EXPLANATION OF TERM “DEMAND”
Kilowatt demand is generally defined as the kilowatt load averaged over a specified interval of time. In any one of the time intervals shown, the area under the dotted line labeled demand is exactly equal to the area under the power curve.
Since energy is the product of power and time, either of these two areas represents the energy consumed in the demand interval. The equivalence of the two areas shows that the demand for the interval is that value of power which, if held constant over the interval, will account for the same consumption of energy as the real power. It is then the average of the real power over the demand interval.
The demand interval during which demand is measured may be any selected period but is usually 5, 10, 15, 30, 60, and in similar increments up to 720 minutes. The demand period is determined by the billing tariff for a given rate schedule.
Demand has been explained in terms of power (kilowatts) and usually this information has the greater usefulness. However, demand may be expressed in kilovoltamperes reactive (kVAR), kilovoltamperes (kVA), or other suitable units.
Coincidental Demand—Many utility customers have two or more revenue meters that meter separate electrical loads. A common example is a large factory that has multiple meters at different locations. Assuming each revenue meter measures demand, then each meter would provide a maximum demand.
Coincidental demand is the maximum demand that is obtained when all metered loads are summed coincidentally. The summation of the individual demands must be performed on a demand interval basis.
In other words, when all measured demands from each individual meter are summed on each interval of the billing period, the maximum total demand obtained from the summation is the coincidental demand. The individually metered maximum demands typically do not occur at the same demand interval in which the coincidental demand occurs.
Therefore, the summation of the individually metered maximum demands will normally be higher than the demand that occurs at the demand interval in which the total coincidental demand occurs.
This is due to the variation in the time in which electrical equipment operates. The total coincidental peak demand is usually less than the sum of the individual maximum demands.
Aggregated Demand—Aggregated demand is similar to coincidental demand in that it is derived from the summation of multiple meters. Typically, aggregated demand is obtained from the aggregation of load profile data from multiple meters.
Totalized Demand—Totalization, as applied to revenue metering, is the addition of two or more metered electrical loads. Totalization is often requested by customers that have two or more metered loads. Benefits of totalization include the ability to obtain coincidental demands, simplified meter reading, and billing and subsequent accounting procedures.
Totalization is the algebraic sum of two identical energy values performed on a real time or near instaneous basis. Simple totalization could be the addition of the kilowatthour useage of two metered loads. Complex totalization could be the algebraic sum of multiple metered loads from different locations, some of which
could be negative values.
It is important to note that totalized demand is derived from totalized energy. Energy is summed on a near instantaneous basis. Because the totalizing device or software knows the time interval over which the demand is desired, totalized demand can then be obtained from the simple relationship, Demand Energy/Time.