Appendix I – Heating, Ventilation and Air Conditioning Impacts on Acoustical Environment

Notify your mechanical consultant that achieving appropriate acoustical performance in classrooms is a primary goal of the project.  The basic concepts behind designing a climate control system that does not contribute to acoustical problems in learning spaces are simple:

First, do not locate any HVAC equipment that employs fans or motors near learning spaces. Minimize the number of moving parts.

Second, limit airflows at delivery points and match duct sizes carefully to minimize noise associated with air movement and turbulence.

Third, run major distribution lines in corridors and use offset branches to serve individual leaning spaces.

Additionally:

-Do not allow learning spaces to become connected acoustically through supply ductwork or return plenums.

-Select equipment based on its low operating noise and include any manufacturer recommended attenuation devices in the specifications.

-Isolate mechanical equipment from structure with manufacturer’s recommended attachment methods for sound and vibration control.

 

The following are the specific requirements of which your mechanical consultant must be made aware to ensure that your goal of an appropriate acoustical environment is met in all learning spaces:

1. Un-ducted systems such as window or wall mount units should not be employed.

2. Grilles and diffusers should have an NC rating of 18 or less for a single diffuser (the total NC contribution of the HVAC system in the room should be 25-30 NC,) and use no dampers directly behind diffusers.

3. Air flow in the trunk ducts should not exceed 800 ft/min.

4. Branch ductwork to match “devices duct correction size.”

5. A duct silencer should be included in the Air Handling Unit (AHU) or the main supply/return if analysis shows that break out noise or fan noise will exceed 35dBA in any classrooms.

6. The ductwork should be fabricated and installed as to achieve low static pressure loss; 3-4 duct diameters of straight duct length going to diffuser.

needs to be CAdified

7. All rotating equipment and equipment with static pressure control dampers should be 10 ft or farther from the classroom. If serving more than one classroom, increase the distance (here we could use some numbers…)

8. Use centrifugal fans with airfoil shaped blades; avoid forward curved blades

Airfoil shaped blades for HVAC

9. Where ductwork that connects classrooms is unavoidable, it should include sound attenuators and/or duct lining to minimize crosstalk.

crosstalk solutions

10. Variable Air Volume (VAV) and fan-powered boxes must not be placed over core learning spaces. Place them over less sensitive spaces, such as a corridor.

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