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Solar heat box

Post in 'The Green Room' started by Billy123, Mar 19, 2011.

  1. Billy123

    Billy123 Member

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    Anyone ever build a solar heat box?

    I was thinking a small box to help heat a basement would be a nice project. I would like to lean it against the house (good south location) and duct the air to a casement window by the screen with some plexiglass. I would open the window on sunny days and close it in the night.

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  2. snowleopard

    snowleopard New Member

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    I think for this to be effective, circulation is going to be your friend. Having a way for the cold air to vent will help pull the warm air in. If you have some ducting running from the lowest spot where air pools or stagnates up through that box where it could vent to the outside, and a place in the box where enough outside air could be pulled in to create equilibrium, and then put a small fan in the ducting, that should do it.

    Duct fans are a bit pricey, and I don't think you need anything that beefed up for this--you can pick up used computer fans for cheap on ebay. Then get a little solar panel, hook it to that (with no storage battery, since you only need it to run when the sun is shining) and you'll be in business.

    I'm finding with my house that heat circulation can be powered by different temperatures in the rooms, IF there's a circuit that allows the air to travel. I don't think you'd need a big fan here to accomplish this, but you're fighting the natural tendency of the cool air to want to stay pooled.

    Wiser heads than mine could probably advise you on the specifics, but here's roughly what I had in mind, just to get the pump primed:

    http://store.sundancesolar.com/small-encapsulated-solar-panels.html
    http://store.sundancesolar.com/coolingfans.html

    Good luck, and let us know how this works out for you.
  3. begreen

    begreen Mooderator Staff Member

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    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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  5. PapaDave

    PapaDave Minister of Fire

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  6. Billy123

    Billy123 Member

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    This one seems easy. https://sites.google.com/site/glenssolarheater/ I wonder if aluminum flashing painted black on the bottom would create even more heat?

    Would if make any difference if the intake was on the top and out take on the bottom?
  7. sesmith

    sesmith Member

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    Hi,

    That design looks nice but is way too restrictive to have good airflow and be efficient. Take a look at some of the screen mesh absorber collectors. A very inexpensive and efficient heater. Here's an example of one:

    http://www.builditsolar.com/Projects/SpaceHeating/solar_barn_project.htm

    I have the larger of the 2 downspout collectors here:

    http://www.builditsolar.com/Projects/SpaceHeating/DownSpout/DownSpout.htm

    It works well but I'm also struggling in the air flow department right now. My problem is that I went with 4" ducts to and from the collector...should have used 6". The downspout design does work well, though, even without optimal air flow.. The collector is supplying about 1/4 of our heat during the year.

    Another great source of info on solar is in the Yahoo groups, "Simply Solar", and "Solar Heat"

    Scott
  8. Billy123

    Billy123 Member

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    Has anyone built some of these designs and measured how well they work side by side?
  9. sesmith

    sesmith Member

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    Gary Reysa of Build it Solar and Scott Davis, owner of the Yahoo Simply Solar group are currently in the process of doing side by side tests of various hot air collector designs. This isn't as easy as it may sound. Just the simple process of measuring air flow volume is not as simple and straightforward as it may sound:

    http://www.builditsolar.com/Experimental/AirColTesting/FlowTesting.htm

    You can spend many hours browsing Gary's site and getting lots of usable information on various designs. Search some of the back posts on Scott Davis's Simply Solar group and you'll find lots of reading on the side by side tests.

    http://tech.groups.yahoo.com/group/SimplySolar/

    Scott
  10. Billy123

    Billy123 Member

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    A good comparison test might be:

    - climate-controlled room (equal temp for all test heaters)

    - sun lamps on the boxes( equal power)

    - different designs built equal sizes

    - duct into climate-controlled room and measure heat gain over set amount of time
  11. fishingpol

    fishingpol Minister of Fire

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    This is a very interesting topic here. I have some pieces of poly-iso foam panel laying around, and today I put some against the house facing the sun, black side out. It hit 125* with the IR gun in just a minute. I can imagine this boxed up with a screen absorber and corrugated clear roof panel would hit upwards of 200* maybe? I would image the air running through it too fast would be drastically cooler, but the solar energy is there, why not take advantage of it.

    I figure on making the box out of foam panel with a screen closer to the panel, using a dryer flex duct to allow cool air into the bottom of the box and flex duct at the top with a small dc fan to pull air through the box. The screen seems to slow the air flow down a little to warm the cool air. Heat rising to the top of the box should help with circulation. If preliminary experiments work, I may get a small collector to power the fan.

