McQuay WGS130AA: WGS140AW, Operating Manual

Page: 19 / 98

OM WGS-5 WGS 130A to 190A 19
Start first circuit.
The first circuit to start is generally the one with the least number of starts, or circuit
one if there is a tie. This 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.
Is flow present?
Condenser pump output on
Wait for condenser water
loop to recirculate.
Yes
No
Keep condenser pump
output on while unit is
enabled and load is present.
Is more capacity
needed to satisfy load?
Has the stage up time
delay expired?
Yes
No
Load/unload as needed to
satisfy load.
No
The first circuit will load and unload as needed in an attempt to satisfy the load. It
will eventually get to a point where it is considered to be at full load. A circuit is at
full load when it reaches 75% slide target, it reaches the max slide target setting, or
it encounters a problem and is running in an inhibited state.
If a single circuit is not enough to satisfy the load, the second circuit will need to be
started.
A minimum time must pass between the start of the first circuit and the second
circuit.
Yes
If load is present, the condenser water pump output will be activated.
After establishing condenser flow, the chiller will wait some time to allow the
condenser water loop to recirculate and guarantee consistent flow. The unit status
during this time is
Auto:Cond Recirc .
The chiller will then wait for the condenser flow switch to close, during which time
the unit status will be
Auto:Wait Cond Flow .
Is unit watercooled?
Yes
No
If the unit is configured as watercooled, the condenser pump will need to be started.
Otherwise, the unit can start the first circuit at this point.
Once the condenser flow has been present for enough time, the unit status will
become
Auto . The tower control logic will start working to control the condenser
water temperature, using outputs from the unit controller to control tower fans,
bypass valves, and vfd's as determined by the tower set points.