Fairbanks engineer patents a way to keep ventilators from frosting in deep cold

A Fairbanks engineer received a U.S. patent on Tuesday for a device meant to keep a type of building ventilator from frosting up in extreme cold.

The ventilators, called energy recovery ventilators, swap stale indoor air for fresh outside air. As the two streams pass each other inside a core, heat and moisture move from the outgoing air to the incoming air, so less heat is lost.

In deep cold, that moisture can freeze inside the core. According to the patent, most systems deal with it by pausing to defrost, which cuts off fresh air while the parts warm back up. At very low temperatures, a ventilator may spend most of its time off, defrosting.

Others warm the incoming air with a heater that runs at a fixed level. The patent says that comes with "a large energy penalty," especially in extreme cold, where power bills are high.

The invention, from Conor J. Dennehy Sosebee, adds a heater that warms the air only as much as needed. Sensors measure the air coming in and going out, and a controller works out the temperature at which frost would start to form. It then runs the heating coil at the lowest setting that keeps the outgoing air above that point.

The patent says that could let a ventilator spend more of its time bringing in fresh air in deep cold, which may improve indoor air quality.

The patent doesn't report test results or say whether a device has been built.

Dennehy is a research engineer at the National Laboratory of the Rockies' Alaska campus. A 2023 study he co-wrote, looking at a ventilator with a fixed preheater at a Fairbanks building, found that adjusting the heater's output would cut the energy needed to warm the air.

The patent belongs to the company that runs the lab for the U.S. Department of Energy. The invention was made with Energy Department support, so the government has certain rights to it.