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1 Phase vs 3 Phase - costs

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  • 11-05-2009 10:54pm
    #1
    Fishtits
    Closed Accounts Posts: 1,382 ✭✭✭


    I want to heat ~100l of water on a daily basis.

    I have the choice of using a single phase element or a three phase one.

    Which is cheaper?

    My own feeling is that the three phase option is better.

    Both outputs are available at site so only running costs relevant.


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    #2
    Pete67
    Registered Users Posts: 1,257 ✭✭✭Pete67


    I'd guess no difference in running costs, if the site has a three phase supply then it will have a three phase meter. All loads, single or three phase go through the same meter. The three phase element may have a higher rating which will heat the water faster, which may be an advantage. It will also help the keep the load on each phase balanced, although on a large site the difference would be negligible.


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    #3
    davelerave
    Closed Accounts Posts: 1,712 ✭✭✭davelerave


    the running costs will be the same for either.3-phase or single phase .prob a 3-phase element for balance .installation and replacement costs may be higher for 1 3-phase element.2 SP elements would give some backup .whats the water like?


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    #4
    Fishtits
    Closed Accounts Posts: 1,382 ✭✭✭Fishtits


    Pete67, Yes three phase meter.

    Interesting. But, if costs are the same, how can the three phase heat faster?


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    #5
    Carlow52
    Closed Accounts Posts: 2,389 ✭✭✭Carlow52


    Fishtits wrote: »
    Pete67, Yes three phase meter.

    Interesting. But, if costs are the same, how can the three phase heat faster?

    I suspect they mean th total cost will be the same but maybe incurred faster:)

    the energy required is the same


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    #6
    Michael Collins
    Moderators, Science, Health & Environment Moderators Posts: 1,849 Mod ✭✭✭✭Michael Collins


    Carlow52 wrote: »
    I suspect they mean th total cost will be the same but maybe incurred faster:)

    the energy required is the same

    Exactly. It's like running and walking up the stairs, all things being equal they require the same energy - but running takes more "power"...


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    #7
    Pete67
    Registered Users Posts: 1,257 ✭✭✭Pete67


    Fishtits wrote: »
    Pete67, Yes three phase meter.

    Interesting. But, if costs are the same, how can the three phase heat faster?

    cost per kWh is the same for single phase or three phase. It takes the same amount of energy to heat the water from say 10C to 60C irrespective of how long it takes (assuming the tank is well insulated) For your example, to heat 100 litres of water from 10C to 60C takes 20.9MJ, which is 5.8kWh. So a 1 kW element will heat it in 5.8 hours but a 5kW element will do it in 1.2 hours. Both will use the same amount of electricity in the process.

    A three phase element may have a higher rating and if it does it will heat the water faster. If both the single phase and three phase elements have the same kW rating, they will take the same amount of time to heat the water and the energy cost will also be the same.


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