Experimental studies of a variable capacity direct-expansion solar-assisted heat pump water heater in autumn and winter conditions

• Published in: Solar energy Vol. 170; pp. 352 - 357
• Main Authors: Kong, Xiangqiang, Sun, Penglong, Li, Ying, Jiang, Kailin, Dong, Shandong
• Format: Journal Article
• Language: English
• Published: New York Elsevier Ltd 01.08.2018; Pergamon Press Inc
• Subjects: Alternative energy sources; Autumn; Capacitors; Direct expansion; Electric power; Evaporation; Evaporators; Experiments; Extreme weather; Gas expanders; Heat exchangers; Heat pumps; Meteorology; Microchannels; Performance evaluation; Pressure; Pumps; Solar assisted heat pump; Solar collectors; Solar energy; Temperature effects; Thermal performance; Water heaters; Water temperature; Winter; Solar assisted heat pump; Direct expansion; Experiments; Thermal performance
• ISSN: 0038-092X; 1471-1257
• DOI: 10.1016/j.solener.2018.05.081

•A variable capacity direct-expansion solar-assisted heat pump was presented.•An experimental setup of the proposed system was designed and built.•A series of tests were carried out in autumn and winter conditions.•The thermal performance of the system is experimentally investigated. A variable capacity direct-expansion solar-assisted heat pump (DX-SAHP) system was studied experimentally under the meteorological condition of Qingdao located in the East China area. It was mainly made up of a solar collector/evaporator, a variable-frequency rotary-type hermetic compressor, a micro-channel condenser, and an electronic expansion valve. A series of experiments were carried out, in order to evaluate the performance of the DX-SAHP system during the autumn and winter period, including the system coefficient of performance (COP), the electric power to the compressor, the evaporating and condensing pressures, and the discharge temperature of the compressor. Experimental results showed that for the base case considered in this study, under the sunny and overcast day conditions in the autumn, the average COP was higher than 4.0 and 3.0, respectively. Even in the extreme weather of the winter conditions, the average COP was also higher than 2.5. In general, with the increase of water temperature, the compressor speed increased gradually, and the corresponding electric power of the compressor increased sharply. The condensing pressure also increases, as does the discharge temperature of the compressor, while the evaporating pressure remains a relatively low level with smaller variations.