Återladdningsförmågan hos en Bergvärmepump
Sammanfattning: Geothermal energy that is being used for space heating with help of heat pumps is getting more and more common. In Sweden 2016, there was over 300 000 different facilities using geothermal energy with the help of bore hole heat exchangers, so called ground source heat pumps (GSHP). A GSHP uses the heat stored in the bedrock to heat a buildings supply of hot water and for space heating. While using a GSHP, the heat extracted from the bore hole leads to a temperature decrease in the hole. During summer periods, when the heat demand for the building is not as high, the GSHP is not in use. When the GSHP is not working the temperature in the borehole has a chance to recharge with the help of the surrounding bedrock and sun’s heat radiation. However, this time period for the borehole to recharge isn’t always enough to ensure that the temperature in the hole is what it once was and will overtime decrease With the help of a GSHP that can satisfy both a heating demand and a cooling demand the GSHP can help with the grounds natural recharge rate. During the winters season when the demand for heat is high, the unit will extract heat from the bore hole resulting in a temperature decrease in the bedrock, during summer when space cooling is of a high demand, the heat pump can use the borehole to instead supply heat back into the bore hole. Helping with the bore holes’ normal recharge rate. The simulations software IDA-ICE was used to compare two different GSHP systems. The first system was designed to only supply a building with its heating demand and its bore holes’ was simulated in a way so that they did not influence another hole. The second GSHP system was the same heat pump and bore hole model. However, this system was designed to cover both the heating and cooling demand for the house. Comparisons between the two systems influences on the bore holes include the power output, mean temperatures and the GSHP overall efficiency. Thanks to using the second GSHP for both a heating and cooling demand the total heat extraction from the bore hole was reduced by 27,5 % compared to the GSHP that only delivered a heat demand. Due to the reduction of the total heat extraction, heat had been returned down the bore hole when the building had a large cooling demand. This heat increased the temperature in the bore hole during summertime when the first GSHP only relied on the grounds normal recharge rate. This meant that the mean temperature in the bore holes during the first year for the combined load GSHP: was 0,17 ᵒC higher than for the first GSHP. After 5 years of simulation time the mean temperature hade increased to be 0,23 ᵒC higher than of the GSHP that only covered the heat demand. Both units had no notable change in their efficiency throughout the simulation period. Keywords: Heat pump, Ground source heat pump. Power output, bedrock, bore hole heat exchange
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