# Solar heat box



## Billy123 (Mar 19, 2011)

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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## snowleopard (Mar 19, 2011)

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.


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## begreen (Mar 19, 2011)

Read up on precaud's installation and lessons learned. It's a good read.

https://www.hearth.com/econtent/index.php/forums/viewthread/57663/


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## BrotherBart (Mar 19, 2011)

I was thinking about this same thing two days ago. Came across this:

http://www.motherearthnews.com/Do-It-Yourself/1977-09-01/Mothers-Heat-Grabber.aspx


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## PapaDave (Mar 19, 2011)

Builditsolar.com has TONS of info on this. 
Here's one I'm thinking of doing. http://www.builditsolar.com/Projects/SpaceHeating/mssungrabber.htm


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## Billy123 (Mar 20, 2011)

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?


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## sesmith (Mar 20, 2011)

Billy123 said:
			
		

> 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?



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


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## Billy123 (Mar 20, 2011)

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


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## sesmith (Mar 20, 2011)

Billy123 said:
			
		

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



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


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## Billy123 (Mar 20, 2011)

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


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## fishingpol (Mar 21, 2011)

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.


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## sesmith (Mar 21, 2011)

fishingpol said:
			
		

> 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.



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


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## fishingpol (Mar 21, 2011)

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.


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## Billy123 (Mar 25, 2011)

Can you post the URL for the screen absorber plans?


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## GaryGary (Mar 25, 2011)

sesmith said:
			
		

> Billy123 said:
> 
> 
> 
> ...



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


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## mayhem (Mar 25, 2011)

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.


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## GaryGary (Mar 25, 2011)

mayhem said:
			
		

> 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.



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


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## fishingpol (Mar 25, 2011)

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.


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## fishingpol (Mar 25, 2011)

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


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## GaryGary (Mar 26, 2011)

fishingpol said:
			
		

> 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



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


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## fishingpol (Mar 26, 2011)

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


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## GaryGary (Mar 26, 2011)

fishingpol said:
			
		

> 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.
> 
> ...



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


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## Billy123 (Mar 26, 2011)

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.


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## GaryGary (Mar 26, 2011)

Billy123 said:
			
		

> 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"?
> 
> ...



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


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## Billy123 (Mar 26, 2011)

Gary,

Nice work by the way! 

Another question:

The screen collector vs. the Flashing type as seen here: (http://www.mobilehomerepair.com/article17solar.htm), both same size, does any type perform better?


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## GaryGary (Mar 26, 2011)

Billy123 said:
			
		

> Gary,
> 
> Nice work by the way!
> 
> ...




Hi,
This is a somewhat unusual design.  
As they mention, most collectors of this type would place the absorber panel over the top of the baffles and run the air behind the baffles.  There would be no air flow between the glazing the absorber.  This is the traditional back pass collector.
They place the absorber behind the baffles and run the airflow between the absorber and the glazing.

This seems questionable to me in that you are scrubbing high speed and hot air over the glazing -- it seems like this would result in increased heat loss out the glazing.  This is bad in that the heat loss out the glazing is nearly all of the collector heat loss -- its basically the reason that typical air heating collectors run at 40 or so percent efficient instead of 90% efficient.  So, generally you want to do things avoid heat loss out the glazing.  

This is a long way of saying that I think the screen collector is probably more efficient.  But, I've never tested the two side by side, so I could certainly be wrong.

Another factor to think about is that the back pass collector (a collector with baffles to force the air to pass over the full absorber surface) had a lot more pressure drop than the screen collector.  This means a bigger fan and nosier fan that uses more power if you want to achieve the same flow rate.  

