52
RLC-SVX09Q-EN
Figure 26. Wiring examples for EDLS and ECWS/
EHWS
Chilled Water Reset (CWR)
The unit controller resets the chilled water temperature set
point based on either return water temperature, or outdoor
air temperature. Return Reset is standard, Outdoor Reset
is optional.
The following shall be selectable:
• One of three Reset types:None, Return Water
Temperature Reset, Outdoor Air Temperature Reset, or
Constant Return Water Temperature Reset.
• Reset Ratio setpoints: For outdoor air temperature
reset there shall be both positive and negative reset
ratios.
• Start Reset Setpoints.
• Maximum Reset setpints.
The equations for each type of reset are as follows:
Return
CWS' = CWS + RATIO (START RESET - (TWE - TWL))
and CWS' > or = CWS
and CWS' - CWS < or = Maximum Reset
Outdoor
CWS' = CWS + RATIO * (START RESET - TOD)
and CWS' > or = CWS
and CWS' - CWS < or = Maximum Reset
where
• CWS' is the new chilled water set point or the reset
CWS
• 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.
Reset
Type
Range
Reset
Ratio
Start
Reset
Max
Reset
Incre-
ment
Factory
Default
Return
10 to
120%
4 to 30°F
(2.2 to
16.7 °C)
0 to 20°F
(0.0 to
11.1°C)
1% 50%
Outdoor
–80 to
80%
50 to
130°F
(10 to
54.4°C)
0 to 20°F
(0.0 to
11.1°C)
1% 10%
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, 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.
Outdoor Air Temperature Sensor Installation
Requirements
The outdoor air temperature sensor is optional. The
temperature sensor probe is shipped separately inside the
control panel.
Installation - Electrical
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