VFD Technology


Boosting energy efficiency remains a top goal of building owners across the country. And why not? Rising utility bills can cause a company’s bottom-line to plummet.

Building owners and managers, then, are investing in efficient lighting, motion detectors, and low-flow toilets and faucets. But there’s one way to reduce energy consumption and increase efficiency that many building owners still neglect: making their pumps and motors more efficient.

Building owners who invest in newer, more efficient pumps and motors will find that their buildings will consume less power each year. And those who explore the evolving technology of variable frequency drives will find that their physical structures’ efficiency levels can soar.

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Distributed Energy magazine recently spoke to two manufacturers about the impact that more efficient motors and pumps can have on the energy consumption of office buildings, retail stores, warehouses, and manufacturing facilities.

We found that efficient motors and pumps can dramatically reduce the amount of money that companies and building owners spend on energy costs each year.

Why Variable Frequency Drives Matter
Leading the charge to more efficient motors and pumps? A key drive.

The biggest advancement in motor technology remains the growing use of variable frequency drives, better known as VFDs. A VFD is a type of adjustable-speed controller used in mechanical drive systems to control AC motor speed and torque by varying motor input frequency and voltage.

That might sound confusing. But Brent Waluzak, business development manager at Siemens’ Building Technologies Division in Buffalo Grove, IL, sums up how VFDs work in layman’s terms: The devices take a steady or constant electrical power signal and convert it to a varying output signal. The VFD, then, adjusts the rotational speed of an electric motor, slowing that speed when possible and boosting it when absolutely necessary.

This saves energy and reduces the power bills faced by building owners. Because a VFD allows electric motors to operate at slower speeds when appropriate, the overall power that these motors consume is lowered, Waluzak says.

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He points to HVAC systems as a good example.

“HVAC systems are designed to handle peak load conditions, but peak load is rarely experienced,” says Waluzak. “This means that most of the time, the system is oversized in comparison to the actual load or demand. This can result in wasted energy, difficult system control, compromised occupant comfort, and unnecessary stress on system components and equipment.”

Waluzak says that reducing electrical consumption by relying on motors that use VFDs is one of the top demand-side energy efficiency boosters available to building and facility owners today.

“VFDs give engineers the capability to match system output to demand and save energy,” says Waluzak.

How much of an efficiency boost can VFDs provide? Waluzak says that in commercial HVAC applications, VFDs can reduce energy bills from 20 to 60%, depending on a number of variables when compared to traditional ways of system balancing and control.

Even with this efficiency benefit, it has taken some time for VFDs to catch on. That’s because historically, the technology was either not available to owners and facility managers, not fully developed, or too expensive. The energy savings that VFDs can produce have always been solid. But when this technology was too expensive, the costs of it were so high that most users couldn’t generate enough energy savings to justify the investment.

Times have changed, with VFDs becoming far less expensive and more widely available. A growing number of managers and owners, then, are relying on these devices to reduce their energy consumption.

“VFDs can save money by reducing overall energy consumption and, just as importantly, can then save on peak demand, as well,” says Waluzak.

The Peak Demand Problem
Savvy building owners and energy managers understand that their utility bill is usually as much about peak demand as it is about energy consumption.

Because of this, there are two primary ways that VFDs save energy. First, they help owners and energy managers reduce the overall energy consumption in a building. Because VFDs allow for the precise control of either a pumping process or fan speed, these devices help owners achieve real, tangible energy consumption savings, Waluzak says.

Just as important, though, is how VFDs help building owners or managers limit the amount of energy they are drawing during more expensive periods of peak demand.

As Waluzak says, a typical motor starter will cause a peak-demand draw that is multiple times higher than that motor’s full-load power draw. This is important; utilities will levy financial penalties against building owners for these peaks. That’s because utilities have to provide the capacity to handle them but don’t see sustained energy consumption. To handle that building’s load, then, utilities would have to upsize their equipment.

VFDs solve this problem by allowing a motor’s amperage to gradually ramp up to full load, something that prevents instances of peak draw.

A Rising Demand
Rick Goetz, vice president of operations with ABM, says that built-in controls and VFDs have both been the most important advancements in pumps during the last five years.

That’s because these technologies allow building operators and managers to control the flow of power through their pumps, something that can result in far lower energy bills.

Goetz points to chill water pumps as an example. Building managers might run these pumps at 90 or 100% during the warmer summer months. But in the fall and spring, it makes more sense from an efficiency standpoint to exert more control over the use of these pumps. There is little reason for chill water pumps to be working as hard during cooler months as they are during the hottest days of the summer.

