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Advice on 2-Pipe Primary/Secondary

Ron R
Ron R Member Posts: 16
I am trying to set up a System for a church- using 2-pipe P/S piping with direct return and cross-over pipes
The only reason I can type those words is because I have been reading them in Dan H.'s book--Primary Secondary Pumping Made Easy.
We have done a lot of 1-pipe P/S but not the 2-pipe method.
My question has to do with sizing the primary piping.
Since the Boilers are in the basement, and (2) of the (8) zones will be connected on the basement level, would I stay out of trouble if I reduced the size of the Primary downstream of the first 2 zones, before sending the rest of the Primary up to the Mezzanine level, then upsizing again after the return gets back to the boiler room?--Or should the primary piping remain the same size for the whole length?
Thanks to anyone who may want to comment.


    EBEBRATT-Ed Member Posts: 15,519
    I would have to see a sketch of how you want to pipe this.

    This is a guess. I think what you want to do is run an extended primary loop to be used as a delivery system ty 1 zone in in the basement and other zones some distance from the boiler.

    This can be done but you have to install "crossover bridges" at each location where a zone is tied in. It is explained in one of @DanHolohan books. It is probably in PSPME.

    Without the crossover bridges you will have increased pressure drop in the primary loop and it wont work well.

    Others will chime in but I see no reason why the primary loop could not be reduced after each crossover take off as long as the return is increased on the way back. You just need to size the pipe for the flow it will see.

    My best guess

  • Ron R
    Ron R Member Posts: 16
    Ed- thank you very much for the reply.
    Yes we would use the cross-over bridges and increase the return line to match the supply.
    We haven't used this method yet, ( I read up on it in "Primary-secondary Pumping made Easy") and it looks like it would work well but I am still second guessing on whether this is the most economical way to put the system together.
    Do you have any books to recommend that cover different piping methods?
    I wonder how a reverse return with a large pump, balance valves instead of zone circulators and no primary loop would work. I think we would have to add a by-pass pressure valve to handle the excess flow when some zones are not calling for heat. I'd like to learn more about how these type systems work.

    HVACNUT Member Posts: 5,834
    It would be awesome if someone would be kind enough to post a piping diagram based on an example of @Ron R .
    If it's from Dan's book I dont want to make it like we're standing in the 7-11 reading the paper for free.
  • hot_rod
    hot_rod Member Posts: 22,131
    A drawing would help see what you have in mind. Page 71 of PSME for example?

    Remember with any serious primary loop you need to account for the temperature drop at each set of close tees.

    A parallel primary loop piping would account for temperature drop, but requires balance valves at each connection.

    Also here are a few reverse return options. With RR the piping could, really should, reduce and increase pipe size as loads take off and return.

    If the loads are zoned, a delta P circulator really shines in these applications.

    Idronics 15 & 19 show some good, and not so good piping options.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream