This audio is automatically generated. Please let us know if you have any comments.
According to Kasey Fowler-Finn, a professor of biology at Saint Louis University, the walls of the facility should be 4.5 feet thick to mitigate the kind of low hum that data centers typically make.
Low-frequency noise emitted by large-scale refrigeration and air-conditioning systems in facilities travels further and is more noticeable than the high-frequency noise that many noise ordinances target, Fowler-Finn said in an interview last week.
“The data center is buzzing [are] they focus on unique frequencies and really stand out from the background noise, no matter how loud or how often that background noise is.” Fowler-Finn told Saint Louis Public Radio on Sept. 24.
Data center noise guidance model that Fowler-Finn published last month, based on research she says she’s been conducting since 2001, focuses on the unique wavelengths of low-frequency hum that large HVAC systems typically emit.
“A facility can comply on paper while still providing audible exposure, or, for very low frequencies, inaudible but still physiologically relevant, daytime and nighttime noise exposure related to numerous health problems,” Fowler-Finn says in the guide.
All sound loses its intensity as it spreads out geometrically, he says. It will weaken by 6 decibels every time it doubles its distance from the source, and it will weaken by 30 dB when extended 3,000 feet. It also loses intensity as it is absorbed by structures in its path. But absorption has less of an impact on low-frequency sound because of the longer wavelength, he says.
“Low frequencies … pass through walls and windows with little loss, as normal building materials are, for practical purposes, ineffective at attenuating them,” he says. “Low-frequency sound can also generate secondary noise by inducing vibrations and rattles in nearby structures.”
A 4-inch wall is enough to mitigate a typical high-frequency noise like a vacuum cleaner, which can reach about 1,000 hertz, but to mitigate a low-frequency noise at 63 Hz, which is typical of large-scale HVAC systems, the wall should be 4.5 feet thick, he says. And for noise as low as 20 Hz, it would need to be 14 feet thick, “not a remotely practical thickness for a building enclosure,” he says.
The commonly used A- and C-weighted decibel measurements are sufficient as a starting point for noise testing, but should be combined with what Fowler-Finn calls a third-octave band sound pressure test, which captures sound levels between 20 Hz and 200 Hz.
“Any tonal or narrowband component of the installation noise is independently identifiable [using that testing] rather than averaging over a single broadband number,” he says, “so a facility can’t spend an overall dBC allowance by averaging a single high low-frequency band against several quieter ones.”
In its guidance document, Fowler-Finn calls for setback distances of at least 1,500 feet, well above what is typically required for data centers, which are often allowed based on setback requirements of 100 to 600 feet for industrial buildings. “These setbacks are generally written for normal or broadband industrial noise,” he says.
Half a dozen lawsuits filed this year against operating data centersfive listed noise as the main problem. “This applies to very different jurisdictions,” says Fowler-Finn. Jurisdictions with pending lawsuits include Vineland, New Jersey, Dowagiac, Michigan, North Tonawanda, New York and Hood County, Texas, according to a alert from the Winter Hale law firm.
The results of a survey published in September by Science for Georgia and Quiet Communities found that more than 80% of people with a data center in their area you can hear the noise of the installation inside their home and more than 70% said it interfered with their ability to relax. Almost 70% said they had considered moving because of it.
“Many described avoiding outdoor spaces, experiencing chronic sleep disruption, and feeling unable to escape the constant noise,” the survey report states.
“Instead of fighting to put them where people live and work, [building owners] should work on technology that makes them more environmentally friendly,” Fowler-Finn said.
