Nobody wants to live in a drafty house, yet checking for substantial air leaks within a home can be a complex process. Scientists have now devised what could be a much easier method of doing so, utilizing a technique that dates back to 1864.
Currently, the modern “blower door test” is one of the most commonly used methods of assessing a home’s airtightness.
This involves mounting a fan in an exterior doorway of the house, then utilizing that fan to draw air out of the building. Doing so lowers the air pressure inside the home, causing the higher-pressure outdoor air to rapidly flow in wherever it can. That boosted airflow is detected using either an infrared camera or a nontoxic smoke-producing device known as a smoke pencil.
Seeking a simpler and less invasive alternative, scientists at the US Department of Energy’s Oak Ridge National Laboratory (ORNL) looked to a 159-year-old technique called schlieren photography. While the exact means by which it works is pretty complicated, it’s a process in which fluid flow – which is invisible to the human eye – can be photographed.
The particular type of schlieren photography utilized in the ORNL system uses tiny shifts in the background of a series of images to visualize leaking air that has a different temperature than the surrounding air. Via the output of an ordinary video camera, those shifts can be seen as a shimmering pattern, much like the mirages seen above hot asphalt roads.
The setup has been successfully tested on assemblages of bricks, concrete masonry blocks and vinyl siding – under sunny and cloudy lighting conditions – in which a ceramic heater blew warm air through a small crack in the material. For now, the system requires an air temperature difference of 12 to 15 ºC (22 to 27 ºF), but lead scientist Philip Boudreaux hopes to get that figure down to 5 ºC (9 ºF).
“We know that a background-oriented schlieren approach for visualizing leakage is reliable at certain temperatures, and it’s showing promise now for quantifying, too,” he said. “We’re going to continue measuring the air flow but the results so far are overall favorable.”
You can see the visualized air flow in the video below.
Background-oriented schlieren optical technique visualization
Source: Oak Ridge National Laboratory