R290 (propane) is an environmental friendly refrigerant with zero ozone depletion potential (ODP) and low global warming potential (GWP). A direct-expansion solar-assisted heat pump (DX-SAHP) water heater system using R290 was designed and built to investigate its thermal performance, which comprised a constant-frequency rotary-type hermetic compressor with rated power of 471 W, a micro-channel solar collector/evaporator with surface area of 2.09 m², a micro-channel condenser with effective heat-transfer area of 0.75 m², and an electronic expansion valve. In order to evaluate the DX-SAHP system performance during the winter period, massive experiments have been carried out with a refrigerant charge of 350 or 410 g. Under these environmental parameters as follows: the average solar radiation intensity of 20–592 W m⁻², average ambient temperature of −3.0–12.2 °C, and average wind speed of 0.01–1.15 m s⁻¹, while the 200 L water at 7.2–15.3 °C was heated to 37.7–54.9 °C, the average system coefficient of performance (COP) ranged from 2.12 to 4.43. Finally, the responses of the DX-SAHP system using R290 to variations in solar radiation intensity and ambient temperature are presented. The transient variations in the refrigerant mass flow rate, the electric power input to the compressor and the electronic expansion valve opening are also analyzed under different weather conditions.

R290（丙烷）是一种环保型制冷剂，臭氧消耗潜能值（ODP）为零，全球变暖潜势值（GWP）低。设计并构建了使用R290的直接膨胀式太阳能辅助热泵（DX-SAHP）热水器系统，以研究其热性能，该系统包括额定功率为471 W的恒定频率旋转式封闭式压缩机，表面积为2.09 m ^2的通道太阳能集热器/蒸发器，有效传热面积为0.75 m ²的微通道冷凝器，以及电子膨胀阀。为了评估DX-SAHP系统在冬季的性能，已经对350或410 g的制冷剂进行了大规模的实验。在这些环境参数下如下：平均太阳辐射强度为20–592 W m ^-2，平均环境温度为−3.0–12.2°C，平均风速为0.01–1.15 m s ^-1，将200 L的水在7.2–15.3°C下加热到37.7–54.9°C时，平均系统性能系数（COP）为2.12至4.43。最后，介绍了使用R290的DX-SAHP系统对太阳辐射强度和环境温度变化的响应。在不同的天气条件下，还分析了制冷剂质量流量，输入到压缩机的电功率和电子膨胀阀开度的瞬态变化。