Low Leaving Water Temperature Cutout - Trane HORIZON ABDA Manual

(9) Low Leaving Water
Temperature Cutout
(LCWTC)
The low chilled water temperature cutout will integrate to
trip when the chilled water leaving temperature approaches
the low leaving water temperature setpoint. The setpoint is
factory adjusted at 38°F and should not be lowered. The
setpoint can be raised using the service settings; field
startup group menu. The range is 35-38°F. The low leaving
water temperature cutout setpoint should never be less
than 1.7°F below the leaving chilled water temperature
setpoint when the cutout setpoint is 38°F. See Figure 17.
Figure 17
Leaving Water Temperature Setpoint
(for example 44°F)
Lowest Setable Leaving Water
Temperature Setpoint (for example
39.8°*)
1.7°F minimum difference between Leaving Water
Temperature Setpoint and Low Chilled Water
Temperature Cutout (LCWTC)
*Lowest setable Leaving Water Temperature in this example is
39.8°F because low chiller water temperature cutout (38°F) plus 1.7
equals 39.7 and setpoint must be greater than this.
66
Control Band
The control band is a region "around" setpoint within
which the leaving water temperature is allowed to drift. The
control band is the setpoint + or - 1.0 degrees F. The control
algorithms are active within this band to maintain control.
A stable control band is a result of a properly tuned control
"Gains ". The control band is affected by Proportional,
Integral, Derivative (PID) gain settings. Factory settings
accommodate most applications. Gain adjustments are
accessible to allow a qualified individual to adjust unit
performance for a given installation. Only qualified
personnel should attempt gain adjustments.
Control band - PID
Leaving Water
Temperature functions
are actively controlling
to setpoint (+ or - 1.8°F)
Low Chilled Water Temperature Cutout
Setpoint (for example 38°F)
Dead Band - no active control