Shape and
Orient the Building for Exposure to Prevailing Winds
Two
principles must be considered when planning to use natural ventilation
as the primary means of cooling buildings:
- Wind induces
high pressures on upwind faces, and low pressures on downwind
faces; and
- Hot air
rises due to buoyancy, or “stack effect” (see SF5).
Wind-induced natural
ventilation depends on pressure differences between air inlets and
outlets, and especially on the strength and direction of the prevailing
wind. Santa Monica has an excellent wind resource for natural cooling,
with moderate on-shore breezes consistently coming from the west-southwest
and the west. 
Although
wind-induced natural ventilation is typically the most powerful, the
best effects are created by using the two in combination
To take advantage
of pressure differences created by wind, air inlets should be placed
in high-pressure areas that face upwind. Outlets should be placed
in downwind, low-pressure areas. Precise orientation to the wind is
not critical; even walls angled up to 30° to the wind create enough
pressure to be useful for natural cooling. (See EN4 for details).
Use irregular,
articulated building footprints to increase the exposure of walls
to low- and high-pressure areas. This provides more opportunities
to catch the wind from different directions in each space, and to
cool and ventilate more interior spaces independently. Low- and high-
pressure areas can be created with articulations of the walls and
roofs, using features such as bay windows, recesses and projections,
roof monitors and clerestories. These shapes can allow designers to
cross-ventilate even spaces with only one exterior wall.
- If the shape
and size of the lot allows it, orient the long face of the building
southwest to create the greatest pressure difference between the
windward and lee faces. This can allow cross-ventilation across
the full depth of the building.
- Most lots in
Santa Monica dictate that the long elevation of the building will
face southeast, limiting the potential for cross-ventilation across
the building. In these cases, use fins, recesses and projections
along walls that face northwest and southeast. These irregularities
create pressure differences along the elevation that can induce
airflow into and out of correctly placed openings.
Cautions
- Effectiveness
depends on the configuration of upwind obstructions.
- Orienting to
the wind and increasing exposed wall and roof area also improves
the potential for daylighting and view, but may increase solar gain.
