This research aims to enhance the efficiency of Ground Source Heat Pump (GSHP)system, specifically the U-tube Borehole Heat Exchanger (BHE)system, through reducing the required loop depth to decrease the installation cost. This will assess in promoting the use of BHE system in commercial and small industrial facilities in the UK. Ground source heat pump (GSHP) systems, due to their high coefficient of performance (COP) and low CO2 emissions are great substitute for fossil fuel to provide more comfortable coexistence of humans and the environment The design optimisation of the BHE is attempted in this research through the reduction of the total thermal resistance value (Rt). This reduction will lead to lower the required loop depth, and therefore enhance the thermal efficiency of the system and decrease the installation cost. The total thermal resistance is a sum of borehole thermal resistance (Rb) and ground thermal resistance (Rg) values. The ground thermal resistance is influenced by soil thermal properties around the borehole, while borehole resistance is influenced by borehole thermal materials and geometric configurations. Measuring the components of the total resistance accurately and finding technique to reduce Rt is highly required in BHE design field. Several equations are available to calculate the value of borehole thermal resistance, however, there is no definite decision about their validity. Furthermore, although there are methods suggested in the literature to reduce Rb, none of them were able to reduce it to satisfactory level. Extensive numerical experimental program was conducted in this study to provide better understanding in the field of the thermal resistance of BHE. The originally of this work rests on the following pillars: I. Conducting a thorough numerical assessment for the available equations in the literature that predict the value of borehole thermal resistance. II. Conducting an intensive numerical characterization for borehole thermal resistance. III. Exploring several methods to reduce the Rb, and Rt and assessing their efficiency numerically.
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