Numerical Modeling of Ground Temperature Response in a Ground Source Heat Pump System (GSHP)

摘要

Ground source heat pump (GSHP) systems use the ground as an energy reservoir and can be installed nearly everywhere, even in areas of low geothermal gradient, to provide an environmental friendly, low-cost, and sustainable energy source for space heating and cooling. This study describes the long-term, cumulative thermal response of the ground around a vertical ground heat exchanger (GHE) operating in both heating and cooling modes, with the dominant GSHP mode being copling. An actual 300-m-deep borehole through varying lithology has been modeled with fully three-dimensional finite element analysis using ABAQUS software. The monthly average surface temperature and temperature at depth were used as boundary conditions, and the monthly heating and cooling loads were applied as constant heat load with depth along the borehole. The modeling results shows that a deep GHE system may be more efficient by taking advantage of the geothermal gradient and is less sensitive to seasonal impacts than shallow GHE systems. Based on the modeling results, the temperature profiles along the borehole and near surface are not constant and vary significantly when the lithology changes. Therefore, the actual thermal conductivity values for each geological material should be considered.