Results 1 to 6 of 6

Thread: Another Humidity puzzler - what are my options

  1. #1
    Join Date
    Aug 2020
    Posts
    3
    Post Likes

    Another Humidity puzzler - what are my options

    Hello all,

    So Ive been reading HT threads for a while but never took the time to post. Finally decided to take the plunge. I've been having issues with humidity in a house we bought almost two years ago. We had two new full Trane systems (S8X2/XL14i) installed last winter due to the old systems being end of life. Ill post all the details below, but basically I'm here because I honestly can not find good help from the contractors in my area. My installer is basically too busy to pay attention to us now that the systems are installed, and I've tried to get appointments setup with at least 3 air quality contractors in the area but none ever reply to my inquiry. Its summer here so I guess everyone is just too busy. While I am a DIYer for HVAC, my profession does lend itself to me being able to read and understand psychometrics and other physics related concepts fairly well.

    My questions are:
    1) Do my units appear to be running efficiently/ setup properly?
    2) Should I bother with duct sealing and all the other potential methods to control humidity, or just go ahead and install a central de-humidifier and humidifier on my lower level system. I want to keep the house in the magic 40% to 60% RH range @~72 temp. In summer, ive seen as high as 71% RH, and as low as 29% in the winter. The second floor always is more comfortable than the lower.

    For example this morning the outdoor temp was 81 with an RH of 65%, with an indoor temp of 71 with RH 62%. It will creep up to around 65% before we call uncle and set the thermostat to 68% to dry the air out. The test data was from a random day I had time to take measurements.


    The House:
    Build Year: 1996 / Sqft: 3400 (2000 lower level - 4 ton, 1400 upper level - 3 ton) / Location: Suburbs outside of Memphis / L shaped layout with a bedroom over a garage and master br/bt on lower level. / Windows and door seals are past design life ($38k quoted to replace) / 2 fire places / 2-1/2 bath, 4 bedroom / Duct work doesn't look like it was done with a lot of care. / Overall a typical cheaply built mid 90's house.

    Test Data:
    Test Equipment: Psychrometer used is a UEI DTH35. Monometer is an AR1890 (If I have to buy a better one let me know). Both units run for approx 15 minutes before taking measurements.
    HVAC Equipment: Lower Level - Trane S8X2 / XL14i (4 Ton) / Upper Level - Trane S8X2/XL14i (3 Ton) / Both installed with new coils in December 2019 / No issues with sensible heating or cooling. / New filters installed for measurements.

    Outdoor Environmental Conditions: Aug 2020 - Temp 81.3 / RH 56.4 / DP 64.3 / WB 69.6 / Partly Cloudy / No Wind

    Lower Level Readings:
    Ambient Temp at Thermostat 71.4 / RH 51.0%
    Return Air Readings (Measured immediately downstream of filter): Static Pressure .-7" / Temp 72.3 / RH 58.7% / DP 57 / WB 62.6 / BTU/h 28.2
    Supply Air Readings (Measured just above coil inside plenum / Pressure measured just before coil): Static Pressure -.44" / Temp 53.5 / RH 68.3% / DP 43.3 / WB 48.1 / BTU/h 19.2
    Calculated Delivered BTU: Total CFM: 1400 (Speed tap 5) / Cooling BTU 56,700 (seems off?)
    Furthest Room Supply Vent: (~60ft run): Temp 58.8 / RH 68.2 / DP 48.4 / WB 52.9


    Upper Level Readings:
    Ambient Temp at Thermostat 73.4 / RH 42.7%
    Return Air Readings (Measured immediately downstream of filter): Static Pressure -.4" / Temp 73.8 / RH 46.1% / DP 51.8 / WB 60.4 / BTU/h 26.6
    Supply Air Readings (Measured just above coil inside plenum / Pressure measured just before coil): Static Pressure .3" / Temp 52.8 / RH 68.0% / DP 42.5 / WB 47.5 / BTU/h 18.9
    Calculated Delivered BTU: Total CFM: 1050 (Speed tap 3) / Cooling BTU 36,300
    Furthest Room Supply Vent: (~35ft run): Temp 55.0 / RH 48.2 / DP 50.0 / WB 49.1

    Thanks in advance for any help - let me know if you need any more info. Despite these issues, its been pretty interesting to learn about psychometrics and really start to understand more in depth about HVAC. I have a new appreciation for the trade!

  2. #2
    Join Date
    Jun 2020
    Location
    Chicago, IL
    Posts
    31
    Post Likes
    It seems a little weird that the RH of the air immediately coming off the coils is only at 68%. When the coil is removing moisture via condensation, the air is at 100% RH (full saturation). Perhaps you didn't keep the hygrometer there long enough for the readings to stabilize. Or maybe your hygrometer doesn't perform well in high RH.

    The other factor to consider is how well air-sealed your home is. As humidity goes up outside, mother nature will try to increase the humidity inside (2nd law of thermodynamics). So don't put all of your focus on just the HVAC system. You might be able to better seal the building enclosure to help reduce humidity.

