Ventilation control within exhaust fan ventilated houses.

Modern one-family houses in Scandinavia are often ventilated by an exhaust fan. Most of the outdoor air probably enters through whatever cracks and openings there are and only a small part enters through the supply vents in many of these houses. The overall supply of outdoor air might be adequate, but some rooms often do not get enough of outdoor air. The constant concentration tracer gas technique was used to examine the supply of outdoor air. Fan pressurization combined with infrared photography were employed to characterize the air leakage of the building. A multi-zone network model was used to further evaluate the measurements. Areasonable level of outdoor air, upstairs in an airtight two-storey house, can be ensured by locating the supply vents upstairs close to the floor. If that is not possible additional exhaust vents can be installed. If more than 3/4 of the outdoor air is to enter through the the supply vents, then the airtightness should be better than 1.0 air changes per hour at 50 Pa. The performance of an exhaust fan system is very much dependant upon the overall airtightness (including open supply vents) and the distribution of the airtightness of the building.