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Thread: Another High Indoor Humidity Thread from Houston

  1. #1
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    Another High Indoor Humidity Thread from Houston

    Hi All, I have read many posts on here and am starting to get an understanding of why our system is not effective in maintaining indoor humidity. I thought I would create a post to get specific advice on our system.

    Now and during the Summer our home indoor humidity level ranges from mid- to high- 60s RH and sometimes hits 70s. The home is two years old, 2 stories, and has two Lennox HVAC units (one for upstairs and one for down), AprilAire fresh air ventilation, and also an AprilAire dehumidifier.

    We have had original installers and other techs look at the system and they simply say this is the best that can be done in Houston. I know this is not the case so looking for help here to make the specific changes needed to get the AC system maintaining 50% RH and letting the dehumidifier maintain when AC isn't running.

    I appreciate any advice you all can provide and let me know what additional info you need on the specifics of our system.

    Thanks

  2. #2
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    We need model and serial numbers of all equipment installed, if possible the commissioning reports of the systems with refrigerant pressures, line temperatures, indoor and outdoor temperatures and humidity, pictures of equipment, duct layouts, and if possible the load calculations for the home.

  3. #3
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    Number of occupants, size of the home and size of the dehumidifier are needed.

    What is the temp/%RH do you get during peak sensible cooling load? Also temp/%RH early morning hours?

    Looking forward to the discussion.

    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"

  4. #4
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    Thread Starter
    Equipment:
    Outdoor Condenser 1: Lennox 14ACX-047-230-05 - 4 ton
    Outdoor Condenser 2: Lennox 14ACXS036-230A22 - 3 ton
    Attic Furnace 1 and 2: Lennox ML180UHE
    Dehumidifier: Aprilaire 1850 - 95 pints/day
    Ventilation Controller: Aprilaire 8120X
    Thermostat: Lennox M30

    5 occupants
    5 bedroom, 4500 sqft, 2-story house

    Upstairs unit:
    Temp/RH% Peak Loading: 73/69 (2pm yesterday)
    Temp/RH% Early Morning: 72/64 (5am today)

    Downstairs unit:
    Temp/RH% Peak Loading: 74/64 (2pm yesterday)
    Temp/RH% Early Morning: 71/64.5 (5am today)

    Thanks for the help.

    Also, our HVAC still has some time left on the home builder warranty. So if the equipment is wrongly sized or incorrectly configured I may be able to get them resolve these issues.

  5. #5
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    Oversized equipment is the most likely cause. Leaky ducts outside the envelope and house infiltration probably are big contributors to the problem as well.
    Oversized equipment does not run long enough to remove humidity, so we ask - how long does the equipment run during peak load?

    Without a load calculation and a blower door test we can only guess about the real cause(s) of the problem.

    I suggest you hire a third party to assess the house and the HVAC systems.
    *********
    https://www.hvac20.com/ High efficiency equipment alone does not provide home comfort and efficiency. HVAC2.0 is a process for finding the real needs of the house and the occupants. Offer the customer a menu of work to address their problems and give them a probability of success.

    Find contractors with specialized training in combustion analysis, residential system performance, air flow, and duct optimization https://www.myhomecomfort.org/


    Site member map HERE!

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  7. #6
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    The home is 2 years old and has a HERS rating of 56. I found a IECC 2015 label and it says among other things: Infiltration is 3223 CFM50 (3.81 ACH50) and Duct leakage is 71 CFM at 25 Pa. Window and Door specs: U-value 0.22, SHGC 0.19, Door is R-2. They did a door blower test post construction but I don't see that I have a report for that.

    I just recently had a third party HVAC company do an inspection. The biggest issues they flagged was that the delta T is too low (15ish vs what they said should be 20), potentially low refrigerant, and that the output air from the dehumidifier is very hot and that gets fed back into the input of one of the air units which could be over working that unit.

    Attached are their reports.

    Checkup Indoor Equipment.pdf
    Checkup Condenser.pdf

    I just timed how long the upstairs unit ran on the most recent cycle and it was 8 minutes. Today is overcast and not as hot as normal though.

