Investigating the thermal behaviour of geothermal pavements using Thermal Response Test (TRT)

Abstract

Geothermal pavements represents a novel approach to shallow geothermal energy applications, in which horizontal ground heat exchangers are implemented within the pavement structure instead of traditional purpose-built trenches, thus decreasing capital costs. This study aims to better understand the feasibility and potential of these systems, by investigating the thermal response of the ground in a full scale geothermal pavements system, the first of its kind in Australasia. For this purpose, a fully instrumented geothermal pavements segment, measuring 20 m × 10 m, was constructed in the city of Adelaide, Australia. The geothermal pavement was subjected to Thermal Response Testing (TRT) and numerical modelling is adopted herein and validated using TRT data to further understand the ground response. In addition to providing insights on the capacity of energy provision for geothermal pavements, this work also introduces and discusses various methods of TRT data analysis for the geothermal pavement, specifically for obtaining the effective ground thermal conductivity, a key parameter in shallow geothermal design. The results indicate that from the considered methods, the conventional semi-log method can lead to overestimation of thermal conductivity, the guarded hot plate model tends to underestimate its value and detailed numerical modelling is most accurate, but computationally more expensive. The results also show that the radius of influence of the geothermal pavement in the examined case is close to 0.5 m and even though the geothermal pavement is considerably affected by the ambient temperature, it can be a viable solution for heating and cooling purposes, showing a heat exchange of 50.2 W/m2 and a rate per length of the pipe of 25 W/m in the case analysed here.