WtW Efficiency gain of lower temp. Load Tank
After studying more, I see the efficiency benefit of going to a 2 tank system.
As suggested by NiHaoMike, Thx.
Smaller (40-50 gallon) DHW tank, heated by NG boiler, 130-140*F to prevent bacteria.
Larger thermal accumulator (120 gallon) tank for radiant floors, 90-100*F
This tank can be heated from boiler or from 1000 gallon Solar storage tank via DIY WtW heat pump.
Radiant floors can also be heated directly (not using WtW heat pump & thermal accumulator) from the Solar storage tank, via a HX loop of 3/4" O2 barrier PEX in top of tank, if water temp. > 90*F
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