Modeling of Geothermal Heat Exchangers

Abstract

Heat pumps (HP) attain higher efficiencies and save energy when they are coupled to ground heat exchangers (GHEs). For this reason we compare, by modeling, the efficiency of the vertical and horizontal GHEs which are two basic types. The modeling of the vertical heat exchanger is represented by two tube lines of 100 m in length, embedded in four different types of ground with an additional bottom base. The horizontal heat exchanger consists of four tube lines, 50 m in length each, embedded in three ground layers. The simulation results of the vertical GHE are validated by comparison to a measured set of data showing very good agreement. Further simulations with the vertical GHE show, as expected, that when the initial ground temperature rises the mean temperature of the heat exchanger fluid increases as well in a linear relationship. For a 50-hour continuous operation, the inlet and outlet fluid temperatures are computed for certain ground temperatures. Comparisons between the horizontal and vertical GHEs reveal that under the same operating conditions and center-to-center distances of the tubes, the vertical heat exchanger keeps a much lower mean GHE show, as expected, that when the initial ground temperature rises the mean temperature of the heat exchanger fluid increases as well in a linear relationship. For a 50-hour continuous operation, the inlet and outlet fluid temperatures are computed for certain ground temperatures. Comparisons between the horizontal and vertical GHEs reveal that under the same operating conditions and center-to-center distances of the tubes, the vertical heat exchanger keeps a much lower meanGHE show, as expected, that when the initial ground temperature rises the mean temperature of the heat exchanger fluid increases as well in a linear relationship. For a 50-hour continuous operation, the inlet and outlet fluid temperatures are computed for certain ground temperatures. Comparisons between the horizontal and vertical GHEs reveal that under the same operating conditions and center-to-center distances of the tubes, the vertical heat exchanger keeps a much lower mean temperature because the initial ground temperature at the buried tube depth is always higher than that of the vertical GHE. Because of this observation one would assume that the vertical GHE is more efficient than the horizontal. Instead, in a proper design, one could increase the distance between the tube centres and in this way decrease the mean temperature of the tube fluid. Simulations, for a 50-hour continuous temperature because the initial ground temperature at the buried tube depth is always higher than that of the vertical GHE. Because of this observation one would assume that the vertical GHE is more efficient than the horizontal. Instead, in a proper design, one could increase the distance between the tube centres and in this way decrease the mean temperature of the tube fluid. Simulations, for a 50-hour continuous temperature because the initial ground temperature at the buried tube depth is always higher than that of the vertical GHE. Because of this observation one would assume that the vertical GHE is more efficient than the horizontal. Instead, in a proper design, one could increase the distance between the tube centres and in this way decrease the mean temperature of the tube fluid. Simulations, for a 50-hour continuous operation and 24°C initial ground temperature, show that the mean operation and 24°C initial ground temperature, show that the mean fluid temperature can stay below that of the vertical GHE if the center-to-center distance of the tubes increases to 1 .