Abstract

Development of air-cooled absorption cycles appropriate for residential applications has been problematic. This study examines an ammonia-water triple effect cycle known as the kangaroo cycle, and investigates its limitations when used as an air-cooled space air conditioner. The triple effect absorption processes were modeled and a methodology for optimizing the design was developed. The arrangement and relative sizes of the heat exchangers thermally coupling the upper and lower loops were studied. The thermal coupling involves the upper rectifier, condenser, and absorber rejecting heat to the lower generator. Contrary to other triple effect studies, internal generator heat exchangers were incorporated in both the upper and lower generators and their optimum relative positions were studied. Also, errors of up to 150 percent were shown to result from conventional LMTD and pinch point analysis due to the highly non-linear temperature-enthalpy relationship in the upper condenser. Three configurations for the upper heat exchangers coupling the upper loop to the lower generator were analyzed, and their relative sizes were optimized. The cycle’s performance was shown to depend on the exit temperature of the lower loop generator, and the COP optimization was demonstrated with respect to this design variable. Operation at air-cooled ambient conditions was investigated. At lower ambient temperatures that are heavily weighted in air conditioning rating standards, the efficiency is very favorable. Equipment development and cost issues need to be addressed.

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