Emerson E2 Manuel D’Utilisation

integral) of the demand window. The integral error rep-
resents how far below or above the setpoint the input has 
been for the entire demand window.

Under non-demand conditions, the integral error will 

be below zero, since the average KW or watt-hour value 
will be below the setpoint.

The current value of the integral error and the current 

value of the KW input are what determine when the 
Demand Control application will begin load shedding. 

Load shedding is the process of curbing the amount of 

kilowatt usage within one or more target applications. 
Most applications that drive mechanical or electronic 
devices, such as lights, heaters, air conditioners, compres-
sors, etc., are configured with special inputs that, when 
active, “shed” the application.

Physically, when a device is “shed,” its control set-

points are altered by a specified amount in a direction that 
will save energy. For instance, an HVAC unit with heating 
and cooling stages that is commanded to shed will have its 
heating setpoints lowered and its cooling setpoints raised. 
This will cause the HVAC unit to operate at a lower capac-
ity, thus saving energy.

Table 11-13 lists a number of E2 RX-300 and BX-300 

applications and how load shedding affects them.

All HVAC applica-
tions (RT-100s, 
MultiFlex RTUs, 
AHUs, Heat/Cools)

Raises cooling setpoints, low-
ers heating setpoints

Sensor Control and 
Analog Input I/O 
Modules

Raises or lowers Cut In/Cut 
Out setpoints (whichever direc-
tion saves energy)

Refrigeration Cir-
cuits

Raises case temperature set-
points

Suction Groups

Raises suction setpoint

Condenser

Raises discharge setpoint

Analog Output I/O 
Modules

Raises or lowers PID setpoint 
(whichever will save energy)

Digital Output I/O 
Modules

Control output is locked OFF.

Some applications have a single input (usually called 

DEMAND SHED) that, when ON, sheds the application. 
Each application is programmed with a specific “demand 
bump” value that is added or subtracted from the control 
setpoints when this input comes ON.

 Other applications, notably HVAC applications, have 

two inputs: a primary and a secondary (usually called PRI 
DEMAND SHED and SEC DEMAND SHED). Each 
input has its own “demand bump” value, so that when the 
primary is ON, the primary demand bump is in effect, and 
when the secondary is ON, the secondary demand bump is 
in effect. When both of these inputs are ON, the demand 
bump values are added/subtracted together and applied to 
the setpoint(s). As a result, two levels of shedding are pos-
sible for a single application.

Each application that you wish to set up for shedding 

must be assigned a priority level in the Demand Control 
application. When a Demand Control application sheds 
loads, it does so by shedding all applications that are in the 
first priority level, and then continuing to shed higher pri-
ority levels until the demand is at an acceptable level or 
until all levels are shed.

Priority levels are simply outputs that connect to the 

demand shedding inputs of one or more applications. 
When a level is shed, the output comes ON and all appli-
cations connected to the output are shed.

There are three types of priority levels:

First Shed levels are the first ones to be shed when 

demand shedding begins. The Demand Control applica-
tion first begins shedding by activating level #1 of the 
First Shed levels. As needed, each level thereafter is shed 
in succession (#2, #3, and so on to #20).

Applications that are part of the First Shed priority lev-

els should be non-vital applications that would have no 
significant effect on the system if it were to be shed for a 
prolonged period of time. Examples: motor room exhaust 
fans, satellite HVAC units and/or lights in low-occupancy