Independent thesis Advanced level (professional degree), 20 credits / 30 HE credits
Geothermal energy can be extracted from an aquifer, where the groundwater is used as heat
exchange medium while heat and cold are stored in the surrounding material in the aquifer
and to some extent in the groundwater. Application of aquifer storage for the use of
geothermal energy is mainly used in large scale facilities and is limited to sites with suitable
aquifers in the form of ridges, sandstone and limestone aquifers.
Löwenströmska hospital in the municipality of Upplands Väsby, north of Stockholm, is
located nearby the northern part of the Stockholm esker. This means that it can be profitable
and environmentally beneficial for the hospital to examine the possibilities of aquifer storage
in the esker material next to its property.
The purpose of this master thesis has been to investigate if geothermal energy storage with a
seasonal storage of heat and cold can be applied within Löwenströmska hospital’s property
area using groundwater modeling. A hydraulic groundwater model was constructed in
MODFLOW based on a simplified conceptual model of the groundwater system. The
hydraulic groundwater model was calibrated and validated against observed groundwater
levels before and after a pumping test. The hydraulic groundwater model was then used to
implement a fictitious geothermal energy storage with MT3DMS. MT3DMS is a modular
function 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 of
about 4 GWh, which covers 85 % of the hospital’s heating demand with an assumed SP-factor
of 4, and the entire cooling demand. To cover 50 % of the peak heating power it was
calculated that a flow of 63 l/s was needed, and according to the model this is possible. The
geothermal energy storage does not need to be completely in energy balance, since the aquifer
is recharged with its natural groundwater. The location of the wells influences which flows
that are needed to create energy balance. A too close placement of the wells leads to a thermal
breakthrough. The hydraulic conductivity of the esker material affects the amount of energy
that can be stored. A higher hydraulic conductivity provides greater energy losses and a lower
hydraulic conductivity favors the energy storage but gives a greater influence area.
A number of assumptions have been made in the model construction of the hydrogeological
model and further investigation of the geological and hydrogeological conditions are desirable
to improve the model.
2014. , 54 p.
Akviferlager, MODFLOW, MT3DMS, geoenergilager, hydraulisk grundvattenmodellering, termisk grundvattenmodellering