A novel solar-assisted ground-source heat pump (SAGSHP) with seasonal heat-storage and heat cascade utilization: Field test and performance analysis

To maintain the energy quality with high temperature and reduce the energy loss of seasonal heat-storage in solar-assisted ground-source heat pumps (SAGSHPs), a novel SAGSHP system with the heat-cascading of borehole heat-exchangers was designed and its field-test was conducted in this paper. The borehole heat-exchangers were divided into two regions: the core region and the peripheral region. The core region can maintain a high temperature (e.g. 45 degrees C), which is much higher than in previous studies, and the heat from this region can be used directly, without the operation of a heat pump. A field-test was conducted in a community in the province Shandong, China. The results indicate that a sufficient soil-temperature gradient (the temperature is high in the core but low at the periphery) can be created and maintained. The monthly averaged borehole-wall-temperature difference between the borehole heat-exchangers (BHEs) at the core and the periphery can be as high as 30.1 degrees C. This means that both cascaded heat-storage and heat-utilization can be realized. In addition, an average performance of CCOP = 5.15 and SCOP = 4.66 can be achieved. Compared with previous studies, despite the lower CCOP, a higher SCOP can be attained, thanks to heat cascade storage and -utilization. The novel approach described in this paper represents a viable alternative for space heating in North China.