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Two pumps

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SeanBeans
SeanBeans Member Posts: 520
We all know people put the circulator pump on the return pumping right into the boiler.

If you have you circulator pump on your supply side pumping away from the PONPC.. would there be any reason to ALSO mount a circulator on the return.

What would that accomplish?
If you set the return pump to pump while boiler is heating and the supply side to run when boiler water has reached temp, what does this accomplish?

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  • Jamie Hall
    Jamie Hall Member Posts: 23,318
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    Nothing except confusion... and more controls... and more wear on the inoperative pump... and...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Solid_Fuel_Man
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
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    I went to a job once (wish I had a camera phone back then) which had 4 or 5 zones. Each with a zone valve on the supply, and a circulator on the return.....

    It was a nice looking job too. But what the.....
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • jumper
    jumper Member Posts: 2,258
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    I went to a job once (wish I had a camera phone back then) which had 4 or 5 zones. Each with a zone valve on the supply, and a circulator on the return.....



    It was a nice looking job too. But what the.....

    Circs can be preferable to zone valves for off/on control. Some come with a curve of fairly limited flow range over quite a wide range of head. But decades ago they didn't come with check valves so zone valves were added to prevent flow through shut off circulators? I've seen chilled water coils controlled that way. Hopefully the valves are disconnected open when the circulators are replaced with modern ones with integral check valve.

  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,004
    edited October 2019
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    The circulator on the return would still circulate water through the system.

    When the circulator on the supply turned on, it would double the pump head. Depending on the size of the pumps, you could possibly hear the flow, it would be going so fast; possibly cavitation as well.

    I once saw a job installed by a GC who thought he knew what he was doing. A Taco 0011 on the supply where a 007 would have done the trick. Added a second 0011 on the return when he couldn't get flow and even that didn't get flow. Was probably air bound.
    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
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,534
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    @Alan (California Radiant) Forbes The water velocity was probably so fast it was impossible to vent it. Entrained air couldn't separate.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,534
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    I have seen a ton of old jobs pumping toward the ex tank that worked without issues as long as the system resistance is low.

    But if the system has too much resistance, forget it

    ZmanSolid_Fuel_Man
  • SeanBeans
    SeanBeans Member Posts: 520
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    In this case you would be pumping towards and also pumping away...?
  • HomerJSmith
    HomerJSmith Member Posts: 2,440
    edited October 2019
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    "The Tale of Two Pumps". "It was the best of times..." Oh well!

    The only reason to use a pump is to move water. To move water you need to overcome the resistance to moving that water, period. Of course there are other considerations in Hydronics like pressure differentials which is what pumps do.

    "...circulator pump on your supply side pumping away from the PONPC..." That's good.

    I always like to mount the pump into the greatest resistance. Mounting a pump on the supply side and a pump on the return side, what you get is two pumps in series which doubles the head energy less the resistance of the boiler and piping in between the two pumps and the problem of pumping into the PONPC.

    In answer to you statement and question--NADA. Why go thru the trouble, just put in a larger pump if flow is the problem.

    A conventional hi-mass boiler the pressure loss thru the HX is about .5' of head based on normal flow. Where the pump is in the circuit really doesn't matter just so you pump away from the PONPC.

    High head Mod/Com are a different story and usually have a primary and secondary circuit.

    The reason pumps are put on the return to the boiler for conventional boilers is because the water is cooler, the pressure loss thru the boiler is low, and the boiler with a pump fits in the carton.


  • jumper
    jumper Member Posts: 2,258
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    SeanBeans said:

    In this case you would be pumping towards and also pumping away...?

    Pump salespeople caution against pumps in series. Unless one truly knows what she is doing and why....