Analysis of thermal response tests on boreholes with controlled inlet temperature versus controlled heat input rate

Abstract

Thermal response tests (TRT) are performed on borehole heat exchangers to estimate design properties needed when the boreholes are coupled to heat pumps. In conventional TRTs the heat injection or extraction rate from an external heater or heat pump is controlled to be nearly constant. More recently some investigators have conducted TRTs while controlling the inlet fluid temperature to be nearly constant. This paper develops computationally efficient heat transfer models that match measured transient temperature curves throughout the entire duration for both types of tests. The models include variable heat rates, thermal storage of the borehole fluid and the different properties between the grout and ground. The models are combined with parameter estimation methods and applied to both types of data sets from the same borehole. An uncertainty analysis indicates the models estimate ground thermal conductivity and borehole thermal resistance with approximately the same uncertainty for both types of tests.