A number of terms are used to characterize the magnitude and intensity of loads. Several such terms are defined and uses outlined below.
Energy—Energy use (over a specified period of time) is a key identifying parameter for power system loads. Energy use is often recorded for various portions of the power system (e.g., homes, businesses, feeders, substations, districts).
Utilities report aggregate system energy use over a variety of time frames (daily, weekly, monthly, and annually). System energy use is tied directly to sales and thus is often used as a measure of the utility or system performance from one period to another.
Demand—Loads require specific amounts of energy over short periods of time. Demand is a measure of this energy and is expressed in terms of power (kilowatts or Megawatts).
Instantaneous demand is the peak instantaneous power use of a device, facility, or system. Demand, as commonly referred to in utility discussions, is an integrated demand value, most often integrated over 10, 15, or 30 min.
Integrated demand values are determined by dividing the energy used by the time interval of measurement or the demand interval.
Demand = Energy Use Over Demand Interval/ Demand Interval
Integrated demand values can be much lower than peak instantaneous demand values for a load
Demand Factor—Demand factor is a ratio of the maximum demand to the total connected load of a system or the part of the system under consideration. Demand factor is often used to express the expected diversity of individual loads within a facility prior to construction.
Use of demand factors allows facility power system equipment to be sized appropriately for the expected loads.
Demand Factor = Maximum Demand/ Total Connected Load
Load Factor—Load factor is similar to demand factor and is calculated from the energy use, the
demand, and the period of time associated with the measurement.
Load Factor = Energy Use/ Demand x Time