Development of a variable water temperature control method for air source heat pump based on the supply-demand balance

Air source heat pump (ASHP) is one of renewable energy technologies, and has been widely used for space heating. In practice applications, the setting value of its supply water temperature is long-term fixed, resulting in the poor coefficient of performance (COP) under partial load conditions. To improve the COP of ASHP, a real-time variable water temperature (VWT) control method for its supply water temperature was proposed in this work. In this control method, the optimal supply water temperature was calculated based on the supply and demand balance, and used as the setting value of supply water temperature. Then using an ASHP-radiant floor heating system, the feasibility and energy-saving performance of the proposed control method were investigated through experiment and simulation. Results indicate that the ASHP heating system can run smoothly when adopting the proposed VWT control method. Compared with the results in constant water temperature (CWT) control method, in the whole heating season, the COP of ASHP unit in VWT control method is 22.88% higher, while the building heating energy consumption is 26.16% lower. Besides, the percentage of predicted mean vote (PMV) between - 0.5 and + 0.5 increases from 48.61% in CWT control method to 87.86% in VWT control method.