44
Fig. 42 — Example: Space Temperature Reset
Demand Limit
There are three types of demand limiting that can be config-
ured. The first type is through switch control, which will re-
duce the maximum capacity to up to 3 user-configurable per-
centages. 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 oper-
ating capacity to maximum and further reduce the capacity if
required. Demand limit control can be based on a calculated
capacity level. If the Demand Limit is enabled and the current
capacity requirement meets or exceeds the current Demand
Limit level, the unit will unload and display Override #9: De-
mand Limit section on page 48.
If the demand limit percentage is set below minimum unit op-
eration, the unit will go into override mode. See Override #91:
Demand Limit section on page 48.
SWITCH CONTROLLED DEMAND LIMIT
The control system is capable of demand limit based on a field-
supplied switch for 1-step demand limit or 2 switches for 3-step
demand limit. One-step demand limit is standard. The 2 or 3-step
switch control of demand limiting requires the EMM. Demand
limit steps are controlled By two relay switch inputs field wired to
TB5-5 and TB5-14 for Switch 1 (LIM_SW1) and TB6-14 and
TB6-15 for Switch 2 (LIM_SW2).
For demand limit by switch control, closing the first demand
limit contact (LIM_SW1) will put the unit on the first demand
limit (LIMIT 1) by capacity. The unit will not exceed the per-
centage of capacity entered as Demand Limit Switch 1 set point.
Closing contacts on the second demand limit switch
(LIM_SW2) and opening the Demand Limit Switch 1 prevents
the unit from exceeding the demand limit (LIMIT 2) entered as
Demand Limit Switch 2 set point. If both demand limit switch
(LIM_SW1 and LIM_SW2) contacts are closed the unit will not
exceed the limit (LIMIT 3) set by the switch limit set point 3.
See the table below.
To use demand limit, select the type of demand limiting to use
by configuring the Demand Limit Select variable (Main Menu
Configuration Menu
General Configuration
Demand
Limit Type Select) to Switch. Configure the demand limit set
points based on the type selected.
If using 2 or 3-step demand limit control, an energy management
module must be installed. The energy management module must
be enabled in the controls. To enable the EMM navigate to Fac-
tory Parameters menu (Main Menu
Configuration Menu
Factory Parameters) and set Energy Management Module to
YES (1).One-step demand limit control does not require the en-
ergy management module. To configure demand limit for switch
control, three parameters for 1-step switch control must be con-
figured. For 2 or 3-step control, additional set point parameters
must be configured. The parameters are: the type of Demand
Limit Selection, the setting for Switch Limit Setpoint 1, the set-
ting for Switch Limit Setpoint 2 (if required) and the setting for
Switch Limit Setpoint 3 (if required).
To configure this option with the Carrier Controller display:
In the following example, 2-step demand limit based on capac-
ity is desired with the first switch closure limiting the capacity
to 60%. The second switch closure is to limit the capacity to
40%. Demand Limit Switch 1 is 60% and Demand Limit
Switch 2 is 40%. Since no third-step demand limit is required,
Switch Limit Setpoint 3 is set at 0%.
0
1
2
3
4
5
6
7
57 07 56 06 80
Space Temperature (deg F)
De
g
ree
s
Res
et (deg
F)
Cooling Reset
Deg. Value
(cr_deg)
Space T Full Reset Value
(spahr_fu)
Space T No Reset Value
(spahr_no)
a30-5884
CONTACT
ACTIVE DEMAND LIMIT
NONE LIMIT 1 LIMIT 2 LIMIT 3
LIM_SW1 Open Close Open Close
LIM_SW2 Open Open Close Close
DISPLAY NAME PATH VALUE
Demand Limit
Type Select
Main Menu
Configuration Menu
General Configura-
tion
Default = 0 (None)
Range None = 0
Switch = 1
4 to 20mA = 2
Switch Limit
Setpoint 1
Main Menu
Setpoint Table
Default = 100%
Range 0 to 100%
Switch Limit
Setpoint 2
Main Menu
Setpoint Table
Default = 100%
Range 0 to 100%
(Not required for 1-Step Control)
Switch Limit
Setpoint 3
Main Menu
Setpoint Table
Default = 100%
Range 0 to 100%
(Not required for 1 or 2-Step Control)
DISPLAY NAME VALUE
Demand Limit Type Select 1
Switch Limit Setpoint 1 60%
Switch Limit Setpoint 2 40%
Switch Limit Setpoint 3 0%
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