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jjackstone

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Finally disassembled my dryer hose collector and saved the box and glazing for use in this new build. This time I went with the two layer screen collector. It’s built similar to most of the others on this site with a couple of minor modifications. The previous version had no internal insulation so I bought a sheet of one inch polyiso and lined the bottom of the collector with it. I tried using spray foam to seal the small gaps, but I really didn’t like the mess it makes so I changed over to silicon rtv caulking. A couple of questions arose during the build that I’m sure you guys can answer for me when we get to that point in the conversation.

So, the insulation is installed and painted. On to the inlet and exhaust. I couldn’t find the type that most of you guys seem to use. The ones I found mount flush but have about an additional one inch riser to a set of tangs.

DUCT.jpg 
CUT AND FLATTENED.jpg 
Wasn’t sure what to do with it at first but decided to just cut a bit between each tang and 
then flatten them out.

SCREEN AND INLET.jpg

One of the changes I incorporated was to make the collector screen end before it reached the inlet port. Since there is an air diffuser above the port I didn’t really see any reason to take the screen all the way to the end of the box and then cut holes in it and still have to  fasten it to the bottom.

AIR SPREADER.jpg  Just made this out of some 10" flashing. Sealed the edges with rtv.

SCREEN MOUNTS.jpg  Mounted with two 3/4" by 3" pieces of angle bracket on each side.

EXHAUST COVER.jpg  Policarb mounted and getting ready to test. Here is one of my questions. How do you guys normally attach the two pieces of panel together? I wasn't sure so all I did was applied rtv and put a screw in about every foot. 

BOWING.jpg  Here is another question. Using a six inch fan caused a bit of bowing especially in the center of the polycarb. Do I just need to cut back on my air flow or is the center normally fastened down some how?

INLET CONNECTION.jpg 

I used a piece of foam exercise mat to attach the fan to the inlet port. While bumpy on the outside, it is nice and smooth on the inside. This makes a reasonably quiet connection and the foam is a half inch thick so can act as an insulator.




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jjackstone

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Reply with quote  #2 
On to the good stuff. Tested the unit between noon and 1:15 today. Clear and sunny day. Low wind at the time. If my math is right a 6 inch hole should be .13sq ft. 
Inlet temp didn't vary much over the hour or so. I'm going to call it 80 degree F. This was measured with a digital thermometer sitting next to the fan so should be fairly close.
Outlet was about 112 degree F measured with Kestrel.

So about a 32 degree rise.

Air flow measured with Kestrel 200 showed 1250 ft/min. Maybe that's why the glazing bowed.

So 1250 ft/min x .13 ft = 162.5 cfm. 

162.5 x 60 x 32 x .075x .24 = 5616 BTU/HR

Pretty happy with that. I think I would like a little higher temperature out and a little lower flow though.
The sun wasn't quite perpendicular to the collector but pretty close. Maybe 10 degrees off. I estimated using a home made sundial. (stick)

ASSuming 1000 watts/sq meter(3414 btu) and approximately 3 sq. meters surface area. Then around 10,240 btu should be available for harvest. 5616/10240=54+% efficiency. I know there is a fair amount of guestimation in my calculation especially since I don't currently have a method of measuring solar intensity but I'm satisfied with this number for now.

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gbwillson

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Reply with quote  #3 
The performance numbers look about right JJ. And yes, with that amount of airflow, pushing the airflow will bulge out the glazing. But the collector is more efficient at higher airflow levels. A simple cross piece bolted or clamped across the middle will take out most of the bow. Slowing the fan will bring up the temps, but you may want to make final speed adjustments once the weather cools quite a bit. While you likely won't have quite as high of an output temp in the winter. 112˚F temp feels a LOT warmer in the winter, and a 35˚-45˚ degree temp rise is pretty good at that airflow level. 

Many people now use twinwall polycarbonate if available, as there is no seam to seal. Also, if the ribs are horizontal, they tend to collector rain, snow and dust. 

Greg in MN
jjackstone

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Quote:
Many people now use twinwall polycarbonate if available, as there is no seam to seal. Also, if the ribs are horizontal, they tend to collector rain, snow and dust. 


Yeah. Best price I can find here in Sacramento on twinwall is $50+. The two ribbed polycarb sheets cost $44. 

