Happy Summer Solstice to those who live in the Northern Hemisphere, and Winter Solstice to everyone in the Southern Hemisphere! Since I live in California, I’ll be talking specifically about the Northern Hemisphere in this newsletter. Here in Los Angeles, the temperature has risen. It even climbed above 90 degrees Fahrenheit already! The seedlings I planted last month germinated very quickly. The red chards are growing so fast! This is the season to sow, for the obvious reason – the Sun is getting closer to this side of the Equator. Now is the best time to talk about solar design strategies. Not only plants, but buildings as well can take advantage of the Sun’s energy: to harvest daylight and heat spaces, both directly and indirectly. This is called passive solar design.
Harvesting daylight is easy. The strategy is to provide a light shelf. The winter sun angle is usually lower at 60 degrees, while the summer sun angle is at 79 degrees. It is beneficial to allow winter sun to come directly into the space – not only for heating purpose, but since the sun is weaker and does not cause as much glare, it can also provide daylighting. By contrast, in the summer, blocking direct sunlight is essential to prevent the building from generating heat. Therefore, the utilization of a light shelf can have dual purposes. A high transom window is installed above a typical window. A shelf-like device is then attached to the sill of the transom window to both reflect light back onto the ceiling, thus flooding the room with natural light and block the direct sunlight in the summer. The aesthetic design possibilities are endless. See the diagram below for a sample light shelf design.
In the Northern Hemisphere we get a shorter amount of daylight from November through February; our winter months. With the Sun at its furthest point from the Earth, it is essential during the planning process to orient buildings to best capture the natural, radiant heat generated by the Sun to warm up spaces during winter months. This orientation will vary depending on the climate where the building is located. Generally, exposing the living areas or open offices due southeast will capture the most radiant energy. Sustainable design strategy actually entails most glazing on the south side of the building. This orientation will capture the most sun throughout the day, allowing occupants not only be exposed to natural light, but also lowering heating cost during those cold winter months.
Another strategy to heat spaces in winter months is to create thermal masses. Thermal (heat) absorbent materials, such as concrete and bricks, store the Sun’s energy during the day, then releases that heat at night after the outside temperature drops. Creating green-house like verandas attached to houses can also help heat the house at night.
Harvesting the Sun’s energy as a heating source is nothing new. The ancient Chinese, Greeks, Romans, etc. all took advantage of the Sun when they designed their shelters – especially a Native American tribe, the Acoma. The “Sky City” that they built not only took advantage of the heating potential of the Sun with the way they oriented their buildings (in an east-west direction), they also utilized thermal walls to heat the buildings in the evening. Below is an excerpt from the book “A Golden Thread: 2500 Years of Solar Architecture and Technology” by Ken Butti and John Perlin:
“The “Sky City,” built atop a plateau, consists of three long rows of dwelling units running east to west. Each dwelling unit has two or three tiers stacked one behind the other as to allow each one full exposure to the winter sun. Most doors and windows open to the south to catch the warm solar rays of winter. The walls are built of adobe. The sun strikes these heat-absorbing south walls more directly in winter than during summer time. The sun’s heat travels through the adobe slow enough to reach the interior as night falls, heating the house through the night. Insulating the ceiling with straw keeps the horizontal roof, vulnerable to the rays of the high summer sun, from allowing too much heat to enter the house.”
Some might argue it is best to maximize northern exposure to provide even, indirect sunlight, which is not entirely false. This design strategy is, however & for the most part, best used in art studios, libraries, museums, or galleries – places where direct sunlight is undesirable. The possibilities of harvesting sun energy in building design are endless. We are just starting to discover a few. The Sun voluntarily provides an infinite amount of energy, which when used in the correct ways, can help to conserve our natural resources for our children in the generations to come. With the increasing demand to lower consumption of mechanical heating, or the use of artificial lighting, it is imperative for designers to take into consideration the use of passive solar design strategies during the design process.