ECO kettle - I don't get it

Discussion in 'Renewable Energy & Energy Saving' started by Stuart Wright, Mar 11, 2013.

  1. Stuart Wright

    Stuart Wright
    AVForums Founder Staff Member

    Joined:
    Jan 24, 2000
    Messages:
    14,852
    Products Owned:
    7
    Products Wanted:
    2
    Trophy Points:
    167
    Location:
    Birmingham, UK
    Ratings:
    +10,806
    Eco Kettle - Introduction to the Eco Kettle

    What's the difference between filling a normal kettle up with the correct amount of water and pressing the ECO kettle knob to fill its boiling chamber up with the correct amount of water? It's the same thing. People can't be bothered to look at the amount - usually because it's measured in centilitres and nobody knows how many centilitres are in a mug full.
    Is the ECO kettle simply all about making people look at the amount they are boiling?
     
  2. IronGiant

    IronGiant
    Moderator

    Joined:
    Jun 7, 2003
    Messages:
    65,969
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    166
    Location:
    .
    Ratings:
    +45,983
    Mostly, it also has a 2.2kW element so that probably makes it slightly more efficient when boiling small quantities of water. Other than that you might just as well buy any kettle with a 1 cup marker on it. You can get kettles with a temperature setting like this one Philips HD4632/20 Eco Temperature Control Kettle, 3000 Watt, 1.6 Litre: Amazon.co.uk: Kitchen & Home which would give a small genuine saving. Note this kettle also claims to save 66% in energy by only boiling the water you need :)
     
  3. DOBLY

    DOBLY
    Well-known Member

    Joined:
    Oct 30, 2006
    Messages:
    1,736
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    116
    Location:
    Dunedin
    Ratings:
    +658
    Smells to me of marketing hype. There might be a small saving as the chamber that the water is heating up in is smaller than a regular kettle, so it comes to the boil sooner, but this will have a pretty small effect on the efficiency.

    I know that on our kettle, 2 mugs worth of water for tea comes to the "750" ml? mark, so that is how much I put in the kettle most often.

    I don't remember the last time I filled the kettle, only to pour some of the water away, unused.

    I suppose that their marketing has worked to some extent - I visited their website, watched the little video etc. but won't be buying one of their products...

    And as the old saying goes : always use freshly-drawn water - when making tea, as it tastes so much better than water that has been boiled time and time again.
     
    Last edited: Mar 15, 2013
  4. EarthRod

    EarthRod
    Distinguished Member

    Joined:
    Jul 15, 2008
    Messages:
    17,691
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    166
    Location:
    England
    Ratings:
    +7,787
    An electric kettle is not very efficient and an ECO electric kettle is a contradiction in terms.

    A better way is to put your cup of water in a microwave. Quicker to boil and much less power used.

    Care needed though! :)
     
  5. johntheexpat

    johntheexpat
    Distinguished Member

    Joined:
    Nov 15, 2006
    Messages:
    9,367
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    166
    Location:
    France
    Ratings:
    +2,811
    The heat capacity of water is about 4.2 J per ml per C. (IIRC)

    So to boil 500 ml of water from 10C to 100C uses 500 X 4.2 X 90 J which is a touch below 190KJ ( so a 2KW kettle would take about 85 seconds to boil it).
    You need maybe 300 ml for your cup, so the excess is 40% of that ie 75KJ

    75 KJ is 0.0208 of a KWh

    A Kwh is about 10p, so each excess cup wastes 0.208p. The cheapest kettle is £35.

    So, after 3500/0.208 cups of tea, you have paid for the kettle.

    Are you prepared to drink 17,000 cups of tea to save the planet?
     
  6. DPinBucks

    DPinBucks
    Well-known Member

    Joined:
    Dec 2, 2008
    Messages:
    6,404
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    136
    Location:
    Burnham, Bucks
    Ratings:
    +1,958
    Not necessarily.

    An electric kettle is 100% efficient; all the power is converted into heat. A microwave oven is about 60% efficient.

    So the latter gains when you're not wasting heat, such as the water left at the bottom of the kettle. Also, a microwave is not recommended for boiling water in a cup or mug; it can be very dangerous.
     
