Estimating Ground Thermal Properties of a Borehole Heat Exchanger using the B2G Dynamic Model

Abstract

In situ thermal response tests (TRT s) are currently the standard methodology used for determining ground thermal properties needed for sizing ground source heat exchangers (GSHE). The main drawback of this methodology is the high cost involved, mainly due to the long injection times needed. Since ground conductivity is a key parameter in the design of a GSHE, any advances in the reduction of the duration of a TRT would result in a lower cost. Hence, the viability of this kind of test would increase. In this context, a dynamic model of the GSHE can be very useful to reduce the amount of data needed in order to obtain the ground thermal properties. The recently developed B2G model has proven to be able to reproduce the short-term response of a GSHE with a great accuracy. One of the main advantages of the B2G dynamic model is that it can be adjusted to any specific GSHE with only a few experimental data (typically, corresponding to 10-15 hours of heat injection/extraction). This model could be used to provide an estimation of the ground thermal properties using less data than a standard TRT. In this work, the B2G model has been adapted to an existing borehole heat exchanger (BHE) located at Universitat Politècnica de València. Experimental data corresponding to a TRT performed in this BHE have been used in order to validate the adaptability of the B2G model and its utility as a ground thermal properties estimation tool.