Functional Control ESIE10-01
2–32 Part 2 – Functional Description
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2.2.8 LWT Target
The LWT Target varies based on settings and inputs.
The base LWT Target is selected as follows:
Leaving water
temperature (LWT)
reset
The base LWT target may be reset if the unit is in Cool mode and it is configured for a reset. The type
of reset to be used is determined by the LWT Reset Type set point.
When the active reset increases, the Active LWT Target is changed at a rate of 0.1°F every 10
seconds. When the active reset decreases, the Active LWT Target is changed all at once.
After resets are applied, the LWT target can never exceed a value of 60°F.
■ Reset Type – None
The Active Leaving Water variable is set equal to the current LWT set point.
■ Reset Type – Return
Introduction: When return water is selected as the reset mode, the controller will adjust the leav-
ing chilled water setpoint to maintain a constant return water temperature equal to the return
water setpoint. The return water temperature is sampled every 5 minutes and a proportional cor-
rection is made to the leaving chilled water setpoint. The corrected leaving water setpoint is never
set to a value greater than the return water setpoint and is never set to a value less than the
actual leaving chilled water setpoint.
Function description
Remark: When the unit is designed for a ΔT of 5°C (at 100% capacity), then the start ΔT and Max
Reset should also be set to 5°C.
Explanation: The return water reset will adjust the leaving chilled water setpoint according to the
evaporator ΔT. In this way the chiller can maintain a constant return water temperature.
Control Source
Set Point
Mode
Input
BMS
Request
Available Modes Set
Point
Base LWT Target
Local OFF X COOL Cool Set Point 1
Local ON X COOL Cool Set Point 2
Network X X COOL BMS Cool Set Point
Local OFF X COOL w/Glycol Cool Set Point 1
Local ON X COOL w/Glycol Cool Set Point 2
Network X X COOL w/Glycol BMS Cool Set Point
Local OFF x COOL/ICE w/Glycol Cool Set Point 1
Local ON x COOL/ICE w/Glycol Ice Set Point
Network x COOL COOL/ICE w/Glycol BMS Cool Set Point
Network x ICE COOL/ICE w/Glycol BMS Ice Set Point
Local x x ICE w/Glycol Ice Set Point
Network x x ICE w/Glycol BMS Ice Set Point
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