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Controlling Sound Levels Using Stealth Units

Noise is always an issue. Noise is often confused with sound. Noise is sound or a sound that is loud, unpleasant, unexpected or undesired. Sound is always present; noise is not. Good design minimizes noise while making good use of sound. Well blended sound is very useful for blocking cross talk within an office. If sound levels are too low, cross talk and typical background sounds become bothersome and move into the category of noise. The sound consultant must study ambient noise levels around the building as well as within a building to successfully predict resultant noise levels in the occupied space. ARI Standard 885 sets guidelines to do just that. Its use will assist the designer in the overall noise prediction for a given application.

When using fan powered VAV terminal units, the generated sound is frequently very useful as a white noise generator for blocking ambient noise and cross-talk. However, this can be carried to a point where the unit generates noise beyond the desired levels if the units are selected incorrectly. Correct selection requires that one evaluate the airflow rates as well as inner liners. Airflow rates are obvious and are listed in the catalog.

Fiberglass liners are the best liners for sound attenuation. That is what is used as a standard for the rating points in Nailor’s catalog. This is consistent within our industry. However, many different liners are available, Steri-liner and different foams as well as perforated and solid metal liners applied over the insulation options. Each has different attenuation characteristics.

Nailor’s STEALTH units have the lowest sound levels available in the industry, today. That does not mean that their application will lower a building’s ambient sound level. It does mean that larger zones can be selected without affecting the noise levels in the occupied spaces. Larger zones mean fewer units, less ductwork, fewer controllers, less wiring and less labor (read lower first cost). Real value engineering can be done when comparing to competitors’ products.

The best example of this is for schools, medical offices or any location where high IAQ requirements would limit exposed fiberglass insulation in the airstream. In these situations, a solid metal inner liner in the terminal units is an excellent choice. This solid metal liner isolates the insulation from the airstream.

In any product other than Nailor’s, the solid metal liner also increases the radiated noise from the unit. Typically, this increase ranges from 2 to as many as 15 decibels in the octave bands that set room NC. In Nailor’s STEALTH units, the radiated noise actually decreases by 2 to 4 NC, depending on the unit selection and the setpoint. The designer does not have to reduce the unit size to meet the noise criteria for the space. In fact, the original value engineering that allows larger zones and fewer units still applies. It is not uncommon to find that Nailor STEALTH can deliver as much as 30 to 40% more air at the same NC levels as our competitors. This can translate into 10 to 15% fewer units as described above; however, detailed attention by the sound consultant is required to make this a reality.

Source: Nailor Product Bulletin, March 18, 2003