Control strategy development of solar-air dual-source heat pumps under low ambient temperature based on meteorological parameters

In high-altitude regions such as Tibet, the solar-air dual-source heat pump (SAHP) has broad application prospects, owing to the low ambient temperature and abundant solar energy resource. However, how to switch the operation modes based on outdoor meteorological parameter remains a key challenge limiting their engineering applications. To address this issue, a SAHP test rig was built in this work. Under different environmental conditions, the effects of the operation modes of the compressors and evaporators on the heating performance are investigated. Then, a control strategy for the switching of evaporators was established. Results show that the compressors should be work in two-stage compression at low evaporation temperatures, and switch to single-stage compression when the evaporation temperature exceeds −6.5 °C. With the increase of irradiance intensity, the operation mode of the experimental SAHP should be switched from air-source (AS) mode to solar-air dual-source (SADS) mode, and then to solar-source (SS) mode. The irradiance intensities for the two switches at −25 °C are 120 W/m 2 and 610 W/m 2 respectively. They decrease gradually with the increase of ambient temperature. When the ambient temperature rises to 0 °C, they decrease to 70 W/m 2 and 280 W/m 2 respectively. Based on the irradiance intensities for the two switches at different ambient temperatures, a control strategy for evaporators switching is developed, which can improve the COP of SAHP efficiently. Compared to those under AS, SADS, and SS modes, the COP under the developed control strategy increased by 8.11%, 8.53%, and 12.45%, respectively.