CLIMATE AND SITE CONDITIONS
SUN

GOAL:
To become aware of the importance of the sun when designing an energy efficient home.

OBJECTIVES:
The student will be able to:

1. Discuss solar heat gain during the various seasons.

2. Demonstrate an understanding of the importance of sun patterns by completing the sunchart exercise.

GLOSSARY:
Fenestration - A term used to signify an opening in a building to admit light and/or air.
Reflectance - The ratio or percentage of the amount of light reflected by a surface to the amount of light shining on that surface. The remainder that is not reflected is either absorbed by the material or transmitted through it. Good light reflectors are not necessarily good heat reflectors.
Ineffective - Has no effect.

LESSON / INFORMATION:
When designing an energy efficient building you need a clear understanding of the environmental factors that affect the building site. These factors will differ from summer to winter. The fall and spring seasons are similar and provide a third climate season. The design should incorporate those positive elements the environment has to offer and protect against those that are detrimental to comfort.

Louisiana receives a large percentage of solar radiation during the summer, and a minimum amount in the winter. What is beneficial, however, is that the sun is high in the sky during the summer and is easy to screen. It is lower in the winter, allowing for deeper penetration through the building's fenestration elements. The sun diagram charts in Appendix C indicate the location of the sun at any time of the day throughout the year. The location of the sun is crucial to proper climatic-responsive design.

Summer.
The need for artificial cooling is usually caused by the humidity and solar heat gain being too great for comfort. The first and most important principle of summer design is to prevent or minimize solar heat gain in the building.

Shading, insulation, and reflectance are the main design elements. It is most important, first of all, to keep the sun off the building. Buildings should be designed as selfshading. Usually, horizontal elements on the southern side and vertical elements on the east and west side of the building are beneficial architectural elements to shade the building. Light colors also work well to reflect heat from the exterior skin.

As the thermal heat penetrates the skin of the building working its way to the interior, insulation is the main defense to stop this heat gain. Insulation is part of the design of the exterior wall and the ceiling below the attic space. Some insulated walls are necessary to separate nonconditioned spaces.

About 40% of the heat penetrating the exterior envelope is radiant heat. Insulation works wells to stop thermal heat, but is ineffective against radiant heat. A radiant barrier is a mirrored metallic material that reflects the radiant heat back to the exterior. A radiant barrier is more effective when used in conjunction with an air space. Radiant barriers should be used in the attic and in all exterior walls.

Winter.
The building design should be such that it takes maximum advantage of the solar heat gain in the winter. Preferably, heat should be collected as early as possible in the morning, and more important, until late as possible in the afternoon. The arc of the sun during this time of year is much shorter than during summer and much lower in the sky. Being lower is very beneficial because the roof overhang, or other shading devices no longer block the sun but allows penetration in the building for the needed heat. It is important to have materials that can store this excess heat otherwise the interior spaces will overheat. Dense material with a high specific heat value, like brick or concrete, are best for heat storage, and the best are used on the floor for direct heat gain.

The area to the south of the building should reflect light and heat into the building. This could be accomplished by light colored ground cover such as shell. Care must be taken in design to avoid glare and heat gain in the summer.

If one has a choice, a south-sloping building site is most beneficial for smaller buildings because greater exposure to the sun and more protection from the north winds will occur. Also, if solar access might be a problem in the future, locating the building on the northern end of the site will generally assure better exposure to the sun from the south.

ACTIVITY:
1. Reorganize the class in groups of three and ask them to complete the following - you will need prepared problems.

2. Use the suncharts for your area (latitude) in Appendix C to project the shading pattern of the trees and other vegetation on the site for the summer, fall, spring and winter.

3. Knowing the height of the tree and the angle of the sun at different times during the day (see sun charts), you can calculate / figure the length of the shadow (See Figure 1).
dr-e40
Figure 1.

4. After the shadow pattern is drawn, evaluate the site for the best location for a house. Look for morning and afternoon shading and summer breezes.

INFORMATION CHECK:
Indicate whether the following statements are TRUE or FALSE.

1. Environmental factors which affect the building site will not change with the seasons.

2. In Louisiana, more solar radiation is received in the summer than in winter.

3. Reflectance refers to amounts of light reflected by a surface to the amount of light shining on that surface.

4. When considering environmental factors that affect a building site, there are usually three climate seasons to be considered.

5. The need for artifical cooling is usually caused by solar heat gain and humidity.

6. Carpets and area rugs are best for heat storage and direct heat gain.

7. Fenestration refers to an opening in a building to admit light or air.

8. It is not necessary to insulate exterior walls or attic space if the building is placed in proper alignment on the site.

TEACHER'S NOTES:
ACTIVITY:
1. Find a site with trees for the students to analyze. Have them measure the site and locate the trees or provide them with a finished site plan. They will need to know the width and height of trees to project the shadow pattern. Have the students practice this in class before they do the activity.

2. You might have the students analyze different sites so they can compare the results. Have the students present their analysis to the class for group evaluation and discussion.

ANSWERS TO TRUE/FALSE STATEMENTS:
1. False
2. True
3. True
4. True
5. True
6. False
7. True
8. False

RECOMMENDED READING:
Natural Louisiana Architecture. Cazayoux, Hebert and Winn. Baton Rouge, LA: Louisiana Department of Natural Resources, 1991.

Site Analysis. E.T. White, Tucson, Arizona: Architectural Media Ltd. (Published), 1983.

REFERENCES:
Natural Louisiana Architecture. Cazayoux, Hebert and Winn. Baton Rouge, LA: Louisiana Department of Natural Resources, 1991.

Comments or questions to: TechAsmt@LA.GOV

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