Gary


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## fishingpol (Mar 27, 2011)

Gary,

Thanks for your replies.  I have some thinking to do.  I'm reading more on BIS and will consider my options for a collector.  I am going to take notice of temperature on the south side of the house.   I did make a small collector today using poly-iso foam foil tape and a piece of regular glass.  I mounted it vertically to the side of the house put in small air holes on the top and bottom to prevent overheating.  I stuck a Weber remote meat probe thermometer into the side that gave me constant readings in the house.  Highest temp was 140* in the collector in the afternoon.  Not bad for a 40* day with wind and clouds.  I will make a slightly larger one as I have some old storm door panels.  When I make the collector, I will probably incorporate the supply air from my basement to travel inside a duct within the collector to reduce heat loss.  It will travel from the top, down along the (in)side in aluminum round duct and to the bottom into a baffle to disperse flow.  It will be separated from the main collector with a foam partition wall.  The window it will be going through is higher than collector so I may also incorporate a fan to move the air through.


I did read through your $2k collector for domestic and radiant floor heating.  It was very interesting with a ton of info.  I am mechanically inclined and everything you posted makes sense and was easy to follow.  

Have you heard of any issues of poly-iso foil de-laminating from the heat? 

Do you recommend painting the poly-iso flat black?   It is a little glossy and possible reflective.

Thanks ,

Jon


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## GaryGary (Mar 27, 2011)

Hi,
I've  not had any trouble with the polyiso delaminating or degrading -- it appears to stand up to collector temps well.

There are several types of face sheets used on polyiso -- a lot of it has a sort of aluminum foil for the face sheet.  
I use a lot of the Atlas R-Board, which is polyiso with a face sheet that appears to be a thin sheet of fiberglass.  It comes in grey and takes paint very well.  Makes a nice inside insulating shutter: http://www.builditsolar.com/Projects/Conservation/HalfShutter/HalfShutter.htm

On the $2K water heater, the absorber is opaque, and basically no sun gets to the polyiso behind it, so it just left it the grey it comes in.  
On the screen collectors, I've been painting the polyiso behind the absorber black to absorb the light that gets through the screen. 
I used to use the Rust Oleum flat black BBQ paint, but this is a little expensive and time consuming for larger surfaces, so I had Home Depot mix up a gallon of flat black latex to see how it would hold up inside the collector.  It seems to be doing fine even when the collector is stagnated.

You do want to be careful about materials used in collectors -- a lot of materials don't hold up will at collector temps.  Particularly important for air collectors since you are breathing and smelling anything that out gasses.

Gary


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## fishingpol (Mar 27, 2011)

Ok, thanks for the info Gary.

Jon


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## Amaralluis (Mar 27, 2011)

how well does those collectors work in the winter in the colder zones like up here in the Maritimes? 
what kind of btus can one expect to achieve with this?


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## GaryGary (Mar 28, 2011)

Amaralluis said:
			
		

> how well does those collectors work in the winter in the colder zones like up here in the Maritimes?
> what kind of btus can one expect to achieve with this?




Hi,
I live in Montana, and the collectors do well here -- we have days where the high is below zero (that's zero F 

This is my shop heating collector at -20F:
http://www.builditsolar.com/Projects/SpaceHeating/SolarGarageCollector/GarCol20F.htm

If you want a quantitative answer, this collector calculator will tell you how much the efficiency and heat output drop with temperature:
http://www.builditsolar.com/References/Calculators/Collector/ColEfic.htm#efic
Just run with a mild (say) 40F, and get the efficiency and output, and then run it again with a colder temp to see how much it changes.  
One thing to bear in mind is that when you look at outdoor temps, you want to look at the high for the day, since that is when you are doing the collecting.  And, you want to look at average outdoor temps for each month of your heating season -- not just the coldest month.  You can get good averages at this nice new weather site: http://weatherspark.com
Don't guess at the average temps -- most people guess way to low.  If you ask someone who lives here in Bozeman what the average January high temp is, they will probably guess around 0F, but in fact its 30F.

Gary


Gary


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## fishingpol (Mar 28, 2011)

I built up a collector yesterday using 1/2" poly-iso.  Roughly 24" x 28" using a 1/4 piece of glass from an old storm door panel.  All pieces sealed with foil tape with two 1/2" holes at the bottom and two at the top so there was some movement of air.  My highest reading was 168*.  I'm sure I could realize higher temps in the collector if the supply was ducted from the basement air at about 65* rather then outside air at 45*  The sky was pretty clear with a very thin haze of clouds.  The depth of the box was 6" deep with no absorber.  The mock-ups are getting bigger.  It would be nice to vent that into the basement in the winter.  Wheels are turning...


