Topics
of Interest
Passive
Solar Design, Sustainable Design
For
building sites with good solar exposure, passive solar heating can provide
25% of your heating needs here in Western North Carolina simply with south-facing
windows. The total south-facing glass area should be no more than 10%
of your home's floor area unless you have thermal heat storage walls or other
heat storing components beyond that in normal light wood frame construction.
Passive solar designs which "overglaze" with window areas
that exceed this 10% rule, can become uncomfortably overheated on sunny winter
days.
Sun exposure is most important between the hours of 10:00 AM and 2:00 PM during
the winter months. For sites where a portion of the sunshine is compromised
by a land form, such that the sun does not appear until 11:00 AM in January,
the amount of south-facing window area or aperture might be increased to as
much as 13 or 14% of the floor area. Some increase in aperture may also
be made to offset shading and reduced solar exposure from deciduous tree trunks
and limbs that will remain in a southerly direction from your building site.
It is very important that your heat collecting south wall be oriented
to face due south, or no more than 15 degrees east or west of due south.
While 25% of your heat is a significant amount, this can tripled to 75% if
the building is constructed with a no-holds barred approach to passive solar.
The south-facing glass or aperture can be increased to 20-30% of the
floor area, as long as the heat from the additional area of solar aperture
is directly absorbed into a heat storage mass. The entire materials
and fabric of the home must not only be a good solar heat collection device,
it must be a good solar heat storage device, and like a thermos bottle, must
be insulated to be a very effective heat trap. For a high aperture,
high mass, high performance passive solar home, you had better consult an
expert in the design to be certain the heat collection and storage elements
are balanced. Attached sunspaces with large glass or aperture areas
can further augment a passive solar design. The attached sunspace is a separate
room or space that can be isolated from the main living area and therefore
can have temperature swings which exceed the normal comfort range. This space
can share heat storage walls with the main living space, and can have operable
doors or vents to bring the heat collected into the main living area.
Sustainable design refers to the broader realm of energy conservation measures
which reduce the use of fossil fuels which thereby reduces CO2 emissions
into the atmosphere. Sustainable design turns to renewable energy sources
where possible and thus passive solar design is part of sustainable design.
Photo-voltaic panels for direct conversion of the sun's energy into
electricity is another example of sustainable design, as are hybrid electric
vehicles and higher efficiency furnaces. Ultimately, all these can be
combined on the right site to make an off-the-grid, autonomous dwelling, but
renewable energy sources are finite and a fundamental aspect of all sustainable
design is energy conservation.
Recommended Reading:
1) The Passive Solar Energy
Book
Edward Mazria, 1979
2) Building with Passive
Solar
Southern Solar Energy
Center, 1981
3) Movable Insulation
William Langdon, 1980
