An investigation of using CO<inf>2</inf> heat pumps to charge PCM storage tank for domestic use

Abstract

Current investigations mainly focused on onefold phase change material (PCM) storage tank charging process, while the integration between a heat-source device and a PCM storage tank has been seldom considered. The investigation of using a carbon dioxide (CO2) heat pump to charge PCM storage tank is unique because PCM can enhance the system efficiency due to the delay of the outlet water temperature increase of the PCM storage tank. However, a systematic investigation about this charging process is still lacking. Therefore, this study conducted the performance investigation about the system using CO2 heat pumps to charge the PCM storage tank. The charging process was simulated by the integration of the heat pump and PCM storage tank models. The reliabilities of these models were validated by experimental data. The effects of different expansion valve opening, PCM types, and tank arrangements on the system performance were analyzed. Both air-source and water-source CO2 heat pumps were considered. The optimal parameters were identified by maximizing the overall performance considering the balance between the charging time and system coefficient of performance. For the system using water-source CO2 heat pump with optimal parameters, charging time and system coefficient of performance were 0.29 h, and 3.48, respectively.