which is more efficient?

Discussion in 'Electrical Forum discussion & Blog' started by GabeS, May 31, 2009.

  1. GabeS

    GabeS Remodel Contractor

    Jan 10, 2007
    Remodel contractor
    Brooklyn NY

    I'm going to buy an air conditioner and am trying to figure out which has a lower operating cost. The AC that is 110 volts or the AC that is 220 volts. The 110 is 15,000 BTU and the 220 is 18,000 BTU, but lets just pretend they are exactly the same BTU.

    Is the 220 more energy efficient because it uses less amps or are they exactly the same?


  2. jimbo

    jimbo Plumber

    Aug 31, 2004
    San Diego, CA
    Other things being equal, they consume the same WATTS, which is what you pay for. 10 amps at 120 volts is 1200 watts. 5 amps at 240 is also 1200 watts. There are some advantages like for the same KW energy usage, you could use smaller wires, and since given same wire size, the higher amp unit would produce more heat ( I-squared_R) , and heat is wasted energy.

    In the case of a window air conditioner, none of the above would be anything to lose sleep over.
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  4. Thatguy

    Thatguy Homeowner

    Aug 27, 2008
    A bounty hunter like in "Raising Arizona"
    15000 BTU/hr = ~4400 watts. If it only pulls 1200 watts (1200/110 = 11A) from the wall the Coefficient Of Performance [COP] is 4400/1200 = 3.7.
    If the 18000 pulls 1200w (1200/220 = 5.5A) it's COP is 5300/1200 = 4.4 so it's more efficient.

    Look on the nameplates to see how many amps each of these draw. Due to Economy of Scale I'd expect the 18000 would have a higher COP.
    Last edited: May 31, 2009
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