Buildings designed for passive solar and daylighting incorporate design
features such as large south-facing windows and building materials that
absorb and slowly release the sun's heat. No mechanical means are employed
in passive solar heating. Incorporating passive solar designs can reduce
heating bills as much as 50 percent. Passive solar designs can also
include natural ventilation for cooling. Windows are an important aspect
of passive solar design—for information on window technologies, see the
Building Envelope section of the EREN Buildings page.
Proper building orientation, so the longest walls run
from east to west, allows solar heat to enter the home in winter, while
allowing in as little sun as possible during summer. Shading and overhangs
also reduce excessive summer heat, while still permitting winter sun. In
passive solar designs, the optimal window-to-wall area ratio is 25-35
Passive Solar Heating
In cold climates, south-facing windows designed to let the sun's heat in
while insulating against the cold are ideal. In hot and moderate climates,
the strategy is to admit light while rejecting heat. Interior spaces
requiring the most light, heat, and cooling are located along the south
face of the building, with less used space to the north. Open floor plans
allow more sun inside.
The simplest passive design is the direct gain system in which the sun
shines directly into a building, heating it up. The sun's heat is stored
by the building's inherent thermal mass in materials such as concrete,
stone floor slabs, or masonry partitions that hold and slowly release
heat. With indirect gain systems, thermal mass is located between the sun
and the living space. An isolated gain system is one where the system is
isolated from the primary living area, such as a sunroom or solar
greenhouse with convective loops into the living space.
Passive Solar Cooling
Many passive solar designs include natural ventilation for cooling. By
installing casement or other operable windows for passive solar gain and
adding vertical panels, called wing walls, perpendicular to the wall on
the windward side of the house, you can accelerate the natural breeze in
the interior. Another passive solar cooling device is the thermal chimney,
which can be designed like a smoke chimney to vent hot air from the house
out through the roof.
Daylighting is using natural sunlight to light a building's interior. In
addition to south-facing windows and skylights, clerestory windows—a row
of windows near the peak of the roof—can let light into north-facing
rooms and upper levels. An open floor plan allows the light to reach
throughout the building. Daylighting in businesses and commercial
buildings can result in substantial savings on electric bills, and not
only provides a higher quality of light, but improves productivity and
health. Daylighting in schools has improved student grades and attendance.
South-facing sunrooms are often added on as a way to retrofit a home to
take advantage of the sun's heat and light. It is also possible to use a
sunroom to help ventilate the rest of the house. Lower vents from the
sunroom to the interior rooms draw air through the living space to be
expelled out the upper vents to the outside along the top of the sunroom.
A Trombe wall consists an 8- to 16-inch thick masonry wall coated with a
dark, heat-absorbing material and covered by a single or double layer of
glass, placed from about 3/4" to 6" away from the masonry wall.
Heat from the sun is stored in the air space between the glass and dark
material, and conducted slowly to the interior of the building through the
masonry. Adding a Trombe wall and south-facing windows is an easy way for
a home to take advantage of solar heat.
Passive solar is not just a design technique for using the sun to heat and
cool a home. Passive solar heating is also a common way to heat water (see
the section on Solar Hot Water), and, particularly in developing nations
where the electrical grid is undeveloped, passive solar heat is sometimes
captured to cook food. Solar cookers can cook just about any food a
conventional oven can. A basic cooker consists of an insulated box with a
glass top. Heat from concentrated sunlight gets trapped in the box and can
be used to heat food enclosed in the box.
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