Modeling and analysis of thermal storage for a district cooling system (DCS)

Abstract

This report explores the economical savings of a district cooling system over building specific cooling systems. Data collection findings on the cooling load demand, for several buildings in Nanyang Technological University (NTU), are used in the development of a DCS model for NTU. Current energy consumptions of 8 plant rooms, supporting 25 different buildings, are placed in comparison with proposed DCS’s energy consumption. Analysis on different water distribution networks and combinations of water pumps are made. Results have shown a more desirable chilled water supply pressure when the DCS main plant room is located at a high ground, near buildings with high cooling demand. In addition, the use of larger and more efficient chilled water pumps brings about a reduction of 25.49% in energy consumption, between the best and worst performing feasible pump solutions. With the centralised plant, the energy consumption by the operating chillers is lowered due to economies of scale. Simulation is done with different chiller capacity and efficiency. Lower energy consumption is observed for all chiller combinations in a DCS when compared against building specific systems. While comparing against current building specific chiller systems, the best performing DCS chiller system registered a reduction in energy consumption of 16.62% and 18.46%, for typical weekday and weekend operation respectively. The use of thermal energy storage tanks further improves the energy savings over building specific from 16.62% to 18.80%. Studies have been done primarily on the water distribution system and the chiller systems, with feasible energy saving methods highlighted through the use of a DCS. Further reduction in energy consumption can be obtained by extending analysis to mechanical equipment such as cooling towers and cooling water pumps. However, it is to note that a DCS is not the perfect cooling solution for all cases, due to limiting factors such as availability of building clusters and ease of installation of the chilled water distribution network.