Trane RTAA-70 Installation & Maintenance Manual page 96

96
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
Reset Type Ratio Range
Return 1O to 120%
Outdoor 80 to -80%
The values for START RESET for each type of reset are:
Start
Reset Type Reset Range
Return 4 TO 30 F
(2.2 to 16.7 C)
Outdoor 50 to 130 F
(10 to 54.4 C
The values for MAXIMUM RESET for each type of reset are:
Reset Maximum
Type Reset Range
Return 1O to 20 F
(-17 .8 to -6.7 C)
Outdoor O to20 F
(-17 .8 to -6.7 C)
Increment Increment
English Units SI Units
1% 1%
1% 1%
Increment Increment
English Units SI Units
1 F 0.1C
1 F 0.1 C
Increment Increment
English Units SI Units
1 F 0.1C
1 F 0.1 C
Factory Default
Value
50%
10%
Factory Default
Value
10 F (5.6 C)
90 F (32.2 C)
Factory Default
Value
5 F (2.8 C)
5 F (2.8 C)
RTAA-SVX01A-EN