EXPERIMENTAL COMPARISON OF FOUR BOREHOLE HEAT EXCHANGERS

摘要

The most common way to exchange heat with the bedrock in ground source heat pump applications isrncirculating a secondary fluid through a closed U-pipe loop in a vertical borehole. This fluid transports thernheat from the rock to the ground source heat pump evaporator. The quality of the heat exchange with thernground and the necessary pumping power to generate the fluid circulation are dependent on the type of fluidrnand its flow conditions along the pipe. Four different borehole heat exchangers are tested using ethyl alcoholrnwith 20% volume concentration. The fluid temperatures are logged at the borehole inlet, bottom, and outlet.rnThe collectors are compared based on their borehole thermal resistance and pressure drop at different flowrnrates. The results indicate that the pipe dimensions play an important roll, spacers might not contribute tornbetter heat transfer, and inner micro fins in the pipes improve the performance of the collectors.