Sunday, April 3, 2011

Electric demand charge

Electricity companies monitor a business's peak electrical draw each month from 10 am to 10 pm ish every 7 minutes. Then the power company will charge the business for supplying enough power to run full time at the peak usage. Machines use up a lot of electricity when starting up-end rush. Frequency drives and locked motor ramps allow machines to start up more slowly so they don't draw too much power at once. They stagger starts of equipment so thepeak usage is lower thus making the electric demand charge fee is lower. If a company used 15 kilowatt hours peak when starting up one day, then 7 kwh the rest of the day, the electric demand charge would be the difference (or percent of the difference) of supplying 15 kwh the entire month during peak hours. So it doesn't matter if the company is using 5 kwh or 15 kwh the entire month.

Higher voltage, lower amperage. There is a high end rush with low voltage chillers. So high voltage machines cost less to operate and use less electricity and draw less peak amperage. Actually half as expensive to run, 240 vs 120. However, there is more risk of death with higher voltage.

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