    We vent the dryer into the basement in the winter anyways, but this may be an interesting project to try. I won't need it in a few weeks though.
  12. sesmith

    sesmith Member

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    Do it. You'll be amazed at the results. You can glaze it very inexpensively with Suntuf or Tuftex clear polycarbonite panels. Use a double layer of screen in the collector.

    Scott
  13. fishingpol

    fishingpol Minister of Fire

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    Just got done reading the screen absorber tests on build it solar. Great info there. I will also taper the screen as they did and put in a baffle to disperse the air coming in at the bottom. Looks like a trip to the box store soon.
  14. Billy123

    Billy123 Member

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    Can you post the URL for the screen absorber plans?
  15. GaryGary

    GaryGary Feeling the Heat

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    Hi,
    Scott and I are still struggling a bit to try to get good and consistent results on air collector comparisons. Turns out that measuring air flow accurately is tougher than it would seem, and you have to have good airflow measurements to get heat output and efficiency.

    Consider the data given at the link above as just sharing thoughts as the testing goes on -- that is, use it with caution as some of it may be wrong :)
    Any thoughts, comments, or suggestions would be appreciated.

    I would say that both of us have been impressed with the collector that uses two layers or ordinary window screen as the absorber. It has performed as well as anything else, has low internal pressure drop, and is very simple to build.

    Gary
  16. mayhem

    mayhem Minister of Fire

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    This is a neat idea. I've got these huge sheets of glass laying around doing nothng too. They're 3x5 sheet os vacuum sealed, double pane low E glass from a construction project that went wrong at work so i got 3 or 4 sheets of it in my truck before they smashed it all in the dumpster...lightly tinted though, so it may not be ideal...but its free.
  17. GaryGary

    GaryGary Feeling the Heat

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    Hi,
    The glass sounds a bit suspect for a solar collector.

    Couple things you might do:
    - Separate the panes -- you can usually do this with a sharp untility knife. Then see if one of the panes is clear and is not low-e coated. The clear pane would be good for a collector -- the other may not be.

    - You could do a test like this one:
    http://www.builditsolar.com/Experimental/TreeShade/TreeShade.htm
    Idea would be that you would make two very simple collectors, and glaze one with the free glass and the other with some kind of clear glazing -- even poly film would be OK for this test. Set them both out so they see good sun all day, and check the temperature of the water container at the end of the day. If the free glass container has not heated up as much by a significant amount, then its not a good choice.

    Other thing you could do is see if you can find the data on the glazing units -- if the SHGC (Solar Heat Gain Coefficient) is low, then they are a bad choice for collector glazing. The SHGC is part of the standard window label, so if the panes have the label or you can look them up, you should be able to find it.

    I could be wrong about this, but I think that any kind of tinting is a pretty big hit on solar gain. www.EfficientWindows.org might have info on tinting.


    Gary
  18. fishingpol

    fishingpol Minister of Fire

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    Here is the link from build it solar.

    http://www.builditsolar.com/Experimental/AirColTesting/ScreenCollector/Building.htm

    I've had nothing but clouds for the past several days. I'm starting to think the northeast may have too much cloudiness for this project.

    The Build it solar website is very interesting and plenty of info on the best panels. Some projects look almost professionally done with decent fabrication.

    Let's keep this post alive with project pics down the road. C'mon sun.
  19. fishingpol

    fishingpol Minister of Fire

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    Geez, I didn't even read all the post until now and see Gary from B.I.S. is here. Great site Gary, glad you are here to have open discussions and pointers.

    Jon
  20. GaryGary

    GaryGary Feeling the Heat

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    Hi Jon,

    My wife says, the B.I.S. has one too many I's in it.

    Hoping at some point to pick up some pointers on a way to heat the water in my Solar Shed storage tank with wood when then sun is not cooperating -- looks like lots of experts here.

    Gary
  21. fishingpol

    fishingpol Minister of Fire

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    Gary,

    This is the place to be for wood burning in just about any heating appliance. It is good to see people doing projects while trying to get the most effiency out of their systems. There are a lot of people who are better wood consumers, including myself, that have gleaned tons of info here.


    Your site has people building collectors directly on the side of houses. Is having the collector as close to perpindicular to the sun the best way to gain heat in a collector? Is it good enough that it just faces in a southerly direction? I have a south facing area on my house that I can put a panel, but I'm not sure if it is vertically positioned that it would be the most beneficial.

    Jon
  22. GaryGary

    GaryGary Feeling the Heat

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    Hi Jon,
    Vertical collectors against a south wall work out well for solar space heating. Reason being that the sun is lower in the winter, so it shines pretty directly onto a vertical collector. If there is a snow field in front of the collector, you can get a very beneficial reflection off the snow on vertical collectors.
    Where we are (45 deg north lat), the sun only gets up to 22 degrees above the horizon on the winter solstice at noon.

