Energy, financial and environmental impact analysis of solar thermal heat pump systems using a direct expansion packed bed evaporator-collector

Abstract

The volumetric efficiency of a compressor in solar thermal heat pump systems was reduced due to excess superheating during maximum sunshine hours. The loss of volumetric efficiency has affected the overall performance of the system. In this research, the compressor volumetric efficiency was enhanced by a direct expansion packed bed evaporator-collector to harvest the solar energy effectively during maximum sunshine hours and maintain the superheat below 5 °C. The excess solar energy harvested during maximum sunshine hours was stored in the evaporator-collector using paraffin wax – graphite composite phase change material. The performances of solar thermal heat pump systems using direct expansion flat plate and packed bed evaporator-collectors are studied and compared in terms of heating capacity, power consumption, coefficient of performance and solar fraction. The results showed that the coefficient of performance of a solar thermal heat pump system with a direct expansion packed bed evaporator-collector was improved by 1–9.5% and the heating capacity was enhanced by 1–10.8% than direct expansion flat bed evaporator collector. Further, the proposed heat pump configuration has pay-back duration of 9.9 months with 70.4% reduced CO2 emissions compared to electrical resistance heaters for the twenty years lifetime.