Ground thermal response and recovery after heat injection: Experimental investigation

Abstract

Monitoring the ground thermal response to a constant heat flux input is common method for determination of effective ground properties needed for sižing the ground coupled heat pumps. In this work, the experimental procedure included two TRT's with different average injection heat fluxes, 4.43 kW and 7.64 kW, applied to the same borehole. Recorded temperatures of fluids, circulated in an experimental borehole heat exchanger U-tube, are used to determine the ground thermal conductivity and the borehole thermal resistance with the infinite line source model (ILS). Additionally, thermocouples placed on the borehole wall up to the depth of 100 m enabled the measurement of temperature profiles of undisturbed ground and during the recovery period between the two TRTs. The results indicate that true undisturbed state after injected heat flux cannot be reached in short time while the use of higher injection heat flux reduces the influence of the ground's inhomogeneity on the results obtained.