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44 TRG-TRC016-EN
notes
period two
Chilled-Water System Design
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.
Manifolded Production Pumps
production
production
pumps
pumps
b
y
p
a
s
s
p
i
p
e
b
y
p
a
s
s
p
i
p
e
isolation
isolation
valves
valves
Figure 50