March-April 2010

Sounds of Silence

As more companies and organizations turn to onsite systems for backup or supplementary power, they also look for improved noise attenuation solutions. 

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“There’s an amazing need for noise attenuation,” insists Lahnie “LJ” Johnson, president and founder of Acoustiblok in Tampa, FL. “People are aware of noise—and they’re not tolerant of it.”

It’s one of the biggest changes he’s seen in the industry, in the 10 years Acoustiblok has been in business.

An increase in the use of onsite power is another noticeable change, as is its proximity to where we live and work. People are using locomotive diesel engines for generators, placing them in 40-foot containers for use as power generator stations.

“It’s very loud for small communities,” he says. “We’re living closer to each other and to industrial noise, but we don’t like it. The public’s tolerance is lessened.”

People are also aware of how noise affects health. Studies indicate that hearing loss is caused by exposure to high noise levels over extended periods of time, meaning that both the level and duration of the noise are associated causes.

Johnson mentions insurance companies canceling policies on oil rigs because of around-the-clock noise. While insurance cancellation can signal a double whammy, attacking both health benefits and finances, sometimes noise takes direct aim on business and finances as well.

Photo: Acoustiblok Inc. Water plant back view

Photo: Acoustiblok Inc. Water plant front view

Photo: Acoustiblok Inc. All-weather sound panels

Photo: Universal Silencer Evander Andrews site

Larry Hansen, principal engineer for Engineered Aeroacoustics in Plymouth, MN, tells the tale of a 5-star resort in Costa Rica that placed a generator next to a spa and a cricket field. Even worse than disturbing the peacefulness of spa treatments, he says the “loss of quiet at night is brutal.” Adding further to the discomfort are the kitchen exhaust fans in the resort’s restaurant.

Unhappy guests may not return—or, they may not stay at all. Hansen refers to a luxury hotel in Mexico City’s “pink zone” (the western tourist area) that lost revenue when 60 rooms couldn’t be rented because of the nearby generators. “The criteria from third-world countries are even tighter than here,” he points out.

Shhh!

Onsite power generation isn’t going away. In fact, it’s becoming more prevalent. South America, the Middle East, Asia, and other parts of the developing world are experiencing big growth in diesel-powered stations, while many island nations are adding extensions to power plants for tourist amenities. Third-world and mobile applications are also increasingly common, particularly where worldwide natural disasters require the use of power generators or self-described eco-friendly resorts abound.  

Hansen sees more dependency on diesel-powered generators, especially now that alternative fuels are becoming popular.

“Biodiesel is a renewable energy source,” he says. “People are also developing plant products from crop waste and pond scum—leaves, wood chips, fast-growing grasses. They’re all derivatives of cellulose—a crop that hasn’t historically been used and is not competitive in the food chain.”

Despite the growing spread of applications, Brad Fennell, vice president of sales with Chillicothe Metal Co. Inc., says businesses in major metropolitan areas on America’s east and west coasts make up 60–70% of the enclosure manufacturer’s business. “The last 10 years have been good for the generator business,” he says. “Data centers have multiple generators onsite. It’s necessary for infrastructure: hospitals, wastewater treatment plants,
utilities....”

The last 10 years have been good for a lot of businesses, including noise attenuation firms. Fennell recalls “only a handful of serious competitors 10 years ago.” New competitors signal the growth of the industry—and of the need for silencing.

Growth of the population, industry, and technological needs are all contributory factors to the heightened need for noise attenuation.

“We’re becoming an urban society,” surmises Hansen. “The issues we face are high-density living and more crowded work environments.”

He believes the situation is exacerbated because many businesses are no longer placing generators far away from buildings. Reasons for the change include shrinking lot sizes, security concerns, and the cost of copper to run long lines to distant power systems. Instead, noisy power systems are now close to buildings … and neighbors.

It’s no surprise, then, that one of the biggest changes in noise attenuation is being driven not by regulation, but by people.

“Regulation is an incentive to implement [noise attenuation], but people are policing noise levels,” explains Hansen. “They don’t want to hear it, especially if the owner is on the premises.”

