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    jstrange's Avatar
    jstrange Posts: 2, Reputation: 1
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    #1

    Jun 30, 2010, 04:06 PM
    3-phase vs single phase power usage
    My currnet a/c is on 3-phase and I'm going to replace it. I want to get a 5 ton 16 SEER ($1500 gov't rebate)but they are available in only single phase. I'm wondering if it will cost significantly more to run a new 16 SEER unit on single phase than a new 13 SEER on 3-phase.
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
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    #2

    Jun 30, 2010, 05:12 PM

    Cost in terms of operation, no. 5HP single phase is also 5 HP 3 phase.

    SEER takes into account the conversion of electrical energy to cooling, meaning power to cool.

    Installation of 3 phase is mixed. Wire costs less. Breakers have to be larger for single phase and smaller, but with an extra one for 3 phase. The conduit may or may not have to be re-sized. Wires would have to be larger.

    3 phase power loss protection is usually added.

    Three phase is much more reliable. There is also less power spiking.

    A 3 phase motor is usually more efficient, but your considering the system.


    A 3 phase power has better starting torque.
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
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    #3

    Jul 1, 2010, 04:36 PM

    If yo were comparing HP to HP on single and 3 phase, the 3 phase system would be more efficient and cost less to run.

    Since your comparing SEER, efficiencies of the various parts are taken into account.

    The real difference is that 3 phase is more reliable and may or may not cost more to install.

    We don't get notified with Agree/disagrees.
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