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Mrs Fiddlesticks
Joined: 02 Nov 2004
Posts: 10460
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dougal
Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
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 Posted: Fri Oct 14, 05 3:15 pm Post subject: |
 
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| Fiddlesticks Julie wrote: |
| hmm still no votes for a hob model then. 3kw to boil a mug ful say in what minute or two compared to same amount on hob which has a ring wattage unknown - well thats helpful isn't it? |
Its important to distinguish between kilowatts (kw, a thousand watts), which measure *rate* of energy usage/supply, and kilowatt hours (kwh or "units"), which measure the *quantity* of energy used.
Use electricity at a *rate* of 1 kw for an hour and the *quantity* of electricity used is 1 kwh.
Ignoring detail pedantries (like heat loss), if you boil a set quantity of water, that will always take the same *quantity* of electricity (for the same quantity of water and the same start temp) regardless of the wattage - but the time it takes will depend on the *rate* that that the kettle uses electricity (ie the rate it supplies heat).
OK, time for detail pedantries. For electricity, its just a question of where heat is wasted. And less is wasted from a plastic kettle with a submerged element than in heating the ceramic hob, and the metal kettle or pan (and heat losses therefrom) as well as the heat that goes around the side of the kettle. And with almost every electric kettle having an auto shut-off (which a hob hasn't) there's no wasted heat/electricity after its up to temperature.
So sadly an electric hob is *not* a good way to boil water.
EDIT: Though an electric *induction* hob will waste much less heat than any conventional electric hob...
Because gas is *much* cheaper than electricity, an inefficient gas hob will usually do the job more cheaply than an efficient electric kettle.
So Sean (probably) didn't make it up... 
Last edited by dougal on Fri Oct 14, 05 10:58 pm; edited 1 time in total |
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Mrs Fiddlesticks
Joined: 02 Nov 2004
Posts: 10460
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wellington womble
Joined: 08 Nov 2004
Posts: 15051
Location: East Midlands
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Lozzie
Joined: 25 May 2005
Posts: 2595
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Mrs Fiddlesticks
Joined: 02 Nov 2004
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Lozzie
Joined: 25 May 2005
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marigold
Joined: 02 Sep 2005
Posts: 12458
Location: West Sussex
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ele
Joined: 05 Sep 2005
Posts: 814
Location: Derby
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jema
Downsizer Moderator
Joined: 28 Oct 2004
Posts: 28239
Location: escaped from Swindon
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dougal
Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
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| Posted: Sun Oct 16, 05 3:42 pm Post subject: |
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| ele wrote: |
I liked the little rant about how you can't buy dishwashers with hot and cold water feeds, when I bought ours I spent ages trying to find one that would  |
Its off topic for this thread, but these days good dishwashers
1/ only use a little water, rather less than 20 litres for the cycle
2/ and don't get it very hot - a 50C wash is usually fine (needing only half the heat energy of an 80C wash).
so, actually, they don't use much energy for heating water.
Also, as the yellowhouse site mentions, there is often a comparable amount of water (cold) in the hot pipe between tank and appliance.
The yellowhouse people insulated those pipes - but STILL run off water at the sink until it 'comes hot'.
This would be very energy wasteful if the water was NOT heated by solar, as the yellowhouse people do.
Adding the hot fill connection, and its extra powered valve and its control system, is going to add a few quid to the cost of the machine, and use more materials, to no good effect for ordinary customers.
So - summary: dishwashers nowadays don't have hot water inlets because there's no benefit, and some disadvantage, for almost all buyers. |
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suse
Joined: 15 Sep 2005
Posts: 1
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thos
Joined: 08 Mar 2005
Posts: 1139
Location: Jauche, Duchy of Brabant (Bourgogne-ci) and Charolles, Duchy of Burgundy (Bourgogne-�a)
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thos
Joined: 08 Mar 2005
Posts: 1139
Location: Jauche, Duchy of Brabant (Bourgogne-ci) and Charolles, Duchy of Burgundy (Bourgogne-�a)
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marigold
Joined: 02 Sep 2005
Posts: 12458
Location: West Sussex
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I've got a ceramic hob, so I guess the difference is negible?
), I usually fill a flask at the same time and use that for the next few drinks.
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