Multi-branch recirculation system

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by dx, Oct 18, 2010.

  1. dx

    dx General Contractor

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    Neither I nor my plumber have experience with multi-branch recirculation systems. We have a 4-branch return system to redo and I'd like to learn a bit. Does anyone have a link to a good design article on multi-branch systems?

    Couple of questions to get me started:
    1. What are the typical choices for a balancing device to get equal flow in the branches? Fixed or adjustable?
    2. Do I need check valves in each branch or is one at the pump enough? Is there ever a possibility of flow between branches if they don't each have their own check valve?
     
  2. Thatguy

    Thatguy Homeowner

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    You want equal flow in each branch or equal volume of hot water in each branch?
     
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    To ensure you get flow through a branch, you might need a valve on each. This would likely only be needed if the length and head was a lot higher on one branch verses another. I think one check valve back at/near the pump would be enough. I'm assuming that this is a dedicated return line system, not using the cold water lines as the return.
     
  5. dx

    dx General Contractor

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    Yes, there are 4 separate return lines, from different parts of the house. Lengths unknown, some may be well over 50 ft. I want to make sure all of the returns have sufficient flow. Depending on length and other factors, the shortest/least restrictive branch would tend to be the path of least resistance and flow much more, at the detriment of the other branches.

    That, and I want to read a primer on multi-branch systems so I don't miss other, finer points on the peculiarities of this type of system.
     
  6. Thatguy

    Thatguy Homeowner

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    This is an "OR function", right? Any one supply pipe OR another, getting too cold at some point on the pipe, starts the pump?

    If this is the case I think equal flow becomes less relevant but check this out
    https://shop.solardirect.com/pdf/water-heaters/solar-hot-water/active-solar/pumps/grundfos-guide.pdf

    Sounds like you'd have one timer with four aquastats wired in parallel. If you have a seasonal shutdown you may want an additional timer that gooses the pump once/week or so, so it doesn't seize.

    100' of half-inch pipe contains one gallon of water that this pump may have to replace.
     
    Last edited: Oct 19, 2010
  7. dx

    dx General Contractor

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    Thatguy, not sure what your point is, but your link contradicts you. It shows balance valves, not aquastats.

    Let's start from this: I don't know. If you are experienced with multi-branch recirculating systems, show a diagram of what a system should look like, and we can take it from there.
     
  8. Thatguy

    Thatguy Homeowner

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    On page 12 they called it a thermostatic control but in the diagrams they called it an aquastat.

    Not experienced; I figured your system would be a variation of one of those shown.

    Sorry to disturb you.
     
    Last edited: Oct 20, 2010
  9. dx

    dx General Contractor

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    You're not disturbing me, no offense intended. I'm just not sure what we're talking about.

    In your link, my system is basically Diagram 3 on page 7. Several "zones", I call them branches. Not sure that diagram is proper and complete, I'd like an expert opinion on that. The diagram doesn't show an aquastat of any kind. Do I need one aquastat per branch? Can I just use a pump with a stat built in? Why or why not? What about those balancing valves shown? What kind? How sophisticated (expensive) do they need to be? Do they need to be pressure-independent? Why or why not?

    That's the kind of info I'm trying to get at.
     
  10. hj

    hj Master Plumber

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    Since all the lines connect together before the pump, they need balancing valves so you can modulate them to compensate for piping imbalances, but since being interconnected COULD allow crossflow, such as the flow from one "backing up" into one of the others if there is a pressure imbalance caused by using a faucet, they should each also have check valves.
     
  11. Thatguy

    Thatguy Homeowner

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    An aquastat only seems necessary to me if you don't run the pump continuously.
     
  12. dx

    dx General Contractor

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    Thank you. HJ, yes I felt that diagram should have had individual check valves for each branch, that's why I said not sure if that diagram is complete. What kind of balancing valves? Are Circuit Setter type valves sufficient or do they need to be the more expensive pressure-independent valves?

    I felt that a pump with internal aquastat would be sufficient, don't see the need for an aquastat on each branch. Am I wrong?
     
  13. Thatguy

    Thatguy Homeowner

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  14. AltaPlumber

    AltaPlumber In the Trades

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    The system in my house is also basically represented by Diagram 3 on Page 7 of that Grundfos guide. We have a Grundfos UP 10-16BN5/ATLC pump installed (built-in aquastat, timer, line cord). However we don't have a return loop from the 2nd floor as shown on that diagram. We have a single return loop from the last fixture in the basement back to the pump near the HWT. Now that we're completely renovating upstairs, I'd like to add another return loop for the master and guest bathrooms on the 2nd floor. Those fixtures are located quite a distance from the supply mains.

    dx - Which balancing valves did you choose? How did you determine what flow rate to use for each branch?

    hj - should the check valves be installed after the balancing valves right before the return loops are tied together? Something like this:

    <--- check valve ---- balancing valve ---- return loop 1
    |
    |---- 1/2 tee ---- recirc pump ---- check valve ----> HWT
    |
    <--- check valve ---- balancing valve ---- return loop 2

    Also, for service and accessibility I'd like to have the above balancing and check valves located near the pump in the basement mechanical room. Is this the most logical place to put everything?

    Thanks for the help.
     
  15. hj

    hj Master Plumber

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    ANY valves can be used for modulating the flow, but they should NOT have handles which could be easily, or accidently, moved to change their settings. The ideal valves would have "screwdriver" slots AND have a thermometer so all of them could be set to return the same temperature water.
     
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