ERVs Safe for IAQ

This has been a concern in the case of energy recovery wheels, the primary component in energy recovery ventilation systems (ERVs). These wheels conduct water vapor between a home's supply air and its exhaust air, drying the incoming air so that the air needs less heating or cooling. What if the wheels also transfer contaminants from the exhaust airstream into the supply airstream, concentrating them in the home?

According to researchers at the University of Alabama, the wheels are safe. Their study examined the concentrations of five common pollutants--ammonia, CO₂, propane, sulfur hexafloride, and m-xylene--in two sizes of absorber wheels, and found only trace amounts in every case but that of ammonia. The wheels absorbed water vapor at much higher levels than the contaminants, leaving little room within their pores for other molecules. The wheel with small pores absorbed ammonia at a high level--up to 400 parts per million (ppm) from an exhaust airstream containing 500 ppm ammonia at 50% relative humidity). However, the study points out that ammonia is typically detectable by the human nose at 50 ppm and is thus unlikely to go unnoticed at high levels for very long in any house.

-- Colleen Turrell  

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