a third embodiment of a solar-powered LiBr-water absorption air conditioning system using hybrid storage according to the present invention. 
           [0011]      FIG. 4  is a schematic diagram of a fourth embodiment of a solar-powered LiBr-water absorption air conditioning system using hybrid storage according to the present invention. 
       
    
    
       [0012]    Similar reference characters denote corresponding features consistently throughout the attached drawings. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]    The solar-powered LiBr-water absorption air conditioning system using hybrid (heat and refrigerant) storage, a first embodiment of which is generally referred to by the reference number  10  in  FIG. 1 , provides an efficient configuration for continuous 24-hour daily operation, i.e., day and night, by utilizing a variety of hybrid heat and refrigerant storage systems or assemblies. The heat storage will store heat during daytime when the solar energy is sufficient and utilize the stored heat at both the nighttime when the solar energy is not available and when the solar insolation is insufficient to produce the required generator temperature for operation of the system. 
         [0014]    As best seen in  FIG. 1 , the solar-powered LiBr-water absorption air conditioning system  10  may include two sets of solar collectors, such as a pair of collectors including a first solar collector  11  and a second solar collector  12 . Depending on operational requirements, each first solar collector  11  and second solar collector  12  may be provided as respective sets or single units. A first collector outflow valve  13  and a first collector inflow valve  15  are coupled to the first solar collector  11 . The first collector outflow valve  13  enables selective flow of heated medium from the first solar collector  11  to a generator  20 , and the first collector inflow valve  15  enables selective flow of heat-depleted medium back to the first solar collector  11  to reheat the medium and recirculate the same during daytime operation. The medium can also be referred to as a heat transfer medium. 
         [0015]    The generator  20  heats an aqueous LiBr solution, the solution being a mixture of water and LiBr in which the water acts as a refrigerant, while the LiBr acts as an absorbent, Heating of this solution releases the refrigerant (water) through evaporation, creating a weak absorbent-refrigerant solution. The evaporated refrigerant travels to a condenser  30 , while the absorbent-refrigerant solution, now weak in refrigerant, passes on to an absorber  50 . 
         [0016]    A first expansion valve  21  is coupled between the generator  20  and the absorber  50  to regulate flow of the weak-in-refrigerant absorbent-refrigerant solution from the generator  20  to the absorber  50 . A heat exchanger  22  can be provided between the generator  20  and the absorber  50  to increase efficiency of the medium flowing therebetween by pre-cooling the weak-in-refrigerant absorbent-refrigerant solution prior to reaching the absorber  50  and pre-heating the medium flowing into the generator  20  from the absorber  50 . 
         [0017]    The condenser  30  undergoes a heat exchange or cooling process, as exemplified by a fan  31 , to change the vapor refrigerant into liquid refrigerant or refrigerant condensate. The liquid refrigerant flows from the condenser  30  to an evaporator  40  where the refrigerant undergoes a throttling process. The throttling process reduces pressure of the liquid refrigerant to an extent that causes the refrigerant to flash into a liquid-vapor mixture and create a cooling effect in the evaporator  40 . This cooling, or cooled air from the cooling, feeds out into a load  41 , such as a room or container. A second expansion valve  32  is provided in the line between the condenser  30  and the evaporator  40  to regulate flow of refrigerant into the evaporator  40 . The heat rejection to the ambient can be facilitated by natural convection or forced by a fan. 
         [0018]    The refrigerant from the evaporator  40  feeds into the absorber  50  to enable absorption of the refrigerant into the weak-in-refrigerant absorbent-refrigerant solution contained in the absorber  50 . Since the weak-in-refrigerant absorbent-refrigerant solution is absorbent-rich, i.e., it has a higher concentration of LiBr, the absorbent-rich solution readily absorbs the refrigerant, resulting in the aqueous LiBr solution mentioned above, now relatively strong in refrigerant. The absorber  50  includes a pump  51  to feed the aqueous LiBr solution to the generator  20 . 
         [0019]    To facilitate daytime and nighttime continuous operation, the solar-powered LiBr-water absorption air conditioning system  10  includes a hybrid storage system or assembly that assists in supplying heat and refrigerant during nighttime operation. As shown in  FIG. 1 , the hybrid (heat and refrigerant) storage system includes a heat storage tank  60  coupled to the second solar collector  12  and a refrigerant storage tank  70  operatively coupled to a flow line between the condenser  30  and the evaporator  40 . The media being stored in the heat storage tank  60  and the refrigerant storage tank  70  can also be referred to as thermal media. Thus, the hybrid storage is a combination of heat storage and refrigerant storage. 
