How Dwell-Vent works - Passive stack ventilation
Passive stack ventilation is a usual way of removing moisture from rooms that are particularly prone to condensation such as kitchens and bathrooms. This is because they are rooms that generate both heat and moisture. Conventionally the air that is extracted is in wintertime replaced by fresh air drawn in from outdoors through trickle vents above windows. To work well the metal ductwork from which the passive stack is constructed, has to rise through the height of the building as smoothly as possible without any sharp bends or lengths that are too close to horizontal. The air rises because it is warm, in the same way that smoke rises off a fire, but if the outlet at roof level is correctly designed then wind blowing across the roof can help as well.
Dwell-Vent uses the passive stack principle in a slightly different way. Trickle vents have been widely used for the last 25 years to supply the relatively small amount of air that is required to maintain good air quality in houses during the winter, when conserving heat is also a priority. Air is usually free to both enter and leave the building through the trickle vents according to the direction of the wind. Dwell-Vent is different, it relies on a new design of vent that not only controls the rate of airflow through the 'supply-air windows' but also has a non-return valve that stops air from within the house going backwards into the window. This is because relatively warm room air would result in a mist of condensation forming within the window if it was allowed to come into contact with the cold outer pane of glass.
The passive stack for Dwell-Vent installations is used not only to draw air from the kitchen and bathroom but also to pull air through from the other rooms of the house as well. This gives a much more controlled standard of ventilation, but the sizes of the vents, the size of gaps beneath doors and the design of the passive stack system have to be carefully designed.
The Dwell-Vent design program that can be accessed from this link can tell from some basic information about your locality, and the basic design of your houses or flats, whether they have the basic requisites for Dwell-Vent to work well.