Sensitivity Analysis and Optimization of the Vertical GSHP (Ground source heat pump)

Abstract:   GSHP (Ground source heat pump), uses geothermal energy which is a form of green and sustainable energy.  Geothermal energy is also a continuous source of energy, unlike wind energy. The results from this thesis work will be applicable for both GSHP that are being used for space heating, and the ones which have a bottom organic Rankine cycle. The bottom organic Rankine cycle and continuous energy production of GSHP make it a potential source for electricity generation.  The GSHP is of various types, in regard to the configuration of the pipe and their setup in the ground and also based on their grouting. In this study only vertical GSHP and with a single u-tube and water filled grout will be analyzed. The GSHP performance is based on a number of parameters including, the depth of the heat exchanging unit in the ground, other key dimensions of the unit like diameter and outer wall thickness, the fluid flow, and the type of working fluid. Therefore it becomes necessary to study the effect of all of these parameters individually and their individual effect on the energy output and the performance of the BHE. One of the thesis objectives is to establish a sensitivity analysis of the BHE based on the above mention parameters and then further optimize the design with the heat enhancement devices. The major findings of this thesis work are how shank spacing (spacing between the inlet and the outlet pipe) affects the heat transfer in the BHE. The shank spacing seems to reduce the energy output of the GSHP, this is contrary to the high conductive solid grout, where the shank spacing doesn't affect the BHE so much. The diameter of the BHE in the water-filled grout has a completely opposite effect from the solid grout. Increasing the depth of the BHE after a certain length only increases the entropy of the system which reduces the energy output. The working fluid with a higher Prandtl number helps in higher energy output. The optimization results suggest that having a deeper borehole is not very energy efficient in spite of the greater thermal gradient available at a higher depth.