Are shallow boreholes a suitable option for inter-seasonal ground heat storage for the small housing sector?

Abstract

In recent years, various researchers have studied the performance of Solar Assisted Ground Source Heat Pump (SAGSHP) systems using borehole heat exchangers. However, the research conducted has been limited to conventional boreholes (30m to 150m depth), which are expensive and not suitable for the small housing sector. This paper reports an experimental analysis of a shallow SAGSHP system with inter-seasonal storage. The system, installed in Leicester UK, consists of seven photovoltaic-thermal (PVT) collectors connected in series with an array of 16 shallow boreholes (1.5 meters depth). Data regarding the energy fluxes involved in the soil-based thermal store have been monitored and analysed for one year. The results show that the shallow soil is able to serve as a storage medium to cover the heating demands of a near zero energy domestic building. However, it was noticed that in addition to the solar heat captured and stored in the soil, the system covers part of the heating demand from heat extracted from the soil surrounding the thermal store. During winter, the lowest temperature reached by the soil so far is 2 °C. Hence, no freezing problems have occurred in the soil. An analysis of the temperature variation of the ground storage under the system operation is also shown.