What is an ERV and how do they work in cold climates?
Energy Recovery Ventilators, or ERVs, are the humidity-loving cousins of Heat Recovery Ventilators, which have become a common ventilation technique in cold-climate homes. Like HRVs, they provide balanced ventilation by exhausting stale air and bringing fresh air into a building. In the process, they harvest heat from the outgoing air and transfer it to the incoming air to save energy and reduce cold drafts in the home. Unlike HRVs, however, ERVs can also transfer moisture to the supply air, which helps maintain higher indoor humidity levels in an uncomfortably dry climate like Fairbanks.
In the U.S., most ERVs contain a central core that facilitates heat and moisture exchange: incoming and outgoing air streams pass through adjacent channels separated by membranes, transferring moisture from one air stream to the other while preventing them from mixing. Heat is also transferred across the membrane surfaces. The core is also surrounded by filters, which must be cleaned every few months, to prevent dust and pollutants from getting into the ERV and the home.
While ERVs are used in warmer climates to get rid of excess humidity, in cold climates they help to boost humidity levels in the home. In testing at CCHRC, they were able to maintain humidity levels between 30-40%, a happy balance which prevents residents’ skin and sinuses from getting too dry while also deterring mold growth or mildew in homes. For comparison, average winter humidity levels in Fairbanks are closer to 10-20%.
There are a few extra considerations to operating an ERV in a cold climate. In the winter, frost protection is necessary to prevent moisture in the core from freezing in low temperatures, which can cause problems like blocked air flow and decreased heat transfer. Some ERVs address this by pre-heating supply air, recirculating indoor air for a short time, or having cold supply air bypass the core so as not to freeze it. Also, it is important with any ventilation system to regularly check outdoor ducts to ensure they are not blocked by snow or frost.