period two
Chilled-Water System Design
notes
Primary-Secondary System Rules
▲The bypass pipe should be free of restrictions
▲Load terminals should use two-way modulating control valves
▲All chillers should be selected for the same leaving chilled-water temperature and ∆T
Figure 58
For simplicity of system control, all of the chillers in a primary-secondary system should be selected to operate with the same leaving-water temperature and with the same temperature difference (∆T). This allows all operating chillers to be loaded to equal percentages.
Control of supply-water temperature is fairly simple. The set points of the individual chillers are all equal to the desired system supply-water temperature. Because water flows only through operating chillers, there is no water mixing in the production loop, and the production loop supplies the water temperature corresponding to the individual chiller set points.