  8. #7
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    7-Tons in 4500 Sq Ft?

    If I'm reading the report correctly 1.1 TEST shouldn't that be .5?

  9. #8
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    Quote Originally Posted by pecmsg View Post
    7-Tons in 4500 Sq Ft?

    If I'm reading the report correctly 1.1 TEST shouldn't that be .5?
    Not sure I know the answer about 1.1 VS 0.5. Do you think 7 tons is oversized? We are in the coastal zone in Houston, hot and humid.

  10. #9
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    .5 is generally the max static pressure allowed yours is double. That’s tell me you have huge duct issue.

    With all the fancy certifications sizing always come in close to the old school 500 sq ft per ton. Old school, inaccurate and just wrong.

  11. #10
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    Quote Originally Posted by gtmg View Post
    Equipment:
    Outdoor Condenser 1: Lennox 14ACX-047-230-05 - 4 ton
    Outdoor Condenser 2: Lennox 14ACXS036-230A22 - 3 ton
    Attic Furnace 1 and 2: Lennox ML180UHE
    Dehumidifier: Aprilaire 1850 - 95 pints/day
    Ventilation Controller: Aprilaire 8120X
    Thermostat: Lennox M30

    5 occupants
    5 bedroom, 4500 sqft, 2-story house

    Upstairs unit:
    Temp/RH% Peak Loading: 73/69 (2pm yesterday)
    Temp/RH% Early Morning: 72/64 (5am today)

    Downstairs unit:
    Temp/RH% Peak Loading: 74/64 (2pm yesterday)
    Temp/RH% Early Morning: 71/64.5 (5am today)

    Thanks for the help.

    Also, our HVAC still has some time left on the home builder warranty. So if the equipment is wrongly sized or incorrectly configured I may be able to get them resolve these issues.
    I think you have all the equipment that you need. Your a/cs are setup correctly. When the a/c run with a significantly cooling load, expect 50%RH after a hot afternoon. If not, the a/c needs service and air flow adjustment. Slowing the air flow through the cooling coil increases the amount of moisture remove and slow the sensible cooling rate. Not all a/c companies understand the concept. The concept is that after the new a/c is connected to the ducts, the air flow is adjusted to provide a 30^F cooing coil temperature colder than the return air temperature. This will remove 3 lbs. of moisture per ton of ton per hour when setup correctly. This a start.

    Next if the ducting of the dehumidifier to the home and a/c system. The warm dry air from the dehumidifier should be routed to the home and not the return air of the air going to the a/c cooling coil. This warm dry air reduces the amount of the moisture removed by the a/c when both are operating.

    A/c cooling temperature and dehumidifier connects are critical to providing <50%RH in the home during humid outside condition and occupancy.

    Slightly oversided a/c is not your problem. Setup of the a/c the first problem and installation of the dehumidifier also is part of the problem.
    i am willing to explain this concept to the installer if needed.
    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"

  12. #11
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    Quote Originally Posted by teddy bear View Post
    I think you have all the equipment that you need. Your a/cs are setup correctly. When the a/c run with a significantly cooling load, expect 50%RH after a hot afternoon. If not, the a/c needs service and air flow adjustment. Slowing the air flow through the cooling coil increases the amount of moisture remove and slow the sensible cooling rate. Not all a/c companies understand the concept. The concept is that after the new a/c is connected to the ducts, the air flow is adjusted to provide a 30^F cooing coil temperature colder than the return air temperature. This will remove 3 lbs. of moisture per ton of ton per hour when setup correctly. This a start.

    Next if the ducting of the dehumidifier to the home and a/c system. The warm dry air from the dehumidifier should be routed to the home and not the return air of the air going to the a/c cooling coil. This warm dry air reduces the amount of the moisture removed by the a/c when both are operating.

    A/c cooling temperature and dehumidifier connects are critical to providing <50%RH in the home during humid outside condition and occupancy.

    Slightly oversided a/c is not your problem. Setup of the a/c the first problem and installation of the dehumidifier also is part of the problem.
    i am willing to explain this concept to the installer if needed.
    Keep us posted.

