[Paleopsych] Passive Solar Cooling
shovland at mindspring.com
Thu Aug 12 14:26:42 UTC 2004
3.1 Ventilation & Operable Windows
A primary strategy for cooling buildings without mechanical assistance
(passive cooling) in hot humid climates is to employ natural ventilation.
(The Fan and Landscape sections also address ventilation strategies.) In
the Austin area, prevailing summer breezes are from the south and
southeast. This matches nicely with the increased glazing on the south side
needed for passive heating, making it possible to achieve helpful solar
gain and ventilation with the following strategies:
Place operable windows on the south exposure.
Casement windows offer the best airflow. Awning (or hopper) windows should
be fully opened or air will be directed to ceiling. Awning windows offer
the best rain protection and perform better than double hung windows.
If a room can have windows on only one side, use two widely spaced windows
instead of one window.
3.1.1 Wing Walls
Wing walls are vertical solid panels placed alongside of windows
perpendicular to the wall on the windward side of the house.
Top View of Wing Walls Airflow Pattern
Wing walls will accelerate the natural wind speed due to pressure
differences created by the wing wall
3.1.2 Thermal Chimney
A thermal chimney employs convective currents to draw air out of a
building. By creating a warm or hot zone with an exterior exhaust outlet,
air can be drawn into the house ventilating the structure.
Sunrooms can be designed to perform this function. The excessive heat
generated in a south facing sunroom during the summer can be vented at the
top. With the connecting lower vents to the living space open along with
windows on the north side, air is drawn through the living space to be
exhausted through the sunroom upper vents. (The upper vents from the
sunroom to the living space and any side operable windows must be closed
and the thermal mass wall in the sunroom must be shaded.)
Summer Venting Sunroom
Summer Venting Thermal MassWall
Thermal mass indirect gain walls can be made to function similarly except
that the mass wall should be insulated on the inside when performing this
Thermal chimneys can be constructed in a narrow configuration (like a
chimney) with an easily heated black metal absorber on the inside behind a
glazed front that can reach high temperatures and be insulated from the
house. The chimney must terminate above the roof level. A rotating metal
scoop at the top which opens opposite the wind will allow heated air to
exhaust without being overcome by the prevailing wind.
Thermal chimney effects can be integrated into the house with open
stairwells and atria. (This approach can be an aesthetic plus to the home
3.1.3 Other Ventilation Strategies
Make the outlet openings slightly larger than the inlet openings.
Place the inlets at low to medium heights to provide airflow at occupant
levels in the room.
Thermal Chimney Effect Built into Home
Inlets close to a wall result in air "washing" along the wall. Be certain
to have centrally located inlets for air movement in the center areas of
Window insect screens decrease the velocity of slow breezes more than
stronger breezes (60% decrease at 1.5 mph, 28% decrease at 6 mph).
Screening a porch will not reduce air speeds as much as screening the
Night ventilation of a home should be done at a ventilation rate of 30 air
changes per hour or greater. Mechanical ventilation will be required to
achieve this (See Fan Section <Fans.html>).
High mass houses can be cooled with night ventilation providing that fabric
furnishings are minimized in the house.
Keep a high mass house closed during the day and opened at night.
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