  7. EarthRod

    EarthRod
    Distinguished Member

    Joined:
    Jul 15, 2008
    Messages:
    17,691
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    166
    Location:
    England
    Ratings:
    +7,787
    We use a microwave to heat a couple of large mugs of water - 700 watts, clean water, no water wastage and only takes a few minutes. Not dangerous at all - timer switches power off. Clean, efficient, quick and easy.

    However, I didn't take into account the energy losses in a microwave:
    1. Heat generated from the magnetron.
    2. AC power transformer losses.
    3. The light in the microwave.
    4. Turntable motor drive.
    5. Control circuit.
    6. Microwave fan.

    The above account for about 35% energy loss in total, so the microwave requires about 1.1KW to deliver about 700W.

    A kettle is not 100% efficient - nowhere near. But it is certainly more efficient than a microwave taking the above losses into account.
     
  8. danmc_82

    danmc_82
    Well-known Member

    Joined:
    Jan 19, 2007
    Messages:
    5,629
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    136
    Location:
    Skynet Border
    Ratings:
    +1,212
    Affraid not, nothing on earth is 100% efficient.
     
  9. stanstedpete

    stanstedpete
    Active Member

    Joined:
    Apr 2, 2009
    Messages:
    71
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    8
    Location:
    Stansted
    Ratings:
    +16
    An electric space heater is virtually 100% efficient.
     
  10. danmc_82

    danmc_82
    Well-known Member

    Joined:
    Jan 19, 2007
    Messages:
    5,629
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    136
    Location:
    Skynet Border
    Ratings:
    +1,212
    Maybe 99% but like I said nothing is 100%. If you created something that was you'd be a billionaire.
     
  11. stanstedpete

    stanstedpete
    Active Member

    Joined:
    Apr 2, 2009
    Messages:
    71
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    8
    Location:
    Stansted
    Ratings:
    +16
    More like 99.99% - where else is the energy going to go?
     
  12. danmc_82

    danmc_82
    Well-known Member

    Joined:
    Jan 19, 2007
    Messages:
    5,629
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    136
    Location:
    Skynet Border
    Ratings:
    +1,212
    No where near 99.99%, look it up.

    Energy is used up as sound and light.
     
  13. EarthRod

    EarthRod
    Distinguished Member

    Joined:
    Jul 15, 2008
    Messages:
    17,691
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    166
    Location:
    England
    Ratings:
    +7,787
    There seems to be some confusion regarding AC power dissipated in an inductive load such as an electric heater.

    There are several different equations relating to types of power, ie resistance, impedance and reactive. Under a resistive/reactive load (for example an electric heater) the power is a function of the circuit's total impedance (Z) and not just it's resistance (R).

    So, total power in an AC circuit, such as an electric heater, both dissipated as heat and absorbed by impedance is measured in VA (Volt/Amps) and not Watts.

    Only power dissipated is measured in Watts, but that does not take into account the phase angle created by an inductive load.

    That is why there is no such thing as 100% efficiency, not even close - in fact nowhere near! There are other losses to take into account.

    Sorry for the technical crap - but things are not as simple as they seem.
     
  14. danmc_82

    danmc_82
    Well-known Member

    Joined:
    Jan 19, 2007
    Messages:
    5,629
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    136
    Location:
    Skynet Border
    Ratings:
    +1,212
    ^^^^ Finally someone who agrees :D My explanation was a bit more simple :laugh:
     
  15. stanstedpete

    stanstedpete
    Active Member

    Joined:
    Apr 2, 2009
    Messages:
    71
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    8
    Location:
    Stansted
    Ratings:
    +16
    My electric heater doesn't make any sound.

    Light and heat are the same thing - simply different frequencies.
     
  16. stanstedpete

    stanstedpete
    Active Member

    Joined:
    Apr 2, 2009
    Messages:
    71
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    8
    Location:
    Stansted
    Ratings:
    +16
    Let's keep it simple - we're not all physicists. If the energy put in doesn't come out as heat, in what form does it come out, and where does it go?
     
