Development and validation of disturbance-considering numerical model for investigation of error in thermal response tests

摘要

Thermal response tests (TRTs) are essential for reliable and accurate design of ground source heat pumps. The approximated infinite line source (ILS) model is widely used to interpret TRTs because of its simplicity. However, in actual field conditions, the constant heat flux assumption of the ILS model is violated in most cases because the above-ground hydraulic circuit, which connects the borehole heat exchanger (BHE) and the TRT rig, is exposed to the outdoor environment. This results in perturbations in the temperature response, occasioned by heat exchange between the circulating fluid and the outdoor environment. This disturbance causes fluctuations in sequential estimation and consequent estimation errors in TRTs. As a first step in investigation of the estimation error in TRTs, this paper reports on the development of an analytical model that considers the heat exchange in the hydraulic circuit connecting the BHE to the TRT rig, and its incorporation into the numerical BHE model. The results of comparison of the integrated numerical BHE model against actual experimental in situ TRT data show very good agreement, with maximum difference and maximum relative error of approximately 0.2 K and less than 0.8%, respectively.