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  1. #11
    Join Date
    Jan 2008
    Posts
    21

    Default Re: Heat Pump Advice Needed

    For a long time I have wondered about burying large diameter PVC pipe and circulating air throught the pipe to pick up the cooler ground temperature.

    Similar to your idea Omer, the cooler air could be blown on the outdoor heat pump unit. 55 degree air blowing on the outdoor unit vs it drawing 30 degree air should help. No reason why this wouldn't work for summer also.

    Maybe a box could be built around the unit and it's fan could help circulate the air through the piping. I also suspect the pipes circulation fan could be cycled On and Off with the heat pumps thermostat.

    As you have stated, many variables need researching.

    Hope this helps,

  2. #12
    Join Date
    Jan 2008
    Posts
    3

    Default Re: Heat Pump Advice Needed

    Quote Originally Posted by Omer Causey View Post
    I am building a log home in Rutherfordton, NC (Blue Ridge foothills). I need advice on HVAC system using an electric heat pump.

    The house footprint is 27' x 33' with finished walk-out basement, 890 sq.ft. of space on main floor (with about half of it open to the roof), 450 sq.ft. on upper floor (guest room & bath). All of this space is to be heated and cooled.


    Roof is 12/12 pitch; R-38 insulation; dark green shingles. Roofed porches East & West along full length of the main floor. Construction is 6" x 8" milled logs. Double-glazed windows and doors.

    T he builder's present recommendation is for an EnergyStar heat pump, 16-17 SEER, 9.2-9.8 HSPF; variable speed air handler; zoned for basement separate from main floor and upper floor; electric supplemental heat.

    Climate: average 122 days per year above 75F., average 91 days per year below 40F., average high 83F., average low 36F. There are about 80 days per year during December, January and February when the minimum temperature is below 28F.

    I understand that the efficiency of heat pumps below 28F is poor. I take that to mean I will be using supplemental heat for more than 3 months per year.

    Questions:


    How much tonnage do I need?

    Can the cold-weather performance be improved by locating the outdoor coils in a sheltered area or enclosure that can be heated by passive solar technology or heat recovered from indoor appliances, etc.?

    Can the hot-weather performance be improved by shading and ventilating the same area while diverting the recovered heat from indoor appliances?

    If the above modifications will work, what are the downsides?

    Comments from contractors, engineers, architects welcomed!

    Just built a log home in Blowing Rock,NC. Have a heat pump, when the temp goes below 30 the furnace (propane) goes on. It works fine

  3. #13
    Join Date
    Jan 2008
    Posts
    3

    Default Re: Heat Pump Advice Needed

    Just built a log home in Blowing Rock, NC. We have a heat pump, when the temp goes below 30 the furance (propane) goes on. It works OK

  4. #14
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,776

    Default Re: Heat Pump Advice Needed

    There was a great book on the market about 30 years ago called "From the Walls In" by Charles Wing. Its out of print now but you might find a used copy at Amazon or Ebay. This will help you with heat loss calculations, the author makes it easy.

    Instead of using solar heated water under the heat pump, i would suggest that you use the solar heated water directly, either for hot water or direct heating in the house. Then build an insulated enclosure around the sides of the heat pump and up to the top. Leave it open for the exhaust fan to blow out. In the center of the slab under the unit, have a hole for a large pvc pipe that goes down about 4-6' and 50' laterally and then up under a tree of something. Cap it with a screen and rain deflector.

    When the fan turns on, it would draw air from the outside, through the underground tube where it warms or cools, then up under the heat pump, up the sides, through the coils and out the top.

    edit: I have had a second thought on this, instead of using s small diameter PVC pipe, use a larger diameter metal ribbed pipe like the ones used under driveways where they cross over to the street. About 8 to 12" diameter should do.
    Last edited by keith3267; 01-18-2008 at 09:19 PM. Reason: add

  5. #15
    Join Date
    May 2008
    Location
    Derby City
    Posts
    42

    Default Re: Heat Pump Advice Needed

    Go with dual-fuel. First stage heating will be heat pump and then your back-up or second stage heating will be fossil fuel. Gives you the "best of both worlds." A/C operation will be the same regardless. Run, don't walk away from the geo-thermal. You will never recover the initial investment and air-to-air systems offer comparable efficiencies in a much more conventional arrangement.

    Start talking about return on investment with geothermal and that is where the conversation goes pear shaped.

    All the best, Irishmist

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