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Posts: 243
Reply with quote  #1 

Lots of people here build solar air heating collectors, which are nice and simple and easy to build.  But, its hard to store the heat for use in the evening.

I was just lately reminded of this scheme in the Shurcliff book "New Inventions in Low Cost Solar Heating".  It uses what looks like a simple and efficient way to transfer heat from a solar collector hot air stream to a water tank.  


To the best of my knowledge no one followed up on this idea, and to me it seems like a good one.

Lots of experimenters here -- maybe someone wants to have a try?


By the way, the book mentioned above has a lot of really innovative ways to use solar -- my all time favorite solar book.


Still a few used copies on Amazon.

Scott Davis

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Posts: 697
Reply with quote  #2 
Very interesting Gary!  Yes, being able to store heat efficiently from hot air collectors would be a great advantage.  Water is definitely the best medium for the reasons they describe.  Hopefully some good brainstorming and experimentation will ensue here!
Take care, Scott MD

Posts: 219
Reply with quote  #3 
I have 2 ways to store my heat for night and shut of my heat pump in my shop.
I have about 40 ft of 5 in duct pipe making a closed loop in my cement floor. Air heat coming out the cement in the morning would be 50 deg, with sun all day the heat at end of the day can be as high as 82 deg. The temp going in at noon is as high as 150 deg and 82 out, so cement is taking the heat.
My other system which I just built as an experiment Is a 500 lb fish box which I put in 3 loops of 4 inch abs pipe and 14 elbows and added fins to the pipe to help transfer the heat to the water.
My water will heat up 20-25 deg on a good day and will lose 12 deg at night if I leave the ends of the pipe open, I can put a small fan on the pipe and get more heat, but just let it radiate out over night.
So there is ways to store heat from hot air panels. I will a bigger water tank next year and hook 2 panels to it.


Posts: 46
Reply with quote  #4 
If someone takes up this challenge I would like to see how the process shown would compare to passing the air through an auto heater core.


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Posts: 2,314
Reply with quote  #5 

I like the premise behind the heater core. It's kinda weird in that it would be working exactly the opposite the way it was designed. A radiator would have more capacity though, as the travel path for the liquid is a lot longer and could gather more heat as a result. Heck, if you go to a junk yard for the radiator, you could probably scrounge the radiator fan and shroud too.

Greg in MN[wave]

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Posts: 1,062
Reply with quote  #6 
Originally Posted by gbwillson
... A radiator would have more capacity though, as the travel path for the liquid is a lot longer and could gather more heat as a result. Heck, if you go to a junk yard for the radiator, you could probably scrounge the radiator fan and shroud too.

Sorta like this setup from the BIS site


That along with an insulated tank would work but since you'd already have a tank and pump I'd be tempted to go all the way and have a hydronic panel too.

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

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Posts: 283
Reply with quote  #7 
Hello again
I had a post on this last night be deleted it because on reading back it felt like it was a bad description. I used the diagram from the book this time for clarity (hope this is allowed? if not let me know and i will delete)
Cowling strips + tank.jpg 

Would something like this work well say to make use of attic air in summer months or any month where it is warm enough? It could be a simple device triggered (fan or blower starts) because of a set temperature difference between the tank water and the surrounding air temperature.
It could be used to pre heat using a coil (inside the water filled tank with cowling strips)on the cold feed . The inlet and outlet points (or duct work) would need to seal somehow when the unit shuts off in order for the tank water temperature to remain insulated. Just a thought anyway.
Regards Mattie


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Posts: 2,240
Reply with quote  #8 
Nice discussion here !

Here is an off-the-wall TANKLESS variant, just experimenting to see how much it would cost...

It could be done *a lot* cheaper by using soldereing instead of expensive brass unions...

Also my price includes the PVC and the aluminum dryer duct ptions, whereas one is cheaper than the other !

The HEX could also be made a lot shorter....

The intent is for the water to be recycled through the exchanger.


Attached Files
pdf GH_A-W-Hex.jpg.pdf (725.50 KB, 42 views)

(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilĂ " unless talking musical instruments...


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Posts: 283
Reply with quote  #9 
Hello all
Nice work G_H did you just think of that on the spot?That brain of yours is concept machine!
My thinking here is more basic and based around sourcing materials and design issues if taking the use attic air to preheat on cold feed route:
Things like :
How much would it cost to build a small square copper tank or a steel tank or source one as shown in the book?(it does not have to be the same dimensions)
What alternatives are there for diy low cost options for a tank? And how might it be sized? With the cost of materials an important factor.
Is there an optimal ratio of coils(if taking the pre heat route) to tank size or water volume to number of cowling strips?
What could be used to make a cheap cowling strips ? Biscuit tins ,aluminum sheets?
What are cheap materials that could be used for the input manifold?
Could a small(ready for the recycling center) freezer be used to house and insulate the tank?
What other alternative cost effective materials could be used for the other parts needed in the design.
My thinking here is do it as cheaply as possible firstly to test how it performs.

Then again its most likely a better idea to start with an allready installed larger tank as it has a lot more surface area, to observe how well heat transfer takes place before a smaller preheat tank idea is looked at.
Regards Mattie

Posts: 243
Reply with quote  #10 
Trying to compare the idea from the Shurcliff book to a car radiator:

I have a nice 15 by 18 inch water to air heat exchanger (like a car radiator) with 3 rows of copper tubes.

Like this one: 
Cost $103.

The heat transfer area is:  
The alum fins are spaced at about 0.08 inches (tight), and there are 216 of them total, each about 3 by 15.5 inches.  

This works out to about 70 sf of fin area for heat transfer.

The total tube tube surface area for the 48 tubes is 7 sf.

For the Shurcliff one, if you assume a 24 inch dia by 48 inch high tank (94 gallons), the total heat transfer area is about 25 sf (the sidewall area of the tank).

So, it seems like for this size radiator and tank the radiator would likely do better.

But, if you used the 10 ft long tank that Shurcliff shows in the book, the heat transfer areas would be about the same.

I guess the advantage of the Shurcliff one might be that if you already have the tank then you would just be adding the cowling strips -- it would be a very simple and reliable system with no moving parts, no additional water leak paths, and no controls?

It would be fun to try the Shurcliff scheme and just see how well it works, but I don't see any straight forward way to make the cowl stirps?

Maybe there is some way to get good heat transfer from the hot airstream to the tank wall with less hard to build parts than the cowl strips?


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