Performance evaluation before and after solar seasonal storage coupled with ground source heat pump

• A solar seasonal storage coupled with ground source heat pump system was designed and implemented.
• The COP of GSHP system and coupled system were calculated and compared.
• The COP of the coupled system was higher than that of GSHP system.
• The soil temperature increased after solar seasonal storage process.

The COP (Coefficient of Performance) of the ground-source heat pump (GSHP) system decreased gradually year after year mainly caused by imbalance of thermal energy inputting, especially in heating-dominated climate zones. An experimental system of solar seasonal storage coupling with ground-source heat pump was designed and implemented. This system was installed in a group of new buildings of the new campus in Tianjin, China, which is located in cold climate zone and heat demand is dominated. To make evaluation to this system, a mathematical method was developed to calculate the COP of GSHP system and the coupled system. In this thermal storage experiment process, a system with 1500 m2 solar thermal collectors and 580 sets of 120 m deep ground thermal exchangers was involved in this research. Results show that the soil temperature has not descended but increased by 0.21 °C, and the COP of system and heat pump unit increased 3.4% and 2.4% respectively compared to the operation data without solar seasonal storage process during last year. Although the effectiveness of solar seasonal storage coupled is not conspicuous as expected during the testing period, it indicates that the tendency of COP declination is prevented, and further illustrating that improving the COP of the system is a long-term work, the application of solar seasonal storage coupled with GSHP system should be encouraged for long-term operation.