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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.