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By monitoring kilowatt usage,
E2 always knows how much energy a store is using at any given time. As
the rate of energy usage increases toward a retailer’s established peak
limit, E2 begins taking pre-defined steps to reduce that location's
energy consumption. Like most utility companies, the E2 uses a sliding
demand window to measure power usage over time. The window may be set
between five and 30 minutes, depending on a customer’s preference. If a
store’s average power usage during a demand window exceeds the
customer’s peak limit, “load shedding” will begin.
 Each
device that is set up for load shedding must be assigned a priority
level in the E2. When the E2 begins load shedding, it sheds all
applications that are in the first priority level. It then continues to
shed higher levels until the demand is at an acceptable level, or until
all levels are shed. There are three priority levels available: First
Shed, Rotational Shed, and Last Shed. Equipment in the First Shed should
be non-critical devices that would have no significant effect on the
store if it were to be shed for an extended period of time. Examples of
this might be motor room exhaust fans or lights in low-occupancy rooms.
Equipment in the Rotational Shed is only shed if all devices in the
First Shed have been deactivated and the store is still using too much
energy. Devices in this Rotational Shed should be more important to a
store’s performance, but not critical, because they will spend more time
in load shed. Finally, equipment in the Last Shed priority is shed only
if all devices in the first two priorities have been shed and an energy
reduction is still required. This equipment should be the most vital to
a store’s performance, since it will be shed only as a last resort and
will therefore spend the least amount of time in load shed.
E2 has three different
modes of operation that determine which priority levels should be
enabled and when. Normally, the E2 operates in the first mode,
proceeding to the second and third modes only if demand is not lowering
at an acceptable rate. The first mode starts when the average power
usage of a store rises above its setpoint in a demand window. When this
occurs, E2 begins load shedding, starting with the first device in the
First Shed priority and continuing through all equipment in the First,
Rotational, and Last Shed priorities. The second mode begins when the
first mode has been in effect for one quarter of a demand window and the
power usage of the store continues to rise. This is similar to the
first mode, except that E2 begins shedding two devices at once instead
of one.
The third and final
mode begins if the store’s average power usage is still above the demand
setpoint and the demand window is almost at the end of its period.
During this final mode, E2 calculates how many devices it needs to shed
to bring the average power
 usage
below the desired setpoint. Because this mode may turn off multiple
devices to bring average power usage below the setpoint, it is only used
as a last resort to prevent a customer from exceeding their energy
target. In addition to the three modes described here, a retailer may
create his own custom demand control algorithm using sensor control
applications. This custom procedure may use any series of actions or
applications to accomplish the desired behavior, allowing the retailer
to have considerably more flexibility.
In all instances, it is
important that store circuits be designed with load shedding in mind.
However, if a facility does not have loads broken out properly,
retailers can still take advantage of this capability with minor wiring
changes.
As a result of these
algorithms, some customers have seen a seven percent decrease in their
utility bills. As energy prices increase and retailers strive to
improve the environmental sustainability of their stores, more retailers
are expected to adopt these strategies.
To learn more about the
E2 Facility Management System or other innovative ways Retail Solutions
helps retailers worldwide lower their energy costs, please
click here to e-mail a sales representative.
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