017. Ventilation in air-tight buildings

The air-tightness of buildings is great from the energy loss point of view but there are serious negative consequences on the indoor air quaiity that must be mitigated. Our personal experience in the conventional 1980s built apartment we currently occupy is that during the winter (i.e. the heating period when we normally have the windows closed) we get the best result by opening all the windows for about 5 minutes, usually twice a day. 'Best result' in terms of our own perceptions of things like humidity and staleness: we haven't done any tests to monitor the actual air quality and things like VOC[1] build-up. A little guide which came with our apartment suggests that we air out the place 'several' times a day, an expectation which we find a tad ridiculous. Not only is this impractical from a scheduling point of view, it also results in the loss of a heat energy through the replacement of the warm indoor air with the cold outside air. While this used to be an acceptable form of ventilation for Minergie homes, as of 2009 mechanical means of ventilation are required.

There are six different standard solutions to choose from and we are probably going to install what's called Komfortlüftung mit Wärmerückgewinnung (comfort ventilation with heat recovery), illustrated in Figure 10. I should mention here that the list also includes an automated window ventilation system, in which the windows are opened and closed by computerized motors and which does not incorporate heat recovery.

Figure 10. Schematic of a ventilation system which incorporates a heat recovery system.

Some people here have an aversion to centralized ventilation systems as they expect them to cause draughts throughout the house and harbor mold and bacteria in the ducts. The first issue is an easy one to address as the rates of flow in a properly dimensioned system are too low to be noticed and this is easily experienced by spending a couple of hours in a house with such an installation. The second one isn't quite so easily answered and one has to convince oneself that a duct system built and maintained to the current recommendations will provide good air quality. More about all this in the next post.

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[1] About volative organic compounds at the Minnesota Department of Health → VOCs in your home