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## GaryGary (Mar 29, 2011)

Hi,
You actually want to move air through the collector fast enough so that it does not get too hot.  

You want about a 50 to 60 F temperature rise from inlet to outlet.

The hotter the collector runs, the less efficient it will be as it will lose more and more heat out the glazing.  
The 50 to 60F temp rise is good in that the air coming out of the collector is hot enough to feel warm, but not so hot as to lose too much heat out the glazing.

To measure collector output you need to measure both the temperature rise through the collector and the flow rate through the collector.  The heat output is proportional to the product of these two, and anything that improves this product makes the collector more efficient.  Measuring just the maximum temperature a collector can produce does not really tell you anything about how well its doing -- except that you know that if the outlet temp is quite high, that the collector is losing a lot of heat out the glazing and won't be efficient.

Some more on measuring collector efficiency/output:
http://www.builditsolar.com/References/Measurements/CollectorPerformance.htm

Gary


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## fishingpol (Mar 29, 2011)

Gary, 

I will read the link.  The final product will have some sort of fan moving air through.  I was also thinking of using "blast gates" that are available through wood working catalogs that can be slid opened or closed to adjust the flow of air.  I was actually thinking a fan would send the air through too quickly and not pick up all the heat potential.



http://www.rockler.com/search_results.cfm?srch=usr&filter=blast+gate&submit;.x=15&submit;.y=12

Thanks for another tip to help with the final design.

Jon


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## Billy123 (Mar 30, 2011)

fishingpol said:
			
		

> I built up a collector yesterday using 1/2" poly-iso.  Roughly 24" x 28" using a 1/4 piece of glass from an old storm door panel.  All pieces sealed with foil tape with two 1/2" holes at the bottom and two at the top so there was some movement of air.  My highest reading was 168*.  I'm sure I could realize higher temps in the collector if the supply was ducted from the basement air at about 65* rather then outside air at 45*  The sky was pretty clear with a very thin haze of clouds.  The depth of the box was 6" deep with no absorber.  The mock-ups are getting bigger.  It would be nice to vent that into the basement in the winter.  Wheels are turning...



Can you post some pictures of that? You have a fan?


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## fishingpol (Apr 2, 2011)

Sorry Billy, playing catchup here.  I am building a slightly larger one in a cellar window.  I'll get some photos up soon.  I just scored some metal shelves that someone was throwing away.  Those will be painted black and put on the back of the collector over the foam panel.  Gotta love free stuff.


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## fishingpol (Apr 9, 2011)

Ok, first picture is the solar collector that I built from poly-iso panels and a storm window.

Second picture is the window with the left panel being removed for the ducting to the basement.  More to follow.


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## fishingpol (Apr 9, 2011)

Next is Poly-iso over 1/2" plywood secured to window frame.  Duct holes were cut with neighbors hole saw bit.  I will have a horizontal baffle separating the input(bottom hole) and output(top hole) to slow air down a little to heat up.  I don't see the screen absorber working here as it is limited space.  I know there is a shadow from a small overhang, but in the winter it is barely covering it. 


Second picture is the sheet metal shelves that I cut to size and painted high-heat black.  I will be working on the vinyl trim frame this weekend.  I have already cut a vinyl sill for the bottom, sides will be today.  Glazing will be after that with a vinyl trim cap last.  I have to locate a small DC fan motor and PV panel to power it.

Three questions:

1.)  Anyone know how to stack pictures one above the other so I can put wording between each picture instead of side by side?
2.) Anyone know where to get an inexpensive PV panel to power a small fan?
3.) Can cheap solar outdoor lights be used?  I read that they have to be wired together to get adequate output to start fan.


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## Billy123 (Apr 10, 2011)

You peaked my interest. Keep us posted.


