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Average Electricity Usage?

Discussion in 'Home Power and Microgeneration' started by Ted Wood, May 30, 2004.

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  1. John W. Hall

    John W. Hall Guest

    I find that strange. The calorific value (which is what most of us are
    interested in) of natural gas varies, depending on the source and
    perhaps time. Here, they periodically measure the calorific value, and
    bill us by the Joule/GigaJoule.
    AFAIK, this (by the GigaJoule) applies to residential, commercial and
    bulk pipeline rates.

    For stripping plants, which remove ethylene etc from the pipeline for
    petrochemicals feedstock, I expect other criteria apply.
     
  2. usually not worth swapping.

    Let's take a couple of guesses at what you're likely seeing (figuring on a
    pretty large and wasteful machine now, and using warm water for the wash,
    unheated for the rinses)

    a) amount of water saved/load: 20 gallons
    (probably half that, but wth...)

    b) amount of heated water saved: 5 gallons

    c) cost of water [1]: $0.005 (1/2 cent) per gallon
    NYC rate. other urban areas are similar

    d) cost of heating water [1] : $0.01 (1 cent) per gallon

    [1] each gallon weighs about 8 pounds,
    figure a 50 degree warmup, so that's 2,000 BTUs.

    An electrical kw-hr costs (typically, rates
    vary a Great Deal) $0.15 (15 cents) and gives
    you 3,500 BTUs. That's $0.0086 (0.86 cents) for
    each gallon... add taxes and summer surcharges.

    e) five loads/week.

    Ok, so just looking at the various water related costs:

    water saved/load: 20 gallons. times 0.5 cents = 10 cents/wash
    electrical savings: 5 gallons, times 1 cent/gal = 5 cents/wash

    total: 15 cents/wash.

    times 5 loads/week = $0.75 or 75 cents/week.
     
  3. I hate it when my fingers slip... Corrected version below, earlier one
    cancelled (but many places will show both. sorry about that.)

     
  4. Guest

    An assertion demands no more than a counterassertion. To effectively
    disagree with basic physics, you need to talk about basic physics...
    It isn't enough to wander around the world hurling insults, denying
    gravity, and soliciting oral sex from other men :)

    Nick

    Tired of Iraq? Do something about it. Learn to halve your energy use
    while having fun with math and science.

    Join solar guru Steve Baer and PE Drew Gillett and PhD Rich Komp and
    me for an all-day workshop on solar house heating and natural cooling
    strategies ("HVAC Nonsense") on July 9 in Portland, OR--see page 25 of
    http://www.ases.org/conferences/2004_call_for_papers/SOLAR2004_prelim_program.pdf
     
  5. Don Ocean

    Don Ocean Guest

    Then perhaps you shouldn't do those things.. A hobby mayhaps?
     
  6. Pete C

    Pete C Guest

    On 31 May 2004 11:33:16 -0400, wrote:

    Hi,

    Also some houses may allow some humidity to seep in overnight, so the
    indoor humidity might be nearly as high as the outdoor humidity by
    morning.

    cheers,
    Pete.
     
  7. Hello all,

    To me, one of the really nice things about this kind of discussion forum is
    that the discussion takes place in writing, allowing me time to think things
    over before blurting them out in public.

    I do not know Nick Pine personally, but I have benefitted from his many
    posts in various newsgroups. His attitude may not always be the most
    sensitive, but his science generally seems very sound (to my limited
    understanding), and his willingness to spend time answering questions is
    quite amazing.

    If you must compete with Nick, maybe you could try improving on his numbers,
    rather than merely criticizing him for using numbers.

    Regards,

    Bert Menkveld
    P.Eng.
    bertATgreentronicsDOTcom

    [ Stuff snipped that doesn't need to be repeated. ]
     
  8. I'm in Elmira, near Waterloo. Are you saying that you don't run your AC in
    the summer?
    Maybe. In terms of the world at large, it's almost certainly worth doing.
    In terms of money, it might be a moot point for the immediate future, but
    energy prices are likely to continue rising (I hope).

    Our washing machine is on its way out of this world, and I'm looking around
    at front loaders. I'd welcome any suggestions for how to assess the likely
    reliability of the many new models out there, with very little history
    available yet.
    It seems natural for people to be set in their ways (I know this from being
    inside my own head :).

