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Bit OT: Off Peak Hot Water

Discussion in 'Hobby Electronics' started by Sylvia Else, Aug 23, 2012.

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  1. Sylvia Else

    Sylvia Else Guest

    We've had a couple of problems with our off-peak hot water recently, and
    last night, at 2:45 am (don't ask!), I noticed that the switch was still
    off. So I called Ausgrid's emergency number, and they organised for
    someone to come out this morning, which they did, at about 6:15 am.

    Anyway, the guy simply bridged the switch, and attached a note saying
    that it needed to be replaced by a time clock because of "ongoing signal


    Can they tell that there's a signal issue when the switching signal
    isn't being sent? Is there a constant pilot signal?

    Or did Ausgrid already know that a problem was likely, and just waited
    for me to complain?

  2. Jasen Betts

    Jasen Betts Guest

    No constant signal, ripple control is 490Hz (or so) on the power line
    a long tone for on and a short one for off (or something like that)

    If the switch isn't switching on/off when it's supposed to it's either
    broken orsomething is eating the signal.
  3. Jasen Betts

    Jasen Betts Guest

    I've got a microcontroller based one with a PROM in a carrier marked
    "Air Conditioner 283Hz" , (I bought a bunch for $1 each mainly for the

    490 was from memory of the resonant reed in an an older waterheating
    one, the latching relay in that one was the mechanism from a telephone
    bell and a couple of opposing microswitches wired in anti parallell.

    It seems they use different frequencies for different purposes, it's
    probably at the whim of the local power company too.
  4. Phil Allison

    Phil Allison Guest

    "John G"

    ** Yep - in Sydney the tones are at 1050Hz.

    ** The 1050 Hz signal would be attenuated by many factors - not least the
    distance from the tone generator to the consumer.

    If you scope the AC ( or better the output of an AC plug pack ) you can see
    the tone super-imposed on the 50 Hz wave - running slowly along it in fact
    as it is not synchronised.

    ..... Phil
  5. Sylvia Else

    Sylvia Else Guest

    This thing has actually worked fine for many years. My expectation was
    that it would simply be replaced. The apparent instant decision to
    substitute a clock based system makes me suspect that either that's the
    standard approach to any failure of a signal based system, with no
    diagnosis involved, or Ausgrid already know of an issue in my area, and
    just wait for complaints before acting.

    I hope the clock has a decent backup for power outages.

  6. swanny

    swanny Guest

    Last clock one I had was a mechanical one, and it stoped during power
    outages. Luckily you could remove the face and re-adjust the time. You
    could also trigger the hot water at any time you wanted to by rotating
    the dial. I thought that they'd be insisting on the smart meters these
    days, have three of these in the new place (one per phase).
  7. Phil Allison

    Phil Allison Guest


    ** Read the Wiwi - fool.

    Clocks simply cannot do the same job that control tones do.

    And your " top ups" idea sounds like pure fiction.

    .... Phil
  8. Phil Allison

    Phil Allison Guest

  9. Sylvia Else

    Sylvia Else Guest

    There's no top-up on the tariff I'm on. In any case, as I understand it,
    top-ups require a separate element, higher up in the storage tank, which
    mine doesn't have.

    Storage hot-water systems rely on the fact that water is a very poor
    conductor of heat, so the water at the top can stay hot even though cold
    water has been added at the bottom as the hot water is used.
    If you try to heat up the cold water at the bottom, you'll create
    convection currents that make the water in the tank mix, and the water
    at the top will be cooled down, after which the only recourse is to heat
    all the water in the tank to the desired temperature.

    Tanks with a separate top-up element lose significantly more heat.

  10. Phil Allison

    Phil Allison Guest

    "Sylvia Else"

    ** That ( oft heard) comment always grates heavily with me - cos water sure
    ain't no thermal insulator !!

    Nothing cools something down faster that dumping it into cold water or
    pouring cold water all over it - fire brigades have relied on this fact
    for quite a while now ....

    Water is a better thermal conductor than the vasty majority of materials -
    except for metals.

    Compared to metals water is a poor thermal conductor PROVIDED that internal
    circulation is prevented However, in most practical situations, this
    provision is *NOT* met.

    Water simply bubbles and convects like crazy when heated and takes away huge
    amounts of heat from any hot surface it comes in contact with - likewise
    pouring hot water over ( or immersing ) an object heats it rapidly.

    Also, compared to metals on a weight for weight basis, water is a FAR better
    absorber of thermal energy - about 5 to 30 times better than common

    It takes 11 times more heat to raise the temp of a gram of water ( by a
    given amount) than a gram of copper.

    ** Hot water is less dense than cold so rides on top of any cold water
    introduced at the bottom of a tank, so heat from the top layer passes
    relatively slowly into the layer underneath PROVIDED there is nothing to
    cause mixing of the two.

    Heat the bottom and the result is very different.

    ..... Phil
  11. Sylvia Else

    Sylvia Else Guest

    Heat transfered by circulation is not heat transferred by conduction.
    Usually there is circulation, and the poor conduction is not apparent.
    Prevent the circulation, and then you see the low level of conduction.
    That is to say, in the absence of convection, and because water has low
    thermal conductivity, the top stays hot and the bottom stays cold.
    Yes, because you get convection, which is what I said.

    I predict a change in the subject line, and some pointless abuse, now.

  12. Phil Allison

    Phil Allison Guest

    "Sylvia Else"

    ** I am not complaining about your post.

    Read my first line, over an over - it might just sink in.

    ..... Phil
  13. Sylvia Else

    Sylvia Else Guest

    Looks to me like you objected to the statement that water is a very poor
    conductor of heat. One can have a debate about what "poor" and "very
    poor" mean, but you justified your objection by reference to the effect
    of circulation, which is a different phenomenon entirely.

  14. Sylvia Else

    Sylvia Else Guest

    But the effect of doing that is to cause convection that mixes the
    remaining hot water with the cold water, which is undesirable except
    when restoring the temperature of all the water to "hot". Unless the
    latter is achieved, users will find that the water is tepid.

    The boost systems use a separate element higher up in the tank. The idea
    is that it only produces convection above it, and so has less water to
    heat back to "hot".

  15. Phil Allison

    Phil Allison Guest

    ** SHAME you are incapable of actual thought.

    ** ROTFLMAO !!

    Wot a FUCKING IDIOT !!!!!!!!!!!

    .... Phil
  16. Phil Allison

    Phil Allison Guest

    "Sylvia Else"

    ** Which, in general, is a fallacy.

    As ELABORATELY demonstrated, by me.

    Context, context,context , context ...............

    .... Phil
  17. Phil Allison

    Phil Allison Guest

    ** ROTFL !!

    A fool informs another fool = fact.

    Wot a hoot.

    .... Phil
  18. Phil Allison

    Phil Allison Guest


    ** Syliva pretty much nailed it.

    Your turn..............

    LOL !

    .... Phil
  19. Sylvia Else

    Sylvia Else Guest

    When the warm fluid rises, colder fluid has to descend, otherwise you'd
    end up with cavities in the fluid, which isn't going to happen.

  20. Jasen Betts

    Jasen Betts Guest

    Why do you expect thermal convection to mix the cold and hot water?
    What could cause the hot water to move down and mix with the cold water?

    as the element heeat the cold water gets warm and rises it soon mixes
    with the cold water above the element and produces a slower less
    heated current, this continues, you won't ge whole tank circulation
    currents until the whole tank is essentially at the same temperature.
    the element will heat all thwe water above it, if you want to heat
    some of the water to hot you need to mount it higher, else you'll spend
    the same energy heating it all he water to warm.
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