Ed Ritchie 2015-11-11 14:11:19
Intrusive noise is a growing concern for both the public and private sector these days. If the power equipment rattles, clanks, and booms loudly, there will likely be complaints—or worse: fines and citations. Consider this: according to the Noise Pollution Clearinghouse ( www.nonoise.org ), 13 states have noise pollution laws, and five provide model ordinances for municipalities to follow. These laws can be quite rigid. For example, the City of Lyme, CT, passed an ordinance that makes any noise above 55 decibels (dB) during the day and 45 dB at night a violation, punishable by a fine of $90 per offense. In Texas, the state law says that noise is too loud if it exceeds 85 dB at the property line. So, listen up. You need to make some sound decisions, and we have some experts and resources that can help. Attenuation, Ventilation, Safety It’s not surprising that power generation equipment has been identified as a source of sound pollution by many government agencies, considering the fact that distributed energy use continues to grow in urban environments. The result, according to Mike Witkowski, COO of enclosure manufacturer Pritchard Brown LLC, in Baltimore, MD, is that engineers are finding their projects often require a high degree of acoustic customization. “The ordinances for sound attenuation are getting more stringent, and at the same time, people have less space to dedicate,” says Witkowski. “Europe is well ahead of us in regard to their requirements for sound attenuation, because they are much more crowded, and they’ve been on top of one another for much longer. Here, the joke used to be that if you want quieter generator sets, you get a bigger piece of land. But that’s changing, and the installations now are so much more power-dense. It’s not uncommon to find big data centers with 20 to 30 megawatts of generator capacity located in a giant generator farm, and the sound from them is substantial. So, designers need to be more creative with mitigating this noise, yet maintaining the proper airflow and fitting within the space constraints of the site.” When it comes to the physics and science for sound attenuation, he notes that the solutions are fairly straightforward, even though new products and materials that help absorb sound are finding their way to the marketplace. “It still comes down to getting creative with moving air. It would be incredibly easy to attenuate generators that didn’t need 100,000 cubic feet per minute of air. Just put a massive box around it and it will be quiet, but the volume of cooling air required means large devices to acoustically treat the ventilation air.” Another consideration is the fact that mufflers for exhaust are different from air handling silencers. There is some new technology in combustion exhaust silencers, but emissions regulations are getting more stringent. “Now you have devices that limit the emissions, and they make it more challenging to treat the acoustics,” says Witkowski. Such high-performance systems typically require the best quality. “We’re talking about premium materials and attention to detail,” adds Rick Grambo, vice president of sales and engineering at Pritchard Brown. “So, fit, finish, and service after the sale are critical, because often you’re well into the project and changes are required.” He continues: “Projects rarely go as planned. Simple things such as equipment that isn’t the size expected, or no equipment, shows up. Or, an engineer calls with a new requirement. Typically, the customers are not the end-users. They are the suppliers of the equipment inside the enclosure, and at the beginning of the project, they give us information on air requirements, space, dimensions, noise signature, and what the customer wants in terms of site installation, such as a roof where it might need to be assembled in pieces. Safety is critically important, so we design a unit that is safe for the people working inside, in terms of space and shelter, and lighting and egress. These are normally emergency power situations, and anybody working on it could be there during a storm or other emergency situation.” For enclosures, there are safety and electrical code clearances from the National Electrical Code, and other building codes. But clearances aside, if the air handling function is not designed properly, it can create a negative pressure or vacuum in the enclosure when the generator set is running, leading to difficulty opening the doors. Finally, Witkowski stresses the importance of having engineers think about the enclosure issues at the very beginning of the project. “When there are sound attenuation and fuel storage and emission controls involved, it’s very important to get the manufacturer involved early so subjects such as limitations can be discussed. I get calls from engineers, and they say their project is 90% done and an intern got the specs out of the manufacturer’s catalog for a one-megawatt generator, but it makes too much noise and sits at the property line. If we were involved at the beginning, we could have developed a solution that would have been less complicated and less expensive than addressing it in the field.” Markets and Orders If the project is fueled by natural gas, planners should also expect longer lead times for materials such as stainless steel, according to Dale Gremaux, sales marketing manager at Harco Manufacturing, Newberg, OR. Harco manufactures heavy-duty commercial exhaust silencers and supporting products, and Gremaux notes that natural gas is different from diesel. “It burns hotter,” says Gremaux. “With all the growth in natural gas, stainless steel requires longer lead times, up to six to eight weeks. So it does help to bring the exhaust and emissions control people into the design process early.” Gremaux has found that Harco’s customers are bringing in projects that are located in more noise-sensitive locations. “It’s getting more common in these kind of sensitive environments and there are more projects now. Also, because the power grid is overwhelmed and not getting any better, we’re seeing more and more of these emergency power projects that need to be available and ready.” Parallel grid operations and peak shaving are also growing, and Gremaux observes that the electrical utility has put up 30 installations in the area for peak shaving. “In some situations, such as universities, they are finding that they can make power more economical than the utility, and what that means to us is that these aren’t generators located out in the middle of nowhere,” says Gremaux.