Dan Rafter 2016-09-20 12:48:09
What kind of difference can a variable frequency drive—better known as a VFD—make for a municipality? A significant one. Just look at the town of Mooresville in North Carolina, where a VFD developed by Eaton has not only boosted the energy efficiency of the municipal water treatment plant, but has also extended the life expectancy of a pair of new 800-horsepower pumps at the facility. And Mooresville is not alone. Plenty of municipalities and the owners of commercial buildings are turning to VFDs to more efficiently operate the motors that power their facilities. By using these drives, which vary the frequency and voltage that is funneled toward electric motors, facility owners can reduce their energy costs and boost the lifespans of their motors. Eric Houg, marketing manager with adjustable speed drivers for the motors and drives division of Toshiba International Corporation, says that the growing demand for VFDs is easy to explain: These drives are simply the most efficient and cost-effective way to control a three-phase induction motor. At a time in which municipalities and building owners continue to watch their bottom lines closely, the cost savings that VFDs can bring is essential. Investing in VFD technology might cost owners extra money upfront, but will result in significant savings in the long run. Manufacturers say that some users can hit the payback period just six months after investing in VFD technology. “For a building owner, there is a very large amount of energy savings that you can achieve with these VFDs,” says Houg. “Anytime you can slow down a fan mechanically or electrically, you can get an energy savings out of that.” How much owners can save varies. But when a motor is running at its nominal load, end-users can expect to reduce the amount of energy it consumes by 3% when using a VFD. That’s not a huge savings, but the savings jump significantly when motors are not running at that nominal load. When a motor is running a 75% load, it will consume about 25% less energy when equipped with a VFD. A motor running a 50% load will consume on average 75% less energy when using a VFD. Those figures are significantly more impressive, and could convince owners to incur the upfront costs needed to purchase VFDs. It won’t take long for them to recoup their upfront investment if they can enjoy energy savings of 50% to 75% on their motors. “With a VFD, you can slow down the fans of these motors,” says Houg. “You then get a lesser air flow and that big energy savings.” Once end-users pay for a VFD system, they can expect a short payback period, Houg says. The energy savings that VFDs generate each year, means that some users will recoup their costs in just six months, while the vast majority will have saved enough to cover their upfront costs in just two years. That’s because end-users can expect to save from 35% to 50% on energy costs after installing a VFD. “We are seeing a steady increase in the number of users who are exploring and then investing in variable frequency drives,” says Houg. “The economic argument is simply so strong for these drives. Once you show users the numbers, once you show them how quickly they can pay back their initial investment, it’s a pretty easy argument to make.” Saving Energy, Boosting Motor Life in North Carolina Public utility officials in Mooreseville are already experiencing the financial benefits of a new VFD system, developed by Eaton, that was installed in their water treatment plant in July 2015. The SC9000 EP series of drives has helped increase the energy efficiency, with a notable reduction in the use of power at the plant. Barry McKinnon, public utilities director with the Town of Mooresville, says that the municipality had a financial responsibility to investigate VFDs. Not looking at a way to save on energy costs would have been a disservice to the community’s residents, he says. “As a representative responsible to the citizens of Mooresville, we wanted to find a way to implement the equipment we had on hand,” says McKinnon. “Eaton’s variable frequency drive solution has helped us ensure water treatment services for our customers.” Mooresville built its new water treatment plant in 2008. The plant was initially rated to pump 12 million gallons a day (mgd) with the ability to grow to 36 mgd if needed. Demand, though, did not rise as quickly as town officials had expected, meaning that the plant’s two new 800-horsepower pumps sat idle for several years. Today, water flow from the town’s old water plant and the new one merge into the municipality’s main pipes. But when the town’s new 800-horsepower pumps did run, the pumps at the older plant could not create enough pressure to overcome the increased pressure in the main system of pipes. That dramatically decreased the efficiency of Mooresville’s old water treatment plant. This left town officials with a challenge: If the 800-horsepower pumps did not run on a regular basis, the odds were high that they would eventually rust out and become unusable. Public utility officials, then, needed to find a way to run the 800-horespower pumps in a way that would not negatively impact the operations or efficiency of the town’s older water plant. This is where Eaton came in. The town of Mooresville hired the company to design and install a VFD that would keep all of the public utility’s pumps running efficiently, preventing the newer, higher-power pumps from overpowering the older water facility. This would allow the town to use both the new and old treatment plants to handle increased capacity and provide all-important redundancy, a necessity in water treatment. Eaton, along with an electrical engineer, delivered a VFD system that controlled the water flow, allowing it to run at a lower speed. This made it possible