Fairbanks engineer is named inventor on patent for ventilator frost-control add-on

The U.S. Patent and Trademark Office on Tuesday granted Fairbanks inventor Conor J. Dennehy Sosebee a patent for an add-on module that preheats outside air only as much as needed to keep energy recovery ventilators from frosting. These ventilators trade heat between outgoing and incoming air through a core.

According to the patent, most systems handle frost by defrosting, which stops fresh outside air from coming in while parts warm back up. Others run a fixed-output preheater, which the patent says is associated with "a large energy penalty," especially in extreme cold where utility costs are high. At very low temperatures, the patent says, a ventilator may spend most of its time switched off trying to defrost.

The patented design uses a feedback loop instead. Sensors read incoming and outgoing air, and a controller calculates the dew point, the temperature at which air becomes saturated. Below freezing, that is the point where frost forms. The controller then sets an electric or liquid-filled heating coil to the minimum output needed to keep outgoing air above that point. The patent says this could let a ventilator spend more time bringing in fresh air in deep cold, which may improve indoor air quality.

The patent reports no test results and does not say a device has been built. It was filed in April 2024, a year after a provisional application.

"Energy recovery ventilators, or ERVs, use the core to exchange both moisture and heat," Dennehy, a research engineer at the National Laboratory of the Rockies Alaska Campus, and three co-authors wrote in a 2021 conference poster. A 2023 paper he co-wrote on a ventilator with fixed preheating at a Fairbanks facility found that adjusting the coil's output would reduce the energy needed to preheat the air.

The patent is assigned to Alliance for Energy Innovation LLC of Golden, Colorado, which manages the lab for the U.S. Department of Energy. The invention was made with Energy Department support, and the government has certain rights in it. The patent says the device is not limited to any one climate.