Bit OT: Off Peak Hot Water

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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
issues".

"Ongoing?"

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?

Sylvia.

Re: Bit OT: Off Peak Hot Water
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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.



--
⚂⚃ 100% natural

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Re: Bit OT: Off Peak Hot Water
Jasen Betts formulated the question :
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1050 hz I think you will find and there are about 25 time spacings to
switch 25 groups of devices.


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--
John G



Re: Bit OT: Off Peak Hot Water
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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
enclosures)

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.

--
⚂⚃ 100% natural

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Re: Bit OT: Off Peak Hot Water

"John G"

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

http://en.wikipedia.org/wiki/Zellweger_off-peak


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** 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





Re: Bit OT: Off Peak Hot Water
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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.

Sylvia.

Re: Bit OT: Off Peak Hot Water

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I wonder if you'll have as effective water heating too?
That is, if a clock makes it come on at night time only, when demand is
low, you'd miss on the occasional top up through the day (during brief
periods when demand is also low). I think that's the advantage of
signalled systems - otherwise we'd all just have clocks?

Re: Bit OT: Off Peak Hot Water

"Jordan"
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** Read the Wiwi -  fool.

http://www.stuff.co.nz/entertainment/celebrities/7540700/John-Lennons-killer-denied-parole

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

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


...  Phil



Re: Bit OT: Off Peak Hot Water

"Phil Allison"


 ** Wrong Wiki:


http://en.wikipedia.org/wiki/Zellweger_off-peak





Re: Bit OT: Off Peak Hot Water
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Go and have a wiwi yourself - you might feel better.

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http://www.stuff.co.nz/entertainment/celebrities/7540700/John-Lennons-killer-denied-parole
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I thought that's what I said.

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Is it that you know for sure that off peak systems will never turn on
during nominal peak times?

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Re: Bit OT: Off Peak Hot Water
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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.

Sylvia.



Re: Bit OT: Off Peak Hot Water

"Sylvia Else"
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** 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
metals.

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


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** 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




Re: Bit OT: Off Peak Hot Water
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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.

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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.

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Yes, because you get convection, which is what I said.

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

Sylvia.


Re: Bit OT: Off Peak Hot Water

"Sylvia Else"
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** I am not complaining about your post.

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



....  Phil




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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.

Sylvia.



Re: Bit OT: Off Peak Hot Water

"Sylvia Else"

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** Which, in general, is a fallacy.

  As  ELABORATELY  demonstrated,  by me.


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



... Phil



Re: Bit OT: Off Peak Hot Water
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Possibly more to do with the latent heat of evaporation than conduction
don't you think?


Re: Bit OT: Off Peak Hot Water
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I don't mean a separate boost element, just that the main element might
come on at any time there is adequate power available.
A plumber told me, and it sounds plausible.


Re: Bit OT: Off Peak Hot Water
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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".

Sylvia.

Re: Bit OT: Off Peak Hot Water
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OK, I'll have to accept that might happen. I didn't think it'd stir
things up that much, thinking just that warmer fluids rise.

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