for the public utility to use both the new and old water treatment facilities. Eaton also designed a compact, integrated control gear system that close-couples the new VFD with the plant’s existing AMPGARD medium-voltage motor control. Because Eaton engineers integrated the VFD and motor control with a bus connection, it was able to install the new drive without requiring the public utility to move expensive cables and equipment. The VFD system remained in one room, with no modifications, and tied back to the plant’s existing communications system. Mooresville public officials say that the drive has performed as advertised, increasing energy efficiency at the plant with no noticeable drop in power usage. The VFD system also controls the pressure from the 800-horsepower pumps, allowing the new and old plants to work in tandem. This, of course, has provided protection to the new pumps. They are no longer at risk of rusting away because of disuse. Jerry Wang, project engineer with Eaton, says that Mooresville, like other municipalities, is benefitting from the main money-saving feature of VFD systems: This technology gives utilities and building owners the ability to change the speed of their motors. For buildings or municipal systems that don’t always need to operate their motors at full power, this can provide a significant cost savings. “Look at a water treatment plant. The demand for water is not always the same,” says Wang. “It’s like at a Super Bowl party. The first commercial hits, and most of the people run to the washroom at around the same time. You need higher water supply at that moment. The old way to do that meant having a large motor trying to pump the water into the city. You’d have that motor running full speed the whole time. If you are constantly doing that, if your pumps are constantly running at full speed, you are wasting a lot of energy. With a VFD you don’t have to do that. You can control the speed of your motors.” As Wang says, with a VFD system, you don’t have to pump anything you don’t need at a given moment. For example, a VFD system could regulate the speed of the motors powering the air-conditioning system at a commercial building. Over time, the energy savings add up. Then there are the savings that come with boosting the lifespan of motors. Houg explains that VFDs reduce the stress on motors. “That’s another important savings tool that sometimes gets lost,” says Houg. “You can expect a longer lifespan on your motors when you are regulating how often they are operating at full speed. It can be expensive to repair or replace those motors. With VFDs, you won’t have to do this as often.” End-users can save money, too, by taking advantage of the rebates and financial incentives that states and municipalities are offering to building owners and municipalities that install VFDs. “These incentives, along with the short payback period, do make a difference,” says Houg. “It allows users to justify spending that extra money for a VFD. If they know that they can qualify for a rebate, and they can pay back their upfront costs in a short period of time, that really is a persuasive argument.” Why Aren’t More Investing in VFD Technology? The energy savings can be significant. So what keeps even more building owners and municipalities from investing in VFD technology? Wang says it usually comes down to cost. These systems do represent another upfront cost that owners and municipal officials have to pay. Wang says that the cost of a VFD can run as much as five or six times higher than a standard full-voltage motor starter. Many companies and municipalities are still struggling with tight budgets. They see the additional costs of installing a VFD system and are hesitant to add it to their already stretched budgets. The problem with this kind of thinking, though, is that VFD systems can save owners and municipalities so much money long-term. Those end-users that don’t have to run their motors full speed all the time can do some basic math to determine how long their payback period would be after investing in VFD technology. If that payback period is short enough, it might convince otherwise wary end-users to make that upfront payment, Wang says. “Sometimes it can be as quick as a half-year to get that payback on a VFD system based on energy savings alone,” says Wang. And that payback period doesn’t even include the savings that end-users can receive by prolonging the lifespan of their facilities’ motors. Motors aren’t run nearly as hard as often when regulated by VFD systems. This means that motors tend to last longer before they need expensive repairs or replacement. Another potential barrier that end-users face is that VFD systems are generally larger than traditional motor starters. Wang says that owners will need a larger space to install these systems and, in certain retrofit situations, they might not have the space required even if they are interested in VFD systems. “You have to take into consideration how much space you need in your equipment room for the system,” says Wang. “That total cost needs to be factored in to see if the final cost is worth it, to see how long that complete payback period will be.” Another challenge? Some building owners and utility officials aren’t overly excited about learning a new technology. And, even though VFD systems are not that new—they became more common in the 1980s—they still represent a change to workforces used to dealing with standard motor starters. Other workers might remember having problems with the VFD systems with which they worked in the past, before the technology behind these systems improved to where it is today. “The early adopters might have had some issues with VFDs, because it is a very complex piece of equipment when compared to motor starters,” says