Page 1 of 2 12 LastLast
Results 1 to 13 of 18
  1. #1
    Join Date
    Jul 2011
    Location
    Tucson, AZ
    Posts
    177
    Post Likes

    Indoor humidity VS Evaporator Split

    Will 55% indoor humidity and a dew point of approximately 66* with 78 dry bulb reduce a split?

  2. #2
    Join Date
    Dec 2004
    Location
    Chicago area
    Posts
    8,724
    Post Likes
    Compared to what?

    55% RH seems like it would yield a reasonable TD in the 18 to 20 territory.


    Sent from my iPhone using Tapatalk

  3. #3
    Join Date
    Jul 2011
    Location
    Tucson, AZ
    Posts
    177
    Post Likes
    Thread Starter
    Compared to 30%.

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    9,669
    Post Likes
    Quote Originally Posted by greenhorn520 View Post
    Will 55% indoor humidity and a dew point of approximately 66* with 78 dry bulb reduce a split?
    Split meaning, return air verses coil temperature- 55%RH @ 75^F, a 60^F dew point return equals 49^F coil temperatue, a 55^F dew point supply air??
    Is this what we are talking about?

    Regards Teddy Bear
    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"

  5. #5
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    9,669
    Post Likes
    Quote Originally Posted by greenhorn520 View Post
    Will 55% indoor humidity and a dew point of approximately 66* with 78 dry bulb reduce a split?
    Split meaning, return air verses coil temperature- 55%RH @ 75^F, a 60^F dew point return equals 49^F coil temperatue, a 55^F dew point supply air??
    Is this what we are talking about?

    Regards Teddy Bear
    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"

  6. #6
    Join Date
    Dec 2004
    Location
    Chicago area
    Posts
    8,724
    Post Likes
    I think he means return to supply temp drop.

    In that case, 30 percent rh return air will yield a hight temperature drop then a 55 rh

    By how much?

    Use this formula to find target outlet temp based on return air conditions

    [(3wb+2db)-112]/4.


    Sent from my iPhone using Tapatalk

  7. #7
    Join Date
    Apr 2003
    Location
    St. Louis
    Posts
    1,269
    Post Likes
    18* to 24* is normal td lets first see what the units doing. If its 90* outside and return is 90* we all no the problem lets.get.some dr y bulb temps.

  8. #8
    Join Date
    Jul 2011
    Location
    Tucson, AZ
    Posts
    177
    Post Likes
    Thread Starter
    Split meaning RA vs SA temp. 97* out door ambient. 78* RA. I was using the check and charge app it was matching up. Just surprised a split can be reduced to 12* from humidity. I actually found some air gaps around the evaporator and was able to improve it to 15* split. 78/63.

  9. #9
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    9,669
    Post Likes
    Are the supply ducts in a hot attic or a cool basement/crawlspace? This is an inaccurate method of judging the measure the cooling, sensible/latent heat. Temperuature/%RH or temp/dew point temp is better way to determine the amount of sensible/latent(moisture). If your target is 50%RH in the home, the cooling coil should be low enough to lower the dew point of the air passing through the cooling coil a minimum of 6^F. An example is 75^F, 50%RH, a 55^F dew point return with attic ducts may have a 60^F, 70%RH, a 49^F dew point at the supply grill. With a basement supply duct, the supply may be 55^F, 85%RH, also a 49^F dew point. Both have enough moisture removal to maintain <50%RH during peak cooling loads. Dew point or grains of moisture per Lb. of air is the more accurate is measure of a good a/c setup.
    This also explains why the %RH goes high when there is low/no sensible cooling, the outdoor dew point is high, plus the home is occupied by moisture generating occupants. A small whole house dehumidifier combined with a well setup a/c setup/sized for the desired condition is ideal.
    Keep us posted.
    Regards Teddy Bear
    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"

  10. #10
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    10,055
    Post Likes
    I saw no mention of airlfow in any post. Too much or too little will swing your delta T. At a 15 Delta I would guess you are moving more air than you need to. Did you take any static readings or check an air flow chart for the system?

  11. #11
    Join Date
    Apr 2003
    Location
    St. Louis
    Posts
    1,269
    Post Likes
    Could be short of gas or piston size / coil size isn't matched. Need pressures and temps of lines.

  12. #12
    Join Date
    Jan 2012
    Location
    Missouri, USA
    Posts
    1,504
    Post Likes
    Name:  A0C4A52B-1149-45BE-BF3F-4F786B2F5D7C.png
Views: 138
Size:  1.21 MB

  13. #13
    Join Date
    Nov 2011
    Location
    East Side
    Posts
    7,059
    Post Likes
    a simple measurement of DB delta is meaningless!

    if you truly want to begin to understand the liquid we call air, get Psychrometrics without tears, by Eugene Silberstein, and read read read! it's a good, basic introduction to air. if you want to learn more, there's a whole other world of AC out there!

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
  •