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Solar Air Conditioning

Air conditioning can be produced from hot water via a sorption chiller. These work on the principle that water will remove heat from a cooling circuit when evaporated in order to be absorbed into a liquid salt solution or adsorbed on to a solid desiccant. Heat from the solar collectors is used to liberate the absorbed or adsorbed water to complete the cycle. Click for more specific information on absorption and adsorption cooling.

Commercial absorption chillers have been used for a long time, typically as part of a district heating and cooling plant or on refrigeration trucks and RV’s. Some systems use water as a refrigerant and a hygroscopic salt as the absorbent while other systems use ammonia as the refrigerant and water as the absorbent. The solar air conditioning system at the WCROC uses a 10 ton absorption chiller made by Yazaki Energy Systems, Inc.   It is energized by a heat medium (hot water) at 158°F to 203°F and the condenser is cooled with a wet cooling tower. The Yazaki absorption chiller uses a solution of lithium bromide and water, under a vacuum, as the working fluid.  Water is the refrigerant and lithium bromide, a nontoxic salt, is the absorbent. 

When the heat medium inlet temperature exceeds 158°F, the solution pump forces dilute lithium bromide solution into the generator.  The solution boils vigorously under a vacuum.  After separation, refrigerant vapor flows to the condenser and concentrated solution is pre-cooled in the heat exchanger before flowing to the absorber.

In the condenser, refrigerant vapor is condensed on the surface of the cooling coil and latent heat, removed by the cooling water, is rejected to a cooling tower.  Refrigerant liquid accumulates in the condenser and then passes through an orifice into the evaporator.

In the evaporator, the refrigerant liquid is exposed to a substantially deeper vacuum than in the condenser due to the influence of the absorber.  As refrigerant liquid flows over the surface of the evaporator coil it boils and removes heat from the chilled water circuit.  The chilled water for air conditioning is cooled to 44.6°F and the refrigerant vapor is attracted to the absorber.

A deep vacuum in the absorber is maintained by the affinity of the concentrated solution from the generator with the refrigerant vapor formed in the evaporator.  The refrigerant vapor is absorbed by the concentrated lithium bromide solution flowing across the surface of the absorber coil.  Heat is removed by the cooling water and rejected to a cooling tower.  The resulting dilute solution is preheated in a heat exchanger before returning to the generator where the cycle is repeated.