Modeling and experiments on energy loss in horizontal connecting pipe of vertical ground source heat pump system

In a vertical ground source heat pump (GSHP) system, horizontal pipe is the connection between borehole heat exchanger (BHE) and building. In current estimation of system performance, the energy loss of fluid circulating through a horizontal connecting pipe is often ignored. However, such energy loss can seriously reduce the thermal efficiency of GSHP systems in cold regions. This paper investigates the impacts of pipe burial depth and pipe insulation on energy loss of horizontal connecting pipes of a GSHP system in Nuremberg, Germany. The fluid circulation in a horizontal connecting pipe is investigated via experimental measurement and numerical simulation. Both the on-site data and numerical results suggest that the fluid temperature is substantially influenced by pipe burial depth as well as insulation. The numerical modeling shows that the daily energy loss can vary in magnitudes, as determined by pipe burial depth. On the other hand, up to 50% energy loss can be avoided by adopting a 25 mm thick insulation. These findings suggest that the both pipe burial depth and pipe insulation are important factors to be seriously considered for energy saving in the design and implementation of GSHP systems.