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Posts: 95
Reply with quote  #1 
Hope you don't mind Scott L Alaska

QUOTE "Has anyone tried putting a tube groove in a downspout?  A 3"x4"x10' chunk of wood with a groove on it slid into the downspout and then beat a piece of rod into it with a mallet to form the groove.  Since we are already building the collector box for air adding water also would be very cheap at that point.  We are only getting 40  or 50 percent efficiency over all so maybe we can take more of the heat out and into the house instead of going back out the glazing.  The air moving through the downspouts is probably not cooling them all that much as air is inefficient compared to water in removing heat plus there is that  air barrier on the inside wall of the downspout that lowers its ability to remove heat.  I think.
What about adding a water collector to the back wall of a double screen collector.  I believe that the double screen only stops about 50% of the sun so that means the other 50% hits the back of the collector.  Now some of that is reflected back to the screen to be turned into heat and removed by the air but some escapes back out the glazing.  As the back heats up part of that heat is carried away by the air flowing through the screen absorber.
What bothers me is that the air coming through the screen is already hot.  Could it be hotter than the heat coming off the back?  Would that mean that the air would not be removing that heat to the house.  I could not find any tests of that.  With out back insulation you will lose heat out the back of the collector though once again I could not find a tests with and with out insulation to see just how much actually goes out the back. 
Putting a reflective back wall so most of the sun hitting it would reflect back to the screen and be turned to heat and taken away by the air headed for the house might be better though you would still lose some out through the glazing.  If the absorber has already maxxed out what it can absorb and radiate just from the sun side what then happens to the reflected light or radiated heat?
  Be a great spot for a Coroplast collector or a tube and fin.  Cooling the back wall would lower heat loss out the back.  Would it be enough to heat usable water?  By removing the heat from the back of the collector with water would that lower the heat collected by the air absorber? 
 We might be able to test it by putting a clear piece of poly on the back of the collector and see how that effected the screen absorber air temp.  If I understand long wave and short wave lengths and keep in mind I might not, most of the light that makes it through the screen absorber will also go through the clear poly so not add any heat to the collector.  This would tell us how the screen is doing as a collector VS. having an insulated back that it might be taking heat from.  Might find that the collector does about as well since it transfers heat so fast being low mass.  If that was true then we have unused heat that is available to us and could be removed with a water collector.
Even if it was not high temp water it would still be great for preheating."
Scott L

Moved here by ChrisJ


Posts: 95
Reply with quote  #2 
This is the type of collector I have thought of building. It would be a collector within a collector, inner hydronic with it's own glazing.
But utilize the air that is in the space between the outer glazing and the inner hydronic collector.
I picture a deeper collector, maybe 1x8 or 2x8, 8' high x say 20' wide. Hizer style hydronic for 4 feet of the 8, covered by it's own glazing. Air with screens in the other 4 feet. Air flow horizontal, would have to make a 180* turn at one end. Have not decided if air flow over hydronic collector first then throught screens or vice versa.
Chris in RI

Posts: 2
Reply with quote  #3 
if the BTUH's that = 500 x dT-*f x GPM (gal/min)  fits , then yes.

an every 5000 BTUH could raise 60* water to 110  (50*f dT)  at this flow=,  steps:   5000/500, =10  and 10/50dT leaves  1/5th or .2 GPM per 5000 BTUh "instant" HW.

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Posts: 2,536
Reply with quote  #4 
Seems to me that Scott has already built the collectors we need, we just need to "marry" them.  I'm thinking of a perforated soffit collector, with the addition of CPVC glued to the soffit.  The soffit and the CPVC/aluminum collectors both seem to be good collectors and easy to build, and one could select air, water, or both at the flip of a switch.
Willie, Tampa Bay

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Posts: 77
Reply with quote  #5 
I was thinking of building a regular pex-al-pex collector but behind the absorber plate (black rolled roofing? Metal?) I was going to leave an air space uninsulated towards the hydronic side and insulated opposite on the back. The plate gets heated, it heats the water but it also radiates heat towards the REAR of the collector where the air could be circulated. Any thoughts on this?

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Posts: 17
Reply with quote  #6 
just a bump to encourage more talk on hybrid.  Im soon to be building a collector and hybrid would be way to go.   

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Posts: 2,536
Reply with quote  #7 
A hybrid might work well for space heating. Air collectors heat up quickly and could warm up a room in the morning. Once the room is warm, a thermostat could switch off the fan and turn on the pump to store hot water for use at night. It would be a neat trick if someone could make it work. Probably would take a big collector, though.
Willie, Tampa Bay

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Posts: 283
Reply with quote  #8 
Great link ChrisJ.
Ive also thought about this recently,taking into account the cp of water vs cp air ,seems to point toward water being used as part of the absorber much like Ken previously pointed at.The insulative properties of a certain thickness of air would also be a useful thought here.

Posts: 3
Reply with quote  #9 
The home built one I reference above would cover the whole south side of you roof as thin film PV produces less electricity but a large collector like this could go a long way to providing most of the the heat and electricity a normal house would use. 

Posts: 2
Reply with quote  #10 
I will be closing on a house in Fort Worth, TX in 10 days that has a 400 ft2 shop. When reconfigured it will be an 80 ft2 finishing room with 320ft2 shop space. I have 320ft2 of clear southern exposure.
I am thinking of an initial thermosiphon system to provide daytime heat during remodeling. When the new floor is put in, I plan on installing a two zone radiant underfloor system and close up the thermosiphon.
I haven't done a solar project since the early 80's, so I am really beginning again.
Where do I find the calculators for how big a thermal storage I will need.
Does this sound practical?
Would it be better to thermosiphon during the day and have underfloor heat at night or just use underfloor?
I don't want the final to be thermosiphon in the finishing room because I don't want to compete with the 8 min air exchange I need while spraying finish.
The finishing room will be maintained near 80F for ideal cure times.
The remainder of the shop will be maintained near 72F in consideration of my aching knees.

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