         [0020]    A second collector outflow valve  14  and a second collector inflow valve  16  are coupled to the second solar collector  12 . The second collector outflow valve  14  enables selective flow of heated medium from the second solar collector  12  to the heat storage tank  60 , and the second collector inflow valve  16  enables selective flow of medium within the heat storage tank  60  back to the second solar collector  12  to reheat and recirculate the medium during daytime operation. 
         [0021]    The heat storage tank  60  includes a generator supply valve  61  and a generator outlet valve  62 . The generator supply valve  61  enables selective flow of heated medium from the heat storage tank  60  into the generator  20 , while the generator outlet valve enables selective outflow of heat-depleted medium from the generator  20  back into the heat storage tank  60 . The generator supply valve  61  and the generator outflow valve  62  are closed during the day and open during the night. 
         [0022]    The refrigerant storage tank  70  includes a refrigerant supply valve  71  coupled to a flow line from the condenser  30  and a refrigerant outflow valve  72  coupled to the same flow line leading into the evaporator  40 . Since the heat storage tank  60  and the refrigerant storage tank  70  process and store thermal media, both tanks  60 ,  70  are preferably insulated. The refrigerant tank  70  may be provided with relatively thinner insulation. The refrigerant supply valve  71  is open during daytime and closed during nighttime to accumulate and store some excess refrigerant during the daytime. While the refrigerant supply valve  71  is open, the refrigerant outflow valve  72  is closed during daytime and vice versa during nighttime. 
         [0023]    In operation, the first collector outflow valve  13 , first collector inflow valve  15 , second collector outflow valve  14 , second collector inflow valve  16 , and the refrigerant supply valve  71  are open during daytime or daylight hours when solar exposure and energy can be harnessed. The generator supply valve  61  and the generator outflow valve  62  are also closed during daytime operation. This allows the heated medium to release the refrigerant in the generator  20  and condense the refrigerant in the condenser  30 . The condenser  30  feeds liquid refrigerant through a throttling valve and then to the evaporator  40  to generate cooling, and the refrigerant flows into the absorber  50  to form the required aqueous LiBr solution to repeat the cycle. Some of the refrigerant condensate from the condenser  30  flows into the refrigerant storage tank  70  for nighttime operation. 
         [0024]    While the heat transfer medium is being heated in the first solar collector  11 , the second solar collector  12  is also heating a medium or heat transfer medium stored in the heat storage tank  60 . Since solar power is not available during nighttime, the heat energy required for nighttime operation is supplied by the heated medium in the heat storage tank  60 . During nighttime operation, the first collector outflow valve  13 , first collector inflow valve  15 , second collector outflow valve  14 , second collector inflow valve  16 , and the refrigerant supply valve  71  are closed, while the generator supply valve  61  and the generator outflow valve  62  are open to enable heat transfer medium flow between the generator  20  and the heat storage tank  60  and drive the cooling process. The refrigerant outflow valve  72  is also open during nighttime operation, while the refrigerant supply valve  71  is closed. The refrigerant storage tank  70  supplies refrigerant accumulated therein during daytime operation to the evaporator  40  via the refrigerant outflow valve  72 . This supplements the refrigerant condensate being fed into the evaporator  40  from the condenser  30  during nighttime operation. Thus, it can be seen from the above that the hybrid storage system of a heat storage tank  60  and a refrigerant storage tank  70  enables continuous operation of the solar-powered LiBr-water absorption air conditioning system  10  during nighttime hours without interruption during any maintenance process. The coefficient of performance (COP) of this system is comparatively higher during nighttime operation. 
         [0025]    A second embodiment of a solar-powered LiBr-water absorption air conditioning system  100  is diagrammatically shown in  FIG. 2 . In this embodiment, the hybrid (cold and refrigerant) storage system includes a cold water storage tank  160  instead of the heat storage tank  60 . 
         [0026]    The solar-powered LiBr-water absorption air conditioning system  100  includes a solar collector set, such as a first solar collector  111 . The first collector  111  is coupled directly to a generator  120  to circulate heat transfer medium therein. 
