Geotermisk förvärmning och -kylning av uteluft med borrhål

Sammanfattning: Mechanical ventilation systems with heat recovery are a common sight in modern buildings. If plate heat exchangers, which are the most common type used in Swedish residential buildings, are utilized for heat recovery there is a risk of frost build-up in the heat exchanger due to the exhaust air being cooled below freezing by the outside air. Frost limits the performance of the heat recovery system and increases the need for extra heat to be added to the supply air by a heating coil. By utilizing geothermal heat to preheat the outdoor air before it enters the heat exchanger the risk for frost build-up can be minimized, and the need for extra added heat, usually by means of district heating, is lowered. Multiple Swedish district heating companies apply a price model containing a fee for peak power requirements, so by minimizing the need for added heat power this part of the bill can be lowered. During summer the geothermal system can be used for cooling the supply air which can improve the indoor climate. A model for geothermal preheating and precooling was created in the building simulation software IDA Indoor Climate and Energy. The model was tested and evaluated using three different cases of varying complexity. In the first case the accuracy of the cooling coil model was evaluated using measurements from HSB Living Lab during winter. The results suggested an overall overestimation of the cooling coil’s performance, however, the validity of these results are uncertain. In the second case the cooling coil model was coupled together with the bore hole model, and the system was evaluated using measurements from an apartment building in Finnboda, Nacka, Sweden. The result from the simulation corresponded well with the measurements. The implementation of the control strategy also turned out well. In the final case a whole building simulation was conducted for a projected preschool in Ursvik, Sundbyberg, Sweden. In this building, the free cooling from the ground is utilized to improve the indoor climate to achieve the highest possible credits for thermal climate in the Swedish standard for green building certification Miljöbyggnad. The simulation suggests a reduction in the maximum heating power demand by 55