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RTAC-SVX01F-EN 83
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
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.
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 F every 5 minutes until the Active CWS equals the desired CWS'. This
applies when the chiller is running.
Reset Type Reset Ratio
Range
Start Reset
Range
Maximum Reset
Range
Increment
English Units
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)