Cut Energy Usage in Retrofits With Drives

Sept. 1, 2003
"Soft switching" technology allows energy service companies to extract major energy savings when fitting VFDs to outdated AC motors. Variable frequency

"Soft switching" technology allows energy service companies to extract major energy savings when fitting VFDs to outdated AC motors.

Variable frequency drives (VFDs) that safely convert old, power-hungry AC motors into energy-sparing equipment now allow plant engineers and facility managers to enjoy the best of all possible worlds. Attached to existing motors that power blowers, pumps, and fans-and installed under the guidance of experienced energy services companies (ESCOs)-these VFDs decrease the need for electricity by 50% or more, while easing maintenance demands by prolonging the life of the motors. As a bonus, hefty rebates from utility companies and financing arrangements from ESCOs allow VFD retrofit projects to require little or no up-front investment. In other cases, any expenses are often recouped within one year of installation.

One retrofit installation at consumer giant Unilever's plant in Edgewater, New Jersey, yielded projected energy savings of 67%¾accounting for an annualized cost savings of $86,708. A calculated ROI of 111% enabled pay-off within nine months of installation. This success story offers valuable insight into the issue of using VFDs to reduce utility expenses at any building or facility that utilizes older AC motors.

VFDs and ESCOs enable benefits for all

By some estimates, motors consume well over half of all the electricity used by industry. Fortunately, some of the most significant gains can be achieved by improving the operating efficiency of these motors, particularly older ones.

Over the last 20 years, ESCOs have led the way for enabling customers to utilize savings from investments in high-efficiency equipment by specifying and installing VFDs. Current ESCO market activity ranges between $1.9 - $2.1 billion annually, according to the National Association of Energy Savings Companies (NAESCO). By specializing only in energy-savings projects, ESCOs find themselves in the best position to write and implement proposals for installing VFDs.

"It's not like plant managers don't know anything about VFDs, but it's not the highest priority on their agenda," observes Bob Hughes, president of Industrial Systems Group an ESCO primarily engaged in performing retrofits to mechanical systems for companies and institutions on the East Coast. "Most engineers are already overwhelmed with other priorities, so they don't have the time to learn how to apply VFDs and work the math and secure the utility rebates. Since that's all I do, I can optimize an installation so that all they have to do is reap the rewards and take the credit."

Funded by the U.S. Department of Energy, a recent study by Lawrence Berkeley National Laboratory (LBNL) of information collected from the NAESCO database found that reductions in electricity consumption accounted, on average, for 80% of total energy savings on a site-energy basis, and the median benefit/cost ratio on such projects is 2.1 for the 309 private sector projects studied.

Like an offer that can't be refused, plant CFOs often buy into energy savings retrofits because the price of entry is so low. Many ESCOs offer delayed payment plans, where the customer does not have to shell out any money until long after the installation is complete. According to the LBNL study, 86% of performance-based ESCOs offer a guaranteed savings contracting mechanism to further assure an organization of the cost-cutting gains to be had by retrofitting VFDs.

Additionally, some states, utilities, and public/private ventures offer financial incentives for qualifying equipment to help customers offset some, if not all, of the added cost to purchase qualifying energy-efficient equipment. For example, the New Jersey SmartStart Buildings program offers a generous ranges of incentives for qualifying equipment to which VFDs are fitted: blowers ($90 - $210 per hp); chilled-water pumps ($60 per hp); electric HVAC systems ($73 - $92 per ton); air-to-air heat pumps ($73 - $92 per ton); ground source heat pumps ($580 per ton); and premium three-phase motors ($45 - $700 per motor).

"The rebates are phenomenal in New Jersey," says Hughes. "To give you an idea, the rebate pays up to $210 per horsepower saved on a blower. So for a 7.5 hp motor, you get back $1,575. But the VFD that accounts for this savings only costs approximately $800."

Proposals from ESCOs that include detailed breakdowns of such savings add further assurance to company controllers. Some proposals also include a documented projection-based on past successes-of how quickly a return on investment can be achieved.

How VFDs bring about savings

VFDs are electronic control systems that manipulate the speed of AC induction motors by changing the frequency and voltage supplied to it. Motor speed, and therefore efficiency, is optimized to fit demands as determined via sensor (in most cases, from a building automation system) input. Most drives are programmable so the user can also dial-in operating conditions suitable for the application.

"If you look at heating and air conditioning loads in a building, it's kind of like a bell-shaped curve¾you only need 100% flow about maybe 5% of the time, depending on what part of the country you live" Hughes points out. "A VFD gives you the ability to dynamically balance your system so the motor handles the load using less horsepower."

With all the benefits offered by VFDs, perhaps the only obstacle blocking their wholesale use has been the fact that the traditional fast-switching technology necessary to generate the variable voltage and frequency required to control the speed of an AC motor, also generates very fast voltage rises (as much as twice the peak voltage) in the output waveform, which induces stress on the motor insulation.

"With fast switching, you basically get very high voltage spikes into the motor, but some of the older motors have lower insulation ratings, so you could burn out the primary winding of the insulation," warns Al Sartorius, an electrical engineer who has spent twelve years handling VFDs for Stevens Drives & Controls, Inc.¾a manufacturers representative serving the industrial and commercial market for AC and DC motors, brakes, wireless communication and mobile electrification equipment from its Pompton Lakes, New Jersey, base. "At that point, the motor is gone. You have to rebuild it."

"If you're putting in new motors, fitting any VFD is usually not a concern, but if it's a retrofit, it can become a big problem," continues Sartorius. "On the other hand, one company, Saftronics, makes some VFDs that have something called 'soft switching' that allows their VFDs work with any existing motor out there, without harming the motor. Other VFDs have to use external reactors or filters to gain this advantage, which adds to the time and cost of installation."

