An experiment system with different types of U-vertical ground coupled heat exchanger (UGCHE) in situ was set up, for example, single or double U-pipes with sandstone backfills, and single U-pipe with cement backfills. Experiments on the thermal performance of UGCHE were carried out in different conditions, such as different inlet temperature, flow rate, soil types, backfill materials, number of U-pipes and the different operation modes. In theory, an inner heat source model was adopted, and the simulation has been done for the underground temperature field with professional porous medium software. (c) 2005 Elsevier B.V. All rights reserved.