Analysis of operational data from a district cooling system and its connected buildings

Abstract District cooling systems are likely to become more common as the cooling demands in cities increase. Their performance is often challenged by low temperature differences between the supply and return water, called low delta-T. Few previous studies have investigated low delta-Ts in district cooling systems with heat exchangers separating the distribution system and the connected buildings, which therefore is the objective of this study. The study is based on an analysis of operational data from both district cooling provider and 37 of the connected buildings chilled water systems, collected from the energy transfer stations during spring and summer of 2018. The design delta-T in the district cooling system is 10 °C, while the actual delta-T varies between 6 and 8 °C. The study shows the main causes to the low delta-T are the following: operation in the saturation zone; too low building chilled water return temperature; too low temperature approach of the heat exchanger's supply streams and non-optimized supply temperatures in the buildings. Potential solutions to resolve the low delta-T include adjusting the supply temperature setpoint on the secondary side; restricting the flow on the primary side; providing economic incentives for the district cooling customers and ensuring compliance with the design guidelines.