88 CG-SVX17D-EN
Installation - Electrical
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.
When the chiller is not running the CWS is reset immediately (within one minute) for Return Reset
and at a rate of 1 degree 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.
Percent Capacity Output Option
CH530 provides an optional percent capacity output for those customers without a communicating
BAS interface. The active unit capacity (AUC) is provided through a 2-10 VDC analog ouput at 1A25
terminals J2-4 and J2-6 (GND). The active unit capacity value (in %) can be derived from the 2-10
VDC output voltage (OV) using the following calculation:
AUC = 100*(OV - 2.0V)/(10.0V - 2.0V)
Note: The percent capacity output is based on the number and size of compressors energized, and
is not adjusted for operating conditions. This value cannot be used as an accurate measure
of total unit current, power or cooling capacity.
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)
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