Page 1 of 2 12 LastLast
Results 1 to 13 of 21
  1. #1
    Join Date
    Jun 2005
    Location
    New England
    Posts
    893
    ME: Residential, 2000 sq ft. New England, 18 year old York system - air handler and ducts in the attic. I'm getting contractors to come and bid to replace it.

    No one can give me a good explanation of what a variable speed fan does for me, except to suggest that with a high-end control system (with a humidistat), it allows for more gradual cooling in cooler (~70-80Deg) humid weather to better facilitate dehumidification. Some people say it facilitates better cooling in hot weather by cranking up the fan, but these new systems have fans that peak (for 4 ton) at only 1600 cfm and my current system pushes 1800cfm all-the-time.

    Can someone explain why a variable-speed fan is really there - is it simply for the dehumidification I explained above, or is there some energy-saving effect that escapes me.

    Thanks
    /j

    PS - I assume I should take with a grain of salt the Trane dealer who said that the quality of carrier systems had gone way down (offshore parts, etc).

  2. #2
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    In addition to dehumidification abilites,which are best with a Carrier Infinity ,with two speed compressor,there is more.

    1.The variable speed fan will ensure the correct cfms,even as resistance increases,with a dirty filter.There are limits of course,but the correct air flow is key to effeciency.

    2. Though your old system,may have a higher cfm rating ,at a certain resistance,the VS may be able to deliver 1600 at a higher resistance.This is often the case.

    3.VS fan uses less wattage ,so you save some their as well.



    IMHO,Carrier products are better today,than in the past.

  3. #3
    And they are quieter too. Can't hear a thunk when they start up. Wish I had one.

  4. #4
    Join Date
    Jun 2005
    Location
    New England
    Posts
    893
    Actually, the guy I like the best is recommending carrier evolution.

    But are you saying that the fan on the new system may actually be capable of much higher RPM than a non-variable one, so that it can maintain an appropriate CFM in different conditions?

    That makes a -lot- of sense
    /j


  5. #5
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    They adjust rpm and torgue to maintain the cfms(air flow ) at what is required.

    With a standard motor ,you pick a speed,and that's it,often the correct speed isn't the one they choose.Even if it is correct,it's cfms are reduced as the filter,coil an blower get dirty.


    Carrier = Infinity

    Bryant =Evolution

    The operate the same way ,Carriers outdoor units are quieter.

  6. #6
    Join Date
    Jun 2005
    Location
    New England
    Posts
    893
    Maybe it was Bryant - he said they were the same company?? (or is carrier the same as someone else? I might have misheard)

    I get it now. So there's a cfm sensor as part of the system.

    /j

  7. #7
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    It's all built into(programed) the VS motor and controls,many brands have similar setups,Carrier/Bryant is just more advanced,at this time.


    Go variable speed regardless of the brand.IMHO


  8. #8
    Join Date
    Jun 2005
    Location
    New England
    Posts
    893
    good advice -thx

  9. #9
    Join Date
    Jul 2003
    Location
    Texas
    Posts
    457

    Thumbs up

    I like the slower speed on start up, it is less likely to wake one up in the middle of the night, and it allows the evaporator coil to get closer to a temperature which will cause the air coming out the vents to feel better. It is the "ramping up" of the fan speed, Either in cooling mode, or, as I have a heat pump, in heating mode.
    In cooling mode, controls can delay going to max air flow so that more humidity (latent heat, I think it's called) can be removed from the air. I believe that air which contains less grains of moisture, can be cooled quicker. That means energy savings.
    There can be additional savings at the end of the run cycle, where the compressor outside is shut off, and the indoor fan is "ramped down" in speed. This supplies you with a little more (heating/cooling) from the temperature of the coil. The ramp down cannot be too long, or (in cooling mode) moisture will be added back in to the air, or (in heating mode) cooler air will be felt by inhabitant.
    This is from a homeowners viewpoint. I've never regretted going to a variable speed air handler, albeit single speed heat pump. No regrets !


  10. #10
    Join Date
    Jun 2005
    Location
    New England
    Posts
    893
    OOPS - forgot to mention (don't know if this makes a difference)

    I keep the fan running 24/7 so as to maximize use of the allergen filter (spacegard).

    What will a Variable-speed fan do when the system isn't calling?

    /j

  11. #11
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Some can be set to run at a lower cfm when the unit is off,increasing the effectiveness of the filter.


    Plus the lower oprating cost of VS ,really saves when you run the fan 24/7,that makes VS a must,IMHO.

  12. #12
    Join Date
    Dec 2002
    Location
    Rochester, MN
    Posts
    5,304
    I am not sure about the other guys.. But I am sure they do the same as Trane..

    Blower on 24/7 will run at a slower speed.. call of heat or cooling blower will ramp up and down..

  13. #13
    Join Date
    Jun 2005
    Location
    New England
    Posts
    893
    I'm sold on VS, and all you say, except I don't understand...

    how does lower cfm make filter MORE effective?

    /j

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event