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electric heater efficiency

Discussion in 'Home Power and Microgeneration' started by james, Nov 26, 2010.

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  1. Josepi

    Josepi Guest

    To understand your switching logic, this means you have the thermostat temp
    contact and a close on high humidistat contact in series?

    ....and you are finding this works more human comfortable and energy
    economical than just a temp. alone?

    Would you set the temp. at the minimum and let the humidtstat run the show,
    mostly then?

    In Ontario the common item pushed is the HRV (heat recovery ventilator) for
    humidity and vapour / fume control. It centrally replaces the bathroom
    exhaust fan and attempts to save heat by "swapping" some of the hot air heat
    for cool intake air. WE have vapour barriered out homes so tightly that we
    can die from CO2 buildup from cooking and other household products,,,like
    paint, formaldehyde (sp?) in manufactured goods etc....

    Whie this works well there are some caveats.

    In the winter, it dries your house right out and a humidifier is needed. I
    got one last winter at 23% humidity...nose bleeds and sore throat get
    common.
    In the summer the exhausted air is replaced by high humidity / hot intake
    air and is hard on the A/C energy consumption.

    After attempting run on humidistat alone for a few years I have discovered
    another input contact on the HRV unit. One to three contact pulses give
    20,40 and 60 minutes of running the HRV and this works well in the smelly /
    humid rooms in all the bathrooms, laundry and skylight windows. My hugely
    expensive thermostats have some cicle control that I have tied into the HRV
    and can guarantee 10-100% of each heat cycle per thermostat setback daily
    quadrant. We find if the HRV doesn't tun at least 10%-20% of the time we
    just don't feel alert and feel headachey...we think, so far.

    More logic is required yet, when I get more time to automate this home I
    have built.





    I took an April-Aire humidity sensor, wired it backwards to
    "make" on humidity rise instead of fall, and inserted it into
    the red wire of the thermostat for my A/C. So that the A/C
    serves as a whole-house dehumidifier rather than trying to
    compete with that big fusion reactor about 8 light-minutes
    away.

    After all, a muggy 73 degrees can be far less comfortable
    than a drier 83 degrees. So the thermostat is set for 73,
    and we adjust the humidistat for comfort, usually at about
    35%, it gets reset at higher temperature.

    And after a shower, it kicks on about 45 seconds after we
    open the bathroom door, runs till the humidity has been
    brought down near it, and we never have a mold or
    mildew issue in the bathroom.

    If I come in from cutting grass and I would like it to be
    running for a while, I just breathe a nice wet breath
    to the humidistat, and it kicks on for a few minutes.
    It has made a difference in my utility bill, and my wife does
    not wake up with a dry throat in the morning.
     
  2. Josepi

    Josepi Guest

    Nothing like a variable system you can close off for recirculate for
    efficiency.

    Biggest trouble is the automation of the system so you can benefit from both
    methods. Need to get small percentage of fresh air when the humidity is high
    and larger amounts when the outside humidity / temp is low. The house should
    have enough fresh air to carry itself normally for a day at a time.



    We figured that out the hard way when we tried to cool our bedroom with one
    of
    those one-hose portable AC units. The problem was, for every cubic foot of
    hot
    air that box blew out of the house, another cubic foot of saturated Florida
    mugginess infiltrated from outside. The result? Cool and uncomfortable.
    Never
    use a one-hose portable AC in a high-humidity area! We sent that one to my
    daughter in California. There, it works great.

    Vaughn
     
  3. Josepi

    Josepi Guest

    Electric blanket comes to mind there!


    There is no need to heat the room I sleep in here in Seattle. I've got 3
    comforters which keep me toasty all night with the house as low as 45F. The
    bed
    room is the last one I'd heat, except for certain special occasions. A
    standard
    space heater takes care of those just fine, and warms up the bed in 2
    minutes if
    needed when I climb in.
     
  4. Bob F

    Bob F Guest

    Those cost are generally included in the price, unless you are going to pick it
    up.
     
  5. Curbie

    Curbie Guest

    Electric blanket comes to mind there!
    That's what I do, 2 comforters with an electric blanket sandwiched in
    between. I haven't heated the bedroom area at all so far, and turn the
    heat way down in the living area at night; I'll see what adjustments
    need to be made for the Nebraska winters.
     
  6. Curbie

    Curbie Guest

    Those cost are generally included in the price, unless you are going to pick it
    up.
    True from a "point of use" perspective, from a "point of production"
    perspective there are transmission losses which aren't included in the
    100% electrical to (useable) heat conversion figure, and from a
    "economical comparison perspective" all cost of goods or services sold
    are reflected in the point of sale price, but from a "ecological
    comparison perspective" not all costs of goods or services sold are
    rolled into the point of sale price and like it or not, we don't know
    what the final cost will be and although we're all going to have pick
    those up.

    Curbie
     
  7. Gordon

    Gordon Guest

    Well, actually it does. There is some heating of the motor
    and the moving air will eventually turn to heat from friction.
    But, air moving over objects and persons will have a cooling
    effect as well. In any case, the standard method of measuring
    efficency does not take the movement of air into account.
     
  8. Gordon

    Gordon Guest

    I think you are talking about economical, not efficent.
    Think $/BTU. Then electricity is not so attractive.
     
