Thermal building mass for storage and its role in smart energy systems

Different storage solutions raise the flexibility of the energy system, fostering integration of variable renewable energy sources. The thermal building mass can serve as a cost-efficient storage solution, as it does not require significant additional expenses. In order to check the potential of the thermal mass for storage on the district heating supply, a detailed dynamic building simulation model was coupled with a system level linear optimization model. Different building archetypes were modelled in order to realistically represent a building portfolio in the city of Sønderborg, Denmark, which was chosen for a case study. Three different scenarios were carried out, with preheating times of zero, two and four hours. The results of those scenarios showed that longer preheating times increase a possible duration of cut-off events, while the cut-off potential was higher in the better insulated buildings, reaching 6 h in the best case. Generally, it was found that the thermal autonomy potential was influenced the most by the overall heat loss coefficient of the building envelope. Flexible demand in the form of thermal mass for storage amounted to 5.5%-7.7% of the total district heating demand and operational savings in a district heating system occurred in all the cases. The savings were in the range from 0.7% to 4.6%. Finally, a sensitivity analysis that was carried out showed that the thermal mass for storage and pit thermal energy storage can serve complimentary roles in the energy systems.