Abstract
Research on the direct-expansion solar-assisted heat pump (DX-SAHP) system with bare plate evaporators for space heating is meaningful but insufficient. In this paper, experiments on a DX-SAHP system applying bare plate evaporators for space heating are conducted in the enthalpy difference lab with a solar simulator, with the ambient conditions stable. The independent effects of ambient temperature, solar irradiation, and relative humidity on the system performance are investigated. When ambient temperature changes as 5°C, 10°C, and 15°C, COP increases as 2.12, 2.18, and 2.26. When solar irradiance changes as 0 W m−2, 100 W m−2, 200 W m−2, 300 W m−2, and 500 W m−2, COP of the system changes as 2.07, 2.09, 2.14, 2.26, and 2.36. With ambient temperature of 5°C and solar irradiance of 0 W m−2, when relative humidity is 50%, no frost formed. Whereas with relative humidity of 70% and 90%, frost formed but not seriously frosted after 120 min of operating. Frost did not deteriorate but improved the heating performance of the DX-SAHP system. The change of relative humidity from 70% to 90% improves the evaporating heat exchange rate by 35.0% and increases COP by 16.3%, from 1.78 to 2.07.
Highlights
Energy consumed for space heating is a large part of domestic energy consumption
Sporn et al proposed the idea of direct-expansion solar-assisted heat pump (DX-SAHP), as one type of solarassisted heat pumps [6]
Under the ambient temperature of 5°C, 10°C, and 15°C and solar irradiance of 300 W m−2, the evaporator temperature is lower than the ambient temperature, and the specific values are 3.1°C, 7.4°C, and 12.0°C, respectively
Summary
Energy consumed for space heating is a large part of domestic energy consumption. The idea of using solar energy is one of the methods to face the energy crisis, since it is renewable and clean. Krakow and Lin [9] studied the performance of the direct-expansion solar source heat pump systems with solar collectors They concluded that the system was promising to utilize solar energy in cold climates. Chyng et al [12] theoretically researched the annual performance of an integrated solar-assisted heat pump water heater with a bare collector. Chow et al [16] developed a theoretical model of a DX-SAHP water heater with an unglazed solar collector They simulated the performance of the system in a whole year, obtained a yearlong average COP of 6.46 in Hong Kong, and proved the system promising. Zhang et al [20] analyzed the effect of R22, R134a, and R744 on the performance of a solar-air hybrid heat source heat pump water heater They pointed out that three refrigerants had a similar operating performance. The conclusions may benefit the design and optimization of DX-SAHP systems of similar structure
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