Alpine space is characterized by a complex, strongly deformed and tectonically variable geological structure with layers that are usually insufficiently productive for the use of open-loop geothermal systems. More suitable and accessible is the use of borehole heat exchangers (BHEs). Mean annual soil temperature, which significantly affects the required length of the BHE, is relatively low in the alpine environment. However, higher precipitation amounts, which as a part of the hydrological cycle affect the distribution of heat in the Earth's crust, are also typical for the alpine world. The purpose of the master's thesis was, by using numerical model, to analyze heat recovery while exploiting shallow geothermal energy with a BHE and in particular to show the effects of rainwater infiltration and groundwater flow.
On the basis of previously performed geological and hydrogeological mapping, I set up a conceptual model for the area of Črni vrh above Novaki (municipality of Cerkno) and estimated a simplified hydrogeological balance of the investigated area. The required length of BHE, that can cover energy demands of one-dwelling building, was calculated in Earth Energy Designer (EED 4.19) software. Numerical modeling was performed in FEFLOW 7.0 software for eight scenarios that take into account different hydraulic conditions.
The results showed that rainwater infiltration decreases geothermal gradient and cools the model, which is reflected in lower temperature of the carrier fluid, however, it can have a positive effect on the stabilization of the system. Infiltration also affects a rise of water table, which may establish a hydraulic gradient and groundwater flow. According to preliminary studies, the latter improves efficiency of BHE. Based on the results of modeling, improved heat recovery can be expected when Darcy's velocity reaches at least 0.046 m/day, which is conditioned by better permeability of the ground.