Kettles are on the list. However they are going to run tests on the possible savings. The fact that kettles are even on the list shows the level of education of some of these people !
Surely they should regulate efficiency, not wattage ?
Is the intention though, to try to make them work with less input power? The critical thing with a kettle is how long it will take to boil if full. If its fast, then one can imply its efficient, but if its slow it might be no better than a higher wattage one is, or indeed worse of course. I suspect the marketing peeps will subtly make kettles lower capacity to disguise the fact that its not more efficient.
What about immersion heaters though? These seem to be not very good. they scale up distort etc, and hence lose any efficiency they had. the best design should be based on some kind of flow inside the tank, so we could soon find that we have to buy a tank with integral efficient heater? Certainly, any element which is efficient could not fit through the usual hole! Brian
But every watt converted to heat does end up either in the water or coming out of the external end of the immersion heater. Even if the heater has to cycle itself for days to get all the water heated to the required temperature! The only improvement in actual efficiency that I can see is to make sure that the sticking-out bit is well insulated from the rest of the immersion heater and the cylinder.
As has been discussed before, all other things being the same, supplying a lower power to a kettle will make it take a disproportionately long time to boil (because of heat losses). A low power kettle would have to have its insulation beefed up to prevent this problem).
Using the principle of 'reductio ad absurdum' (*see below), it seems to me that if kettles boil very quickly, the chances of having a great number of kettles on at the same time are pretty low. On the other hand, if they take a long time to boil, the chances of having them on at the same time are greater.
*Imagine if kettles boiled instantly. It's highly unlikely that large numbers are going to be switched on at exactly the same instant.
All electric heaters are 100% efficient. The trick is to beef up the insulation and in the case of kettles for instance, make sure no more water is heated than needed. A jug thing is the best, you can heat just a cupful of water.
To quote Scotty "Ye cannae change the laws of physics"
If all else is equal, it takes less energy to bring to the boil a given quantity of water the faster you do it. This makes a 50 kilowatt electric kettle more energy efficient than a 1 kilowatt kettle. (Ignoring external losses in the wiring) A better insulated 50 kW kettle is more energy efficient than an otherwise identical 1 kW kettle.
This applies no matter how much water is in the kettle, and no matter how well it's insulated, as long as that insulation isn't 100% perfect.
But, if you have a kettle as well insulated as a Thermos flask, it makes very little difference to the total energy used, so you could, in theory, have a 60 watt kettle with perfect insulation if you had enough spare time to let it heat the water. Think about a very well insulated slow cooker. It has a 60 watt element, which doesn't run all the time, but keeps the food inside it just below boiling point using a fraction of the power and energy of a normal hotplate doing the same.
You can but try telling SWMBO'd that. We did have a kettle that had a minimum level of under 500 ml, but if she ever filled the kettle for just a single mug of brew it was filled to at least the litre mark. Once she'd made her brew she'd top it up and reboil "ready for the next one" (in two or thre hours...).
That's a type usually sold as a "Travel Kettle" :-)
In this case, it really makes extremely little difference to the immersion element's _efficiency_ (or, for that matter, efficacy). For a start, they use a much lower wattage per inch loading than the typical 1.5 /1.7 KW rated kettles since they have the luxury of being able to use a much longer length of element.
Even when scale builds up on an immersion element, all that happens is the element temperature increases until it reaches a new balance of thermal flow across the extra thermal resistance of the limescale 'barrier'.
I haven't seen any figures for typical limescale thermal resistance but I suspect it may only require an extra 10 or 20 degrees C increase in element temperature to balance the heat flow compared to its original performance when new.
The fractional temperature rise may cause a rise in resistance of the element reducing the power consumption by a small fraction, leading to a slightly longer heating time but, apart from that, the heating efficiency will remain unaltered (a 20 deg rise in element temp is unlikely to translate to a rise of more than 1 or 2 deg at the immersion element head).
Assuming it's for a beverage you can 'brew in the cup', the choice is more a case of "Damned if you do, dmaned if you don't."
You either heat up twice as much water as required with 100% efficiency or else heat the exact amount at around the 50 to 60% electrical to microwave radiation conversion efficiency, typical of most MW ovens.
For a single cup/mug of hot beverage, the microwave is as good a choice as using a kettle. I reckon that when it comes to preparing more than a single mug's worth of hot beverage at a time, the kettle will have the edge, especially when brewing tea in a teapot rather than pouring the water onto a teabag in each mug or cup (or, for those of a cheaper disposition, teabagging the two mugs of hot water with a single teabag on a string).
How about single-cup immersion heaters? Exactly the right amount of water and, I suspect, more efficient than a microwave. Might be a bit slower.
If you really want to save you have lots of other options. Like making super-strong tea (one bag and 30ml of water) or coffee (a teaspoonful of instant and again 30ml of water) - and a glass of cold water to wash it down.
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