3275 -- Pipe Spacing for Double-Layer Ground Heat Exchangers PDF

A computer program based on a one-dimensional mathematical model was used to simulate a heat pump system coupled with a double-layer ground heat exchanger (DLGHE) over a period of three or more years. With the depth of the first pipe fixed at 0.5 m, an increase in the distance between the first and the second pipe improves the seasonal performance factor (SPF) of a heating season. The distance corresponding to the maximum value of the SPF varies generally from 4.0 to 4~5 m depending on a free ground area (FGA). Further increase of this distance causes a sluggish decline of the SPF. It appears that the SPF is more influenced by the FGA than by optimal spacing. A shorter distance between pipes, e.g., of 2 m, provides a smaller but more stable SPF over a longer period, even up to 10 years.