The influence of outdoor air vents and airtightness on natural ventilation - calculations based on measurements.

Many modern buildings in the Nordic countries have mechanical ventilation. Passive stack ventilation is, however, an accepted ventilation system in the Nordic countries according to the current building codes. The building authorities need to be able to supply guidelines on natural ventilation systems in modern buildings, in order to fullfill the requirements on a healthy indoor climate at a reasonable energy cost. Therefore a project was initiated by the Nordic committee on building regulations. The aim of the project was to present functional and technical requirements on natural ventilation systems. The paper discusses the influence of outdoor air vents and airtightness on passive stack ventilation for Nordic dwellings. Calculations, based on measurements, were performed for a one storey one-family house, a 1.5-storey one-family house and two apartments in a threestorey building. Cumulative distributions of ventilation rates for a year were calculated, using a multi-zone air flow model, for individual rooms. It is shown that the ventilation rate will vary very much, without any interaction from the occupants or an automatic control system. A modern system for passive stack ventilation must include a system for control of the air flows in order to avoid excessive use of energy and inadequate indoor air quality.