Trane SYS-APM001-EN manual Pipe size, Water, Power, Application Considerations

Application Considerations

Creating one centralized chilled-water system takes significant foresight, initial investment, and building development with a multi-year master plan. If the initial plant is built to accommodate many future buildings or loads, the early challenge is operating the system efficiently with much lower loads than it will experience when the project is complete. The system may need to blend parallel and series configurations (“Series–Counterflow Application” on page 77) to accommodate the wide range of loads the plant experiences during phased construction.

Another type of large chilled-water system could actually start out as more than one chilled water-system. An existing set of buildings can be gradually added to the central system, or two geographically distant chilled-water systems can be connected. “Plant Expansion” on page 83 discusses the unique control and hydraulic challenges of “double-ended” chilled-water systems.

Operating large chilled-water systems can be different as well. As system load drops, chillers are turned off. Individual chiller unloading characteristics are not as important, because operating chillers are more heavily loaded.

Pipe size

Practical pipe size limitations start to affect the maximum size of a chilled- water system. As the systems get larger, it becomes more difficult to accommodate the increasing pipe sizes, both in cost and in space. Large ΔTs can help reduce flow and required pipe size. (See “Selecting Chilled- and Condenser-Water Temperatures and Flow Rates” on page 27.) In general, the larger the system, the higher the ΔT should be.

Water

Large systems are almost always water-cooled. Both chilled water (a closed loop) and condenser water (usually an open loop) pipes will have to be filled with water. In some locations, it is difficult to find enough fresh water to fill a very large system with water, especially if the chilled-water system is quite distant from the loads. Cooling towers consume water, which can be significant and difficult to obtain in some locations. The search for both locally available make-up water and energy savings can lead to the exploration of alternative condensing sources like lake, river, or well water. (See “Well, river, or lake water” on page 72.) In rare instances, salt water or brackish water can be applied if the system uses an intermediate heat exchanger, or if the chiller is constructed with special tubes.

Power

Large chilled-water systems can be challenged by site power availability. Transformer size may be dictated by local regulations. On-site power generation may be part of the project, leading to using higher voltages inside the chilled-water system to avoid transformer losses and costs. Alternative fuels for some or all of the chillers may be attractive (“Alternative Energy Sources” on page 82).

SYS-APM001-EN Chiller System Design and Control 23