OM 780-2 Page 59
Figure 23. Typical Condenser Water Loop
Chiller #1
Condenser
Common entering condenser water temperature
Common leaving condenser water temperature
Entering condenser
water temperature
Leaving condenser water temperature
Chiller #2
Condenser
Optional cooling tower bypass
a0159
Tower Staging Logic
Cooling tower staging logic depends on whether or not there is a bypass valve in the system, and if there is, it further
depends on how the valve is controlled. There are three possible applications, which are described below:
1. Tower staging only
2. Tower staging with low-limit controlled bypass valve
3. Tower staging with intrastage controlled bypass valve
In all of these applications, the CSM controls up to 16 digital outputs, which can be arranged in up to 12 stages. The
number of outputs does not need to match the number of stages. A separate temperature setpoint is provided for each
cooling tower stage. You can change each of the 12 tower stage setpoints.
Control Temperature
The CSM controls the tower stages and the tower bypass valve (if any) to maintain a desired condenser water temperature.
This temperature is called the Control Temperature, and it can be either the common entering condenser water temperature
or the common leaving condenser water temperature. You can specify which one it is with the Control Temperature Source
variable.
Tower Stage 1 Setpoint Reset
The Stage 1 Setpoint may be reset, in which case all the other setpoints will be adjusted along with stage 1 based on their
original offset from stage 1. Reset is possible in two ways:
• Set by the BAS
• Continually Reset by the CSM to maintain a constant approach temperature differential between the condenser water
supply temperature and the wet bulb temperature
To set up Constant Approach Reset of the cooling tower’s Stage 1 Setpoint
1. Set the Constant Approach Flag = ON
2. Set the Constant Approach Temperature Differential as required
3. Set the Constant Approach Reset – Minimum Setpoint
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