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How a VFD Can Improve your HVAC System

How a VFD Can Improve your HVAC System

How a VFD Can Improve your HVAC System 150 150 Amy Gasca

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Variable Frequency Drives are proven to advance energy costs when combined with your HVAC components. VFDS have been around for more than two decades and have improved and are said to be the most effective energy management tools to supplement HVAC units. Before, application was limited based on the horsepower of a system. But with time, they can now be applied to most commercial and industrial components. As VFDs continue to evolve, they become more and more powerful in energy management.


What is a VFD?


Variable Frequency Drives are a motor type that drives an electric motor by varying the frequency and voltage supplied to the electric motor. Frequency goes hand in hand with the motors speed. A VFD is helpful in managing the frequency and voltage of an electric motor’s load. This is helpful in applications that do require its electric motor to run at full speed.




How does this work in conjunction with an HVAC system?


HVAC systems are designed to operate at a consistent speed no matter the demands that are needed by its user. Building load, as you may know, is never constant. The drive motor continues to work at full capacity no matter the demand. Mechanical throttling provides a good level of control, but it is not efficient by any means. HVAC systems are designed and sized for peak load conditions but are needed less than 5% of annual operating hours. But, a VFD can be used to adjust the drive motor to gradually operate when the demand is needed rather than at full speed when it’s not appropriate. This means energy efficiency is directly affected as energy expended is dependent on the motor speed. A VFD, in short, can help the system match the load.


Which equipment in an HVAC can a VFD be applied to?


Chiller pump motors benefit from a VFD because it can moderate water flow for cooling demands appropriately by increasing or decreasing gallons per minute. Cooling tower fan motors can be manipulated by dropping speed of the fan motor to better meet the process requirements of a building.


What are the direct benefits?


Energy savings! As previously discussed, since peak load performance has been choked by the VFD, the system is not longer wastefully working at full capacity. This directly effects energy output. This will be reflected in your energy bills being drastically reduced.

Reduced stress on motor. Early motor failure is eliminated since the start/stops on the motor are reduced.

Matching of process requirements. Since most HVAC systems are designed for worst case, they are oversized for normal conditions. A VFD can help motors match load requirements more appropriately.

Noise reduction. Since fans and motors aren’t working at max capacity, you’ll notice less noise coming from your HVAC components.



Implementing a VFD to your HVAC system is a complicated process. You must first do an analysis of your existing system. For a VFD to be effective, it must be applied to a system that delivers variable flow through applying constant speed motors with mechanical restrictions. Systems that require constant flow will more than likely require a mechanical redesign for a VFD to be useful. A system that is a good candidate for VFD implementation is a pump and fan system that already has the mechanical means of reducing flow. But these means, whether they be dampers or valves, will need to be removed in lieu of VFD installation.




VFD use in retrofitting a HVAC system comes with many opportunities for a system and energy efficiency. Implementation is a detailed process that must be approached carefully in order to reap the benefits of its addition. It is important to ensure that the retrofit will yield expected savings. None the less, VFDS have rightfully earned their reputation as powerful energy savers.


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