“If you don’t have a drive, that pump is running either on or off,” says Goetz. “There is no control. There is no variance in how much that pump is working. With a VFD, though, you can see some real energy savings from chill water pumps during the cooler months of the year.”

In positive news, Goetz is seeing a rising amount of demand for VFDs. He also sees building owners and managers who are more focused today on consuming less energy. That trend is a good one for both pump manufacturers and the makers of technology such as VFDs.

Building owners who might not have invested in newer, more efficient pumps are now more likely to consider the impact these pumps could have on their bottom-lines.

“We are putting in a lot of VFDs these days,” says Goetz.

ABM does a significant amount of performance contracting, too. Under such an arrangement, the company studies the energy consumption of buildings and then offers bundled solutions. ABM guarantees the owners of these buildings energy savings if they invest in the solutions that the company suggests.

VFDs also play an important role in these efficiency-boosting packages, Goetz says.

“We are slapping VFDs on pump motors and on fan motors to control the load,” he says. “You might have a pump that is not that energy efficient when it is running at 100%. But if you can get it to run at 75%, maybe that is where that pump’s maximum efficiency levels are at. With a VFD installed, we can run that pump in that range more often.”

Like all technology, VFDs do come with a price tag. Goetz says that installing VFDs in pumps and motors can be pricey. But the building owners who invest in this technology usually see a quick payback, he says.

“If they are willing to give you four or five years, they’ll usually see a payback from the reduced energy consumption,” says Goetz.

Of course, there are times when the payback period has to be even shorter. Goetz points to big industrial clients. These clients, with their large and sprawling facilities, often rely on huge numbers of motors. Installing VFDs on all these motors is particularly expensive, Goetz says. These industrial users, then, often want a quicker payback period, often hoping to recover their upfront investment costs in just 10 or 12 months.

Municipalities often exist on the opposite end of this spectrum. Goetz says that municipalities are often satisfied with a payback period that lasts as long as 10 or 15 years. These clients look more at the long-range picture.

This focus on the efficiency of motors and pumps is a good change, Goetz says. For a long time, building owners rarely thought about pumps or motors when thinking of ways to boost the efficiency of their buildings.

That’s because motors and pumps are rather utilitarian: you need them and they go. Efficiency? That had long been far down the list when building owners thought about the merits of these pieces of equipment.

“It’s true that building owners, when looking at efficiency gains, looked first at other components, not pumps and motors,” says Goetz. “They didn’t think of a motor as being something that can be more efficient. You need it and it better run. That’s what they were most concerned about.”

VFDs are playing an important role in increasing the efficiency of motors and pumps. But it’s not the only strategy that building owners are relying on to decrease their energy bills.

Goetz also cited fan walls as a way for owners to consume less energy with motors and pumps.

Picture a large building, maybe one that stretches five stories tall or more. That building might have air handlers that are the size of two or three entire rooms.

The problem comes when it’s time to replace components. Building maintenance staff might have to pull out a huge motor. They might then have to move a large fan assembly that they can’t fit through any of their building’s doors.

Fan walls are different. Instead of one huge air handler, fan walls are made up of several smaller motors. As Goetz says, where buildings once had one huge motor, they now will have 10 or 12 smaller ones with a drive in each. Not only are these smaller motors easier to repair or replace, but they are also more efficient than one large motor. Goetz says that fan walls can reduce the amount of energy a pump consumes by a solid 15% or more.

“They make these in little cubes,” says Goetz. “And you install them in an area where space is limited.”

What do building owners do with what Goetz calls those old monster motors of 30 years ago? When owners need to replace one of these, do they take out an entire wall in their facilities? Or, as many are now doing, do they instead invest in a fan wall? If building owners do, their maintenance personnel can now deal instead with smaller cubes that they simply need to stick in place.

Ease of maintenance and higher efficiency are big benefits, of course. But fan walls come with built-in redundancy, too, which helps building owners provide a more reliable source of power for their tenants.

“There are 10 or 12 fans,” says Goetz. “If one fails, you ramp up the speed of the other ones to compensate for it. There’s a drive on each fan and motor combo, so replacing or repairing is a far easier process.”

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Credit: ABM
Bush boiler

Lower Maintenance Costs
Fan walls are still relatively rare. VFDs, though, are ever increasing in popularity.

This isn’t surprising. Not only does this tech provide big energy savings, but VFDs can also result in lower maintenance costs. That’s one more way in which these drives can save building owners and companies money each year.

