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Table 3. Values for start reset types
The values for “RESET TYPE” are:
Reset Outdoor Return Const Return
Type: Disable Air Reset Reset Reset
The values for “RESET RATIO” for each of the reset types are:
Reset Reset Increment Increment Factory
Type Ratio English SI Units Default
Range Units Value
Return 10 to 120 percent 1 percent 1 percent 50 percent
Outdoor -80 to 80 percent 1 percent 1 percent 10 percent
The values for “START RESET “ for each of the reset types are:
Reset Start Increment Increment Factory
Type Reset English SI Units Default
Range Units Value
Return 4 to 30°F 0.1°F 0.1°C 10°F (5.6°C)
(2.2 to 16.7°C)
Outdoor 50 to 130°F 0.1°F 0.1°C 90°F
(10 to 54.44°C) (32.22°C)
The values for “MAXIMUM RESET” for each of the reset types are:
Reset Maximum Increment Increment Factory
Reset English SI Units Default
Range Units Value
Return 0 to 20°F 0.1°F 0.1°C 5°F
(0.0 to 11.11°C) (2.78°C)
Outdoor 0 to 20°F 0.1°F 0.1°C 5°F
(0.2 to 11.11°C) (2.78°C)
Constant Return
CWS’ = CWS + 100 percent
(Design Delta Temperature) - (TWE-
TWL) and CWS’ > or = CWS and
CWS’ -CWS < or = Maximum Reset
Notice that Constant Return is
nothing more than a specific case of
Return Reset offered for operator
convenience.
When any type of CWR is enabled,
the UCP will step the CWS toward
the desired CWS (based on the above
equations and setup parameters) at a
rate of 1°F every 5 minutes until the
Active CWS equals the desired
CWS’. This applies when the chiller
is running only.
Using the Equation for calculating
CWR for Outdoor Air Temperature
Equation:
Degrees of Reset = Reset Ratio*(Start
Reset - TOD)
The chiller will start at the Differential
to Start value above a fully reset CWS
or CWS for both Return and Outdoor
Reset.
The graph on the next page, shows
the reset function for Outdoor Air
Temperature: Note: This graph
assumes that Maximum Reset is set
to 20 degrees.
Degrees of Reset:
Degrees of Reset = Active CWS -
Front Panel CWS
or
Degrees of Reset = CWS’ - CWS
To obtain Active CWS from Degrees
of Reset: Active CWS = Degrees of
Reset + Front Panel CWS
Machine Protection
and Adaptive
Control
(* = multiply)