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Start-up and Commissioning
You can trend various points (i.e., chiller leaving supply temperature, pump speeds, chilled water valve positions)
to get a better estimate of the response time.
NOTE The nominal response time is between 15 and 20 minutes. For smaller water loops in small or medium-
sized commercial buildings, it may be lowered, but only after the timing is verified. Otherwise, unstable operation
may occur.
You can get an approximation of the response time by locking the chilled water reset signal in Chilled Water
Temperature Optimizer Reset (page 68) > Optimized Chilled Water Supply Setpoint AV to a value between 40
and 50°F and 3°F higher than the current value, then verifying response in the chiller manager program. The
response time will be larger than the time it takes to achieve the temperature rise of 3°F. It includes the total time
it takes for everything below to occur:
The time it takes for the chilled water supply temperature to reach the new temperature
The time it takes after the water temperature has stabilized for the air handling unit valves to open or close,
based on new chilled water temperature
The pumps have reached their new speed in response to valves opening
The air handler supply air temperature has risen or dropped (if applicable)
All the changes in consumption (kW) above result from the chilled water setpoint change. The effect of this change
must propagate through all the devices in the system until it is stable. You may need to tune some chiller
programs or properties to get a proper response. It is important that the chilled water setpoint be reset predictably
and quickly enough for the optimization program to work reliably. Good response is essential and the actual
response time depends on the system.
Make adjustments
Section 3 - Manual Overrides of Chilled Water Reset - and other Settings > Minimum & Maximum Reset
Increments & Algorithm Reset Gains
After the program has been running awhile, adjust the Minimum Reset Increment and Maximum Reset
Increment as shown below, if necessary.
Minimum Reset Increment
If the chilled water system is not responding to each supply temperature increment, it could be the
○
minimum reset increment is too small. If so, increase it by 0.5 (deg) above its current value.
If the system is still not responding to each temperature increment, increase it by another 0.5 (deg).
○
NOTE Setting the minimum reset increment to more than 1.75 (deg) may cause overshoot. Set the
minimum to match your system and chiller type, as some chillers require a larger minimum increment.
Maximum Reset Increment
If the chilled water system is responding too much for each supply temperature increment, the maximum
○
reset increment is too high. Decrease it by 0.5 (deg) below its current property value.
If the system is still responding too much for each temperature increment, decrease it by another 0.5
○
(deg). It is preferable to have the Maximum Reset Increment at least 1.5 (deg) above the Minimum
Reset Increment.
Chilled Water System Optimizer v2
Installation and Start-up Guide
38
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