http://www.mobilehomerepair.com/solarrules.htm
When designing your own solar air heater, these rules will help keep you on the path to success.
1) Don't let the size of the collector exceed 20 percent of the house's heated floor area, assuming the home is reasonably well insulated and you aren't using a heat storage system.
2) Baffle layout should be such that no single "air run," the distance between an inlet and outlet, exceeds 32 feet. Larger collectors should be divided into zones with more than one inlet and outlet, although it could still be powered by a single fan. Or outlets could have openings into various parts of the house or ductwork.
3) Fan-powered air flow should equal an "actual" two cfm per square foot of collector at sea level, and 3 cfm per square foot at an altitude of 7000 feet, because of decreasing air density. A square foot is defined as 1 foot x 1 foot x 1 inch deep. For a collector that's 4'x5'x2" deep, the formula would be cfm=(4x5x2)x3 for an answer of 120 cfms.
4) The air gap is a function of the air flow (volume over time) and the air velocity (speed over time). The optimal air flow is 800 feet per minute (fpm). Divide the calculated cfm by 800 fpm to get the area (in square feet) of the air gap cross-section. In the example in step 3, 120 divided by 800 = 0.15 square feet. To convert to square inches, multiply 0.15 x 144 for an answer of 21.6 square inches.
The gap (size of pathways) is then found simply by dividing the cross-section area by the width of the collector air way in one direction of air flow. In our example in number 3, the total cross-section width is 48". As we calculated in step 4, each pathway should have an air gap of about 21.6 square inches. Now start dividing. 48 divided by 3 = 16. 16" wide x 2" deep = 32 square inches. Nope, that's more than 21.6 square inches. So divide 48 by 4 and you get 12. 12" wide x 2" deep equals 24 square inches. Now we're getting closer.
To make 4 pathways, you'll need 3 dividers. Let's say those dividers are made from 1x boards which are 3/4" wide. With three dividers, you would subtract 1.5" from the total 48" width for a total width of 46.5". Divide 46.5 by 4 and you get 11.62 inches. Multiply that by two and you get 23.25 square inches which is as close as you are going to get to 21.6 square inches in this example. However you could adjust the depth of the panel to 1.75" to get an even closer air gap of 20.33. If you are custom-cutting your own glass, you can size the collector to the exact measurement. If you are already working from a piece of glass you've found, then all you can do is get as close as possible. Again, adjusting the depth of your panel is also one way to control your air gap. Keep in mind that the narrower your depth, the sooner your panel will heat-up. I would not go deeper than 2.5".
5) The collector inlets and outlets should be of a size equal in area to the air way (between dividers) they serve. For example, our airways in the above example ended up being 23.25 square inches. If you collect to a round duct, you'll need to find a size that gives you the closest area to 23.25 square inches. The formula for determining the area of a round duct, first measure across the duct to get the diameter and then divide by 2 to get the radius. So if you have a 5" duct, the radius would be 2.5". Then plug the radius of 2.5 into this formula to get the area: (radius x radius)x 3.14159 = area OR (2.5 x 2.5)x 3.14159 = 19.63 square inches. If you run the same numbers for a 6" duct, you'll get an area of 28.27. So ideally, you need a 5.5" duct which would give you an area of 23.75 which would almost exactly match the 23.35 square inches you need. But you won't be able to find round ductwork that's 5.5", so you would be OK to either use the 5" or 6" ductwork. If you plan on ducting the air into different areas of the home, I would lean towards the 6" size because your ducts will be longer.
6) Storage. A rule of thumb on storage sizing calls for 50 -- 60 pounds of rock per square foot of collector. Working with Btus, the specific heat of rock is such that one cubic foot stores 20 Btus for every 1 Degree F. it rises in temperature. In the case of a 40 Degree F. rise, a cubic foot would store 20 X 40 or 800 Btus. Let's say also that the collector output is 150,000 Btus per day. In order to store that much heat (at a 40§F. design temperature rise): 150,000 Btu/day/800 Btu/cubic feet of rock = about 187.5 cubic feet of rock needed, or about 18,750 pounds of the stuff. That's roughly seven cubic yards, one cubic yard weighing 2700 pounds. The storage bin also should be proportioned for minimum surface area to minimize storage heat loss. It should be stressed that incorporating storage into the collector system is no simple task, and because of space limitations we've by no means included all the information needed to do the work. Only the skilled craftsman who has some experience with forced-air heating systems should make the attempt. A good source of information on these air collectors and storage systems is the Domestic Technology Institute. Their publications available through Solstice Publications, Box 2043, Evergreen, 80439. Ask for publication g BP-044 "Solar Forced Air Heating System Plans," which is a set of six 18 X 24-inch blueprints available $16. Another source of plans for an air heating collector and rock storage system is the Ayer's Cliff Center for Solar Research, Box 344, Ayer's Cliff, Quebec, Canada JOB 1 CO. Phone: 819-838-4871.
7) The ideal angle to tilt the panel for the low winter sun is 62 degrees. With that in mind, it may be better to mount your solar heating panel on a wall than a roof with a low pitch (3/12 roof pitch for example).
8) Aluminum and copper conduct heat much better than regular metal. Whichever you choose, use the same type throughout your panel to prevent corrosion (the reaction between two different metals).
Some of the above guidelines have been developed by the Small Farm Energy Project and others working to optimize air-heating collectors.
40/41 Rodale's New Shelter May/June 1980 and 72 Rodale's New Shelter May/June 1981
Комментариев нет:
Отправить комментарий