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## bucketboy (Apr 13, 2011)

In january my daughter and i built a pop can heater, for 2 reasons, it was a school project to start with then i claimed it to heat a space in our home when she was done with it. The tough part, we made it up as we wnt as no real plans were avaliable during our net search. we overcame some common problems, sealing all the seams on the containing box, sealing the cans together, paint blistering on the cans, air movement through the box. All the hype that you can use computer fans, or duct fans is rubish. we have a 4 x 8 heater the duct fans do not push against resistance in the collecting manifold. Computer fans do not have enough cfm volume to make the generated heat circulate in the space your heating. We finially overcame all the shortcomings and expenses of trying different fans and went with a small furnace fan and the unit works great . we do achieve very high temperatures before the fan comes on but during the running of the fan we get 60 to 70 degrees of temperature rise and comfotablly heat a 20 x 20 finished space with no other heat source to 75-76 F for 6 hours a day temperture starts to drop off around 330  and settles at low 60 s overnight Our unit is 32 sq feet of collection area, it has about 44 hours of construction time and a cost of the unit to build was $400. we have started rounding up materials to build 3 more this summer and i suspect it will assist the temperature in the house particularly in shoulder season. These are great ideas to assist in raising heating costs. i m sure there are lots of folks that could or have tweeked the unit design and operation but an average do it yourselfer can build this unit sucsessfully and enjoy the free heat for years. Also the fan is hooked to an 80 watt solar panel and a storage battery ( Not in the 400 building costs) as there was no plug avaliable in the area of installation.


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## begreen (Apr 13, 2011)

Sounds like an awesome project bucketboy. Did you document it with photos somewhere on the web? How is its performance on cloudy days?


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## bucketboy (Apr 13, 2011)

Thanks, my daughter and I took pictures along the way , i have some, i will attempt to post to show you. they work poorly on cloudy days but there are alot of sunny days in the winter to take advantage of. Overall i am pleased with the operation, now that we have a few of the BUGS worked out


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## fishingpol (Apr 13, 2011)

Bucketboy,

Do you think the computer fan would be enough to move air through a smaller collector?  I just need some type of fan to move air without letting the collector get too hot loosing heat through the glazing.  Gary from BIS made the suggestion above.  Where did you get your panel from?  That was an encouraging post you put up there.  If mine works out, I will look for parts for a larger one to build this year...


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## jebatty (Apr 13, 2011)

In the early 80's I built the equivalent of a solar heat box, but mounted it on the roof: 4' x 8' with corrugated steel collector painted black. I ducted air from the main level of our house into the bottom of the collector, air flow across the bottom of the collector to the other end, across the top side of the collector, and then ducted back into the basement. I used a 50 cfm bathroom exhaust fan for the blower and a snap-disc thermostat in the collector to cycle the fan. On a clear sunny day, even in January with -20F outside air temp and 70F air in, I got 120-140F air out in full sun. This was at 45N latitude, and a really low sun angle. The collector failed after 4 years due to moisture condensation inside the collector which rotted the wood components. This was little more than a plywood box with fiberglass insulation on the bottom and a polycarbonate greenhouse glazing panel. 

Good luck on your project.


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## fishingpol (Apr 13, 2011)

We are very fortunate to have such an array of materials available that were not around 20 years ago.  Imagine 20 years from now what materials will be available.  Thanks for these encouraging stories.


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## bucketboy (Apr 14, 2011)

we had poor results with the computer fan circulating the air, in fact the paint blistered off the cans. as mentioned before , i m sure that there are folks that can modify the design to suit their situation and materials avaliable to them. we had a terrible time with trial and error to come up with something that worked adaquately. the snap themostat turns the fan in and off. the unit we built works well in our envirorment (southern ontario) one thing you need to keep in your mind when searching the net for ideas, take everything with a grain of salt. we found lots of ideas, but the one thing no one on the net shared was the pit falls people also closely gaurded their mistakes and bragged of the sucess. the collectors will give you the 150 f output if left in the sun, the trick was to circulate the heat into the room and exchange it back into the collector. pop cans worked as we were able to get them from the school cafeteria. we tried high heat bbq paint but opted for motor paint . washing the cans is important as was scuffing them to paint. the net sugested silicon to join the cans, we used high heat morter (fire place type and expensive) also sealing the box was important to ensure the input air goes throught the cans to be returned to the room heated. We used double pane glass the i was able to get from a recycle depot. to ensure good operation we had to measure the angle of the sun and build a frame to mount the collector on. we also hard piped the unit into the house and insolated the heat line. we found 4 in duct works but 6 inch give more volume of air. so if your going to build a collector, give it some serious thought to avoid some of the costly , time consuming  errors we underwent.

