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Community and Q&A

Single tank, twin circuit heat pump for domestic hot water and radiant heat

BryceWA | Posted in Mechanicals on

Does anybody know of a single heat-pump unit available in the U.S. that will heat water for regular domestic use (water faucets) and radiant floor heat in a slab?
Water from the main should flow out the faucets via the heat pump. Meanwhile, the radiant system would contain its water in a separate closed circuit using the same heat source.
Heat-pump format options: 1. Water-to-water geothermal (preferred)
2. Air-to-water split system with exterior unit

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  1. Steve Knapp CZ 3A Georgia | | #1

    Have you looked at the Sanden SANCO2™ High-Efficiency Heat Pump Water Heater?

  2. BryceWA | | #2

    Thanks for the tip, Steve. I'll look into Sanden.

    1. Expert Member
      Dana Dorsett | | #4

      The Sanden isn't likely going to cut it as a combi-unit on either efficiency or capacity. While the CO2 compressor efficiency is high at a high delta-T needed to make hot water out of cold incoming water, it's pretty lousy at the small delta-T from output to return in a hydronic heating loop. It also has pretty limited BTU/hr rate, especially at the lower efficiency it would have in a radiant slab. R410A refrigerant systems are a better bet.

      See response #3 regarding LG's Multi-V S fully VRF system.

  3. Expert Member
    Dana Dorsett | | #3

    LGs Multi-V S with their low temp Hydro Kit unit can be used for both potable hot water and radiant floor. The hydro units aren't potable-compatible, and the radiant floor systems would need a buffer tank to keep from short-cycling the heat pump anyway, so using a "reverse indirect" water heater such as a ErgoMax or TurboMax functions as both:

    The Multi-V S is also compatible with most of LG's ductless & ducted mini-split heads/cassettes.

    As a fully VRF heat recovery system these things can heat water or provide space heat to one zone and while air conditioning another at the same time. A major retrofit on a house in Jamestown Rhode Island covered last year by This Old House used a Multi-V S + Hydro Kit. You may need to design in more buffering tank volume (beyond the volume an ErgoMax or TurboMax provides) for the potable end when using the Hydro Kit also for space heating. This would have to be designed, not hacked.

    1. DCContrarian | | #8

      The Hydro kit is pretty slick, thanks for the info.

  4. Maximilian T | | #5

    Link to the This Old House project Dana mentions:

    1. BryceWA | | #6

      Dana, Maximilian, thanks for the detail. I have plenty more research to do.

    2. DCContrarian | | #7

      Man, how can anyone watch that show? I played it at 1.5 speed and it still took forever for them to get to the point. Mechanicals are about 3 minutes starting at the 15 minute mark. They don't get into much detail and there's not much that would be new to a regular here.

      They describe the solar array as 18 panel but it looks like 36 to me, which seems more realistic for net-zero at that latitude.

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