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  1. #1

    3-phase compressor vs. single phase ?

    I am building a new home (10,000 sq. ft. AC space). The old home I tore down had 3-phase power to the older AC's. My contractor wants to replace them with single phase AC's believing them to be better.

    Since I have 3-phase power available to me - shouldn't I use that benefit?
    Who makes 3-phase AC compressor's for residential use?

  2. #2
    Join Date
    Dec 2007
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    I would probably keep the 3 phase since you have 10k sq ft you could probably step-up to a commerical size unit that would use 3 phase.

  3. #3
    Join Date
    Jul 2000
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    The question you need to be asking first is of your electrician. Have them explain to you the pros and cons of 3 phase in your new home as far as meter charges, peak charges, wiring charge differences etc.. Once you have that question answered to your satisfaction then it's time to move on to which type of AC equipment is a better choice as far as operational costs and preferences. It's possible that your contractor (the techs) has limited experience with commercial 3 phase equipment and is concerned with service capabilities in the future.

    Condensing units max at 5 tons on single phase, but so do residential furnaces as far as capacity to move the required air.

    Bottom line is you're building a new house and have a perfect opportunity to start fresh and get the best systems and reliability that will give you the best chance at trouble free use for many years to come. Clean the slate so to speak and look at everything from a fresh perspective.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  4. #4
    Join Date
    Sep 2006
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    Quote Originally Posted by mjz2 View Post
    I am building a new home (10,000 sq. ft. AC space). The old home I tore down had 3-phase power to the older AC's. My contractor wants to replace them with single phase AC's believing them to be better.

    Since I have 3-phase power available to me - shouldn't I use that benefit?
    Who makes 3-phase AC compressor's for residential use?


    Most typical US systems are single phase as that is what most homes have. Some of those manufacturers offer their systems in three phase also, but not sure that it really does anything for you.

    Since you have not yet determined what your HVAC system is going to be, you may want to look into the fully modulating systems (known as VRV or VRF) available from several Japanese manufacturers such as Daikin, Sanyo and Mitsubishi.

    Each of these manufacturers offer single phase systems in the 3 - 5 ton range for typical residential applications. These systems are the smaller version of commercial versions three phase systems that start at around 6 tons. They are available as either a heat pump or a heat recovery unit. Heat recovery can cool areas at the same time that it heats others. Not sure where you are located, but the heating capacity of inverter systems is significantly better than the typical US type system. That, plus you can size these systems to the higher of your cooling load or heat load as you don't have to worry about oversizing them.

    The beauty of these is the fully variable capacity of the outdoor unit. As an example the Daikin can operate in a range of 14% to 100% (others are similar) of the rated capacity with nearly seamless steps in between. This is done using inverter technology.

    One outdoor unit connects to a dozen or so indoor units that operate as separate zones. The indoor units are also fully modulating in capacity, adjusting the refrigerant flow and fan speed to maintain a certain output temp. The refrigerant piping is all that goes to each indoor unit which eliminates the complicated, oversized duct work in the typical US type zoned system. Indoor units can be either ducted units (which are quite small physically) or ductless, depending on your application.

    The system is fully communicating with all indoor and outdoor units connected to a central controller that can be installed in an out of the way location while each zone will have a small match book sized sensor.

    These systems, and this technology, is the direction of HVAC and has been used outside of the US for decades as most of the world has higher energy costs than the US.

  5. #5
    Thanks for the update - I will look into the variable units! Seems like a smarter way to go.

  6. #6
    Join Date
    Jan 2004
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    Lancaster PA
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    3 phase is current exempt from the 13 SEER regulation.
    So you may find better efficiency with single phase.

    Don't believe the hype that 3 phase is more efficient then single phase when it comes to cooling you home.
    A 15 SEER single phase is more efficient then a 10.9 SEER 3 phase.
    Next, not all resi techs are comfortable, or good working on 3 phase equipment. So keep service down the road in mind.
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  7. #7
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    Sep 2006
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    Quote Originally Posted by mjz2 View Post
    Thanks for the update - I will look into the variable units! Seems like a smarter way to go.
    Not sure about the others, but Daikin has just released the VRVIII which has significant improvements from the prior generation. Cooling EER at nearly 13 and it is better at part load conditions (probably over 20). At this point not a lot of info available on the web site, but a Daikin qualified contractor should have some good info to share with you.

    Good luck.

    http://www.daikinac.com/commercial/d...-%20Daikin.pdf

  8. #8
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    Before you have one of those installed. Better check to see if there is more then one contractor in your area that can work one them.
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    How many times must one fix something before it is fixed?

  9. #9
    My old house had 3-phase (Ruud) and Facilities Mechanical (commercial) did the maintenance work. I have asked them to look into doing this job for me, but my contractor has his own guy (who he likes a lot) and he is strongly recommending single phase for the reasons cited earlier in this thread.

    I just want to go the best route since this is a new Home. I am located in Houston. AC is vital to survival or you die.

  10. #10
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    If your builder isn't ruling out your prefered congtractor. Have them give an estimate using single phase equipment.
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    How many times must one fix something before it is fixed?

  11. #11
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    Jun 2003
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    Chicago, IL
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    In many areas the power company charges extra for residential 3 phase service. Even though you already had 3 phase in the old house, you may have to pay alot to get it hooked up to the new house. Some even have a monthly surcharge for 3 phase. Before considering 3 phase equipment, check if you will be subjected to these charges.

    also take into account that 3 phase air conditioners usually are less efficient because of their exemption from efficiency requirements like beenthere said.

    they are generally more expensive because they sell less of them

    on the plus side they are more durable and have fewer (but more expensive) parts.

  12. #12
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    Des Plaines,IL
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    Quote Originally Posted by beenthere View Post
    3 phase is current exempt from the 13 SEER regulation.
    So you may find better efficiency with single phase.

    Don't believe the hype that 3 phase is more efficient then single phase when it comes to cooling you home.
    A 15 SEER single phase is more efficient then a 10.9 SEER 3 phase.
    Next, not all resi techs are comfortable, or good working on 3 phase equipment. So keep service down the road in mind.
    Will new 3-phase R22 equipment stop being made after Jan 1, 2010?
    Stuart
    Lack of airflow destroys compressors.

  13. #13
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    Jan 2004
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    Yep.

    The phase out is on the R22 refrigerant, and not based on weather its single or 3 phase electric.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

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