Machine Protection
and Adaptive
Control
Controls Chilled Water Reset (CWR)
Chilled water reset is designed for those applications where the design chilled water temperature is not required at partload. In these cases, the leaving chilled water temperature setpoint can be reset upward using the CWR features.
When the CWR function is based on return water temperature, the CWR feature is standard.
When the CWR function is based on outdoor air temperature, the CWR feature is an option requiring an outdoor temperature sensor module installed in the UCP panel, and sensor installed outdoors.
The type of CWR is selected in the Operator Interface settings Menu along with the Reset Ratio, Start Reset Setpoint, and the Maximum Reset Setpoint.
The following equations and parameters apply for CWR.
Return Water
CWS’ = CWS + RATIO (START RESET - TWE - TWL) and CWS’ > or = CWS and CWS’ - CWS < or =
Maximum Reset.
Outdoor Air Temperature
CWS = CWS + RATIO (START RESET
-TOD) and CWS’ > or = CWS and CWS - CWS < or = Maximum Reset.
Where
CWS’ is the new chilled water setpoint.
CWS is the active chilled water setpoint before any reset has occurred.
RESET RATIO is a user adjustable gain.
START RESET is a user adjustable reference.
TOD is the Temperature Outdoor Sensor.
TWE is entering evaporator water temperature.
TWL is the Leaving Evaporator Temperature.
MAXIMUM RESET is a user adjustable limit providing the maximum amount of reset. For all types of reset, CWS - CWS < or = Maximum Reset.
Both Return and Outdoor Reset do not apply to Heating Mode where the UCP is controlling the Leaving Condensing Hot Water Temperature.
Constant Return Reset will reset the leaving water temperature setpoint so as to provide a constant entering water temperature. The Constant Return Reset equation is the same as the Return Reset equation except on selection of Constant Return Reset, the UCP shall automatically set RATIO, START RESET, and MAXIMUM RESET to the following:
The RATIO = 100 percent
The START RESET = Design Delta Temperature
The MAXIMUM RESET = Design Delta Temperature
The equation for Constant Return is as follows:
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