Thermal Peak Load Shaving Through Users Request Variations in District Heating Systems

Peak shaving is a relatively new approach aimed at increasing the primary energy efficiency in District Heating Systems. This is mainly performed using thermal storage units that can be charged when the thermal request is small, usually at night, and discharged to cover peak requests. Thermal storage typically allows one increasing the utilization of waste heat, renewables and cogeneration systems while reducing the use of boilers. An alternative option to conventional thermal storage is "virtual storage". This consists in modifying the thermal request profiles of buildings in order to reduce their contributions in peak hours. Such modifications rely on the thermal capacity of buildings in order to comply with end-user requirements on the internal temperatures. The analysis of possible operational strategies should be performed using an integrated simulation, which considers both the thermos-fluid dynamic behavior of the network and the thermal behavior of the buildings. In this paper, a physical tool specifically conceived for the analysis of peak shaving in large networks through virtual storage is presented and applied to a portion of the Turin district heating network. Detailed information about thermal requests of buildings obtained from a pervasive metering system is used in order to characterize their behavior. This piece of information is then adopted for constraining and checking possible different operational strategies. Two different scenarios are analyzed and compared with current operation in terms of primary energy consumption, showing that primary energy savings of the order of 5% can be achieved without affecting the comfort perceived by the users.