Making the most of a site’s solar potential is step one in the design process, coming even before any aesthetic sketches are developed. Orienting a building toward the sun, specifying the size and type of windows, and balancing light and thermal mass are all elements of passive solar design. Unlike solar hot-water systems or photovoltaic panels, which are active or mechanically controlled solar components, passive solar design relies on nothing more than good planning and design to help make the building more energy self-sufficient.
Get to Know the Site
Begin the design process by spending time on the site. Feel the way the environment works. Every place has its own microclimate. As much as climate data will help in the macro design, the relationship in the southern sky, the available breezes, the existing vegetation, and the side of a slope the house is to be built on all create a zone that will affect the performance of a passive solar home. Use basic geometry to determine the angle of the winter sun. Is it blocked by existing trees? Do the winds wrap around a hill and hit the house from a different angle than the prevailing direction? Mature trees in the immediate vicinity can reduce the actual temperature around the house by 15°F in summer. There are not elements that will be analyzed by computer software, but they affect the quality of life in a house built on that spot.
Orient the House for Energy Savings
Every building has some passive solar potential. South-facing windows should be considered early in the design process so they can be integrated into the overall architecture of the house. In the late 1970s and early 1980s, the biggest mistake in designing passive solar houses was to include too many south-facing windows. Entire walls of glass cooked homeowners during the summer. Now, with better insulation in exterior walls, successive passive solar designs need many fewer windows — the equivalent of between 8% and 12% of the floor area in rooms with south-facing windows. That translates to only two or three additional (and strategically placed) windows on the south side of the house to increase comfort and energy efficiency.
There’s another advantage: more daylight means less reliance on electric lights. In a house with sensible solar orientation, it may be possible to keep the lights completely turned off during the day and still see perfectly well. Besides, dogs and cats love nothing better than a patch of sunshine.
From David Johnston’s Green Diary
One of David’s first projects for a production builder was to take a model the company had built hundreds of times and “green it.” I was stuck with the floor plan — that couldn’t be changed — but not the way the house was oriented. One wall of the house was mostly glass, and this typically faced west to make the most of mountain views.
The first thing I did was to rotate my project house 90 degrees so the glass wall could do a better job of capturing sunlight. Along with modifying the standard type of window glass the builder was using and extending roof overhangs, this simple change reduced the heating and cooling load by 40%. As a result, we started with a building that was 25% more energy efficient than government Energy Star standards.
Even in winter, rooms with south-facing windows can be warm and comfortable. The key is balancing window area to relative mass of floors and walls illuminated by sunlight.