Comparing the Thermal Performance of Ground Heat Exchangers of Various Lengths, Effstock Int. Conference, Stockholm, June 2009.

In many ground-coupled heat pump systems, borehole heat exchangers (BHE) represent the most important cost item. Therefore, alternative BHE construction should be investigated. In this paper the possibility of using short BHE (drilling depth lower than 50 m) is considered, based on the premise that shorther BHE drilling technologies and procedures could result in a lower cost per unit length of ground heat exchanger. The objective of this study is to compare the thermal performances of standard depth BHE with short ones, for a given building load. The thermal response of several BHE arrangements, expressed in the form of g-functions, are obtained using the so-called “finite line source” method with appropriate spatial superposition. The results are discussed with reference to literature data and also examined with respect to annual hourly simulations, in order to assess advantages of short BHE arrangements compared to current drilling solutions