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Passive Solar and Energy Efficient Home Design
EVERY HOME IS A SOLAR HOME
http://www.txses.org

It is a fact, that everything we build is solar. When we ignore solar energy during the design stages, what we end up with is a building which may benefit from solar, although it is just as likely to be beat up by solar energy.

A passive solar design will not only lower your utility bills, it will be comfortable. Comfort is priceless.  The following guidelines are drawn from research and practical application, from successes and failures, from the experience of our ancestors who lived in caves, and from recent computer generated studies.

The solar guidelines in this article are just that, guidelines.  However, we hope that they help you as you start planning for your solar home.

Orientation: The longest wall of the home should face south. The winter sun rises South of East and sets South of West. Placing more glass on the South wall will ensure that your home receives free solar energy.

This same orientation helps to prevent the high summer sun from entering the home.

A compass will point to magnetic North/South, but a solar home or collector works best when it faces TRUE SOUTH.

Why not a compass?
A compass does indicate magnetic north/south, however the needle is awfully small and it can be tricky to get accurate readings. Even after steadying the compass and determining what it is trying to say, you still have to convert "magnetic" north to "true" north. This conversion is no simple matter because the lines of magnetic flux on the surface of the earth vary significantly depending on your region.

If not with compass, then how?
Every day the sun rises in the east and sets in the west. At some point during the day it crosses over the midpoint: solar noon. At the exact moment of solar noon, a vertical pole will cast a shadow that is precisely oriented along the north/south line. This line is accurate and easy to create using the string of a plumb bob.

When is Solar Noon?
Solar Noon is a simple concept (when the sun is half way across the sky in any given day). The problem is that when our watch says 12:00, the sun is rarely half way across the sky - there are three reasons for this:

1) Time zones artificially place large geographic areas on the same clock time (hint: when solar noon occurs in Calais, Maine, the sun still must travel several hundred miles before reaching solar noon over Buffalo, New York - yet these two cities are in the same time zone.) Basically, every degree of Longitude away from the Standard Time Meridian for your time zone counts for 4 minutes of clock time.

2) Equation of Time: as it turns out, days on planet earth are not of constant length. As the earth orbits the sun, our speed of rotation on our own axis actually varies slightly each day. This means that we must take this variation into account when calculating solar noon: in February the sun is more than 14 minutes behind schedule while in October it is more than 16 minutes ahead. You can see a graph of the equation of time at: http://www.srrb.noaa.gov/highlights/sunrise/eqntime2.gif

3) Daylight Saving Time - don't forget to adjust the calculation for the appropriate method of time keeping. Daylight Saving Time starts the first Sunday of April and ends the last Sunday of October.

Sound a litle complicated?
Go to the NOAA web site (http://www.srrb.noaa.gov/highlights/sunrise/sunrise.html) to calculate "Solar Noon". This page also calculates the Equation of Time, Apparent Sunrise and Sunset. Make sure you click the Daylight Saving Time checkbox after the first Sunday in April (and before the last Sunday in October). Once you enter your latitude and longitude (or a city near you), click the "calculate sunrise/sunset" button and the time of solar noon will appear in its box below.

Solar Access: Buildings or trees too close to your home could block the low winter sun.  Make sure that if you plant trees close to your home, that they lose their leaves in the winter-if you live in a climate where the trees lose their leaves.

Windows: The amount of glass on the South wall may equal 7% of the homes total square footage.  (Example: 2,000 Sq. Ft. = 140 Sq. Ft. of glass.)  To avoid overheating, this amount of glass should not be exceeded. The 7% applies to conventional home construction with standard floor coverings such as carpet, vinyl tile, or wood. Increasing glass area above 7% will require additional thermal mass, i.e. concrete/tile floors, rock, brick, concrete or adobe walls.

The 7% amount is NET sq. ft. or the total window area less the trim etc.
Multiply the entire window by .8 to get the net glass area.

Example: A 3'0"X5'0"window is 15 sq. ft.
15 X .8 = 12 sq. ft. net

East and North glass should be limited to no more than 4% of total sq. ft. (Maximum)

West glass should not exceed 2% of total sq.ft.(MAXIMUM)

Landscaping: Plant deciduous or evergreen trees on the east, west and north sides of the home. Xeriscape! 

Avoid dark colors, inside and out.

Insulation:
Insulate exterior of slab/foundation with extruded polystyrene sheets. R-5 for moderate climates, R-10 for colder climates.

Sole Plate:
Install sill sealer under the bottom plate of all exterior walls, on both the first and second floors.

Walls:
In moderate climates use 2X4 frame walls with R-13 batts and R-4 rigid insulated sheathing boards (1" expanded polystyrene). For Cold climates, use 2X6 frame walls with R-19 batts and the same R-4 sheathing.  Sprayed cellulose insulation should be considered because, though more expensive than batts, is more effective because it fills voids and reduces air leakage."

Attic:
Ceiling Install R-30 insulation, blown in type is preferable, for moderate climates. Levels of R-38 to R-50 are recommended for colder climates

IMPORTANT:
Prior to installing wall insulation, use cans of expanding foam insulation and/or caulk to seal all electrical and plumbing penetrations, around doors and windows.

Tape/seal all joints in ductwork. Duct work should be installed in interior (heated) space so that heat or cold is not lost to unheated spaces (attic). Furrdowns should be sheathed and sealed prior to installing duct.

Insulate walls surrounding furnace closets and seal return air plenum.

Doors:
Install steel or fiberglass insulated exterior doors that have an insulation value of R-5.9 or greater. Lower R-value doors can be used in conjunction with a storm door.

Ventilation:
Place and size windows to take advantage of natural ventilation and prevailing breezes.

Fans:
The use of ceiling fans can drastically reduce the running time of air conditioners.

Contact your local county agent or state energy office for recommendations specific to your area.  And again, it's your solar home, so you can design it how you want to.  However, these simple recommendations are a good place to start.

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