Sound familiar?
The Greeks faced an environmental crisis in the 5th century B.C.E. Wood was in high demand for ships and buildings, making the primary heat source for comfort-charcoal-increasingly scarce and expensive.Most of the Greek peninsula and the islands had been denuded so they were forced to import wood from faraway places. This drove the ancient architects to reevaluate how they built their buildings…
A more contemporary example is the salt box design favoured by the early colonists in New England. Saltbox houses were oriented to the south with a two story elevation fenestrated by windows. The north roof sloped down to one story and had few windows. This took the chill out of cold New England winters when the sun was out. Roof overhangs and decks the length of the house on the second floor shaded the south-facing glass in the summer.
The two-story side of the house faces south for solar heat in winter. while the low north side has few to no windows and the sloping roof diverts cold north winds. The rear roof line is often extended to cover cord wood for winter heating. Shutters are operable to reduce heat loss in winter and solar overheating in summer on east and west windows.
These examples show, until fairly recently humans know how to adjust to climatic conditions, however by the middle of the 20th century, with the invention and commercialization of air-conditioning, we started to loose direct contact with variations in climate and weather. Power heating and cooling system took over, allowing builders to use the same house designs in Alaska and Florida. After thousands of years of planning shelter around the cycles of the sun, we stopped worrying about where the sun would be located in the summer and winter sky.
Passive Solar Design Process
Making the most of the site’s solar potential is step one in the design process, coming before any aesthetic sketches.
Orienting building towards the sun, specifying the size and type of windows and balancing light and thermal mass are all elements of passive solar design.
- Orient the house within 30 degrees of due south. Due south is the equivalent of the 100 percent potential solar heat gain through windows. Rotating the house within 30 degrees of due south still provides about 90 percent of the potential solar gain and allows latitude for adjusting the house to lot limitations. Further than 30 degrees start to make architectural shading difficult and can lead to over heating.
- Use design software to optimize passive solar heating.
- Super-insulate and air-seal the house. The lower the heating and cooling loads of the house, the less solar heat is necessary to provide comfort through much of the year.
- Design the size of south glazing to meet the heat-loss of the house. The size of south -facing glass is determined by location, the potential amount of sunshine, degree days of the local climate. In an ideal design, south windows would be distributed across the south wall to provide heat gain to as may areas of the house as possible.
5. Design thermal mass to absorb sunlight. Concrete, Concrete Masonry Units, brick, stone and tile are typical materials used as thermal mass inside the building.
6. Determine appropriate overhangs for all south side. All south glass needs shading in the summer to prevent overheating. Depth of the Overhang needs to be calculated.
7. Limit east, west and north glass while providing for cross-ventilation. East and west windows loose and much heat as they gain. They provide an important function in creating cross-ventilation in rooms or for the entire house.
Passive Solar and Zero Energy Homes
Combining Passive solar design with zero energy homes makes cost-effective heating and cooling possible. Solar is most important factor in zero energy home. Orientation comes first, enabling the building to take the fullest advantage of the sun.
Designing a house to reposed to its site and climate is the first prerequisite of zero energy building. Finding ways to heat, cool and light space with the barest amounts of energy is the next.
Reference:
- Toward a Zero Energy Home: A Complete Guide to Energy Self-Sufficiency at Home, by David Johnston, Scott Gibson.