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Demand limit is a feature that allows
Demand Limit —
the unit capacity to be limited during periods of peak energy
usage. There are three types of demand limiting that can
be configured. The first type is through 2-step switch
control, which will reduce the maximum capacity to 2 user-
configurable percentages. The second type is by 4 to 20 mA
signal input which will reduce the maximum capacity linearly
between 100% at a 4 mA input signal (no reduction) down to
the user-configurable level at a 20 mA input signal. The third
type uses the CCN Loadshed module and has the ability to
limit the current operating capacity to maximum and further
reduce the capacity if required.
NOTE: One-step Demand Limit is standard.
The 2-step switch control and 4 to 20-mA input signal types
of demand limiting require the energy management module
(EMM).
To use demand limit, select the type of demand limiting to
use. Then configure the demand limit set points based on the
type selected.
2-STEP SWITCH CONTROLLED — If using 2-step de-
mand limit control, an energy management module must be in-
stalled. One-step demand limit control does not require the en-
ergy management module. To configure demand limit for
2-step switch control, three parameters must be configured:
Demand Limit Select (Configuration
Switch Limit Setpoint 1 (Setpoints
Switch Limit Setpoint 2 (Setpoints
following example, Demand Limit Switch 1 is 60% and de-
mand limit Switch 2 is 40%. Demand limit steps are controlled
by two relay switch inputs field wired to TB5 for Switch 1 and
TB6 for Switch 2. See Table 31.
For demand limit by 2-stage switch control, closing the first
stage demand limit contact will put the unit on the first demand
limit level. The unit will not exceed the percentage of capacity
entered as Demand Limit Switch 1 set point. Closing contacts
on the second demand limit switch prevents the unit from ex-
ceeding the capacity entered as Demand Limit Switch 2 set
point. The demand limit stage that is set to the lowest demand
takes priority if both demand limit inputs are closed. If the de-
mand limit percentage does not match unit staging, the unit
will limit capacity to the closest capacity stage without exceed-
ing the value. To disable demand limit configure DMDC to 0.
1
0
0
9
0
8
0
7
0
6
0
5
0
4
0
3
0
2
0
1
0
0
0
RSET
DMDC),
MISC
DLS1) and
MISC
DLS2). In the
2
4
6
DEMAND LIMIT SIGNAL (mA)
Fig. 24 — Demand Limit
EXTERNALLY POWERED (4 to 20 mA Controlled) — The
energy management module is required for 4 to 20 mA
demand limit control. To configure demand limit for 4 to
20 mA control three parameters must be configured. They are:
Demand Limit Select (Configuration
for 100% Demand Limit (Configuration
and mA for 0% Demand Limit (Configuration
DMZE). In the following example, a 4 mA signal is Demand
Limit 100% and a 20 mA Demand Limit signal is 0%. The 4 to
20 mA signal is connected to TB6-1 and TB6-2. The demand
limit is a linear interpolation between the two values entered.
See Table 32 and Fig. 24.
Care should be taken when interfacing with other control
systems due to possible power supply differences such as a
full wave bridge versus a half wave rectification. Connec-
tion of control devices with different power supplies may
result in permanent damage. ComfortLink™ controls
incorporate power supplies with half wave rectification. A
signal isolation device should be utilized if the signal
generator incorporates a full wave bridge rectifier.
In Fig. 24, if the machine receives a 12 mA signal, the
machine controls will limit the capacity to 50%.
CCN LOADSHED CONTROLLED — To configure demand
limit for CCN Loadshed control, the unit Operating Type
Control must be in CCN control, (Operating Modes
SLCT
SP.SE=2) and be controlled by a Chillervisor module.
The Chillervisor module can force the demand limit variable
and directly control the capacity of the machine. Additionally,
the unit's set point will be artificially lowered to force the chill-
er to load to the demand limit value.
Remote Alarm and Alert Relays —
er can be equipped with a remote alert and remote alarm
annunciator contacts. Both relays connected to these contacts
must be rated for a maximum power draw of 10 va sealed,
25 va inrush at 24 volts. The alarm relay, indicating that the
complete unit has been shut down can be connected to TB5-12
and TB5-13. For an alert relay, indicating that at least 1 circuit
was off due to the alert, a field-supplied and installed relay
must be connected between MBB-J3-CH25-3 and TB5-13.
8
1
0
1
2
41
RSET
RSET
CAUTION
1
4
1
6
1
8
DMDC), mA
DMMX)
RSET
The 30RB chill-
2
0
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