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I am old and forgetful...

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Glenn Sossin_2
Glenn Sossin_2 Member Posts: 592
Maybe use a larger diameter pipe which will have significantly lower losses?

Viega recently started selling 11/4 and 11/2 pex. Apparently they are doing very well with it. I have ordered fittings in these sizes 3 times over the past 2 weeks and I'm getting some back orders by the factory.

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  • Rocky
    Rocky Member Posts: 121
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    head, flow, and pump sizing....again

    I must have early onset dementia..cannot seem to remember about head, flow and pump curve. I'm only 44, but it looks like my face has worn out three bodies! And my brain is not far behind. Here is the scenario.
    Have a system with 7 remote manifolds (radiant). Am using MultiCor to supply these manifolds from a central header in the boiler room. One remote manifold needs 6.4 gpm. My CDAM says if I want to move 6.4 gpm of 120 degree 50/50 PG through 3/4" MultiCor, it will cost me about 19.5 feet of head. Now, I add this to my longest 1/2" pex loop from this manifold for an additional 3 feet of head, for a total head loss of about 22.5 feet of head, give or take another foot or two for header piping, etc. So say 24.5 feet of head to get the 6.4 gallons of water from my header back to my header. All the other remote manifolds do not have anywhere near this head, most of them around 8 feet or so. So, since this one manifold has the highest head loss, I just size my pump to handle all the combined flows to all manifolds (22.5 gpm) while satisfying the highest head of any one manifold? In this case the 24.5 feet of head? So do I pick a pump that will pump 22.5 gpm at 24.5 ft of head? Or, do I pick a pump that will pump 6.4 gpm at 24.5 feet of head, since all other manifolds have much lower head requirements? Am getting all twisted up here. Must be heat stroke as Fairbanks reached about 85 today, and brother, thats HOT for Fairbanks! Going to my handy dandy Grundfos book, one would be either a 32-80 or 32-160, while the other would only be a 26-99 Superbrute, quite a difference. Help a poor, heat-stroked, pre-dementia brother out, would ya?
    Warm regards from not-so-chilly Fairbanks,
    Rocky
  • Josh_10
    Josh_10 Member Posts: 787
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    24.5 Feet? How remote is this manifold? China?
  • Rocky
    Rocky Member Posts: 121
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    180 feet, round trip

    Am actually gonna use 1" MultiCor and that will drop the head loss down to about 9.5 feet, with floor circuit included. Just wanted to illustrate the situation I am having trouble wrapping my pea brain around tonight. I know that flow is cumulative and head is not, but I always seem to go wacko when I am dealing with multiple manifolds with various flows and heads. I mean if the pump can pump 6.4 gallons at 24.5 feet of head, won't the other manifolds kinda take care of themselves? Its not like all the other manifolds need 23 gpm at 24 feet of head.
    Regards,
    Rocky
  • Josh_10
    Josh_10 Member Posts: 787
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    That would be pretty helpful. If you get the head down that far you might be able to use something like a 0012 with success. With the relatively flat curve it won't be so noisy when the other manifolds are calling for heat without the long distance one.
  • Steve Ebels_3
    Steve Ebels_3 Member Posts: 1,291
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    Could you............

    Just thinking out loud here.

    Is there any way you could isolate that one manifold/loop and use a single pump for that while using another one for the rest of the system?
    The head for that one zone sounds like it's way different from the rest. Might be best to use two circs that are each sized right for the task at hand.
  • heatboy
    heatboy Member Posts: 1,468
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    Didn't you mention.........

    ........that your home is 6,000+ ft2? Do you really want to use one pump?

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  • Josh_10
    Josh_10 Member Posts: 787
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    I third the motion to use separate pumps.
  • Rocky_3
    Rocky_3 Member Posts: 232
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    oNE 26-99 superbrute

    and 8 zone valves, with a differential bypass valve at end of header, or 8 circ pumps. I don't know how it is not 6 one way or half a dozen the other. if I use the 1" multicor the head and flows now becomes doable for one pump. Why use 8? Just curious. Is it a personal preference to zone with circulators? Zone valves with a single pump is pretty common here. but we are kinda getting off topic to my original post. does pump need to be able to handle all flow at the highest head? ie: find a pump that will move total system flow at highest head of any circuit? ie: 23 gpm at 24 feet head (for example), or only 6.4 gpm at 24 feet of head and let rest of system shake itself out?
    Thanks,
    Rocky
  • heatboy
    heatboy Member Posts: 1,468
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    Yes.

    Total GPM of the system and the highest pressure drop circuit, ie. 23 GPM @ 24' of head for a single pump system.

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  • Maine Doug_64
    Maine Doug_64 Member Posts: 27
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    Old and Forgetful

    I'm sorry, could you repeat the question.....
  • John Barba_3
    John Barba_3 Member Posts: 30
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    Add the flow...

    and use the worst case head. Try a 00-VS variable speed pump and set it up to work on Delta-T. It'll go faster or slower as the zone valves open or close. Ask your guys about it...

    All the best..

    JMB
  • Rocky_3
    Rocky_3 Member Posts: 232
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    thanks, John

    Was actually considering that in the final design. By-the-by, my guys REALLY enjoyed the Taco training class. I have already bid 4 jobs utilizing the VS pumps in their various modes to accomplish some pretty cool stuff.

    Regards from not-so-chilly Fairbanks,
    Rocky
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