November 3, 2014
Whether you are designing a central energy plant for a hospital, or a smaller generator for a commercial facility, be sure to dedicate some time to your engine exhaust system specifications. Federal regulations are becoming stricter each day. And, at the local level, noise and air quality are becoming more and more important to permitting authorities and field inspectors according to this report from Onsite Power Advisor.
Noise attenuation is one of the biggest concerns, of course. Excessive noise will bring unwanted attention to your installation, and this can create enormous problems. If your project resides within city or county lines where a specific noise ordinance is in place, know what these limits are, and tie your specifications to those limits. Your noise attenuation specifications should set clear and measurable targets. If sound levels are measured in decibels, it seems logical that a sound attenuating device (silencer) should be specified to provide “x” dB(A) attenuation, when measured at a certain distance from the source (i.e.: engine exhaust outlet).
One last point on attenuation: When you visit the jobsite, look around and consider how the adjacent properties might reflect the sound originating from the engine exhaust outlet.
Steel or stainless steel? Indoor or outdoor?
Exhaust silencers are available in carbon steel, aluminized steel and stainless steel. Carbon steel silencers generally receive a primer followed by a high-heat black paint finish. Aluminized silencers are sometimes painted, but most often not. Stainless steel silencers are almost always left unpainted. The material you choose will be important if your installation is outdoors, visible to the street, or exposed to damaging conditions.
As you may have guessed, exhaust silencers are subjected to large temperature swings (diesel engines produce exhaust gas temperatures in the 800°-1200°F range). These temperatures, combined with the frequent start/stop exercise cycle of generators, already create a serious challenge to the exterior paint used on carbon steel silencers. It is not uncommon to see poor quality paint that flakes off after a few engine start/stop cycles. If your installation is surrounded by a corrosive environment (think water treatment plants, chemical plants or coastal installations), rust will be a serious threat, and you should already be planning to have all exposed exhaust components built in 100% stainless steel.
Want to avoid rust but don’t have the budget for stainless steel? Whenever possible, consider installing the exhaust silencer indoors. This will help in the aesthetics department and will make the architect very happy. When installing indoors, space is critical, but be aware that newer silencer designs allow low profile installations, even when the overhead clearance is very limited. If you are concerned about the high temperatures, be sure to look at internally-insulated models, or consider external insulation such as thermal wraps for any component that might present a hazard to personnel.
What this means to you
Excessive noise will bring unwanted attention to your installation, and this can create enormous problems. If your project resides within city or county lines where a specific noise ordinance is in place, know what these limits are.