96 RTAA-SVX01A-EN
Controls Interface
The equations for each type of reset are:
RETURN WATER TEMPERATURE RESET
CWS' = CWS + RESET RATIO
[START RESET - (TWE - TWL)]
and CWS' > or = CWS
and CWS' - CWS < or = MAXIMUM RESET
OUTDOOR AIR TEMPERATURE RESET
CWS' = CWS + RESET RATIO
[START RESET - TOD]
and CWS' > or = CWS
and CWS' - CWS < or = MAXIMUM RESET
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 outdoor temperature.
TWE is the entering evaporator water temperature.
TWL is the leaving evaporator water temperature.
MAXIMUM RESET is a user adjustable limit, providing the maximum amount
of reset.
NOTE: When any type of CWR is enabled, the UCM 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. This applies when the chiller is
both running and off. Normally the chiller will start at the Differential-to-Start
value above a fully reset CWS or CWS'.
The values for RESET RATIO for each type of reset are:
Reset Type
Reset
Ratio Range
Increment
English Units
Increment
SI Units
Factory Default
Value
Return 1O to 120% 1% 1% 50%
Outdoor 80 to -80% 1% 1% 10%
The values for START RESET for each type of reset are:
Reset Type
Start
Reset Range
Increment
English Units
Increment
SI Units
Factory Default
Value
Return 4 TO 30 F 1 F 0.1C 10 F (5.6 C)
(2.2 to 16.7 C)
Outdoor 50 to 130 F 1 F 0.1 C 90 F (32.2 C)
(10 to 54.4 C
The values for MAXIMUM RESET for each type of reset are:
Reset
Ty p e
Maximum
Reset Range
Increment
English Units
Increment
SI Units
Factory Default
Value
Return 1O to 20 F 1 F 0.1C 5 F (2.8 C)
(-17.8 to -6.7 C)
Outdoor O to20 F 1 F 0.1 C 5 F (2.8 C)
(-17.8 to -6.7 C)
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