Of the various parameters deciding the air change in a building, the influence of wind and the stack effect have in particular been focused on. Concurrently, with the increase in quality of buildings and the tightening of existing buildings, the influence of the climatic parameters is reduced, and other parameters gain a greater influence on the air change. One of the parameters having a great influence on the air change in tight buildings are the users. The air change rate is greatly influenced by the users not only in naturally ventilated buildings, but also in mechanically ventilated buildings.
On the basis of continuous measurement of the air change in 28 dwellings, the proportion between the total air change (air change in house with occupants) and the basic air change (air change in a sealed house) is discussed. The air change in each of the dwellings has been measured for a period of about one week during occupancy. The measuring principle applied is the method with constant concentration of tracer gas. The measuring equipment utilized is computerized and capable of measuring in up to ten separate rooms for periods of more than one week without supervision.
The main conclusion of the measurement was that, even though the average air change rate for occupied dwellings is higher than 0.5 times/h (which is normally recommended in Denmark), some 20% of the dwellings have an air change rate so low that indoor climate problems may easily arise. Only a small percentage of the dwellings have ventilation systems that can be adjusted to provide the recommended rate of air change. The mechanical ventilation system usually gives too high a rate of air change, while the natural ventilation system usually provides too low a rate.