As Fennell says, “there’s not a lot new as far as mechanics, but specs are policed better, and sound regulations are enforced more.”

Indeed, OSHA is more aggressively enforcing noise limits in the power-generating industry.

Hansen describes “phases of concern” that motivate OSHA and the EPA. However, Cary Bremingan, vice president of engineering for Universal Silencer Co. in Stoughton, WI, says the regulations are the same ones they’ve had for years. The difference is that the nearest receptor is closer now.

“They didn’t need to change the regulations,” says Bremingan. “People are closer due to population density; that impacts the steps to reduce noise. You don’t need the Federal Energy Regulatory Commission to step in.”

Sounding Board
Whether used as standby power or in prime applications, reciprocating engine-powered generator sets produce noise and vibration. Usually, their operating sound levels must be reduced to meet limits established by local, state, or federal ordinance, typically ranging from 45 dB(A) to 72 dB(A), depending on zoning restrictions. Some communities have instituted property line noise restrictions that use octave band frequencies to reduce the amount of low-frequency noise. Because genset noise levels can reach 100 dB(A) or higher, noise mitigation and location of the generator have become critical.

State and municipal noise ordinances concern noise that migrates beyond property lines and disturbs the public, but isn’t considered a safety hazard. OSHA sets federal safety regulations regarding noise levels in the workplace to protect the health of workers. Other countries have similar agencies that establish standards to control noise.

But you can’t manage what you don’t measure. In 1974, the EPA began using the Noise Reduction Rating to measure hearing protector effectiveness in reducing noise levels. Although it comes under fire for results produced in idealized laboratory testing, it set a baseline for testing noise levels.

Manufacturer testing is “all based on a perfect world,” adds Fennell. “We have to adapt to site conditions."“Specifications typically read ‘free field,’” points out Hansen, but such conditions don’t exist in an urban environment and noise-mitigating equipment “doesn’t perform the same in a corner, or near buildings. Those manmade canyons act as mechanical amplifiers.”

That’s why Chillicothe tests engines with no enclosures and takes sound measurements onsite.

“The results can be lower than the published decibels,” states Fennell.

Real-world testing is critical, Hansen adds. Factoring in prevailing winds and flow system from buildings, as well as compatibility with support or neighboring systems, is important in containing sound.

In addition, “if you’re going to be precise, you have to know the topography and application,” says Hansen. Using satellites and radar altimeter to computer model sound patterns allows Engineered Aeroacoustics to design for specific locations.

Sound Waves
Airflow has always been important to engine development. Now it’s important to end-users too. While aerodynamics improves functionality of today’s bigger, clean-burning Tier 2 engines that require a tremendous amount of air flow, air still conducts sound waves. Aeroacoustics is a combination of the science of aerodynamics and acoustics.

Engineered Aeroacoustics uses computational fluid dynamics (CFD) to predict the performance of a design or system. Using CFD, they can look at airflow to and from the engine generator and at the discharge, which must be compatible aerodynamically. For new designs, they build a computer model for the proposed site and three-dimensional air paths. They then evaluate the engine manifold exhaust pipe. Exhaust from ground generators has been known to foul cooling towers on the roof because of airflow.

Photo: Acoustiblok Inc. Wheelabrater after noise attenuation implementation

“It’s an even bigger problem with chillers if you foul the inlets,” notes Hansen. “That’s a problem for data centers that need high-capacity chillers to cool their electronics, plus backup power.”

It’s only going to get worse as the increased demand for airflow is juxtaposed against spatial considerations. For security reasons, companies are moving generators closer or incorporating them into the building, often compromising airflow as a result. It can be a problem, Hansen says, that can be offset with the proper aeroacoustics.

“Traditional designs for enclosures and placement don’t work,” he says. “They don’t support the space required for combustion and cooling.”

Placement is always important, Fennell acknowledges—particularly in major metro areas where real estate is at a premium. Because specifications dictate the targeted sound level and the allotted footprint is frequently unchangeable, he says the “package is a big deal.”

