Natural - Cross and Stack -
Home Ventilation
The
Importance of Ventilation
Homes need fresh air in order to provide oxygen to their
residents, and also to control humidity and to eliminate odors.
Contaminants such as formaldehyde or radon can
accumulate in poorly ventilated homes, causing health problems;
and high humidity levels (caused by inadequate ventilation) can lead
to mold growth and cause damages to your home… Ventilation
is, indeed, a key element in the whole home environment.
Mechanical Ventilation
Because of central heating and cooling systems, or to avoid
energy losses, most people don't open windows and doors often
enough. In these cases, air infiltration through holes and
cracks has become the main way of getting fresh air.
But this natural exchange of air is far from
satisfactory: it doesn’t produce the right moisture control and
the best air quality.
In cold climates, and in well sealed houses, traditional methods
of ventilation - opening a window, common fans… - do not provide
adequate ventilation. Only
mechanical systems
of ventilation - HRV (Heat
Recovery Ventilation) and ERV (Energy Recovery Ventilation) -
using fans to maintain fresh outdoor air into the house while
exhausting out an equal amount of stale indoor air can provide
good ventilation and indoor air quality.
Natural ventilation
In some cases,
mechanical ventilation is inescapable, but there are also many
situations where you should consider
Natural Cross Ventilation and
Natural Stack Ventilation.
Avoid it in
hot and humid
climates.
But consider it in most other climates. Natural ventilation may
save you lots of energy and money.
Natural
Cross ventilation
Cross ventilation is part of natural ventilation and is based on
the paths of breezes and wind. Cross ventilation techniques use
high and low pressure zones created by wind and breezes to draw fresh air
through a building. The wind (breezes) enters in a window (or
another vent, in an appropriate side of the building) bringing
fresh air and pulling staled air to exit through opposite openings of
the house. The schemes below (from the Division of Architecture
of
California Government
and of
Greenbuilder.com)
illustrates the process.
Knowing the wind flowing patterns and a correct orientation of
the house and placement of windows, doors and other openings is
crucial for the success of this strategy.
Natural
Stack Ventilation: the
«Chimney Effect»
Natural stack ventilation uses the chimney effect: high and low
pressure zones created by rising heat air, causing convection
currents: the warmer indoor air rises up through the house till
the attic or other top part of the building; this rising warm
air reduces the pressure in the base of the house rooms,
allowing cold air to infiltrate through strategically placed open spaces
(windows or other openings)…
This technique can be implemented in a home by designing an exit
window (or other openings) that draws warm air out of the top of
the building/room and another window/vent/opening in a lower
level of the building where cool air could enter.
The scheme
below (from the Division of Architecture of
California Government)
illustrates the process.
Wing
Walls
Wing walls
are vertical panels placed alongside of windows - perpendicular
to the wall on the windward side of the building. The scheme
above shows how wing walls work, They are, in some cases, an
interesting natural ventilation technique.
Basics on cooling through natural ventilation
Cooling the house through natural ventilation involves:
- Cross-ventilation techniques
- Stack ventilation techniques
-
Cathedral-style ceiling s with cupola and operable windows
- Large windows or other openings in the sides of the house
- Other landscape measures (trees,
windbreaks...) and right orientation
of the house
Besides these central strategies there are other more common
and useful practices:
-
Ceiling fans
- Bathroom
exhaust fans
- Closing of windows and doors
during the hottest weather and opening of windows at night.
- Opening of the windows or doors in milder weather.
Ventilation and heating
Ventilation is mostly used to cool a house and to add fresh air
to it. But in temperate climates and in the right weather conditions
natural ventilation may also be used to heat homes: opening the windows in
winter's hotter hours, or closing them when temperatures are colder
is an obvious practice…
Obviously, such strategy has a limited scope of
application, and is highly dependent on the climate, outdoor and indoor
temperatures and also of location, orientation and surrounding landscape
of the house.
For heating a house in an earth-friendly way you should seek
other strategies and means:
solar energy solutions,
geothermal heat pumps,
proper orientation
of the house or adequate
landscaping…
See also:
Energy Efficient House Basics
Mechanical ventilation: HEV and HRV
Air
sealing and home air leakage
Air quality: good and bad indoor air
quality
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