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  1. #1

    Two-stage vs. Single-stage Compressor

    Hey! I have now narrowed the choice for my replacement heat pump systems to two local companies; one installs American Standard and the other Lennox. Both HVAC makers offer a 16 SEER heat pump, which has a two-stage compressor (Am. Std. Heritage 16 and Lennox Elite Series XP16). I am wondering if there are any known issues with this type compressor? I plan to use variable speed air handlers and in reading the brochures, et al. it sounds as if they are much more energy efficient, thus less costly to operate than a single-stage compressor. Is this true? And the cost of the two-stage heat pumps are not that much more than the lower 14 SEER single-stage units. Especially since I am having to buy 3 separate systems -- I think the dealers feel sorry for me and are ready to deal! Should I seriously consider this two-stage type compressor or stay with the tried and true single-stage? Your comments are welcome!

  2. #2
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    Your money! With the unloading scroll, net effect on low is about 80% of high. Will that be a big enough deal to justify the money? I wonder... Personally I don't see one in my future even though I like neat stuff.

    I also noticed in Trane's specs that the latent capacity (translation: humidity removal) on low with the 16i isn't that great. Can't comment on Lennox.

    Personally I'm more fired up about the 50/100% split of the top Trane model and the mid line Bryant/Carrier units.

  3. #3
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    On the mid temp days, you get good use out of the 2 stage systems.
    As baldie pointed out, on the mildest days with high humidity, the Scrolls lack latant ability.
    With a good stat, Honeywell IAQ. The blower can be kept at a lower speed to compensate for this.

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    But if you can afford them, and they're sized right, you'll wish you had the from the beginning.

    If they're over sized, you could end up cursing them.
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  4. #4
    Quote Originally Posted by BaldLoonie View Post
    Your money! With the unloading scroll, net effect on low is about 80% of high. Will that be a big enough deal to justify the money? I wonder... Personally I don't see one in my future even though I like neat stuff.

    I also noticed in Trane's specs that the latent capacity (translation: humidity removal) on low with the 16i isn't that great. Can't comment on Lennox.

    Personally I'm more fired up about the 50/100% split of the top Trane model and the mid line Bryant/Carrier units.
    Thanks for your feedback. It is American Standard or Lennox equipment only at this time. Humidity is a concern as I live in South Georgia. So, would it be your opinion that I would be just as pleased with the comparable 14 SEER models from these vendors using a variable speed air handler? I'd save about $1k off the total cost.

  5. #5
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    My vote is save the thou! For that you can blow more insulation in the attic or buy a few new windows!

    Get the Vision Pro IAQ control like been said, it can be used for extra dehumidification out of any variable speed blower.

  6. #6
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    Quote Originally Posted by BaldLoonie View Post
    Your money! With the unloading scroll, net effect on low is about 80% of high. Will that be a big enough deal to justify the money? I wonder... Personally I don't see one in my future even though I like neat stuff.

    I also noticed in Trane's specs that the latent capacity (translation: humidity removal) on low with the 16i isn't that great. Can't comment on Lennox.

    Personally I'm more fired up about the 50/100% split of the top Trane model and the mid line Bryant/Carrier units.
    I am interested in understanding better what you said about the XL16i latent capacity. Is it OK to assume ARI rating conditions and 3.0 ton sizing? For the 4TWX6036B1 model I see 36,800 total BTUH if you go with Trane's best 17.0 SEER rating using 4TEE3F40A1 air handler, 27,200 BTUH sensible. If I understand correctly that is 74% SHR (sensible heat ratio) for this combo. Is that bettered by the other equipment you have researched?

    The other ARI matches usually yield lower capacities, but the couple of combos that I looked at, were nearly the same SHR. It is apparent that most of these combinations are on the light side for a nominal 3.0 ton size. With the XL14i heat pump it appears easy to get 38,000 BTUH total and 27,600 sensible for a SHR of 73%. These numbers are from some Trane technical documents that I got ahold of, if you want to dig into details I could give exact identity of them (but I figure you probably don't).

    Every time I read something of yours it seems right, so I just wanted to get a better understanding of what you said. So far I read that a Trane model might require a higher nameplate tonnage in some cases, to get actual BTUH capacity a house needs.

    Thanks -- Pstu

  7. #7
    Join Date
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    Well, I disagree, I think the unloading scroll is a great advancement and all it is is a DC solenoid. Nothing to really break. I live in central VA with a similar load as you have in GA. I got the two stage scroll and see no need to connect advanced dehumidification controls because the latent work is being done by added run time. I dont like the 50/100 units because of the added compressor or in many cases added contactor. Some have poor latent capcity when at lower stage, but consideration needs to be given that it will shift into high more often.

    Dont get me wrong, Bald is my hero too, but living up north, he'll tell you that a 2 stage heating system is better than a single stage. You my friend, live in the south where cooling is a priority. Fact is, he cant justify the cost of no significant cost savings with 16 SEER but on those mild days that cycle the units, nothing gets done and humidity is not dealt with when the unit is off.

  8. #8
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    Quote Originally Posted by WayDownSouth View Post

    It is American Standard or Lennox equipment only at this time. Humidity is a concern as I live in South Georgia. So, would it be your opinion that I would be just as pleased with the comparable 14 SEER models from these vendors using a variable speed air handler? I'd save about $1k off the total cost.
    COMFORT (humidity and noise) and cost are rather $ubjective.

    The use of 2-stage would improve humidity control in the shoulder seasons as docholiday mentioned .

    MANY Mild days in the rather lengthy shoulder seasons of April - May and Sept - Nov in South Georgia. So I would opt for the 2-stage compressor and variable speed air handler to improve humidity control during your off-peak cooling period$.
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  9. #9
    In a warmer climate where cooling is used more often look at the EER value instead of the SEER rating. A five ton Heritage at 16 SEER will give you a 10.7 EER value where the Lennox Xp at 16 SEER will give you 11.5, a Rheem Prl will give you 12.15 and a Carrier Infinity 16 will give you 11.1 so there is a farily large difference between brands.

  10. #10
    Quote Originally Posted by buddylee View Post
    In a warmer climate where cooling is used more often look at the EER value instead of the SEER rating. A five ton Heritage at 16 SEER will give you a 10.7 EER value where the Lennox Xp at 16 SEER will give you 11.5, a Rheem Prl will give you 12.15 and a Carrier Infinity 16 will give you 11.1 so there is a farily large difference between brands.
    Thanks! Can you give me the EER value for a three ton Heritage 16 and also a Heritage 14 using a variable speed air handler? Then I can make an apples to apples comparison.

  11. #11
    The 14 SEER Heritage will give you an EER of 11 to 11.4 depending on the air handler model with an average cooling cost of $240 and heating cost of 550.
    The 16 will give you 11.4 to 12.4 "" "" $190 and 500.
    This is according to ari directory but with different climates the average cost could change rapidly.

  12. #12
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    pstu, in Trane's specs, available on their dealer site, they showed the 16i in most common matches having around a .8 SHR on low speed. The .73 that ARI shows is high speed.

    So Doc, is there that much difference between high & low with the unloading scroll? Even Copeland admits capacity on low is more like 80% of high than the 67% figure usually thrown around. Rheem's SHR on the RASL is .77 on low so a bit better than the Trane. You think the slightly longer run periods makes up for the higher SHR? On that system, high is .74 sensible.

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