Installation - Electrical
RTAC-SVX01J-EN 91
• Maximum Reset Set Points.
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.
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 DeltaTemp.
MAXIMUM RESET = Design DeltaTemp.
The equation for Constant Return is then as follows:
CWS' = CWS + 100% (Design DeltaTemp. - (TWE -TWL))
and
CWS' > or = CWS
and CWS' - CWS < or = Maximum Reset
When any type of CWR is enabled, the MP will step the
Acti
ve 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.
Communications Interface
options
Optional Tracer Communications Interface
This option allows theTracer CH530 controller to exchange
information (e.g. operating setpoints and Auto/Standby
commands) with a higher-level control device, such as a
Tracer Summit or a multiple-machine controller. A
shielded, twisted pair connection establishes the bi-
directional communications link between theTracer
CH530 and the building automation system.
Important: T
o prevent control malfunctions, do not run
low voltage wiring (<30 V) in conduit with
conductors carrying more than 30 volts.
Field wiring for the communication link must meet the
following
requirements:
• All wiring must be in accordance with the NEC and
local
codes.
• Communication link wiring must be shielded, twisted
pair
wiring (Belden 8760 or equivalent). See the table
below for wire size selection:
• The communication link cannot pass between
buildings.
• All units on the communication link can be connected
in
a “daisy chain” configuration.
LonTalk Communications Interface for
Chillers (LCI-C)
CH530 provides an optional LonTalk Communication
Interface (LCI-C) between the chiller and a Building
Automation System (BAS). An LCI-C LLID shall be used to
provide "gateway" functionality between a LonTalk
compatible device and the Chiller. The inputs/outputs
Range Increment
Reset
Type
Reset
Ratio
Start
Reset
Max
Reset
IP
Units
SI
Units
Factory
Default
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)
Table 44. Wire Size
Wire Size
Maximum Length of Communication
Wire
14 AWG (2.5 mm
2
) 5,000 FT (1525 m)
16 AWG (1.5 mm
2
) 2,000 FT (610 m)
18 AWG (1.0 mm
2
) 1,000 FT (305 m)
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