50 WGS 130A to 190A OM WGS-5
Additional stages can turn on (up to the number specified by the Tower Stages setpoint)
when above conditions are met for the next stage.
Down staging shall occur when the following conditions are met:
The stage down timer completes
The Condenser EWT is < Stage #X ON (Temp) setpoint – Stage Differential (Temp)
setpoint
Bypass valve position is < the Stage Down @ setpoint (only if Valve/VFD Control
setpoint = Valve Stage)
VFD Speed is < the Stage Down @ setpoint (only if Valve/VFD Control setpoint =
VFD Stage OR Valve SP/VFD Stage)
Each stage up or stage down event shall restart both the stage up and stage down timers.
Only one fan output shall be switched at a time (except that all outputs switch OFF when
the condenser pump state equals OFF).
Cooling Tower Bypass Valve
When the Valve/VFD Control setpoint is set to None OR VFD Stage, this output shall be set
to 0. Otherwise, it shall be controlled as described below.
Initial Valve Position
When the condenser pump is not in the RUN state, the valve output shall be set as a
function of entering condenser water temperature (ECWT)) per the following graph.
Max Position @
Set Point
(90°F)
Min Position @
Set Point
(60°F)
Min Start Position
Set Point (10%)
Initial Valve Position
(values are examples only)
Max Start Position
Set Point (90%)
Operation After Start
When the condenser pump is in the RUN state, the valve output shall be controlled in one of
two modes as specified by the Valve/VFD Control setpoint. The controlled parameter shall
be the condenser entering water temperature. When the desired output signal varies from 0
to 100%, the output voltage shall vary as shown below.
0 to 10 VDC (Valve Type = NC to tower)
10 to 0 VDC (Valve Type = NO to tower)
Valve Setpoint Mode
This mode is operational when the Valve/VFD Control setpoint is set to Valve setpoint OR
Valve SP/VFD Stage. In this mode the valve output is varied with a proportional-derivative
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