44 WGZ030D through WGZ200D OMM 1130-2
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.
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
Compressor Start/Stop Timing
This section determines when to start or stop a compressor. There are two separate functions used, one
for staging up and one for staging down.
Stage Up Now
The Stage Up Now flag is set based on the following tests:
If
Unit mode = Cool AND
no compressors are running AND
LWT error > Start delta + 0.5 * Control Band AND
Motor Protect Timer expired AND
Stage up timer expired THEN
Stage Up Now = True
If Unit Mode = Cool AND
At least one compressor is running AND
LWT error > 0.5 * Control band AND
Pulldown rate <= Max pulldown rate AND
Compressors running < unit capacity limit AND
Stage up timer expired THEN
Stage Up Now = True
If
Unit mode = Heat AND
no compressors are running AND
LWT error > Start delta + 0.5 * Control Band AND
Motor Protect Timer expired AND
Stage up timer expired THEN
Stage Up Now = True
If
Unit Mode = Heat AND
At least one compressor is running AND
LWT error > 0.5 * Control band AND
Pulldown rate <= Max pulldown rate AND
Compressors running < unit capacity limit AND
Stage up timer expired THEN
Stage Up Now = True
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