Environmental Engineering Reference
In-Depth Information
to an electrical generating system. It is measured over a short, fixed pe-
riod of time, usually 15 to 30 minutes. The electrical demand is measured
in kilowatts and recorded by the generating company meter for each mea-
surement period during the billing month. The highest recorded electrical
demand during the month is used to determine the cost of each kilowatt
hour (kWh) of power consumed.
Linking power management systems to control systems allows the
power information to flow from both systems. Load profiles can be devel-
oped to find any energy inefficiencies. Energy scheduling can be used to
find the optimum energy schedule for new product lines or processes.
Real-time utility pricing means that production schedule energy re-
quirements need to be compared with energy rate schedules for optimum
energy benefits. The new energy supply market requires more companies
to give back energy capacity during peak energy use times by scheduling
lower-energy production. This can result in significant savings.
Intelligent metering and monitoring systems offer a low-cost meth-
od for quickly implementing energy saving practices. A Cutler-Hammer
plant in Asheville, NC, installed a power management system in early
1997 when energy bills were running close to $45,000 a month. After 6
months of installation, the plant energy saving was $40,000. The power
management system allowed plant engineers to identify wasteful proce-
dures, shift loads to level the demand and perform preventive mainte-
nance. Better control of area lights during off hours was possible. Large
electric oven loads were timed during the late shifts when the total energy
demand was lighter. Maintenance technicians were able to locate abnor-
mal conditions with monitoring screens and then service the equipment
before it broke down. The total return on investment was predicted to be
less than two years.
LOAD SHEDDING
Some power management devices are known as load shredders.
They reduce the demand or average load in critical demand periods by
interrupting the electrical service to motors, heaters, and other loads for
short periods. Since the load which has been turned off would normal-
ly have been operating continuously, the overall effect is to reduce the
average load or demand for that period of time. The instantaneous load
when the load is operating remains the same. When the period involved
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