FLASKS Will Save Us!

Astria

Olinda99 said:

Pete99 said:

Boiling one cup of water 6 times a day will use around the same amount of electricity as boiling 6 cups of water in one go.

not strictly true as in the former case you have to heat a cold metallic and glass kettle (mine weighs 1.5kg) from room temperature six times whereas in the latter case only once.

The difference in amount of extra energy used however is negligible, probably about 0.2p ?

pochase

QrizB said:

pochase said:

Why would you need to heat the whole kettle surface to get hot water? I just heat the one cup of water.

Because, by the time the kettle boils, it is full of steam and the entire kettle is hot.

Try putting your hand on the kettle next time you boil it, you'll see.

Yes, I am completely aware of that steam and even hot water will also heat up the kettle, but that is different to having to heat up the kettle first before you get hot water.

Steam comes from boiling water, before the water boils you don't have steam. 

Benny2020

Astria said:

Olinda99 said:

Pete99 said:

Boiling one cup of water 6 times a day will use around the same amount of electricity as boiling 6 cups of water in one go.

not strictly true as in the former case you have to heat a cold metallic and glass kettle (mine weighs 1.5kg) from room temperature six times whereas in the latter case only once.

The difference in amount of extra energy used however is negligible, probably about 0.2p ?

Given that the average person has 500,000,000 cups of tea in their life that would be a saving of £1m, though i may have made up some of those figures.

Astria

Benny2020 said:

Astria said:

Olinda99 said:

Pete99 said:

Boiling one cup of water 6 times a day will use around the same amount of electricity as boiling 6 cups of water in one go.

not strictly true as in the former case you have to heat a cold metallic and glass kettle (mine weighs 1.5kg) from room temperature six times whereas in the latter case only once.

The difference in amount of extra energy used however is negligible, probably about 0.2p ?

Given that the average person has 500,000,000 cups of tea in their life that would be a saving of £1m, though i may have made up some of those figures.

Yes, I think 13,000 cups of tea a day, assuming you live to 100, is over estimating it slightly.

Then again, in 10 years, energy might be £10/unit...

Section62

pochase said:

QrizB said:

pochase said:

Why would you need to heat the whole kettle surface to get hot water? I just heat the one cup of water.

Because, by the time the kettle boils, it is full of steam and the entire kettle is hot.

Try putting your hand on the kettle next time you boil it, you'll see.

Yes, I am completely aware of that steam and even hot water will also heat up the kettle, but that is different to having to heat up the kettle first before you get hot water.

Steam comes from boiling water, before the water boils you don't have steam. 

Not strictly true.  Long before the water boils there will be steam and water vapour leaving the surface of the water in the kettle and transporting some of the heat enegy to other parts of the kettle and out into the atmosphere.  That's in addition to the heat transfer through conduction in the solid parts of the kettle.

'Steam' is produced in circumstances where water vapour can condense into fine droplets, hence on a hot day it is sometimes possible to see 'steam' coming off a road surface immediately after a rain shower.  Fortunately the road surface doesn't need to be at 100 degrees or above for that to happen.

When the water approaches boiling point the rate of evaporation and water droplet formation will be much greater than at lower temperatures - which is why we tend to notice the steam more from boiling water than at lower temperatures.

But whichever way, some of the heat energy we wanted to go into the water will end up going into the atmosphere instead.

luvchocolate

There's a long thread about kettles and flasks already!!!

Olinda99

When you turn on the kettle with a cup of water, energy is used to first heat the lump of metal that is the heating element to a temperature well above 100C - maybe 200C

This energy is then used to heat the base plate where the water sits - again, another lump of metal which you have to raise in temperature.

The energy is then transferred to the water, but some of the the energy leaves the water to heat the sides of the kettle.

I have no calculations but if E is the energy required to boil the cup of water I would not be surprised if 2E or even 3E is also wasted heating the various bits of the kettle as well.

Boiling 6 cups uses only one lot of wasted energy. Boiling one cup six times uses six lots of wasted energy.

greyteam1959

Why not just buy a one cup water heater ??

Spoonie_Turtle

Astria said:

… Most commercial kettles/urns only heat the water upto approx 92c.

That's why they make terrible cups of tea.

I have used the flask for multiple cups of tea on particularly bad fatigue days when I can only make it to the kettle once, and the tea by the last cup really isn't that grand.  (My flask holds enough for 3 mugs.)  Better than nothing, but I certainly wouldn't do it every day by choice.

Astria

greyteam1959 said:

Why not just buy a one cup water heater ??

Because some of those so called "one cup water heaters" actually boil a lot more than one cup!

It's best to just use a kettle which has a low minimum marker (say 250ml) and use that.