    Another advantage is that vertical collectors are much less likely to overheat in the summer because the sun is quite high and makes a large incidence angle with the collector.

    I also like the look of vertical collectors, and they save some materials and labor -- its easier to just build one big frame on the wall that carries the full absorber area rather than building several separate smaller collectors of the same total area.
    Also like the idea that you can keep the supply and return plumbing runs inside the collector and/or wall and avoid outdoor runs.

    If a little tilt is desired, it would be relatively easy to still build against the wall, and kick the bottom out a bit for some tilt -- see the link just below.

    One thing to watch out for on vertical collectors is the roof overhang. If you have a large (or even not so large) roof overhang, it will cast a shadow on the collector that cuts down output. A little of that is OK in mid summer, but you don't want the collector shaded by the overhang during fall, winter, spring. Good overhang tools here to check this on: http://www.builditsolar.com/References/SunChartRS.htm#Overhangs

    For DIY solar water heating only systems, I like a system with an excess of collector area, and a fairly steep (but not vertical) tilt. This way, you get good performance through the winter when most commercial systems fall off, and the steeper tilt keeps you from getting a lot of overheating in the summer. Like this system: http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm

    My new system does both solar water and space heating, and uses a larger vertical collector. So far, this is working out well. Even though the collector is much larger than we would need for hot water in the summer, it does not overheat due to the vertical orientation.
    This is it: http://www.builditsolar.com/Projects/SpaceHeating/DHWplusSpace/Main.htm

    Still, a more tilted, or roof mounted collector can work fine too.

    Gary
  23. Billy123

    Billy123 Member

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    Some questions on the screen method:

    The layers on the collector are spaced at 3/8". (He uses 3) How is that framed? Does he cut the wood to 3/8"?

    How would a 1"x2" do as a frame with a screen layer on both sides. Would the 3/4" space be too much?

    I wonder if the screen was painted flat black, if that would boost performance?

    Also, based on the test results for screen layers, I wonder if a layer of painted black aluminium sheeting on the bottom would boost performance.
  24. GaryGary

    GaryGary Feeling the Heat

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    Hi,
    The "he" in the pictures is me (Gary).

    The 3/8 thick edge frame is a piece of 3/8 inch thick plywood siding material I had left over that is ripped into strips about an inch wide to make the frame.

    I don't believe that the 3/8 is at all critical. I think that a 1 by 2 that would give a 3/4 inch spacing would be fine.
    No one has tested the effect of spacing, but I can't think of any reason that spacing the layers a little further apart would make much difference.

    The screen I used is the "charcoal" insect screening. It is pretty close to black, and I don't think painting it black would help it. It might hurt the performance if the paint tended to block up the screen openings.

    I painted the back of the collector flat black. The idea being that radiation that gets through the layers of screen will be absorbed by the back of the collector, and this will heat up and transfer heat to the air. The screen lets a significant amount of light through, so even with three layers some light gets through all three -- I think you want the back surface of the collector to be dark enough to absorb this light. This little test I did indicates that 3 layers of screen absorbs about 80% of the light.

    http://www.builditsolar.com/Experimental/ScreenAbsorber/ScreenAbsorber.htm

    There was some discussion on whether it would be better to make the back of the collector box reflective (say alum foil) in that this would reflect the light that gets through the layers of screen back to the screen where it would have a 2nd chance to be absorbed.

    I don't see any performance benefit in making the back surface aluminum?
    The back surface of this test collector is the face sheet on the polyiso insulation sheet -- I think that when its painted black, it will absorb and transfer heat just as well as an aluminum sheet?

    One thing that is important on air collectors is to get the air spread out uniformly across the full absorber surface. Parts of the absorber that don't get enough airflow run hotter and lose more heat out the glazing. Hopefully the diffuser plate at the inlet and the back pressure of the screen tend to spread the flow -- but, to the best of my knowledge, no one has really tested how uniformly the air gets spread out.

    Edit: I should have mentioned that I did collectors with both the aluminum insect screen and the black fiberglass insect screen. The fiberglass is nice to work with, but the fiberglass I used wanted to out gas and coated the glazing with a kind of gooey liquid when the collector was stagnated and hot, so I don't recommend the fiberglass screen -- the aluminum screen is fine.
    http://www.builditsolar.com/Experimental/ScreenAbsorber/ScreenAbsorber2.htm

    Gary
  25. Billy123

    Billy123 Member

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