  17. stanstedpete

    stanstedpete
    Active Member

    Joined:
    Apr 2, 2009
    Messages:
    71
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    8
    Location:
    Stansted
    Ratings:
    +16
  18. danmc_82

    danmc_82
    Well-known Member

    Joined:
    Jan 19, 2007
    Messages:
    5,629
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    136
    Location:
    Skynet Border
    Ratings:
    +1,212
  19. stanstedpete

    stanstedpete
    Active Member

    Joined:
    Apr 2, 2009
    Messages:
    71
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    8
    Location:
    Stansted
    Ratings:
    +16
    You were right when you said that an electric kettle isn't 100% efficient, because not all of the heat generated fulfils the intended purpose of boiling the water - energy is lost to the environment through radiation, convection, as steam and as sound.

    In the case of a space heater the intended purpose IS to heat the environment - therefore the efficiency of the heater is virtually 100%. Even though some of the electricity used heats the heater itself, this stored heat is released to the environment when the electricity is switched off (in a system where the electricity is never switched off it becomes an infinitely small percentage).

    Whilst an ordinary space heater can never output as heat more than 100% of the energy input in the form of electricity, a heat pump can - in a well-designed system the heat output can be 3 to 4 times the electricity input and the theoretical limit is even higher.

    The real question, given the subject of this thread, is whether it would be possible to make a highly-efficient kettle (or equivalent) using heat pump technology?
     
  20. danmc_82

    danmc_82
    Well-known Member

    Joined:
    Jan 19, 2007
    Messages:
    5,629
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    136
    Location:
    Skynet Border
    Ratings:
    +1,212
    That doesnt make sense, how can a heat pump produce more heat than electricity going in? You either have one or the other.

    And even if it did, it doesnt make the unit 100% effecient. How much sound is produced?

    Regarding the space heater, what about electrical current producing magnetic waves as it travels down the copper wire, and you say theres no sound, there always is with electrical and mechanical devices. Even if its not audio-able to you.
     
  21. stanstedpete

    stanstedpete
    Active Member

    Joined:
    Apr 2, 2009
    Messages:
    71
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    8
    Location:
    Stansted
    Ratings:
    +16
    There are many sites where you can learn about heat pumps. This one has a calculator:

    Heat Pump efficiency calculator
     
  22. danmc_82

    danmc_82
    Well-known Member

    Joined:
    Jan 19, 2007
    Messages:
    5,629
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    136
    Location:
    Skynet Border
    Ratings:
    +1,212
    You miss my point, You cant produce more energy than what is being used to power it. Remember Einsteins quote.

    And remember heat pumps only work in very insulated homes due to the lower temperature of the water.
     
  23. stanstedpete

    stanstedpete
    Active Member

    Joined:
    Apr 2, 2009
    Messages:
    71
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    8
    Location:
    Stansted
    Ratings:
    +16
    The COP (Coefficient of Performance) is the ratio between the electrical energy going in and the heat coming out. Typically it will be 2 or 3 but heat pump manufacturers typically quote 4. Follow up the link I posted earlier to learn more.

    Insulation is not the issue - it's the type of heating. Underfloor heating is best, radiators really aren't suitable.
     
  24. johntheexpat

    johntheexpat
    Distinguished Member

    Joined:
    Nov 15, 2006
    Messages:
    9,367
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    166
    Location:
    France
    Ratings:
    +2,811
    Kettles aren't 100% efficient in the sense that you nearly always boil more water than necessary. Therefore boiling the excess water is inefficient. If you have twice the volume of water in the kettle than your mug will hold, then you are using 100% more electricity to make your cuppa than you need to.

    They are also not 100% efficient because generating electricity isn't 100% efficient, more like 40%. So it is a 60% loss to start with. (It may not be you losing it, but it still counts). And then there are transmission losses too.

    Gas may do better, but there are also significant transmission losses there. (The stuff comes, in part, from the other side of Russia, for goodness sake, it must take quite a lot of energy to get it half way across the planet.)

    If you want an environmentally friendly cuppa, there is a lot to be said for a Kelly Kettle

    Kelly Kettle® - Original & Best | Camping equipment | Camping gear | Survival kit - Home

    Just use some scraps of wood that are only going to decay anyway. No fossil fuel, no transmission losses and if you are having to collect sticks to boil a kettle, you take more care no over-filling it with water you won't use.
     
  25. riseabdn

    riseabdn
    Standard Member

    Joined:
    May 13, 2013
    Messages:
    7
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    1
    Location:
    Aberdeen
    Ratings:
    +0
    If you conccider the efficincy of a kettle is a function of the energy consumed during the boiling period against the energy gained by the water.

