Hydronic/Forced Air Combo
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  1. #1

    Hydronic/Forced Air Combo

    Getting really frustrated by the lack of "professional" knowledge on this subject in my area. I lurk around here a lot and know you guys will be able to point me in a better direction.

    2,600sf rambler with 2,600 sf basement. Client wants radiant floors both levels and forced air A/C on main level only. Nat. Gas is available, but client will be installing solar power at a very reasonable cost. That makes efficient electric heating more attractive. For this reason, geothermal is being considered.

    Heat Loss = 68,000BTUH
    Sensible Heat Gain = 19,000BTUH
    Latent Heat Gain = 500BTUH

    I've found the WaterFurnace Synergy 3D that will allow for both hydronic and forced air. But, it would be located in the basement for the hydronic, and client wants forced air in attic. No ducts running through main floor. Assuming the radiant floors are supplied by a geo heat pump, how would I best utilize the cooling ability of the heat pump, while locating the A/C blower in the attic?

  2. #2
    BTW, I'm not suggesting that I would DIY this. Just really looking for which equipment will best accomplish this task. Seems a real shame to install a water-to-water geo system for the heat, and then let it sit idle all summer while using a conventional air-to-air A/C system.

  3. #3
    Join Date
    Jan 2004
    Location
    Sanborn, IA
    Posts
    191
    an option:
    a water to water geo unit. for heating the geo unit heats water in a buffer tank and that water is pumped through the floors for heating. for cooling the geo cools the water in a buffer tank and that water is pumped through a hydronic coil in an air handler that is up in the attic.

    personally i hate anything in the attic b/c it is a billion degrees up there in the summer and your ducts aren't insulated worth crap (most times). if you can insulate your ducts to R30 then i would do it. i would push for a ducting system in the basement. in the winter the air in your ducts cool and fall down into the house causing heat loss.

    waterfurnace and a few others produce a single unit that heats and cools air and water. i'm personally not a big fan of those. too many valves and moving parts inside of them. i'd do the geo with a buffer tank by B&D Manufacturing of scranton, ia. have your hvac guy look into it.

    the water to water geos have recently been included under 30% federal tax credit. yay for you.

  4. #4
    Join Date
    Jul 2008
    Location
    Poestenkill, NY
    Posts
    769
    Yup. Use a water coil in an air handler and cool with chilled water in the summer.

    Prolly need freeze protection if the attic gets cold. Otherwise - this is pretty straight forward...

  5. #5
    Join Date
    Jan 2004
    Location
    Sanborn, IA
    Posts
    191
    you will want freeze protection even if the chilled water coil is not in the attic. if you happen to have a leak and the flow of water stops going through the geo unit the water will freeze in the heat exchanger coil before the unit's freeze protection catches on and shuts the unit down and pop! your unit is shot.
    need to have it freeze protected no matter what. i've learned the hard way to never start a geo unit without glycol freeze protection.

  6. #6
    Join Date
    Nov 2007
    Posts
    6
    I am in northern Illinois and have had an Econar Ultra Hydronic in my new house for a year now. I have my 1700 sqft basement floor heated. The first floor has the air coil in the basement and the second floor has the air coil in a closet on the second floor. That way only two water lines go to the second floor and each elevation is then zoned. I also ran tubing using plates stapled up on the underside for the bathroom tiled floors.
    I run the unit at 102 – 110 degrees when it is the coldest outside. I use an outdoor reset that will take the buffer tank temperature lower as the outdoor temp goes up. That also has a warm weather shut down.
    Everything works well but for all the cost involved in the hydronics in hindsight I think I would run a forced air geothermal and use gas water heater for the basement floor. It doesn’t take much to heat the basement.
    Using geo for the bathroom floors in the staple up configuration doesn’t work the best. I think for a staple up you need hotter water. I think I was told I can safely run mine up to 115 degrees but I still don’t think that would help much. If the tubing was installed on top of the subfloor I am sure it would work better.

  7. #7
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,190
    Why wouldn't you consider some radiant cooling as well? Is you low latent load a typo or are you in a dry place? Even so the radiant cooling even with water temps that don't get close to dewpoint would reduce the load to latent and some of the excess.
    Maybe that really small chiller could be matched with a really deep coil for max latent

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