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Thread: DC central air

  1. #1
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    DC central air

    Somebody told me that central air systems with DC motors can run at very low speeds and dehumidify more. Is this true and do you know of central AC brands that have the option of DC power?
    thanks
    Laura

  2. #2
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    some v drive furnaces and blower coils can slow the blower down when controlled by a thermostat like the Honeywell IAQ.

    not sure about other manufacturers but i know Lennox units can do this.

  3. #3
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    I would hazard the guess that about any variable speed product can do that. The blower slows down 10-15% to dehumidify. The "very low speed" happens during the fan on cycle where most brands switch to 50% speed. In a big space, you may not even feel air coming out.

  4. #4
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    Quote Originally Posted by BaldLoonie View Post
    I would hazard the guess that about any variable speed product can do that. The blower slows down 10-15% to dehumidify. The "very low speed" happens during the fan on cycle where most brands switch to 50% speed. In a big space, you may not even feel air coming out.
    So are there actually DC central air cond's? I looked online a bit and all I saw was for truck cabs! Was that bad info I got about getting one with a DC motor?

    So if it can run at very slow speed, I wouldn't have to worry too much about getting AC that's oversized? If it were somewhat too big you would just run it on slow and it would dehumidify OK?

    Laura

  5. #5
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    Quote Originally Posted by plarian View Post
    So are there actually DC central air cond's? I looked online a bit and all I saw was for truck cabs! Was that bad info I got about getting one with a DC motor?

    So if it can run at very slow speed, I wouldn't have to worry too much about getting AC that's oversized? If it were somewhat too big you would just run it on slow and it would dehumidify OK?

    Laura
    Your line of thinking is way off base. All manufacture's of central cooling systems offer models that have variable speed indoor blower motors (DC current motors) that are very efficient and have the capabilities of being set up to decrease humidity. That does not mean that we through all other aspects of cooling and dehumidifying out the window and oversize the system. Oversizing any cooling system is going to have adverse affects no matter what other factors are involved.

  6. #6
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    You may be thinking of the Inverter systems.
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  7. #7
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    Quote Originally Posted by beenthere View Post
    You may be thinking of the Inverter systems.
    How would an inverter system decrease humidity? Is there any value to oversizing an inverter system?

  8. #8
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    If you have a system that's somewhat oversized, that is able to run at a very slow speed, will it dehumidify well? My target is below 50% rh but I don't expect the AC to do that by itself, at least not all the time.

    Quote Originally Posted by everythingair View Post
    Oversizing any cooling system is going to have adverse affects no matter what other factors are involved.
    I know, I know ... All I was saying is, if I go with a contractor's recommendation I wouldn't be concerned it it turns out to be slightly oversized - yet I can dehumidify fine by running it very slow. If that's the case I won't go for something at the low end and risk having it undersized.

    Here is the comment (not from this site), which I was wondering about:
    > > When an AC runs it cools and dehumidifys, VSDC motors that can be set
    > > at very low speed dehumidify 50% more than regular AC with AC motors
    > > at the lowest speed, Carrier , Bryant and maybe Lennox offer this
    > > option
    >I bet only a few
    >offer the real low speed and watt option of Direct Current motors and
    >controls. Im talking about blowers that can run using only near 90-100
    >watts for real low speed, vs the near-400 watts that are standard on
    >Alternating Current motors. These units do remove 50% more moisture at
    >very low speed.

    Laura

  9. #9
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    I will repeat what I have already said; All manufacturer's of HVAC equipment have comparable models of variable speed blowers that can be set up to do the same type of dehumidification. Whether all of the controls are built into the brandeds system, such as Carrier's Infinity, or if additional after market brand controls need to be added, such as Goodman/Amana systems using Honeywell thermostats, all brands of HVAC equipment have the capability of addressing dehumidification beyond the standard cooling.

    If you tell us what you are expressly looking to achieve rather then giving your way of doing whatever it is you want to do, we can help you a lot better.

  10. #10
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    Some inverter systems run between 40-118 percent of nominal capacity. That does not mean you should over size a sysytem. When they are in dehumidification mode, once they make set temp. ,they can run below set temp. 2 degrees and blower slows to a crawl if dehumidification settings are not met yet. There are safeties in place, so if the coil temp. drops below 38 degrees, or the unit runs in dehumid for 10 minutes or longer, the compressor and blower will ramp up for a period of time to facilitate oil return and avoid freezing, and then ramp back down to dehumidify. Very efficient and very effective.
    Sound installation practices is the key to success. Equipment is only as good as the person installing it.

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  11. #11
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    Quote Originally Posted by everythingair View Post
    How would an inverter system decrease humidity? Is there any value to oversizing an inverter system?
    No where did I say its ok to over size, or suggest it.

    But. To answer your question. The inverter systems can lower their capacity to much lower percentages then 2 stage systems can.

    The split system inverter units can drop compressor capacity dow to 40%, and also go to a turbo mode of 120% capacity.

    With their communicating thermostats, they also control air flow better then standard 2 stage systems.

    Their not for everyone.
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  12. #12
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    Quote Originally Posted by TMH58 View Post
    Some inverter systems run between 40-118 percent of nominal capacity. That does not mean you should over size a sysytem. When they are in dehumidification mode, once they make set temp. ,they can run below set temp. 2 degrees and blower slows to a crawl if dehumidification settings are not met yet. There are safeties in place, so if the coil temp. drops below 38 degrees, or the unit runs in dehumid for 10 minutes or longer, the compressor and blower will ramp up for a period of time to facilitate oil return and avoid freezing, and then ramp back down to dehumidify. Very efficient and very effective.
    What brands have inverter AC's?
    Yes, an inverter sounds like what that person I quoted was talking about.
    Is it a lot quieter running in dehumidification mode? If so maybe that is the quiet whole house dehumidifier I'm looking for!
    Quote Originally Posted by everythingair View Post
    If you tell us what you are expressly looking to achieve rather then giving your way of doing whatever it is you want to do, we can help you a lot better.
    I'm not trying to give my way. I was just asking about what the person I quoted said, and whether it's something I should be looking for in choosing a system. They said that not all brands have what they're talking about.
    I would like AC to dehumidify to below 50% RH if possible. Emphasizing dehumidification over cooling. I would also like it to be as quiet as possible. I don't know whether I want central air or a mini-split. I know mini-split is more expensive, but maybe it works better? Maybe it could sit on my roof and deliver air more effectively to individual rooms? How would it do for dehumidification? It would probably be very quiet sitting on my roof.
    thanks,
    Laura

  13. #13
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    A ducted split system with inverter technology, is a lot more expensive then a ductless mini split with inverter technology.
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