Influence of centralized and distributed thermal energy storage on district heating network design

Future district heating networks have to be flexible enough to absorb the heat load variations and additional heat production variations imposed by increasing intermittent renewable energy sources. Thermal energy storage is a proven, efficient and cost effective technology to provide such flexibility. A centralized hot water storage tank near the source is the most common thermal energy storage configuration in district heating systems today. Though this configuration provides flexibility and reduces peak load capacity, it doesn't impact the network peak transport capacities since the heat still needs to be transported from the source location during peak demand periods. This paper investigates the benefits of placing thermal storage tanks in the distribution networks to decrease the network peak transport capacities and balance the heat loads locally. Building heat demand data is extracted using the open source street level gas consumption data and appropriate heat demand profiles are chosen based on the building type. A case study comparing centralized and distributed storage is carried out using these input data with Comsof Heat, an automated district heating network routing and planning tool. The effect of these storage configurations on total network cost is compared and several scenarios are explored with different storage sizes. The case study results show that centralized storage can reduce the total network investment cost by 4%, the substation level storage can reduce the costs by 5% and the building level storage can reduce the costs up to 7% for the given inputs.