“In our passive solar house, we only turn on the air conditioner two weeks out of the year,” says Joseph Pro, a New York City-based architect with more than 20 years of experience in passive solar home design.
Passive solar is a great option for environmentally conscious buyers, Pro says. “With the proper orientation, insulation and windows, as well as a commitment to passive solar, you can greatly diminish or even eliminate your energy consumption.”
The first article of our series on solar energy focused on PV (photovoltaic) panels, while Part Two takes an in-depth look at harnessing the sun’s energy through passive solar design.
What's the Benefit?
If you choose a passive solar design for your new house, count on it improving your home’s natural light and organically regulating its indoor temperature — while reducing your electric bill and impact on the environment.
At its core, passive solar design elements use sunlight to naturally ventilate, warm, cool and light your home’s interior. Your home’s orientation is essential to taking advantage of sunlight: toward the south in the northern hemisphere or toward the north in the southern hemisphere.
“Siting the house is one of the most important elements to passive solar design. About 60 percent of houses have the wrong orientation — the garage is usually southern-facing and absorbs the most heat from the sun,” Pro says. “We get tons of requests from homeowners to change the garage into the living room to take advantage of the sun.”
Passive Solar Design Has 5 Key Elements
With the proper orientation, a passive solar home relies on five elements to regulate its climate. The first element, the aperture, is the opening (often a window) through which heat and sunlight enter the space. An ideal aperture is within 30 degrees of true south and receives unobstructed sunlight from 9 a.m. to 3 p.m.
Once sunlight passes through your southern-facing windows, it must hit the absorber. The second element of passive design, the absorber is the dark, hardened surface of the storage element, which sits in the direct path of the sunlight. The absorber is typically a masonry wall, floor, partition or water container that initially absorbs the sunlight as heat.
Once captured, the energy from sunlight must be stored for later use. That requires thermal mass, the third element of passive solar design. Consisting of materials that retain the heat produced by sunlight, thermal mass is the material behind or below the exposed absorber surface. It's often a concrete slab, brick wall or tile floor.
Thermal mass can’t heat or cool your home on its own — that’s where heat distribution, the fourth element, comes in. Heat distribution is the method by which solar heat will circulate from the collection points (aperture and absorber) and storage points (thermal mass) to different areas of the building. Some buildings may require fans, ducts and blowers to supplement natural heat transfer.
It’s imperative to use shading, the fifth element, to control the amount of sunlight your home receives in the summer. Roof overhangs or trees are popular options. A well-designed overhang will allow four hours of direct solar access during the winter while limiting it during warmer summer months. Landscaping also helps cool air near the home, as mist or dew collect on plants in the morning and evaporates. Simply open the windows to take advantage of this natural cooling effect.
In practice, effective implementation of passive design will require insulation and air sealing, careful window placement, glazing and shading, careful consideration of thermal mass and type and sometimes auxiliary heating and cooling systems.
Your Home Can Heat and Cool Itself Much of the Year
If the five design elements above are implemented correctly, your home will maintain a comfortable temperature much of the year without the need to turn on your air conditioner or furnace. The temperature range is dependent upon a variety of variables and your commitment to temperature regulation.
“We open the windows early in the day, to take advantage of the cooler morning air. The hot air rises through natural convection and exhausts itself through the windows,” says Pro.
Tip: In climates where excessive heat is a problem, a porch outside your windows can limit the amount of heat due to sunlight your house receives in the summer. A white or silver roof will reflect sunlight instead of absorbing it — yet another way to naturally control your home’s temperature.
“The most important factors to consider are the regional climate and solar rotation of the location where you plan to build or update,” says Ryan McEvoy of Gaia Development in Los Angeles, Calif., a green-building consulting company that creates cost-effective solutions for efficient sustainable buildings. Because passive solar homes rely so much on the sun’s energy, they are best suited to sunny climates such as California or Colorado, though elements of the design certainly work anywhere.
The cost savings you’ll get from passive solar design is dependent on each individual situation. “The dollars you put toward passive solar techniques will be dollars saved in the long run,” Pro says. “It just depends on the extent of the design." On average, energy savings are between 5 percent and 50 percent, depending on the scale of passive solar elements included in your home’s design. And remember, it isn’t just for new homes; existing homes can be retrofitted to include passive solar elements.
Simple Lifestyle Changes Can Maximize Your Benefit
“Be ready to be active in your house if you want a purely passive home,” Pro says, though he believes the benefits of a passive solar lifestyle far outweigh the minor inconveniences. Pro and his wife move their bed to various rooms based on the season to take advantage of the natural heating and cooling areas in their passive solar home. If you’re willing to commit to reducing your energy consumption, a passive solar design may be ideal for you.
In addition to eco-friendly features and lower energy costs, “[Passive solar homes] are free of the semi-allergic reactions associated with unnatural heating, cooling or lighting units,” McEvoy says.
In the event of a blackout or natural disaster, a passive solar home will remain a comfortable temperature without requiring a back-up generator. Due to their sustainable construction, passive solar homes can require less maintenance than a conventional home.
As energy-conscious design becomes the norm, homebuyers can expect to find energy-saving design elements such as passive solar techniques standard in many new homes. Passive solar design helps insulate owners from rising fuel costs in the future and increases the resale value of your new house.
Obviously, there are many ways to go “passive.” Whether you hire an architect or choose to do it yourself, are building a new home or simply retrofitting your existing home to include passive solar elements, there’s a passive solar solution for everyone.