The transition to renewable energy in the heating sector faces significant challenges, particularly the mismatch between the availability of renewable thermal energy sources and fluctuating demand. High Temperature Aquifer Thermal Energy Storage (HT-ATES) systems offer a promising solution to mitigate this mismatch and further decarbonize heating systems by bridging the gap between supply and demand.

This thesis explores the integration of HT-ATES into the heating system at TU Delft, which is transitioning from gas-fired boilers and a combined heat and power plant to a geothermal well-based thermal energy system. During periods of low demand in summer, excess geothermal energy will be stored in the HT-ATES system, to be utilized during high-demand periods in winter when the geothermal well's capacity is exceeded. The objective is to meet 85% of the annual heating demand through sustainable thermal energy sources.

In this study, two design options for integrating the HT-ATES into the heating system are analyzed. Besides the geothermal well and the HT-ATES, the heating system also comprises a heat pump to reach the required supply temperatures. One option is to locate the HT-ATES behind the evaporator of the heat pump and therefore use the previously cooled down temperature to extract thermal energy from the HT-ATES. In the second option, the HT-ATES is located directly behind the heat sink in the system, using the return temperature of the consumers to discharge the HT-ATES.

An energy system model is set up using TESPy and coupled to a numerical model to simulate temperature changes in the HT-ATES. With the results of the model, the influence of the integration concept on the system performance is explained. Furthermore, the effect of varying input parameters such as supply and return temperatures as well as overall demands in the system are examined.

The results indicate that, when comparing the two design options with HT-ATES, locating the HT-ATES behind the evaporator yields the better results across all evaluated performance indicators – mainly a reduction of GHG emissions, an improved system SCOP and a better thermal recovery efficiency of the HT-ATES. However, compared to a base design without HT-ATES, the integration of a HT-ATES leads to additional financial costs and a substantial intervention into the subsurface. Due to its lowest electricity consumption, the base design also shows the best system SCOP.

Aquifer thermal energy storage (ATES) is a sustainable technology that provides thermal energy to buildings in temperate climates. The principle of ATES is to temporary store thermal energy in aquifers in a warm and cold well in order to use this thermal energy for heating and cooling in the next season. Because the available subsurface space is limited, congestion problems can occur in areas with high ATES density. In these areas a conflict of interests exists between private parties who want to achieve maximum efficiency by avoiding negative influence of other systems (leading to large buffers between wells), and the public interest to maximize the amount of thermal energy stored in the aquifer. One solution to this problem is to reduce the distance between wells of the same temperature, creating one large thermal zone around the wells. The main goal of this research is to quantify the change in performance of ATES systems when their thermal zones are connected. The results of this research are as follows. Connecting the thermal zones of wells of the same temperature increases the thermal recovery efficiency of individual systems. This increase is between 8-15% for an average ATES system with a storage volume of 250.000 m³. It is even higher for smaller systems, 15-40% for a system with a storage volume of 50.000 m³. This is crease in efficiency is due to lower losses to the surroundings due to a lower area of the thermal zone compared to the volume of the thermal zone. The reduced distance between wells leads to an increase in pumping energy. Therefore an optimal distance between wells of the same temperature of 0.5 times the thermal radius is found. The distance between wells of opposite temperature should be larger than 3 times the thermal radius.