Mixed-mode Ventilation

Within energy assessment, mixed-mode ventilation refers to a hybrid system involving both natural ventilation and mechanical ventilation of the same conditioned a space. Typically, this will consist of operable (opening) windows controlled automatically and interlinked with the mechanical ventilation system. As such, a Building Management System (BMS) is usually present.

This kind of system allows maximum benefit to be made of the external environment for conditioning the building. The mechanical system is only used to effect changes not possible in consideration of the external conditions. In simple terms, the system will automatically open windows if it is cooler outside than in and the building is too hot. The opposite is also true. More complex systems also analyse other characteristics of weather and air quality to determine the more energy efficient manner of achieving the optimal conditions inside the building.

The key to a building being considered to be ventilated using a mixed-mode is the presence of an interlink between the natural ventilation and the mechanical system. A building where both systems are present but not controlled together would be considered to be mechanically ventilated.

Related Terms

Ventilation systems

Extraction systems

Natural ventilation

Mechanical ventilation