  3. #3
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    10,424
    Post Likes
    Quote Originally Posted by JWebs View Post
    Hello all,

    So Ive been reading HT threads for a while but never took the time to post. Finally decided to take the plunge. I've been having issues with humidity in a house we bought almost two years ago. We had two new full Trane systems (S8X2/XL14i) installed last winter due to the old systems being end of life. Ill post all the details below, but basically I'm here because I honestly can not find good help from the contractors in my area. My installer is basically too busy to pay attention to us now that the systems are installed, and I've tried to get appointments setup with at least 3 air quality contractors in the area but none ever reply to my inquiry. Its summer here so I guess everyone is just too busy. While I am a DIYer for HVAC, my profession does lend itself to me being able to read and understand psychometrics and other physics related concepts fairly well.

    Fairly well?? Best info I have seen in while!

    My questions are:
    1) Do my units appear to be running efficiently/ setup properly?
    2) Should I bother with duct sealing and all the other potential methods to control humidity, or just go ahead and install a central de-humidifier and humidifier on my lower level system. I want to keep the house in the magic 40% to 60% RH range @~72 temp. In summer, ive seen as high as 71% RH, and as low as 29% in the winter. The second floor always is more comfortable than the lower.

    For example this morning the outdoor temp was 81 with an RH of 65%, with an indoor temp of 71 with RH 62%. It will creep up to around 65% before we call uncle and set the thermostat to 68% to dry the air out. The test data was from a random day I had time to take measurements.


    The House:
    Build Year: 1996 / Sqft: 3400 (2000 lower level - 4 ton, 1400 upper level - 3 ton) / Location: Suburbs outside of Memphis / L shaped layout with a bedroom over a garage and master br/bt on lower level. / Windows and door seals are past design life ($38k quoted to replace) / 2 fire places / 2-1/2 bath, 4 bedroom / Duct work doesn't look like it was done with a lot of care. / Overall a typical cheaply built mid 90's house.

    Test Data:
    Test Equipment: Psychrometer used is a UEI DTH35. Monometer is an AR1890 (If I have to buy a better one let me know). Both units run for approx 15 minutes before taking measurements.
    HVAC Equipment: Lower Level - Trane S8X2 / XL14i (4 Ton) / Upper Level - Trane S8X2/XL14i (3 Ton) / Both installed with new coils in December 2019 / No issues with sensible heating or cooling. / New filters installed for measurements.

    Outdoor Environmental Conditions: Aug 2020 - Temp 81.3 / RH 56.4 / DP 64.3 / WB 69.6 / Partly Cloudy / No Wind

    Lower Level Readings:
    Ambient Temp at Thermostat 71.4 / RH 51.0%
    Return Air Readings (Measured immediately downstream of filter): Static Pressure .-7" / Temp 72.3 / RH 58.7% / DP 57 / WB 62.6 / BTU/h 28.2
    Supply Air Readings (Measured just above coil inside plenum / Pressure measured just before coil): Static Pressure -.44" / Temp 53.5 / RH 68.3% / DP 43.3 / WB 48.1 / BTU/h 19.2
    Calculated Delivered BTU: Total CFM: 1400 (Speed tap 5) / Cooling BTU 56,700 (seems off?)
    Furthest Room Supply Vent: (~60ft run): Temp 58.8 / RH 68.2 / DP 48.4 / WB 52.9

    The coil on this unit is a little on the cold side. If the air flow was increased, the sensible cooling would increase and latent decrease. More capacity, but less latent. Do not change unless you add the whole house dehumidifier.


    Upper Level Readings:
    Ambient Temp at Thermostat 73.4 / RH 42.7%
    Return Air Readings (Measured immediately downstream of filter): Static Pressure -.4" / Temp 73.8 / RH 46.1% / DP 51.8 / WB 60.4 / BTU/h 26.6
    Supply Air Readings (Measured just above coil inside plenum / Pressure measured just before coil): Static Pressure .3" / Temp 52.8 / RH 68.0% / DP 42.5 / WB 47.5 / BTU/h 18.9
    Calculated Delivered BTU: Total CFM: 1050 (Speed tap 3) / Cooling BTU 36,300
    Furthest Room Supply Vent: (~35ft run): Temp 55.0 / RH 48.2 / DP 50.0 / WB 49.1

    Thanks in advance for any help - let me know if you need any more info. Despite these issues, its been pretty interesting to learn about psychometrics and really start to understand more in depth about HVAC. I have a new appreciation for the trade!
    All things considered, a good setup for max moisture removal. If you install a dehu, you could warm the t-stat to 74^F, 50%RH, a 54^F Dew point as target. If the home was unoccupied for extended time, the a/c temp could be raised or off depending on recovery. The dehu would maintain the %RH at 50%. The a/c would get a good long run on return to the house. This would remove a big load of moisture.
    Judging from the homes ability to maintain low humidity, my guess is that this does not leak much in calm winds in mild seasons. If would benefit from adding fresh air filtered air ventilation during mild conditions and being occupied. 100 cfm of make-up to purge indoor pollutants and renew oxygen, healthy and more comfortable for the occupants. No fresh air needed windy or when stack effect is high. Humidifier for <40%RH times.

