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Heat Pumps: most efficient heat source

Discussion in 'Home Power and Microgeneration' started by News, Feb 8, 2005.

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  1. News

    News Guest

    Air to air heat pumps extract less heat from the air than ground source
    pumps. Water stores about 3 to 4 times more heat than earth, so typically
    will water provide more heat than the ground?
     
  2. Gymmie Bob

    Gymmie Bob Guest

    That first statement is a complete lie.
     
  3. Mel

    Mel Guest

    News a écrit :
    typically, heat pumps used for heating homes will be more efficient if
    they extract heat from a water source (if the water source has
    sufficient flow), followed by ground then air. But this is only a very
    broade generalisation, and many variables can mean that in some
    circumstances, a heat pump in the ground will be better suited to your
    job than in a water source.
     
  4. Steve Spence

    Steve Spence Guest

    Heat pumps move heat from one place to another, so in winter, when air
    temperatures are well below ground temperature, his statement appears
    true. In spring or fall, when air temps might be above ground
    temperature, but still less then comfortable, his statement appears
    false. In neither scenario is it a lie, just not enough information to
    make a fact based decision. Of course, if you take the quote literally,
    which I don't believe what he meant to write came out exactly the way he
    thought, GSHP's don't extract any heat from the air, so instead of a
    lie, I'll call it a misspeak. Like most of New's posts. And GB's as well
    ......


    Steve Spence
    Dir., Green Trust
    http://www.green-trust.org

    Contributing Editor
    http://www.off-grid.net
    http://www.rebelwolf.com/essn.html
     
  5. daestrom

    daestrom Guest

    News a écrit :
    typically, heat pumps used for heating homes will be more efficient if
    they extract heat from a water source (if the water source has
    sufficient flow), followed by ground then air. But this is only a very
    broade generalisation, and many variables can mean that in some
    circumstances, a heat pump in the ground will be better suited to your
    job than in a water source.

    And of course, the relative cost of each source installation varies. And
    not all homes have ready access to enough flowing water.

    daestrom
     
  6. Vaughn

    Vaughn Guest

    Speak for yourself.

    Vaughn (south Florida)
     
  7. News

    News Guest

    Well I'm sure I am speaking for the majority of heat pumpers.
     
  8. Nope, it gets might hot here in the summer
     
  9. Gymmie Bob

    Gymmie Bob Guest

    Try a laxative for that problem.

     
  10. Steve Spence

    Steve Spence Guest

  11. News

    News Guest

    I know exactly what and how a heat pump works and does, thank you. I'm
    concerned you are morphing into a troll.
     
  12. daestrom

    daestrom Guest

    No doubt. But most folks don't try to 'extract heat from ground/water' in
    hot climates. It was clear the OP was concerned with a 'heating season',
    not a 'cooling season'.

    daestrom
     
  13. Gymmie Bob

    Gymmie Bob Guest

    What is the life expectancy of a home heating heat pump system? I have not
    seen 1 of about 12 I know of that have lasted more than 12-15 years. That
    needs to be added into the cost.
     
  14. Vaughn

    Vaughn Guest

    You should look up the definition of "heat pump". You are obviously
    confused.
    The comment from "news" is "Thanks. It is in winter I am more concerned
    with as that is the time you
    In my climate, that is an incorrect statement.

    Vaughn (with a grin)
     
  15. Steve Spence

    Steve Spence Guest

  16. Caleb Hess

    Caleb Hess Guest

    One data point:

    My house was built in 1976 with two GE air-air heat pumps. One of the original
    units is still running, the other was replaced with a Trane about 12 years ago.
    Maintenance in the 10 years I've lived in the house has consisted of finding
    and fixing a freon leak and replacing a motor start capacitor on one compressor.
     
  17. Gymmie Bob

    Gymmie Bob Guest

    Most people here are done with the air heat pumps. Never to go back again.
    Too expensive to maintain and the a/c sucks. the unit is too large for a/c
    moisture removal. Have they resolved that at all?
     
  18. Gymmie Bob

    Gymmie Bob Guest

    I have a NG high efficiency furnace and the maintenance in 10 years has been
    to replace the air filter a few times.
    My previous house was 24 years old and resulted in the same. Oh yeah. I
    oiled the motor once.
     
  19. Steve Spence

    Steve Spence Guest

  20. Astro

    Astro Guest


    Back to your original question about efficiency...


    IFF you have an "ample" ground water supply, you can go open loop, draw
    ground temp water from one well, run it through the heat exchanger then
    back out. Where it goes varies, but for now, just assume that you're
    pouring it back into the aquifer.
    Water temperature in this case will be pretty much constant throughout the
    year. Say 50F for the mid atlantic state. At this temperature, you'll get
    the heat pump's rated output which is typically given at around this
    temperature.

    If you don't have enough ground water to waste, you can use a "standing
    column well". this is a deep well where you get water from the bottom of
    the well and pour the "used" water back in the top. If the well is deep
    enough, then the water drawn out will be a fairly constant temperature.
    Downside is the depth of the well will cost you.

    If you don't have an ample ground water supply, you can go vertical closed
    loop. Ground temperature down below ~15' is essentially constant. However,
    as you draw heat from the ground, it will cool. Depending on how fast the
    heat can get back in to where the loop is, the cooling of the ground will
    vary. If the loop field is poorly designed, it can drop to significantly
    and your heat pump output and efficiency will diminish.
    Vertical loops will require lots of drilling in most situations to "do it
    right". Typical ~250ft/ton but this varies on ground conditions.

    If you can't go vertical and go horizontal, you have seasonal ground temp
    variations to consider as well as temperature drop from loop use. But
    excavation costs will likely be far lower than drilling. And, keep in mind
    that a good horizontal loop will be far better than a poorly designed
    system of other sorts.

    Finally, you have air source. As other posters indicated, if the air
    temperature is higher than the ground temperature, all else being equal,
    then the air source system will be more efficient but during the cold of
    the winter, this is unlikely to be the case. If you look at the "bin data"
    for your region, you can find the amount of the year that is at each
    temperature.

    Beware however!!! As soon as you start running a ground source system, the
    ground temperature will start dropping. The longer you run it, the more it
    will drop. When you stop running it, the ground temperature will recover.
    The problem is, if you have a stretch of cold weather where you run the
    system many hours a day, the ground may never have a chance to recover and
    will just drop in temperature until the energy extracted balances the
    energy that can return. As such, the system will perform worse than
    expected. Moreover, it may take some time for the temperature to recover,
    so you might find that from December through February, your system is
    running at, say, 20F rather than the stated ground temperature of 50F.
    Then you'll be getting less than 70% of the rated heat output and far less
    efficiency.
     
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