The effectiveness of mechanical exhaust ventilation in dwellings

Ventilation systems play an important role in providing a good indoor air quality in dwellings. Mechanical exhaust ventilation systems implement natural vents to supply outdoor air to the dwelling. Natural driving forces, i.e. wind and thermal draught, influence the flow rates through these supply vents. Therefore, the flow rates depend on the weather conditions and vary in time. This study considers the influence of the wind and thermal draught on the operation of a mechanical exhaust ventilation system in a reference dwelling. Furthermore, the influence of the sizing of the natural vents and the airtightness of the dwelling envelope are taken into account. This paper covers a simulation study investigating the effects of wind, thermal draught, the sizing of the natural vents and the building airtightness on the flow rates in the dwelling by using multizone airflow and contaminant transport calculation software (Contam). Wind and thermal draught create a spread on the supply flow rates. Therefore, the flow rates through the vents are not always as designed. The airtightness also influences the flow rate through the vents. Both effects (wind/thermal draught and airtightness) depend largely on the sizing of the natural vents.