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  1. #1
    Join Date
    Oct 2007
    Location
    Long Island, NY
    Posts
    2

    Inverter on cool only Mini-Split?

    Hi all- long time lurker, first time registered and posting.

    Need your advice on whether to spring for an inverter model of mini-split which will be used for cool only. 1950’s colonial house has central a/c (2 separate compressors, one up and one down) but a 20x20 cathedral ceiling family room extension on a slab with southern exposure is consistently 5-8 degrees hotter than the rest of the house. It doesn’t help that it’s the last duct on the run, with the compressor 40 feet away. Also, one 20 ft. wall is open to the kitchen (and the hot lights and oven).

    The three contractors I have had over all recommend a cool-only mini-split (no need for heat as the room is fin baseboard on its own zone) but they say no need to go with an inverter model, as the unit will only cool, not heat.

    As this is the most used room in the house and the a/c will be on more than any of the central a/c units, I want to make the right choice in terms of both comfort and energy efficiency.

    Would you recommend upgrading to an inverter model? The Mits inverter models start at 15,000 BTU, so oversizing may be an issue.

  2. #2
    Join Date
    Jun 2001
    Location
    DFW
    Posts
    683
    I think the inverter version will make the room more comfortable, and the energy savings will help pay for the extra cost.

  3. #3
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,086
    Comfort AND energy efficiency?

    Inverter driven mini-split, hands down.

  4. #4
    Join Date
    Feb 2007
    Location
    Southern California, LA Metro
    Posts
    387
    and the carrier inverter is wisper quiet........!
    Larger Duct, Larger Duct, More Air, More Air
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  5. #5
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,543
    Just because you have baseboard does not mean you would not use a heat pump to keep that room warmer for lots less than the boiler costs to run.
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  6. #6
    Join Date
    Feb 2006
    Location
    Taylors, SC
    Posts
    403
    I agree with freezeking, go for the heat pump, the cost difference between a cooling only and a heat pump is very very little.
    Poor planning on your part doesn’t necessarily constitute an emergency on my part.

  7. #7
    Join Date
    May 2004
    Location
    Rapid City, SD
    Posts
    7,403
    Dumb question time... what's an inverter on these minisplits?
    "If you call that hard work, a koala’s life would look heroic."

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  8. #8
    Join Date
    Jun 2001
    Location
    DFW
    Posts
    683
    The worst people to work with are those that don't ask questions.

    The inverter system gives you a variable speed compressor.

    It does this by taking the 60Hz line power, turning it into DC, and then turning the DC into a variable frequency power (maybe 60-120Hz) to drive the compressor.

    Larger whole house central systems are headed this direction as well.

  9. #9
    Join Date
    May 2004
    Location
    Rapid City, SD
    Posts
    7,403
    Ahh., ok I've heard of them before, guess I just never heard the technical term for them. Now if I can just remember it!

    FWIW, we installed a Mitusbishi City Multi System in a school (office). 15 indoor units and one outdoor unit, 13 tons I think. Anyway of course its variable speed compressor and condenser fan motors. That think is SO quiet.. when it's running about half load, you can easily talk right next to it.
    "If you call that hard work, a koala’s life would look heroic."

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  10. #10
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,826
    Definitely go with the heat pump model. As others have stated, the energy savings is there for cooling and you can heat the room with the heat pump in moderate outdoor temperatures for lots less than fossil fuel baseboard systems. We do those installs with central AC systems and the savings is significant. As far as the inverter technology, it allows the compressor to operate anywhere between approximately 13% to as much as 120% of rated capacity. The higher number is with multiple indoor unit(s) or zones but the savings when less than maximum output is needed is substantial. I wouldn't ever recommend a non-inverter model to any of out clients. I'd really feel like I'd be cheating them. Usually the people who don't recommend the inverters don't really understand the technology and telling you they only recommend it for HPs means they don't want to sell heat pumps and don't want to work with the inverter technology units. It's just a cheap 'out', IMO.
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  11. #11
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,543
    Quote Originally Posted by skippedover View Post
    Definitely go with the heat pump model. As others have stated, the energy savings is there for cooling and you can heat the room with the heat pump in moderate outdoor temperatures for lots less than fossil fuel baseboard systems. We do those installs with central AC systems and the savings is significant. As far as the inverter technology, it allows the compressor to operate anywhere between approximately 13% to as much as 120% of rated capacity. The higher number is with multiple indoor unit(s) or zones but the savings when less than maximum output is needed is substantial. I wouldn't ever recommend a non-inverter model to any of out clients. I'd really feel like I'd be cheating them. Usually the people who don't recommend the inverters don't really understand the technology and telling you they only recommend it for HPs means they don't want to sell heat pumps and don't want to work with the inverter technology units. It's just a cheap 'out', IMO.
    What he said.!
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  12. #12
    Join Date
    Sep 2006
    Location
    Winter Springs, Fl
    Posts
    1,755
    Quote Originally Posted by paul42 View Post
    The worst people to work with are those that don't ask questions.

    The inverter system gives you a variable speed compressor.

    It does this by taking the 60Hz line power, turning it into DC, and then turning the DC into a variable frequency power (maybe 60-120Hz) to drive the compressor.

    Larger whole house central systems are headed this direction as well.
    Trane had a system like that more than a decade ago. The CU model was a XV1500. It used a communicating Tstat and a var. speed AHU along with the dc driven var. speed compressor. I think the reason it didn't catch on was it was way ahead of it's time, so far ahead that hardly anyone could work on them without shooting in the dark with new parts.
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  13. #13
    Join Date
    Sep 2006
    Posts
    1,253
    Quote Originally Posted by skippedover View Post
    Definitely go with the heat pump model. As others have stated, the energy savings is there for cooling and you can heat the room with the heat pump in moderate outdoor temperatures for lots less than fossil fuel baseboard systems. We do those installs with central AC systems and the savings is significant. As far as the inverter technology, it allows the compressor to operate anywhere between approximately 13% to as much as 120% of rated capacity. The higher number is with multiple indoor unit(s) or zones but the savings when less than maximum output is needed is substantial. I wouldn't ever recommend a non-inverter model to any of out clients. I'd really feel like I'd be cheating them. Usually the people who don't recommend the inverters don't really understand the technology and telling you they only recommend it for HPs means they don't want to sell heat pumps and don't want to work with the inverter technology units. It's just a cheap 'out', IMO.
    Depending on the system and the actual load it may well meet the heat needs too. I have specs on a 4 ton Diakin multi-split system, at 10* it has a rated output of 38K BTUs. Compare that to a 4 ton Carrier 25HNA6 putting out about 22K or even the Carrier 5 ton putting out only about 27K. Plus, with the inverter Daikin, the higher the percentage of indoor unit consumption of the BTUs the lower the cost to operate. At 130% the power usage is 17% less than at 100% (Note: BTU output from the indoor units does not go up meaningfully, but the power input declines).

    They are quiet, highly sophisticated, can handler multiple indoor air handlers, and efficient. I'm not sure why these systems have not been more widely accepted here as they are the dominate players in the rest of the world.

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