Natural Ventilation
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Contents
What is It?
Natural ventilation is an ancient technique of cooling and ventilating buildings. It relies on a combination of buoyancy (hot air rising or the stack effect), and wind (cross ventilation) to allow fresh air to flow in the building. Natural ventilation can be used anytime the outdoor weather conditions are approaching the human comfort zone.
Why is it Important?
- Strengthens our relationship to the earth...all are connected to the fresh air from outside.
- Keeps the building comfortable.
- Reduces energy use from fans and cooling equipment.
When to Use It?
- Buoyancy or "stack effect" ventilation can be used anytime that warm air is allowed to escape the building through the roof or a high window.
- Wind or cross ventilation can be used whenever outdoor conditions are favorable (wind is blowing, comfortable temperature and humidity).
- Reduces energy use by moderating indoor conditions without using any fuel or power.
- Should not be used when it's raining or very cold or hot or humid outside.
- Should be used with caution if there is a risk of bringing in dust or air pollution.
- Should be used with caution if security is an issue.
- Should be used with caution in noisy places.
Green Garage Use of Natural Ventilation
Sustainability Goals
- Promote a strong connection to the outdoors.
- Allow for passive cooling and ventilation when outdoor conditions are right.
- Allow building users control over their environment and energy use.
Strategy and Conceptual Design
Cross Ventilation
- Allow the cooler air to enter the building through operable windows on the windward walls.
- Allow the warmer indoor air to escape through the leeward wall.
- Casement windows can be used as fins to guide the wind into the building when it is coming in at an angle to the window.
- Outdoor plantings of trees and shrubs can also be used to guide the wind.
Stack Ventilation
- Allow the cooler air to enter the building through low operable windows or vents.
- Allow the warmer indoor air to escape through windows or vents high in the wall or in the roof.
- It's also possible to build a stack that will induce more airflow by designing it to be heated by the sun, which increases the buoyant effect.
- Wind cowls may also be used to enhance the airflow by creating a pressure difference. The cowl positions itself with changes in wind direction so that it creates a negative pressure at the top of the stack, which in turn causes more airflow from below.
Hybrid Cross-Stack Ventilation
- It is generally more reasonable to combine cross and stack ventilation into a hybrid system to take advantage of both strategies.
- Cool air enters through low windward openings and warm air exits through high leeward openings or stacks.
- Placement of the inlets and outlets will determine the distribution path.
Notes
- Natural ventilation in general works better with more openings; however more openings impact the heating and cooling loads and the appearance of the building. Through integrated design, all of these competing features are optimized.
- The operable windows are mostly for fresh air access and connection to the outdoors.
- The Earth Tubes will be the primary means of supplying ventilation air when conditions are not favorable for natural ventilation. (That is because a certain amount of outside air must be supplied during occupied hours.)
- Natural ventilation also provides the opportunity to implement night purging. Night purging is a strategy to cool out whatever built-up heat has accumulated during the day and pre-cool the building for the next day.
Supporting science:
- Using natural ventilation can save 10-30% on overall energy use and up to 65% of cooling energy use.
- Using Detroit's climate and weather data, we estimate we can use natural ventilation when it's not raining, hot, or humid from April 15-October 15.
Proposed Materials / Suppliers
Development Story
The Natural Ventilation - Development Story page contains many images and videos documenting the process used at the Green Garage to design, build and operate our natural ventilation system.
