OM 200MICRO
31
stage down time. The number of stages also will be decreased when the maximum number of stages is
less than the current stage.
The sequence described above allows stages to be turned on based on temperature only or on a
combination of temperature and time. Control may be based only on temperature by setting the stage
1 set point lowest and the other stages set points successively higher. This provides automatic reset
of the condenser water as the tower capacity requirements increases. If a specific entering condenser
water temperature is desired at all times, the set points for all stages can be set to the same value and
staging is based on that temperature and the stage up and stage down timers.
Menu 19, Cooling Tower Control
Item
Screen
Line
Display
Field
Range
Extended Name
Yes
Tower Control=Yes
1
No
Tower Control
1
Tower Stages=2
2
1-4
Total Cooling tower Stages
StageUp time=2Min
1
2-60 Min
Stage Up Delay
2
StageDn Time=5Min
2
1-60 Min
Stage Down Delay
1
3
Stage Differential=3.0°F
1
1-10°F
Staging Differential
Stage #1 On=70.0°F
1
40-120°F
Stage #1 Set point
Stage #4 On=70.0°F
2
40-120°F
Stage #4 Set point
Stage #2 On=70.0°F
1
40-120°F
Stage #2 Set point
2
1
Stage #3 On=70.0°F
1
40-120°F
Stage #3 Set point
Tower Control=
Set this value to 'yes' for fan staging control or by-pass valve control and 'no' if
condenser water temperature is not controlled by the MicroTech.
Tower Stages=
This value will determine how the MicroTech calculates the time to increase or
decrease the cooling tower controlling sequence. The number of stages refers to cooling tower fans
or to bypass valve control.
Stageup Time=
This value will delay the MicroTech from starting the staging control. This can be
used to provide specific system control requirements.
Stagedn Time=
This value will delay the MicroTech from staging down for the time specified. This
can be used to provide specific system control requirements.
Stage Differential=
This value is the control band for the fan staging control logic. This value must
be exceeded to stage up or down.
Stage #1 0n=
This value determines when the first stage control will start. This value plus 1/2 the
stage differential determines the control point value. This value is active on stage up and stage down.
Stage #2-4 0n=
Same as
Stage #1 On=.
Press the "NEXT MENU" key and menu 20 will be displayed. This menu will provide control of the
cooling tower valve. If a bypass valve is to be used to provide a low limit for the tower, the valve set
point should be set for the Valve Control method and the valve set point should be less than the fan
stage 1 set point. In this situation, the number of cooling tower stages is increased only when the
valve position exceeds the maximum position set point so the valve is fully open to the tower when
any cooling tower stage is on. The entering condenser water temperature will vary as stages are
turned on and off.
If a relatively constant entering condenser water temperature is desired, the valve set point should be
selected as the Stage Control method. In this situation the valve is modulated to maintain the current
stage temperature set point. The number of cooling tower stages is increased only when the valve
position exceeds the maximum position set point and the temperature and time requirements described
above for staging up are met. The valve will then modulate closed when the temperature starts to
drop after the fan stage is added.