Did You Ever Wonder: Mark Modera Did You Ever Wonder Web Site Michael Siminovitch
Slowing the flow

Leaks in a home's supply ducts cause uneven air delivery and blow heated or cooled air into attics or crawl spaces, where it is lost to the outside. Leaks in a return duct pull in outside air, so the system has to work extra hard; return leaks can suck in chemical fumes, exhaust, or other pollutants.

The best way to seal most leaks is with an aerosol system developed by Berkeley Lab's Indoor Environment Department. After registers are sealed so that air can escape only through leaks, microscopic polymer particles are injected into the ducts. These stay airborne until forced to exit at a leak.

"It's like driving your car fast, which is fine on the freeway, but if you turn too sharply you skid out," Modera explains. "The air flow has to turn a sharp corner at a leak, and the particles skid out and smash against the edges."

An infrared image, courtesy of Sierra Pacific, reveals hot air leaking from the attic.










The sealant builds up and closes leaks in ducts made of metal, plastic, or any other material, sealing all gaps up to a quarter inch wide within 15 minutes. Ducts sealed this way show no leakage after four years of high pressures and constantly cycling temperatures. Under the same conditions, duct tape typically fails within three days!

Modera founded Aeroseal, Inc., to commercialize the technology. The Aeroseal company supplies equipment — including laptop computers to run diagnostic and monitoring programs — and trains and licenses contractors across the country. If a duct system needs sealing, the cost can be recouped in energy savings in one to three years.

The technology was named one of Popular Science magazine's "Best of What's New," consumers voted it one of the best products to come out of the Department of Energy, and a panel of experts chose it as one of the 100 best innovations in DOE's first quarter century.

  • More about Aeroseal, Inc., and aerosol-based duct sealing
Sealing off Commercial Waste

Commercial buildings use over a third of the electricity and almost a fifth of the natural gas consumed in California. In commercial buildings, more people use more lighting and equipment; space for space, energy waste in commercial buildings can be double that of residences.

Berkeley Lab researchers have studied energy loss in the ventilating systems of light commercial buildings such as shops and libraries and in large commercial buildings like office towers as well.

Light commercial buildings are typically only one or two stories high and use the same materials and construction techniques as homes. Their heating, ventilation, and air conditioning (HVAC) systems are rarely custom designed; instead an HVAC "package" is installed on the roof — which usually consumes more power than is needed.

Ducts are usually inside, but many of them run through ceiling spaces where leakage causes the same kind of loss as home attics. In large commercial buildings, leaks lead to huge increases in the electricity needed to power fans and blowers.

In addition to using the right size of HVAC unit, and heating or cooling only the needed volume of air, the best way to save energy in commercial buildings is to fix leaking ducts. Aerosol sealant is the most effective, but duct systems in commercial buildings are more extensive and more complicated than in the typical home and need special techniques. Rather than one big injector for the whole system, for example, a compact particle injector used for various segments works better in large commercial buildings.

  • More about heating and cooling commercial buildings

  • More about Mark Modera and his aerosol sealing system

Did You Ever Wonder Web Site
Ernest Orlando Lawrence Berkeley National Laboratory