    Some municipalities apparently ban clothes lines, but allow the smaller
    "umbrella" type of outdoor clothes hanging structures.

    You could try hanging the clothes to dry indoors for a few weeks and see
    what your electrical energy consumption looks like.
     
  9. I've never done any "scientific" investigation, but I would guess that a
    Hills Hoist clothes line ("umbrella") would dry clothes quicker and
    reduce wrinkles more than a fence style clothes line (any wind will make
    everything turn, which means that even the clothes that didn't catch the
    breeze benefit from the breeze... (Am I making sense?)

    Not to mention that they can be demountable, foldable etc so that you
    can take it out and put it away when you want to use the space for
    something else (BBQ, reception, soccer game...)

    If you need to dry washing indoors, my own experience has shown that the
    best place to put the clothes rack is:
    - the room that has a computer on often (extra heat from the computer
    helps dry quicker)
    - the room that is the "driest" - (works well in my bedroom for really
    dry days, slightly humid air is much healthier than dry air)
    - the room that has electric heating if you are in a reasonably dry
    climate (I don't mean in English climates - helps humidify the air). But
    best not to have electric heating at all

    Other tips:
    -put your drying rack as high up as possible - 1 meter in height can
    make a huge difference in time to dry clothes in winter (heat rises)
    -best is to have it just below ceiling level
    -don't cook sardines or cauliflower when you've got a load of washing
    drying. Your clothes will smell (personal experience)
    - leave air gapes between the clothes to make sure you get a good air
    movement.


    About the worst place is in a bathroom that doesn't have a window.


    Also, if you hang clothes carefully, you can reduce (or even eliminate)
    the need for an iron.

    Mel

    Bert Menkveld a écrit :
     
  10. I see Nick's efforts as generally containing some substance and some modest
    real experience. A good counter point to my much more theoretical approach.
    I second Bert's position.
     
  11. ....
    Note to self. Humidity may be regarded in two ways. One is absolute
    moisture, the other relative humidity which is a function of the absolute
    moisture and the temperature. A shower can put a lot of moisture into a home
    in an absolute sense. The heater takes none of this out, even though the
    relative humidity can drop like a rock, and your sweating is much more
    effective at cooling you off. The air conditioner chills this moisture out
    of the air, reducing relative humidity and absolute moisture levels. So when
    you open the house at night you can cool it, and raise the relative
    humidity, while at the same time removing absolute moisture from the house.
     
  12. Guest

    There's no change in the absolute humidity above, and no dehum needed
    for comfort, but even if so, that's not so bad, if it's only humidity,
    vs incoming mist or condensation inside the house. A 2400 ft^2 1-story
    house holds 19.2K ft^3 of air that weighs about 1440 pounds. At 75 F
    and 50% RH, the humidity ratio w = 0.00942 pounds of water per pound
    of dry air, so the air contains about 181 pounds of water vapor. If
    the 61.8 F outdoor air had had 100% RH, it would have had w = 0.0119,
    and we decided we could live with w = 0.0134:
    If we could somehow crank up the RH of the indoor air to 90% at 75 F
    overnight, it would contain 325 pounds of water vapor. Removing the extra
    325-181 = 144 pounds takes takes 14.4K Btu, which is still a lot less
    than the 32.6K Btu in scenario 1.

    When is it better to keep the windows closed at night and AC vs vent,
    based on humidity gain? It seems better to keep the windows closed if
    the temperature of any part of the house is less than the dew point of
    the outdoor air, in order to avoid condensation and house heat gain,
    but what if the house is warmer than the dew point of the outdoor air?

    If the house has volume V and thermal conductance G and continuous heat
    gain P (V = 19.2K ft^3 and G = 200 Btu/h-F and P = 2000 Btu/h above), and
    we want to maintain indoor temp Ti and humidity ratio wi, and outdoor air
    has a 24-hour average temp Ta and wo > wi, and opening windows at night
    eliminates the need for AC cooling, we need to dehum 0.075V(wo-wi)1000
    Btu/day, but we've saved 24h(P+(Ta-Ti)G) Btu, so opening windows saves
    24(P+(Ta-Ti)G)-0.075V(wo-wi)1000 Btu/day, net. Plugging in numbers gives
    24(2000+(71.8-75)200)-0.075(19.2K)(wo-0.0134)1000 = 51.9K - 1440Kwo, which
    is greater than 0 whenever wo < 0.0360, ie whenever the outdoor air temp
    is less than 94 F at night. Looks like opening windows always make sense
    in this case, from a humidity point of view.

