Survey of geothermal energy
During winter 2014–2015, Aalto CRE assigned the Geological Survey of Finland (GTK) to conduct a survey of geothermal energy potential in Otaniemi. Being a renewable and local source of energy, geothermal energy would be an ideal part of the goal of making Otaniemi energy self-sufficient. However, its usability depends on geological properties, especially the bedrock temperature and heat conductivity, as well as the thickness of the soil cover. The purpose of the survey was to identify the possibility of using geothermal energy in Otaniemi. In addition, more detailed surveys of geothermal energy solutions in two buildings, Väre and Maarintalo, were conducted.
Geothermal energy potential in Otaniemi
The map of geothermal energy potential in Otaniemi is the first block-level survey ever conducted in Finland. The survey used GTK's existing information about the geological properties of the area. In addition, the energy production properties of the bedrock and an energy well were evaluated by means of thermal response tests (TRT) using three test holes of 300 metres deep.
On the basis of the survey, nearly 99% of Otaniemi has an excellent or good geothermal energy potential. The bedrock is made up of granite which has good heat conductivity properties, and there is no thick soil cover on the bedrock. However, the use of geothermal energy is restricted partly by large underground facilities, such as the metro tunnel.
Geothermal energy modelling
In addition to the energy potential of Otaniemi, GTK modelled geothermal energy solutions for Väre, Maarintalo and Dipoli in more detail. These were modelled taking into account the geological properties of the area and the need for heating and cooling energy in these buildings. In addition, two TRTs were conducted to identify the geothermal properties of the bedrock. On the basis of the results, an Earth Energy Designer (EED) simulation will be created to calculate the number and depth of energy wells, the geometric shape of the field and distances between wells. The modelling also helps to simulate how temperatures in the well field develop over 50 years. This ensures that temperatures remain at a good level throughout the service life, even if the temperatures fall slightly every year as a result of the supply of geothermal energy.
Two test wells were drilled in the Väre area for conducting TRTs. The average effective heat conductivity of the bedrock was 3.3 W/(mK). This makes the use of geothermal energy highly possible. Six modelling results were obtained, in which the distance between wells ranges from 13 m to 15 m, the number of wells ranges from 49 to 64 and the well depth ranges from 285 m to 305 m. In all models, the energy well field can cover the heating energy needed by the building by 95%. If the field was dimensioned by focusing on free cooling, a larger well field would be needed, in which case some wells would have to be located outside the building.
The models prepared for Maarintalo resulted in six different instances, in which the amount of thermal energy produced using a ground heat pump ranged from 100% to 80% and the field was loaded annually with 0, 110 or 330 MWh. In the example cases, Maarintalo had 4–16 energy wells, with the depth of a single well being 152–290 m. A field of approximately nine energy wells can produce all the thermal energy needed in the building. A secondary energy source would mainly be needed to cover cooling demand.
Dipoli premises have room for 15–19 energy wells. Rototec drilled a test well in the Dipoli premises, modelled the energy field and identified any safe distances and possible well locations. In the light of the information obtained, there are 19 wells in Dipoli that produce 750 MWh of heat annually.
According to the survey, geothermal energy is an ideal source of heating and cooling energy in Otaniemi. The possibilities to use geothermal energy will be investigated further on a site-specific basis.