Impact of thermal masses on the peak load in district heating systems

During district heating operations, part of the heat supplied to the network is used to increase the temperature of the various components (e.g. transport and distribution networks, heat exchangers installed in the substations, heating circuits and heating devices in buildings). The mass of these components acts as a thermal storage, storing heat when their temperature increases and releasing heat when they cool down. The impact may become significant, especially during shutdown or setback. In this paper, the components are analyzed in order to estimate the impact of their thermal capacity on the district heating demand. This provides a clear image of the additional supply used to heat the other thermal masses, that can be managed differently since partially independent from the indoor temperature. Results show that in the case study analyzed, i.e. large system mainly switched off during night, the heat absorbed by the thermal masses corresponds to the 4% of the heat supplied during the entire day and 70% of the heat provided during the peak. The various thermal masses affect the extra heat absorbed to a similar extent (except for radiators). Results provide a clue that proper management of thermal masses for energy saving might be considered.