Intégration des énergies renouvelables pour le chauffage et la climatisation des bâtiments en utilisant les pompes à chaleur.

Abstract

To exploit shallow geothermal energy or the very low temperature geothermal energy, coupling ground source heat pump system (GSHPS) with borehole heat exchangers (BHE) represents the best tool. In many previous studies, only a single or few factors that influence the sustainability and efficiency of a GSHPS were investigated, in the present paper a numerical 2D axissymmetric transient model has been built using the finite volume method then implanted in MATLAB, which is suitable to predict transient temperature distributions of the heat carrier fluid and the surrounding soil over the well depth for a borehole field (accounting for thermal interferences), it’s been compared against two analytical solutions and the numerical code COMSOL where the results have been found identical. In this thesis, the first part of the results tends to an inducement and this is to better clarify the occurrence of heat transfer and thermal interferences in the sub-ground; the second part of the results treats the impact of different physical processes in the surrounding soil, this is to get closer to the real case and so ensure a more precise design; the impacts that have been studied are: axial effects, porosity, undergroundwater flow and phase change in the soil, a coaxial borehole heat exchanger has been selected regarding to its better performances. In the third part of the results, a performance and optimization study has been carried out with different borehole inner and outer diameters and the inlet fluid temperature. The model parameters are based on local conditions of Constantine area. The results show, for the impact study in the surrounding ground, that porous grounds are more suitable for these systems, when porosity is 0% the thermal load decreases by 15.725% than the case where porosity is 45%; also, it’s been found that after occurrence of phase change in the saturated sub-ground, effective thermal properties changes in a way to make the withdrawn thermal load decreases in a more intense manner, it reduces by 5.36% than the case where the process isn’t accounted for and this is during the last 843 h (35 days) since the process start; the last part of the impact study yields that the underground-water flow is favoured for the system performance. The optimization part resulted that the increase in diameters causes an increase in the COP, but starting from a certain threshold, this increase in diameters becomes useless where it yields a negligible increase of the COP value and only causes an increase in the investment cost uselessly, also, it’s been found that the inlet temperature, in order to keep the COP as higher as possible, decreases linearly function to the decrease in the BHE wall temperature, in order to implement this concept in the practice and follow the dependency of the inlet temperature to the BHE wall temperature, a 3-way valve has been conceived and suggested, this valve is responsible for regulating the inlet temperature by regulating the mixture of the fluid directly exiting the evaporator and the one directly exiting the well. The fourth and the last part of the results has been carried out as a case study and this is to show the applicability of these systems.