  9. vaughn

    vaughn Guest

    That's exactly the point I though I was making.

    Vaughn
     
  10. Curbie

    Curbie Guest

    Jim,

    I asked the question in the context of comparing different fuels for
    estimating costs of space and water heating; it seems to me that heat
    flow for any particular home would be about constant for any heater
    regardless of the fuel. I've been planning for solar heating, but as
    with anything AE, a back-up seems necessary and since reading some of
    your posts, I've been taking a harder look at wood as a back-up.

    Thus the 60-65% for estimations in wood stove planning question.

    Curbie
     
  11. Josepi

    Josepi Guest

    Seems like a good way to go but the bathrooms are vented through this system
    also and I would be afriad of the stink being transfered.

    Anybody know if this is the case? I know the recirculating ones it would
    happen. That was an option I let go...and the prices were higher yet.


    Enthalpy (moisture transfer) heat exchangers:
    http://cipco.apogee.net/ces/library/tdew.asp

    jsw
     
  12. Josepi

    Josepi Guest

    That is the trouble with so many "green" technologies. A complete backup
    system that is reliable needs to be in place and the economy gets
    questionable considering, loss of income on investments and other long term
    factors.


    Jim,
    I asked the question in the context of comparing different fuels for
    estimating costs of space and water heating; it seems to me that heat
    flow for any particular home would be about constant for any heater
    regardless of the fuel. I've been planning for solar heating, but as
    with anything AE, a back-up seems necessary and since reading some of
    your posts, I've been taking a harder look at wood as a back-up.

    Thus the 60-65% for estimations in wood stove planning question.

    Curbie
     
  13. Josepi

    Josepi Guest

    Air moving over objects does **NOT** cool them unless they are warmer than
    the air passing over them and surroundings.

    Air passing over a moist item, like a human will tend to cool them, though.


    Well, actually it does. There is some heating of the motor
    and the moving air will eventually turn to heat from friction.
    But, air moving over objects and persons will have a cooling
    effect as well. In any case, the standard method of measuring
    efficency does not take the movement of air into account.
     
  14. Josepi

    Josepi Guest

    Air moving over objects does **NOT** cool them unless they are warmer than
    the air passing over them and surroundings.

    Air passing over a moist item, like a human will tend to cool them, though.


    Well, actually it does. There is some heating of the motor
    and the moving air will eventually turn to heat from friction.
    But, air moving over objects and persons will have a cooling
    effect as well. In any case, the standard method of measuring
    efficency does not take the movement of air into account.
     
  15. Josepi

    Josepi Guest

    Air moving over objects does **NOT** cool them unless they are warmer than
    the air passing over them and surroundings.

    Air passing over a moist item, like a human will tend to cool them, though.


    Well, actually it does. There is some heating of the motor
    and the moving air will eventually turn to heat from friction.
    But, air moving over objects and persons will have a cooling
    effect as well. In any case, the standard method of measuring
    efficency does not take the movement of air into account.
     
  16. Josepi

    Josepi Guest

    Air moving over objects does **NOT** cool them unless they are warmer than
    the air passing over them and surroundings.

    Air passing over a moist item, like a human will tend to cool them, though.


    Well, actually it does. There is some heating of the motor
    and the moving air will eventually turn to heat from friction.
    But, air moving over objects and persons will have a cooling
    effect as well. In any case, the standard method of measuring
    efficency does not take the movement of air into account.
     
  17. Curbie

    Curbie Guest

    Jim,

    I had a chat with a local tree service who pays to dump at the local
    dump, that load includes both a majority (by volume) of chipped
    branched and a minority of raw logs. Since I might have interest in
    both (compost and fire wood logs) as long as they can come in at their
    convenience and dump the whole load, the owner I talked to seemed ok
    with the idea.

    Curbie
     
  18. Curbie

    Curbie Guest

    I agree there's an issue with AE technologies requiring back-up and
    that certainly plays into the economics of return on investment. I
    also consider thing other than ROI like security (self-sufficiency)
    and "Green" (political and ecological) concerns into my "return on
    investment" calculations because those notions have value to me also.

    I also feel pretty comfortable in looking at supply and demand trend
    lines for energy prices, instead of using current prices in "return on
    investment" calculations.
     
  19. Josepi

    Josepi Guest

    That was the point of my injection. Fans doe not cool objects unless they
    are damp or warmer than the room.

    Your point about elect. heater eff. is well made though.



    The moving air will evaporate water and make the object cooler. However
    that heat goes into the room so the net effect is no heat is gained or lost
    from this process. The fan motor will heat up the room somewhat and the
    friction of moving air will add some heat.
    Total results is that the ammount of electricity used is still converted to
    100 % heat. This is not counting the loss of the wiring in the walls.
     
  20. Josepi

    Josepi Guest

    That was the point of my injection. Fans doe not cool objects unless they
    are damp or warmer than the room.

    Your point about elect. heater eff. is well made though.



    The moving air will evaporate water and make the object cooler. However
    that heat goes into the room so the net effect is no heat is gained or lost
    from this process. The fan motor will heat up the room somewhat and the
    friction of moving air will add some heat.
    Total results is that the ammount of electricity used is still converted to
    100 % heat. This is not counting the loss of the wiring in the walls.
     
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