         [0027]    The generator  120  heats an aqueous LiBr solution, causing an increase in partial pressure without changing the total pressure. In this instance, the solution is a mixture of water and LiBr in which the water acts as a refrigerant, while the LiBr acts as an absorbent. Heating of this solution releases the refrigerant (water) through evaporation, resulting in an absorbent-refrigerant solution that is now weak in refrigerant. The evaporated refrigerant travels to a condenser  130 , while the weak absorbent-refrigerant solution passes on to an absorber  150 . 
         [0028]    A first expansion valve  121  is coupled between the generator  120  and the absorber  150  to regulate flow of the weak-in-refrigerant absorbent-refrigerant solution from the generator  120  to the absorber  150 . A heat exchanger  122  can be provided between the generator  120  and the absorber  150  to increase efficiency of the medium flowing therebetween by pre-cooling the weak-in-refrigerant absorbent-refrigerant solution prior to reaching the absorber  150  and pre-heating the medium flowing into the generator  120  from the absorber  150 . 
         [0029]    The condenser  130  undergoes a heat exchange or cooling process, as exemplified by a fan  131 , to change the vapor refrigerant into liquid refrigerant. The liquid refrigerant flows from the condenser  130  to an evaporator  140 , where the refrigerant undergoes a throttling process. The throttling process reduces pressure of the liquid refrigerant to an extent that causes the refrigerant to flash into a liquid-vapor mixture and create a cooling effect in the evaporator  140 . This cooling, or cooled air from the cooling, feeds out into a load  141 , such as a room or container. A second expansion valve  132  is provided in the line between the condenser  130  and the evaporator  140  to regulate flow of refrigerant into the evaporator  140 . The heat rejection to the ambient air can be facilitated by natural convection or forced by a fan. 
         [0030]    The refrigerant from the evaporator  140  feeds into the absorber  150  to enable absorption of the refrigerant into the weak-in-refrigerant absorbent-refrigerant solution contained in the absorber  150 . Valve  142  is disposed between the absorber  150  and pump  151  to regulate the flow of strong-in-refrigerant solution from the absorber  150 . Since the weak-in-refrigerant solution is absorbent-rich, i.e., it has a higher concentration of LiBr, the weak-in-refrigerant solution (or absorbent-rich solution) readily absorbs the refrigerant from the evaporator  140 , resulting in the aqueous LiBr solution mentioned above, i.e., the absorbent-refrigerant solution in the absorber  150  becomes strong in refrigerant upon absorbing refrigerant from the evaporator  140 . The absorber  150  includes a pump  151  to feed the aqueous LiBr solution, now strong in refrigerant, to the generator  120 . 
         [0031]    To facilitate daytime and nighttime continuous operation, the solar-powered LiBr-water absorption air conditioning system  100  includes a hybrid storage system that assists in cooling during nighttime. Moreover, the hybrid storage system ensures continuous, uninterrupted operation should a tank fail. As shown in  FIG. 2 , the hybrid storage system includes a refrigerant storage tank  170  operatively coupled to a flow line between the condenser  130  and the evaporator  140  and a cold water storage tank  160  coupled to the evaporator  140 . The media being stored in the refrigerant storage tank  170  and the cold water storage tank  160  can also be referred to as thermal media. 
         [0032]    The refrigerant storage tank  170  includes a refrigerant supply valve  171  coupled to the flow line from the condenser  130  and a refrigerant outflow valve  172  coupled to the same flow line leading into the evaporator  140 . The refrigerant supply valve  171  is open during daytime and closed during nighttime to accumulate and store some excess refrigerant during the daytime. While the refrigerant supply valve  171  is open, the refrigerant outflow valve  172  is closed during daytime and vice versa during nighttime. 
         [0033]    The evaporator  140  also includes an auxiliary refrigerant outflow valve  143  and an auxiliary refrigerant inflow valve  144  connected to separate lines feeding into and out of the cold water storage tank  160 , respectively. The cold water storage tank  160  stores cold water, and the auxiliary refrigerant outflow valve  143  and the auxiliary refrigerant inflow valve  144  enables circulation of the refrigerant from the evaporator  140  to cool and maintain the water in the cold water storage tank  160  at a desired or predetermined cold temperature, preferably a temperature that can facilitate cooling of the load  141 . These auxiliary valves  143 ,  144  are open during daytime and closed during nighttime. The cold water storage tank  160  is also provided with a cold water outflow valve  161  and a cold water inflow valve  162  coupled to separate lines extending between the cold water storage tank  160  and the load  141 . The cold water valves  161 ,  162  are preferably open during nighttime and during periods of insufficient solar insolation, and closed during daytime. 
