Multi-layered soil effects on vertical ground-coupled heat pump design

Heat transfer in multi-layered soils with vertical ground-coupled heat pumps was investigated experimentally and numerically. Experiments were conducted to simulate the heat transfer from hot water in a copper tube to a three-layered soil system comprised of coarse sand, clay, and fine sand. A two-dimensional, transient, heat conduction model was also developed and solved numerically. The experimentally measured and computer simulated temperatures agreed well (R² = 0.95, alpha = 0.001) and the heat transfer rates were found to be discontinuous between soil layers. The coarse sand and the fine sand dissipated over 62 and 27% more heat than the clay, respectively, during 24 hours of operation. Vertical temperature gradients existed between the coarse sand and clay and fine sand and clay layers in the early stage of heat transfer. These temperature gradients decreased as the operation time elapsed due to the vertical heat flow.