Demand Limit - Carrier AquaForce B Series Controls, Start-Up, Operation, Service And Troubleshooting Instructions

7
6
5
4
Cooling Reset
Deg. Value
3
(cr_deg)
2
1
0
6 0

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.
CONTACT
NONE
LIM_SW1 Open
LIM_SW2 Open
Space T Full Reset Value
(spahr_fu)
6 5
Space Temperature (deg F)
Fig. 42 — Example: Space Temperature Reset
ACTIVE DEMAND LIMIT
LIMIT 1 LIMIT 2 LIMIT 3
Close Open Close
Open Close Close
Space T No Reset Value
(spahr_no)
7 0 7
To use demand limit, select the type of demand limiting to use
by configuring the Demand Limit Select variable (Main Menu

Configuration Menu
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
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:
DISPLAY NAME PATH
Main Menu
Configuration Menu
Demand Limit

Type Select
General Configura-
tion
Switch Limit Main Menu
Setpoint 1 Setpoint Table
Main Menu
Switch Limit
Setpoint Table
Setpoint 2
Main Menu
Switch Limit
Setpoint Table
Setpoint 3
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%.
DISPLAY NAME
Demand Limit Type Select
Switch Limit Setpoint 1
Switch Limit Setpoint 2
Switch Limit Setpoint 3
44
5 80
a30-5884

General Configuration

Configuration Menu
VALUE

Default = 0 (None)
Range None = 0
Switch = 1
4 to 20mA = 2

Default = 100%
Range 0 to 100%

Default = 100%
Range 0 to 100%
(Not required for 1-Step Control)

Default = 100%
Range 0 to 100%
(Not required for 1 or 2-Step Control)

Demand

VALUE
1
60%
40%
0%