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Appendix B: The Chilled Water System Optimizer Commissioning view of the Properties page
Section 2 - Automatic Overrides of Chilled Water Reset
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The chilled water reset is automatically overridden by:
Automatic "Pause & Hold"
Automatic "Quick Cool Down"
You must configure the following properties to balance chiller stability.
Automatic "Pause & Hold"
In Automatic "Pause & Hold", the reset pauses its operation and holds the supply temperature at its current setpoint under
any one of the 3 following conditions:
The chilled water return temperature gets too cold.
1
This indicates a low load condition, or low temperature difference across the air handling unit cooling coils, which could
cause the chiller to cycle off. The chiller could be held on longer and operate under more stable conditions, if the supply
temperature is not reset any higher. Input the preferred low temperature trip point and the delay that best fits your
system.
The temperature difference across the evaporator gets too cold.
2
This can happen as the chilled water supply temperature rises faster than the chilled water return temperature. This
could create low load conditions across the chiller and could cycle off too often. The chiller could stay on longer if the
chilled water is not reset any higher. This allows time for the return water temperature to rise, and the load across the
chiller to remain high enough for it to continue to run. Input the preferred low temperature trip point and delay that best
fits your system.
The building relative humidity gets too high.
3
The program has the option to monitor relative humidity (up to 20 sensors) throughout the building. If the user-
configurable average or maximum RH rises above a predefined threshold, the program holds its chilled water reset. If
the humidity continues to rise, then the program lowers the chilled water supply temperature setpoint as described
below.
The thermal load gets too high.
4
The program has the option to pause if the thermal load to capacity rises above a certain threshold. If the thermal load
to capacity rises above a predefined threshold (in percentage), the program holds its chilled water reset. If it continues
to rise, then the program lowers the chilled water supply temperature setpoint as described below.
The remote pause is enabled.
5
The program has the option to pause if there is a remote BACnet pause signal. If the remote pause input is enabled, the
program holds its chilled water reset.
Chilled Water System Optimizer v2
Installation and Start-up Guide
Properties
Control Program
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Section2 - Automatic Overrides of Chilled Water Reset
70
Chilled Water Temperature Optimizer Reset
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