Performance of decentralised mechanical extract ventilation in airtight homes

The main aim of this research was to establish if new-build dwellings fitted with dMEV systems in moisture producing rooms, coupled with a reduced area of trickle ventilation in habitable rooms of 2,500m2, can maintain satisfactory ventilation in a real-life context. The study undertook a survey of 231 homes to ask occupants about their knowledge and operation of their ventilation system, and a subset of these (41 homes) were monitored to examine the actual ventilation performance and determine the factors that affect this. A further study was undertaken in a selected dwelling to experiment with different ventilation strategies using dMEV to identify key factors. The monitoring found over 50% of homes were poorly ventilated overnight and that bedrooms were a particular cause for concern. There were several variables that affected this. These included the nature of the trickle vents, the window coverings, the path between the room and the dMEV and the installation and performance of the system. Essentially homes with shorter, more open paths for air movement performed better, but rooms which relied on more remote dMEV systems frequently had poor ventilation. The findings suggest that whilst there are some situations where a dMEV system can assist with the ventilation provision of modern airtight homes, the ability to act as a whole house system is limited, particularly in larger more complex layouts, and where ventilation loads are high.