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Natural Ventilation  »  Mixed-mode ventilation

• Overview
• Description
• Impacts
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Technique

Mixed-mode ventilation strategy combines both natural and mechanical ventilation. The heating, cooling and ventilation systems are designed in such a way that to allow for natural ventilation when the ambient weather conditions are suitable. The control strategies to enable mixed mode strategies such as window opening etc. can be both automated or individually controlled by the occupants. Mixed-mode ventilation occurs in one of the three following types (WHO, 2009):

• Fan assisted stack ventilation
• Top-down or balanced ventilation
• Buried pipes

Implementation

They are suitable for most climates and weather as more controlled and comfortable environment are achieved by the assistance of mechanical ventilation during extreme weather conditions.

Improvements

The installation of exhaust fans require an extra care, especially for large fans, otherwise the performance might be lower. Noise, particularly from high-power fans and air flows, from neighbouring room or corridor) is also required to be minimised. If the air flow is not as desired, the room temperature might increase or decrease, which allow use of more mechanical ventilation and require extra energy cost for cooling and heating (WHO, 2009). The use of sensors for measuring indoor temperature, CO₂ level, air speed, as well as the use of weather station for outdoor temperature, wind speed, solar radiation and precipitation optimise the installation of mixed-mode ventilation and improve air quality (Hybrid Ventilation Centre, 2002).