68 TGZ 040A through TGZ 190A OMM TGZ-1
Tower Stages is the number of tower fans to be staged by the controller, choices are 0, 1, or
2. "0" indicates control will be by a bypass valve or variable speed pump controlled by the
MicroTech II controller.
StageUP/DN imposes a time delay between fan stages when turning on or turning off.
SET TOWER SPs (2)
Stage ON (Temp)°
°°
°F
#1 #2
XXX XXX
Stage ON Temp is the entering condenser water temperature (ECWT) that will turn on
tower fan #1 and #2. Default settings are 70F and 75F. Cold condenser water will
improve unit efficiency but too cold can cause erratic operation. Settings below 60F are
not recommended.
SET TOWER SPs (3)
StageDiff = XX.X°
°°
°F
StageDiff is the number of degrees below the Stage ON that will turn off the tower fans.
For example, if Stage ON #1 is 70F and StageDiff is 5F, tower fan #1 will stage off
when the ECWT drops to 65F and stage the fan on when the ECWT rises to 70F. The
same is true for fan #2.
Stage Up timer is the number of minutes that must elapse between the condenser pump
starting (it starts with the unit) and fan #1 starting or the time between fan #1 starting and
fan #2 starting.
StageDown is the elapsed time between staging down the fan motors.
SET TOWER SPs (4)
Valve/VFD Control=
ValveSP/VFDStage
Valve/VFD Control settings are None, Valve Setpoint, Valve Stage, VFD Stage, or
ValveSP/VFDStage. Default is None which results in no control of the tower from the
MicroTech II controller.
Valve Setpoint, the valve will control (bypass tower) to hold the minimum temperature as
established by the Set Tower SPs in screen (5) below.
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
(PD) algorithm (with deadband) in order to maintain the controlled parameter (CP) at the
desired value. The output is always limited between the Valve Control Range (Min)
setpoint and the Valve Control Range (Max) setpoint. A valve increment shall be computed
once every 5 seconds according to the following equation. (Error Gain and Slope Gain are
set in menu screen #8.)
Increment = [(Error) * (Error Gain setpoint)] + [(Slope) * (Slope Gain setpoint)]
Where: Error = ECWT – Valve Setpoint
Slope = (Present CP) – (Previous CP)
When the Error is > the Valve Deadband setpoint, the valve position analog output (% of
full scale) is updated according to the following equation.
New %Position = Old %Position + Increment/10
Valve Stage, controls from the fan stage setpoint in use. It is recommended that the Valve
Setpoint method explained above be used rather than this mode.
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