Do I want to have my fan speed slowed down for humidity control?
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  1. #1
    Join Date
    Apr 2008
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    27

    Do I want to have my fan speed slowed down for humidity control?

    From what I've read here, I'm beginning to think that my heat pumps are oversized. I live in Central Florida, so it's pretty hot and quite humid here... especially in the summer.

    I've been setting the thermostats back to 85 when I leave for the day and when I'm home I keep them at about 78. The house still feels pretty humid and I have a cheap little indoor/outdoor thermometer thing that also shows indoor humidity. I have no idea how accurate that is, but it showed my humidity at around 60 to even 65 percent. I thought maybe that leaving the units off during the day was allowing the humidity to build up too much, so as an experiment I tried to leave them set to 78 for a couple of days and that helped a bit, but the humidity still stayed between 55 and 60 percent.

    I only have a single stage system, but I saw from a post here that I might be able to have someone come in and slow the fan speed down which could help keep humidity levels down.

    Does that sound like something I should investigate? This is a new house and the system came with it, so I don't have an HVAC company to ask yet, so I'm hoping you guys might have some good advice.

    Also, if I do go ahead and have the fan slowed down, would that affect run times significantly? I'm assuming it would cause the compressor to run longer (and have more of a chance to dehumidify the air), but I'm also concerned that if it runs much longer then it would be more expensive to operate. I want to keep the humidity down for comfort, but I don't want to pay a lot more for that... basically... I want it all

    Thanks much,
    Brett

  2. #2
    Join Date
    Jul 2008
    Location
    new jersey
    Posts
    12
    I would start asking around about finding a good HVAC COMPANY and get it looked at

  3. #3
    Join Date
    Nov 2000
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    Eastern PA
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    68,923
    Lower air flow will cause the indoor coil to become colder which will remove more humidity during cooling operation. However, depending on the type of blower you have, just lowering the amount of air can also cause other problems that are even worse then high humidity.

    Call a couple of HVAC contractors. Insist on talking to the service manager to explain exactly what you are looking to do (lower humidity) and make an appontment with the first one who sounds like they understand what you are talking about.
    Government is a disease...
    ...masquerading as its own cure…
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  4. #4
    Join Date
    Apr 2007
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    623
    Have them check static pressures, before they adjust the fan speed.

  5. #5
    Join Date
    Apr 2008
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    27
    Thanks for the replies... I was hoping it would be an easy "Yes, slowing the fan speed will decrease the humidity at little cost", but I guess nothing is ever that quick and simple. I'll start calling around to see if I can find someone to come out and check out my system.

    Thanks

  6. #6
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    18,836
    Quote Originally Posted by Bretts View Post
    Thanks for the replies... I was hoping it would be an easy "Yes, slowing the fan speed will decrease the humidity at little cost", but I guess nothing is ever that quick and simple. I'll start calling around to see if I can find someone to come out and check out my system.

    Thanks
    Ask if they can bring the fan data chart for your brand and test the ESP to set the cfms at around 350 per ton,If not keep dialing.They might do along with a annual check and clean,for a small charge.

    What brand,and you're located in which city?

  7. #7
    Join Date
    Apr 2008
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    27
    Quote Originally Posted by dash View Post
    Ask if they can bring the fan data chart for your brand and test the ESP to set the cfms at around 350 per ton,If not keep dialing.They might do along with a annual check and clean,for a small charge.

    What brand,and you're located in which city?
    Lennox and Lake Mary, FL, which is about 20 minutes north of Orlando... if you know anyone in the area, please let me know.

    This is a brand new house and the system was just installed in late Jan or early Feb, so it probably doesn't need much yet, but as long as someone is coming out it might not hurt to have it looked it.

    Thanks,
    Brett

  8. #8
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Try,

    Suma A/C
    Address: 15519 W. U.S. Hwy 441
    Eustis, FL 32726


    Phone: (352) 357-4162
    Fax: (352) 357-4168

  9. #9
    Join Date
    Apr 2004
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    STL
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    111
    Quote Originally Posted by RoBoTeq View Post
    Lower air flow will cause the indoor coil to become colder which will remove more humidity during cooling operation. However, depending on the type of blower you have, just lowering the amount of air can also cause other problems that are even worse then high humidity.
    With all due respect, what are the other problems that can occur.

    Thanks,
    Jim

  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,694
    Quote Originally Posted by electrajim View Post
    With all due respect, what are the other problems that can occur.

    Thanks,
    Jim
    Frozen coil. Liquid flood back to the compressor, killing the compressor.
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  11. #11
    Join Date
    Apr 2004
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    STL
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    Quote Originally Posted by beenthere View Post
    Frozen coil. Liquid flood back to the compressor, killing the compressor.
    If lowering the blower speed does produces the desired R/H and room temps, without moisture freezing anywhere on the coil, how likely would this cause liquid flood back and compressor death? Does it happen often?

    Is there any relation to the "oversized coil" to reduce humidity theorie?

    EDIT.....meant to type 'UNDERsizeing" instead of oversized...sorry

    Jim

  12. #12
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,255
    If your %RH meter is ok, check the temperature of the air and %RH coming out of the supply ducts closest to the a/c. If you have a 20-25^F temperature drop, slowing the fan may not be an option. At the end of 2-3 hour a/c run, the %RH should be <50%RH. Excess duct leakage has potiential for raising the moisture level. Your heat pump should be able to maintain ,50%RH during high cooling load conditions. During cool damp weathe with low/no cooling loads and adequate fresh air, you will need supplemental dehumidification. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  13. #13
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    Larger coils don't remove more moisture.

    If the system is set up right, then you won't have problems with the compressor being damaged.
    The system should be checked when they slow the blower.
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