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  1. #1
    Join Date
    Nov 2019
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    Heat pump plus hydronic floor heat

    Our home is presently heated and cooled mostly by forced air, with the heat supplied by a propane boiler. We have a large kitchen, on an insulated slab with embedded hydronic loops in addition to the forced air outlets in the ceiling.

    We are replacing our AC compressors (upstairs/downstairs) with heat pumps (Bosch BOVA) with the goal of minimizing propane consumption. In the kitchen, our goal is to have the floor be comfortable in the winter while having the heat pump supply most of the heat.

    The question is how to control this. With the present system, both forced air and floor heat come on whenever the thermostat calls for heat, so the balance between the two is set by the temperature control on the hydronic loops. Is there a better way? Our contractor doesn't see an obvious one. There is no temperature sensor in the slab, though we do need to deal with some loose tiles and could place one when we do so.

    Thanks!

  2. #2
    Join Date
    Jan 2012
    Location
    Broomall, PA
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    Temperature sensor probably won’t help. You’ll get overshoot on the floor, unless you can control the floor with a separate thermostat acting as a high limit and dialing in the outdoor reset, using constant circulation.
    The problem with this is now your boiler is completely oversized to run one zone, and will short cycle. The money you save with the heat pump will be offset by inefficiency of the boiler operation.

    Mixing these 2 systems are problematic as the radiant heats by radiation, slow and direct, heating everything in the room. And the forced air heats by blowing warm air across your body, convection, and not necessarily warming all objects in the room.
    If I do a job in 30 minutes it's because I spent 30 years learning how to do that in 30 minutes. You owe me for the years, not the minutes.

  3. #3
    Join Date
    May 2006
    Location
    Philadelphia, PA
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    2,187
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    Head over to heatinghelp.com and see if there is someone close to you. The only way I know to achieve what you want is placing a sensor in the kitchen slab and have it control a mixing valve to keep the slab warm. Would be a good ide if the kitchen is it's own zone from the heat pump or the room may overheat.
    Climate Control Solutions for your Home or Office

    Serving Northeast Philadelphia and Surrounding Areas

  4. #4
    Join Date
    Nov 2019
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    Thread Starter
    Quote Originally Posted by comfortdoc View Post
    Head over to heatinghelp.com and see if there is someone close to you. The only way I know to achieve what you want is placing a sensor in the kitchen slab and have it control a mixing valve to keep the slab warm. Would be a good ide if the kitchen is it's own zone from the heat pump or the room may overheat.
    Thanks. The kitchen is its own zone. With the current hydronic floor / forced air setup, both come on at once. The floor stays warm (very warm on cold days) but the room never overshoots except on sunny, temperate days (the room has large windows with southern exposure). This might be because the space is very open to the adjacent space, though if we lower the kitchen zone it does stay cooler.

    I might start by setting the existing mixing valve to a somewhat lower temp to shift the balance to the heat pump, then looking into a controller.

    Thanks again. Any other advice is appreciated!

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