Cross ventilation occurs when openings in a building are deliberately arranged on opposite or adjacent walls to encourage air to enter and exit, bringing in fresh air as well as managing interior temperatures. Designing natural circular airflow through a home brings multiple benefits:
- Helping to moderate internal temperatures
- Helping to moderate internal humidity
- Replenishing oxygen levels
- Reducing the accumulation of moisture, odour, bacteria, dust, carbon dioxide, smoke, and other contaminants that can build up during occupied periods
- Creating air movement, which improves the health and comfort of the homeowners
Some fenestrations such as casements and awnings provide full openings (100% of the available space), unlike horizontal or vertical sliders (only 50%). The difference is sufficient to directly influence the direction of the winds (vertical, horizontal, or inclined) and the percentage of movement of the air mass. Full openings provide abundant ventilation and, simultaneously, allow for thermal equilibrium through active airflow and constant air change. This is passive ventilation in action.
Induced Natural Ventilation
Induced natural ventilation refers to fenestration designed and arranged to conduct air cooling. Also called buoyancy-driven stack ventilation, the basic principle is that warm air is lighter than cold air, so as the warm air goes up, the cold air goes down. In this ventilation system, venting openings are positioned close to the ground, so the cold air enters the space and pushes the mass of warm air up, where air outlets are positioned at ceiling level, such as operable clerestory, which then completes the circle of flow. Taller structures generate more powerful induced ventilation than flatter designs.
To help this airflow, floor level awnings can be manually operated, while high clerestory windows can be pole operated or motorized depending on the height from the finished floor. With motorized options, it’s increasingly common to design the window with a valance that conceals the motors and preserves sightline continuity. Wrapping the motor in sound abatement material helps maintain tranquility, which is particularly important if there are multiple motorized sashes. If a screen is incorporated and a valance is not an option, the bottom rail height of the screen sash can be increased to conceal the motor.
While motors and their associated power needs may seem to contradict the concerns for sustainability, this is certainly offset by the ability to activate a building’s natural ventilation capabilities at the push of a button.
Once the air flow enters the building, the interior design comes into play. Partial walls, sills, panels (solid or perforated), and furniture can also directly influence the direction, level, and speed of ventilation. Designing the fenestration and interior components into a coordinated flight plan for air flow offers the optimal results.
Passive ventilation within a building is an essential component of architectural sustainability. Accordingly, the design of the fenestration is one of the chief means by which effective airflow is achieved, boosting health benefits, reducing energy consumption, and minimizing the carbon footprint. This article has outlined how architects have continued to engage these realities in creative, functional, and sustainable ways.