Thermal performance of the ground in geothermal pavements

Shallow geothermal energy utilises the ground at relatively shallow depths as a heat source or sink to efficiently heat and cool buildings. Geothermal pavement systems represent a novel concept where horizontal ground source heat pump systems (GSHP) are implemented in pavements instead of purpose-built trenches, thus reducing their capital costs. This paper presents a geothermal pavement system segment (20m × 10m) constructed and monitored in the city of Adelaide, Australia, as well as thermal response testing (TRT) results. Pipes have been installed in the pavement at 0.5 m depth, and several thermistors have been placed on the pipes and in the ground. A TRT has been performed with 6kW heating load to achieve an understanding of the thermal response of the system as well as to estimate the effective thermal conductivity of the ground. The results show that the conventional semi-log method may be applicable to determine the thermal conductivity for geothermal pavements. The geothermal heat exchanger at shallow depth is considerably under the influence of the ambient temperature; however, it is still acceptable for exchanging the heat within the ground. It is also concluded that the impact radius of heat exchanger in geothermal pavement during the TRT is around 0.5m in the vertical and horizontal directions for this case study.