This is a solar air convection heater for my garage that is powered by the low angle winter sun. It's easy to build and it works very well. With enough building insulation, this can be a primary heat source with a secondary needed for cloudy days. The idea and design is from Mother Earth News December/January 2007
Ingredients:
2x8 lumber
2x6 lumber
2x4 lumber
2x2 lumber
glass, plexiglass, or some kind of clear material.
black aluminum window screen
caulking, paint, screws, lag screws, staple gun + other tools
I have some results on temperature differences from the first weeks of operation. Just like when you put up your first wind generator, the wind won't blow for days/weeks, I had overcast and mostly cloudy weather the first few days operating this thing. The heater puts out 87 to 104 degrees F at the vents on partly cloudy days to sunny days. The uninsulated garage hits about 17 to 30 degrees F above outside temps, very comfortable for me. It seems the colder it is outside, the bigger the temperature difference between the garage and outside. If you want more heat in an uninsulated area I would recommend possibly 1/3 more collector area than the ratio I give in the instructions. Seal up any drafts, it will do a lot to hold the heat. This thing works great.
Ingredients:
2x8 lumber
2x6 lumber
2x4 lumber
2x2 lumber
glass, plexiglass, or some kind of clear material.
black aluminum window screen
caulking, paint, screws, lag screws, staple gun + other tools
I have some results on temperature differences from the first weeks of operation. Just like when you put up your first wind generator, the wind won't blow for days/weeks, I had overcast and mostly cloudy weather the first few days operating this thing. The heater puts out 87 to 104 degrees F at the vents on partly cloudy days to sunny days. The uninsulated garage hits about 17 to 30 degrees F above outside temps, very comfortable for me. It seems the colder it is outside, the bigger the temperature difference between the garage and outside. If you want more heat in an uninsulated area I would recommend possibly 1/3 more collector area than the ratio I give in the instructions. Seal up any drafts, it will do a lot to hold the heat. This thing works great.
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Make a box to mount on the wall of building (A south wall, SE and SW also can work.) This should be mounted vertically on a wall; the higher in the sky summer sun won't hit it as directly as the low winter sun. The walls of the box are 2x6 lumber; the angled "roof" of the box is a 2x8. I found it good to prebuild the box on the ground and then mount it to the wall. Make the box based on stud spacing in the walls; I have 24" studs, so my box is 8' wide with vents cut into four sections.
I sized the solar collector based on the numbers from the Mother Earth article where the guy built 160sq ft. of collector for his 700 sq ft building; using that ratio I built a 48 sq ft collector for my 200 sq ft garage.
I sized the solar collector based on the numbers from the Mother Earth article where the guy built 160sq ft. of collector for his 700 sq ft building; using that ratio I built a 48 sq ft collector for my 200 sq ft garage.
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I have had success with a design similar to this. I used black spray-painted aluminum sheets, polystyrene (i think) insulation, scrap 2x4's, and a ton of caulk. It was by no means perfect and some of the glass is even cracked, yet just after peak sunlight today (about 60 degrees in January, weird) it was pushing around 130 degrees consistently. I was surprised. It is a small unit, between 6 and 7 ft tall and 1 and 1/2 ft wide. I was expecting less, honestly.
My question is, then, how would it perform if the box was taller or wider and if it was perfectly sealed. Would either of these modifications make a large difference? I would like to build a non-prototype model of this for actual use, but was wondering if anyone would be able to assist me by answering these couple of questions.
Thanks
ND Dell.
Yes, more box area gathers more energy, so bigger box = more heat energy collected. Perfectly sealed helps with heat loss of the building itself, like leaving the window cracked open a bit; this hurts most on windy days.
Good luck Nddell
What is the difference between using plexiglass (perhaps glazed, or double glazed) and using two panes of actual glass? Does one conduct heat better than the other?
Thanks
ND Dell
Here's a great link for more home build solar ideas: http://www.builditsolar.com/
What about plexiglass used for greenhouses? I feel like that would be a good choice as it is made for the purpose of creating an environment hot enough to start plants in late winter and spring.
If it is the best option (or most reasonable costwise) then I will probably go with plexiglass of some sort. I have also considered the idea of making a really giant collector and using insulated piping to transfer the heat from the collector to the house. This, I'm sure will create a whole new set of issues, though.
Fogged glass might be an issue with the homemade double pain. Anything clear for greenhouses would probably work here.
Let me know if you run duct work or pipes off of the collector or make an instructable; I'm thinking the same for my house. I'd like to see your version; maybe it'll need small booster fans.
On that note, this might be quite a long time in coming, since I am trying to balance this with College and job (note what is capitalized and what is not).
And yes, fogged glass has been a problem with the small prototype unit I built with homemade double pane. On one hand, it works just fine (130 degrees on any day in direct sun) given that it is cracked and very very small. On the other hand I do wonder how much less efficient it is (that drives me insane!).
Also, does anybody know how to theoretically calculate the amount of heat produced by any given system using specific heat and physical properties?
