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  Nov. 17, 2011 10:08 a.m. DrBoost SuperDork

  I’m goin to start building a solar collector for free supplemental heating for my garage. I’m looking for some info from you folks (since GRM seems to be the defacto knowledge-base for everything). What I’m looking to figure out is the flow rate I should expect through the panel, the size fan I’ll need (CFM), and I think that’s it (I can figure out the size of the solar panel to power the fan mys self).
  As far as what I’m doing, I’m building a box, either 4’ or 6’X8’X3”. I’ll have black screen material that the air will flow through. There should be very little restriction but I have no idea what size fan I should have. I’m not looking to heat my garage completely with this thing, just to help take the edge off.
  

  I’m not sure what other info to put here, but if you have any questions, please let me know. Here’s a link to what I want to do.
  http://www.youtube.com/watch?v=EW_ga-b0-Gs

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  Nov. 17, 2011 12:02 p.m. alfadriver SuperDork

  Doc You are a car guy, would it be a reasonable question to ask if you have 3 spare radiators?

  The reason I ask is that I've had an idea of making a coolant based heat absorber, where outside you have two radiators that absorb heat, and one inside that puts it back off. Find a paint that is best at absorbing heat, and find some that is good at reflecting at a wave lenght that the cover won't let out, and there you have it.
  

  Not much heat, but like you say, take the edge off.

  Seems like it would work....

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  Nov. 17, 2011 12:56 p.m. fasted58 SuperDork

  From what I saw in the video looks like he's using PVC pipe to circulate air through the collector, Is that the plan?

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  Nov. 17, 2011 2:33 p.m. DrBoost SuperDork

  Alfa, I was thinking about that sort of thing. Then by my research I found that the plan in the video outperforms every other type of solar collector (to heat air). The guy was measuring 160F air coming out of that thing!
  Now, I have a similar idea to head my veggie oil. I'll have a matrix of copper or aluminium (as the brits would say) to absorb the heat, then a trans cooler submerged in my settling tank to warm the oil. That's in the plans next.
  In the meantime I'm going to do this simple air heater as a phase 1 experiment. If it works well enough, I might do something similar, but larger for the house.
  Fasted, he's using pipe to get the air into and out of the collector. Once in there it just flows through the screen material for the heat transfer.
  

  Heck, maybe I'll try those 2-liter bottle solar lights as well...

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  Nov. 17, 2011 2:48 p.m. RossD SuperDork

  If you can determine how much heat can be absorbed in an hour (Btu/hr or MBH) and you know how much you'd like the temperature to rise you can figure out the CFM.

  (Btu/hr)/(1.1*(temperature difference))=CFM

  Example: 19,800 btu/hr; -15°F to 75°F; gets you to 200 CFM.

  The fan would probably need a static pressure capability of around 0.05"-0.1" of water column. Maybe up to 0.5" if you throw a couple of elbows into direct it.

  http://www.builditsolar.com/

  I'd buy an 'el cheapo' brand toilet fan and blow the 'exhaust' end into the room and just see how it works.

  If you get some of your expected numbers for heat gains and sizes I'd be happy to try to help out.

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  Nov. 17, 2011 7:01 p.m. fasted58 SuperDork

  DrBoost, thnx, I know how it works, I don't know what fan(s) he is using, just wondered why for what looks like 4" PVC supply and return pipe in the video.

  I'd GRM the motherberkeleyer and build a prototype collector and pipe in a 6" booster fan w/ a cut-in/ cut-out temp switch in the collector:

  

  6" pipe 150 cfm $40

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  Nov. 17, 2011 8:09 p.m. alfadriver SuperDork

  In reply to DrBoost:

  I've been thinking about the idea for a while, but after I posted it, I thought about it for a little while. Not a great idea. The reason is that I'm introducing a fluid that I really don't need- whereas the air system you want to build doesn't even require a second heat exchanger. So what you want to do is a lot simpler, and should work fine.

  The only thing I'll add to your question, which I'm sure you will do- make sure the fan is pushing cold air instead of pulling hot air. Motors like to be cool.

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  Nov. 17, 2011 8:49 p.m. DrBoost SuperDork

  Thanks FastEd for the linkys. I hope it didn't seem like I think you're a doofus or don't know about the system. I just didn't know how much you knew about it. I like that inline fan, that kicks butt. I was envisioning a 12V fan so I could have a solar panel built into the collector and a small riding-mower battery to power it. That way the heat really is free. But dang that price is nice!
  Alfa, I had the same thought process you did. Heck, I was even thinking "man, I could put base-board heat in the garage!" Then I remembered the old K.I.S.S. (not the sub-par band from the 70's [man am I going to get flamed for that one]). My first thought was just to allow convection move the air around, but I don't think that'll do what I want it to do.
  So, I'm going figuring out how much cfm I'd need to make the most efficient heater. Too much air flow and there won't be enough time for a good heat exchange, too little and I'm not pulling the most free btu's I can. I'll post my progress and findings for sure.

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  Nov. 17, 2011 10:00 p.m. donalson SuperDork

  just wondering if you've considered a non fluid based system?...

  saw a few of the "coke can solar heaters" on instructables and seems like a neat idea... had thoughts of that along with a batch water heater for the house... just not going to work for this house.

