Additional demand control measures
can produce savings by strategically responding to the changing price of electricity. Some utilities offer plans where energy rates change frequently (usually by the hour, but as frequently as by the minute), based on the market price of electricity. This results in a lower price for most periods of the month, with only a few, short periods of high prices. Users that can respond to these ongoing price fluctuations by lowering consumption during high peak periods can realize a significant improvement in their average energy costs.
Demand Control in Your Facility
Several levels of demand control, the
process of sensing and/or predicting monthly peak demand situations and tak- ing action to minimize them, are available to metalcasters: • Manual Action. Some metalcasters avoid running or ramping furnaces at the same time manually or by tying lights or alarm beacons to util- ity data to show when demand has reached a high level. These options require consistent human action, as one miss during peak demand times can spike the monthly bill.
• Demand Limiter. Devices are avail- able that sense power usage and close electrical connections when the usage approaches a pre-set limit. Many of these devices work from instanta- neous data, but some accumulate data and provide a linear projection of interval energy usage. These devices require the metalcaster to select loads
An automated peak demand controller can be input with the user’s pre-set energy usage parameters and allowed to function independently.
and limits to the amount of curtail- ment allowed. These systems are similar to those used in commercial or retail building applications.
• Self-Created Demand Control. Some metalcasters create their own demand control system using an existing programmable logic controller or distributed control systems, such as those available from Honeywell, Allen-Bradley or GE. The metalcaster must maintain these systems using internal resources, as utility rates and calculations change over time. These self-made options can incur ongo- ing costs and open-ended program
development needs, but incremental reduction in peak demand will occur.
• Intelligent Demand Control. Intelli- gent demand control uses predictive algorithms to allow minimal curtail- ment action with maximum savings. Because the predictions made by the systems are accurate and false alarms are filtered out, an aggressive energy limit set-point can be used.
Capture and Control Manufacturers wishing to optimize
energy spending can examine each of the following energy events: 1. a spike in demand;
interval is most common. The power company’s electric utility system must be scaled
P
to deliver not just average demand loads but peak demand loads. For example, when an electric motor is turned on, it will require increased current to start but less when at operat- ing speed, thus creating a spike in power demand. Because of this peaked demand on your utility company’s electrical system, the company makes large investments in auxiliary generation and distribution equipment. This auxiliary equip- ment buffers capacity, making the electric company capable of producing the highest power demand you might require during any given interval. The incurred investment costs are
MODERN CASTING / December 2010 What Is Peak Power Demand?
ower demand is a monthly rate charge that is based on the highest level of energy usage by a metered service (facility) recorded in a defined measurement interval. A fixed, 15- to 30-minute measurement
passed to customers in the form of peak demand surcharges. The energy demand of most industrial and commercial
facilities is typically uneven over an extended period of time. The result is a peak demand charge that represents a large fraction (usually 30-40%) of the total power bill. Since demand loads roughly follow a curve throughout
the day, utility companies define periods of time when the cost of power demand increases. Demand loads often reach their maximum in the sum-
mer or winter months (although dual-peaking rates also exist), and power companies divide the days during that service time into categories—peak, partial-peak and off- peak. The remaining months are divided into partial-peak and off-peak hours.
MC
—Robert Murillo, plant engineer, Pacific Steel Casting Co., Berkeley, California
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