019. A simple ventilation plan

This post follows from an earlier one in which I mentioned the Komfortlüftung mit Wärmerückgewinnung (comfort ventilation with heat recovery) system. The primary consideration for the indoor air quality in terms of designing a ventilation system is the amount of CO₂ in the air. On average, a person produces between 30 and 40 grams of CO₂ per hour. According to current Swiss building code, the concentration of this gas should not exceed 1000 ppm.

Figure 12. A simple ventilation scheme for a residential unit.

A schematic of the ventilation plan is depicted in figure 12 above. There are two parts, the supply and the exhaust and there's a heat exchanger (a topic for several other posts, no doubt) through which upto 90% of the heat of the stale air can be transferred to the fresh air. There's no physical mixing of the gases and an optional filtering system can remove pollen and dust from the incoming air. Odors though are another matter. The exhaust vents are installed in the kitchen and the bathrooms so that the air from these areas isn't dragged through the house. Fresh air is let into the living areas and the bedrooms. The system is configured to operate continuously during the heating period with an option to also run during the summer. People who live in noisy areas, such as near heavily used streets, can choose to run the system during the summer as well so that they can keep out the noise.

Based on the limit on the CO₂ concentration in the air, the recommendation is for an hourly intake of 22 m³ to 36 m³ of fresh air per occupant. A different method of calculating the intake that is independent of the number of occupants is to assign an hourly replacement rate of 30 m³ per room, except for bathrooms and kitchens which are designed to have a higher rate with a minimum of 40 m³ per hour. The sums of the supply and the exhaust must equal each other so that there's no pressure difference between the inside and the outside of the house, and so the higher rate of the two is chosen. This is best explained with an example: Consider a unit with 3 bedrooms and a combined living/dining room which is counted as 1.5 rooms, so a total of 4.5 rooms → 135 m³/h of fresh air coming into the unit. If there are 2 bathrooms and a kitchen then the exhausts from those add up to 120 m³/h. In order to not create a pressure difference between the house and the outside, the exhausts should be raised from the prescribed 40 m³/h to 45 m³/h per room.

I haven't mentioned anything about humidity in this post, though I have mentioned in the previous post that too much of it is a serious problem during the heating months in our current apartment where we must manually ventilate to avoid problems such as mildew associated with high humidity and cold surfaces on which condensation can occur. With the ventilation set-up described in this post, the usual result is that the air is too dry in the winter. Plants can help and there are certain types of heat exchangers that also recover some of the humidity from the outgoing air. Humidifiers are not recommended due to issues of hygiene and the additional energy usage.

Exactly how the system is going to be for our house is not yet defined.

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Much of the information here is based on that at the following site → Luftwechsel: Die Platform für Wohnungslüfter