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solarusmc

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Posts: 180
Reply with quote  #21 
Greg,

I've never measured the cfm coming back into the house. Don't really know what I'd use to measure that accurately.

My thoughts on the smaller collectors were to make them 'skinnier' to hopefully heat the box space up quicker once the sun hits them and it worked out perfectly. I made some using 2 x 6 metal studs but they don't create the same higher temps as the 4ft x 6 ft ones I built with 2 x 4 metal studs.

After building 3 others before these last ones I figured out real quick that I am not attempting to 'store' any hot air in the box so making the box deeper as I did before wasn't going anywhere. No increase in air temps.. no real noticable volume of air flo increase.

My end conclusion is that solar hot air collectors 'are what they are' [smile]

They collector hot air and the second they get hot I want to remove that air as quickly as possible back into the house.

as far as fan noise goes I figured that out along the way too.

If I used metal tubing with insulated duct slid over the metal tubing to the house the noize was horrible so I removed the metal tubing approx 6 to 8 ft from the house.

So the last 6 to 8 ft is nothing but 6 inch  insulated flex hose and 'all noise went away' except for a very slight noise. You have to go over to the vent and lean over to hear the noise now which is 'sweet'

Air flo I'm pegging at around 150 to 200 CFM

I could not be happier with the 4ft x 6 ft collectors.
On good sunny days they are kicking out 120 degrees back into the house.. and it doesn't matter what the outside temps are....

no bull.

Last month I helped my brother build a 8ft x 12 ft hot air collector using the same exact design specs as mine. We installed 1 - 8 inch fan on his unit. Mounted it to the roof and cut 8 inch holes right thru his roof for the supply/return. You should see that baby kick out heat and ZERO fan noise cuz we made sure we installed approx 12 feet of flex insulated ductwork between the fan and the output registers.

If you would like to see a big 6 meg pdf file full of pictures showing how I built mine just email me and I'll send it over to you anytime.  [thumb]

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Pat B. Warwick, Rhode Island Rest Assured! Comments and/or suggestions I make here at the forums on 'your' projects as well as my own have all been carefully and scientifically calculated by the 'seat of my pants'

ggtaft

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Posts: 5
Reply with quote  #22 
Hi
I am considering building a backpass style hot air collector.  I thought that it might make the collector more efficient to build the  collector with what I will call a double backpass.  What I mean by this is that the air will run in front of the absorber and then behind it for a second pass with a "U" shaped pass in the front and the same in back.  Any comments on this would be appreciated.
solarusmc

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Posts: 180
Reply with quote  #23 
GG..

sounds cool.
I'd enjoy seeing a few drawings of your design so I could understand your concept better..

Thanks!

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Pat B. Warwick, Rhode Island Rest Assured! Comments and/or suggestions I make here at the forums on 'your' projects as well as my own have all been carefully and scientifically calculated by the 'seat of my pants'
netttech

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Posts: 720
Reply with quote  #24 
GG,
I agree with USMC, if you could use MS Paint or some other app to create a drawing it would help.

That being said...how hot do you want the air to be?? USMC is getting around 120, my hot air panels (3) range from 100 - 120 degrees (different sizes), with only 1 pass thru the panel. So how much more hot air are you hoping to achieve?

Don't get me wrong I'm not trying to sound discouraging on the idea. All of us here are constantly thinking up different ideas, so go for it. I think we just can't figure out a two pass system.

You are using this site for it's intention, share ideas, ask questions. [smile]

USMC,
You can try the garbage bag air flow test. Get a plastic garbage bag where you know the capacity (usually in gallons). When the panel/fan is running, place the open end over the opening, count how long it takes to fill the bag. There's an equation to convert gallons size to cfm & using the of seconds. I don't know the equation off-hand, but it may be on this forum, in another category. It's a cheap method to give you a good idea of actual air flow.

Jeff
Central IL
Scott Davis

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Posts: 697
Reply with quote  #25 
Hi Gang,

This Excel spreadsheet will do the bag inflation calculations for you:

http://www.n3fjp.com/solar/AirflowBagTestCalculator.xls

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Scott Davis

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Reply with quote  #26 
Hi ggtaft,

The double backpass sounds interesting.  The more heat you can scrub from the absorber, the more potential efficiency you may achieve, as long as you don't lose the heat in other ways during the process.  Please draw up and share your idea!

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solarusmc

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Posts: 180
Reply with quote  #27 
Hey thanks for all that info on measuring my air flo Jeff and Scott
I'll give it a try..

the design GG is speaking of will be interesting to see once it's drawn up.

He made me think on that a bit but because he's talking about running air accross the 'front' of the collector first.. it kinda thru me off.

I was thinking that if a header air chamber was constructed up top containing supply/return holes the ROOM Return air could enter thru the top/back of the header chamber.. run down the backside of the absorber plate... go around the 'bottom' of the absorber plate then back up to the top front chamber of the header and eventually exit thru the supply hole to the house.

Matter of fact.. I think I'll draw up something and attach it to my next post cuz I like this design idea the more I think of it. Thanks for bringing this idea to the forum GG. Gets us 'all' thinking.

I better draw something up right now. Get back to everyone. 

PS: If I don't draw it right this second, I'll forget what the heck I was thinking. [confused]
That's what happens when ya retired guys. Ho Ho![smile]

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Pat B. Warwick, Rhode Island Rest Assured! Comments and/or suggestions I make here at the forums on 'your' projects as well as my own have all been carefully and scientifically calculated by the 'seat of my pants'
joebehr

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Posts: 109
Reply with quote  #28 
Pat
I'm anxious to see your sketch...still deciding on what type of collector to build for my carport sides of approx. 6'x6' sq. each...should be able to create around 110-115 sq ft for total collector area for my 450 sq ft shop...might make a dent.
joebehr
gbwillson

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Posts: 2,275
Reply with quote  #29 
It seems like the biggest drawback to backpass  collectors is the flow restriction even if your flow area is greater than your duct size. How much larger does the backpass spacing have to be in order not to be restricting the flow of air?

Greg in SUNNY(for the moment) MN[wave]
Scott Davis

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Reply with quote  #30 
Hi Greg,

Yes, flow resistance was definitely a problem that both Gary and I experienced with the backpass design. Now, we only allowed one inch as I recall from the back of the panel to the absorber for the backpass.  Another inch, or less, might have been the ticket to solve the air flow problem. 

Flow resistance aside, the performance of the back pass was good, but not as good as the screen collector.  Here are the results with balanced air flow.  The fiberglass screen provided a 4.2  degree additional temperature rise.

[TemperatureRise]

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