The earth's axis is tilted, we
learned that in elementary school. As a result of the earth's tilt, the sun
rises lower in the winter sky and rises higher in the summer sky. In
planning for passive solar in our homes, we must remember that in a Northern
Hemisphere, the winter sun rises in the South East, stays low in the South sky,
and then sets in the South West. The summer sun rises more in the North
East, quickly gains height to a higher elevation than in winter, and then sets
back in the North West.
So the best things to do in the
Northern Hemisphere are:
Let the sunshine in to heat
a thermal mass. Orient the house such that the major axis runs
Carefully place the windows.
Limit the number and size of windows on the Northern side of the house, to
reduce Summer heating of the interior. Place more windows on the Southern side
of the house. Use wide eaves and tall shade trees to limit solar radiation
in the Summer, yet provide plenty of solar heating in the Winter. Clerestory
windows and dormers can bring winter light into otherwise dark areas of the
house (minimize skylight use). Use a solar path chart to design a building so
that low winter sun shines in and high summer sun is blocked by effective use of
windows, overhangs and shade.
High R values with minimal
air leaks are key to any low-energy house.
Do a blower door test to verify house tightness.
Invest in a high performance ventilation system; an air to air heat exchanger
recovers the heat in exhausted ventilation air.
Thermal mass, inside the
building, moderates temperature swings by storing heat during the day and
releasing it a night. Materials
commonly used for mass include water, concrete, masonry, and earth. Keep the
mass at 3-4” thick, and keep it in the direct sun for best effectiveness. Mass
must be carefully balanced with glazing area to perform properly in a given
Do your homework before
building. Time spent on the
building site observing sun, wind, rain, and ground water pays off in selecting
the ideal location and design for the house.
In colder climates, it's
important to store as much of the incoming solar energy during the day as
possible, and then allow it to continue heating the house during the night.
The best way to store this heat is in a large thermal mass. One popular (and
patented) way to do this is with a thick slab floor. This floor could be
solid concrete, or a layer of rock. Since the incoming sunlight will only
heat the South side of the slab (via the windows) several ingenious methods have
been devised to circulate air through the slab. This air serves to moderate
the temperature of the slab during the day, and help heat the air within the house
during the night.