Page 1 of 5 12345 LastLast
Results 1 to 10 of 44
  1. #1
    Banned
    Join Date
    Jan 2005
    Posts
    711

    Default Hot water cyclinder:How does it work and how much power....

    Ok i have a standard hot water cylinder at my house, if I used up all the hot water from it,does to hot water cyclinder use MORE power to heat the stone cold water back into hot water? And once and hot water has reached the correct temperature does it go into a kind of standby mode where it uses LESS power then when it's heating cold water to hot water?

  2. #2
    Senior Member godfather's Avatar
    Join Date
    Dec 2004
    Location
    Central New Munster
    Posts
    3,053

    Default Re: Hot water cyclinder:How does it work and how much power....

    Its just like your electric jug, except it has a thermostat and should be well insulated to reduce most of the heat escaping out the sides..

    When the water reaches the desired temperature, the thermostat switches off the power to the element. As the water slowly cools a bit, the thermostat will cut in, allowing the element to heat it up a little bit again so its always at the right temperature.

    The power used is dependent on the power needed to raise incoming cold to the set thermostat temperature. Use a little hot water, the overall temperature drops, the element comes on for a while.

    Use a lot, the element comes on for a lot longer.

    Power use is directly proportional to water running out the hot tap.

    Add to this that it may also be dependent on what tariff you are on with your power company, they may stop the element coming on at peak times, the re-heating will be delayed until off-peak.

  3. #3
    Pedant and proud of it
    Join Date
    Dec 2004
    Location
    Christchurch
    Posts
    6,047

    Default Re: Hot water cyclinder:How does it work and how much power....

    The amount of energy needed to heat water depends on the quantity of water, and the temperature difference required. There is always a bit more needed, because the water isn't held in a lossfree container. You have to heat the cylinder (which is why cylinders always used to be made of copper --- its "specific heat'[ is small), and the insulation.

    When the water is up to temperature, the only energy used (as long as there is no draw off) is that needed to replace the losses through the insulation to the outer shell (where it is lost to the air), and any losses through conduction to the pipes.

  4. #4
    Banned
    Join Date
    Jan 2005
    Posts
    711

    Default Re: Hot water cyclinder:How does it work and how much power....

    so here a 2 scenarious:

    1)i use up all the hot water each day and the water is stone cold.

    2)i DON'T use up all the hot water each day(say i only use half of the hot water)


    What scenario would use the MOST power each day?

    And how much approximate power do hot water cyclinders use per month on scenario 1 and scenario 2?

  5. #5
    Senior Member godfather's Avatar
    Join Date
    Dec 2004
    Location
    Central New Munster
    Posts
    3,053

    Default Re: Hot water cyclinder:How does it work and how much power....

    1) The amount of power depends on the amount of hot water used (the amount of water running out the hot tap)

    2) As above but if its the same cylinder, and you have only used half the heated water it will cost half as much as heating it from cold.

    We don't know the cylinder size, so we cannot tell you how many units it would cost to completely heat a stone cold cylinder.

    Again I repeat, the cost is directly proportional to the amount of water you use. There is no magic involved.

  6. #6
    In a 1920s time warp Terry Porritt's Avatar
    Join Date
    Dec 2004
    Location
    Upper Hutt
    Posts
    4,500

    Default Re: Hot water cyclinder:How does it work and how much power....

    Try taking a cold shower each morning, it has a remarkable curative effect on the brain cells:
    http://www.associatedcontent.com/art...ers_arent.html

  7. #7
    Pedant and proud of it
    Join Date
    Dec 2004
    Location
    Christchurch
    Posts
    6,047

    Default Re: Hot water cyclinder:How does it work and how much power....

    Say you've got a 200 litre water cylinder.

    Ignoring the losses:

    to heat 200 kg of water from 10 degrees C to 60 degrees will take 50x200 000 calories, which would be 4.184 x 10^7 joules, which comes to 4.184/3.6 x 10, 11.6 kWh. I think that's right.

    If you use only half the water each day, you will use half that much electricity to heat it.

    Add a bit for the losses. If you use all that water in one long shower, you will lose less heat to the pipes. If the pipes cool down and have to be heated again you lose more. You pay to heat the cold water in the pipes which comes out when you first turn on the hot tap, remember.

  8. #8
    Lets play Metla's Avatar
    Join Date
    Dec 2004
    Location
    Mega City One
    Posts
    16,182

    Default Re: Hot water cyclinder:How does it work and how much power....

    Bugger that, Buy an on-demand water heater.
    better Dredd then dead

  9. #9
    Senior Member godfather's Avatar
    Join Date
    Dec 2004
    Location
    Central New Munster
    Posts
    3,053

    Default Re: Hot water cyclinder:How does it work and how much power....

    Quote Originally Posted by Graham L
    11.6 kWh. I think that's right.
    11.67 kWh according to me, but I am not the pedant here...

    Quote Originally Posted by Metla
    Bugger that, Buy an on-demand water heater.
    The on demand (electric) waterheater will use 11.67 kWh as well. Just no ongoing storage losses, but then the tariff is usually higher in c/kWh as its "uncontrolled load".

    Cheap answer - don't shower.

  10. #10

    Default Re: Hot water cyclinder:How does it work and how much power....

    Those on demand gas water heater are the best

Similar Threads

  1. In hot water
    By beetle in forum PC World Chat
    Replies: 7
    Last Post: 18-11-2007, 04:57 AM
  2. Replies: 15
    Last Post: 06-06-2007, 06:51 AM
  3. Replies: 1
    Last Post: 19-06-2006, 06:21 PM
  4. Electrics and water.....
    By beetle in forum PC World Chat
    Replies: 5
    Last Post: 09-02-2006, 07:23 PM
  5. Water Cooling
    By ApeNz in forum PressF1
    Replies: 13
    Last Post: 29-10-2004, 10:37 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •