What makes a comfortable home? Lots of natural light and fresh air, comfortable warmth in winter and pleasant coolness in summer. All of this is possible with passive solar design. Let’s break down what passive solar is and how it works.
Key takeaways
Passive solar design is based on a fundamental understanding of how sunlight interacts with buildings. Knowing these principles, we can naturally heat, cool, ventilate and light living spaces by reflecting, absorbing and transmitting solar light and warmth.
By itself, passive solar design requires no special equipment, ongoing investment, or effort. All objectives are met through thoughtful design, material selection, and building orientation. Yet, these aspects should be considered before construction begins, as changing them later will be hard or just impossible.
Solar panels also love the south-facing side. If you want to install a solar system, make sure you have enough space on the southern slope of your roof.
South-facing windows capture the most sunlight during the day, especially in the winter months when the sun is lower in the sky. The south side is best for playrooms, living rooms and spaces you spend most of your day in. The east side is ideal for bedrooms to wake up with the first rays of the sun, while the north side is good for rooms that don’t need daylight, such as the garage or bathrooms.
Windowsills can help increase the amount of light in the room. They should be light-colored and slightly angled to the room. This way, the sunlight falling on them will be reflected and scattered, making the room brighter. You may also use window light reflectors for the same purpose.
It costs us a lot to maintain a comfortable home temperature. Heating and cooling account for about a quarter of your electricity bill, according to the U.S. Department of Energy. Passive solar offers you two ways to give your air conditioner and heater a small break and lower your energy costs. Passive heating is achieved with the help of thermal mass and trees.
Thermal mass materials absorb, store and release heat. Common examples include concrete, brick, stone, and tile. During the sunny part of the day, sunlight streams through windows and warms these thermal mass elements. The absorbed heat is then released gradually throughout the cooler evening and night, providing natural warmth.
Thermal mass works best when combined with good insulation, slowing down the heat transfer process
In summer, thermal mass materials work the other way around. Cooled down during the night, they keep your home comfortable during the day, slowly absorbing the sun’s heat to release it at night, providing passive heating.
Polished concrete floors or exposed brick or stone walls can be a beautiful design feature, while also providing thermal mass benefits. You can use them as an accent or incorporate them into your passive solar house plan. Large tile walls and countertops can act as thermal mass elements in kitchens, absorbing heat generated during cooking and releasing it later. There are three approaches to incorporating those elements.
This is the most straightforward method. Sunlight directly enters the living space through south-facing windows and strikes interior surfaces like floors, walls, and furniture. These surfaces absorb the solar energy and store it as heat. The stored heat is gradually released into the living space throughout the day and evening, providing warmth.
Direct solar system is closely related to the lighting tips above, as it relies on direct sunlight. You need to maximize solar gain during the winter and provide overhangs or shading devices to prevent excessive solar gain during the summer.
This method is not as obvious as the previous one. Sunlight enters the building indirectly, passing through the windows and striking a thermal mass wall, often made of concrete or masonry and located between the windows and the living space. The wall absorbs and stores the solar energy. Then, the heat is gradually conducted from the wall into the living space. The brightest example is the so-called Trombe wall.
The Trombe wall is a passive solar heating system that uses a thick, south-facing wall to absorb and store solar energy. Sunlight passes through a glass or glazing and hits a thick, high-mass wall, typically made of material like concrete, brick, or stone, absorbing the solar energy. The stored heat is then gradually released into the living space through:
Indirect solar system provides more controlled heat release and can be more effective in dealing with summer overheating. But compared to direct gain, it is more complicated to implement.
Isolated gain systems collect and store solar energy in a separate, enclosed space, often called a sunspace, solarium, or greenhouse, that is attached to the main living area of the building. This space acts as a solar collector and heat exchanger.
How it works: Sunlight enters the sunspace through large south-facing windows. The sunspace typically contains thermal mass elements like concrete floors, masonry walls, or water-filled drums that absorb and store the solar heat.
The warmth is then passed through:
Wind increases the rate of heat loss from your home. Even if the air temperature isn’t that low, the wind makes it feel colder. Evergreen trees or shrubs placed on the north side of your home can create a barrier that slows down and disrupts winds approaching your house from the north. This reduces the windchill effect on your exterior walls, keeping the heat inside.
