Thermal performance investigation of several types of vertical ground heat exchangers with different operation mode

The thermal performances of several types of vertical ground heat exchangers (GHEs) for ground source heat pump system have been investigated with different operation mode. Short time period of operation, discontinuous of 6 and 12 h operations in a day, and continuous operation modes were applied in the GHE system. The short time period of operation includes discontinuous 2 h operation in cooling mode and alternative operation mode with operating the GHE in cooling process and heating process to provide hot water supply. The models of three types of vertical GHEs, including U-tube, double-tube, and multi-tube GHEs, were built and simulated using the commercial computational fluid dynamics software FLUENT. The heat exchange rates of the GHEs have been investigated. The numerical results show the reasonable agreement with the experimental results. The off-time period in the discontinuous operation and extracting heat from the ground in the heating process in the alternative operation mode contributed significantly to the increasing the heat exchange rate. Operating the GHEs with different operation mode shows the different characteristic in their heat exchange rates. It can be constructive information for design of the GHE system in practical engineering.