Effects of groundwater flow direction on performance of ground heat exchanger borefield in geothermal heat pump systems using 3-D finite difference method

The effects of groundwater direction on performance of geothermal heat pump systems were analyzed using a 3-D finite difference method with rectangular meshes. Each borehole was approximated by a square column with the actual circular borehole section circumscribing the approximated square section. The fluid temperatures inside each borehole were calculated by discretizing borehole vertically into different segments. Simulations made on various borefield configurations under several loading conditions at different groundwater velocities and directions showed that the percentage variation in leaving fluid temperature was highest for continuous constant load. With a daily operating schedule of 12 hours, the maximum percentage variation was reduced by more than 40%. The introduction of a cyclic load decreased it further but to a much lesser extent. Moreover, the percentage variation generally increased with the scale of the borefield. Hence, a more precise estimation on the groundwater characteristics is necessary when designing a large borefield.