Estimating soil thermal diffusivity with interference analyses

The development of ground source heat pumps has facilitated the use of geothermal power at shallow depths. Initially, ground heat exchangers were buried in trenches or boreholes, but recent investigations and increasing congestion of landscapes have suggested the use of foundation structures as heat exchangers with the ground. Foundations are shorter than conventional borehole heat exchangers and are closer to each other to ensure structural support. The thermal inertia of grounds wherein seasonal heat storage is achieved, therefore, becomes an important parameter for the design of such structures. Although thermal response tests have been developed to estimate bulk thermal conductivity on the scale of geo-thermal boreholes, only laboratory or shallow in situ test methods have been developed to estimate the thermal diffusivity of the ground. This paper investigates the potential for using a periodic pumping test procedure to measure the thermal diffusivity of soils in a scaled model of a geothermal borehole. The thermal diffusivity estimates obtained are in agreement with values reported in the literature and illustrate the potential of the proposed method.