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Sound Attenuation

In order to reduce the impact of power outages, businesses and industries are adding more and larger emergency standby generators. Finding a location for these generators can often become a problem, as stand-alone buildings or large mechanical rooms are not an option in many applications. In the case of existing facilities or other sites with limited space or installation obstacles, outdoor generator enclosures can be the solution.

As emergency standby generators have become more vital to the continuation of business, it follows that outdoor generator set enclosures that are properly designed, ventilated, secured and located have become more valuable to organizations. The overall cost and ease of installation of an outdoor generator set will depend on the physical location of all elements of the system generator set, fuel tanks and accessories. Several types of enclosures are available, including weather protective, sound attenuating and walk in. Weather-protective white all metal enclosures provide weather protection, these basic enclosures only secure the generator set and provide protection from the elements. They do not retain heat, hold temperatures above ambient in cold weather or provide cooling beyond the ventilation and airflow offered by incorporated louvers or perforated panels. Sound attenuation is minimal and, due to their tight fit, access panels or doors are required for maintenance and inspections.

Sound-attenuating - these enclosures are generally larger and more costly than strict weather-protective type, due to the design features required to reduce generator set noise. This variety on enclosure may be specified when noise reduction is needed to meet local ordinances. Walk-in In this term encompasses a wide variety of enclosures that are custom-built to a specific application. Walk in enclosures often include sound attenuation, as well as space for power switching and monitoring equipment, lighting, fuel tanks and other equipment. They can also accommodate insulating and heating capability; and may be treated as a building by local inspection officials. Virtually any size generator set can be housed in an outdoor enclosure however; there are several factors you will need to contemplate if you are considering a new generator to be housed outdoors.

Choosing a site

The location for your outdoor enclosure should be level, well drained and secure from flooding, fire icing and vandalism. For reasons of reliability, the generator set should be located near the main electrical service but not so close that localized problems at the service entrance will interfere with the generator set, for example, a fire at the utility service entrance would be less likely to affect a standby generator set located some distance away. Control panels and connections should have ample clearance for easy access, and the fuel tank should be located so that refueling is convenient. The National Electrical Code (NEC) requires that all outdoor generators include an inside or outside service disconnect, either at the generator or at the point where the generator feeder enters the building. Also keep the generator location away from building openings, combustible materials or building ventilation inlets. In multiple generator applications, it is essential that there is adequate spacing between generators and that the enclosures are oriented so that the heat from one generator is not drawn into others. Sometimes, as a last resort, the only outdoor location for an enclosed generator set may be a rooftop. Provided the roof is properly designed or modified to take the extra weight, this can often be a space saving solution in urban areas. However it is worth bearing in mind that supplying fuel, load bank testing and maintenance could be more difficult.

All Weather protection

It is recommended that any outdoor generator set enclosure have a corrosion-resistant finish (often aluminum or painted steel) Stainless steel hinges, corrosion-resistant handles and other hardware. In addition to rain shields on cooling air intakes and exhaust, which may need motorized louvers that open when the generator set, is started and close automatically when it’s off in order to protect against precipitation. In any case the amount of weather protection needed is often a matter of geography. For example in tropical climates, the principal weather challenges are sun, heat, rain, salt spray, windstorms, blowing sand and lightning. Whereas in more northern locations a threat is posed by ice storms, heavy snow and severe cold.

The outer surfaces of the enclosure can be primed and painted sheet metal either steel or aluminum.

The paint needs to be of a quality and thickness to retain gloss and resist minor impacts and corrosion due to salt spray, humidity and water in accordance with appropriate ASTM (American Society for testing and Materials) Standards. Within 60 miles of the ocean, aluminum enclosures will resist corrosion from salt air. In areas where ice and snow accumulate, it is necessary to provide for regular removal of snow and ice around doors, louvers and dampers. In cold climates, it’s possible an electric space heater in addition to having a coolant heater on the generator engine would be required. For NFPA (National Fire Protection Association) life-safety applications, NFPA 110 requires a minimum ambient temperature of 40 degrees f inside the enclosure. Also, diesel fuel may need to be heated to prevent gelling. In flood prone areas, the generator and enclosure should be installed well above the highest expected water level on an elevated platform or a rooftop. For other locations with potential weather issues, specially designed enclosures are available. For example, in storm prone areas and enclosure with enhanced strength to withstand high wind loading, which can resist wind speeds of over 150 miles per hour may be necessary. While earthquake -prone areas might require a seismic-certified enclosure.

Cooling Temperature

Generator sets can maintain their rated power output provided ambient air temperature flowing into the enclosure doesn’t exceed the cooling system ambient air rating and static restriction. If this air temperature is exceeded, the output of the generator will have to be reduced to prevent overheating of the generator set. Cooling requirements for the enclosed generator set can also be affected by site selection. Whenever possible, locate the enclosure in an area where there is free airflow. Avoid locations such as covered parking ramps or other nearby walls or overhangs that may restrict cooling air flow or require complex routing of the engine exhaust. An enclosure with adequate flow -through ventilation that keeps temperatures in the optimum operating range will allow the generator set to operate at its nameplate rating. It is also essential to keep cooling air intakes and exhausts clear of obstacles. The best enclosures incorporate advanced radiator, fan and louver designs that provide optimal airflow to control engine and generator operating temperatures even in the most severe environments.

Security

Vandalism is a common problem that can compromise a standby power system’s reliability. Lockable access points to connections, switches and valves deter unauthorized persons from interfering with system operation. Access to the fuel tank and system controls must be restricted.

Sound attenuation

Although generator sets used for standby power do not run often, controlling the noise they produce is a concern if the units are located near the property line or in a crowded urban environment. Most locals have ordinances that set limits on permissible sound levels at the property line. While exhaust silencers can greatly suppress exhaust noise, much of the noise from an enclosed generator set comes from the cooling air fan. Although harder to control it can be greatly reduced by careful design of the air intake and exhaust plenums. Sound attenuating is dependant on many factors, including the sound level produced by the generator engine, the design of air intake and exhaust plenums, the type of exhaust silencer and local conditions. Work with your generator set and enclosure supplier to determine the level of noise suppression needed to comply with local regulations, most offer one or more levels of sound attenuation as options.

Additional issues regarding sound attenuation include:

  • Critical sound-attenuation remedies will increase the overall footprint, complexity and cost of an installation.
  • Sound-attenuating materials in the walls and ceilings of the enclosure not only trap sound but also heat
  • If sound attenuation is required, specify non-hygroscopic and non-flammable material to prevent moisture build-up inside the enclosure
  • Pay particular attention to noise generated at cooling air intake and exhaust plenums. The design of airflow through the enclosure is critical to minimizing this noise.

Fuel

For increased security and to reduce the footprint of your installation, many generator sets can be ordered with an integrated high-capacity fuel tank. These protect fuel lines and filler connections within the enclosure and provide a very compact installation. Look for tanks that include dual-wall

construction, fuel gauges and provisions for catching fuel leaks, ruptures and overflows. Be sure to allow sufficient clearance around the enclosure to allow access to fuel trucks, and consult with local authorities regarding fuel tank codes.

Maintenance

In walk-in enclosures, it’s important that there is sufficient room within the enclosure for easy maintenance access to key generator set components: skin- tight enclosures should have large access doors and panels. Good interior and exterior lighting can make all maintenance and trouble shouting tasks easier.

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