         [0034]    In operation, the refrigerant supply valve  171 , the refrigerant valve  142 , the auxiliary refrigerant outflow valve  143 , and the auxiliary refrigerant inflow valve  144  are open during daytime or daylight hours when solar exposure and energy can be harnessed, while the water outflow valve  161  and the cold water inflow valve  162  remain closed. This allows the heated medium to release the refrigerant in the generator  120  and condense the refrigerant in the condenser  130 . The condenser  130  feeds liquid refrigerant to the evaporator  140  to generate cooling, and the refrigerant flows into the absorber  150  to form the required aqueous LiBr solution to repeat the cycle. Some of the refrigerant from the evaporator  140  also circulates through the cold water storage tank  170  to cool and maintain the water therein at the desired temperature. 
         [0035]    Since solar power is not available during nighttime, all the open valves  142 ,  143 ,  144 ,  171  from daytime operation are closed, and the cold water outflow valve  161 , the cold water inflow valve  162 , and the refrigerant outflow valve  172  are open for nighttime operation. This configuration allows stored refrigerant from the refrigerant storage tank  170  to flow into the evaporator  140  and facilitate part of the required nighttime load. The remainder of the nighttime load is accommodated by heat rejection from circulating cold water. This can be facilitated by natural convection or by forced fan providing airflow over cold water lines. In this embodiment, the generator  120 , the condenser  130 , the absorber  150 , and related components operate at daytime only. Moreover, the control requirements for the solar-powered LiBr-water absorption air conditioning system  100  are less complex due to the reduced number of valve closing and opening operations during the daytime. 
         [0036]    A third embodiment of a solar-powered LiBr-water absorption air conditioning system  200  is diagrammatically shown in  FIG. 3 . In this embodiment, the hybrid storage system includes a cold water storage tank  270  instead of a refrigerant storage tank  70 . 
         [0037]    The solar-powered LiBr-water absorption air conditioning system  200  may include two sets of solar collectors, such as a pair of collectors including a first solar collector  211  and a second solar collector  212 . A first collector outflow valve  213  and a first collector inflow valve  215  are coupled to the first solar collector  211 . The first collector outflow valve  213  enables selective flow of heated medium from the first solar collector  211  to a generator  220 , and the first collector inflow valve  215  enables selective flow of heat-depleted medium back to the first solar collector  211  to reheat the medium and recirculate the same. The medium can also be referred to as a heat transfer medium. 
         [0038]    The generator  220  heats an aqueous LiBr solution, the solution being a mixture of water and LiBr in which the water acts as a refrigerant, while the LiBr acts as an absorbent. Heating of this solution releases the refrigerant (water) to evaporate, so that the absorbent-refrigerant solution is now weak in refrigerant. The evaporated refrigerant travels to a condenser  230 , while the weak-in-refrigerant absorbent-refrigerant solution passes on to an absorber  250 . 
         [0039]    A first expansion valve  221  is coupled between the generator  220  and the absorber  250  to regulate the flow of the weak-in-refrigerant absorbent-refrigerant solution from the generator  220  to the absorber  250 . A heat exchanger  222  can be provided between the generator  220  and the absorber  250  to increase efficiency of the medium flowing therebetween by pre-cooling the weak absorbent-refrigerant solution prior to reaching the absorber  250  and pre-heating the medium flowing into the generator  220  from the absorber  250 . 
         [0040]    The condenser  230  undergoes a heat exchange or cooling process, as exemplified by a fan  231 , to change the vapor refrigerant into liquid refrigerant or refrigerant condensate. The liquid refrigerant flows from the condenser  230  to an evaporator  240 , where the refrigerant undergoes a throttling process. The throttling process reduces pressure of the liquid refrigerant to an extent that causes the refrigerant to flash into vapor and create a cooling effect. This cooling, or cooled air from the cooling, feeds out into a load  241 , such as a room or container. A second expansion valve  232  is provided in the line between the condenser  230  and the evaporator  240  to regulate flow of refrigerant into the evaporator  240 . The heat rejection to the ambient air can be facilitated by natural convection or forced by a fan. 
