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  1. #1
    Join Date
    Aug 2009
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    16

    Two Stage or Single Stage Pump?

    I've got a heat pump quote with one unit with a two-stage pump and one with single-stage, both units have variable speed fan on air handler. Contractor included estimated energy use/cost. There is so little difference that I'd have to keep the system for 20 years to justify cost of two-stage pump. What is the advantage of a two-stage pump and when would you consider using it?

  2. #2
    Join Date
    Mar 2007
    Location
    South Texas
    Posts
    216
    Most of the time your comfort level is better, air flow quieter and more energy savings than what most contractors can guarantee. Due to the lower humidity we are able to run our temperature higher in the cooling season and still feel comfortable.

  3. #3
    Join Date
    Aug 2009
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    16
    SouthTex, maybe I need more knowledge about what the two-stage pump does and how it operates. The compressor pump moves the refrigerant throught the system and produces a high and low side. Are both stages/pumps the same size? In a two-stage system under what conditions does the second stage run and when does the first stage run?

  4. #4
    Join Date
    Jun 2007
    Location
    The Twilight Zone
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    2,964
    Quote Originally Posted by pieatro View Post
    SouthTex, maybe I need more knowledge about what the two-stage pump does and how it operates. The compressor pump moves the refrigerant throught the system and produces a high and low side. Are both stages/pumps the same size? In a two-stage system under what conditions does the second stage run and when does the first stage run?
    What part of the country?

    I would consider a 2-stage condenser if I lived in a region that had long summers.

    Depending on the mfr and model number, a 2 stage condenser can be 50% capacity on first stage, or 66%, or 80% of capacity (or some other percentage).

    In cooling mode, a 2-stage condenser allows for better humidity removal when it runs on 1st stage (less cycling on/off, more run time at lower capacity). Also in cooling mode, EER (Energy Efficiency Ratio) is higher on 1st stage than second stage.

    The thermostat usually determines when to kick the system into 2nd stage.

    2 stage condensers are more for comfort than energy savings.

    If you can afford it, go for the 2-stage. If not, a single stage condenser (properly sized and installed) should work just fine.

    Take care.

  5. #5
    Join Date
    Mar 2007
    Location
    South Texas
    Posts
    216
    Some mfg use 2 seperate compressors and some use single compressor that unloads. Each mfg has a different split on the capacity of each stage. On a call for cooling the first stage comes on if the temp continues to go up the second stage comes on. My varible speed fan changes with the stage change, thus at first stage my air flow is less and quieter. 100 degrees here for 37 days and mine has stayed in first stage most of the time. House is of average construction, would do even better with sealing the house better and sealing the ducts.

  6. #6
    Join Date
    Aug 2009
    Posts
    16
    Yes gary_g I'm beginning to understand that location matters. I live in North Carolina. We certainely get our share of mid 90s in summer but usually our severe summer is only for about 2 months. It appears a 2 stage pump has more value/pay-back in places like Florida, Louisianna, etc. but I'm doubting energy savings here in NC. I can see advantage of long run times with lower humidity with 2 stage but can't seem to justify the extra cost. Does 2 stage pump factor into heat pump heating cycle?

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,875
    Common misconception, that 2 stage is better in hotter/longer summer areas.

    A 2 stage in an area with a mild summer, canstill provide better comfort then a single stage.
    And in some cases, save money on operating cost.
    Many people find they can set their thermostat up a degree or 2 because of thelower humidity. And save money on operating cost.

    In heating. The longer run time in first stage helps provide a more even temp through out the house. And reduce the feeling of a cool draft that you can sometimes get from a short on cycle.
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  8. #8
    Join Date
    Jun 2006
    Posts
    628
    Its more about comfort and quiet than dollars and sense. Comfort is temperature and humidity together, and with two stage cooling the lower stage keeps you in the comfort zone better. Single stage on the less than hottest days will cycle off too long, so you have much larger changes in humidity and associated comfort.

  9. #9
    Join Date
    Oct 2008
    Location
    Bellevue, WA
    Posts
    194
    Are you comparing apples to apples? The two stage units tend to be higher end units that carry higher SEER/HSPF numbers. They typically use higher quality parts and often have a better warranty.

    I'm not sure when they rate the 2 stage units if they are "averaged" or just assuming conditions that require total capacity. If the later then I can see where real world numbers would be much better with the 2 stage.

    Even here in Washington State the the heating and cooling system has a huge range over which it must operate. While a single stage might be "just right" 80% of the time that other 20% it's really nice to be able to shift gears.

    I'm amazed at how much water the AC pulls out of the air. Our coil drains to a sump in the basement. The sump will run even in the summer because of the ground water so I hadn't really thought too much about it. I was down in the basement the other day after it had emptied and was shocked at how much water was draining into the sump from the AC. We don't have heat spells all that often but that makes it all the worse when we do because nobody is accustomed to it. It's made even worse by the fact that it's almost always a muggy heat. A very nice bonus to have the dehumidifier

  10. #10
    Join Date
    Aug 2009
    Posts
    16
    Quote Originally Posted by Alden_Sloe View Post
    Are you comparing apples to apples? The two stage units tend to be higher end units that carry higher SEER/HSPF numbers. They typically use higher quality parts and often have a better warranty.
    Carrier 25HPA524A30 - 15.5 SEER, 8.5 HSPF Total annual cost = $709
    Single-stage pump

    Carrier 25HNA924A30 -17.9 SEER, 9.0 HSPF, Total annual cost = $738
    Two-stage pump

    What am I getting from 2 extra SEER, .5 HSPF and almost 30% more $$? - If the contractor's calculated cost is correct. He stated he got his estimates of cost from Carrier. Warranty is the same.
    Last edited by beenthere; 08-05-2009 at 04:10 PM. Reason: Removed price.

  11. #11
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,875
    No prices, we don't talk prices here.

    I removed it.
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  12. #12
    Join Date
    Oct 2008
    Location
    Bellevue, WA
    Posts
    194
    I think he's quoting estimated operating cost which should be OK but the numbers make no sense. The higher efficiency unit will cost less not more. Look up the numbers on the AHRI website. Note that the coil used and blower/furnace selection makes a big difference (that's why the advertising always says "up to" 17 SEER - your mileage may vary). Also get the contractor to write down the actual model numbers of the furnace and coil on the contract; and then make sure that's what they actually install. Not everyone's as upright as the Pros on this forum

  13. #13
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,875
    No, he had a price, which I edited out. That you can't see.
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