Sunday, November 7, 2010

Would Wide Solar Collectors Work Better With Horizontal "Risers"?

DIYers will often build collectors that are quite wide (20+ ft) for solar space heating.  The usual approach is to run a manifold along the top and bottom of the collector, and then connect the two manifolds with closely spaced risers that have fins attached to capture the sun's heat  and transfer it into the water flowing through the risers.

It has been suggested by Alan Rushforth that it would save material and might also result in a more uniform water distribution to the risers if they were run horizontally instead of vertically.  You end up with a much smaller number of much longer risers (hisers?).   This reduces manifold material, and reduces the number of manifold to riser joints -- these joints are time consuming and expensive, so reducing the number of them would be a good gain.

In order to push this idea along a little further, I did a test by turning my old prototype copper tube/aluminum fin collector on its side so that the risers run horizontally and the manifolds are vertical. 

In a nutshell, the test appears to show that at least for this small collector, the startup process, flow distribution, and drain back all work without problems -- I think it looks promising. 
What do you think?

All the details on the results here...

This idea has been discussed some in the Yahoo Simply Solar group and the Yahoo Solar Heat if you want to see a bit more on it -- these are both good groups for solar heating questions (and answers :).



  1. Gary

    Are the horizontal runs pitched? I thought I saw someone built a 4'high x 24' long collector. That's a long run I would be afraid of a slight dip that would retain water and freeze. It would be veryhard to keep everything perfect over 24' but maybe I did not read it right.


  2. Well, I learned a new word today (hisers)! I built my horizontal 4 X 6 panels (see blog entry on Sandy's $1k solar water heating system on Prince Edward island) with hisers primarily to save on material. I cut about 6 inches off of each 6 foot piece of copper hiser and used the smaller pieces on the vertical manifolds resulting in virtually no wasted copper pipe. Also, I saved on Ts and associated cutting and soldering. My system seems to work OK and Gary's tests lends further support to this concept. Copper pipe is available in 12 foot lengths (and also plywood and polycarbonate glazing, so 12 X4 foot horizontal panels might work (though they would be heavy)!


  3. Hi Knick,
    Yes -- the idea is to pitch the hisers about about a quarter inch per foot.
    I agree that getting that right would take some care, and would be more difficult than getting proper drain back pitch with a regular riser system. Have to think about a good way to do it -- there would definitely have to be some intermediate support of the hisers for wide collectors.

    I suspect your system is churning out the BTUs now that the sun is lower and shining more directly on the collector?


  4. Hi Sandy,
    I had forgotten that you had the horizontal risers.
    Good to know they are working out -- another vote for hisers :)


  5. As someone hoping to build at least a small test setup next summer, I'm wondering if the horizontal run but in a serpentine setup would be efficient. Have the water fill from the top and run side to side (and a slight angle downwards) and then out the bottom.


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