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JPWright

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Reply with quote  #1 

I love my dual screen absorber air heater (https://simplysolar.supporttopics.com/post/jps-horizontal-screen-collector-7297736?pid=1286206033. It has been working great for two winters. I am so pleased with it that I want to make a hydronic drain back water heater even though they are considerably more complicated. I was waiting for the big breakthrough, like the discovery of the screen as absorber for the air systems. Alas, not yet.

The space that I have available is on my garage roof and will hold a 4x10 ft panel. I need a landscape orientation that will be mounted vertically (90 degrees towards the south). I am mostly interested in heating the garage in the winter. To get me started I have two questions:

In your opinions which harp style is the best? I like the first one because it is less work.
Secondly, can I run the hot water return from the upper right to the lower left INSIDE the panel?

hydronic solar panel horzontal harp.jpg 
hydronic solar panel verticle harp.jpg 

Thanks all for continuing to help me out.



SolarInterested

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Reply with quote  #2 
Quote:
Originally Posted by JPWright
To get me started I have two questions:

In your opinions which harp style is the best? I like the first one because it is less work.
Secondly, can I run the hot water return from the upper right to the lower left INSIDE the panel?

I agree with your choice. Hisers (horizontal risers) will require less fittings too. Gary has some info on his site:
http://www.builditsolar.com/Experimental/HiserTest/HiserTest.htm
https://www.google.ca/search?q=hizer%20site:www.builditsolar.com

I believe the answer to your second question is also yes and that there are examples on the forum somewhere. I'll try to find a link for you.


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Both temperature rise and airflow are integral to comparing hot air collectors
SolarInterested

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Quote:
Originally Posted by JPWright
... I am so pleased with it that I want to make a hydronic drain back water heater even though they are considerably more complicated. I was waiting for the big breakthrough, like the discovery of the screen as absorber for the air systems. Alas, not yet. ...

Have you considered an ARETHA type collector?

ARETHA Project, solar panel with car radiator (link)
ARETHA type collector compared to cpvc-flashing collector (link)
Willie's Cinefoil dual pass ARETHA (link)

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Both temperature rise and airflow are integral to comparing hot air collectors
JPWright

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Thanks for the quick reply. I am off to make some fins!  I thought that I had been to every corner of the site. I thought experimental meant lots of math.

Aretha will not work for me. I have no way to get the air up to the roof.

I will keep you posted on the build. It will be very traditional.
solardan1959

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Reply with quote  #5 
JPwright,
"Aretha will not work for me. I have no way to get the air up to the roof."

You would be able to do the same thing, it uses water the same as your panels.  You do not need to get air to the roof,  the air in the panel is just used as a medium to circulate the heat around the box and more importantly though the radiator to heat up the air. Water is heated just like in your panel and that is what is routed to your garage.  It just saves on copper pipe and instead uses a radiator to transfer the air heat to the water rather than use the air to cool the water in the conventional way.  The downside is you need power for a fan to blow the air through the radiator.
Dan
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Reply with quote  #6 
JPwright you should also cost out the fins and "harp" for traditional panel vs the cost of screen and a heat exchanger for an Aretha. You'll be surprised. That said, I don't know how well it work work as a drain back, especially the heat exchanger.
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Both temperature rise and airflow are integral to comparing hot air collectors
SolarInterested

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Quote:
Originally Posted by JPWright
I will keep you posted on the build. It will be very traditional.
When you get started on your build, please start a new topic in the 'Members Projects' section.

Thanks

Admin

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Both temperature rise and airflow are integral to comparing hot air collectors
JPWright

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Reply with quote  #8 

As I was making fins, you folks got me thinking a little more. Since my demands are for some heat in the garage a few days a week, would a thermosiphon work. The tank could be in the garage upstairs or on a rack near the ceiling. If it were up stairs I would need a fan to circulate the warm air from upstairs to the down stairs.  My preference would be to have the tank located on the first floor. I found this diagram on http://www.backwoodshome.com/7-solar-water-heating-system-designs

thermosiphon with low tank.jpg 

I like the idea of two, low mounted 55 gal drums, right in my workspace. Will this work? Will this work with a collector that is only 2 ft high and 20 ft long?


JPWright

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Reply with quote  #9 
Here is what I have in mind.
garage and panels.jpg 

stmbtwle

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Reply with quote  #10 
check valves can turn around and bite you.  "clapper" valves tend to stick in one position or the other and either will prevent water flow or will allow a reverse thermosiphon to dump all your heat during the night, I've had both happen. spring check valves likely won't open by the slight pressure of a thermosiphon and may even cause a centrifugal pump to become airbound.

The vented loop or air gap is most reliable but unless very carefully designed may not allow thermosiphon either. I'd recommend a small 12/24v brushless centrifugal pump (NOT a bilge pump) and a small PV panel to run it.  SOME 12v pumps (not all) have a problem with the high voltage put out by a 12v panel (21v). so a 12v/24v pump is probably a better choice.

Also installing your collector on the ground means you can't use drainback, and you're risking freeze damage.

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