    Nick
     
  13. Note to self - absolute humidity is not a factor in human
    comfort. Cool air with high RH is uncomfortable, and promotes mold
    growth. Thus, opening the house during cool damp nights leads to
    discomfort and mold growth.



    Paul ( pjm @ pobox . com ) - remove spaces to email me
    'Some days, it's just not worth chewing through the restraints.'

    HVAC/R program for Palm PDA's
    Free demo now available online http://pmilligan.net/palm/
    Free Temperature / Pressure charts for 38 Ref's http://pmilligan.net/pmtherm/
     
  14. Guest

    The ASHRAE 55 comfort zone is defined with absolute humidity limits.

    Nick
     
  15. Bullshit. Utter simplistic complete bullshit.

    Are you reading impaired, on top of everything else ?

    http://resourcecenter.ashrae.org/st...method=and&subjectcategoryid=&advancedsearch=

    "This standard specifies the combinations of indoor space environment
    and personal factors that will produce thermal environmental
    conditions acceptable to 80% or more of the occupants within a space.
    The environmental factors addressed are temperature, thermal
    radiation, humidity, and air speed; the personal factors are those of
    activity and clothing. "

    http://www.sfu.ca/FacilitiesManagement/operations/hvac_standards.html




    Paul ( pjm @ pobox . com ) - remove spaces to email me
    'Some days, it's just not worth chewing through the restraints.'

    HVAC/R program for Palm PDA's
    Free demo now available online http://pmilligan.net/palm/
    Free Temperature / Pressure charts for 38 Ref's http://pmilligan.net/pmtherm/
     
  16. Guest

    And the upper and lower boundaries of the 1981 standard zones are
    absolute humidity limits of w = 0.0045 and w = 0.012. RH isn't part
    of the comfort zone definition.

    Nick
     
  17. ....
    I offer this, for fun and profit. Mostly from living in the LA area and up
    in Seattle . Except when fiercely cold, we always open the window at night,
    and whenever the air is warm enough to let circulation take place without
    too much discomfort. Fresh air smells better, and the humidity, usually from
    30-70% is much more comfortable than the dead "inside" air. Can't speak to
    mold. Not a problem in LA, and in Seattle we keep our house too cold to mold
    much. Push the RH up to around 100%, as in serious fog, and it smells damp
    and heavy and I expect I would agree. Cool modestly damp nights (as in 70%
    RH I think), not so much.

    The reason I introduced absolute humidity as an issue is the turning point
    of temperature. A standard heating system does not change the absolute
    humidity but raises the temperature and thus lowers the RH, partly
    contravening the advantage since it causes your sweat to cool you faster.
    The inverse of this is a cool night air with a high RH, but less absolute
    moisture than the internal house air. If you are concerned with the power it
    takes an AC to remove the moisture, you must evaluate temperature and
    absolute moisture levels, not just RH. So you could dry the house and cool
    it with a colder outside air with a high RH, and your AC would have less
    labor, not more. In general, unless you are actually sitting in fog, I go
    for the cool night air. I am only vaguely aware of how much this changes
    when you are cooking in the steam heat of Ga in summer, but I still usually
    go for the fresh air.
     
  18. ....
    Shouldn't it be? It is certainly critical to comfort in all the environments
    I have experienced?
     
  19. ....
    Can't say that I really follow the argument, but the result sounds
    consistent with my personal experience.
     
  20. What he just said is 'open the windows if it's less than 94 F
    outside'

    Tell me - when it's 90 degrees outside at night, do you open
    your windows and find it comfortable to sleep ?



    Paul ( pjm @ pobox . com ) - remove spaces to email me
    'Some days, it's just not worth chewing through the restraints.'

    HVAC/R program for Palm PDA's
    Free demo now available online http://pmilligan.net/palm/
    Free Temperature / Pressure charts for 38 Ref's http://pmilligan.net/pmtherm/
     
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