In my introductory post from a few months ago I stated that what I would like to do is build a bunch of these and give them away if I could build them for near zero dollars by getting materials off Craigslist. I used to see tempered glass on there regularly because I was looking into building a small greenhouse a couple years ago. Many of the source now seemed to have dried up. I look daily still but materials now seem few and far between. I still plan to contact window and door companies to see if they would be willing to donate old tempered glass doors and window screens from demo or refurbished buildings. 1" x 6" wood is around a buck a foot out here and will likely increase with the new Canadian tarriffs. 1" X 6" fence boards however are only a couple bucks for a six foot length. Guess I can splice a couple of them together to make eight or twelve foot lengths. 
I'll keep plugging away however slowly it goes.

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gbwillson

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Reply with quote  #5 
JJ-

If you add in the cost of the filler for the ends of the corrugated ribs, whether it be wiggle strips or a whole lot of silicone, the cost is pretty much the same. I do like your idea of re-tasking windows. You might check with window install companies. Once they understand you are giving these solar heaters away, they might so to have more stock of old removed windows than you can handle. It might even be a tax write-off for them. 

The issues with using glass is you are limited by the size and weight, and if you don't use tempered glass, safety. Old patio doors work too. Something else you might look at for glazing is a heavy plastic film. While the film rolls you get from the hardware store will work for a season or two, the UV breaks the plastic down pretty quickly. So check online for UV treated films. They aren't stiff like the polycarbonate, so you have to keep that in mind. But it does work, is light and is cheaper than the polycarbonate sheets.

Here in Minneapolis, there are several local sites where people advertise free or very cheap stiff that is often set out on the curb. People don't want it, but they don't want to throw it in a landfill. I know I've seen old windows and doors before. It's worth a look...


Greg in MN
jjackstone

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Reply with quote  #6 
Quote:
Old patio doors work too. Something else you might look at for glazing is a heavy plastic film. While the film rolls you get from the hardware store will work for a season or two, the UV breaks the plastic down pretty quickly. 


Yep. Pretty much all patio doors are required to be tempered...at least the ones made in the last 20 odd years or so. Most of them are also double layered galss so would be good for two heaters. Many of them are tinted, some darker than others so that would cost some efficiency, but for free so what. 

Film is an option. I used clear shower curtain that I found cheap in my first build and it worked fine in a test. 

For wood frames I find that the local landfill sells scrap/used lumber for $10 a truck load. I haven't been to check it out yet but it sounds like they let you go through it and pick what you want.

On a different, yet related subject. If one wanted to build a solar oven and needed smaller pieces of glass I have recently discovered that glass shelves in refrigerators are tempered glass. There are always people getting rid of deceased refrigerators. Of course they prefer you take the whole thing 😉.

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dbc

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Reply with quote  #7 
JJ - That's great that you're looking to 'spread the wealth' by building low-cost collectors and give them away.  That will surely stimulate interest in the community.  I gotta warn you though - you'll have so many new ideas once you get into it that you'll probably never build the same design twice, unless you are building a batch at the same time.

That device you're using to connect the ducts is called a starting collar.  They have a few varieties at Home Depot, although they are all pretty similar.  There is also a similar device (think they call it a duct take-off) which has a back-side gasket and metal ring, but it is a special order item.  I just used a generic flex-duct splice.  I cut notches around one end and flattened the tabs over, similar to what you did.  It works OK, and it allows you to fasten to the inside, but it is a 'snap-together' design (some of the starting collars are also), so you need to seal the joint.  I used a couple wraps of foil tape.  That also worked OK, but I think the take-off design looks better and probably works better too.
jjackstone

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Reply with quote  #8 
Quote:
 I gotta warn you though - you'll have so many new ideas once you get into it that you'll probably never build the same design twice, unless you are building a batch at the same time.


Yeah I already have designs in my head for narrower collectors, window collectors, etc. I will try to build a lot of the same though just to make things go faster.

Quote:
It works OK, and it allows you to fasten to the inside, but it is a 'snap-together' design (some of the starting collars are also), so you need to seal the joint.  I used a couple wraps of foil tape. 


Same thing here. Aluminum tape and RTV to seal the collar in.

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jjackstone

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Reply with quote  #9 
Finished up the mods. Added a cross member at midpoint and the glazing no longer bows out. Easy fix. 1" x 2" board and a couple aluminum straps.

MID SUPPORT.jpg 
Put on two light coats of stain on the wood to make it prettier. I can run about 10% more air flow through the system now without the bowing. Temperature difference only a couple degrees cooler. On to the next version.


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JJ
dbc

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Reply with quote  #10 
Like your cross brace.  Easy to build and install; it works, and it looks good too.

You might want to keep an eye on the wood strip to make sure it doesn't split or crack.  It will take a beating out there in front.  Should be easy to repair/replace if you have any problems though.
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