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Ground source heat pumps (GSHP) are the most efficient heat pump systems currently in use for residential sector today. Although these systems outperform all other heat pump systems when considering the energy source, the installation costs represent an ongoing issue. For the market to increase in this area, multi-criteria optimization for the ground heat exchanger (GHE) is the main research topic today. The main objective of this study is to search ways to optimize the horizontal ground heat exchanger focusing on two distinct viewpoints: physical and energetic optimization. To achieve this goal, the entropy generation number and the coefficient of performance based on several configuration are studied. Using the Pareto optimal set obtained from two objectives provides useful information about the design optimization. In comparison with traditional single objective optimization, multi-criteria optimization avoids cost increase when regarding only the performance or performance decrease when regarding only the cost. The results indicate that the use of a cheaper heat source such as solar panels to mitigate the energy needed for peak loads during the heating and cooling systems can reduce the horizontal ground heat exchanger size and therefore the installation cost. A hybrid solar assisted ground source heat pump system, using more than one renewable energy source, shows a much higher flexibility for residential purposes than a heat pump system that uses only one renewable energy source.

Human interference with the Earth’s climate cannot be ignored any longer. Renewable energy sources need utmost attention in all energy sectors. For buildings, geothermal energy for heating, cooling, and domestic hot water is a sustainable solution. Horizontal ground heat exchangers (HGHE) demonstrate promising results with low installation costs. Research is focused on increasing their thermal performances by structural improvements and ground thermal proprieties improvements, with little research on using auxiliary heat to increase their performances. A numerical model for an HGHE was established to investigate the effects of auxiliary heat sources on the performances of the HGHE. The results demonstrate that heat transfer into the HGHE increases the overall ground temperature at the end of the heating season by 138.50% compared with no heat transfer from auxiliary heat sources. The ground freezing period decreased by approximately 24.74% by having a heated basement, approximately 40.20% by transferring heat with solar thermal panels, and approximately 62.88% by using both auxiliary heat sources. The difference between the undisturbed ground temperature and the ground temperature with no auxiliary heat sources at the end of the season was 3.45 °C. The difference between the undisturbed ground temperature and the ground temperature with all auxiliary heat sources resulted in 0.92 °C.

Ground heat exchangers represent the barrier between installing a ground source heat pump (GSHP) or a heat pump that use another source as water or air. While the vertical ground heat exchangers (VGHE) yield better results than horizontal ground heat exchangers (HGHE), the installation cost is higher than HGHE. Although, HGHE installation cost is a lot more affordable for residential use, it has the disadvantage of requiring a large installation area and lower efficiency than VGHE due to the temperature variation at the surface of the ground throughout the year. This study focuses on investigating possible use of the energy that is lost through the ground from basements in general, to help the heat pump when the HGHE is installed in the proximity of the basement. In order to achieve concluding results, an experiment was conducted at the University of Transilvania from Braşov, at the Faculty of Civil Engineering. In the experiment the HGHE was installed next to the basement exterior wall. In addition, a CFD numerical study was conducted. Firstly, to verify the experimental measurements and secondly, to obtain results with different working parameters. The results indicate that the thermal insulation degree of the basement wall and floor is an important parameter when considering heat loss into the ground. Likewise, the thermal state of the basement, heated or unheated, contributes considerably to the final results. Consequently, positioning the HGHE in the proximity of basements can represent an energetic optimization, especially when the basement is heated and it isn’t thermal insulated, as can be the case for an existing building.

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