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recirc with mixing valve

ck111 Member Posts: 1
does anyone know if it makes a difference if the return line on a domestic system goes in to the cold supply anywhere or it needs to go close to the mixing valve ? , see attached drawing from a job we did and whenever it goes true the mixing valve the pumps are making problems and the mixing valve manufacture is saying we should add a bypass line see in red and its a lot of work to do just to try if it will solve the problem , does anyone have any input ? just to understand its a big building with 6 return pumps


    EBEBRATT-Ed Member Posts: 15,840
    maybe they think the domestic flow through the mixing valve plus the added pump flow is too much for the mixing valve so they want to inject the return water closer to the mixing valve. Does not seem like it would make a difference to me.
  • neilc
    neilc Member Posts: 2,716
    edited September 2023
    recirc return has to get back to the mix valve, otherwise, on a no flow/no use situation, recirc to the HW tank will force Hot thru the mix valve and overheat the recirc,
    either tie into the cold, with checks, or some valves, not yours, have a 4th recirc port,
    known to beat dead horses
    Mad Dog_2
  • hot_rod
    hot_rod Member Posts: 22,479
    It depends on the type of mixing valve. Does that brand shut off the cold port 100%?
    There needs to be a path back to the tank to prevent recirc creep. The line will heat above mix valve setting if it creeps during periods of no or low use


    Two piping options for valves that close the cold port 10o%

    What is the concern? Temperature droop or temperature creep? Unstable outlet temperature?

    Does that valve need  a minimum flow to mix accurately? Most  valves need a minimum gpm, so the piping and pump size needs to provide that If the building cannot.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream