A thermal response method of calculating a soil's thermal properties when backfill material information is unavailable

The accurate definition of soil thermal properties around a borehole is helpful when designing a ground source heat pump system. Existing thermal response methods for obtaining a soil's thermal properties require knowledge of the backfill material's conductivity, which is difficult for a technician to obtain in situ. This study developed a new method to calculate a soil's thermal diffusivity when the backfill material's thermal conductivity in the borehole is unavailable. The developed model was verified by a theoretical calculated method. An experiment was conducted in situ to measure a soil's thermal conductivity for use with a ground source heat pump system and the results were used to verify the proposed method. The soil conductivity was measured as 1.98 W/(m K) and the thermal diffusivity was 2.79 × 10−7 m2/s when the backfill material's thermal conductivity was available, while the new method gave a thermal diffusivity of 2.81 × 10−7 m2/s. The results indicated that the proposed method would be useful in future engineering projects, especially those lacking information on a backfill material's properties.

► We developed a model to calculate soil thermal properties when backfilled materials information is not available.
► The new method was verified by theoretical perfectly.
► The new method was also agreed well with field test in situ.
► The model can be applied in the engineering and reduced the requirement of situ technician.