Blessed Be a Sunny House

We knew that we wanted and needed to let the sun shine into our dwellings during the winter months for heat and to shield from it during the summer.  It was a matter of practicality.   The history of solar architecture is really a history of indigenous architecture.  “The solar orientation of buildings was discussed by Socrates, Aristotle, Vitruvius and others.  Solar building was employed in ancient Greece, China, Asia Minor and by the Anasazi and Sinagua Indians in America.”1

The Industrial Revolution preempted our wise ways in favor of something “modern”.  Today, as we look to stretch our dollars, our energy and our environment, we can often look to our ancestors for answers.  Since the Arab oil embargo of the 1970’s, there has been renewed interest in solar energy.

When we think of solar energy in our culture, what comes to mind are solar cells or photovoltaics which convert sunlight into electricity or solar panels that create heat transfer through the movement of fluids.  These are called active solar systems.  Passive solar systems on the other hand, allow the sun to penetrate the building directly without mechanical means and provide some additional heat.  “Passive systems are simple in concept and use, have few moving parts and require little or no maintenance. These systems do not generate thermal pollution, since they require little or no external energy input and produce no physical by-products or waste.  Since solar energy is conveniently distributed to to all parts of the globe, expensive transportation and distribution networks of energy are also eliminated.”2  Recall what it feels like to enter a greenhouse or a closed up automobile on a sunny day.  It is warm or even hot.  Solar radiation passes through glass as short-wave radiation or light, but when it is absorbed by the interior surfaces, the light is changed to thermal energy, also known as infrared radiation, thermal radiation or heat. The reason why the greenhouse, the automobile or a poorly designed home will overheat on a sunny day is because the interior air and surrounding surfaces have little ability to absorb and store the heat.  Reducing the temperature swing to create a more even temperature is a function of good design.   Good design in this case would be to calculate the appropriate amount of thermal mass in the interior of the building to absorb the excess heat on sunny days and release back into the building at night or on cloudy days.

After consideration of the landscape and climatic conditions, a buildings’ design orients the solar collecting windows facing true south (in the Northern Hemisphere) or within 15 degrees of true south.  Understanding the seasonal movements of the sun and the angle in which sunlight passes through the atmosphere will allow you to maximize heat gain during the winter months and provide appropriate shading devices via overhangs, louvers or vegetation to reduce unwanted heat gain in the summer.  Sun path diagrams included in most passive solar design books illustrate this clearly.

Once inside the building the solar radiation is best utilized when absorbed by thermal mass materials in floors and walls.  The most commonly used heat storage materials like stone, brick, concrete, adobe, earth and water have the ability to absorb considerable amounts of heat and re-radiate it back into the structure when the temperature warrants.

Passive Solar Rules of Thumb

From “The Solar House” by Dan Chiras

• Incorporate 7% of the floor area in south glazing
• An additional 1 square foot of glazing should be added for every 5.5 SF of sunlit thermal mass floor ,40 SF of mass floor not in direct sun & 8.3 SF of thermal mass wall
• Advocate for provisions to insulate shutter or quilt in some way the glazing at night to reduce the loss of that precious solar gain.

Good passive solar design takes into account all aspects of heat loss/gain factors.  Energy and heat conservation practices are necessary to make efficient use of that precious solar energy.  For example, window glazing must by accompanied by an insulated and tight fitting curtain, quilt or shutter system.  Without it, the energy gained by the sun during the day will quickly be lost through the glass at night, resulting in a net heat loss.  This is a critical component often overlooked and sited by solar naysayers.  Speaking of naysayers, I recall an incident recently where a window salesperson was chiding me for specifying so much southern glass in our work.  She was complaining about faded fabrics, carpets and furniture.  Of course, these issues become part of design schemes that minimize the impacts like this

In a cold, cloudy climate such as ours, most people do not even consider solar energy as an option.  While we cannot expect to achieve a cost effective, 100% solar heated house here, we can greatly reduce our external heating requirements with thorough planning.  It has been my experience that a well designed, insulated and maintained passive solar home needs little external heat input during the swing months of spring and fall.  During  the depths of a cloudy winter is when the home needs some added heat.  I've been in homes where only 6 cords of wood or less per year were used in a back up wood stove to maintain a comfortable temperature.  When constructing passive solar homes in the winter months, I have been pleasantly surprised to find how toasty a space can become on a sunny day and how comfortable it is the next morning.  These experiences have been in unfinished, uninhabited dwellings without back up heat or window coverings.

As with all things,  we have many choices available to us.  Reducing our demand on the earth’s limited resources can fuel the desire to create buildings that reflect these principles.  Someday maybe we will develop tax incentives, mortgage rates and building codes that support this thinking.  Perhaps the struggle over Arab oil and our gasping for good air and water will help us choose a solar-wise future. .  Let the sun shine in: it is a gift.  As we notice the changes in the amount of sunlight throughout the seasons, let us once again claim our solar heritage.

References:

• The Healthy House: Creating A Safe, Healthy and Environmentally Friendly Home, Sydney and Joan Baggs, Harper Collins Publishers.
• The Passive Solar Energy Book, Edward Mazria, Rodale Press.
• Passive Solar Energy: The Homeowners Guide to Natural Heating and Cooling 2nd Edition, Bruce Anderson and Malcolm Wells, Birch House Publishing Company.
• The Passive Solar Construction Handbook, Steven Winter Associates, Inc., Rodale Press.
• The Solar Greenhouse Book, Edited by James McCullagh, Rodale Press.
• Other Homes and Garbage: Designs for Self-sufficient Living, Jim Leckie, Gil Masters, Harry Whitehouse and Lily Young, Sierra Club Books.

Raise High the Solar Greenhouse, Carpenter

Place your hand in the sun
Like an oak length of beam,
Turn your wrist until the roots of the pulp deliver muscle
And sap to the garden roof.
Walk the property line
Like a child, swaggering and sure,
Marking with your toe the axis
Which is a flush as equator heat.
Raise your arms overhead
Like a sextant
Vbringing down the heavens in an arc
Making an A with your hands
And imagine what green will sprout
From that blessed plot.

- James C. McCullagh