Experimental study on the applicability of ungrouted ground heat exchangers on thermal response tests

The applicability of ungrouted ground heat exchangers (GHEs) in thermal response tests (TRTs) has not been confirmed since TRTs are generally carried out in grouted GHEs. In this work, two TRTs were carried out in a 102 m GHE of 100 mm casing ID under ungrouted and grouted conditions. The TRT results were interpreted through the conventional graphical method and more advanced approach using the cylindrical source function and optical fiber thermometers. The interpretation results of thermal conductivity in the ungrouted and grouted GHE showed reasonably good matching in both interpretation methods, indicating the applicability of the TRTs to ungrouted GHEs for the optimum design and the development of potential maps of ground source heat pump systems.