Wang. “There might be some hesitation about taking on this new piece of equipment.” That fear, fortunately, has lessened over the years as VFD technology continues to improve. Manufacturers say that today’s VFDs rarely break down. If they are maintained properly—and maintenance is simple—they can run without problems for a decade or more. This is a big change from the earliest days of VFDs. Another improvement? VFD units have shrunk in size over the years, meaning that utilities, municipalities, and commercial building owners don’t need to reserve as much space for their drives. The actual number of components in a drive has come down, too, leaving VFDs with fewer moving parts than in the past. All end-users have to do when it comes to keeping their VFDs operating efficiently is to maintain the cooling fans and clean out the heat sink at least once every two to three years. Users who do this can expect a lifespan of at least 10 years from their VFD units. At the same time, a growing number of public utility officials and commercial building owners have learned that the higher upfront cost, and the learning curve associated with VFDs, is a small hurdle to overcome when you factor in the energy savings that comes with this technology. Wang says that he expects the demand for VFDs to only grow in the future. “We will definitely see more interest in these systems,” says Wang. “When the economy is good and everyone is making money, there is not as much attention paid to cost savings and reducing energy use. But when business starts to get tougher—and this cycle always happens—end-users look to reduce costs in the long run. That’s when they will turn back to VFD systems.” The key is the payback period. When manufacturers can demonstrate to end-users that the payback period that comes with investing in VFD technology is a short one, these users will be more likely to invest in the technology, Wang says. “There are times when they are more likely to listen, such as when the economy gets a bit tougher and they have to stretch their budgets as far as they can,” says Wang. “For many users, installing VFDs is just a smart financial move.” When VFDs Make Sense Ken McQuillen, marketing manager at the building technologies division of Siemens, says that his company’s VFD systems can save building owners and municipalities from 20 to 50% in energy costs each year, depending on how these end-users use their motors. Even better? Today’s VFD systems are more technologically advanced. The BT300 from Siemens, for example, features a keypad with start-up wizards and easy-to-read graphics and displays. This makes it easier for end-users to get their systems up and running. The start-up wizards and displays also allow users to display nine different user-defined values at one time. This means that end-users can customize the data that their VFD systems provide them with. The T300 comes, too, with a real-time clock that allows users to control their buildings’ HVAC systems in different ways, depending upon how busy their office or commercial facility is at different times of the day. There’s also a sleep mode that starts and stops the drive automatically on demand. If demand happens to be low, the drive’s sleep function will kick in, saving energy. If demand spikes, the drive will automatically switch on. Yaskawa, another important player in the VFD space, has boosted the technology behind its variable frequency drives, too. For instance, the company offers the Z1000U HVAC Matrix Drive that provides low harmonic distortion in a space-saving design. The single-component drive hits its low-distortion levels on its own, without requiring additional equipment such as passive filters or multi-pulse arrangements. The drive eliminates the need for the rectifying circuit and DC bus used in traditional AC-drive inverters. McQuillen says that the market for VFD systems is a deep one. Some users are interested in optimizing their facilities’ chillers, while others rely on VFD systems for variable-speed pumping functions. McQuillen says that cruise ships often invest in VFD technology to operate their ocean liners more efficiently. YMCAs and high schools have invested in the technology to heat their swimming pools. One might also find VFD systems powering exhaust fans in laboratories and rooftop fans of ocean-view condominiums or hotels, McQuillen says. While VFDs aren’t a smart investment for all users, they make sense for many. The key? According to Wang, it all depends upon how often an end-user turns down its building’s motors throughout the day. Wang says that facilities in which workers have to shut down the motors every day, two to three times a day, or more are a good fit for VFD systems. End-users that invest in Eaton VFD systems are involved in heavy industry or large commercial manufacturing. Others work in the mining industry, while others make their money in the oil and gas industry. They use their VFDs to conserve energy on the pumps that extract oil from the earth. Large ships rely on Eaton VFD systems so that they consume less energy as they cut through the water. “Anywhere where you see that things are moving, that is usually a good fit for a VFD system,” says Wang. “Anything that moves and requires a motor could use a VFD.” Houg says that he expects demand for VFDs to only grow as more users search for ways to extend the lifespans of their motors and reduce their yearly energy costs. “I anticipate seeing more end-users moving to these drives,” says Houg. “There has already been a big shift with commercial buildings. They have already gone over to VFDs. In the future, I think you are going to see even private homes going to the VFD setup.” BE Dan Rafter is a technical writer and frequent contributor.
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