3 Second Kettle

[StuartDH]

Tefal have developed a kettle that heats water in 3 seconds The water in the kettle is passed through a spiral heating system to instantly heat the water without preheating...in only seconds

But the best thing about the 3 second kettle is that they claim that it saves energy by 65%, so it's also good for the environment

[jdurbo]

It would have boiled before i'd even get the cups out!!! never mind put the coffee in the cup
jen xxx

[jnb]

A quick search on this found another forum where someone had done the calculations and found that to raise 250ml of water from 20 degrees to 90 degrees in 3 seconds would require a 28KW power supply. At most a domestic socket can only provide 3Kw so someone somewhere isn't telling the entire truth. It appears that while it might start "boiling" in 3 seconds it won't provide a full cup in three seconds instead it pours it out slowly (or as they described "about as fast as an old man with a prostate problem").

Might save energy though simply because it only heats the amount of water that is delivered but wouldn't save any time and needs to be watched while you use it so you can keep your finger on the dispense button. Of course one could just not overfill a conventional kettle.

Edit - I've just done a few calculations and assuming they haven't rewritten the laws of physics and are being charged typical electricity prices then their claimed savings of about £30 pa (and the kettle costs £60) are equivalent to boiling a full kettle a dozen times a day but only using a couple of cups of water from it. Of course if the kettle is only a third full you will save that £30 pa anyway.

[StuartDH]

I hope the person hasn't got a decimal place wrong, because the kettle is actually 2.8kW

Either he's got it wrong, or Tefal are going to have egg on their face with a kettle that doesn't do what it claims until everyone gets an industrial power supply...I know who I'd put my money on I think it would certainly have to be more than 3 seconds to actually fill 250ml as that's quite a fast flow rate.

The video on the tefal page shows it probably wouldn't fill in 3 seconds, but it's not exactly just dribbling out either.

Tefal QuickCup

I actually need a kettle, so I might go and get one of these tomorrow and plug it into an energy meter to run some realworld tests

[kshotton45]

On the BBC news this morning they said that the water never reaches boiling point.
I suppose that this would be O.K for coffee but not tea.

Keith.

[StuartDH]

yep, apparently it gets to 90 degrees, but do we need to boil water for tea anyway? I usually let the kettle boil, then pour 20/30 seconds later when it's probably dropped to 90 degrees.

[jnb]

Warning - calculations ahead

To raise 1ml of water 1 degree C requires 1 calorie
1 calorie = 4.2 Joule (ish!)
1 watt = 1 J/s
so to heat a cup of water from 20 degrees to 90 degrees requires

250 ml * 70 calorie/ml * 4 J/calorie ~ 70 000 Joules

To do that in three seconds

70 kJ / 3 s ~ 23.3 Kw !

Or the other way around to do that with a three Kw supply would require about 23 seconds.

[StuartDH]

I'd go with that, but Tefal obviously have the opportunity to work from different cold water temperature, size of cup and hot water temperature. 23 seconds is still pretty fast, but I think my old 'millenium' kettle used to do a litre in one and half minutes, so about the same speed.

I was thinking of buying one, but then I saw how much replacement Claris filters cost

[Goosegogs]

A while ago, someone said to me that it was more efficient to use a microwave to make a cuppa coffee. You'd heat only the amount of water you require.
Then, a while before that at one of the Christmas Lectures (DVDs were the size of LPs?), I think he was director at EMI research or something, where there was mention of using radio waves for cooking.

[eeyore]

Originally Posted by Goosegogs

A while ago, someone said to me that it was more efficient to use a microwave to make a cuppa coffee. You'd heat only the amount of water you require.
.

while this is true you would probably find that by heating the water in the cup you had rendered the cup to hot to touch.

Originally Posted by StuartDH

I'd go with that, but Tefal obviously have the opportunity to work from different cold water temperature, size of cup and hot water temperature. 23 seconds is still pretty fast, but I think my old 'millenium' kettle used to do a litre in one and half minutes, so about the same speed.

I was thinking of buying one, but then I saw how much replacement Claris filters cost

surely the sailient point is that the energy required to raise a given volume of water to boiling point (or 90 degrees) is the same whatever method is used - the energy saving comes about by only boiling the ammount you need which you can do in a bog standard domestic kettle with a little care.

also if you are making multiple cups of tea ( in our office the last tea run was 23 cups) then you want all the water to be hot at the same time - not at half minuite intervals over a nearly 12 minuite period.

Originally Posted by StuartDH

but Tefal obviously have the opportunity to work from different cold water temperature, size of cup and hot water temperature.

but even assuming that the cold water temp was the optimistic end of the room temp definition and was 25 degrees to raise it to 90 degrees in 3 secs with a domestic supply would require a cup size of only 2.85 cc - presumably the kettle is for hobbits or borrowers ???