Comparison of the performance of different configurations of a finned coil evaporator for an air-to-water propane heat pump

In the electrification process to decrease CO2 emissions, heat pumps technology plays a crucial role to decarbonise residential and service heating sector. Hence, it is essential to increase the performance of heat pumps working with natural, low GWP refrigerants such as R290. An essential component for a heat pump good performance is the evaporator, whose design is challenging due to the 2-phase flow, therefore it is often the cause of severe inefficiencies in the cycle. The present study, which was carried out at the Universitat Polit´ecnica de Val´encia, aims to compare the experimental results of an air-to-water propane heat pump working with different fin-and-tube evaporator configurations. The research wants to understand how different factors i.e. distributor or fins type can affect the evaporator performance and thus the efficiency of the heat pump system. In literature several experimental studies about maldistribution in evaporator circuits are available, however, not many are focused on fin-and-tube heat exchangers. Moreover, maldistribution on refrigerant side and air side are not usually studied separately. To better understand whether maldistribution affects the reference prototype performance, two new configurations are compared to the reference one: the first with a Nozzle type distributor, different from Venturi type taken as the reference; the second with plain fins on the air side, as compared to wavy fins of the reference heat exchanger. Results show that refrigerant maldistribution is slightly affecting the heat pump performance and possibly, airflow maldistribution on secondary side is more often the cause of superheated channels in the evaporator. However, it is the combination of refrigerant maldistribution and airflow maldistribution which is affecting the performance. Moreover, air side proves to be the limiting side for the heat exchange, in line with literature. In fact, the presence of a low heat transfer coefficient on air side results to be significantly more detrimental to performance than having some refrigerant maldistribution caused by the distributor.