period two
Chilled-Water System Design
notes
Manifolded Production Pumps
production pumps
isolation valves
Figure 50
Alternatively, the production loop can be configured with manifolded pumps and automatic, two-position isolation valves at each chiller. When turning on a chiller, a pump is turned on and the isolation valve is opened.
This manifolded-pump configuration provides greater redundancy because the system can change the pump-and-chiller combinations. This redundancy is at the cost of system complexity, and somewhat limits the flexibility of selecting chillers of different capacities and types. If the production pumps are manifolded, the chillers must be selected with the same evaporator-water pressure drop, or else some method of flow balancing must be employed. Pump sizing also becomes an issue if chillers are of different capacities and flow rates, because the proper pump needs to be turned on to match the chiller flow rate.
The drawback of manifolding production pumps is that the chiller flows become hydraulically coupled again. If an isolation valve is opened before a pump is started, flow through the operating chillers will drop suddenly, causing potential control instability. If a pump is started before a valve is open, the operating chillers will see a momentary flow increase, causing control instability or water hammer.
