Glossary
The following terms are used throughout this manual.
They are defined here so as to assist you in under-
standing their meaning and use.
Average Demand:
The average rate of electric usage
during the demand averaging period. The average
demand is calculated by dividing the total number of
kilowatt-hours used by the number of hours in the
averaging period. For example, if 2 Kwh's were used
during an averaging period of 15 minutes, the aver-
age demand would equal 2 divided by .25 (15 min-
utes) or 8 KW.
Averaging Period:
An interval of 15, 30 or 60 minutes
over which the average demand is calculated. The
demand controller should be set to the same averag-
ing period as the utility's demand meter.
Customer Charge:
A flat charge on an energy bill
used to help the utility company recover fixed
costs associated with serving a customer. It is
independent of the demand or consumption of the
energy provided. Also called monthly service charge
or basic charge.
Declining Block Rate:
A method of charging for
electric service where the cost per Kwh is usually
reduced as the total Kwh use increases.
Demand:
The rate of use of electricity during a
certain period of time. Demand is measured in kilo-
watts.
Demand Billing Rate:
A method of charging for
electric service where the cost of electricity is based
on both total energy consumed (Kwh) and peak
demand (KW).
Demand Charge:
A charge that recovers some of
the utility's capital and operating costs based on
the customer's highest average use during the
billing interval. It appears on an electric bill, along
with the customer charge and the energy charge.
Demand Limit:
The set point, expressed in KW,
below which energy is being consumed at an
efficient rate. As this limit is approached, the
Energy Sentry Controller begins shutting off pre-
determined loads to control peak demand.
Demand Meter:
A utility meter which measures both
total energy consumed in Kwh and the highest aver-
age demand (peak) in KW. Most demand meters have
a digital readout showing the peak demand register.
Demand Peak:
The highest average KW demand
over the billing period. Averages may be determined
over 15, 30 or 60-minute intervals depending upon
the utility.
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Energy Charge:
A charge that recovers a utility's
general and other operating costs. It appears on an
electric bill, along with the customer charge and the
demand charge.
Energy Rate:
A method of charging for electric
service where cost of electricity is based only on Kwh
consumption multiplied by a fixed cost per Kwh. Kwh
cost remains the same regardless of number of Kwh’s
used. Also called “Flat” Rate.
Instantaneous Demand:
The electricity in kilowatts
currently being drawn by the electrical service of a
building at any instant in time.
Kilowatt (KW):
1,000 watts. A measure of an electric
load's size or how much power it demands.
Kilowatt Hour (Kwh):
The basic measurement of
electric power (energy) consumption as recorded by
the electric meter. (If you were to turn on ten 100 watt
lights for one hour, you would have consumed one
kilowatt hour of electrical energy.)
Load:
The amount of electricity used by a particular
energy consuming device or group of devices. Usu-
ally expressed in watts or kilowatts.
Minimum Off Time:
The minimum time that a control
point must be shut off before it can be restored by the
demand controller. The Minimum Off Time can be
set from 0 to 20 minutes. Control Points having a
heat pump or air conditioner compressor or other
motor load connected to it should have a Minimum
Off Time of at least 6 minutes. Resistive loads
should not have Minimum Off Times.
Minimum On Time:
The minimum time that a control
point must be restored before it can be shed by the
demand controller. The Minimum On Time can be set
from 0 to 20 minutes. Control Points having a heat
pump or air conditioner compressor or other motor
load connected to it should have a Minimum On Time
of at least 5 minutes.
Priority:
The relative importance of each controlled
load to all other controlled loads, as assigned in the
demand controller. As the demand approaches the
demand limit, the demand controller uses the priority
of each load to determine which loads to shut off first.
A load with a priority of "1" is the highest priority and
is shed last and restored first. A load with a priority
of "8" is the lowest priority and is shed first and
restored last. Loads of equal priority will rotate being
shed and restored.
Watt:
A measure of electrical power or rate of doing
work. It is analogous to horsepower where one horse-
power is equivalent to approximately 746 watts.
Appendix A