good luck
bucketboy


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## fishingpol (Dec 1, 2011)

I finally had some time to finish the collector before the cold sets in.  I am not a numbers and formula guy, but more of a figure what will happen and then build it.  The glazing is just clear acrylic with silicone caulk around the perimeter.  Inside I have a dc computer fan on the outlet, connected to the solar panel.  I put a snapstat in, but not using at this time since the fan won't spin if the sun is not in reasonable direction to the panel.  The fan is very quiet and it blows directly in the area of my workbench.  I do realize that this is not going to heat my basement that much, but I am collecting heat and it is cheap BTU's over time that I would otherwise not be gleaning.  I made the absorber screen of aluminum, and kind of wished I had doubled the screen layer.  When I put a piece of air filter over the intake, the temp does go up a few degrees, probably from the air flow slowing down just a little.  Overall this has been a fun project, and I'll tweak things as time goes on.  I would have made a larger collector, but I need to get some free or low-cost glazing.  I will find some at some point.  I have enough material and insulation to make a larger one.  

The sun is effective from about 11:00 am to 3:30pm.  I have a better location, but time will tell if I build one over there.  This fall has been a bit overcast, so I didn't get the full potential.  Maybe once the cold is here and cold fronts push through with clear skies, it will be more consistent.  Input temps are around 62* and outlet temp at its' peak has been 84*.  I plan on putting a small stick in front of the collector as sort of a sundial to cast a shadow and see if the highest output temps are when the sun is directly perpindicular to the panel.

I could put a larger collector, actually a huge collector above the window, but the house bumps out a little and could pose a challenge running insulated ducts down a few feet to the basement.  But I may figure it out.  The collector does not change the look of the house at all, and I think it is quite clean looking.


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## woodgeek (Dec 2, 2011)

I'm confused by this project.  You replaced a window that had passive gain with a collector of the same area with active gain.  Aren't you right where you started, in terms of input?  Overall, you might be getting less input since the air behind the collector pane is warmer than it was (higher parasitics), but your losses when the sun is not shining are also lower.

What am I missing?


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## fishingpol (Dec 2, 2011)

This was an experiment to see if I can gain a higher temperature using the collector.  I used the window as a base to work with without modifying the side of my house to see if the location is good.  I would like to double or triple the area of the collector or even the design.  This is new waters to me, and I don't have a background in solar heating, so it is just an experiment.  The window may have better solar gain, but I am trying this out to see what works and what doesn't.

The window is at grade level, so it has been covered on the inside for privacy so there was little solar gain to begin with.


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## woodgeek (Dec 2, 2011)

now I gets it.


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## Slow1 (Dec 2, 2011)

One thing that confuses me on these collectors - I see that folks put the fans pulling the hot air out of them.  Yet we often preach that it is "better to push cold air to the stove".  It would seem to me that perhaps some of the same logic may apply in terms of being easier to push dense cold air into the collectors than to pull the 'thinner' warm air out.  Can anyone explain the logic here?  Is there any particular logic one way or the other?


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## woodgeek (Dec 3, 2011)

I think for a closed system like these air collectors, it shouldn't matter (except the fan will run hotter).  I think the main reason why blowing the cold air to the stove makes so much sense is simply that 99% of the time fans go on or near the floor, where the natural cold air return is flowing anyway.  If we put similar fans blowing sideways on our ceilings, I bet we would find that they work well blowing away from the stove.  Of course, those little doorway fans come to mind, but I always thought most of them were far too small to be worth messing with.


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## karl (Dec 3, 2011)

Has anybody built a large one or a serious of small ones and posted a website about them?  I'm talking a hundred square feet of collector or more.  Maybe even placed on a roof.


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## fishingpol (Dec 3, 2011)

check out builditsolar.com


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