Natural Ventilation Design Guidelines

Geometry of space

Good room height – at least 2.5m/8.2ft. and preferably 2.7m/8.9ft. or more. Single sided ventilation – the room depth should not exceed 2.5 times the room height, and never more than 10m/33ft. Cross ventilation - the room depth should not exceed 5 times the room height. Stack ventilation – the distance from the facade to the rooflights should not exceed 5 times the room height.

Window opening

Highly placed openings/windows in the facade - preferably 2m/6.5ft or more above floor level and with sufficient clearance between the top of vent and ceiling for inward opening vents so as not to limit the achievable opening area. Bottom hung inward windows or top hung outward openings in the facade. Window height, facade: Approximately 400-600mm/15.7 - 23.6in. A window width of approximately 1.2-1.4m/3.9 - 4.6ft. is often optimal, since often you need two window actuators if the width exceeds 1.2-1.4m/3.9 - 4.6ft. (subject to window profile material and type, due to frame flex with single pull point). Openings evenly distributed. Bottom hung inward windows or top hung outward openings in the facade.

Other natural ventilation guidelines

Optimised Natural night cooling.
Preferably include thermal mass for optimum benefit of night cooling.
User control e.g. timed override facility by local keypads.
Preference for cross ventilation, stack ventilation or hybrid ventilation in high occupancy spaces e.g. in classrooms.
Preferably a minimum 7m³ per person in e.g. classrooms.
Maximum air changes:

Winter: Approximately 2.5 - 3 h-1 (average during occupied hours).

Summer: Workstations: 4 - 6 h-1 can easily be accepted.

Atriums and similar transient spaces where people stay for shorter periods: 10 – 15 h-1 can be accepted.

Specifically for supplementary mechanical exhaust

In most cases the capacity of the exhaust should be at least the minimum required air change.
The exhaust should be controllable by variable speed.

Project References

City of Glasgow Colleges - an engaging and energizing building

City of Glasgow Colleges took a definitive commitment to the environment by embracing several sustainable design strategies such as automated natural ventilation. To reduce heat loads and maintain air quality, the atrium acts as a natural stack to drive cross ventilation through the building.
See the full case
HouseZero on Harvard University's campus raises the bar for energy efficiency

HouseZero of Harvard University was renovated to inspire others by how older, existing structures can be altered to become ultra-efficient facilities. The older indoor climate systems were fully replaced with a new indoor climate paradigm which relies on the addition of thermal mass and radiant surfaces.
See more
UCL Student Centre at Gordon Street - a BREEAM building with a holistic IAQ approach

The new Student Centre of the University College London is a flagship for sustainable development in the urban environment. UCL’s strategy was to focus on a “passive first” approach to the indoor climate to reduce energy use and thereby carbon emissions.
Learn more
MECD - fresh learning spaces in Manchester

MECD is Manchester University’s brand-new Engineering Campus. Intelligent actuator technology was key to providing the best indoor climate possible via fresh air ventilation. MotorLink® communication technology was chosen because it ensures seamless integration between the BMS and window automation.
Read the case
Intelligent automation at Augusta University Cancer Research Center

Augusta University Cancer Research Center chose WindowMaster actuators and MotorControllers as part of the building’s heat and smoke management strategy. The actuators and controllers are enabled with MotorLink® so that they can communicate directly with the building management systems about their position and status.
Read more