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  1. #1
    Join Date
    May 2013
    Posts
    3

    Help with Carrier AC decision

    Hoping to solicit some advice from the pros here... We currently have a Carrier Infinity 96% efficiency furnace, variable speed blower, 2 stage gas valve, 80k btu furnace with the Infinity controller. The AC portion was an existing install, Kenmore 14SEEER. The compressor is making a very loud 'bang' every time it kicks off and we've had several techs from different companies give us bids to fix it. All bids have been what I consider to be too much in comparison to investing in a new system.

    In any case, we are looking at the Carrier Infinity and Bryant Evolution communicating series of AC and heat pumps. I do know I'd like at least a dual stage compressor for comfort, but beyond that I don't know what to do. The sales guys are all trying to sell the highest seer available (obviously) and are pushing the heat pump as a good option saying that they'll both save us a ton of money. I'm not so sure and the information out there on money savings with a higher seer rating is mostly sales literature.

    In AC, we are looking at the 24ANB6, 24ANB7, and 24ANB1 in a 3 ton with 3.5 ton coil. Manual J calculations have been performed by 2 of the bidders with the same results.

    In heat pump, looking at the 25HNB6, 25HNB9, and 25VNA0 in a 3 ton with 3.5 ton coil.

    Can anyone advise if there is any financial benefit to going with the higher SEER/EER rated units? I'd love to lower our utility bills but the higher units are significantly more expensive.

    Live in Utah, where summers are hot 90-100*, winter is cold 10-40*, and spring and summer can be mild or any combination thereof. Rates for our power are as follows:

    Summer:

    1-400kw 8.6c/kw
    401-1000kw 11.2c/kw
    1001+kw 14c/kw

    Winter:

    1-400kw 8.6c/kw
    400+kw 9.6c/kw

    Rates for the gas as follows:

    Summer:

    1st 45dec 6.95/dec
    45+dec 5.69

    Winter:

    1st 45dec 7.91/dec
    45+dec 6.52/dec

    Thanks for any help or advice you can give!

  2. #2
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    You are facing hte same decision I made when installing my downstairs system recently. You have fairly low gas rates compared ot electric rates, so you'll gain a little in milder weather with dual fuel. Personally, I like the extra 2 stages of heat, expecially with a 2 stage furnace.

    With dual fuel and in a dryer summer climate and with 4 seasons, there's not much benefit to the Greenspeed. Greenspeed makes more sense in all electric or a propane dual fuel setup. It actually has a lower COP below abotu 40F than a Infinity 19 HP. The Infinity 19 is also quite a bit quieter than the Infinity 16/17. I have both. The 17 is very quiet, but hte 19 on low stage is almost whisper quiet cooling. A little louder in heating, but not much.

    The heat pump with those low gas rates won't "save you a ton", but again the extra stages of heating are very nice in mild weather since you existing furnae only drop to about 50k BTU in low stage. The heat pump will fill the gap with heat outputs over 35F of between about 24-39k depending on whic hstage and outdoor temps. Low stage on you furance is probably abotu 750CFM. Low stage on the heat pump is around 550-700 depending on outdoor temps. Infinity will vary the blower speed depending on outdoor temprature in heating and in cooling will vary based on outdoor temp and indoor humidity. IN comfort mode the air tmeps are kept pretty warm on the heat pump. Its' never cool or drafty. If sized right then, you system would be running continously with either the heat pump or furnace below abotu 40F. Right now it probably doesn't run continous until it's under probably about 20F? That's a big jump in comfort. Less cycling means more even temperatures.

  3. #3
    Join Date
    May 2013
    Posts
    3
    Thanks for the advice, I appreciate the insightful post. Our furnace doesn't really run continuously at all, even when it's 20* (although it will run quite a bit more). We've replaced all the doors and windows in our house and done quite a bit of insulation, so that has helped with keeping the house moderate.

    So it sounds like I have little to gain in cutting down our bills by going to a heat pump and that the end result would be mostly comfort? Is a higher seer system worth going to (17, 19, or 21 vs the 16) or is the savings so small the payoff would take many years?

    One of my contractors advised me to go with a 4 ton vs a 3 because 'it would cool the house down faster and run less in the summer'. All the others are recommending a 3 ton with a 3.5 ton coil inside. The current 3 ton does run for hours at a time in the summer trying get the house down in temperature but I had always thought this was the most efficient way for AC to run. All the contractors say they have run a load calculation.

  4. #4
    Join Date
    May 2013
    Posts
    3
    One more question I forgot to ask... Is the recommendation to upside the coil to 3.5 ton with a 3 ton compressor based on an improvement in efficiency or just selling more equipment?

    All the contractors are telling me it's ok to keep the old lineset and flush for the new refrigerant. I did read somewhere that the newer units use a larger size line and wondering if this is true?

    Thanks!

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