    You could train a/c techs on some of these finer points.
    You might consider using CO2 control for fresh air. When the CO2 levels are +650 PPMs, bring in 100 cfm of fresh air would appear to automate the fresh air ventilation when occupied and no wind/stack effect.
    Amazon <$150 control CO2 with dehu fan/fresh air vent/damper.
    If you do the dehu, important to get return from open part of the home to dehu. Connect the dehu supply to the a/c to the isolated rooms. The dehu dry/filtered/fresh air will go through isolated rooms back to dehu via the door undercuts to open part of the home to the dehu. Fresh air is via dampered 6" fresh air duct to the dehu return.

    Comment of how coils remove moisture, at the coil surface, the air is 100%RH, but then mixes with the air flowing through gaps not having coil contact. Thus the %RH is lowered. Also any warming from the ducts lowers the %RH. It all appears normal.
    Of course, evenings and rainy days in a properly ventilated home, the air in all homes become outdoor dew points plus the moisture the occupants minus the moisture absorbed by the materials in the home. Size the dehu to handle this load. 4-6 lbs. per hour of supplemental dehumidification will improve this home dramatically.
    2-3 lbs.of humidification per hour with a fan on the humidifier will do.
    Keep us posted.
    Find a solid young tech that will appreciate your help.
    Check out the Ultra-Aire 120 dehu with fresh dampered air.

    Regards Teddy Bear
    Keep us posted.
    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"

  4. #4
    Join Date
    Aug 2020
    Posts
    3
    Post Likes
    Thread Starter
    Hey guys,

    Thanks for the replies. Teddy I know you’re the guru on this stuff so especially appreciate your in depth analysis. If I may ask a couple follow up questions:

    1) “Judging from the homes ability to maintain low humidity, my guess is that this does not leak much in calm winds in mild seasons.”

    I’ve been reading and re-reading this sentence to try and better understand. Are you saying that the house isn’t necessarily leaky because it has a proven ability to stay dry in the winter? Are there any general rules for seasonality of homes and how the humidity naturally moves (you mentioned stack effect)? Feel free to just point me in the right direction and I’ll do the research.

    2) Regarding the dehumidifier units. You mentioned getting a unit that can pull 4-6lbs/hr. I’m sold on the ultra-air units since they seem to be very popular. Is that 120H sufficient for a 3400sqft house? Or do I need to run the psychrometrics calculations to figure out how many grains per hour I need to remove? From what I’m reading, I should be installing it on the lower level system since apparently the humidity naturally sinks to the first floor of a house.

    Thanks again guys!

  5. #5
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    10,424
    Post Likes
    Quote Originally Posted by JWebs View Post
    Hey guys,

    Thanks for the replies. Teddy I know you’re the guru on this stuff so especially appreciate your in depth analysis. If I may ask a couple follow up questions:

    1) “Judging from the homes ability to maintain low humidity, my guess is that this does not leak much in calm winds in mild seasons.”
    Even leaky homes to not leak much with low/no winds or stack effect. Also your home is fairly dry when the a/c cooling load is high.

    I’ve been reading and re-reading this sentence to try and better understand. Are you saying that the house isn’t necessarily leaky because it has a proven ability to stay dry in the winter? Are there any general rules for seasonality of homes and how the humidity naturally moves (you mentioned stack effect)? Feel free to just point me in the right direction and I’ll do the research.

    Outside air infiltrates via wind, stack effect, and mechanical air movement like the clothes drier and exhaust equipment. The dew point of the air passing through the home less moisture removed by the conditioning equipment plus the moisture added by the occupants determines the indoor dew point. Dry during cold weather and wet during high outdoor dew points.

    2) Regarding the dehumidifier units. You mentioned getting a unit that can pull 4-6lbs/hr. I’m sold on the ultra-air units since they seem to be very popular. Is that 120H sufficient for a 3400sqft house? Or do I need to run the psychrometrics calculations to figure out how many grains per hour I need to remove? From what I’m reading, I should be installing it on the lower level system since apparently the humidity naturally sinks to the first floor of a house.

    Thanks again guys!

    A home your size will be much improved with the addition of a 4-5 lbs. per hour dehumidifier. that you will be satisfied.
    But do the calculations and confirm my estimate.
    Installation is important to get circulation throughout the home.and connected to the a/c in a way allow both of the a/cs to contribute to the moisture removal of up to 15 lbs. of moisture per hour during peak latent loads. The dehu has the lesser of the load during cool damp weather and occupancy plus fresh air.

    The Ultra-Aire 120 is one of our more efficient dehus at 7-8 pints per KWH. Merv 13 air filter and able to circulated air through out the home.
    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"

  6. Likes JWebs liked this post.
  7. #6
    Join Date
    Aug 2020
    Posts
    3
    Post Likes
    Thread Starter
    Thanks for the info Teddy.

    Anyone have any recommendations for a good/reliable motorized damper? CO2 controllers like Teddy mentioned?

  8. Likes hotandhumidfl liked this post.

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •