DrBoost
DrBoost SuperDork
1/18/12 9:08 a.m.

My attempt at being green starts now. Well, I do have the Greasecar already, so I guess it isn’t starting here. In fact, I’m not really trying to be “green” as much as I’m a cheap guy. So, anyway I have been thinking about building a solar collector to harness the solar energy bouncing off the south side of my house. I don’t have any windows on the south side of my house, but I do have an entry door that needs to be replaced. The window panes don’t seal well at all and it looks like crap.
So instead of scrapping it just yet I decided to build a small collector in place of said swiss-cheese windows to test the concept. Here’s what I did.
I removed the windows by popping the trim out that holds in the panes of glass.

The funny thing is, the outside of the door didn’t have trim holding them in. It was actually milled into the wood so there was no “popping them out” on the other side. I had to use a circular saw to make the initial cut, then follow it up with a jig saw.

Then I built a basic frame out of 1X8 lumber. For once my measurements were spot on. With the door closed there’s about ½ an inch of clearance between the storm door and the box.
I used corrugated panels because they were cheaper than flat stuff, though that made construction much more complex. The panels are attached at the top and bottom with one brace in the middle for support.
Now, I made one major change from standard that will (greatly) reduce the effectiveness of the panel. My wife didn’t want a solid door since the door let in so much light (and cold air!!) before. So, I decided to put clear plexi on both sides. Normally the “back” side is usually made of solid wood painted black to trap more heat. In theory though, the heat will not be lost as it’ll pass through the panel and warm the floor like before but still……. I installed a fan on the top of the panel because my entry door is 2 stairs below the rest of my house. This results in a cove above the entry door. I was afraid if I relied on convection to move the air, the warm air would just collect in that cove, not doing anything for us. So, I installed a fan in the top to blow the heat down and out into the kitchen. For the collector material I put three passes of black aluminum screen material. There have been many test that show this to be the most efficient material. Here’s the screen mounted in the frame.
I totally brain-farted and forgot to get a finished pic from inside, but here’s what it looks like from the outside.

It’s been cloudy since I finished so I don’t know how well it works. The next leg of the project is to figure out the solar panel. The motor is a 10V motor, using about 10 watts.
I’ll let you know how it’s working if we see sun again…….

N Sperlo
N Sperlo SuperDork
1/18/12 9:50 a.m.

Harness the sun. Contact Simpson. They should have something to fit your needs.

alfadriver
alfadriver SuperDork
1/18/12 10:02 a.m.

One "experimental" question- will your wife be ok with half the door letting light in? You could put a panel on the bottom, outside flat black, inside matching white, to see if you get better performance.

Nice fabrication, though!

DrBoost
DrBoost SuperDork
1/18/12 11:26 a.m.

Thanks for the compliment Alfa! I'm fairly happy with how it turned out. It's not painted yet so it still looks raw, and I wasn't too concerned with making it pretty since this is still an experement. But I'll say this. During the daylight hours, you can NOT see inside the house even if you push your face right up against the door.

The motor was a PITA to mount. The fan takes air in the center and "blows" it out the sides, 360 degrees, this will make it ideal for this use. Most folks have a computer fan or 5. This air is directional so they need baffles to ensure even air flow. This fan will keep the air flow even. But I had to get the motor mounted, then drill the 2 1/8th hole on the front board perfect. So, I used the shaft of the motor (protrudes .75" out the back plate for another reason) to mark the mounting plate

center point. Then I transferred that hole to the front board, there's an app for that!

It worked well. Here's a picture of the motor mounted in the frame. The picture is of the top of the frame.

N Sperlo
N Sperlo SuperDork
1/18/12 11:30 a.m.

So your door is kinda supercharged. Cool.

pigeon
pigeon SuperDork
1/18/12 12:11 p.m.

Nice work! I can tell you this - my front door is solid (with 2 small square windows at the top), painted black, and faces West. I have a storm door in front of it. On sunny winter days I can barely touch the inside of the door If your collector is even 1/2 as effective as my door, blowing some air through there ought to net you some nice heat gains, especially replacing a cold, leaky window.

Query - what about summertime?

DrBoost
DrBoost SuperDork
1/18/12 2:22 p.m.
pigeon wrote: Query - what about summertime?

Most folks put a simple flap on the bottom hole to prevent backflow (needed at night as well). Since my panels are not flat, I will either put a flap up top that I manually put in place at night and the summer, or fab up something down below that allows a flap to operate. That way, it'll be closed unless there's positive pressure in the box.

carguy123
carguy123 SuperDork
1/21/12 11:27 a.m.

So you are trapping some air in the door, letting the sun heat it and then are blowing that little bit into the house?

Woody
Woody SuperDork
1/21/12 1:00 p.m.

I'd be concerned about trapping that much heat in an enclosed area attached to my house. I'm thinking about hot summer days when you are away at work.

donalson
donalson SuperDork
1/21/12 1:25 p.m.

so it's basically this http://www.instructables.com/id/Solar-Heater/ with an active fan instead of using convection then?

at some point I'd love to do something along those lines... and a solar water heater

DrBoost
DrBoost SuperDork
1/21/12 1:41 p.m.