Here’s how this works: Waluzak says that there are resonance frequencies within mechanical equipment that can cause severe vibrations. If the vibrations become too severe, they can seriously damage the equipment.

A VFD directly controls the power to a pump. Because of this, these dangerous resonance frequencies can be skipped. Because the pumps won’t be dealing with such severe vibrations, then, they are far less likely to be damaged.

Maintenance is important for keeping pumps and motors operating at their most efficient. But when should building owners and facility managers consider replacing older pieces of equipment? How can they determine which pumps or motors actually need to be replaced instead of simply serviced?

Goetz says that individual circumstances vary. But he recommends that owners target those motors and pumps that have become maintenance headaches first. If the budget allows for it, owners can replace these pieces of equipment with newer, more efficient models. That might require a big upfront cost. But it will also save building owners from having to constantly spend on maintenance.

If paying for a big replacement, though, is too costly, owners and managers can instead schedule regular preventative maintenance and repairs on these motors. Again, it makes sense to concentrate on those pumps and motors that are causing the most problems first. After all, these are the ones that are eating up the most dollars on a consistent basis already.

Next, Goetz says, it makes sense to target the larger pumps for maintenance. Again, these pumps consume the most energy and cost the most to run. It’s a smart financial move to schedule maintenance on these pumps first, then. It will have the biggest impact on a building owner’s budget.

“That typically means going after the chilled water or condenser water pumps first,” says Goetz. “They are big and the most expensive. You also have other pumps, such as hot water pumps. They are typically smaller and don’t run as much. Those don’t have to be a priority for repair work.”

Another bonus of a regular repair and replace program? With new pumps and motors usually come VFDs, Goetz says. And the addition of these drives in more motors makes a big difference for the entire efficiency level of a building.

“Back in the day, pump motors were controlled based on head pressure,” says Goetz. “You would design around that head pressure. Now we can look at flow rates. We can adjust the speed of motors. That results in a big difference in efficiency. That is huge. You have a 30-horsepower pump running all out. That consumes a lot of energy. If we change the frequency and reduce power consumption, we can see big-time savings.”

Striving for LEED
More efficient pumps and motors, especially those featuring VFDs, can also make a big difference when building owners are trying to earn LEED certification for their office towers, industrial facilities, and warehouses. Fortunately, a growing number of owners are aiming for this certification.

As Goetz says, LEED certification can be a strong selling point today for building owners.

“If the tenants are paying the utility bills, the landlord or building owner might not care so much about spending that extra 10% to 20% per pump,” says Goetz. “But if you want to head toward having a LEED-certified building, you’ll need those efficiency gains. And having LEED certification can really pay off. You can almost sell the building to tenants based on that efficiency.”

And Goetz doesn’t expect this trend to change. He says that a growing number of potential tenants do want to work from buildings that have earned LEED certification.

Of course, this certification won’t be more important than some other key factors, such as pricing and location. But the certification does help when it comes to attracting a certain kind of company that wants to work in a highly efficient building, Goetz says.

“Having that LEED plaque on the building is nice,” says Goetz. “A lot of companies are looking for that. Not everyone, of course. We still have plenty of bad, highly inefficient buildings out there. The owners of those buildings don’t want to spend money. But there are a lot of others that are seeking certification. And the owners of those buildings will consider everything, including making their motors more efficient.”

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Credit: ABM
Bush pumps

A Growing Demand
More building owners and managers are investigating VFDs today, Waluzak says. Much of this stems from recent changes and updates to energy codes. At the same time, a growing number of building owners are seeking LEED certification. To hit this building benchmark, more owners will explore VFDs and how they can help their structures consume less energy.

Waluzak points to the new ASHRAE 90.1 standard. This is an international standard that lays out the minimum requirements for energy-efficient designs for all buildings except for low-rise residential ones. The original ASHRAE 90 standard was published in 1975. The new version, obviously, is stricter when it comes to energy matters.

The new standard, for example, requires VFDs on unitary water pumps greater than 5 hp and on other types of water pumps greater than 10 hp.

“There are not many water loops with pumps less than 5 horsepower,” says Waluzak. “Therefore, building owners will start to see more VFDs on their systems.”

Goetz says that he expects building owners and facility managers to be even more focused on pump and motor efficiency in the coming years. While in the past people have often overlooked these pieces of equipment, the ever-growing drive to operate more energy-efficient buildings means that all equipment in a facility has to be considered, he says.

And pumps and motors? They are a great potential source of energy savings, Goetz remarks.

As Goetz says, pumps and motors can account for 15% of the energy load of a building.

“A big motor is a lot of watts,” he says.  De Bug Web

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