The Role of Variable Speed Drives in HVAC systems

This is a sidebar to the feature story "Automating Energy Consumption" which appears in the March, 2008 Issue of Automation World.

Most energy at plants is consumed by motors. According to the U.S. Department of Energy, electric motors, centrifugal pumps and fans account for 64 percent of the electricity used by industrial systems.

A report from the Energy Center of Wisconsin, a private, non-profit organization dedicated to improving energy sustainability, translates that figure to $33 billion in electricity per year. According to automation vendor Schneider Electric, in Palatine, Ill., significant energy savings can be taken when a plant switches to variable frequency drives, or VFDs, in the heating, ventilation and air conditioning (HVAC) systems.

According to Schneider, most HVAC systems are designed to work at full capacity on the 10 or so hottest days and the 10 or so coldest days of the year. On the other 345 days, the HVAC system will operate at a reduced capacity. Variable speed drives can be used to match the output to actual heating and cooling demand. The cost savings can be significant.

A 50 horsepower fan running at full speed for 10 hours per day, 250 days per year, for example, consumes $7,460 in electricity per year. Controlling with a VFD under normal circumstances, the cost would be $4,177.60, an annual savings of $3,282.40.

To view the main story "Automating Energy Consumption", go to: www.automationworld.com/view-3995.

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