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  Nov. 18, 2011 8:39 a.m. DrBoost SuperDork

  donalson wrote:

  just wondering if you've considered a non fluid based system?...

  Yup, that's what I'm doin first. I'm doing an air heater for the garage, then a fluid heater to heat my veggie oil settling tank.

  donalson wrote:

  saw a few of the "coke can solar heaters" on instructables and seems like a neat idea... had thoughts of that along with a batch water heater for the house... just not going to work for this house.

  The pop can heater works, but it is quite restrictive to air flow. There are a few guys that have done side-by-side testing. The most efficient one was 2 or 3 layers of window screen in the box on a diagonal.

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  Nov. 18, 2011 11:14 a.m. fasted58 SuperDork

  I dig where this thread is goin'. I always had an interest in solar energy, keep us posted good Dr. I bet you gonna like the fluid heater.

  Over 30 yrs ago back in tech school we built a flat plate solar collector for water heating. Pretty crude for the time and just using material laying around the shop.

  For the absorbing plate 4' X 8' galvanized duct tin cut down to match the glass we scrounged, crude bead rolls for the tubing to lay in. 1/2" OD refrigeration copper tube headers, 6 or 7 3/8" flow tubes soldered to the tin (galvanized stripped w/ acid), roll on flat black paint coated the plate, 2X4 box frame w/ roll insulation under the absorber plate, frame boxed in w/ more galvanized tin. Small boiler pump w/ aquastat control for circulation, bout a 40 gal tank w/ insulation wrap, feed and return lines w/ foam wrap.

  We kept a log book on it. IIRC, max outlet temp was 180+ degrees, holding tank would maintain 140-150 deg w/ minimal loss overnight. Not bad considering the collector was put in use in Sept., had a non-tracking fixed mount and only got sun from 10 a.m. to about 3 p.m. on the rooftop, lotta shading from taller buildings.

  I always wanted to build another collector out of a good shop, w/ premium material... and a tracking system, maybe that'll be a good retirement project.

  Good luck and keep us posted

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  Nov. 18, 2011 11:30 a.m. alfadriver SuperDork

  DrBoost wrote: The most efficient one was 2 or 3 layers of window screen in the box on a diagonal.

  Do you have a link for that? I've wondered how the clear tubes absorb the heat over other materials. Or how they think it does.
  

  Would the design work better if the tubes were, say, copper? And you have the heat absorbing screen materials. The idea that people have done some experiments- I'd love to read about them.

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  Nov. 18, 2011 12:00 p.m. DrBoost SuperDork

  ^^looking right now^^

  When you mention "clear tubes" are you meaning evacuated tubes?

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  Nov. 18, 2011 12:04 p.m. DrBoost SuperDork

  Ok, found it. http://builditsolar.com/Experimental/AirColTesting/Index.htm This guy also has some good youtube videos as well, search for gscottvideos, he has quite a few good video's on the different designs.

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  Nov. 18, 2011 12:15 p.m. alfadriver SuperDork

  DrBoost wrote:

  ^^looking right now^^

  When you mention "clear tubes" are you meaning evacuated tubes?

  No- my mistake- at the end of the video you posted, he had the new one up against some old ones, and the ends plus the waviness of the screens looked like there were clear tubes. So I was assuming that there were tubes in there absorbing the heat. Silly assumption.

  Which makes this design REALLY simple. The more I look at it, the better it is.

  What I was planning on doing was a simple supplamental heater that I can place in my driveway and run lines under the door on a sunny day. The problem would be that it lowers the number of useful hours, and that I have to come up with some way to move the air in and out without big holes....

  But now that I think more about it, I can use the windows..... hmmm. Which is two heaters that I can do.... low power motor, 12v solar power supply... really on to something.

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  Nov. 18, 2011 12:28 p.m. alfadriver SuperDork

  DrBoost wrote:

  Ok, found it. http://builditsolar.com/Experimental/AirColTesting/Index.htm This guy also has some good youtube videos as well, search for gscottvideos, he has quite a few good video's on the different designs.

  Lots of different ideas there, and the variety makes me think some- I have some vinyl soffet material from building as spare, and could use it- looks like it works well.

  (and the other thing that got me confused was the corregated clear plastic they were using).

  I even have some clear plastic I can use for a cover. A trip to the recycling store may find the rest of the materials that I need for a reasonable garage warmer. Or less colder...

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  Nov. 18, 2011 12:39 p.m. DrBoost SuperDork

  You're on the right track now Alfa! This stuff can be done on the cheap. I don't plan on using the corrugated stuff. It requires finishing strips top and botton and supports in the middle. There are double-wall plastic panels that are flat (negating the need for finshing strips) and offer insulation against heat-loss from the glazing itself!
  I'm getting materials lists together now. I want to make these before the end of the year, hopefull by December 1st.
  I can't seem to find it right now but there is a design that you put out in the winter and can take in during the summer months. Something like this:
  
  it goes in a partially open window (like a A/C unit). I have NO south-facing windows though.

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