Estimation and Experimental Validation of Borehole Thermal Resistance

Abstract

This paper focuses on an evaluation of current borehole-thermal-resistance-estimation models based on a Thermal Response Test (TRT). For the TRT, a U-type heat exchanger was installed in a single medium formed in a model box, and the test performed for about 18 hours. In order to estimate the borehole thermal resistance, two imaginary circles were regarded as the borehole boundary where the two Resistance Temperature Detector (RTD) sensors were buried. The values of thermal resistance determined from the series-sum and multipole methods were compared to each other, as well as to the results from the thermal response test and numerical simulation. With reference to the experimental results, numerical analysis and multipole methods and Remund's model predicted reasonable results. Using the multipole method and numerical simulation, it was possible to estimate the borehole thermal resistance in a composite region. It was found that the thermal conductivity of the grout had a great influence on the borehole thermal resistance. However, this effect became smaller as the grout thermal conductivity increased.