Variable-frequency drives greatly increase the efficiency and cost-effectiveness of the system.

The use of drives in commercial applications is one of the fastest-growing segments in the HVACR industry, not only in new construction but also in retrofit applications. So, what is preventing installing contractors from mainstreaming this technology even more than they do today?


The choices of brands are many. The newest drive technologies, especially variable-frequency drives (VFDs), are relatively unknown among many contractors.

The confusion that normally exists around new technology is being addressed by the Air-Conditioning, Heating, and Refrigeration Institute (AHRI), formerly known as ARI. The manufacturing association is the industry’s certification body that creates standards that play across the breadth of product lines common to competing manufacturers. In other words, AHRI ensures that customers are able to receive what they expect - consistency of efficiency and performance - no matter which brand of a product they may choose to purchase.

There are currently eight member companies of the recently formed AHRI Drives section. These companies are working toward standardization that will make the decision-making process much more streamlined for contractors and building owners. There are also about four other major companies that are eligible to join the AHRI unified effort, and make for a less-confusing marketplace.


Annual industry shipments of HVACR drives in the United States are currently estimated to be from $210 million to $220 million.

The AHRI Drives section is seeking to ensure customers of consistent and reliable performance through the development of an AHRI certification standard. If you happen to work for one of the manufacturing companies, the benefits to membership are more important than ever before.

The explosion of drives being used for myriad purposes brings into focus the need for end users to expect consistent performance from a variety of product offerings. As building regulations become more focused, the reliability of HVACR equipment is being held up to much closer scrutiny.

The HVACR industry is a relatively new frontier for drives. Most manufacturers have focused on other industries for years such as food and beverage, material handling, automotive, and textile. Nevertheless, no manufacturers’ association for VFDs exists in any industry, anywhere in the world. Unfortunately, as a result of there being no established performance standards, our industry and its customers are often faced with confusing terms and fast-and-loose performance claims.

In addition, a lack of standardized testing and reporting practices makes it difficult for a person specifying or purchasing a drive to make informed decisions. That is where AHRI comes in to play. By establishing performance standards, as is done for so many other HVACR products, the industry and consumers will benefit. It has been demonstrated over and over again that the consumers’ perception of credible standardized ratings is one of the key elements in growing an emerging industry.


If you are a contractor, you know that the green movement is having a profound impact on the commercial building scene. Efficiency requirements have already been adopted for most federal, state, and local government buildings. The Leadership in Energy and Environmental Design (LEED) program of the United States Green Building Council (USGBC) has become the model for promoting sustainability, energy efficiency, and environmentally responsible building operations.

In the big picture, by the year 2020, it is expected that VFDs could be a requirement in many commercial buildings, not just the government sector. In addition, the HVACR industry is adopting new standards like ASHRAE 90.1 that demand better energy efficiency from new and existing HVACR equipment.

Today, drives have become a “must have” for energy-efficient building HVACR systems.

Long considered a high-tech item for the most elaborate HVACR systems, drives are now in the mainstream, enjoying new popularity as the price of the drives decline and the cost of energy increases. The cost of drives has gone down by more than 66 percent in the last 10 years, while their reliability has increased exponentially.

Drive technology for fan motors alone can save as much as 50 percent to 80 percent of the energy that is typically used.

A motor is most efficient when operating in the 60 percent to 80 percent range of its full-load amps. Motor controllers are increasingly going to be adjustable-speed or variable-speed drives as energy guidelines and mandates make owners aware of the benefits of part-load management.

Still, a lack of knowledge of how drive technology lends itself to address current issues such as energy efficiency and part-load management may be limiting the opportunity.


There are a number of key operational aspects of adjustable-frequency drives that are important to consider when selecting a drive for an HVACR application. Two are: motor stress and drive system efficiency.

Modern adjustable-frequency drives efficiently control the speed of the driven motor by controlling the frequency and voltage of the electricity applied to the motor. This is most commonly done by supplying a series of brief pulses of voltage to the motor’s stator coils, using a method called pulse width modulation (PWM).

While PWM provides efficient motor speed control, it can stress various parts of the motor. These most commonly are the motor’s stator insulation, through the generation of high peak voltages, and the motor’s bearings, through the coupling of voltage to the motor’s shaft.

While different adjustable-frequency drives produce varying degrees of stress in motors, other factors, such as motor design, the length of the power lead between the motor and the drive, and details of the installation also have a significant impact on the stress applied to the motor. Since there is currently no standardized test procedure for comparing adjustable-frequency drives, it is virtually impossible to make an informed, impartial drive selection.

The AHRI Drives section has a project on the chalkboard that would define standardized methods that can be used to compare drives. It may also be able to provide best practices recommendations to indicate what installation techniques are effective in reducing drive-induced motor stress.

All modern PWM adjustable-frequency drives will have efficiencies in the range of 95 percent to 98 percent. However, this isn’t the efficiency value that is important in the application. The important concern is the efficiency of the drive-motor system. This value depends in part on the losses that the drive generates in the motor. Unfortunately, claims regarding system efficiency are hard to verify because they depend on the choice of motor, the operating speed, and the load.

Another AHRI project would establish standardized testing and rating procedures that can be used to compare different adjustable-frequency drives so that rational specifications can be made regarding this important aspect of drive system operation.


Industry sources estimate that 70 percent of all HVACR drives are field-engineered and installed typically in an equipment room by installing contractors. The remaining 30 percent are factory-installed as a component by an HVACR manufacturer.

The tremendous growth in the use of drives that is projected in coming years because of mandatory energy requirements and because of the common-sense reasoning that drives save money, all lends to a common theme: HVAC contractors and building owners are seeking reliable, energy-efficient technologies that are easy to understand.

The manufacturing companies that are members of the AHRI Drives section are working diligently to provide consistent and reliable solutions for the commercial contractor.

Sidebar: AHRI Member Companies

For more information on variable-frequency drive technologies, visit the following companies:

ABB, Inc.


Emerson Industrial Automation

Honeywell International, Inc.

McQuay International

Square D


Johnson Controls Inc.

Publication date:05/05/2008