Trane CVHE Troubleshooting Manual page 117

The values for MAXIMUM RESET for each of the reset types are:
Maximum Reset
Reset Type
Return
Outdoor
Both Return and Outdoor Reset do not apply to hot water control mode where UCP2 is
controlling the Leaving Condenser Water Temperature.
In addition to Return and Outdoor Reset, UCP2 will provide a menu item at the Clear
Language Display for the operator to select a Constant Return Reset. Constant Return Reset
will reset the leaving water temperature setpoint 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, UCP2 will automatically set RATIO, START
RESET, and MAXIMUM RESET to the following.
the RATIO = 100%
the START RESET = Design Delta Temp.
the MAXIMUM RESET = Design Delta Temp.
The equation for Constant Return is then as follows:
Constant Return
CWS' = CWS + 100% (Design Delta Temp. - (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, UCP2 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. When the
chiller is not running the CWS is reset immediately (within one minute) for Return Reset and
at a rate of 1°F every 5 minutes for Outdoor Reset. The chiller will start at the Differential to
Start value above a fully reset CWS or CWS' for both Return and Outdoor Reset.
CVHE-SB-32A
Increment
Range (English Units)
0 to 20°F
(0.0 to 11.1°C)
0 to 20°F
(0.0 to 11.1°C)
Increment (SI
Units)
1°F 0.1°C
1°F 0.1°C
Factory Default
Value
5°F (2.8°C)
5°F (2.8°C)
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