Thanks,
N.D. Dell
Have seen one made with gutter drains but a lot more work.
There is a site that is just solar, they make all kinds, the hot air collectors, solar cells and water heaters.
They have experimented with plastic and metal screen...make a 1x2 frame and wrap one long piece front and back.
They said the results seem as good from the plastic screen as the metal. Some of them used 4 inch pvc to run an air vent from the top and one from the bottom. on the inside of the house they ran 4 inch pvc down to the floor to collect cold air.
..
seems if you want a fan there is a small one that you can connect to the hot side of the pipe (fits inside) with a thermo switch that cuts on when air gets to 90 degrees and off at 80.
Also had a vent flap on the hot side so that at night hot air didn't go back into the collector. The vent only opened when the fan runs...like a dryer vent...
As for the summer, they suggested covering collector with one of those reflective "survival" blankets and it would stop the collector from collecting heat. No wiring required, just plug the fan into a regular wall socket.
I have a video of them building the screen part of the collector at
http://solarplanet1.blogspot.com/
May need to scroll down. If you go look there shoud be a link to the simply solar site also.
Cararta
First the warning:
In the summer block off the sunlight to the collector (cover it) don't just close off the vents.
I bought a house with a homemade passive solar heater attached. It was mounted wrong (bad airflow) and didn't work well. I decides to remove it.
While the house was vacant it had been "turned off" by shutting off the air vents into the house.
The outside frame work was wood. It had gotten so hot that the interior had caught fire. The only thing that saved the house was the lack of oxygen. The fire smothered itself.
P.S. This was during the winter - ouside temperature doesn't mean the collector isn't going to get very warm.
Okay now why you wouldn't want this on your house.
A passive (no fan) solar panel should be mounted lower than the area you are heating. Otherwise it turns into what is called a "heat siphon" on cloudy days or when the sun goes down and will cool instead of heating.
The reason for this is simple: heat rises. If the panel is on the same level or higher with the area you are cooling once the temperature inside it gets lower than your inside temperature the airflow reverses and it draws the warm air from your house instead of heating it.
This can be defeated by mounting it lower than the area being heated or by having the vents shut off at night or in cloudy weather. (see earlier warning).
As to the risk of fire, I'm surprised. Wood doesnt combust, I think, until about 540 F. Maybe the paint caught fire, though?
The flapper valves that stop reverse flow are very very effective. The pressure differential that the reverse flow causes sucks the light plastic film against the hardware cloth that backs them up tightly enogh that you can see the pattern of the wire mesh through the film. They are actually more effective than the commercial motorized dampers that are used in some systems because they don't have any leakage around the edges. Have a look at the pictures in the Home Power article at this link, and I think you will be convinced:
http://www.builditsolar.com/Projects/SpaceHeating/solar_barn_project.htm
On the issue of collectors causing a fire: I run a solar website that gets 4000 visitors a day -- including many that own collectors. Yours is the first case of a non-concentrating collector causing a fire that I have ever heard of or read about.
Gary
My website is www.BuildItSolar.com -- it now averages about 7000 visits a day, and it most certainly exists. I put up a new page that shows a picture of the flapper vents -- the page name is dropkick, so (hopefully) this will convince the site is real and is mine -- you are a tough sell :)
http://www.builditsolar.com/Projects/SpaceHeating/DropKick.htm
The flapper valves work quite well. Its true that there is an air inlet from the room to the collector at near floor level, and an air outlet from the collector to the room at near ceiling level. The flapper valve is installed on the outlet vent only because if you stop air from entering the collector at the top (as it would do at night when the collector is cold), you stop flow through the collector and there is no need to put a flapper valve on the entry and exit vents. If you look at the collector at night from the inside, the upper flapper valve is pulled tightly against the hardware cloth so that you can see the pattern of the hardware cloth through the plastic -- it seals quite well. If you put your hand near the floor vent you can't feel any flow at all from the lower vent. This does not mean there is absolutely no flow from the lower vent, but it is very small -- one could certainly add a 2nd set of flapper valves on the lower . The flapper valves for my collector are made from about 2 mil plastic film. During collection periods, the warm air from the collector easily blows the flapper out of the way. There is a half inch mesh hardware cloth across the exit vent opening, and at night, when the collector wants to backflow, the the flapper valve is pushed against the hardware cloth and very effectively seals the opening and prevents airflow through the collector.
I'm not the inventor of these flapper valves -- the have been used on this type of solar collector since the 70's and probably before -- a number of books on solar collectors include a description of them.
The collector is now entering its 5th season, and it continues to work well, and has already paid its cost in fuel saving several times over. It has required zero maintenance, and fully heats the shop on sunny or part sunny days.
Gary
When I was designing my passive collector, I seriously considered avoiding polyisocyanurate insulation because of the high temperatures that could occur in a stagnant collector. Instead, I specified a bi-metallic thermostat to open vents during overheating conditions.
Please, I'm open to suggestions. Until then, I feel like my solar heater project was a waste. Thanks for your help.