That's exactly it donalson. Since I want to push the heated air out of the bottom I'm using a fan as opposed to allowing convection do the work for me. Right now (I don't have the solar electric panel yet) it's just convection and just like I suspected, the air is going up into the cove area.
But I'm excited to feel it work so well.
Woody, no worries. The panel is open to the house on the top and bottom, and in the summer there's not much direct sunlight on that side of the house.

donalson
donalson SuperDork
1/21/12 2:36 p.m.

being that hot air rises it seems more logical to use the natrual convection (as its going to be pulling in the cooler air closer to the floor and releasing the heated air up top... that does present a problem with a bit of the top wall bit blocking it in... perhaps mount a small fan above the door to blow that hot air into the rest of the house?

DrBoost
DrBoost SuperDork
1/21/12 5:14 p.m.
donalson wrote: being that hot air rises it seems more logical to use the natrual convection (as its going to be pulling in the cooler air closer to the floor and releasing the heated air up top... that does present a problem with a bit of the top wall bit blocking it in... perhaps mount a small fan above the door to blow that hot air into the rest of the house?

I thought about it, but decided to mount the fan in the box for simplicity sake. I know I'm fighting convection, but this fan is already stronger than I think I'll need.
With the convection I felt the air 8" in front of the hole and 12" above it. How do I calculate BTU and CFM???

CarKid1989
CarKid1989 Dork
1/21/12 11:25 p.m.

interesting project

aussiesmg
aussiesmg SuperDork
1/22/12 8:42 a.m.

I have been looking at building one of these when I get some time, my plans include using a solar powered fan to drive the air.

DrBoost
DrBoost SuperDork
1/22/12 8:50 a.m.
aussiesmg wrote: I have been looking at building one of these when I get some time, my plans include using a solar powered fan to drive the air.

Do you have any ideas as far as the fan goes? I used the fan I did because I had one or two lying around. I thought about computer fans as well. If I was smarter, I'd have figured out my CFM needs and sized the fan to match....

DrBoost
DrBoost SuperDork
1/22/12 8:51 a.m.
DrBoost wrote:
aussiesmg wrote: I have been looking at building one of these when I get some time, my plans include using a solar powered fan to drive the air.

Do you have any ideas as far as the fan goes? I used the fan I did because I had one or two lying around. I thought about computer fans as well. If I was smarter, I'd have figured out my CFM needs and sized the fan to match....
I'm guessing I'm getting a significant amount of BTU's since the heat, coming out of a 2 1/8" hole was blowing 6-8" out with no fan needed. In fact, that heat was blowing through the fan so that adds some resistance.

aussiesmg
aussiesmg SuperDork
1/22/12 9:13 a.m.

There are a few options out there, this seems to be a reasonably priced and well made option.

http://www.ebay.com/itm/Solar-Powered-Attic-Vent-Greenhouse-Fan-NEW-/320831328087?pt=LH_DefaultDomain_0&hash=item4ab3098f57

a few $ more

http://www.ebay.com/itm/Solar-Panel-Powered-Attic-Vent-Greenhouse-Fan-/190629787258?pt=LH_DefaultDomain_0&hash=item2c626bb67a

aussiesmg
aussiesmg SuperDork
1/22/12 9:18 a.m.

I am however planning on building my own solar panel to drive my fan, this will save a few $ and give me the satisfaction of building my own, I intend to make the unit more repeatable for reproducing the heater for other buildings.

Any money not paid to the Electric/Gas company is wonderful IMHO.

DrBoost
DrBoost PowerDork
10/31/12 7:04 a.m.

Since the cold months are coming again I'm eager to see how the panel performs this year. Last year was VERY cloudy, hardly any sun (even for Michigan) but when there was sun, it worked great. But I can report that the summer is no problem at all. There isn't much direct sun light on the door so there it little to no heat build-up at all.

Brett_Murphy
Brett_Murphy SuperDork
10/31/12 10:25 a.m.

If your fan is that strong, isn't it possible you'll be pulling in cold air through the leaks in the door?

DrBoost
DrBoost PowerDork
10/31/12 11:55 a.m.

There's no more leaks now. Everything is caulked and or w/stripped now.

aussiesmg
aussiesmg UltimaDork
12/30/12 11:33 p.m.

So how is it performing, or do I have to send a parade of utes down your street?

DrBoost
DrBoost PowerDork
12/31/12 7:25 a.m.

Please, no utes!!!
It performs GREAT. With maybe 15 minutes of sun it starts putting out heat. Just about as soon as the sun is gone the heat stops. If I were to build a bigger one, I'd add some thermal mass to it to act as a flywheel of sorts. After a few minutes of sun, I get 120 F or hotter air. If I had a solid back, of if I took Alpha's suggestion of making the lower 1/2 solid I know that'd go higher.
I'm not going to build a bigger one because there's just no sun in Michigan. There were only 3 clear days in Michigan in December. It'll put out some heat on partly cloudy days, but not a lot.
There's a guy I was talking to in upstate NY that built a large one, like I wanted to do. It was about 4' tall and 35' long and could be broken down into 2 parts and stored in the garage during the summer. He had 2 6" ducts with in-line fans to pull the heat out of the box. I think, with full sun he was getting 180F heat from both ducts bowing full strength. That's some serious heat for free!

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