Most Canadians know the pleasure and comfort of sitting in front of a south facing window on a sunny winter’s day. What’s less well known is that the warmth you feel can also significantly reduce your heating bill. For years, innovative designers of houses have designed and built houses using passive solar design tactics that take full advantage of the sun’s energy to provide a significant proportion of household heating needs and natural lighting – all with no moving parts or complex systems. In fact, a well designed house in Canada can get a third to a half or more of its heating needs from the sun.
Passive solar design elements
One of the most important elements of passive solar design is the design of the house and how it is positioned on the lot. Ideally, the house will be highly insulated and airtight to hold the heat captured from the sun in the house as long as possible. The house should also be positioned to have the most window area facing towards the south with less towards the north. The floor plan is also important as more solar energy can be captured by a house with a rectangular floor plan where the long side of the house faces south. Sunlight can also penetrate farther into houses with more narrow floor plans than houses with deeper, square floor plans. Ideally, the amount of west and east facing window area is limited as the low position of the sun early in the morning and later in the day permits high solar gains that can cause overheating and glare. While skylights offer natural lighting, they tend to capture little solar heat in the winter and too much in the summer, which can lead to overheating and increased air conditioning costs.
Another important passive solar design element is shading. The sun is positioned lower in the sky during the winter and higher in the summer, low in the mornings and afternoons and high at noon. Properly designed shading takes the position of the sun into account to allow solar gains in the winter when needed and prevent them in the summer when they are not. Shading can be provided by roof overhangs, awnings or even deciduous trees strategically located on the building site. Interior curtains and shades are not as effective as exterior shading in preventing unwanted solar gains. The most effective shading is also adjustable so that you can control the amount of shading provided given the location and position of the sun and whether or not solar gains are needed or not.
Energy efficient windows are also key to passive solar design. Windows with low emissivity (Low E) coatings are available that allow good solar gains while reducing heat losses. Triple and quadruple pane
windows that include inert gases such as argon or krypton between the panes can cut heat losses significantly as well. Window pane spacers and frames can also be a source of heat loss and should be well insulated. Energy efficient windows can also reduce the potential for condensation and can minimize the amount of outdoor noise that can find its way into the house. Given the wide range of window available, look for those that are ENERGY STAR certified.
Adding high mass elements to the interior of the home such as concrete floor toppings, brick masonry and other materials capable of absorbing and holding heat is another passive solar tactic. Such features can be used to absorb and store heat from the sun and release it later when the sun is no longer directly warming the room overnight or during cloudy periods.
Benefits of passive solar design
Effective passive solar design will also ensure that there is good air circulation in the house to transfer the heat gained throughout the house and to help even out temperature differences between rooms. An open floor plan will permit solar gains to circulate more freely throughout the home than closed interior spaces. Windows can be located to promote natural cross ventilation while strategically placed ceiling fans can help circulate air within rooms year round.
Apart from benefiting from reduced heating energy costs, homes that include passive solar design elements can also offer improved natural lighting, brighter interior spaces, less overheating and will offer much better chances of weathering a mid-winter power outage with less discomfort or having your pipes freeze. While simple in concept, passive solar design is best left to those knowledgeable and experienced in the design and construction of low-energy homes as caution is needed to ensure that your home is not overheated by the sun as rooms can become too hot for comfort, which can lead to increased air conditioning costs in the spring, summer and fall. With careful planning, skilled designers can achieve the right balance between reducing heating bills and keeping things comfortable.
To learn more about the passive solar design strategies used in the highly energy efficient houses constructed under Canada Mortgage and Housing Corporation’s EQuilibrium Sustainable Housing Demonstration Initiative, visit CMHC’s website (www.cmhc.ca) or call 1-800-668-2642 to request information.
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