Page 2 of 3 FirstFirst 123 LastLast
Results 14 to 26 of 29
  1. #14
    Join Date
    Apr 2012
    Location
    Princeton NJ
    Posts
    125
    tedkidd, thanks for the comment (and thanks to all others), the home is 1995 and was told when we bought it 2 years ago it was super well built. (other than the poorly designed duct work i guess, i am working on this--other post). The attic is well insulated, but can't verify the cathedral ceiling, or if they put insulation over the 10+ can lights. Or verify the wall insulation. Really no air leaks or other obvious problems. Can't imagine an easy way to improve it.

    There are 2 heat load zones for this unit--2500sq ft total, 500 sq ft is cathedral ceiling 14 foot high, other ceilings are perhaps 10 foot. 135 sq ft of west/south windows. I have tried lowering the blinds, and it makes a DRAMATIC difference in how hot the room gets/previous unit worked.

    What do you think? Take a small chance and go for the 4 ton? Or take a risk of high humidity?

    Steve

  2. #15
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,062
    You are going to need a dehumidifier for perfect humidty control anyway. During the low/no cooling loads, a/cs donot run enough to provide 50%RH. I would make sure I had enough capacity to handle the hotter weather we have been seeing the last couple years. This undersizing thing is over rated.
    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"

  3. #16
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,455
    Quote Originally Posted by teddy bear View Post
    You are going to need a dehumidifier for perfect humidity control anyway. During the low/no cooling loads, a/cs do not run enough to provide 50%RH. I would make sure I had enough capacity to handle the hotter weather we have been seeing the last couple years. This undersizing thing is over rated.
    Regards TB
    The problem I see with so-called undersizing is that the install & setup with the duct system & airflow ends up Lowering the delivered Btuh capacity way too much...

    I get perfect comfort results in all weather conditions with little window units that anyone would say couldn't possibly get the job done on both humidity & temperature...but they do.

  4. #17
    Join Date
    Apr 2012
    Location
    Princeton NJ
    Posts
    125
    Mr. T. Bear, thanks for the comment. It makes some sense, but in my previous home, and this current home with r22 based single stage conditioners, I never ever ever had even a hint of high humidity in the house. Are the puron based conditioners really that much worse at removing humidity?

    Steve

  5. #18
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    IT's not the refrigerant itself. It's the shift to larger evaporator coils on 13+ SEER units. 10 SEER had smaller coils so the surface temps was lower, but efficiency suffered.

  6. #19
    Join Date
    Apr 2012
    Location
    Princeton NJ
    Posts
    125
    I am so embarrassed, i did not understand the humidity issue at all. I just did more reading, and yes to all of you, I would be incredibly upset living with on oversized unit and high humidity. I will get the 4 ton.

    I also notice Mr. T. Bear mentions adding a dehumidifier frequently. I don't mean at all to insult him by asking this, but are other professionals experiencing humidity problems with correctly sized units? Am I really going to end up adding a dehumidifier to a bit undersized 4 ton unit???

    Steve

  7. #20
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,755
    Quote Originally Posted by teddy bear View Post
    You are going to need a dehumidifier for perfect humidty control anyway. During the low/no cooling loads, a/cs donot run enough to provide 50%RH. I would make sure I had enough capacity to handle the hotter weather we have been seeing the last couple years. This undersizing thing is over rated.
    Regards TB



    Ok, I'll agree with you on this one. LOL
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  8. #21
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,062
    Quote Originally Posted by udarrell View Post
    The problem I see with so-called undersizing is that the install & setup with the duct system & airflow ends up Lowering the delivered Btuh capacity way too much...

