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Flow rate problem

mbbaum
mbbaum Member Posts: 7
in Radiant Heating
Hi all,

I am looking for suggestions on why I can’t get adequate flow rate on a zone. 10 circuits on one zone with smaller pump have good flow. Added a bigger pump to second zone with only 2 circuits and can’t get adequate flow. Pump was same as first initially, no difference in flow rate with bigger pump. I’ve checked for debris in system and all zone circuits in each of the 2 zones are a little less than 500 ft each in 3/4 HePex. Thanks


Comments

  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,206
    Could be an air problem. Have you power purged all the loops involved?
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • neilc
    neilc Member Posts: 2,784
    i'm thinking it's those small ID 90s that I don't see on the 10 loop circuit,
    but then you have couplings , , ,
    known to beat dead horses
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,248
    @mbbaum

    Is this a new problem or has the problem always existed?
  • mbbaum
    mbbaum Member Posts: 7
    Alan (California Radiant) Forbes said:
    Could be an air problem. Have you power purged all the loops involved?
    Loops were purged. Flow rate is good with an aux pump hooked to zone only. 
  • mbbaum
    mbbaum Member Posts: 7
    EBEBRATT-Ed said:
    @mbbaum Is this a new problem or has the problem always existed?
    New system. 
  • JUGHNE
    JUGHNE Member Posts: 11,248
    How about a close up shot of those pumps?

    Just had a call last week for no heating. Maint man had changed out a pump ...mounted upside down....easy to do.
  • mbbaum
    mbbaum Member Posts: 7
    JUGHNE said:
    How about a close up shot of those pumps? Just had a call last week for no heating. Maint man had changed out a pump ...mounted upside down....easy to do.
    It is easy to do. In this case though the pump is mounted correctly. 
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,206
    I'm not sure which manifolds you have, but they sometimes come with integral valves on each loop. Check to make sure they are all open.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • mbbaum
    mbbaum Member Posts: 7
    Alan (California Radiant) Forbes said:
    I'm not sure which manifolds you have, but they sometimes come with integral valves on each loop. Check to make sure they are all open.
    Both loop valves for supply and return are wide open. 
  • hot_rod
    hot_rod Member Posts: 23,041
    A kink in the tubing could be the problem, easy to do with 3/4" if the ends were tight radius?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Robert_25
    Robert_25 Member Posts: 549
    What model circulator are you using?
  • Zman
    Zman Member Posts: 7,610
    What are your design flow rates across the common piping?
    What size is the piping?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,206
    Five hundred feet of hePEX flowing at 1.2 gpm per loop will give you 5' of head which you can easily move with a Grundfos 15-58 on low speed.

    There's an obstruction there somewhere. If you've flushed both loops with water and there's a steady flow in and out, it's not debris or air stopping the flow, at least not in the tubing. Have you flushed the copper piping to and from the manifold? I don't see any purge valves.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • mbbaum
    mbbaum Member Posts: 7
    hot_rod said:
    A kink in the tubing could be the problem, easy to do with 3/4" if the ends were tight radius?
    Flow rate is great with aux pump attached to zone manifold directly. 
  • mbbaum
    mbbaum Member Posts: 7
    Alan (California Radiant) Forbes said:
    Five hundred feet of hePEX flowing at 1.2 gpm per loop will give you 5' of head which you can easily move with a Grundfos 15-58 on low speed. There's an obstruction there somewhere. If you've flushed both loops with water and there's a steady flow in and out, it's not debris or air stopping the flow, at least not in the tubing. Have you flushed the copper piping to and from the manifold? I don't see any purge valves.
    I think the problem has something to do with the return but I’m not sure what is going on. The other zone with smaller pump and 10-500ft loops has great flow. 
  • Zman
    Zman Member Posts: 7,610
    If the common piping is undersized, the one circ may be competing with the other. Circ specs, design flows, and pipe size info would help eliminate that possibility.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein

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