Solar Geometry and Solar Responsive Design Quiz
Note: All questions are based on the northern hemisphere. The questions apply equally to the southern hemisphere except that there would be certain changes such as “north” and “south” would be reversed.
1. Does the sun ever shine into north windows?
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yes
2. If yes, for how many days each year? days
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180 days – the sun rises south of east for half of the year and north of east for the other half of the year
3. For how many days each year does the sun rise from due east and set due west? days
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two – only on March and September 21
4. For how many days each year are there 12 hours of daylight and 12 hours of night? days
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two- the equinoxes
5. Is that true everywhere on the planet? If not, where not?
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no – at the equator, every day of the year has 12 hours of daylight and 12 of nighttime
6. On June 21, the sun rises how many degrees north of east? degrees
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it varies with latitude
7. What is the smallest horizontal (azimuth) angle that the sun rises north of east on June 21 anywhere
on the planet? degrees
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at the equator the sun rises 23.5° north of east on June 21 (azimuth of 23.5⁰)
8. Is there any place where the sun shines into a north window from due north?
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yes
9. If yes, where?
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At the Arctic Circle the sun rises 90⁰ north of east on June 21 at midnight (azimuth of 180⁰). Going north of the arctic circle, the sun shines directly from north for increasing number of days until at the north pole it shines directly into north windows at midnight for half of the year.
10. What is the maximum angle of altitude of the sun on June 21 at the north pole? degrees
What is the minimum angle? degrees
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At the north pole the altitude of the sun on June 21 is 23.5° all day long. On December 21 the altitude is -23⁰ all day long.
11. When all of the Arctic ice is melted, what time of year would be most popular for taking a cruise ship to the north pole and why?
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In the summer one has 24 hours of daylight with the sun revolving overhead at constant altitude angles. In the winter there are 24 hours of nighttime with the possibility of seeing the northern lights. However, at the equinoxes, there will be 24 hours of sunset or is it 24 hours of sunrise? Would that not be a great time for a honeymoon at the north pole?
12. What is so special about the Tropic of Cancer?
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Heading south from the north pole, the sun is higher and higher in the sky with June 21 at 12 noon always the highest altitude angle. At the Tropic of Cancer the sun reaches 90⁰ altitude for the first time (i.e. the sun is overhead for the first time) on June 21 at 12 noon.
13. For a south facing window that is 5 feet high, what is the correct size of fixed overhang so that the window is completely shaded during the whole overheated period which ends September 21 and fully exposed to the sun during the whole underheated period which ends on March 21? What is the answer for any latitude in similar climate regions? What does the answer tell you about the potential of fixed overhangs being very effective in climates that need both winter solar heating and summer shading?
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Fixed overhangs are not very good in climates where both winter heating and summer shading are required. After all, the sun takes the same sun path on March 21 and September 21. A fixed overhang cannot both fully shade and fully expose a window to the sun if the sun is at the same altitude. Any fixed overhang will not shade enough in the summer, if it is designed to collect most of the winter sun, and vice versa. Thus, a fixed overhang is a poor performer in any climate were much heating and cooling is required, and the world now needs high performing building systems. Consequently, in such climates south windows should have movable overhangs such as retractable awnings.
14. Since a primary function of windows is to provide a view, what shading system should be used on east and west windows so that the view is mostly maintained and the sun is mostly shaded?
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There is no shading system for east and west that can fully shade windows while maintaining a good view. Vertical fins perpendicular to the windows do not shade well, and they reflect daylight to the right and left creating glare. Not only do louvers shade east and west windows a little better, they also reflect the light up to the ceiling for superior daylighting. Slanted fins work better than perpendicular fins but restrict the view even more. Thus, avoid east and west windows whenever possible, since there is not any good shading system for those windows.
15. Is it true that skylights collect more sun in the summer than the winter?
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yes!!!!!!!!
16. If yes, is that a good idea?
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no!!!!!!!
17. If not, what is better than a skylight to harvest the sun through the roof so that the most sun is collected in the winter and the least in the summer?
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Use clerestories facing south where winter heating is required and facing north where winter heating is not required.
18. Is there such a thing as “a free lunch" in solar responsive design?
(i.e. you can save energy forever without any additional first costs)
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yes!
19. If yes, how?
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It is possible to design a solar responsive building at the same cost as a conventional building and yet use less energy and thus cost less to operate. A “free lunch” can be achieved by the informed use of the following strategies:
1. Form and orientation of building
2. Size and placement of windows as compared to the same number of windows equally distributed around the building as is quite typical.
3. Using white or very light colors for the roof and exterior wall surfaces (a white roof has 50% less heat gain than a black roof and a white wall has 35% less heat gain than a black wall or 25% less than exposed red brick)
20. Is there such a thing as a “free lunch that you get paid to eat” in regard to building design
(i.e. a building that uses less energy forever and costs less to build than a standard building)?
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yes!
21. If yes, how?
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The strategies mentioned in question 19 will even reduce the first cost because the cooling system will be smaller (i.e. smaller compressor, AHU, and ducts). (borrowed from Amory Lovins)
22. Is it smarter to buy a house (either free standing or row house) on a north-south street or an east-west street if they cost the same?
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It is much smarter to live on and east-west street because then most windows will face mainly north and south, while on the north-south street the window will face mostly east and west and will therefore be blasted by the summer sun while getting little help from the winter sun.
23. The house on which street would cost less to build?
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The houses on the east-west street not only save in heating and cooling energy costs, but they can also have a smaller cooling system and therefore cost less to build.
24. Is it a good idea to have a deciduous tree on the south side of a building because it will provide summer shade and winter sun?
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No! Not only do deciduous trees shade anywhere from 20 to 60% of the winter sun by their branch structures (depends mostly on the species of tree), but they will shade the roof in the summer which is unfortunate since the south facing roof should have an active hot water collector and eventually PV if not right away.
25. Deciduous trees should be on which side of a building?
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Deciduous trees are best on east and west windows that need a maximum of shading in the summer.
26. Should north windows be shaded?
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yes. Although shading north windows is not the top priority, the solar exposure of north windows (½ of each year) does contribute to the cooling load. Windows on the first floor may be shaded by trees and neighboring structures, but windows on a multi-story building will be exposed to the summer sun. Ironically, the solar exposure of north windows increases with latitude. Thus, north windows in Canada may require more shading than windows in the U.S. South. This is especially true for large office buildings which need much cooling.
27. Is a solar design successful if the south windows are shaded on June 21 and are fully exposed to the winter sun on Dec. 21?
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Absolutely not !!!!!!!! The high June 21 sun is the easiest to shade on south windows requiring only a small overhang which will not shade the low December 21 sun. Such a small overhang appears to work exceedingly well but erroneously.
28. If not, what dates should be used to design and prove the effectiveness of a shading system?
Summer Winter
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The logical goal is to shade windows while it is too hot outdoors. That time of year is called the overheated period, and windows should be shaded during the whole overheated period. Thus, a shading device should be designed to shade until the end of the overheated period, which in some U.S. climates is during September but never on June 21.
Similarly, shading devices should not block the winter sun during the whole underheated period. No sun should be shaded until the end of the underheated period, which in some U.S. climates is March but never Dec. 21.
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