Energy flexibility quantification of the building’s thermal mass for radiator and floor heating systems

The adoption of renewable energy sources requires solutions to reduce the temporal mismatch between power demand and supply. Buildings’ energy demand shifting can mitigate the problem. The objective of this paper is to quantify the time-dependent energy flexibility provided by the building's thermal mass. This flexibility is highly dynamic, as it is influenced by temperature levels, environmental conditions and various disturbances. This time-evolving evaluation is preceded by a preliminary assessment of the energy flexibility, through the calculation of the available storage capacity and storage efficiency, aimed at evaluating the performance of the heat storage process in the building's thermal mass. Flexibility is quantified for two heating systems: radiator and floor heating. The results show that the case with a floor heating system recovers 50% of the heat stored in the thermal mass after one day, while the case with a radiator takes 3 days to achieve 50% heat recovery. Finally, time-dependent flexibility is almost constant for the radiator case and the average flexible power is up to 12.3 W/m2, while for the floor heating system it is variable along the day and the maximum flexible power varies between 24.6 W/m2 at midday and 86.2 W/m2 at night.