Hydraulisk och termisk grundvattenmodellering av ett geoenergilager i Stockholmsåsen
AkviferlagerMODFLOWMT3DMSGeoenergilagerHydraulisk grundvattenmodelleringTermisk grundvattenmodellering
Geothermal energy can be extracted from an aquifer, where the groundwater is used as heatexchange medium while heat and cold are stored in the surrounding material in the aquiferand to some extent in the groundwater. Application of aquifer storage for the use ofgeothermal energy is mainly used in large scale facilities and is limited to sites with suitableaquifers in the form of ridges, sandstone and limestone aquifers.Löwenströmska hospital in the municipality of Upplands Väsby, north of Stockholm, islocated nearby the northern part of the Stockholm esker. This means that it can be profitableand environmentally beneficial for the hospital to examine the possibilities of aquifer storagein the esker material next to its property.The purpose of this master thesis has been to investigate if geothermal energy storage with aseasonal storage of heat and cold can be applied within Löwenströmska hospital?s propertyarea using groundwater modeling. A hydraulic groundwater model was constructed inMODFLOW based on a simplified conceptual model of the groundwater system. Thehydraulic groundwater model was calibrated and validated against observed groundwaterlevels before and after a pumping test. The hydraulic groundwater model was then used toimplement a fictitious geothermal energy storage with MT3DMS. MT3DMS is a modularfunction used with MODFLOW, which can be modified to simulate heat transport.The result shows that the geothermal energy storage can store seasonal heating and cooling ofabout 4 GWh, which covers 85 % of the hospital?s heating demand with an assumed SP-factorof 4, and the entire cooling demand. To cover 50 % of the peak heating power it wascalculated that a flow of 63 l/s was needed, and according to the model this is possible. Thegeothermal energy storage does not need to be completely in energy balance, since the aquiferis recharged with its natural groundwater. The location of the wells influences which flowsthat are needed to create energy balance. A too close placement of the wells leads to a thermalbreakthrough. The hydraulic conductivity of the esker material affects the amount of energythat can be stored. A higher hydraulic conductivity provides greater energy losses and a lowerhydraulic conductivity favors the energy storage but gives a greater influence area.A number of assumptions have been made in the model construction of the hydrogeologicalmodel and further investigation of the geological and hydrogeological conditions are desirableto improve the model.