Residential Solar - Passive Systems-Design:

Taking advantage of the sun's energy through passive means is not new. Ancient civilizations understood how to orient their buildings to help maximize the potential heat input from the sun in cold seasons and how to shade or block the sun in the warm/hot seasons. Anyone who ever grabbed a steering wheel on a hot summer day can attest to the fact that the sun can make objects quite hot.

We are fortunate to live in the era when passive solar design drawings and details are readily available from a number of sources (including this website) and to have access to sophisticated software that can optimize the passive solar features of any project. So, let's begin with passive solar fundamentals and proceed from there:

Direct-Gain Passive Solar

Passive Solar Graphic - Direct Gain

Passive Solar Graphic - Direct Gain

Direct gain passive solar can be as simple as orienting the windows on a building toward the South (Northern Hemisphere) to let the sun shine in during the winter months. An overhang can be designed to block the sun's rays in the summer months, thus adding heat when needed and blocking sunlight when no additional heating is required. The addition of a masonry (dense) material, such as brick, stone, tile or concrete, can help store the sun's heat for a certain length of time that is actually calculable using simple mathematic formulas.

Trombe' Wall Graphic - Courtesy US DOE

Trombe' Wall Graphic - Courtesy US DOE

Passive Solar Graphic - indirect Gain - Trombe' Wall

Passive Solar Graphic - indirect Gain

Basically, the thicker the material the longer it takes for the heat energy to pass through. Also, thicker materials store more of the heat energy and will release it at lower temperatures. The nearby graphics depict both direct and indirect gain options for passive solar.

There are several other options to take advantage of passive solar energy that are covered much more extensively in the books and websites listed at the end of this article. There are also a few items to look out for when incorporating passive solar features into any building so please be careful that you don't:

  1. Install too much overhead glass (glazing) without consideration of summer shading options - It is relatively easy to overheat a building and not so easy to cool it back down. Plus, adding to an air conditioning load can certainly increase summer cooling bills with little offsetting benefits for winter heating boost. If you want to install skylights or overhead glazing for daylighting purposes then please consider the use of a tubular skylight or similar device that brings in light without the corresponding heat energy.

    South Wall Glazing Without Overhangs

    South Wall Glazing Without Overhangs

  2. Add vertical glass (glazing) without consideration of appropriate overhangs - Older solar energy books tend to showcase solar homes with extensive amounts of vertical, south-facing glass and little or no overhangs. This type of design does lend itself to maximum amounts of winter sun but also allows the summer sun to enter as well, forcing the cooling system(s) to work overtime and negate any benefits you may have received from the boost in winter heat energy. Remember that you are trying to strive a balance in your design that reduces your winter-time heating bills without seriously impacting your summer cooling bills. These factors can be adjusted depending upon your geographic location and climate zone but they basically hold true no matter where you build.
Recommending books and other references is not something we do very often at DesignCharrette.com but there are a few exceptions. The book entitled; "The Solar House: Passive Heating and Cooling" by Dan Chiras is a relatively new and affordable reference for passive solar design considerations. Mr. Chiras has written over 25 books, including textbooks, that primarily focus on renewable energy, sustainable design & construction and natural non-toxic materials. We feel this book should prove helpful to you.