Green Home

Heating Things Up with Passive Solar Design

Passive Heating & Cooling with Passive Solar Design

Passive solar design offers an affordable alternative to expensive active solar energy systems to use energy from the sun to heat and cool a building.

Many of us are trying to reduce our carbon footprint by consuming less energy. We can install solar panels to provide us with an alternative source of power, and we can install solar hot water systems to heat up our water using energy from the sun. These are both active solar systems that utilize the sun’s energy to perform these tasks. They are also prohibitively expensive for the average home owner to install. However, the sun’s energy can also be harnessed passively to provide a source of light, and to both heat and cool our homes without the need for expensive equipment. All that is required is some careful planning to incorporate the principals of passive solar design when we build, renovate, or retrofit our homes.

5 Key Elements of Passive Solar Design

Passive solar design consists of five basic elements that collectively maximizes radiation from the sun, and uses it to heat and cool a home:

  1. An aperture, which consists of a large glass window, or windows, that allows sunlight to penetrate into the home to warm it up, is the fundamental element in passive solar design. Windows must face the sun to collect sunlight effectively – they should ideally face within 5-15 degrees of true south in the northern hemisphere (or true north in the southern hemisphere) for maximum benefit, and be unshaded during the hottest part of the day in summer. When designing a home, pay careful consideration to orientation, in order to maximize the potential of solar design in your home. Increasing the number of windows on the south facing wall (north facing in the southern hemisphere), a technique known as sun tempering, will also increase efficiency. A solar greenhouse or sun-room built into the south facing wall is a good way to provide an insulating buffer between the house and the exterior. During the day, the sun will heat up the greenhouse or sun-room; this warmth will circulate to the rest of the house when opened up, but at night it can be closed off from the house to prevent heat from escaping.
  2. An absorber, which absorbs the warmth from the sun as it enters the room. This is an exposed surface that lies in the direct path of sunlight entering the home, and can consist of a brick wall, glass panel, flooring, or any surface that is able to absorb heat.
  3. A thermal mass, which lies behind the absorber and is able to retain the heat that has been absorbed. These usually consist of the materials in walls, flooring, or partitions that lie behind the absorber (the surface exposed to sunlight). A technique commonly used in passive solar design is a trombe wall, which consists of a glass panel positioned approximately two inches from the surface of the wall. The air space between the wall (thermal mass) and the glass panel (absorber) is sealed. As sunlight penetrates through the glass pane, it heats up the air trapped in the space between the wall, which not only heats up the thermal mass, but also radiates heat out into the room. As water retains heat for twice as long as masonry, it also has excellent thermal mass properties, and can be used effectively in passive solar design. Water walls constructed of containers that are filled with water are often used in passive solar design, but an indoor pool or hot tub can serve the same purpose.
  4. Distribution – the manner in which the absorbed heat is transferred throughout the home. Heat is distributed from warmer to cooler materials until a temperature equilibrium is reached. Heat is transferred by either convection, conduction, or radiation. Passive solar design takes these principles into consideration to determine how heat will be distributed throughout the building, and makes use of them to both heat and cool a living space.
  5. ControlKey Elements of Passive Solar Designsome manner of controlling the amount of heat that is allowed to penetrate is necessary, to prevent overheating. Simple measures like roof overhangs, awnings, and blinds can be used effectively to control the amount of sunlight that is allowed to penetrate the home. Roof overhangs can prevent sunlight from entering a room in summer when the sun is higher in the sky, but allow sun to penetrate a room in winter when the sun’s position is lower. Retractable awnings can be adjusted to allow or block sunlight penetration, while blinds offer a cheap and convenient method of controlling the amount of light entering a room, depending on the time of day, or weather conditions.

The above five elements form the essential core of passive solar design. Each element performs a separate function, but in order for them to be effective, they need to work together collectively, making each element a vital component of passive solar design.

Insulation is a Vital Component of Passive Solar Design

Good insulation is key to prevent heat from escaping, so take the necessary steps to ensure that your house in well insulated and energy efficient:

  • Use energy efficient windows.
  • Make sure windows are well sealed.
  • Find and seal any air leaks around doors, ducts, openings for plumbing and electrical wiring, or any other areas that heat can escape.
  • Provide extra insulation in walls, ceilings, and floors to keep heat in and cold out in winter, and heat out in summer.
  • Close drapes at night to improve insulation, in summer; in winter, open drapes to allow cold night air to cool thermal masses within the home, to help keep it cool during the day.

Take the time to incorporate passive solar design concepts when planning your new home, or retrofitting an existing home or living space. Not only will you have a comfortable living space, but with a little foresight and planning you can save substantial amounts on your heating and cooling bills by using standard construction materials, which don’t necessarily cost more.


Featured Image by Michael Shealy via Flickr
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