Analysis and thermal response test for vertical ground heat exchanger with two U‐loop configuration

An in situ thermal response test (TRT) is applied to evaluate the thermal performance of the vertical ground heat exchanger (GHX) with two U‐loop configuration. A line source method is used to derive the thermal conductivity and borehole thermal resistance from the measured data. Analyses are made to improve the interpretation of TRT data and to investigate the active area of interest in the borehole. Load tests of the GHX are performed to examine the daily variations of ground and mean fluid temperatures associated with daily intermittent operation of ground source heat pump system. Results show that while the ground thermal conductivity of two U‐loop GHX is moderately increased, the borehole thermal resistance is significantly reduced, compared with the single U‐loop GHX. Of the borehole thermal resistance components evaluated, the grout thermal resistance is the most governing one in the borehole heat transfer (77% of the total borehole thermal resistance), whereas the convective thermal resistance in the tube is almost negligible (less than 2%). Copyright © 2015 John Wiley & Sons, Ltd.