That’s why Chillicothe developed cooling software that can predict sound levels and change the airflow as needed. Chillicothe can calculate dB(A) ratings and layouts, taking into consideration airflow, exhaust, heat, and genset dimensions.

“We may be using the same materials—14-gauge galvanized steel housings—as we used to, but we’re becoming more sophisticated in designing air flow,” says Fennell. “The biggest obstacle is keeping the engine cool and knocking down sound. It’s all about the tortuous path.”

One Engineered Aeroacoustics client, a prominent water treatment facility, had two design engineers working on the same legacy design for generator buildings at separate sites.

“One firm used the design,” relates Hansen. “The other contacted us for analysis.”

Credit: Universal Silencer How noise attenuation works

Thanks to a 3-D scale computer model, they discovered that airflow was choking due to engine demand. Without altering the footprint, they modified the design by placing aeroacoustic baffles inside the freestanding building. “Now all the acoustics in the building flow correctly,” says Hansen. “In the other building, the same Tier 2 engines overheated. The manufacturer pulled the warranty.”

It’s not some Rube Goldberg scheme. Hansen says they’re doing more remediation for aerodynamics and that some clients come just for CFD analysis, including 4–5 major data centers that “bristle with engine generators because of high demand.” Issues they face include prevailing winds and compatibility with support systems, chillers, a cooling tower, and recreational courtyards.

“By looking at the totality of the problem, we can anticipate growth and help an organization stay in compliance as the community grows.”

Blocking Out the Noise
Unlike traditional enclosures that absorb sound, a new all-weather sound panel blocks it, creating a more effective sound barrier. Acoustiblok panels, made of a one-eighth-inch-thick viscoelastic polymer with a high-density mineral content, transform sound energy into inaudible friction energy as the material flexes from sound waves, producing only trace amounts of heat.

In effect, Johnson says, sound “vibrates” the material, transferring energy. “It’s more effective than 12 inches of poured concrete.”

Test results from Riverbank Acoustical Laboratories indicate it can reduce sound transmission by as much as 30 decibels.

The custom-situated panels provide access to power systems for maintenance and can be installed for permanent or temporary use. Easily configured, configurations can be changed or added on to. The closer the panels are positioned around the exhaust and intakes, Johnson says, the more effective they are. However, they absorb and block virtually all sound waves without obstructing airflow. Johnson says that’s important, particularly with chillers, which emit a high-pitched whine from the compressor and need a lot of air around them. “They reduce sound without sealing in the chillers.”

They don’t seal in generators, either—unlike block walls that merely bounce sound out, or interior silencers that don’t do the job, Johnson claims. Acoustiblok is rated at Sound Transmission Classification 2.9 for blocking noise: at NRC 1.00, the maximum absorption rating, for absorbing noise.

“All sound that can be absorbed, is.”

A “hurricane panel” that can withstand a 270-mile-per-hour wind load is also available. 

They even increase sound blocking from 100 HZ down, the most difficult ranges to mitigate the low frequencies from 30 to 100 HZ.

“In Miami [FL], New York, and Arabia, emergency generators are placed on top of buildings, but neighboring buildings complain about noise,” explains Johnson.

The challenge, however, is erecting sound-attenuating structures that can withstand high winds at those altitudes.

Another iteration of the sound-transforming panels can withstand extreme heat. ThermaBlock incorporates aerogel (also referred to as “frozen smoke”) suspended in a unique, flexible composite material.

Developed in conjunction with NASA, it wasn’t previously used, Johnson says, because of its fragility.

“Now we can put it into fabric, remove the moisture, and leave it in the fabric.”

The one-half-inch-thick material can be cut to size and used to reduce sound from hot pipes.

Exhaust: Out-of-the-Box Thinking
Space is a huge factor—but not the only one—concurs Jeff Harris, general manager of operations, Harco Manufacturing Co., Portland, OR.

“We try to meet the sound requirements within the space constraints and the back pressure of the engine.”

To save space, they use internal baffling. “We wear out the exhaust energy using area or volume,” he explains.

They create a maze inside the silencer to “run the decibels out of energy.”