    In boiling the kettle, you will also:
    Produce sound
    Warm up the work surface
    Have heat loss though the sides
    Heat loss via evaportation

    to name but a few.

    Sadly, the marketing people believe a 1kW kettle is half the cost to run of a 2kW kettle and i a massive 1/3rd the cost to run of a 3kW kettle.

    If you concidder that one of the largest losses of the kettle after evaporation is heat losses from the side of the kettle.

    If you remember the loss is related to the Delta-T (temperature difference) between the hot thing and cold thing.
    This loss can be expressed in Watts of power which over time becomes energy in watt-hours, or watt-minutes in the case of a kettle.

    If we agree that a 1.5kW kettle heats water from 10C to 95C, just as a 3kW kettle heats water from 10C to 95C.

    If both kettles also had the same degree of heat loss, measured in W/K (1 K = kelvin = 1C of temperature difference).

    If both kettles were boiled at the same ambient temperature, then you will have a temperature difference (between the water and room) gradient.

    The greater the time it takes the kettle to boiler, will mean this gradient exists for longer so the losses are greater.

    As a result, if you run it though with numbers (real or for the sake of arguments), you find its more efficient to boil the water as quickly as possible from a point of view of case losses.

    An ideal kettle would be well insulated (nobody seams to insulate kettles!) and operate around the maximum a 13A socket could take, i.e 2.86 to 3.25kW.

    If the discussion even needs to come down to losses in the wiring in the house, then the street then the power station then its such a fine line as to make no difference at all.

    That said, when designing the power network in, say, a hotel. That horrible 700w kettle can save £10's of thousands on the grid connection costs when the engineer works out the diversity loadings.

    Lower power kettles would also make life easier for these guys : BBC video on 1 million kettles


    Stuart
     
  26. stanstedpete

    stanstedpete
    Active Member

    Joined:
    Apr 2, 2009
    Messages:
    71
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    8
    Location:
    Stansted
    Ratings:
    +16
    It is - or certainly was - possible to buy an insulated electric kettle (I used to have one). This improves efficiency by limiting heat loss during boiling and also afterwards (if more water than needed has been boiled - either inadvertently or because less than the minimum was needed).

    Sound is a factor, but a relatively minor one. Evaporation is more of a problem, but is limited by having a kettle that shuts off promptly when boiling point is reach.

    A bigger potential saving can be made by using a kettle that will switch off at a given temperature - if you're making coffee you don't want the water to be at 100C. However when Which? reviewed a kettle with a thermostat they found it was inaccurate. Good idea, though.

    Something else to consider is that water for drinking is usually drawn from the mains, typically at 10-15C. If the ambient temperature is warmer than this there's a potential saving from filling the kettle in advance (or filling a jug) and allowing it to warm.
     
  27. riseabdn

    riseabdn
    Standard Member

    Joined:
    May 13, 2013
    Messages:
    7
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    1
    Location:
    Aberdeen
    Ratings:
    +0
    At a company i used to work for, we had a normal stainless steel kettle and my college was really bad for boiling the full thing, making a phone call whilst the kettle was boiling then forget about it.

    After the thing was boiled 4 times without ever having been poured one day, i took some high temperature solar thermal insulation and used an epoxy adhesive to glue a 20mm thick layer around the kettle.

    An hour after boiling, the thing was still hot enough to make a cuppa. I remember looking into developing it as a product but had no idea how at the time.
     
  28. DF Eco Worrier

    DF Eco Worrier
    Novice Member

    Joined:
    Oct 3, 2018
    Messages:
    1
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    1
    Location:
    Warwickshire
    Ratings:
    +1
    Best option is getting into good habits with support from the right technology. The good habits are all to do with not overfilling kettles and boiling only what you need. The right technology is to includes minimizing losses through good energy rating, double wall insulation and temperature control. Some drinks don't need water at 100 deg C such as green tea, speciality teas and instant coffee so temperature setting is good.

    For example a 3 Kw kettle in use for 30 minutes a day, unit cost 10 p will costs about £55 per year to run.
     
    Last edited by a moderator: Oct 3, 2018

Share This Page

Loading...