Investigation on the performance and optimization of heat pump water heater with wrap-around condenser coil

Abstract

A numerical investigation on the performance of heat pump water heater (HPWH) with wrap-around condenser coil was carried out. In this study, a coupled model was developed to simulate the static energy storage process of HPWH, which consisted of a multi-heat flux CFD model to describe the flow and heat transfer in water tank and a vapor-compression system model established in MATLAB to simulate the system operation characteristics. Heat flux in superheated steam, two-phase flow, and subcooled liquid regions of the condenser was obtained from the system model as boundary conditions of water tank model. The simulation results of the coupled model were in good agreement with experimental results. Heat transfer coefficient, COP and water temperature distribution of variable-pitch and constant-pitch coil were obtained by simulation. The results indicated that the heat transfer coefficient and average COP of variable-pitch coil were increased by 21.91% and 10.75% respectively, compared with constant-pitch coil. In addition, it was found that by appropriately reducing spiral pitch and coil diameter, average water temperature was increased by about 1 °C and maximum temperature difference in the vertical direction was no more than 7.50 °C. This work provides meaningful guidance for performance optimization of heat pump water heater.