Passive Solar Design has a long and storied history. It’s a welcome alternative to the carbon-intensive energy sources of modern building.
While Passive Solar Design has captured the imaginations of modern builders and homeowners, it isn’t a new technology by any means. We can look to indigenous peoples in North America and see great examples of efficient, passive heating and cooling in homes – sustainable methods that came well beyond solar cells and even wind turbines.
For instance, the Ancient Pueblo peoples of the extraordinarily unique and beautiful Mesa Verde cliff dwellings in Colorado mastered the heating and cooling of their homes and structures – without electricity, insulation, natural gas, air conditioning or modern building techniques.
Early adopters of passive solar design, this pre-contact Native American civilization built homes – entire communities – that were comfortable year-round heated mostly by passive solar energy and thermally massive building materials.
Shaded from the hot summer sun by the natural overhang conveniently provided by the cliffs above, the ancient pueblo homes are kept cool and airy all season long. Conversely, during the winter months and long periods where the sun is low in the sky, its warm light washes over the homes, heating the adobe and storing energy in the thermally massive building material. The heat is absorbed during the day and released slowly at night.
Thanks to effective passive solar design the Pueblo peoples enjoyed warm homes through the winter and blissful cool relief from the blazing summer sun.
In contrast, think about modern North American homes today. You would think that, given the significant time we spend in colder temperatures during the year, our homes and communities would be better oriented towards the sun.
To the contrary. We take little consideration of the earth’s primary source of light and heat when we develop neighbourhoods and communities. Rather, we build homes that are cold and draughty in winter and overheat in the summer.
A city like Edmonton, Alberta, for example, sits at 53 degrees latitude and the “warm season” has an average temperature of 18 degrees Celsius yet homes are built with air conditioners.
Fortunately, the innate know-how of the past is seeing a resurgence today. There is a welcome movement among builders, architects, and homeowners to rediscover passive solar design in modern building.
Harnessing the Power of the Sun in Sustainable Design
Passive solar design refers to the use of the sun’s energy for the heating and cooling of living spaces through exposure to the sun. This method of design fosters an alternative, renewable – or green – energy, and promotes the safe, healthy and sustainable means of harvesting energy as opposed to the harmful, irreparable impacts of burning fossil fuels.
The fundamental principles of passive solar design include:
- Orienting buildings along an east-west axis;
- Organizing interior spaces so that those areas requiring the most heating (living room, etc.) are directly exposed to south- facing windows;
- Using roof overhangs to shade south-facing windows from strong summer sun;
- Building “thermal mass” into the home so that the sun’s rays can be absorbed and later radiated as heat.
These principles employed in conjunction with modern building technologies like exceptional insulation, and sealed building envelope and an adequate HRV system go a long way towards achieving net zero for your home.
The Basics of Passive Solar Design
A complete passive solar design has five elements:
Aperture/Collector: The large glass area through which sunlight enters the building. The aperture(s) should face within 30 degrees of true south and should not be shaded by other buildings or trees from 9 a.m. to 3 p.m. daily during the heating season.
Absorber: The hard, darkened surface of the storage element. The surface, which could be a masonry wall, floor, or water container, sits in the direct path of sunlight. Sunlight hitting the surface is absorbed as heat.
Thermal mass: Materials that retain or store the heat produced by sunlight. While the absorber is an exposed surface, the thermal mass is the material below and behind this surface.
Distribution: Method by which solar heat circulates from the collection and storage points to different areas of the house. A strictly passive design will use the three natural heat transfer modes – conduction, convection, and radiation – exclusively. In some applications, fans, ducts, and blowers may be used to help distribute the heat through the house.
Control: Roof overhangs can be used to shade the aperture area during the summer months. Other elements that control under and/or overheating include electronic sensing devices, such as a differential thermostat that signals a fan to turn on; operable vents and dampers that allow or restrict heat flow; low-emissivity blinds; and awnings.
Passive Solar Heating & Cooling
The objective of a passive solar heating system is to capture the sun’s heat within the building’s components and elements and to effectively release it during periods when the sun is absent. It is this process that maintains comfortable room temperature.
The two primary elements that contribute to passive solar heating are south facing glass and thermal mass to absorb, store, and distribute heat.
Passive solar cooling systems work by reducing unwanted heat gain during the day, producing non-mechanical ventilation, exchanging warm interior air for cooler exterior air when possible, and storing the coolness of the night to moderate warm daytime temperatures.
To reduce unwanted heat gain in the summer, windows are typically shaded by an overhang or other devices such as awnings, shutters, and trellises.
If the source of shade on a south facing window extends to half of a window’s height, the sun’s rays will be blocked during the summer, yet can still penetrate into the house during the winter.
Curious about how Mandala Homes harnesses passive solar design and solar energy in our home building? Talk to us!