    Regards Teddy Bear
    Teddy,

    Thanks for the response.

    Regarding the airflow, is there a specific technique the tech needs to follow to lower the speed enough to achieve the 30 degree differential you described? How should the measure the coil temp? The report they gave me measured temp just before entering filter and then just on the other side of coil, that difference was about 15 degrees and the tech said we need to get it to 20. Is this the measurement that you say should be 30?

    Regarding dehumidifier, the air temp coming out of the dehu was slightly over 100 degrees F. So you are saying just send that to an output in the house? Wouldn't the area receiving that hot air be warmer?

  13. #12
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    Where did they take their Air temperature split readings? They need to be taken right at the air handler. If you have a 20F split at the air handler and then they take the supply temp a at a register and get 15F, you have airflow and/or duct infiltration issues in cooling.

    Sent from my SM-G965W using Tapatalk

  14. #13
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    Quote Originally Posted by BALloyd View Post
    Where did they take their Air temperature split readings? They need to be taken right at the air handler. If you have a 20F split at the air handler and then they take the supply temp a at a register and get 15F, you have airflow and/or duct infiltration issues in cooling.

    Sent from my SM-G965W using Tapatalk
    See attached picture. The arrows are where their temperature probes were and my understanding is that they measured 15 degrees across these two points. The tech said it should be 20 and that once the condenser gets full charged up with refrigerant than it would be closer to 20. They never said anything about reducing blower speed.

    Name:  temp meaurement.jpg
Views: 276
Size:  2.53 MB

  15. #14
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    Quote Originally Posted by gtmg View Post
    Teddy,

    Thanks for the response.

    Regarding the airflow, is there a specific technique the tech needs to follow to lower the speed enough to achieve the 30 degree differential you described? How should the measure the coil temp? The report they gave me measured temp just before entering filter and then just on the other side of coil, that difference was about 15 degrees and the tech said we need to get it to 20. Is this the measurement that you say should be 30?

    Regarding dehumidifier, the air temp coming out of the dehu was slightly over 100 degrees F. So you are saying just send that to an output in the house? Wouldn't the area receiving that hot air be warmer?
    All of temperatures become confusing.

    Using the return air temperature from the home is the start. We want 75^F, 50%RH, a 55^F dew point in the home. Assuming 75^F air from the home is entering the cooling coil, adjust the air flow to get a 30^F coiling coil temperature. This would be measured by monitoring the refrigerant pressure. Techs use the pressure to determine the coil temperature. The air temperature of the air leaving the coil should be 53-55^F, 90%RH, +-50^F dew point. You can look for the 5^F reduction of the house air as it passes through the cooling coil.

    The greater the reduction of the cooling coil temperature, the more moisture is removed. Slowing air flow increases the moisture removed and decreases the sensible cooling rate.

    Let us talk about the dehumidifier supply. Assume 250 cfm of 100^F air @ 20% RH. Adding this to the a/c supply to 800 cfm of 55^F cold air warms the supply several degrees. Ok to route the dehumidifier warm air to a basement but not a single warm area unless you want the space heated.

    Show this your tech. If there are questions, let us discuss them.

    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"

  16. #15
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    Quote Originally Posted by gtmg View Post
    Teddy,

    Thanks for the response.

    Regarding the airflow, is there a specific technique the tech needs to follow to lower the speed enough to achieve the 30 degree differential you described? How should the measure the coil temp?

    The report they gave me
    measured temp just before entering filter
    and then just on the other side of coil
    ,
    that difference was about 15 degrees and the tech said we need to get it to 20.

    Is this the measurement that you say should be 30?

    Regarding dehumidifier, the air temp coming out of the dehu was slightly over 100 degrees F.

    So you are saying just send that to an output in the house?
    Wouldn't the area receiving that hot air be warmer?
    It IS
    IMPOSSIBLE to achieve a 30'F AHU Air Temperature split
    on a typical residential Air Handler Unit.
    Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities

  17. #16
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    Quote Originally Posted by teddy bear View Post
    All of temperatures become confusing.

