INFLUENCE OF THE SOURCE AND SINK TEMPERATURES ON THE OPTIMAL REFRIGERANT CHARGE OF A WATER-TO-WATER HEAT PUMP

摘要

This paper presents the results of a simulation study that was carried out in order to elucidate the influence of the source and sink temperatures on the optimal charge of a water-to-water heat pump. A water to water chiller previously employed in a charge optimisation study carried out by the authors, was modelled in detail with IMST-ART software and a full simulation study was performed, first as a chiller, keeping constant the outlet water temperature from the evaporator at 7 ℃ replicating the experimental campaign, and then as a heat pump, keeping constant the hot water supply temperature at the outlet of the condenser, replicating the test campaign carried out with a water to water heat pump at KTH (Stockholm). The results of the simulations were in very good agreement with the test results obtained at UPV when the sink temperatures (condensation temperatures) were varied, and show the same trends found at KTH when the source temperature (evaporation temperature) was progressively decreased. The simulation allowed to study the refrigerant distribution among the different components of the system at different operating conditions and showed that the great variation of the optimal charge with the variation of the evaporation temperature is mainly due to the variation of the amount of refrigerant into the oil. Regarding the refrigerant distribution among the components, most of the charge was found in the condenser (50-80%), a considerable part in the evaporator (around 15%) and a substantial amount in the compressor oil (10-35%).