RECOVERY TIMES AFTER THERMAL RESPONSE TESTS ON VERTICAL BOREHOLE HEAT EXCHANGERS

Paper in proceeding, 2011

The design of a ground source heat pump system requires accurate knowledge of properties, such as ground thermal conductivity and borehole thermal resistance. These properties are often determined using an in-situ thermal response test of a pilot borehole. These tests are sometimes interrupted by unexpected circumstances and occasionally a retest is required. For a retest to be conducted, the ground temperature must return to within 0.1-0.3 K of the initial undisturbed ground temperature. This paper addresses the issue of borehole retesting and reports on a systematic series of thermal response tests conducted to study the times needed for the ground temperature to return to within 0.3 K of the pre-test ground temperature. Tests were conducted using various heat injection rates and different time durations. Following a test, the development of ground temperature was studied for up to 2-3 months. A mathematical model was used to validate the experimentally measured ground temperatures and to extend the results to other testing conditions.