20
WGS 130A to 190A
OM WGS-5
Start second circuit.
Load/unload as needed to
satisfy load.
Can one circuit handle
the load?
Yes
Shut down one circuit.
No
Load/unload as needed to
satisfy load.
Is load satisfied?
No
Shut down last circuit.
Yes
As the load drops off, the circuits will unload accordingly. If the LWT gets low
enough, or both circuits unload enough, one circuit can shut off.
With one circuit running, the load may drop off to the point where even minimum
unit capacity is too much. The load has been satisfied when the LWT drops below
the shutdown point. At this time the only running circuit can shut down.
Both circuits will now load/unload as needed to satisfy the load. In addition, they will
load balance so that both circuits are providing nearly equal capacity.
The second circuit will go through its start sequence at this point.
A number of fans may be started with the compressor based on the OAT. Fan
stages will be added/removed as needed to control condenser pressure. The EXV
will begin controlling at this point as well. The compressor cannot start loading until
it has at least 22
o
discharge superheat for more than 30 seconds.
The first circuit to shut off is generally the one with the most run hours. The circuit
will do a pumpdown by closing the EXV and continuing to run the compressor until it
reaches the pumpdown pressure or exceeds the pumpdown time limit. Then, the
compressor and all fans will be turned off.
The single running circuit will load/unload as needed to satisfy the load.
The last circuit running now shuts down. The circuit will do a pumpdown by closing
the EXV and continuing to run the compressor until it reaches the pumpdown
pressure or exceeds the pumpdown time limit. Then, the compressor and all fans
will be turned off.
The unit should be ready to start again when the LWT gets high enough. The unit
status at this time will be
Auto:Wait for load
.
Turn off condenser pump
and tower control.
The condenser pump and tower control outputs are turned off until the LWT is high
enough to start again.
Summary of Contents for WGS130AA: WGS140AW
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