Variable-Frequency Drives Match System Output, Load Requirements
Variable-frequency drives (VFD) are one of the most effective tools managers can use to control a facility’s energy use. As organizations struggle to curtail costs in every possible way, VFD applications offer some of the best available returns on investment. Simple payback for a VFD typically falls between six months and three years.
For years, managers have used drives successfully for a range of applications, such as reducing energy use in fans, pumps, chillers, and cooling towers by up to 50 percent. While VFDs have proven effective in reducing energy use, technology advances are making them even more appealing.
Making a Match
A building’s energy-using systems traditionally have enough capacity to meet the estimated peak load for that building, even though peak load typically occurs for no more than 1 percent of the annual hours of operation.
When a system operates at less than capacity, HVAC systems traditionally use a number of different devices to reduce the flow of air or water. This method of throttling output to match load requirements is effective in controlling the flow but is not the most energy-efficient strategy.
VFDs offer an alternative means of matching system output to load requirements by slowing the motors that drive HVAC-system components. Unlike throttling, where a motor’s energy use decreases only slightly with the decreasing system load, slowing a motor to match a decreased load results in a rapid drop-off in a motor’s energy requirements.