Evergreens also provide a secondary layer of insulation. They can act as a snow catch, trapping snowfall near the foundation. This trapped snow acts as an additional insulation layer, further reducing heat loss from the house.
In summer, southern rooms may face the overheating problem, when the sun turns them into a greenhouse, trapping heat inside. The best way to avoid this is to protect south-facing windows with a special awning or to extend the southern slope of the roof. The summer sun rises high in the sky and this awning will safely hide you from its scorching rays, while not preventing the low winter sun from entering the room.
Ponds or fountains add a cooling element to your outdoor space, particularly in drier climates.
Trees planted south and west of your home or vines on pergolas or south-facing walls can also provide shade in summer, acting like a natural awning. Their leafy canopy blocks the sun’s rays during hot months, keeping your home cooler. In winter, they shed their leaves, allowing sunlight to penetrate windows for natural warmth.
Consider prevailing wind directions when designing your house layout and window placement. This will help you maximize airflow through the space.
Natural ventilation is all about using nature’s forces to bring fresh air into your home and remove stale air, instead of relying on fans and air conditioners. There are two main drivers of natural ventilation: wind and temperature differences.
By opening windows and vents on opposite sides of your home, you can let winds blow through your house, forcing hot and stuffy air out faster. During cooler nights, this also cools the thermal mass elements which can then absorb heat slower the next day when the sun warms the space.
Stack ventilation uses temperature variations to induce airflow. Warm, less dense air rises, and buildings can be designed to take advantage of this. For example, opening high windows allows hot air to escape, while opening lower windows on the opposite side draws in cooler air.
Enough theory - time to get down to practice. Passive solar design has been used for thousands of years and is now seeing a revival of interest from both simple homeowners and top architectural and construction companies. Let’s explore some eye-catching examples of passive solar design from different parts of the world.
Earthships are a unique type of sustainable architecture developed in the late 20th century to early 21st century by architect Michael Reynolds. Earthships originated from Mexico, but can now be found all over the world, including Africa, Australia, New Zealand, North and South Americas, and Europe. They are designed to be self-sufficient and off-grid, using natural resources and recycled materials.
As the name hints, they are earth-sheltered, meaning that a significant portion of the structure is built into the earth, being better insulated and keeping stable temperature inside. Large south-facing windows capture solar heat in the winter, while overhangs and earth berming provide shade in the summer. Electricity is usually generated by solar panels and wind turbines.
Earthships often incorporate a wide range of recycled materials, such as tires filled with earth, glass bottles, and aluminum cans, for construction. Rainwater is collected and stored, and the wastewater is recycled in greywater systems.
This historic building in Toronto, Canada, demonstrates how passive solar design principles can be integrated into large-scale industrial architecture, even in older buildings. The building features expansive south-facing windows providing maximum solar heat gain during the winter. The thick masonry walls of the building act as thermal mass, absorbing and storing heat during the daytime and releasing it slowly at night. Natural ventilation strategies, such as strategically placed windows and vents, help to regulate internal temperatures.
This iconic building in Prague, Czech Republic, is famous for its unique, dynamic shape, resembling a dancing couple. Though its primary design intent was artistic expression, it also incorporates some passive solar design elements. The building’s orientation ensures maximum solar gain during the winter months. The building’s curved facade regulates sunlight penetrating throughout the day. Overhanging sections of the building provide shade during the summer months, reducing solar heat gain.
This art museum in Los Angeles, California, showcases how a combination of architectural and landscape design strategies can create a highly energy-efficient and comfortable environment in a challenging climate. The buildings are oriented to maximize solar gain in the winter and minimize it in the summer. Deep overhangs and adjustable louvers shade windows from direct sunlight. The use of concrete and other high-mass materials helps to regulate internal temperatures. The surrounding landscape plays a crucial role in shading the buildings and mitigating the effects of the hot Southern California climate.
Passive solar design not only reduces energy consumption and reliance on traditional HVAC systems but also creates a more comfortable and sustainable living space. Yet, it’s just one piece of the puzzle. Introducing energy-efficient practices, using renewable energy sources like solar panels – there are so many ways to make our homes a better place. Stay tuned and check out our articles for more sustainable tips.
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Years of experience in translation and a love of nature help Julia find the right words to encourage going solar. She joined the team in 2023 and is happy to make her contribution to a greener future.
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