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.

This report contains the findings of a multidisciplinary project in Mozambique which ran from mid-November 2018 to mid-January 2019. This study is part of the IWACA-TECH project, which is an abbreviation for “Improved Water efficiency Control based on remote sensing TECHnologies. The goal is to increase water efficiency and crop yield without increasing the consumptive use of water, using remote sensing and Model Predictive Control (MPC). The structural water scarcity in the region points out the relevance of the IWACATECH project and with that this study. The research, carried out by students of Delft University of Technology, is of importance for both the company Tongaat Hulett and all inhabitants who are direct or indirect dependent on the water of the Incomati river. The study area on the plantation in Xinavane copes not only with inefficient irrigation water use but also suffers a sugarcane yield decline in recent years ??. Therefore, the overall aim of this report is to improve water efficiency and crop yield within Tongaat Hulett. To achieve this from a multidisciplinary perspective several research questions have been formulated. Although they all contribute to the overall aim, they do so from different angles and in varying degrees. Therefore, to increase the readability of the report, the research questions have been divided into three sections: (1) Irrigation Practices, (2) Field Assessment on Yield Variability and (3) Decision Support System. Fieldwork was conducted over a five week period in order to gather data. Groundwater levels were measured, water quality of irrigation, ground- and precipitation water samples was analysed and soil moisture content was measured. This led to further research of soil types and quality. Soil profiles along the edges of both fields were made revealing a shallow aquifer in the bad-performing field. Irrigation water quality seems to form no hazard, but ground water quality analyses revealed significantly high electrical conductivity levels and a high sodium adsorption ratio in areas without growth. These findings, combined with an analysis of the digital elevation map and socio-technical data revealed that evaporation of irrigation water seems to be a large contributor to the impaired crop growth. When excess water cannot run off, puddles are formed. When these puddles evaporate, salts can be taken up by the soil once the thickened irrigation water infiltrates. This process is strengthened by the clay soil layer and the shallow aquifer, which prevent water from infiltrating deeper into the ground. Results concerning remote sensing prove the relationship between soil moisture content and precipitation for meteo-station XNA-20. Combining spatial and temporal variability of soil moisture content with remote sensing can play an essential role in managing irrigation practices. For the decision support system, and in specific the controller part of the system, measurements have been done. It can be concluded that storage area and delay times can be considered insignificant, and that canals do not have to be modelled. This makes the controller significantly easier and thus more time and effort can be spend on other aspects of the controller.