CASE

Geoenergy survey

During winter 2014-2015 Geological Survey of Finland (GTK) made a study of the geoenergy potential of Otaniemi by the commission of Aalto University Properties. Geoenergy as renewable and local energy source would fit well as a part of Otaniemi energy self-sufficiency goal, but its usability is dependent on the geological characteristics of the area, especially the temperature and thermal conductivity of the bedrock and the thickness of the soil. The goal of the research was to map the geoenergy potential of Otaniemi. In addition more specific studies were done of the geoenergy solutions of two buildings, the New Building and Maarintalo.

Otaniemi geoenergy potential

The geoenergy potential map of Otaniemi is the first block level study in Finland. In the study GTK utilized the existing geological information of the area, and in addition the energy production capacity of the bedrock and the heat well were assessed with Thermal Response Tests in three 300 meters deep boreholes.

According to the research 99% of Otaniemi is excellent or good geoenergy potential. The bedrock in the area is granite, which thermal conductivity is good and there is no thick soil blocking the way above the bedrock. However some underground spaces, such as metro tunnel can hinder the utilization of geoenergy.

Geoenergy simulations of the New Building, Maarintalo and Dipoli

In addition to the geoenergy potential of whole Otaniemi, GTK has done more specific simulations about the geoenergy solutions of the New Building, Maarintalo and Dipoli. In the simulations the geological characteristics and the heating and cooling needs of the buildings are taken into consideration and the geothermal characteristics of the bedrock are measured with a thermal response test. Based on the results an Earth Energy Designer simulation is done, based on which the quantity, depth and distance of the wells and the geometric shape of the field can be calculated. It is also possible to simulate thermal development of the borehole field even during 50 years, which is done to ensure that the temperature stays at a good level durig the whole use time, even though the temperature of the field decreases a bit every year because of the heat extraction.

Two boreholes were drilled on the site of the New Building for thermal response tests. The average effective thermal conductivity of the bedrock in the research area is 3.3 W/(mK), which enables well the utilization of geoenergy on the site. As a results six simulation results were got, in which the distance of the wells changes between 13−15 meters, the amount of wells between 49−64 and the depth of the wells between 285−305 m. In all simulation cases the borehole field can produce 95% of the heating needs of the building. If the field is wanted to be scaled by emphasizing free cooling, a bigger field would be needed, in which case part of the wells would need to be placed outside of the building.

As a result of Maarintalo simulation six different cases were got, in which the range of heating energy produced by geothermal heat pumps differed between 100%−80%, and the field was yearly charged with 110 or 330 MWh of energy. In the example cases the amount of energy wells was 4−16 and the depth of the wells 152−290 m. The whole heating energy need of the building could be produced with a borehole field of approximately 9 wells. Other supportive energy source would be needed mainly for cooling.

The plot of Dipoli fits approximately 15−19 energy wells. At the moment calculations about how much the energy wells could cover of the heating and cooling energy needs of the building are ongoing. Rototec has drilled a test borehole on the site of Dipoli and done an energy field simulation. The clearances and possible locations of boreholes are already known.

Conclusions

According to the results geoenergy fits well to be used as a heating and cooling energy source in Otaniemi. The possibilities of utilizing geoenergy will be assessed further on different sites.