Drink green tea, you only heat to 80C?a saving of 20% of normal cuppa and less energy wasted in evaporation and the eddy currents. Also less energy lost to kettle material and room as Delta with environment is lower. I'm pretty sure my induction pans don't get as hot as the kettle too ie they somehow transfer more of the energy to what's inside the pan. But induction pan lids are not sealed like a kettle
It really is a simple test, heat water in both, record time and temp change, and do watts X time comparison
Ah. One of those people who thinks that heating the odd 350ml of water
20C less will save more than heating a whole 6000 cu ft house 0.1C less.
Once again the ability to Do Sums shows that saving money by heating less water or water less is simply completely irrelevant in the context of heating a whole house.
Especially since the heat in the water ends up in the house anyway. So you are probably only looking at the marginal cost of heating it via electricity rather than gas...or oil.
A microwave is about 50 percent efficient. Most of the energy is lost in the process of converting electricity to microwaves (which are part of the electromagnetic spectrum).
An electric stovetop is about 70 percent efficient, although that varies widely depending on the type of pot or kettle you use. Most of the energy is lost heating the air around the stove.
An electric teakettle is about 80 percent efficient, although again this varies from kettle to kettle. Electric kettles are generally very well insulated, and the heating coils sit directly in the water, so less heat is lost to the air.
An induction stove or hot plate is about 85 percent efficient. It creates an electromagnetic current directly in a pot to generate heat, losing very little to the air.
To me, the results make no sense. Common sense.
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Table 2. Cooking efficiency results measured according to EPRI test procedure
Large Vessel Small Vessel
Half Power Full Power Half Power Full Power Induction Cooker A 74.9% 77.6% 76.5% 77.4% Induction Cooker B 75.7% 77.2% 75.6% 75.1% Electric Coil 81.6% 83.4% 48.2% 41.5% Natural Gas 41.7%* 35.2%* - 30.2%* <=== *bogus technique... not that it matters
So the message here, is that electric kettle designers don't give a rats ass about efficiency. If they did, they would beat the induction design. The design of the vessel ("large" vessel versus "small" vessel) is making a big difference to the test result there.
This has been discussed in another context. Induction charging for electric cars is proposed. However, the off-the-cuff analysis for the induction technique, saw an additional 10% energy wasted in the induction feature. Making it less attractive when scaled to national scale. I would hope we continue to plug in the cars, using the various connector designs, to save on that
10% waste. As that 10% waste could represent the entire output of a single power plant (for nothing).
It's possible with an electric coil, to *completely insulate* the test case. Resistive heating is 100% efficient (P=V*I type heating) barring the usage of stupidly thin power cabling, leading up to the element. If you had to, you could hard wire the heating appliance, to reduce losses.
But the appliance designs are cheap, with the emphasis on cheapness. Nobody is going out of their way to shave 5% losses off a kettle.
Although the attempt to ban toasters was interesting... :-) And that fight probably isn't over.
Interesting that those efficiency figures are for 'cooking efficiency'.
Induction heating by it's very nature does not have such a high efficiency when you consider the actual eddy losses. ie power input v power induced out.
Out of interest, did you copy/paste this table? The headers don't line up and I wonder whether that's because of how you did it, or whether it's your or my Usenet client.
Yes, this needs to be discouraged.
The Yanks, with their cheese-paring 110V mains, have to use stupidly thick cable on their appliances in order to transmit any useful power.
Exactly. Both a kettle and an induction-heated pan will have some loss of energy as heat that is radiated / conducted from the pan or which causes convection heating of the surrounding air, but eddy "losses" are precisely the way in which an induction pan heats the water.
Energy in => induction heating in pan ("eddy losses") + heat lost to surroundings (radiation, convection and conduction)
If the object of the exercise is to bring the water to the boil and then stop heating (eg when boiling water for a cup of tea) then I imagine thermal mass is a significant factor. But for boiling vegetables, where you *keep* the water boiling gently for tens of minutes, it may be less significant because the pan will take longer to cool so the hob can be turned off shortly before cooking needs to end.
