District chilled water is distributed from the cooling plant to the customer through supply pipes, also known as a pipe distribution network, which is returned after cooling the buildings water. Pumps distribute the chilled water by creating pressure differentials between the supply and return pipes.
The district cooling system has one of two ways to connect to the customer, direct or indirect connects. The indirect connection consists of an Energy Transfer Station (ETS) which embodies a heat exchanger. The indirect connection allows the district cooling water and the buildings water to be divided through the heat exchanger, where the both water sources run through parallel plates, cooling the building water before being dispersed to the fan coil units within the building, whilst the district cooling’s water is returned to the cooling plant to be re-cooled.
The indirect system allows control over cross contamination of the water, both water sources are in closed circuits, ensuring the separation of water. This allows the systems to work independently with different temperature and pressure controls, allowing more flexibility for both systems, and optimizing the district cooling systems economics. By optimizing the district cooling economics it provides benefits for the customer such as reduced costs in the pipe distribution connects, the need for smaller pumps and energy reductions in operations.
Direct connections to the district cooling system eliminates the need for an ETS, as the cooling plants water is fed straight to the building through a number of pipes, however this means that the cooling plants water and the buildings water function as one. The water quality and pressure in a direct system are the same, as apposed to the indirect connection, which affects the supply temperature.
With the two water sources merging into one system there are risks associated with leaks or water contamination, if either party encounters a leak or contamination the other will be affected too.
Both direct and indirect connections offer the same energy and efficiency benefits and have the same technological requirements, with regards to the district cooling plant.
A district cooling system allows the building owner to eliminate their on-site operations and maintenance. By doing so the building owner no longer needs to operate and maintain chillers and replace them at the end of their life cycle. District cooling has high operational efficiencies and the ability to utilize inexpensive waste energy sources which allows the building owner to expect more stability in their energy costs.
In addition, the overall capital costs are reduced by eliminating the need for a chiller room which allows the building owner to use the space for revenue generating space.