Trane RTWD Installation Operation & Maintenance page 66

Installation – Electrical
Reset ratio
Reset type
range
Return 10 to 120%
Outdoor 80 to -80%
The equations for each type of reset are as follows:
Return
CWS' = CWS + RATIO (START RESET - (TWE - TWL))
and CWS' > or = CWS
and CWS' - CWS < or = Maximum Reset
Outdoor
CWS' = CWS + RATIO * (START RESET - TOD)
and CWS' > or = CWS
and CWS' - CWS < or = Maximum Reset
where
CWS' is the new chilled water set point or the "reset
CWS"
CWS is the active chilled water set point before any reset
has occurred, e.g. normally Front
Panel, Tracer, or ECWS
RESET RATIO is a user adjustable gain
START RESET is a user adjustable reference
TOD is the outdoor temperature
TWE is entering evap. water temperature
TWL is leaving evap. water temperature
MAXIMUM RESET is a user adjustable limit providing
the maximum amount of reset. For all types of reset,
CWS' - CWS < or = Maximum Reset.
66
Start reset Maximum reset
range range
2.2 to 16.7°C 0.0 to 11.1°C
10 to 54.4°C 0.0 to 11.1°C
In addition to Return and Outdoor Reset, the MP
provides a menu item for the operator to select a
Constant Return Reset. Constant Return Reset will reset
the leaving water temperature set point 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 MP will automatically set Ratio, Start Reset, and
Maximum
Reset to the following:
RATIO = 100%
START RESET = Design Delta Temp.
MAXIMUM RESET = Design Delta Temp.
The equation for Constant Return is then as follows:
CWS' = CWS + 100% (Design Delta Temp. - (TWE - TWL))
and CWS' > or = CWS
and CWS' - CWS < or = Maximum Reset
When any type of CWR is enabled, the MP will step
the Active CWS toward the desired CWS (based on
the above equations and setup parameters) at a rate
of 1 degree C every 5 minutes until the Active CWS
equals the desired CWS'. This applies when the chiller is
running.
When the chiller is not running the CWS is reset
immediately (within one minute) for Return Reset and at
a rate of 1 degree C every 5 minutes for Outdoor Reset.
The chiller will start at the Differential to Start value
above a fully reset CWS or CWS' for both Return and
Outdoor Reset.
Increment SI Factory default
units value
1%
1%
50%
10%
RLC-SVX14H-GB