“They are downtown or in places that have sound requirements and they want them quiet, along with being hidden from sight. In a situation like that we’re talking about 25 to 65 decibels, and sometimes it’s requirements such as 75 decibels at three meters from the source. Nine times out of 10 you have to put it together and deal with space challenges. Even a lot of the hospitals and data centers are putting generator sets into an enclosure and maybe putting them on a roof. So, whatever it is we’re making to attenuate the noise, it has to fit in that box.” In such environments, heat is often a factor. “You do have heat, and it’s critical in the design, especially if we know it’s going inside the enclosure; so, it requires additional insulation. We do quite a bit of computer simulation and testing, and we have our computer aided design and a plasma table as well. This is a computer-run plasma cutting machine. The difference between a water jet and a plasma cutter is that the waterjet can cut through a piece of steel over foot thick. While the plasma can’t do that, it cuts very fast. So if we need a bunch of components cut, we can maximize that sheet of steel quickly. We can create parts faster, and in certain instances we might save three weeks if we had to get some American-made flanges. With the new equipment and growing market, we added 15,000 square feet of manufacturing space to satisfy the demand.” Sensitive environments, such as hospitals, have long been a market driver for the industry. For example, in 2009, Maxim Silencers, Stafford, TX, released new models with higher attenuation to meet industry needs. The new models included the Hospital Plus Grade M62 (35–50 dBA), Hospital Plus Grade Spark Arresting MSA55 (35–50 dBA), and Hospital Grade low-pressure drop MT52 (35–42 dBA). Currently, the company’s most efficient products are its chamber type silencers, which provide the best noise control across the entire audible range. The basic design incorporates non-resonant side tube arrangements to permit passage of the exhaust gases from one chamber to another. The design is also flexible and can be configured with side inlet and outlet exhaust connections. When hospital space is limited, Maxim can provide compact chamber silencers, engineered to give critical to “hospital” grade attenuation, in minimal spaces. Dual inlets and other custom designs can be easily incorporated, and the low temperature design reduces skin temperature, plus radiated noise as well. As the industry expands, some companies are looking to acquisitions to have the products to satisfy the market’s demands. For example, Universal Acoustic & Emission Technologies, Stoughton, WI—a manufacturer of solutions for noise control, emissions, and air filtration— acquired Ojibway Enclosure Systems, Janesville, WI—manufacturer of enclosures and packager of generator sets for power generation systems. Ojibway also provides laser cutting, welding, and forming of a variety of metal products, and they’re active in the installation of generator sets in the field. With the growth of onsite power systems on the rise, Ojibway and Universal have supplied common customers, including engine distributors that need silencers or emissions treatment products, as well as data centers, hospitals, and other large-scale facilities wanting complete power generation packages. Universal’s engineers focus on the demands for higher performing sound attenuating products, and have seen many changes. Traditionally, a 25-dBA reduction could meet Universal’s customers’ requirements, but as power systems become common near more residential and public locations, the requirements of designers often includes the use of silencers, which are typically integrated into the enclosure. More Applications and Solutions Sometimes the source of noise isn’t stationary. For example, mobile generators are finding widespread adoption for emergencies such as natural disasters. To prevent generator noise from aggravating a bad situation, Girtz Industries, Monticello, IN, offers its Z-CUBE line of containerized industrial equipment for mobile applications. The Girtz Z-CUBE ISO container-based packages balance low noise, ease of service, and durability. Three sizes of containers accommodate gensets from 4,00 kW to 2,250 kW. All packages utilize a similar mechanical and electrical design resulting in a consistent look and feel for the operators and service technicians. If a mobile application is far enough away from a sound-sensitive environment, engineers may opt for a removable, reusable blanket, such as the Insultech Blanket Insulation line of products, from Shannon Enterprises of WNY Inc., Tonawanda, NY. Shannon’s blanket insulation is design engineered for treatment of machinery and process piping for both thermal and acoustic performance. Products include thermal blankets, acoustic and heat shields, rain shields, and passive fire protection blanket insulation. Firwin, a company based in Toronto, Ontario, Canada, is another resource for removable insulation blankets and heat shields for diesel, gas, and steam engines. These blankets will cover engine exhaust manifolds, turbos, exhaust piping, flexes, bellows, purifier, and