    I get perfect comfort results in all weather conditions with little window units that anyone would say couldn't possibly get the job done on both humidity & temperature...but they do.
    I find that the long term indoor dew point of any home is the same as the outside dew point plus or minus the moisture added or removed from the inside of the home. The occupants add moisture. The a/c and dehumidifiers remove moisture. When the outdoor dew point is +60^F and the occupants are adding moisture, the indoor %RH will be elevated. We have hot dry, hot wet, cool dry, and cool wet weather. This is hot dry year and you have mostly perfect conditions, with a very small a/c, overcooling, and added heat, OK. Most have full sized a/c with large cooling coils and unable to deal with cool wet.
    Any home with recommended ASHRAE fresh air changes rates, normal occupancy, outdoor dew points of +60^F will need supplemental dehumidification. Also humidification may be needed during extreme low outdoor dew points and low occupancy.
    Add adequate fresh air change and normal number of occupants, you benefit from a high efficiency whole house dehumidifier. Our comments of the lack of a need for dehumidification for reqular well ventilated homes does not help the typical poster on this site.
    If you have any points of mine that need clarification, please post.
    Thanks for raising the issue, 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"

  9. #22
    Join Date
    Nov 2011
    Location
    Central Va.
    Posts
    263
    Quote Originally Posted by jimj View Post
    LOL.

    By the way if your sales person is trying to sell you a 19i you need to tell him Trane replaced them about 2 years ago with the 20i.
    lol

  10. #23
    Join Date
    Apr 2012
    Location
    Princeton NJ
    Posts
    125
    Mr. T. Bear,
    This is more complicated than I imagined. Thank you for your patience. I have to think about this a bit. I kind of understand the how the problem occurs. But what percent of the time are the homes with adequately sized/just undersized conditioners needing a dehumidifier? Why didn't anyone else who commented mention a dehumidifier (not sure how to interpret beenthere's comment)?

    I'm thinking also that I could make the first stage, 2 tons, my little work horse. I know there is a switch on the zone panel for 1 hour on first stage. So even two zones calling, still 2 tons. Perhaps that would help. Another question would be just how much worse are the higher seer/big coils at dehumidification? A 5 ton 8 seer running for 15 minutes---would it dehumidify about as much as a 2.5 ton 16 seer running for 30 minutes? (if so, my current crappy set up controls humidity perfectly, so I think I would be fine).

    Steve

  11. #24
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,631
    Quote Originally Posted by central nj View Post
    (if so, my current crappy set up controls humidity perfectly, so I think I would be fine).

    Steve
    4 ton 2 stage, you are likely to be ecstatic so long as you don't open windows when dew point is >55 or so.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  12. #25
    Join Date
    Jun 2012
    Location
    Northern NV
    Posts
    124
    Tbar; Ifiin you have a variable speed blower and an inverter driven condensing unit and they communicate, then why would the undersized high efficiency unit not remove the humidity? These puppies are designed to maintain a constant TD across the evap no matter what. So if it is nominally undersized, it should theoretically remove the latent load at most any outside condition needing cooling and can typically be biased towards more latent removal via a dip sw.

    As to ventilation air: Use an enthalpy, or energy recovery ventilator. Venmar and others make a residential model. Here in the DRY west we can use them to keep the moisture inside. You guys in swampy environs can use 'em to keep Mr Muggy out. They work and save a lot of A/C run time.....

  13. #26
    Join Date
    Aug 2012
    Location
    NE wisconsin
    Posts
    392
    Quote Originally Posted by Juan Madera View Post
    Tbar; Ifiin you have a variable speed blower and an inverter driven condensing unit and they communicate, then why would the undersized high efficiency unit not remove the humidity? These puppies are designed to maintain a constant TD across the evap no matter what. So if it is nominally undersized, it should theoretically remove the latent load at most any outside condition needing cooling and can typically be biased towards more latent removal via a dip sw
    As to ventilation air: Use an enthalpy, or energy recovery ventilator. Venmar and others make a residential model. Here in the DRY west we can use them to keep the moisture inside. You guys in swampy environs can use 'em to keep Mr Muggy out. They work and save a lot of A/C run time.....
    Dehumidifier is turned on and off by humidity and ac is turned on and off by temp, unless the communicating furnace and ac also communicate with a tstat that senses rh it will be ineffective at removing humidity unless its hot enough to run for long enough. Get the correct size ac and if you have a problem with humidity get a good whole home dehumidifier, that is the most energy-efficient way to keep the home comfortable.

Page 2 of 3 FirstFirst 123 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