OMM TGZ-1 TGZ 040A through TGZ 190A 45
Tower Fans (Cooling Mode Only)
Tower fan control is active when the unit is set up as water cooled (WaterCooled=On),
Tower Control is set to Temperature, and the condenser pump is in the RUN state. Staging
is based on Entering Condenser Water Temperature (ECWT). Operation depends on the
following parameters.
Condenser pump state
ECWT
Stage up and stage down timer values
Tower set points (Tower Control, Tower Stages, Stage Up Time, Stage Down Time, Stage
Differential ,Stage #1 ON, Stage #2 ON, Stage Down @, Stage Up @)
When the condenser pump starts, the stage up timer starts. The first stage turns ON when
the following conditions are met:
The stage up timer completes
The ECWT is > Stage #1 ON set point
Bypass valve position is > the Stage Up @ set point (only if Valve/VFD Control set point =
Valve Stage)
Additional stages can turn on (up to the number specified by the Tower Stages set point)
when above conditions are met for the next stage plus the following condition:
VFD Speed is > the Stage Up @ set point (only if Valve/VFD Control set point = VFD
Stage OR Valve SP/VFD Stage)
Down staging occurs when the following conditions are met:
The stage down timer completes
The ECWT is < Stage #X ON (Temp) set point – Stage Differential (Temp) set point
Bypass valve position is < the Stage Down @ set point (only if Valve/VFD Control set
point = Valve Stage)
VFD Speed is < the Stage Down @ set point (only if Valve/VFD Control set point = VFD
Stage OR Valve SP/VFD Stage)
Each stage up or stage down event will restart both the stage up and stage down timers.
Only one fan output will 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 set point is set to None OR VFD Stage, this output will 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 will be set as a function
of entering condenser water temperature (ECWT)) per the following graph.
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