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Provision for a buffer tank

Hot Rod,

I have never used a buffer as part of the primary loop. Do you try to design for constant circ. to use the latent heat in the buffer tank.

Comments

  • Pete_31
    Pete_31 Member Posts: 26
    Will I need a buffer tank?

    I am beginning to pipe an MC-50 in my 700sf workshop. I was told my load is right at it's lowest firing rate. Local inspector (St Paul MN) told me water heaters are not allowed. The shop has 1 zone, 3 loops 250' each, no domestic water. Should I install openings for a buffer tank? Which loop do they go in? I was going to pipe the boiler loop with 1-1/4"and a B&G NRF-22. The secondary loop with 1" and a Grundfos 15-42.
  • Brad White
    Brad White Member Posts: 2,393
    Not sure what

    brand an MC-50 is but if it is a ModCon, I would install the buffer tank on the inlet side to the boiler to prolong condensing.

    My ideal setup would be to have an automatic motorized full-port ball valve in the main with a tee on each side of it. The first tee in direction of flow takes water to the buffer tank, the one downstream of the motorized valve takes water from the buffer tank and back to the boiler.

    The valve would close when the upstream return water temperature rose above say, 120 degrees. The valve would open again once it dropped to below that.

    What flow rate and pressure drop do you have on your boiler-side circuit? That NRF-22 sounds like a good bit of pump; if 5.0 GPM, 12 feet of head.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • Pete_31
    Pete_31 Member Posts: 26


    I am starting to think I'm in over my head. The boiler is a Munchkin Contender 50. Manual says 6.5' at 20 degree delta T, 5gpm. I was hoping to keep things as simple as possible. Are buffer tanks always fed by an automatic valve?
  • hot_rod
    hot_rod Member Posts: 15,070
    HTP makes a nice 20 gallon

    insulated tank with four 1-1/2" connections. It makes a nice buffer/ separator/ air elimiator in one package. Not a lot of buffer capacity but it would help with cycling.

    Here is a simple drawing.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Pete_31
    Pete_31 Member Posts: 26


    Thanks for the advice guys. It seems I'm better off using the tank as the link between primary and secondary as opposed to teeing in.
  • So then ...

    A weather responsive control (if used) would fire the boiler based on the temperature output of the tank??!!

    hmmmm....

    nice
  • scott markle_2
    scott markle_2 Member Posts: 611
    Buffer

    I recently posted a question on short cycling in the vitodens dejour post. Do you have anything to add to this? Paul points out that constant circulation allows these short burns to work effectively

    Thing is my curve is so low that I'm in the low end range for a majority of the heating season. I really want to find a way to deal with this. Your temperature actuated buffer tank is a nice idea, I like that it does not require an additional circulator. Unfortunately in my case these short burns are not a result of quickly rising return temps. This is inherent issue with an ignition sequence that starts on high fire in low load/temp. conditions. Any thoughts?
  • Pete_31
    Pete_31 Member Posts: 26


    An outdoor reset did come with the boiler. Do they adjust boiler return or supply temp?
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
    2nd Exp Tank

    HR -

    Since these 2 loops are isolated, I believe there should be a expansion tank on both sides? If secondary pump becomes air bound or fails, the boiler relief will start blowing off.

    Or is this a tank with 4 tappings and the 2 circuits are not isolated? At first I thought this was something like a Phase III tank in a tank.

    Glenn
  • Pete_31
    Pete_31 Member Posts: 26


    If I'm understanding Hot Rod, this tank would have 4 openings to the same space, basically just a really big decoupler right?
  • Rob Blair
    Rob Blair Member Posts: 227


    I just built the same thing as HR did with a 40 gallon electric water heater. Brought the supply in the pressure relief and the return out the drain at the bottom. Piped the supply to the zone out the hot on the top and the return from the zone into the cold on the top. Works great. This was a job that someone had used a Quietside that only modulates down to 40K and the load at design day was only 10K. I will send some pictures.

    Rob
  • Pete_31
    Pete_31 Member Posts: 26


    My original plan was a water heater instead of a boiler, until my inspector shot me out of the saddle. As I swallowed the additional expense and complexities of the mod-con, I tried to look on the bright side, "well at least I won't lose floor space to a water heater". I didn't do my research. Looks like I'm gonna have a big tank setting there anyways.
  • hot_rod
    hot_rod Member Posts: 15,070
    That HTP 20 tank is

    low enough to set the boiler right on top. I think it is 27" tall just perfect for a boiler height. HTP has talked about making a stand or bracket to do that.

    I've also used stubbly electric tanks as buffers. I use the element holes for additional taps.

    It didn't sound like your inspector wantrd to see a HW tank in the system so I suggested the HTP tank.

    Yes it is just one tank with four connections. One expansion tank works fine.

    I have also used the Triangle Tube/ Weil indirect tank as a buffer. Use the tank capacity as the boiler loop and pull the radiant from the "outer" area.

    You might just run a season the way it is to see how it cycles. easy enough to add a buffer later.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Pete_31
    Pete_31 Member Posts: 26


    Thanks again Hot Rod

    I,ll check tomorrow with wholesale house about that tank. If he doesn't stock them, maybe I'll just make one. Welding a couple caps and some thread-o-lets on a 30" long piece of 18" pipe is definetly more in my comfort zone than designing this relatively simple system. A couple of U-bolts and chunks of Unistrut and I could put it on the wall.
  • hot_rod
    hot_rod Member Posts: 15,070
    Build one from

    a steel compression tank. They often have ASME listings and are plenty stout.

    I had a shop with certified welders add a bunch of taps to this tank for a mini tube injection system with two Clean Burn boilers P/sed into the tank.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Ted_9
    Ted_9 Member Posts: 1,718
    Munchkin Contender

    Nice unit. Make sure you refer to the installation manual and do a proper combustion set up with an analyzer.

    I found a couple of drawings. I'm not sure who did them though.
  • Pete_31
    Pete_31 Member Posts: 26


    I can't find any shop drawings on any of these HTP buffer tanks. The guy I bought the boiler from isn't really specialized on this radiant equipment. He has a 30 gal boiler buddy he'll sell me for 500. After seeing what some of the guys here have said, I probably should just pipe it without one and see how it works.
This discussion has been closed.