I wonder how heat losses from a silvered steel pan compare with from a plastic kettle.
If you were designing a water heater, you could make the "kettle" out of plastic or glass and place a magnetic plate inside and entirely surrounded by water. An induction source outside would make that plate heat up. Which could be a neat approach.
I actually thought it was neat enough that you could have one kettle for water, another for milk. Both able to tell the base unit what temperature they were at. You could heat water for green tea, milk for baby, or whatever is needed, very accurately. Especially of the kettles had something to swirl the contents - also driven by the induction field.
I haven't used our kettle for over a year, since we've lived in our new house that has an Aga. I've got it down to a fine art: put pan of cold water on the boiling plate (the hotter of the two hotplates), retrieve cafetiere and cereal bowl from dishwasher (*) and put in a spoonful of coffee, put cereals in bowl and stir in the milk, water is bubbling nicely by then so pour over coffee, then put cereal in microwave - and start emptying rest of dishwasher. All that makes me sound like a time-and-motion nerd who has spent ages working out the critical path analysis ;-)
The last time we got the kettle out was when we had some building work and the builders needed to make tea.
I never know about the economics of a gas-fired Aga versus a gas cooker or electric cooker, but any waste heat keeps the kitchen warm so that radiator's thermostatic valve rarely turns on. And it's great being able to cook things *now* without having to wait for an oven to heat up.
(*) I get flak from my wife if I forget to empty the rest of the things in it ;-)
In message <rbbmq0$p9e$ snipped-for-privacy@dont-email.me, NY snipped-for-privacy@privacy.invalid writes
I think this is an age thing.
Lots of us have had exposure to time and motion studies but I am beginning to believe it comes down to making the best use of the time you have left for routine activities.
You could, but a traditional element would probably waste less and cost way less and last longer.
Or you could go the whole hog & make it a stinger kettle.
ok in winter, dire in summer.
Re the 80 something % efficiency figure for kettles, I've always suspected it, it seems unlikely. Does the author have a motive for exaggerating a kettle's losses? IIRC yes.
Our house had both an Aga and a conventional electric oven fitted by the previous owners. We've found that the extra heat given out by the Aga in hot weather isn't a problem, mainly because we tend to have windows open anyway (even to let out "greenhouse heat" from the sun) in hot weather. Our Aga has AIMS, a system which allows you to control how much gas is used at different time of day, so it allows the Aga to cool overnight and (when we weren't working from home!) between breakfast and dinner. I always wonder how much energy is used to maintain a constant temperature versus letting the device cool down and then heating it back up to operating temperature. I think last year we just turned the Aga down to minimum (we didn't have the courage to turn it off completely in case we couldn't relight it!) for a week last summer when it was very hot, and used the electric oven/grill, and a little portable induction hob for veg.
Our central heating is "always on" in the sense that it *can* come on at any time the temperature drops below what the thermostat is set to. During the sunny period I think it came on once in early morning when the house had cooled at bit overnight, but now the sun has gone, it's on every morning and intermittently throughout the day as required. We have Hive controllers (two, for radiators in two different "wings" of the house) and these allow you to set different temperatures at different times of day - eg 20 during daylight hours and 15-17 overnight. In winter, this will prevent the house getting very cold overnight, while keeping it cooler at night than during the day. The ability to control the heating from a mobile phone when away from home is brilliant - when we go away on holiday we set the temp to about
10 deg (to prevent fridges/freezers getting too cold, since modern ones are fussy about that) and then when we are a few hours away on our way back, we turn up the thermostats to 20 so the house is warm for when we get home.
A kettle will lose *some* heat by radiation and conduction to the air, but I'd be surprised if it was as much as 20%. It's easy enough to work out how much energy it takes to heat a known volume/mass water from about 10 degrees up to boiling (assumed to be 100), and to measure the power consumption (probably better than using the rated power on the appliance plate!). From this you can calculate how long it would take to heat the water and compare this with how long it actually takes.
I'll have to try it some time: I'll be intrigued by the result.
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