McQuay AC 40A, Руководство по применению

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Multiple Chiller Installation
In most cases, one single chiller will not be sufficient to provide the cooling load of a system.
Several chillers must be combined together to give the required loading.
Generally, these chillers will be installed together in
parallel. There are several ways to do
this:
1) Common Supply and Return Headers
Check valve
CHILLER 3
CHILLER 2
CHILLER 1
Chiller water return
Chilled water supply
Supply header
Return header
This method is most preferred and commonly used because of the lower cost and ease
of installation.
Each chiller is normally set at different return water temperature to facilitate load staging.
As the temperature becomes colder, the chillers will switch off one by one.
Generally, the header pipe size is larger than the supply and return pipes, e.g. one or two
size larger. This is to have a low pressure drop along the header. Check valves are usually
located along each chiller supply pipe to prevent back flush of water once the chiller is
switched off. Such back flow may damage the water pump.
However, this method has several drawbacks:
a) Proper balancing of the water flow rate through each chiller is crucial.
b) If any one chiller is off, the water flow to the load will be affected. So much so
that during low load conditions, when the return water temperature is cold, and
all the chillers have cycled off, no water will be pumped to the load. To
overcome this problem, it is necessary to wire the chiller controls for continuous
pump running as long as one fan coil unit is in operation. See Section 11.
Section 2 Page 17