Trane CenTraVac Duplex CDHE, Operation & Maintenance Manual

Page: 83 / 116

83
CDHF-SVU01C-EN
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:
Machine Protection
and Adaptive
Control