Natural and passive ventilation and cooling
In order to minimise energy demand, natural or ‘passive’ ventilation approaches should be prioritised over mechanical ventilation where possible, since mechanical systems are generally considered to be a mal-adaptation (unless a heat recovery function is included offering energy efficiency and carbon reduction benefits). Effective window design is essential in naturally ventilated buildings and windows should allow ease of control by all potential building occupants, taking account of Building for Life standards. This should be designed into new buildings as early as possible.
Roof window acutator which can be operated
by occupants for ventilation
Source: AECOM
The most effective form of natural ventilation is cross ventilation, where air is able to pass from one side of a building to the other. If this is not possible, such as in deeper plan offices, natural ventilation can be achieved by introducing a central atria and making use of the “passive stack” effect to draw air from the outer perimeter and up through the centre of the building. The use of passive stack ventilation systems can be applied to most buildings, including houses.
Model simulating natural ventilation within a building
Source: AECOM
Buildings with an open stairwell can provide integral passive ventilation. The use of a solar chimney allows moist, warm air to rise and escape from the top of the property and draw in fresh air at the bottom. Earth tubes are another way of tempering air with limited need for mechanical intervention. Earth tubes work by drawing air into a building through tubes buried in the ground, allowing the air to gain or lose energy (depending on the season) with the ground. The system’s success will depend on a suitable temperature difference between outdoor air and the soil temperature at the tube depth. In Hertfordshire this system could potentially temper the ventilation air in winter and pre-cool the air in summer.
Passive stack ventilation at Crawley Fire Station
Source: AECOM