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 Green
Building
Requirements
Guidelines
 Introduction
Siting
and Form
Siting
& Form Introduction
Req'd/Suggested
Practices Runoff
Mitigation Plan
Daylight/Views/Cooling
Solar
Cooling Loads
Solar
Heat in Winter
Prevailing Winds
 Buoyancy
Airflow
Solar
Energy Collection
Landscape
Transportation
Envelope
and Space Planning
Materials
Water
Systems
Electrical
Systems
HVAC
Systems
Control
Systems
Construction
Management
Commissioning
Appendices
Case Studies
Additional Resources
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Map
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Induce Buoyancy
Airflow Into & Out of Interior Spaces
Pressure differences
due to buoyancy are directly proportional to both height and the temperature
difference between incoming and outgoing air. As a result, there are two
ways to increase buoyancy-driven flow: increasing the height of spaces,
and heating air within the building. Buoyancy,
or “stack effect,” can induce natural cooling and ventilation
within a building, though typically it creates lower pressure differences
than wind. Columns of warm air rise, and if allowed to exit from the top
of a space, will draw air in at lower levels. Stack ventilation is especially
useful for deep core spaces, spaces with only one exposed side, and with
atria and courtyard designs.
In general, natural
cooling should be examined on a whole-building basis to ensure airflow
paths into, through and out of occupied zones and spaces, and to ensure
safety in the event of fire. Room-by-room analysis is helpful when placing
windows and openings, and to help place interior partitions.
- Use roof monitors,
atria or tall chimneys to increase stack height, and thus buoyancy
pressure differences. These features can be placed at the center of
a building, creating cross-flows from the sides of the building; or
at one end of the building, creating cross-flow from one side to the
other.
- Limit the maximum
depth of spaces from the air inlet to the stack outlet to less than
five times the ceiling height (~45 to 50 ft.).
Examine possible
ways of reinforcing the stack effect by installing:
- outlets in negative
pressure areas due to winds. Outlets should be placed downwind of
prevailing breezes to avoid overwhelming the stack effect, i.e., on
east and southeast orientations.
- solar chimneys,
where sunlight at high levels heats outgoing air above the occupied
volume.
Cautions
- Airflow should
be examined at low, mid and high heights within the building to ensure
adequate ventilation under a variety of wind conditions.
- Interior spaces
should be arranged to ensure that dead-air pockets in occupied zones
do not occur.
- Ventilation openings
must be carefully sized, with smaller openings at lower floors, and
larger openings at higher floors to provide equal ventilation rates.
- Smoke & fire
implications of natural ventilation strategies must be carefully considered.
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