Based in Fort Myers, Florida, Saftronics is an innovator of advanced, energy-saving variable-speed drives and starters for electric motors. One of the last of the independent drive companies, Saftronics continues to focus its R&D efforts only on drives such as VFDs, improving the package hardware and software to meet a wide range of applications.

Saftronics' VFDs utilize pulse-width modulation, employing microprocessor-based algorithms and "soft switching" gate control that lowers a motor's peak terminal voltage to reduce overheating and prolong motor life. Such technology allows VFDs to improve the operation of most every existing motor application.

To further extract efficiency gains from older motors, Saftronics VFDs incorporate SMART Bypass; a control system that allows the motor to operate directly from the AC line instead of from the solid state controller when 100% speed is required. SMART Bypass monitors the load and transfers to bypass when demand exceeds a user programmable limit. In this manner, an additional 3-5% energy saving is achieved.

"The Saftronics equipment is so reliable, it's like turning on your car radio," observes ISG's Hughes. "Once it's integrated into a plant's HVAC system, then it's a hands-off process. Set in motion, it becomes transparent. It's really that good."

VFDs yield a 111% ROI at Unilever

Unilever is one of the world's leading suppliers of fast-moving consumer goods, offering popular trademarked brands such as Dove soap, Ragu spaghetti sauce, Lipton tea, and Ben & Jerry's ice cream. As for all businesses today, increasing electric utility costs threatened to erode any sales gains.

"The company established an 'energy team,' with representation from both major components, Unilever Bestfoods and Unilever Home and Personal Care Products," recalls Lee Tyler, maintenance and operations manager for the Unilever Research and development Center in Edgewater, New Jersey. "Our ongoing goal is to drive energy savings throughout the organization and improve efficiencies at our various facilities in North America."

"As an organization, Unilever is especially sensitive to environmental issues," stresses Tyler. "Even outside of our energy team, the environment is part of everyone's concern who works within this organization. We place a very high value on energy conservation. We want to lead the way by setting an example of burning less fossil fuels and generating less harmful by-products¾in other words, carbon dioxide¾as a result."

So sincere is Unilever's resolution, that it makes public its Environmental Performance Report that gives an overview of the company's environmental accomplishments. Unilever's energy-management team sought to reduce energy consumption even further, and at first utilized some simple energy-savings measures. However, the team knew that even more could be accomplished through demand-side management initiatives.

"The Unilever Edgewater facility partnered with the local utility company, Public Service Electric and Gas, and through their Standard Offer agreement we have retrofitted our existing T-12 lighting system to the new T-8 technology, which has provided a substantial rebate from the utility company and a significant savings on electricity cost," explains Tyler. "That experience led us to pursue other energy savings initiatives such as motion detectors, hi-efficiency motors and VFD applications."

In late 2001, Bob Hughes contacted Unilever to solicit business for his energy services company, Industrial Systems Group, Inc.

"Hughes' experience and success at other companies which we were affiliated with, along with his basic enthusiasm for energy savings, were very convincing," explains Tyler.

A formal proposal was submitted in April of 2002, which detailed the retrofitting of VFDs to 13 air/heating units, 5 chilled water pumps, 5 condenser water pumps and approximately two dozen fans located in cooling towers and the laboratory air supply and exhaust system.

"Engineers have never been sued for making things too big," observes Hughes wryly. "So in most older buildings the majority of the water pumps, fans and blowers are oversized. That's what happened at Unilever. All their old motors were basically designed for future uses that never materialized, so they were oversized and drawing way too much current. I knew that VFDs would help immensely."

Unilever's Energy Team agreed to accept the proposal, not only because of the calculated increase in energy-savings, but also because of the financial benefits.

"The proposal for the installation of VFDs by Industrial Systems Group provided a guaranteed performance-based agreement of energy savings, and an aggressive payback on our investment," says Tyler. "This was your classic win-win situation, which was further enhanced by a terrific rebate offer from the local utility company."

According to Tyler, the installation of the VFDs went well, based on the composite effort of Unilever's in-house maintenance staff and the Industrial Systems Group personnel.

"I supplied the VFDs in the Unilever retrofit," notes Stevens Drives' Sartorius. "I also started them all up to make sure they worked correctly. Since Unilever had existing motors, I delivered VFDs with soft switching technology so they didn't have to worry about burning out these old motors. Not needing external reactors or filters saved parts costs and labor costs and everything else associated with it."

To act as a safety net, Hughes had specified VFD packages that included bypasses.

"The VFDs for all the pumps had bypasses on them, so that in the event of a drive failure, they would automatically trip a relay and go right across to 100% of line current, voltage and frequency," adds Hughes.

Before installation, a projected energy-savings of 67% was projected, accounting for an annualized cost savings of $86,708. Factoring in the utility rebate of $34,425 and then comparing these savings to the net project cost yielded a return on investment of 111%.

"Once installed, the new VFD technology has provided us with the ability to accurately control the building ventilation systems, the required air changes, and the proper air flow for our laboratory fume hood operation," explains Tyler. "It has been a success story for us in energy savings, maintenance and operational efficiency. One side benefit is that we are now generating less greenhouse gases."

By Hughes calculations, the project will annually eliminate 4,289 pounds of sulfur dioxide, 2,266 pounds of nitrogen oxides and 580,176 pounds of carbon dioxide. The CO2 reduction is roughly equivalent to planting 4,463 trees, since one tree consumes approximately 130 lb. of CO2 per one year.

Given the success experienced at Unilever and other similar companies, the use of soft-switching VFDs means that even older, existing plants and buildings can take advantage of utility-cost containment opportunities and hefty rebates, without the worry of increased maintenance from damaged motors. As a bonus, they can actually improve the environment within which those plants operate.

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