    Using the return air temperature from the home is the start.
    We want 75'F, 50%RH,
    a 55'F dew point in the home.

    Assuming 75'F air from the home is entering the cooling coil,
    adjust the air flow to get a 30'F coiling coil temperature.

    This would be measured by monitoring the refrigerant pressure.
    Techs use the pressure to determine the coil temperature.

    The air temperature of the
    air leaving the coil should be 53-55 'F, 90%RH, +-50'F dew point.

    You can look for the 5'F ? reduction
    of the house air as it passes through the cooling coil.

    The greater the reduction of the cooling coil temperature, the more moisture is removed. Slowing air flow increases the moisture removed and decreases the sensible cooling rate.

    Let us talk about the dehumidifier supply.
    Assume 250 cfm of 100'F air @ 20% RH.
    Adding this to the a/c supply to 800 cfm of 55'F cold air
    warms the supply several degrees.
    Ok to route the dehumidifier warm air to a basement but not a single warm area unless you want the space heated.

    Show this your tech. If there are questions, let us discuss them.

    Regards, Teddy Bear
    How does one achieve a Coil temperature 45'F lower than the Return Air temperature?
    Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities

  18. #17
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    Quote Originally Posted by teddy bear View Post
    All of temperatures become confusing.

    Using the return air temperature from the home is the start.
    We want 75^F, 50%RH, a 55^F dew point in the home.

    Assuming 75^F air from the home is entering the cooling coil,
    adjust the air flow to get a 30^F coiling coil temperature.


    The greater the reduction of the cooling coil temperature, the more moisture is removed.
    Slowing air flow increases the moisture removed
    and decreases the sensible cooling rate.

    Let us talk about the dehumidifier supply.

    Assume 250 cfm of 100^F air @ 20% RH.
    Adding this to the a/c supply to 800 cfm of 55^F cold air warms the supply several degrees.

    Ok to route the dehumidifier warm air to a basement but
    not a single warm area unless you want the space heated.

    Show this your tech.

    If there are questions, let us discuss them.

    Regards, Teddy Bear
    How much is the Sensible Cooling capacity reduced ?

    ___ 30% due to adding heat from the dehumidifier
    ___+ _ _ % due to limiting the air flow
    .. ~40 % Sensible Cooling Capacity reduction
    Attached Images Attached Images  
    Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities

  19. #18
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    Quote Originally Posted by teddy bear View Post
    All of temperatures become confusing.

    Using the return air temperature from the home is the start. We want 75^F, 50%RH, a 55^F dew point in the home. Assuming 75^F air from the home is entering the cooling coil, adjust the air flow to get a 30^F decrease in coiling coil temperatureMy mistake, 75^F return air, a cooling coil that is 30^F colder than the return air temperature, 75^F minus 30^F equals 45^F coil temperature. This would be measured by monitoring the refrigerant pressure. Techs use the pressure to determine the coil temperature. The air temperature of the air leaving the coil should be 53-55^F, 90%RH, +-50^F dew point. You can look for the 5^F reduction of the house air as it passes through the cooling coil.

    The greater the reduction of the cooling coil temperature, the more moisture is removed. Slowing air flow increases the moisture removed and decreases the sensible cooling rate.

    Let us talk about the dehumidifier supply. Assume 250 cfm of 100^F air @ 20% RH. Adding this to the a/c supply to 800 cfm of 55^F cold air warms the supply several degrees. Ok to route the dehumidifier warm air to a basement but not a single warm area unless you want the space heated.

    Show this your tech. If there are questions, let us discuss them.

    Regards, Teddy Bear
    Thank you Dan. Sorry. The numbers get confusing.
    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"

  20. #19
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    Thread Starter
    Thanks for all the input. Is there a consensus recommendation?

  21. #20
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    Quote Originally Posted by gtmg View Post
    Is there a consensus recommendation?
    Yes! and I think you might agree, you can't control the humidity in Houston, it controls us.
    __________________________________________________ _______________________
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