©2025 Copeland LP.
026-1803 R13 Supervisor I&O User Guide 9 - 27
9.15.2 Demand Calculation
Average KW (Demand) Calculation
The power company's peak demand charge is an average
KW value over an interval window.This interval is usually in
the 15 to 30 minute range, but can be as short a five minutes.
Some pulse meters provided by the power company
provides a signal that determines when a new demand
interval is starting. In general the control strategy cannot
count on this signal being available. Therefore, the demand
control window used by the application must be set to the
same value as the power company’s demand window.
Load Shedding Activation
The application integrates the power level above and below
the setpoint on a rolling demand window of the same length
as the utility demand window. That way, if the average KW in
the rolling window is kept below the setpoint, the electric
utility never detect a demand usage exceeding the setpoint.
Once the KW input rises above the setpoint, levels start to
shed.
The amount shed depends on several factors:
• If the integral error is approaching zero, the amount shed
is the KW input minus the setpoint.
• If the KW input has been continuously above the setpoint
for 1/4th of the demand window and the KW input is not
going down, shed two levels at a time.
• Shed one level at a time. If the KW input goes below the
setpoint, it starts to shed one level at a time.
If the KW input goes below the setpoint minus the hysteresis
and the integral error is less than zero, the levels start to
restore. They continue to restore until the KW input goes
above the setpoint.
Demand Setpoint Determination
The demand setpoint is determined based on the current
season - Summer or Winter. For each season, there are two
setpoints available. The active setpoint is chosen based on
the state of a setpoint switch input. In this way, different
demand setpoints may be selected depending on the time of
day or some other signal.
9.15.3 Shed Outputs
There are up to 60 shed requests for a system. These shed
requests are placed into three categories.
During the configuration of the various control applications, a
user assigns a particular shed request to any of the following
control loop:
• First Shed - Loads assigned to First Shed Requests are
shed first when the demand goes above setpoint and are
the last loads to be restored. They are shed sequentially
in assigned order.
• Rotational Shed - Loads assigned to Rotational Shed
Requests are shed in a rotational scheme after the First
Shed loads are shed. On each new demand condition
the next rotational load in the sequence is shed first. This
is done so that the DLC burden is shared equally.
• Last Shed - Loads assigned to Last Shed Requests are
only shed once the First Shed and all available Rotational
loads are shed. They are shed sequentially in assigned
order. These loads are the first loads to be restored.
When a level is shed, the shed timer is started and the staging
interval timer (minimum time to wait before shedding the next
load) is set to the value programmed for this shed level.
The shed sequence depends on the type of loads that are
available to be shed. Loads assigned as first shed are always
the first shed in the user assigned sequence. Once all the first
shed loads are shed, the rotational loads are shed. Assigning
a load to be a rotational scheme is done to balance the
burden of demand shedding among all the loads. This means
that the application will not shed the same load until all other
rotational loads are shed. After all available rotational loads
are shed, the last shed loads are shed in the user assigned
sequence.
The loads are restored based on the following rules:
• Last shed loads are restored first in a last shed first restore
order.
• Rotational loads are restored based on which one are
shed the longest.
• First shed loads are restored in a last shed first restore
order.
• After a load is restored, the staging interval timer is set (set
to the same value used when this load is shed). Once the
staging interval expires the next load is restored if the
power level is still below the setpoint minus the
deadband.
• If a load is restored due to maximum shed time-out that
counts for the restored load for that application update
interval.
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