silencer systems. The company’s removable insulation blankets provide heat and noise control at temperatures up to 2,000°F. We’ve talked about insulation, but how about isolation? It’s certainly a tool in any sound engineer’s toolbox. And it can be a very simple process to install. For example, Soundown, Fort Lauderdale, FL, offers its line of type BRB mounts (Machinery Mounts 50, 60, 80, and 110). These are rubber antivibration elements that support mechanical sources of sound. Their tall-height profiles produce large deflections, low natural frequencies, and vibration isolation is the result. Intrusive sound and vibration can be detrimental to indoor work environments, says David Lehrer, LEED AP, Center for the Built Environment, UC Berkeley. “The center studies indoor environmental quality and we’ve done surveys of about 1000 buildings. We look at a lot of different characteristics in an office, such as air quality, thermal comfort, acoustics, layout, maintenance, and lighting. Acoustics is the one thing that people are least happy with—after thermal comfort. Buildings do have to contend with acoustical issues, such as a chiller on the roof. Those can be very loud, and they have to be isolated.” The Center’s study is available for use by design and engineering professionals ( www.cbe.berkeley.edu/research/survey.htm ). Noise and emissions often go hand-in-hand with power projects, and the environment and generator designs have added new levels of complexity for noise control systems manufacturers. But, new technology is catching up. For example, Miratech, in Tulsa, OK, supplies emission solutions for stationary natural gas and diesel reciprocating engines, and designs from the company’s customers reflect the fact that noise and emissions control are important. Miratech’s customers are now seeing that stiff regulations in some states have made pollution control a critical issue. The state of California is a good example, and Miratech recently announced that it received CARB Level 3 Plus (California Air Resources Board) Conditional Verification for its new diesel particulate filter system technology called the LTR (Low Temperature Regeneration). The LTR is used by stationary diesel engine owners/operators and consists of a single housing assembly containing a DOC (Diesel Oxidation Catalyst) and DPF (Diesel Particulate Filter) modules. For noise control, the LTR product line also includes options for integrated silencing and an electronic monitor/data logger/and alarm. With higher standards and stricter regulations for noise popping up nationwide, companies are often required to monitor and test their noise attenuation products. Not surprisingly, there’s a wide range of sound monitoring equipment available. For example, Scantek Inc., Columbia, MD, recently launched the ScanMonitor, a Realtime Datalogger for construction and community noise monitoring. The noise monitoring system includes a sound level meter, real time datalogger, communications, enclosure and software to process. Data is stored on high capacity local memory and also can be transmitted in real time by GSM, WiFi, or Ethernet connections. Power can be provided by mains, batteries, or solar panels. The ScanMonitor’s data is accessible via wireless or wired LAN or GPRS. It contains an on-board Web server so sound level meter, parameters, and sampling time, are all configurable. The software is Web-based for easy learning, and data can be graphed, customized, and printed. You won’t see much of a reading on your sound level meter if you point it at the backup generator enclosures at the Water Treatment Plant for the Lewis & Clark Regional Water System in Vermillion, SD. All three gensets are protected by custom, sound-attenuated generator enclosures from Lectrus, Chattanooga, TN. These 2-MW CAT diesel generators act as standby power sources for the eight pumps at the treatment plant, and they’re also supplying power for both the facility and the local power utility during load shedding. The UL-listed genset packages each contain a generator set, exhaust system, and fuel tank. They feature a compact footprint and low-profile design with easy servicing access to all major components. As a genset manufacturer, Cummins Power Generation Americas, Minneapolis, MN, is uniquely qualified to provide sound-attenuated and weather protective enclosures. The company tests their products at the Acoustical Testing Center (ATC) at the Fridley plant of Cummins Power Generation. Acknowledged as the largest generator set testing facility of its kind in the world, the ATC features a 13,000-square-foot, state-of-the-art hemi-anechoic (no echo) chamber. Test results allow Cummins to meet the strictest sound requirements and provide optimum protection from inclement weather for both the power generation diesel and spark-ignited generator sets. Systems are pre-assembled, pre-integrated, and delivered as part of the entire power package, with the goal of providing fast installation time and reduced costs. Cummins offers three levels of sound-attenuation, depending on model size, and enclosures are constructed of steel or aluminum, which is preferred in coastal regions or other environments where corrosion is a concern. Ultimately, we’ve looked at a broad range of products for noise control. From simple blankets, to the most sophisticated enclosures, these solutions address sound, exhaust, and safety issues. You’ll be needing these solutions, because the issue of intrusive noise isn’t going away. In fact, according to the National Network for Public Health Law ( www.networkforphl.org ), governmental responses to noise and related issues has resulted in 135 units of government discussing whether to pass new or adjust existing laws. So, keep it quiet—they’re listening. Ed Ritchie writes frequently on energy and technology issues.
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