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Variable Speed Injection Mixing

Tombig_2 Member Posts: 231
Paul, your drawings are always so concise. I remember the Knight/Tn4 set you shared with us. I was so impressed I downloaded the set for future perusal. Haven't looked at them since of course.

Do you scale the assembly as you're drawing it? Or was it just instinct that told you there was no room for the injection pump on the supply side? Do you assemble the panels in the shop? Is it usually built as you envisioned? A line on paper is always easier than an installed idea. That's one of my standard lines to the architects I deal with.

I just piped my first VSI in four years. I've been installing single temp mod-cons mostly. As usual I learned something new on The Wall today because of your question. Thanks

Tom G


  • Paul Rohrs_4
    Paul Rohrs_4 Member Posts: 466

    ever pipe the variable-speed injection-mixing circ on the return leg.

    For the sake of argument, all tee's shown are closely spaced. I am running out of room on this project and the zone in question is for snow-melting. It seems like I could buy some much needed room if I placed my circ on the return leg of the injection mixing loop.

    The bright yellow circle is not the "Sun", but a semi-crude attempt at highlighting the area in question. Crayons are my friend.


  • ALH_4
    ALH_4 Member Posts: 1,790
    No Problem

    Should make no difference at all.
  • Wayco Wayne_2
    Wayco Wayne_2 Member Posts: 2,479
    Nice drawing

    What program do you use? I don't think it is a problem either. My only question is, where is the expansion tank in relation to it? I looks like your variable speed circ is on the secondary side of a heat exchanger. Why not make the primary side the variable speed, and have the system circ go throught he secondary side of the heat exchanger. Save a circ. :) WW

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  • hot_rod
    hot_rod Member Posts: 22,144
    That's how I do it

    what goes into a tee must come out of a tee, regardless of the pump placement.

    I've piped them on the return for many years.

    Not that it makes a huge difference but it puts the circ in a much cooler fluid stream. Possibly 80F as opposed to 180F.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Weezbo
    Weezbo Member Posts: 6,232
    Looks good to me...

  • Paul Rohrs_8
    Paul Rohrs_8 Member Posts: 9


    Still plugging away with the Visio program for drawings.

  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
    Good Idea

    Like that one.
  • Paul Rohrs_8
    Paul Rohrs_8 Member Posts: 9

    We mounted the 4x8 aluminum diamond plate on the wall and of course it starts to look smaller immediately. I have ge 3 separate Uponor Duomix-201 controls and a ton of low-voltage and sensor wiring to run, so I wanted to mount the controls and wiring gutter prior to the copper going up.

    The "Canvas" has been substantially reduced even before one copper fitting goes on. I think moving that pump will buy us some more space, but I think the bigger space savings will come by using copper sweat fittings instead of copper propress. This is a 2" primary loop withlad 3 sets of 1" tapping for 3 different injection mixing zones.

    Scale is something that I would like to do a better job with. Usually, that is not my priority and my CAD drawings say "No Scale". I have drawn quite a few of my own stencils that I can resize, but up til now, I haven't invested the time to make them scale.

    This job will be piped on site, but usually I would prefer to pre-build them in the shop.

    Thanks for all of the Kudo's, but I can honestly say that I learn something new from The Wall every day myself.


  • Kal Row
    Kal Row Member Posts: 1,520
    keep the injection circ..

    cause you want max flow through snowmelt loops for even melting and not run glycol molasses through the tiny holes in the FPHX’s end tubes.

    put #20 filter screens on both sides of the fphx, and make sure you have freeze protection on the fphx, a tekmar snowmelt control doesn’t give you freeze protection on the fphx, i.e. if the injection and the snowmelt pumps system are going and bringing 25F solution off the slab to your fphx and the boiler side pump is off, the cupful of fresh water on the other side of the plates will freeze real fast and bust your fphx, I use a Johnson Controls A419 (apx $77 street http://www.houseneeds.com/shop/manuals/johnsoncontrol_a419bulletin.pdf ) and just epoxy the sensor to the front of it
  • Weezbo
    Weezbo Member Posts: 6,232
    looks like a clean picture...

    strainers are good.
This discussion has been closed.