SonicLQ: Reconnecting Acoustics and Airtightness
September 7, 2017
Back in the early days of airport noise mitigation programs, there was a pretty strong link between air leakage and sound. A document titled “Tips for Insulating Your Home Against Aircraft Noise” noted, “Sound travels from the exterior to the interior of the home in two ways: through solid structural elements and through the air…. Wherever air can infiltrate a home, sound can as well.”
In fact, around 1986 — when the price of oil dropped from $32 to $11 a barrel and President Reagan slashed funding for a slew of energy-efficiency programs started by President Carter — it was airport noise and the passage of the Airport Noise and Capacity Act of 1990 that served as a bit of a bridge for programs such as the pioneering Minnesota Energy Office program.
There's an ASTM standard for that
Using sound to track air leakage is not a new idea. An ASTM standard, ASTM E1186 – “Standard Practices for Air Leakage Site Detection in Building Envelopes and Air Barrier Systems,” has longed contained an option (“Generated Sound in Conjunction with Sound Detection”) that uses acoustic information to characterize air leakage.
But note that ASTM E1186 is all about qualifying air leakage in buildings, not quantifying it: ASTM E1186 techniques are only about site detection.
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The new connection: SonicLQ
Building innovatively on the sound detection option within ASTM E1186, researchers at the Argonne National Laboratory have developed SonicLQ, a system that uses sound to locate and size air leaks in building exterior enclosures (the LQ stands for Leak Quantifier). The system can be used to test any building, during construction or after the building is completed or occupied, and during any season of the year. (You don’t need the temperature difference that infrared imaging requires). Acoustic data are presented to the user in a visual format that identifies where air leaks are located on the building façade — as well as the size of specific leaks — so that informed decisions can be made to seal the largest leaks and realize the greatest energy savings while minimizing assessment and diagnostic costs.
Image #1 (above) is a schematic of how the Acoustic Building Infiltration Measurement System (ABIMS) (the approach used by the SonicLQ equipment) works. Image #2 (below) shows the components. Image #3 is a close-up of the microphone array. Image #4 shows how the ABIMS is actually a two-step process.
Essentially, low-frequency sound (about 60 decibels or so, roughly the same as conversation in a restaurant or background music) is generated from the speaker and picked up by the microphone array. The sound data are wirelessly sent to a laptop computer, which translates the data into a “sound” picture, which can be overlaid with a digital one. Testing an office — one measuring about 12 feet by 12 feet — would take 2 to 4 minutes.
“Distant” acoustic measurement identifies target areas of air leakage; these measurements currently cover about 100 square feet of exterior enclosure, but the goal is to increase this significantly. The near-field acoustic measurements assess 3 feet by 3 feet areas of leakage. Summing up the identified and quantified targeted areas of leakage involves simple proportional surface geometry.
Inventor Ralph Muehleisen, principal building scientist at Argonne National Laboratory, adds, “The keys to this technology moving from a lab concept to real-world measurement are the recent advances in near-field acoustic holography (NAH) and the digital micro electrical-mechanical system (MEMS) microphones. The NAH advances have dramatically improved our acoustic capabilities while the MEMS advances have decreased their cost by a factor of ten while making the microphone arrays much lighter weight and more rugged.”
Researchers have applied for a patent
So how would this work on a two- or three-story home or a multifamily building? The microphone array is lightweight enough that a drone can be used to track with the internal speaker location (see Image #5, below.) Will the equipment work? Muehleisen continues, “We have published our patent application, started testing our field prototype, and have funding from the Department of Defense to do comparative field testing of conventional blower door and our ABIMS. We will be ready for pilot projects within the next 9 months.”
The new approach has promise
I decided to check in with Terry Brennan of Camroden Associates on this new technology for air leakage testing. “This is definitely real,” said Terry. “The math holds up. I am not sure that this approach will be a real advantage over existing approaches for new, tight, buildings, but this has real promise.” Brennan has some particular questions regarding how well SonicLQ will do with complex, circuitous air leaks — for example, air leaks through wall assemblies that include steel studs with fiberglass insulation, gypsum sheathing, and brick veneer (leaks that sometimes extend past the top of wall into a soffit or coping). He also says that the SonicLQ might do better than existing depressurization techniques for features such as trash chutes.
Brennan is also very interested in the Department of Defense comparative testing project, emphasizing how important it will be to have experienced blower door experts working with SonicLQ on the testing.
Brennan also had the following insight: “The test standard I recommend is the ABAA Standard Method for Building Enclosure Airtightness Compliance Testing. I recommend it for the following reasons:
- It was developed to be used to determine whether or not a building meets an airtightness target, including methods for determining how to interpret the results and calculated uncertainty.
- It contains requirements for building setup that includes handling things found in large buildings (e.g. elevator shafts, linen and rubbish chutes, laundries, fire egress stairwells, isolated boiler rooms with makeup air, mechanical rooms with entrances to outside and inside.
- It allows the use of E779 (multipoint shell pressure regression analysis) and E1827 (single and two point repeated reference pressure tests)
- It was developed by an ABAA committee that included testing agencies, envelope consultants, air barrier systems manufacturers, architects, engineers, test and balance contractors, and the manufacturers of blower door testing equipment over the course of three years, including two rounds of voting and two rounds of external review.
- The ABAA board of directors voted to accept and publish the standard.
I’d like to get word out about this standard, as I believe it is the best one to reference for conducting large building tests.”
NOTE from Brennan: “The only caveat regarding this ABAA standard is it’s hard to find the right place to click on the ABAA whole building test page. While you might think it should be in the list of standards in the list at the top of the page, it’s not. It’s at the end of the paragraph below that is headed ‘ABAA – Standard Method,’ where it says, ‘For a copy of this standard, click here.’”
What about long tortuous leak paths?
Gary Nelson is president and founder of The Energy Conservatory, one of the oldest companies building blower door systems. Nelson is not so sure about SonicLQ. Nelson said, “Sonic leak detection has been around for a long time and sometimes is very useful. But [it does not] work for all types of leaks, especially long tortuous paths, sometimes going through or around sound absorbing insulation. I’m very skeptical that it will ever be able to measure the same leakage that a blower door does on a whole building. Blower door testing big tight buildings can be pretty easy.”
I will keep you posted as SonicLQ is put through its paces in the field in the upcoming year.