Solar heat pump configurations for water heating system in China

Abstract

The solar-assisted heat pump (SAHP) water heating system has a high potential to minimize the fossil fuel consumption in space heating. Among its various configurations, the serial configuration of solar energy and heat pump remains to be examined systematically as to whether it is worth the electrical work of water-source heat pump (WSHP) to collect more solar energy. To address this issue, this study compared the seasonal energy performance between a serial SAHP system and its parallel counterpart for space heating applications in 39 cities across China using a validated TRNSYS model. The results show that the parallel system performs better than the serial system in general if an air-source heat pump (ASHP) is the auxiliary source. It is otherwise when electrical heating is the auxiliary source. Higher solar radiation and warmer climates favour the parallel configuration while a more efficient WSHP favours the serial configuration. In the Tibet plateau with high solar radiation, the parallel system can achieve twice the efficiency of the serial system. At a supply temperature of 45 °C in Shanghai, the serial system starts to outperform the parallel system if the WSHP can achieve a rated coefficient of performance greater than 6.9. Higher supply temperatures also favour the serial configuration. It is recommended that the SAHP takes the form of a parallel configuration when an efficient auxiliary source, such as ASHP, is available. However, in the severe cold regions, the serial system can be a better choice if an efficient WSHP system is available and the starting temperature is optimized.