English

 The trend towards natural ventilation and low energy cooling systems is affecting the ways in which engineers design and operate heating systems in low energy buildings             

A new mechanical ventilation system which continuously controlled the indoor-outdoor pressure difference was installed in six houses, where the long-term radon levels ranged from 670 to 3 080 Bq/m³. When the new system had operated for several months, the indoor radon levels decreased to levels from 120 to 600 Bq/m³ , the effective dose reductions being from 40 % to 88 %.

In most cities, vehicles are the main sources of pollutants. The concentration of pollutants is then known to vary with traffic intensity. Ventilation flows should be adjusted accordingly, which would give improved air quality, especially in dwellings.

The indoor-outdoor comparison of volatile organic compounds was made in 52 private homes in the City of Munich, Germany. The VOC concentrations were measured by trapping with activated charcoal tubes and analyzed by capillary GC. The infiltrated NO, was monitored in the indoor air. It can be concluded that the benzene concentration in the indoor air is controlled by the outdoor concentration for approximatively 30 % of the investigated cases.                

ASHRAE's definition of acceptable indoor air quality demands air in which there are no known contaminants at harmful concentrations and air with which a substantial majority (usually 80 %) of the people exposed do not express dissatisfaction. Investigations on indoor air pollutants and emission sources are the scientific way to a good indoor air quality tomorrow. To guarantee pleasant and healthy breathing indoors today the control of IAQ is necessary. Demand ventilation control by unspecific sensors is one possible way there.