46 TGZ 040A through TGZ 190A OMM TGZ-1
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 will be controlled in one of
two modes as specified by the Valve/VFD Control set point. The controlled parameter will
be the condenser entering water temperature. When the desired output signal varies from 0
to 100%, the output voltage will vary as shown below.
0 to 10 VDC (Valve Type = NC to tower)
10 to 0 VDC (Valve Type = NO to tower)
Valve Set Point Mode
This mode is operational when the Valve/VFD Control set point is set to Valve Set Point
OR Valve SP/VFD Stage. In this mode the valve output is varied with a proportional-
derivative (PD) algorithm (with dead band) in order to maintain the controlled parameter
(CP) at the desired value. The output is always limited between the Valve Control Range
(Min) set point and the Valve Control Range (Max) set point. A valve increment shall be
computed once every 5 seconds according to the following equation.
Increment = [(Error) * (Error Gain set point)] + [(Slope) * (Slope Gain set point)]
Where: Error = ECWT – Valve Set Point Slope = (Present CP) – (Previous CP)
When the Error is > the Valve Deadband set point, the valve position analog output (% of
full scale) is updated according to the following equation.
New %Position = Old %Position + Increment/10.
Valve Stage Mode
This mode is only operational when the Valve/VFD Control set point is set to Valve Stage.
In this mode the valve output is controlled as for Valve Set Point mode (above) except that
the active set point for the controlled parameter is selected according to the following table.
Number Of
Fans ON
Active Set Point
0 Valve Set Point
1 Stage #1 ON
2 Stage #2 ON
Cooling Tower Fan VFD
When the Valve/VFD Control set point is set to None, Valve Setpoint, OR Valve Stage, this
output will be set to 0. Otherwise, it will be controlled in a manner identical to Valve Stage
Mode (above) except that (1) it will be kept at zero until the first fan stage is ON and (2)
the following set points do not apply.
Valve Control Range (Min)
Valve Control Range (Max)
Valve Type
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