Exergetic performance analysis of heat pumps: two alternative approaches

Abstract

This paper evaluates the performance of a compressor driven and an absorption heat pump on the basis of exergy analysis using two different approaches. Approach 1 is based on the calculation of the effective heat absorbing and emitting temperatures and the entropy generation rate. Approach 2 is based on the commonly used exergy analysis where the real ambient temperature is used. The main goal is to analyse how these two approaches differ from each other. Approach 1 gives the exact improvement potential (Wreal - Wreal) of the heat pump while Approach 2 underestimates it. The average flow temperature also approximates the correct improvement potential with sufficient accuracy when temperature change of the flow is relatively small. Both approaches can be used when performances of heat pumps are compared. Both approaches also give a more realistic view of the performance than the commonly used COP, especially regarding the absorption heat pump.