Long Term Performance Prediction of a Borehole and Determination of Optimal Thermal Response Test Duration

Abstract

Capacity loss becomes a vital problem especially for long term usage of Ground Source Heat Pump Systems (GSHPS). Therefore long term prediction of heat transfer rate per unit borehole length (unit HTR value) is an important issue to reliably determine the borehole quantity in a project. In this study, constant temperature thermal response test (TRT) is considered since it has some advantages over constant heat flux TRT. An analytical model is developed to determine heat diffusivity and thermal conductivity of ground by using the experimental TRT values. Long term (3-6 months) HTR values of a borehole are predicted by using the experimental data collected during TRT in the developed model. The effect of TRT duration on long term predictions is analyzed. Variation of the predictions for HTR values at end of heating/cooling season with duration of TRT value is examined. Optimal TRT duration is determined. Results can be used for long term performance predictions as well as the optimization of TRT duration. This model can also be used for estimation of efficient borehole life time.