Ground temperature profile while thermal response testing

Abstract

In the context of a project funded by the Spanish Ministry of Science and Innovation, a reference borehole heat exchanger installation was constructed in the Universitat Politècnica de València campus. Its purpose was to improve the procedures to characterize thermal properties of Mediterranean area grounds. Borehole depth is 40 meters, with two independent Upipes inside, first one 29 meter depth and second one 39 meter depth. First thermal response test executed in this installation was started on December-15-2010 at 11:00am and inserts 2449 W of thermal power to the shorter U-pipe. Test duration was seven days, finishing on December-22-2010 at 10:30am. Second U-pipe was used to measure ground temperature profile while the test was performed, by inserting a temperature sensor in this pipe several times, measuring ground temperature every meter. This contribution presents these experimental measurements. First temperature profile was measured one day before the test was started and second one when thermal power was switched on. Then, temperature profiles were acquired one day, two days, five days and seven days after, when thermal power was switched off. Main conclusion of this contribution is the clear identification of layers with quite different thermal behaviour, indicating the presence of ground water flows at several depths (10, 18 and 25 meters). This contribution also analyses thermal response test data to estimate effective ground thermal conductivity and borehole thermal resistance, and presents measurements of the temperature profile after the test was finished, showing the time that the ground needs to recover from this injection test.