How to get even heat from h/w panels

Discussion in 'Solar and Geothermal Water Heating Forum' started by aztom, Jan 9, 2012.

  1. aztom

    aztom New Member

    Messages:
    7
    Location:
    Arizona
    Hi,
    I've got three solar h/w panels plumbed in parallel. They are almost level, and I have the feed and outlets going through T's of 1/2" copper.
    I'm not getting any circulation through the first two panels, only the farthest panel cools down, (indicating water flowing through it)
    I have an underpowered pump. Would a larger pump help or only make it worse, as far as balance goes.
    I suspect the venturi effect is keeping the glycol pulled down instead of pressurizing the panel as I had hoped.
    Could I use some sort of Y connection instead of the T's, or possibly step up to larger diameter tubing at the T to reduce the venturi effect?
    Any ideas are much appreciated, Tom
  2. Dana

    Dana In the trades

    Messages:
    2,969
    Location:
    01609
    To get balanced flow through a parallel array, they must be identical, and plumbed with the incoming water on one end of the array, the exit on the other end, like this:

    [​IMG]

    If that's how they're plumbed, there can either be obstructions, or vapor-lock/air-bubbles limiting flow to the other two. Air-purging the system would help the latter, but not the former.
  3. aztom

    aztom New Member

    Messages:
    7
    Location:
    Arizona
    Thanks. I'll try leveling them better, they're just sitting on the ground. That should help the vaporlocking.
    I tried pinching the hoses with vise-grips today to equalize the flow (temporarily, to test the concept, til I get valves installed at the lower feed manifold t's) It worked pretty good, I got a lot higher temp water feeding into the house.
    Thank you so much for your input, Tom
  4. Dana

    Dana In the trades

    Messages:
    2,969
    Location:
    01609
    Setting up purge-valves inappropriate places can help, and any hydronic heating sytem should have an air-scoop/expansion tank/automatic air-vent for purging the bubbles that remain or you may end up purging multiple times before vapor locks are prevented. Getting and keeping the air out is important for the longevity of the pumps too. By pinching flow and forcing 100% of flow through one panel at a time may clear a vapor lock out of an individual panel, but if the air is still in the system there's ample reason to believe it can recur.

    An underpowered pump might result in a large delta-T across the panels, and a lower collector efficiency, but too large a pump and a low delta-T can use a lot of electricity. Determining the right balance in a particular system is a subject too subtle and involved for "design by web-forum" optimization. It's fair say that if you're running 100F deltas under winter sun after you've successfully air purged and balance the pump, you could probably do better with a bigger pump, and you may need it to keep from popping the cork with a steam explosion come July.
  5. aztom

    aztom New Member

    Messages:
    7
    Location:
    Arizona
    Thanks Dana for that cogent analysis. I wish I had come to this site before cobbling together my project.
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