Ventilation and airtightness in energy balance analyses

The air exfiltration part of ventilation is often difficult to determine and its part of the energy balance is therefore usually determined as a remainder or given a constant value. This paper examines ventilation systems in six different modern houses. The constant concentration tracer gas technique tended to underestimate the total ventilation. A simplified theoretical one-zone model made accurate estimations of the air exfiltration. For detailed information on air flows a multi-zone network model was useful. Different levels of airtightness should be required depending upon the ventilation system. It is recommended to couple predictions with tracer gas measurements. Determining the energy balance, e.g. using a constant air change rate for the mechanical and/or natural ventilation is in most cases inaccurate, unless the house is very tight.