Interaction between UTES systems

Abstract

Underground thermal energy storage (UTES) is an efficient technique to fulfill the heating and cooling demand of buildings. UTES uses stable subsurface temperatures store and extract energy. This study covers two types of UTES systems: aquifer thermal energy systems (ATES) and borehole heat exchangers (BHE). UTES systems in the Netherlands have seen a significant growth over the past years (Bloemendal, 2018) and are expected to contribute up to 20% of the heating and cooling demand of buildings by 2050 (Naber et al., 2016). As more UTES systems are installed, the risk of unwanted interaction between different system increases. However, ATES-BHE interaction is largely unknown. The objective of this study is to gather more insight in the interaction of ATES system on the efficiency of BHE systems. A numerical model is used to simulate an ATES well near a BHE system using SEAWAT (Langevin et al., 2008). The model is used to run different simulations, from which the efficiency of a BHE system is computed under different circumstances over a five year period. Four conclusions are drawn from the results. First, groundwater and temperature interference from ATES systems affect the efficiency of a BHE system differently. Simulations show that the effect of groundwater flow induced by an ATES system always has a positive effect on the efficiency of a BHE system. The effect of temperature interference is dependent on the temperature of the ATES well. Groundwater was also found to interfere at larger distances between both systems compared to temperature. Second, the degree of interference is related to the distance between the ATES and BHE system. For distances smaller than 0.5 times the thermal radius of the ATES system, interference from temperature was found to be dominant in the simulations. For distances larger than 0.5 times the thermal radius of the ATES system, groundwater interference was found to be the dominant factor. The third conclusion is that the depth placement of the ATES well screen has little to no effect on the amount of interference on the BHE system. Fourth, it is important to realize that no energy is spontaneously generated or lost as BHE efficiencies increase or decrease respectively. Energy is simply exchanged between the ATES and BHE system through the subsurface. Whether that is disadvantageous depends on the energy demands of both systems. Most energy demands are imbalanced, meaning either cooling or heating demand is larger than the other. It is recommended to consider UTES system installations from a holistic point of view.