Optimal dimensioning power of GSHP with district heating in an educational building

European Union (EU) have set great goals to reduce carbon dioxide (CO2) emissions and mitigate global warming trend. In this context, energy performance of buildings should be improved by enhancing the use of renewable energy sources in heating and cooling. For that reason, a hybrid energy system where a ground source heat pump (GSHP) integrated with borehole thermal energy storage (BTES) system is used together with district heating (DH) has become increasingly popular in Finland during the last years. In those hybrid GSHP systems, GSHP is used as a primary energy source and DH is used for supplementing energy during peak heating load period in wintertime. While in summertime, the borehole field is used for free cooling and DH is providing heating energy for domestic hot water. In this study, a large educational building complex in Finland applying a hybrid energy system consisting of a GSHP and DH was modelled in IDA ICE 4.8. Three simulation cases were studied to analyze the effects of the GSHP power ratio on the whole system energy consumption and CO2 emissions. The results show the total CO2 emission obtained the minimum when the GSHP heating power ratio was 50%. However, compared to 100% district heating solution, 25% power ratio of GSHP in the hybrid system can already realize 50% reduction of CO2 emissions as the total cooling demand was fully satisfied by borehole free cooling and 98% DH consumption was reduced.