Demand is the rate at which electricity is used. Energy use is the total amount of electricity consumed over a period of time. Demand is usually measured in kilowatts. Energy use is measured in kilowatt hours.
Demand meters are used for measuring electricity used in commercial and industrial buildings, as well as, other installations billed under Nova Scotia Power's demand energy rates. They measure and record the amount of energy used, and the highest rate of demand over a specific period of time.
The most common types of demand meters are thermal and electronic.
A thermal demand meter records the amount of energy consumed and the rate of that demand. So reading a thermal demand meter means taking two different readings — one for energy and the other for demand.
- Taking your energy reading
Read all the dials at the top of your thermal meter, beginning with the dial on the far right. Write the reading down in the same order (from right to left). When the pointer is between two numbers, read the lower number. When the pointer is directly on a number, read that number. Subtract this reading from the reading shown on your electric bill to calculate the number of kilowatt hours used since your last meter reading.
- Taking your demand reading
Read the black pointer on the demand scale to determine your maximum demand since the meter was last read by our meter reader. The demand scale has two pointers, one black and one red. As power flows through the meter, the red pointer moves up the scale, dragging the black pointer along with it. When the power flowing through the meter is reduced, coils inside the meter contract and the red pointer moves back down the scale. The black pointer remains at the point of maximum (peak) demand. The black pointer indicates the maximum demand during the billing period.
Rather than having dials and pointers, an electronic demand meter uses an LCD display to indicate energy (kWh) and maximum demand (kW max or kVA max). The LCD display continuously scrolls through these and a series of other programmed values. Energy is recorded over a fixed time interval, typically 15 minutes, and the average demand is calculated based on the accumulated energy. The meter repeats this function every 15 minutes and stores the maximum value in its memory as the peak demand (the kW max reading) for the billing period. Only sustained demands, fifteen minutes or longer, will fully register on the meter. The demand is reset by NSP meter readers after each reading.
A daily load profile can graphically illustrate your energy demand during a 24-hour time period. By seeing where and when your maximum demand occurs, it's possible to determine what contributes to high demand and where savings can be made.
Daily Load Profile
To create a daily load profile:
- Every hour, record the numbers registered by the red pointer on the demand register.
- Plot the numbers on a graph.
- Think about the equipment operating at the time of your peaks.
- Look for opportunities to reduce your peak demand.
Reducing means shifting a portion of the electrical load operating at your highest demand times, to a time when the load is smaller.