         [0041]    The refrigerant from the evaporator  240  feeds into the absorber  250  to enable absorption of the refrigerant into the weak-in-refrigerant absorbent-refrigerant solution contained in the absorber  250 . Since the weak-in-refrigerant solution is absorbent-rich, i.e., it has a higher concentration of LiBr, the absorbent-rich solution readily absorbs the refrigerant, resulting in the aqueous LiBr solution mentioned above, the absorbent-refrigerant solution now being strong in refrigerant after absorption of refrigerant from the evaporator  240 . The absorber  250  includes a pump  251  to feed the aqueous LiBr solution (now strong in refrigerant) to the generator  220 . 
         [0042]    To facilitate daytime and nighttime continuous operation, the solar-powered LiBr-water absorption air conditioning system  200  includes a hybrid storage system that assists in supplying heat and cooling during nighttime without any interruption in operation if one storage tank is taken away for repair. As shown in  FIG. 3 , the hybrid storage system includes a heat storage tank  260  coupled to the second solar collector  212  and the cold water storage tank  270  operatively coupled to the evaporator  240 . The media being stored in the heat storage tank  260  and the cold water storage tank  270  can also be referred to as thermal media. 
         [0043]    A second collector outflow valve  214  and a second collector inflow valve  216  are coupled to the second solar collector  212 . The second collector outflow, valve  214  enables selective flow of heated medium from the second solar collector  212  to the heat storage tank  260 , and the second collector inflow valve  216  enables selective flow of medium within the heat storage tank  260  back to the second solar collector  212  to reheat the medium and recirculate the same. 
         [0044]    The heat storage tank  260  includes a generator supply valve  261  and a generator outlet valve  262 . The generator supply valve  261  enables selective flow of heated medium from the heat storage tank  260  into the generator  220 , while the generator outlet valve enables selective outflow of heat-depleted medium from the generator  220  back into the heat storage tank  260 . The generator supply valve  261  and the generator outflow valve  262  are closed during the day and open during the night. 
         [0045]    The evaporator  240  includes an auxiliary refrigerant outflow valve  243  and an auxiliary refrigerant inflow valve  244  connected to separate lines feeding into and out of the cold water storage tank  270 , respectively. The cold water storage tank  270  stores cold water, and the auxiliary refrigerant outflow valve  243  and the auxiliary refrigerant inflow valve  244  enable circulation of the refrigerant from the evaporator  240  to cool and maintain the water in the cold water storage tank  270  at a desired or predetermined cold temperature, preferably a temperature that can facilitate cooling of the load  241 . These auxiliary valves  243 ,  244  are open during daytime and closed during nighttime. The cold water storage tank  270  is also provided with a cold water outflow valve  271  and a cold water inflow valve  272  coupled to separate lines extending between the cold water storage tank  260  and the load  241 . The cold water valves  271 ,  272  are preferably open during nighttime and closed during daytime. 
         [0046]    In operation, the first collector outflow valve  213 , first collector inflow valve  215 , second collector outflow valve  214 , second collector inflow valve  216 , auxiliary refrigerant outflow valve  243 , and auxiliary refrigerant inflow valve  244  are open during daytime or daylight hours when solar exposure and energy can be harnessed. The generator supply valve  261  and the generator outflow valve  262  are closed during daytime operation. This allows the heated medium to release the refrigerant in the generator  220  and condense the refrigerant in the condenser  230  during nighttime operation. The condenser  230  feeds liquid refrigerant to the evaporator  240  to generate cooling, and the refrigerant flows into the absorber  250  to form the required aqueous LiBr solution to repeat the cycle. Some of the refrigerant from the evaporator  240  also circulates through the cold water storage tank  270  to cool and maintain the water therein at the desired temperature. 
         [0047]    While the heat transfer medium is being heated in the first solar collector  211 , the second solar collector  212  is also heating a medium or heat transfer medium stored in the heat storage tank  260 . Since solar power is not available during nighttime, the heat energy required for nighttime operation is supplied by the heated medium in the heat storage tank  260 . During nighttime operation, the first collector outflow valve  213 , first collector inflow valve  215 , second collector outflow valve  214 , second collector inflow valve  216 , auxiliary refrigerant outflow valve  243 , and auxiliary refrigerant inflow valve  244  are closed, while the generator supply valve  261  and the generator outflow valve  262  are open to enable heat transfer medium flow between the generator  220  and the heat storage tank  260  and drive the cooling process. The cold water outflow valve  271  and the cold water inflow valve  272  are open for nighttime operation. The stored heat energy from the heat storage tank  270  meets some of the nighttime load, while the remainder of the nighttime load is accommodated by heat rejection from circulating cold water. This can be facilitated by natural convection or forced by a fan providing airflow over cold water lines. As with the previous embodiments, the hybrid storage system enables continuous, uninterrupted operation should one of the storage tanks is down form maintenance or repair. 
