Experimental thermal performance analysis of ground heat exchangers for space heating and cooling applications

Abstract

In recent decades, ground source heat pump systems have become popular for space heating and cooling applications. In both modes of operation, GSHP needs to interact with the ground through GHX. The thermal performance analysis of single and double U-tube heat exchangers are discussed in this paper by focusing on its effectiveness, ground temperatures, heat extraction & injection rate and its effects on surrounding ground formations. Initially the method of calculating length of GHX for a given heat load is explained, then the effectiveness of GHX is defined. Experimental set up used to study the performance of single and double U-tube GHX at bureau of geological and mining research (BRGM), France is explained. Results obtained from the experimental study shows that the average effectiveness of single U-tube heat exchanger in heating and cooling modes are 0.34 and 0.40 respectively and for double U-tube, it is 0.46 and 0.57 respectively. In both the heat exchangers, the average effectiveness is observed to be high in cooling mode operation, the reason may be that in cooling mode operation, the temperature difference between the heat carrier fluid and the ground is found to be high compared to the difference observed during heating mode operation.