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System Setpoint
The Chiller Setpoint is derived from the System Setpoint, which is the CSM’s chilled water supply setpoint for the system.
You can set the System Setpoint manually using the Operator System Setpoint variable or let the CSM reset it
automatically. In either case, the System Setpoint is limited to a range defined by the Minimum System Setpoint and
Maximum System Setpoint.
The System Setpoint and Chiller Setpoint can be viewed on the System Status screen.
Unit Option
The Unit option simply sets the Chiller Setpoint equal to the System Setpoint.
The Unit option should be used for systems in which the flow through each chiller’s evaporator is isolated when not
operating. These systems are by far the most common. They include, for example, chillers with dedicated primary pumps
or isolation valves (see Figure 18).
When the Unit option is used in systems with isolated chillers, the supply water temperature usually is very close to the
System Setpoint even though there is no direct control. (This may not be true if your system is using load balancing.) The
Common option can also be used in these systems, but the Unit option is simpler and the effect is usually the same.
Figure 18. Typical System with Isolated Chillers
Cooling Loads
Chiller #1
Evaporator
Chilled water return temperature
Chilled water supply temperature
Optional secondary pump/decoupler line
Leaving evaporator water temperature
Chiller #2
Evaporator
Chiller #3
Evaporator
a0146
Low Temperature Operation
The CSM has a software safety built into it that does not allow three chilled water setpoints to be adjusted below 40.0°F
(4.4°C): Minimum System Setpoint, Maximum System Setpoint, and Minimum Chiller Setpoint. If your system can
withstand low temperature operation with no danger of freezing, you can override the safety by setting the Glycol Flag to
“Yes.” This allows the above setpoints to be adjusted down to 0.0°F (–17.8°C).
To set up chilled water temperature control
Set the Operator System Setpoint as required.
Setpoint Reset
By automatically varying the leaving evaporator water temperature to suit the building’s cooling load, chilled water
temperature reset can make some chiller systems more energy efficient. The CSM provides four types of reset, which are
described below:
• Return Water
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