Evaluation of heat extraction using compact shallow ground heat panels with the interaction of stormwater- a residential case study

A bespoke parallel shallow horizontal Ground Source Heat Pump system (GSHP) with a small footprint (50 m2) was installed to provide space heating and domestic hot water for a residential house in the North of England. The shallow GSHP was combined with a storm water infiltration trench and both were installed with an adjacent control house which was fitted with a standard gas boiler for space heating and hot water. Up to 350 metres of High Density Polyethylene (HDPE) pipe with an external diameter of 40 mm connected in 2 parallel compact panels was used at the front and back of the house with the GSHP. The paper aims to (i) present data for the response of the ground to heat extraction using shallow ground heat panels and (ii) analytically model the heat gain in the ground heat exchanger panel, accounting for the thermal resistivity between the heat exchanger pipes and the surrounding soil, as well as the varriations in ground temperature and thermal conductivity. Internal and external ambient air temperatures, rainfall, coolant flow rate, coolant temperature, ground temperature and ground water level were monitored for a full year. The comprehensive field data were analysed to demonstrate the ground response and evaluate the performance of the shallow parallel ground heat extraction panels. Field data indicated that rainwater enhanced heat extraction and caused temporary increase in the ground temperature. Results from the analytical model are compared with measured temperature at five points on the ground heat extraction panel. The model showed good levels of predictive performance of the coolant temperature along the ground panel. However, it was noted that the model overestimates the coolant temperature at the centre point of the ground panel.