“That’s a lot of chambering,” exclaims Harris. Internal insulation keeps the external shell cooler while adding supplementary attenuation, thus serving a dual purpose.

Established in 1948, the engine exhaust fabricator uses engine exhaust routing to diminish exhaust stream noise from any diesel or natural gas engine, stationary, prime, and standby.

“We can’t eliminate mechanical noise, but we can eliminate noise inside the engine and coming out of the engine,” confesses Harris.

Harco exhaust silencers are designed to work with any dual inlet or outlet configurations, making costly Y-headers unnecessary in most cases. The custom-built silencers hit all hertz with the design (high and low) and maintain low backpressure.

According to Bremingan, exhaust is a scapegoat.

“The cooling air fain can leak mechanical noise from the engine,” he says. “The enclosure can leak noise. You have to view it as a system.”

For instance, he says that in some cases it can be more cost effective to put individual silencers on the engine intake than on the exhaust.

Universal Silencer Co. manufactures both intake and exhaust silencers for everything from diesel engines to gas turbines, as well as products for blowers, high-pressure vents and industrial fans. Silencers, Bremingan says, can eliminate a significant amount of noise.

“Power systems should be unobtrusive,” he says.

In fact, confirming what his colleagues stated, due to customer demand, the general trend is to make them even quieter. The challenge is space.

“A lot of companies offer gensets in standard ISO shipping container,” says Bremingan. “The silencers have to be inside, which creates additional heat issues.”

Another obstacle in achieving optimal acoustical performance involves engine emissions. Bremingan explains that a range of after-treatment silencer applications is available, but “no one set works everywhere,” because there are “various flavors of emissions controls and regulations in place.”

Emitting Less Noise
While most regulations, he adds, remain unchanged in recent years, they vary locally. When Universal Silencer installed gensets on the roof of the London Stock Exchange, for example, they had to adhere to some very aggressive acoustic regulations.

Tighter, more challenging specifications have led to more complex, advanced designs, Harris believes, complete with tools like autocad and cyber modeling for simulated testing. He sees advancement on the “customer learning curve” leading to increased demand as their knowledge increases. 

“In years past, they wanted simple performance,” says Harris. “An ear test on noise levels was OK.” Now they are more educated and expect more testing and better results.

What was simple in the past, Hansen observes, has become much more complex. More equipment is required to achieve the stringent requirements on noise.

Bremingan agrees: “There are a lot more things to manage. It used to be simple: just a catalog part on the shelf. Now, in addition to noise, we have to deal with heat, emissions, cost, et cetera.” He sees parallels with what was happening within the auto industry in the 1970s.

The landscape is changing, Bremingan concedes. “It’s not as simple as picking something out of a catalog anymore.” He anticipates the response to approaching new challenges in the market will have to involve integrated systems solutions: silencing and emissions. A system design must work together for efficiency.

Designs these days typically include “huge” mufflers due to the emissions criteria, Hansen comments. But size isn’t the only difference. “We seldom design without a primary and secondary muffler,” he says.

The emissions component to attenuation is new, Harris states, but the market is far from hitting the ceiling with emissions. “It’s almost a requirement in California, but not everywhere.”

Currently, there are emissions control devices available that don’t require the higher priced ultra-low sulfur fuel, but are designed to reduce toxic levels of diesel particulate matter, carbon monoxide, and hydrocarbons. Harco was one of the first to introduce a low-profile catalyst exhaust silencer with filters mounted inside. Diesel particulate filters do affect the sound, he points out, with a side benefit of “taking some dB(A)s out.”

Emissions regulations indicate increasing government oversight of power generation. Engines and fuels are becoming cleaner and more efficient by mandate. Harris believes the sound attenuation industry will answer the call and challenge the rules of physics to address the demands of reducing noise from power generation systems.

However, in an effort to silence a bustling world, there’s little doubt that they soon will.“The industry is just now becoming aware to the audience,” contends Johnson. “There are a myriad of uses, but like new technology, people don’t see a need yet.”

Author's Bio: Writer Lori Lovely focuses on topics related to transportation and technology.