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The gas-fired Generator-Absorber heat eXchanger (GAX) heat pump is being considered for space conditioning in residential and light commercial applications. In order to meet the national building codes for ammonia absorption heat pumps, a secondary fluid is used to interface with the air-coils. Proper choice of a secondary fluid maximizes the economic advantage of the GAX heat pump. The secondary fluid transfers the heating and cooling loads from the absorption heat pump to and from outdoor and indoor air-coils. The physical properties of secondary fluids influence the heat transfer performance in the heat-exchange equipment and hence the effective lift, thereby determining the cycle coefficient of performance (COP). Additionally, the pumping power for each fluid varies depending on the density and viscosity at operating temperatures. The variation in cycle COP and pumping power as a result of fluid properties is ultimately manifested as changes in electric and natural-gas cost. An analysis was carried out to evaluate six secondary fluids for a GAX absorption heat pump. A performance model was developed to simulate the secondary-fluid flow loops and the absorption heat pump. The utility costs for heating and cooling were determined for a typical building. The effects of ambient conditions and local utility rates were determined by modeling the annual utility costs in four cities: Atlanta, Chicago, Los Angeles, and New York. These four cities provided wide variations in heating and cooling requirements, and utility rates for natural gas and electricity. The results from this study provide a basis for selecting secondary fluids for heat pumping in different locations.Copyright © 2003 by ASME |
