Daikin WGZ030DW Operating And Maintenance Manual page 43

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 shall occur 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.
Max Position @
Min Position @
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.
OMM 1130-2
Initial Valve Position
(values are examples only)
Set Point
(90°F)
Set Point
(60°F)
Min Start Position
Set Point (10%)
Max Start Position
Set Point (90%)
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