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Thread: high humidity

  1. #1

    Confused high humidity

    Hello i have a 3 ton r-410 condensor and 3 ton furnace and a 3 ton r410 coil with txv. The whole system is oversized by a ton for a 1,000 square ft hom in Houston. Could i change the condenser to a 2 ton r410 and have it work with the 3 ton furnace and coil? Thank You
    Last edited by high humidity; 03-04-2009 at 03:49 PM.

  2. #2
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    Is the entire system oversized by one ton or just the TXV? Your post makes it sound as though the TXV is a 4 ton valve.
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  3. #3

    Hello Doc

    Quote Originally Posted by doc havoc View Post
    Is the entire system oversized by one ton or just the TXV? Your post makes it sound as though the TXV is a 4 ton valve.
    Hello Doc & Thank You or your quick reply, The whole system is 3ton running r410refrig, I would like to know if i could change the condenser to a 2 ton and if it would work with the larger furnace and coil inorder to stop the short cylce and humidity problems Thank You

  4. #4
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    Be sure that it's oversized first.

    Post the model numbers and brand ,someone can likely look it up and see if it is a correct match.

  5. #5

    oversize ac

    Quote Originally Posted by dash View Post
    Be sure that it's oversized first.

    Post the model numbers and brand ,someone can likely look it up and see if it is a correct match.
    My home is 1,000 square ft and live in Houston, the ac wont dehumidify due to being oversized @ 3 tons, if i changed to a 2 ton condenser would the ac condencer and work right (run longer) system is all trane matched and 2 years old Thank you

  6. #6
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    There may be an AHRI listed match with a 2 ton condenser, but a 3 ton coil on a 2 ton condenser still isn't giving the best latent capacity (humidity removal).

  7. #7
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    Quote Originally Posted by RyanHughes View Post
    There may be an AHRI listed match with a 2 ton condenser, but a 3 ton coil on a 2 ton condenser still isn't giving the best latent capacity (humidity removal).
    My home system that is a 2 ton condenser with a 3 ton evap, is only .01% different S/T than they same condenser with 2 ton evap.

    high humidity,
    1) Find out exactly what you space needs capacity wise first. Have some do a manual J.
    2) Yes there might be an ARI match up for you evap coil with a 2 ton condenser. Need more info.
    3) Biggest problem is trying to get the proper cfm from the furnace, if it isn't a ECM. Even if it is, you still might not get the proper airflow for 2 tons.

  8. #8
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    Quote Originally Posted by high humidity View Post
    My home is 1,000 square ft and live in Houston, the ac wont dehumidify due to being oversized @ 3 tons, if i changed to a 2 ton condenser would the ac condencer and work right (run longer) system is all trane matched and 2 years old Thank you
    On a hot day, what is the temperature and %RH inside the home? What is the lenght of cooling cycle (on/off)? What is the room temperature and the a/c supply temperature during the cooling cycle? Do you operate your fan "on" mode?
    With the outside temp at 100^F, a 2 ton may operate non-stop removing 7 lbs. of moisture per hour. The max latent load for a houtson house with 4 people is 3-4 lbs. per houur of moisture to maintain <50%RH. A oversized 3 ton a/c will operate 67% of the time remove 5 lbs. of moisture per hour. This is mainly because all a/cs require 8 minutes to make the coil cold enough to removes moisture from the air. The 3 ton removes enough dehumidification to maintain <50%RH during high cooling loads. As the cooling load declines, the on/off cycles increase more for both sized units. The latent load per hour of the home remains the about the same because of the high outdoor dew point. Expect the 2 ton a/c to have a couple cycles less than the 3 which is 16 minutes of addition dehumidification. This a 1-2 lbs. per hour of additional moisture removal. During evenings and rainy days neither a/c will remove any water and you still the 3-4 lbs per hour moisture load without any a/c operation. You still high outdoor latent load and moistue from the occupants.
    So the smaller a/c is a little better dehumidifier in a light cooling load condition but unable to handle a home with 4 occupants and natural infiltration/adequate fresh air ventilation. The industry has sold this a/c sizing thing to the point where customers believe a one ton oversized a/c can not maintain low %RH in a humid climate. From my testing of homes, a two ton will not provide <50%RH during low/no cooling conditions with occupants and typical fresh air. Get a good ducted 65-90 pint whole house dehumidifier and get <50%RH any sized a/c during any weather that Houston hit you with.
    Regards TB
    Last edited by teddy bear; 03-04-2009 at 04:40 PM. Reason: missing words
    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"

  9. #9
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    Quote Originally Posted by ascj View Post
    My home system that is a 2 ton condenser with a 3 ton evap, is only .01% different S/T than they same condenser with 2 ton evap.
    Good to know. Maybe it's just with this specific matchup, but I was under the inclination that it would make more of a difference. Just goes to show how little a difference there often is among coil sizes.

  10. #10
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    Here's an alternative to concentrating on your a/c system to resolve your high humidity problems: find out where outside air is leaking into your house, and see what is needed to reduce that leakage. It may be your system is still oversized, but reducing the amount of humidity it has to remove is never a bad thing.

    The manufacturer of your equipment would know best if the configuration you propose would help you meet your goal of increased dehumidification. My initial observation is that a larger indoor coil coupled to a smaller condenser is a net loss in both sensible and latent capacity, but I could be off-base. It would all depend on what the ARI numbers are for any match-up you're considering. What would be concurrently helpful is a heat load calculation performed on your house, along with a blower door test to determine how leaky it is. There are smart ways to resolve this problem, and there are ways that waste time and money. Choose wisely.
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  11. #11
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    Call the installing Trane dealer.
    He can tell you if a 2 ton condenser will match up.
    And, he may feel guilty since he over sized it.
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  12. #12
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    and if he doesn't feel guilty?
    try a stand alone dehumidifier located in
    the conditioned space.
    won't stop shortcycling..but will remove quite
    a bit of humdity.

    oh and what shophound said...stop air infiltration
    texas is like la...high humidity!

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  13. #13
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    can you lower the blower speed any more?

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