Window-opening unreliable for ventilation, study finds

This article was originally published in issue 39 of Passive House Plus magazine. Want immediate access to all back issues and exclusive extra content? Click here to subscribe for as little as €10, or click here to receive the next issue free of charge

The study was carried out by MVHR manufacturer Zehnder and presented at the 2021 International Passive House Conference by Bart Cremers. The four flats formed the ground and first floor of a single block, so weather, outdoor pollution, noise etc were identical for all.

The ground floor flats had whole-house MVHR installed, while the upper floor relied on window opening for ventilation. Monitoring of window opening behaviour showed that over the course of a year, windows were open around the same amount of time during winter in all flats, and slightly more upstairs than downstairs in summer.

However, while air quality in the flats with MVHR was consistently good (only one per cent of the time above 1,000 ppm CO2) the upstairs flats had much poorer air quality. Between 30 and 60 per cent of the time, CO2 levels were over 1,000 ppm