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Max Tower
Valve Position
Setpoint
This value is used as a stage-up condition for interstage and low limit control when a tower valve is used (the CSM will not
increase the tower stage until the valve position is greater than this setpoint). Range = 0% - Tower Valve Control Range Max.
Default = 80%
Tower Valve
Type
Defines whether the tower bypass valve is normally open or normally closed to the tower. Range = NC to Tower, NO to Tower.
Default = NO to Tower
Tower Valve
Deadband
This value sets a Deadband around the Tower Valve Setpoint if a tower valve is used. No tower valve control action is taken when
the current Control Temperature is within this Deadband around the Tower Valve Setpoint. Range = 0 – 9.5°F (0 – 5.2°C).
Default = 2°F (1.1°C)
Tower Valve
Propband
This value sets the “proportional band” used in the PID control function that modulates the tower valve position. In general,
increasing this value has a slowing effect and decreasing this value has a speeding effect on the control of the valve position.
Range = 1 – 60°F (0.5 – 33.3°C). Default = ±7.5°F (±4.1°C)
Tower Valve
Sample Time
This value sets the “sampling period” used in the PID control function that modulates the tower valve position. In general,
increasing this value has a slowing effect and decreasing this value has a speeding effect on the control of the valve position.
Range = 1 – 3600 seconds. Default = 15 seconds
Tower Valve
Integral Time
This value varies the “integral time” used in the PID control function that modulates the tower valve position. In general,
increasing this value has a slowing effect and decreasing this value has a speeding effect on the control of the valve position.
Range = none. Default = 120 seconds
Tower Valve PI
Function Graph
A graph of the tower Control Temperature vs. Time is shown at the bottom of the page when the Tower Valve Control Option is
not equal to “None”, to assist in tuning the Tower VFD PI loop.
Min Tower Valve
Start Up Position
Used to define the initial tower valve position (before any chillers enter the Running mode). See the Start-Up Valve Position
Control section of this document. Range = Tower Valve Control Range Min – to - 100%. Default = 0%.
Max Tower
Valve Start Up
Position
Used to define the initial tower valve position (before any chillers enter the Running mode). See the Start-Up Valve Position
Control section of this document. Range = 0% - Tower Valve Control Range Max. Default = 100%.
Min Tower Valve
Start Up Position
@ (OAT)
Used to define the initial tower valve position (before any chillers enter the Running mode). See the Start-Up Valve Position
Control section of this document. Range = 0-120 °F (-17.8 – 48.8°C). Default = 60°F (15.5°C)
Max Tower
Valve Start Up
Position @
(OAT)
Used to define the initial tower valve position (before any chillers enter the Running mode). See the Start-Up Valve Position
Control section of this document. Range = 0-120 °F (-17.8 – 48.8°C). Default = 90°F (32.2°C)
Tower Stage
Table
Pressing this button takes you to the Cooling Tower Sequence Order Table.
Cooling Tower Output Sequence Order Table
Name Description
Stage 1, Output 1
Stage 1, Output 2
Stage x, Output y
This table is used to assign tower outputs to cooling tower stages. Setting a tower output to ON in a stage #’s row will close the
associated relay whenever that particular tower stage is reached.
The CSM can control a cooling tower system that has up to 12 stages of heat rejection. It can also control a tower bypass
valve, but this is not required.
A typical condenser water loop is shown in the Figure 23. Notice that the condenser pumps at the chillers pump water
through the system. The CSM does not directly control the operation of these pumps; the chiller controllers do.
When to Use the CSM’s Cooling Tower Control
MicroTech II water-cooled chiller unit controllers and the CSM both have cooling tower control capability. If the cooling
tower system is piped so that it is common to all chillers, you should use the CSM for cooling tower control. This type of
configuration is shown in Figure 23. If each chiller has a dedicated cooling tower, you should use the chiller controllers for
cooling tower control.
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