Short- and long-term heating performances and optimization of solar heating coupled with groundwater source heat pump (SH-GWSHP) system for 24-h running buildings in Tibetan Plateau, China

Abstract

Tibet is rich in solar energy and has significant heating demand for buildings. Hence, developing a multi-source complementary heating system based on solar energy is a feasible approach to address local heating issues in the Tibetan area. However, the design of a solar energy-based heating system for 24-h running buildings is challenging due to the mismatch between solar energy availability and nocturnal heating load. To fill this gap, a solar heating system coupled with a groundwater source heat pump (SH-GWSHP) is proposed in this study. The heating performance of the proposed SH-GWSHP system for 24-h buildings under Tibetan weather conditions is explored and optimized. A field test is conducted to assess the short-term performance of the SH-GWSHP system at Xigaze Peace Airport. Furthermore, a transient system simulation (TRNSYS) model of the coupled heating system is developed and utilized to analyze and optimize long-term system performance. The results show that the average temperature of a water tank is higher than 50 °C for 4 h and the measured energy efficiency ratios (EERs) of the SH system, combination heating mode, and GWSHP system are 8.52, 3.79, and 3.38, respectively. The maximum daily average collector efficiency is 0.4 and the average value is approximately 0.3 during the middle heating period. In addition, the overall solar fraction is only 0.20 over the entire heating season. The optimal volume of the water tank for performance optimization is 30 m3. The collector area should be maximized to fully utilize solar energy for heating, and the temperature of the heating water should be minimized to achieve optimal heating efficiency.