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  1. #1
    Join Date
    Feb 2011
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    Is a dual stage heat pump compressor reliable?

    Hello and thank you for this service. I live in Jacksonville, Florida. I have a 20 year old Trane heat pump that I am replacing. I have a few questions I need professional advice on. I have a 5 ton heat pump for 2600 sq ft with two returns in the house.

    1. Are dual stage heat pump compressors reliable? One Carrier dealer recommends it (Performance Series) and another says to stay away from all dual stage heat pumps as the compressors have a very high failure rate, including Carrier. The second dealer says there is no savings in my electric bill to the two stage heat pump system either and that the single stage Comfort series is the way to go. Who is right? Do dual stage have high fail rates? And is there really no savings?

    2. Of course, I have to replace the air handler. Again, one contractor tells me I should go with the variable speed with a thermidistat and the second says that I should not need a variable speed air handler. What is recommended? Will the variable speed provide better comfort? What about additional savings in electric costs? The variable speed is about $ more.

    3. The return duct work. Again, another contradiction. Contractor one says that my 18" return duct work will have to be replaced with 20" up to the box, where the duct splits. The second contractor says the 18" duct is perfectly fine because I have 2 positive returns. Who is right?

    As you can see, I have two entirely different proposals from two reputable Carrier dealers; each having received their own "awards" for various reasons. I need some very objective advice as to what I should do to replace this unit. The difference is cost is almost $ and I can't afford to make the wrong decision.

    Thanks to all in advance for your valuable opinions and advice.
    Last edited by beenthere; 02-21-2011 at 06:22 PM. Reason: price

  2. #2
    Join Date
    Feb 2011
    arlington va
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    Dual Compressor just as reliable

    1.A dual stage compressor is no more efficient than a single stage as a function. However dual-stage compressors only come on more efficient models. The reason is because the more efficient models are considered a premium item. Premium items have more features(as with most products), the true function of a two-stage compressor is the two stage capability. Just like a two-stage furnace it is able to operate at lower speeds at more moderate outdoor temperatures thereby circumventing the "on/off" necessity of a conventional single speed/stage system. The first stage of operation is 66% of total capacity and second stage being 100%. On the performance system this is controlled by the fact that the control board on the outdoor unit has an ambient sensor/temperature sensor. This creates comfort as it is able to cool more constantly. You definitely want to incorporate an infinity control with it as the performance series has an infinity board. And an infinity air handler, fe4anf005 or 006 will work. As for the 5 ton unit it seems a bit oversized however if you have poor insulation that would explain the necessity. The variable speed motor is much more efficient than a single speed motor. However if you get the two-stage unit definitely go with the variable speed or infinity unit for communicating functionality. As for the return duct a five ton system has a 20" line going into the unit, the correct answer is a 18" return is fine and 20" which not change things very much. No need to spend money on adapting the return, save it and put it towards the better equipment, at least that's what i would do. Hope this helps.

  3. #3
    Join Date
    Jul 2008
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    It depends on the size of the equipment and setup, but 2-stage scroll compressors can provide an energy efficiency gain in 1st stage.

    For example, my 3-ton 2-stage scroll compressor on my heat pump in cooling mode is about 6.4% more efficient in first stage. The numbers don't hold across all sizes so your results will vary.

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