         [0048]    A fourth embodiment of a solar-powered LiBr-water absorption air conditioning system  300  is diagrammatically shown in  FIG. 4 . In this embodiment, the hybrid (heat, refrigerant, and cold) storage system includes a heat storage tank  360 , a refrigerant storage tank  370 , and a cold water storage tank  380 . 
         [0049]    The solar-powered LiBr-water absorption air conditioning system  300  may include two sets of solar collectors, such as a pair of collectors including a first solar collector  311  and a second solar collector  312 . A first collector outflow valve  313  and a first collector inflow valve  315  are coupled to the first solar collector  311 . The first collector outflow valve  313  enables selective flow of heated medium from the first solar collector  311  to a generator  320 , and the first collector inflow valve  315  enables selective flow of heat-depleted medium back to the first solar collector  311  to reheat the medium and recirculate the same. The medium can also be referred to as a heat transfer medium. 
         [0050]    The generator  320  heats an aqueous LiBr solution, causing an increase in partial pressure without changing the total pressure. In this instance, the solution is a mixture of water and LiBr in which the water acts as a refrigerant, while the LiBr acts as an absorbent. Heating of this solution releases the refrigerant (water) to evaporate, so that the absorbent-refrigerant solution is now weak in refrigerant. The evaporated refrigerant travels to a condenser  330 , while the absorbent-refrigerant solution, now weak in refrigerant, passes on to an absorber  350 . 
         [0051]    A first expansion valve  321  is coupled between the generator  320  and the absorber  350  to regulate flow of the weak-in-refrigerant absorbent-refrigerant solution from the generator  320  to the absorber  350 . A heat exchanger  322  can be provided between the generator  320  and the absorber  350  to increase efficiency of the medium flowing therebetween by pre-cooling the weak-in-refrigerant absorbent-refrigerant solution prior to reaching the absorber  350  and pre-heating the medium flowing into the generator  320  from the absorber  350 . 
         [0052]    The condenser  330  undergoes a heat exchange or cooling process, as exemplified by a fan  331 , to change the vapor refrigerant into liquid refrigerant or refrigerant condensate. The liquid refrigerant flows from the condenser  330  to an evaporator  340 , where the refrigerant undergoes a throttling process. The throttling process reduces pressure of the liquid refrigerant to an extent that causes the refrigerant to flash into vapor and create a cooling effect. This cooling, or cooled air from the cooling, feeds out into a load  341 , such as a room or container. A second expansion valve  332  is provided in the line between the condenser  330  and the evaporator  340  to regulate flow of refrigerant into the evaporator  340 . The heat rejection to the ambient air can be facilitated by natural convection or forced by a fan. 
         [0053]    The refrigerant from the evaporator  340  feeds into the absorber  350  to enable absorption of the refrigerant into the weak-in-refrigerant absorbent-refrigerant solution contained in the absorber  350 . Since the weak-in-refrigerant absorbent-refrigerant solution is absorbent-rich, i.e., it has a higher concentration of LiBr, the absorbent-rich solution readily absorbs the refrigerant, resulting in the aqueous LiBr solution mentioned above, now strong in refrigerant. The absorber  350  includes a pump  351  to feed the aqueous LiBr solution (now strong in refrigerant) to the generator  320 . 
         [0054]    To facilitate daytime and nighttime continuous operation, the solar-powered LiBr-water absorption air conditioning system  300  includes a hybrid storage system that assists in supplying heat and cooling during nighttime without interruption in operation during maintenance procedures in daytime or nighttime. As shown in  FIG. 4 , the hybrid storage system includes a heat storage tank  360  coupled to the second solar collector  312 , a refrigerant storage tank  370  operatively coupled to a flow line between the condenser  330  and the evaporator  340 , and the cold water storage tank  380  operatively coupled to the evaporator  340 . The media being stored in the heat storage tank  360 , the refrigerant storage tank  370 , and the cold water storage tank  380  can also be referred to as thermal media. 
