Performance analysis of solar graded heat storage–assisted dual–source heat pump system

The traditional solar heat pump system suffers from insufficient utilization of solar energy resources, which limits the improvement of its energy efficiency and widespread application. To enhance the utilization rate of solar energy in the solar–air source heat pump system, this study establishes a Solar Graded Heat Storage–Assisted Dual–Source Heat Pump (SGHS–DSHP) system, which consists of a solar collector (SC), a dual source heat pump (DSHP), high/low temperature water tanks (HTWT/LTWT), and a load water tank (LWT). A high/low temperature water tank switching strategy was proposed. Taking a nursing home building as a case, TRNSYS simulations were conducted for typical cities in four types of solar resource zones in China to analyze the impact of the DSHP source switching strategy and the high/low temperature water tank shunt strategy on the system performance. The research results show that the dynamic coefficient of performance (COP) switching strategy significantly improves performance compared with the static temperature switching strategy, with the solar energy utilization rate increasing by an average of 4.58%–6.02% and the comprehensive system energy efficiency improving by 4.04%–6.21%. The high/low temperature water tank shunt strategy can increase the solar energy utilization rate from 47.1%–58.2% to 61.5%–70.8%, and the maximum system COP reaches 4.736 kW/kW. Multi–city verification indicates that the two–tier collaborative control composed of the COP switching strategy and the high/low temperature water tank shunt strategy can effectively improve the utilization of low and medium solar irradiance resources, providing a solution for low–carbon building heating.