Trane RTAC 150 Series

44 RTAC-SVX002A-EN
Installation Electrical
• Start Reset Set Points.
• Maximum Reset Set Points.
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
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:
Tab. IV-04 – Reset Type
Reset Type Reset Ratio
Range
Start Reset
Range
Maximum
Range
Increment
Reset
Increment
SI Units
Factory Default
Value
Return: 10 to 120% 4 to 30 F 0 to 20 F 1% 1% 50%
(2.2 to 16.7 C) (0.0 to 11.1 C)
Outdoor 80 to -80% 50 to 130 F 0 to 20 F 1% 1% 10%
(10 to 54.4 C) (0.0 to 11.1 C)
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.
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 F every 5 minutes
until the Active CWS equals the desired
CWS’. This applies when the chiller is
running.