Evaluations of heat pump water heater with liquid-separation condensation from perspectives of performance enhancement and heat exchange area reduction

Abstract

Heat pump water heater (HPWH) offers great potential to reduce energy consumption in water heating applications. But its performance enhancement and/or initial cost deduction are the main challenges to promote market penetration. In this paper, a heat transfer improvement technology, i.e., liquid-separation condensation (LSC), is implemented to HPWH and screen to achieve the maximized COP (E-HPWH) or reduced condenser area (R-HPWH). A model of HPWH with LSC is developed and validated, and its predictions are in good agreements with tested results from the baseline (B-HPWH) with an average deviation of 4.92 % at most. By using this validated model, E-HPWH and R-HPWH are obtained by adjusting the path arrangement and separation efficiencies. With the same heat transfer area, the COP of E-HPWH reaches 4.48, which is 7.43 % higher than that of B-HPWH, and the heating time is shortened by 13.1 %. With the same COP of B-HPWH being 4.17, the heat transfer area of R-HPWH is reduced by 22.2 % and heating time is shortened by 4.1 %. Then transient heating-up process of three HPWHs are comparatively investigated. Results indicate that E-HPWH has the highest compressor power as well as pressures and temperatures at the inlets of condenser and evaporator, followed by R-HPWH and B-HPWH. E-HPWH and R-HPWH overperform B-HPWH in terms of heat capacity before 4220s, due to the increased mass flowrate. Compared to B-HPWH, E-HPWH and R-HPWH have averagely 15.02 % and 7.29 % higher COP before 2790s and 1860s, respectively. Their states are less differentiated as the water temperature increases.