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Buffers for Air to Water Heat Pump

I tried to post this the other day, but I don't see it...

I'm spec'ing and am preparing to install a heat pump in a very tight, efficient house. Heat will be by radiant floor (maybe ceiling), cooling by hi-wall fan coils. The two air-to-water heat pumps that I'm looking at (we only need 2 tons/20kBtu) are the Daikin Altherma and the Aermec ANK (there aren't any brands with a big current US presence that offer this kind of machine, though Daikin is trying hard to break into the market here).

Anyway: I would love to hear some opinions about buffer tank locations (I HAVE spent over an hour reading historic posts of buffer tanks here, and as far as I can tell none of them address my question). The recommendation by Aermec is that the buffer tank has both the supply & return of the heat pump piped to it, and same thing with the primary loop of the heating system. It sort of sits between them. I don't love this design approach for a few reasons, and left to my own devices I think I'd put it on the return line, after last secondary and just before it returns to the heat pump. There are a few things, particularly perhaps the relatively low delta-T, that differentiate this from a boiler system, IMO.

I'm attaching a pdf of both piping options, the only difference is the location of the tank. There are some details that are not shown on the drawings, like the fact that the manifolds have purge valves, lest you get drawn into a critique of minor points. That said, I'm wide open to critiques. Pump sizing is tentative, in fact that entire table is sort of a placeholder.


  • SWEI
    SWEI Member Posts: 7,356
  • Keith W.
    Keith W. Member Posts: 29
    OOps: double post

    Yep, I figured that out a little later. Sorry.
  • SWEI
    SWEI Member Posts: 7,356
    No worries

    though I'm somewhat surprised to be the only reply there.  HINT.  HINT.
  • don_9
    don_9 Member Posts: 395
    buffer tank

    Really matter not where you put is really nothing more then to keep the condenser from short cycling.The tank makes everything netural if you will when it comes to the pump being of different sizes and zones for that matter.along with all your distribution system starting and ending back at the tank.

    The rule is 10 gpm for every 10.000 btus so a 10 ton system would require a 100 gpm storage tank I like to call them.That rule can be bend with  two stage equipment using two stage aquastat.

    Sound like a nice project.We just finish a roughin on a three story with all infloor for heat and chill water in the summer time using force air with high supply and returns. Final should be coming up soon  I cant wait.

    Good luck with your project hope to hear more of how it turns out.
This discussion has been closed.