Ventilation is the controlled movement of the air between the inside and the outside of the house.
Ventilation is the controlled movement of the air between the inside and the outside of the house. Adequate fresh air can usually be achieved through the building fabric. Materials that “breathe” such as rammed earth allow for the slow exchange of fresh air through the walls. Rammed earth walls also have the unique ability to control humidity levels to internal spaces.
For airflow to have a cooling effect on our bodies, greater air speed is needed.
Our bodies most effective cooling method is the evaporation of perspiration. High humidity levels reduce evaporation rates. When relative humidity exceeds 60%, our ability to cool is greatly reduced. Evaporation rates are influenced by air movement. Generally, a breeze of 0.5 m per second provides a one-off comfort benefit equivalent to a 3°C temperature reduction.
Where the climate provides cooling breezes, maximising their flow through a home when cooling is required is an essential component of passive solar design. These breezes tend to occur in the late afternoon or early evening when cooling requirements usually peak.
Cool breezes work best in narrow or open plan layouts, but they are less effective in:
- buildings with deep floor plans or individual small rooms
- long periods of high external temperature
- locations with high noise, security risk or poor external air quality, where windows may need to be closed.
Coastal breezes are usually from an onshore direction (south-west in most west coast areas, e.g. the ‘Fremantle Doctor’).
In hilly areas, cool breezes often flow down slopes and valleys in late evening and early morning, as heat radiating to clear night skies cools the land mass and creates cool air currents.
Thermal currents are common in flatter, inland areas, created by daily heating and cooling. They are often of short duration in early morning and evening but with good design can yield worthwhile cooling benefits.
Cool night air is a reliable source of cooling in inland areas where cool breezes are limited and day/night temperature ranges usually exceed 6−8°C. Hot air radiating from a building fabric’s thermal mass is replaced with cooler night air drawn by internal−external temperature differentials rather than breezes. Full height double hung windows are ideal for this purpose. Further cooling can be gained by including ceiling fans or whole of house fans.
The ideal house should be narrow, no deeper than 2 rooms with an open plan layout to allow for good cross ventilation.
Cool breezes work best in narrow or open plan layouts
Openings should be located to receive the prevailing cooling breezes for cross – ventilation. Openings can be at 45 degrees to prevailing breezes and still receive adequate airflow. Openings should be located opposite or diagonally opposite to each other to allow for through ventilation.
Another passive form of ventilation is locating openings at a higher level in the building creating a “stack effect”. This encourages the movement of warm air up and out of the building and drawing cooler air in at the lower level.
Diagram from yourhome.gov.au.