VFD -Variable Frequency Drives

In today's energy conscious environment it is more critical than ever, to be efficient in the consumption of electrical power. Older equipment and often, more recent equipment, were designed to run at full motor speed. Cost and available technology were factors in the design of equipment used in the HVAC/R systems. Quite often the design criteria for this equipment was established on worst case scenarios, where as, in actual applications the size of the selected components will be too large. To compensate for this oversize factor it is possible to reduce the output of the component by slowing the operating speed to match the actual requirement.

Using today's technology it is possible to precisely control the operating speed based on an output requirement. The speed of a three-phase induction motor can be controlled using a variable frequency drive (VFD) to simultaneously control output frequency and voltage. The frequency of the supply power to the motor is what controls the speed of a motor and depending on the design of the motor, it will run at 3600, 1800 or 1200 RPM, at line voltage and 60 hz frequency. The VFD uses state of the art technology called "Pulse Width Modulation" which controls both the frequency and the voltage supplied to the motor. The AC power source when connected to the VFD rectifier is converted to direct current (DC) and then inverted in a logic-controlled output of DC pulses of varying width (voltage) and polarity (frequency). The inductance field in the motor windings resists the rapid voltage changes, smoothes out the DC pulses and makes them appear, to the motor, as a three phase sine wave. This type of control will limit the power consumed by the motor to only that which is needed, at any point in time, necessary to achieve the desired output from the equipment. This type of control can be used on air handling equipment, chillers, and pumps, all of which are integral components of an HVAC/R system.

The benefit to the consumer is that by using a VFD they can realize tremendous savings on their electric bill. If, for example, you were able to reduce the speed of a fan by only 20%, there would be a reduction in the power to run the fan, by as much as 60%.

San Diego Chiller Service, Inc. is a supplier of Yaskawa (formerly Magnatek) drives. If you would like to have us help you analyze your system for potential applications of VFD's please contact us using our contact page.