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DEMAND LIMIT (SCN Loadshed Controlled) — To con-
figure Demand Limit for SCN Loadshed control set the De-
mand Limit Select (DMDC) [Configuration, RSET] to 3. Then
configure the Loadshed Group Number (SHNM), Loadshed
Demand Delta (SHDL), and Maximum Loadshed Time
(SHTM) [Configuration, RSET]. See Table 27.
The Loadshed Group number is established by the SCN
system designer. The ComfortLink control will respond to a
Redline command from the Loadshed control. When the
Redline command is received, the current stage of capacity is
set to the maximum stages available. Should the loadshed con-
trol send a Loadshed command, the ComfortLink control will
reduce the current stages by the value entered for Loadshed
Demand delta. The Maximum Loadshed Time is the maximum
length of time that a loadshed condition is allowed to exist. The
control will disable the Redline/Loadshed command if no Can-
cel command has been received within the configured maxi-
mum loadshed time limit.
Cooling Set Point (4 to 20 mA) —
A field supplied
and generated, externally powered 4 to 20 mA signal can be
used to provide the leaving fluid temperature set point. Connect
the signal to TB6-3,5 (+,–). See Table 27 for instructions to
enable the function. Figure 21B shows how the 4 to 20 mA sig-
nal is linearly calculated on an overall 10 F to 80 F range for
fluid types (FLUD) 1 or 2 [Configuration, OPT1]. The set point
will be limited by the fluid (FLUD) type. Be sure that the
chilled water loop is protected at the lowest temperature.
Care should be taken when interfacing with other manufac-
turer’s control systems, due to possible power supply
differences, full wave bridge versus half wave rectification.
The two different power supplies cannot be mixed.
ComfortLink™ controls use half wave rectification. A sig-
nal isolation device should be utilized if a full wave bridge
signal generating device is used.
50% CAPACITY AT 20 mA
75% CAPACITY AT 12 mA
100% CAPACITY AT 4 mA
0
2
4
6
8
10
12
14
16 18
20
DEMAND LIMIT SIGNAL – 4 - 20 mA INPUT
100
80
60
40
20
0
MAX. ALLOWABLE LOAD (%)
Fig. 21A — 4- to 20-mA Demand Limiting
100
(38)
80
(27)
60
(15)
40
(4.4)
20
(-7)
0
(-17)
4 6.3 8.6 10.9 13.1 15.4 17.7 20
4 TO 20 mA SIGNAL TO EMM
SET POINT, F (C)
90
(32)
70
(21)
50
(10)
30
(-1)
10
(-12)
(FLUD = 2) MINIMUM
SET POINT 14 F (-10 C)
(FLUD = 1) MINIMUM
SET POINT 38 F (3.3 C)
MAXIMUM
SET POINT
70 F (21.1 C)
Fig. 21B — Cooling Set Point (4 to 20 mA)
EMM —
Energy Management Module