         [0055]    A second collector outflow valve  314  and a second collector inflow valve  316  are coupled to the second solar collector  312 . The second collector outflow valve  314  enables selective flow of heated medium from the second solar collector  312  to the heat storage tank  360 , and the second collector inflow valve  316  enables selective flow of medium within the heat storage tank  360  back to the second solar collector  312  to reheat the medium and recirculate the same. 
         [0056]    The heat storage tank  360  includes a generator supply valve  361  and a generator outlet valve  362 . The generator supply valve  361  enables selective flow of heated medium from the heat storage tank  360  into the generator  320  while the generator outlet valve enables selective outflow of heat-depleted medium from the generator  320  back into the heat storage tank  360 . The generator supply valve  361  and the generator outflow valve  362  are closed during the day and open during the night. 
         [0057]    The refrigerant storage tank  370  includes a refrigerant supply valve  371  coupled to a flow line from the condenser  330  and a refrigerant outflow valve  372  coupled to the same flow line leading into the evaporator  340 . The refrigerant supply valve  371  is open during daytime and closed during nighttime to accumulate and store some excess refrigerant during the daytime. While the refrigerant supply valve  371  is open, the refrigerant outflow valve  372  is closed during daytime and vice versa during nighttime. 
         [0058]    The evaporator  340  includes an auxiliary refrigerant outflow valve  343  and an auxiliary refrigerant inflow valve  344  connected to separate lines feeding into and out of the cold water storage tank  380 , respectively. The cold water storage tank  380  stores cold water, and the auxiliary refrigerant outflow valve  343  and the auxiliary refrigerant inflow valve  344  enables circulation of the refrigerant from the evaporator  340  to cool and maintain the water in the cold water storage tank  380  at a desired or predetermined cold temperature, preferably a temperature that can facilitate cooling of the load  341 . These auxiliary valves  343 ,  344  are open during daytime and closed during nighttime. The cold water storage tank  380  is also provided with a cold water outflow valve  381  and a cold water inflow valve  382  coupled to separate lines extending between the cold water storage tank  380  and the load  341 . The cold water valves  381 ,  382  are preferably open during nighttime and closed during daytime. 
         [0059]    In operation, the first collector outflow valve  313 , first collector inflow valve  315 , second collector outflow valve  314 , second collector inflow valve  316 , refrigerant supply valve  371 , auxiliary refrigerant outflow valve  343 , and auxiliary refrigerant inflow valve  344  are open during daytime or daylight hours when solar exposure and energy can be harnessed. The generator supply valve  361  and the generator outflow valve  362  are closed during daytime. This allows the heated medium to release the refrigerant in the generator  320  and condense the refrigerant in the condenser  330  during nighttime. The condenser  330  feeds liquid refrigerant to the evaporator  340  to generate cooling, and the refrigerant flows into the absorber  350  to form the required aqueous LiBr solution to repeat the cycle. Some of the refrigerant condensate from the condenser  330  flows into the refrigerant storage tank  370  for nighttime operation, and some of the refrigerant from the evaporator  340  also circulates through the cold water storage tank  380  to cool and maintain the water therein at the desired temperature. 
         [0060]    While the heat transfer medium is being heated in the first solar collector  311 , the second solar collector  312  is also heating a medium or heat transfer medium stored in the heat storage tank  360 . Since solar power is not available during nighttime, the heat energy required for nighttime operation is supplied by the heated medium in the heat storage tank  360 . During nighttime operation, the first collector outflow valve  313 , first collector inflow valve  315 , second collector outflow valve  314 , second collector inflow valve  316 , refrigerant supply valve  371 , auxiliary refrigerant outflow valve  343 , and auxiliary refrigerant inflow valve  344  are closed, while the generator supply valve  361  and the generator outflow valve  362  are open to enable heat transfer medium flow between the generator  320  and the heat storage tank  360  and drive the cooling process. The cold water outflow valve  381  and the cold water inflow valve  382  are open for nighttime operation, as well as the refrigerant outflow valve  372 . The refrigerant storage tank  370  supplies refrigerant accumulated therein during daytime operation to the evaporator  340  via the refrigerant outflow valve  372 . This supplements the refrigerant condensate being fed into the evaporator  340  from the condenser  330  during nighttime operation. 
         [0061]    The stored heat energy from the heat storage tank  360  meets some of the nighttime load, while the remainder of the nighttime load is accommodated by heat, cold water storage, and refrigerant. This can be facilitated by natural convection or forced by a fan providing airflow over cold water lines. 
         [0062]    It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.