Data Center Noise: What Should Be Measured?

Data-center noise is not one sound and should not be evaluated with one number alone. ASHRAE identifies exterior heat-rejection equipment—such as cooling towers and air-cooled chillers—and emergency or prime power-generating equipment as important sources of community sound around data centers.

The first question is what equipment is making the sound. Cooling fans, chillers, cooling towers, transformers and pumps can operate for long periods, while backup generators may operate intermittently for testing, maintenance or emergencies. A facility using generators for primary or behind-the-meter power can create a different operating pattern from a facility whose engines run only for emergency backup.

The second question is where the sound is measured. ASHRAE notes that community sound limits are commonly expressed at property lines or on the property of a potential complainant. A measurement taken beside a machine therefore answers a different question from a measurement at a neighboring residence.

Timing also matters. Background sound can change substantially between daytime and nighttime, and equipment operating modes can change with weather, computing load, generator testing or emergency conditions. A useful assessment should identify the operating condition and the ambient/background conditions present during measurement.

Finally, sound character matters. ASHRAE's noise-control guidance notes that fans can generate low-frequency sound and distinct tones. Two sources with similar overall A-weighted sound levels can therefore be perceived differently. Where tonal or low-frequency sound is a concern, frequency-band information can add context that a single dBA value does not provide.

There is no universal data-center noise limit that applies everywhere in Ohio. Applicable requirements can depend on local zoning, ordinances, permit conditions and other project-specific rules. The better public question is: What sound is being produced, measured where and when, under what operating condition, and compared with what baseline or applicable limit?