Good day sunshine! That classic Beatles hit says it all. Life is good, you feel good when the sun is shining. One of my friends on Facebook begins his posts every day with a cup of coffee and this cheerful, positive message, “Good Morning, Sunshine.” As costs of energy have continued to spiral up, more new homes and commercial buildings are being designed to let the sunshine in, by incorporating passive solar techniques. Passive solar uses the sun’s energy to efficiently heat and cool interior space.
Why is it called passive solar? Because there’s really nothing mechanical about it! No solar panels although that may be what first comes to mind. Passive solar energy is the sunlight you enjoy when you walk outside on a beautiful day and its available sunrise to sunset. Homes can be professionally designed to take advantage of the natural energy characteristics in materials and air created by exposure to the sun. This not only offers substantial savings on monthly utility bills but it’s also good for the environment.
Think of a big flat rock in the middle of a stream, growing warm in the sun. It holds its warmth beyond sunset and gradually releases it back into its surroundings. How does this apply to buildings? A greenhouse is a perfect example of a structure putting passive solar to work, harnessing a natural occurrence, the sun, to grow plants whatever the weather.
Passive solar design is used in one form or another throughout the world and has been proven to produce low energy costs, buildings that require less maintenance, and superior comfort. The most effective designs are based on a specific understanding of a building site’s wind patterns, terrain, vegetation, solar exposure and other factors often requiring professional architectural services. A basic knowledge of these issues can have a significant effect on the energy performance of a building.
According to the Department of Energy, the key considerations in a passive solar design are site, climate and materials. I would add another to this list- a design professional to assist you. One that is experienced in designing custom homes that successfully utilize passive solar technology. Next, select a site for your new passive solar building. A must when it comes to your site is that the south side of the building has an unobstructed view of the sun, one that will stay that way.
It’s similar to finding the perfect, unobstructed spot for your satellite dish. You don’t want small trees to grow tall enough to block the sun. Is there room for someone else to build a tall structure to the south of you, effectively blocking the sun? Is there an opportunity to landscape and provide adequate shade. These are important considerations, especially in warm, humid climates. A landowners’ solar access may be protected by local zoning ordinances where you plan to build. If not, try to choose a lot that has depth from north to south and build as far north on the site as you can. Be sure your design professional sees and approves of the site.
Now for the design. Exactly how does passive solar work? Quoting from Energy.Gov http://energy.gov/energysaver/passive-solar-home-design, “In simple terms, a passive solar home collects heat as the sun shines through south-facing windows and retains it in materials that store heat, known as thermal mass. The share of the home’s heating load that the passive solar design can meet is called the passive solar fraction, and depends on the area of glazing and the amount of thermal mass. The ideal ratio of thermal mass to glazing varies by climate. Well-designed passive solar homes also provide daylight all year and comfort during the cooling season through the use of nighttime ventilation.”
Speaking of well designed, incorporating passive solar techniques does not limit the aesthetics of a building. While there may be certain challenges for your designer to meet passive solar goals, essentially, your creativity is limited only by requirements for Insulation and air sealing, window location, glazing type and window shading, thermal mass location and type, auxiliary heating and cooling systems. The custom design professional will apply these elements to your passive solar building design. Techniques include direct gain, indirect gain, and isolated gain. What are these various gains and how do they differ from each other? Let’s take them one at a time to understand the differences.
Referring again to Energy.gov and the article sited earlier, “In a direct gain design, sunlight enters the house through south-facing windows and strikes masonry floors and/or walls, which absorb and store the solar heat. As the room cools during the night, the thermal mass releases heat into the house.
An indirect-gain passive solar home has its thermal storage between the south-facing windows and the living spaces. The most common indirect-gain approach is a Trombe wall (named for French engineer Félix Trombe). The wall consists of an 8-inch to 16-inch thick masonry wall on the south side of a house. A single or double layer of glass mounted about one inch or less in front of the dark-colored wall absorbs solar heat, which is stored in the wall's mass. The heat migrates through the wall and radiates into the living space. Heat travels through a masonry wall at an average rate of one inch per hour, so the heat absorbed on the outside of an 8-inch thick concrete wall at noon will enter the interior living space around 8 p.m.
The most common isolated-gain passive solar home design is a sunspace that can be closed off from the house with doors, windows, and other operable openings. Also known as a sunroom, solar room, or solarium, a sunspace can be included in a new home design or added to an existing home.Sunspaces should not be confused with greenhouses, which are designed to grow plants. Sunspaces serve three main functions -- they provide auxiliary heat, a sunny space to grow plants, and a pleasant living area. The design considerations for these three functions are very different, and accommodating all three functions requires compromises.”
Consider the advantages of incorporating passive solar into your building’s design: Passive solar is highly energy efficient, reducing energy demands for heating, cooling and lighting; it can reduce heating bills by as much as 50%; it reduces consumption of fossil fuels and production of greenhouse gases and various pollutants; it uses a renewable energy source.
Is there a downside? Passive solar’s initial building costs can be higher, requiring more thought and planning, even engineering expertise; appropriate glass and other materials must be used to maximize benefits; use of the technique can increase warm season cooling requirements if appropriate landscaping and shading has not been provided. Check the Energy.gov website for possible tax credits, rebates and other savings available for using solar technology.
Two things are clear. Without question, passive solar requires an investment upfront but it’s an investment which will pay big dividends going forward. And, to maximize return, it’s important to get good advice from a design professional experienced in the use of passive solar technology.