Simply following the ANSI recommendations for HVAC design and waiting to take measurement until after construction is not recommended as you can follow all of the recommendations but still have a noisy system, and not achieve credit compliance. Following the calculation path, as outlined above, is recommended.
Projects complying with the credit requirements through the ANSI standard should also consider researching the design recommendations for HVAC in the 2007 HVAC Applications ASHRAE Handbook, Chapter 47. This handbook will provide you with useful information when designing HVAC systems for noise reduction.
Compliance with the ANSI standard requires projects to limit maximum allowable background noise levels from HVAC equipment based on section 4.3 of the ANSI standard and provide after construction measurements to verify compliance. Projects will have a better chance of meeting the measurement requirements by following these practices. (See the ANSI standard—and in particular Annex B—for full details.)
If you decide to take measurements after construction, you will need to comply with ANSI standard S12.60-2002 and meet the after construction measurements requirements.
ASHRAE has guidelines on running the calculations without software, but these are fairly detailed measurements and a consultant will most likely be needed. See the Sample Background Noise Calculations in the Documentation Toolkit for more information.
The calculation for background noise level can be performed by a mechanical engineer if they are familiar with the calculations or have common software, such as the Trane Acoustics Program (TAP). (See Resources).
It is usually better to run calculations during design, to allow for changes to meet the requirements, if necessary. If measurements of the completed building show that you do not meet the credit requirements you will be required to make costly changes.
When it comes to documenting the credit through LEED Online, you will have two choices: performing calculations during design, or taking measurements after construction. Choose your path now.
HVAC system layout also plays a large role in mitigating background noise from mechanical equipment. It is important to avoid placing fans and mechanical systems directly above classrooms and core learning spaces and insulating ducts. Projects may also want to consider displacement ventilation, which uses lower-velocity air and is quieter.
