Natural Ventilation: Permeable Buildings

Cross ventilation relies on wind for cooling. When wind blows on a building, a pressure difference is created between the windward (wind-facing) and leeward walls. Openings (i.e. windows) placed on opposite sides of a building will allow the cooler external air to enter the building while warmer internal air is sucked out from the leeward side openings.

The new Environmental Building at Garston has been built as a demonstration building for the Energy Efficient Office of the Future (EoF). A key part of this specification is the need to reduce energy consumption and CO2 emissions by 30% from current best practice.

The degree of passive cooling is determined by the size and placement of the building and ventilation openings, as well as the regularity of wind. As a result, while cross ventilation can provide effective cooling, it can also be unreliable when naturally occurring wind is not available. As a result, larger buildings will typically require mechanical ventilation systems or passive stack ventilation in order to ensure ventilation continues in the winter and when wind is unavailable.

For cross ventilation to be effective, the building must be in a location with regular summer winds. The windward wall should ideally be oriented to be perpendicular to typical summer wind; perpendicular orientation may not always be possible in existing buildings. The building itself should ideally be relatively narrow to ensure fresh air is distributed throughout the building.

The Research Office Building in Garston, UK has an open plan allow natural ventilation. Building suing this strategy are called permeable buildings.

The Research Office Building has an open plan allow natural ventilation. Buildings using this strategy are called permeable buildings.

Extensive internal partitions will inhibit air flow and render cross ventilation impractical. Assuming a building’s location and orientation allow for cross ventilation, operable windows/openings are required to ensure effective ventilation. Given the extensive building conditions required, it is typically more practical to design a new building for cross ventilation rather than retrofit an existing building. However, if the building conditions are met, retrofitting for cross ventilation can be a cost-effective, energy efficient passive cooling strategy.

Benefits:
•Allows for building cooling and ventilation with minimal maintenance and no operating costs.
•Particularly for new buildings, cross ventilation can be built into the building design at minimal cost.
•Cross ventilation is fully passive and requires no energy.
Cross ventilation can be combined with active mechanical ventilation or passive stack ventilation to minimize building energy costs while ensuring more regular ventilation and cooling.

Drawbacks:
•Must be combined with another form of ventilation (e.g. mechanical or stack) in order to ensure ventilation continues when wind is unavailable and in cold months when windows will be shut.
•Building occupants may shut operable windows (due to comfort, noise, etc.), reducing the effectiveness of cross ventilation.
•Cross ventilation cannot reduce indoor temperature significantly below outdoor temperature. •As a result, in extreme heat events, air conditioning will still be required to keep indoor air temperature at comfortable levels.
•Open windows in urban environments can increase exposure to external noise.

 

 

 

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