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  1. #40
    Join Date
    Aug 2006
    Location
    Dallas (Plano), TX
    Posts
    168
    Quote Originally Posted by teddy bear View Post
    Looking forward to more discussion with those interested. Regards TB
    Some time ago, Lennox made a publication, that with respect to maintaining lower RH in residences during periods of partial or no HVAC system loading, said in part:

    1. Eliminate moisture sources.
    2. Maximize amount of dehumidification done during the cooling cycle by getting the coil as cold as possible (lower air speed).
    3. Prevent re-evaporation of condensation back into the supply air by not running blower motor continuously, and managing condensate.
    4. Properly vent appliances, i.e., dryer

    And here's a chart where Lennox shows what happens when the blower motor is run continuously:



    The entire reference is available at http://www.dca.state.fl.us/fbc/commi...pplication.pdf

    Best regards,

    Bill

  2. #41
    Join Date
    Oct 2005
    Location
    MN
    Posts
    133
    FWIW

    My power company gives me a discount for being able to interupt my AC for something like 20 minutes per hour on peak demand days. I am able to tell EXACTLY when they are doing this, because there is a NOTICABLE increase in the humidity levels during this time (I run my fan on continuous).

    Frank

  3. #42
    Join Date
    Apr 2005
    Location
    Kingston Ontario Canada
    Posts
    1,210
    Quote Originally Posted by frankt View Post
    FWIW

    My power company gives me a discount for being able to interupt my AC for something like 20 minutes per hour on peak demand days. I am able to tell EXACTLY when they are doing this, because there is a NOTICABLE increase in the humidity levels during this time (I run my fan on continuous).

    Frank
    Frankt, that's a good reason not to run your fan on continuous!!! When the compressor is shut off intentionally or otherwise, the coil is wet and with the fan running continuously it sends humidity from the wet coil all thorugh your conditoned space and increases the humidity almost instantly. Hope this helps some.

    thorton
    __________________
    Tell it like it is and let the chips fall where they may

  4. #43
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,360
    Quote Originally Posted by a0128958 View Post
    And here's a chart where Lennox shows what happens when the blower motor is run continuously:



    The entire reference is available at http://www.dca.state.fl.us/fbc/commi...pplication.pdf

    Best regards,

    Bill
    Good illistration. What is the %RH in the ducts as the moisture evaporates of the coil during the a/c/fan off cycle. My guess is that the ducts down stream from the cooling coil are +90%RH during much of the a/c season. The a/c return and air filter will also be damp as the coil dries off. This ideal for mold growth in the supply ducts. Also during the partial a/c load time of the day/week/month, the water on the coil does slowly evaporates and migrates back to the home. This may explain the moisture/mold on grills. Personally, I feel that the ducts should be dry for several hours everyday to prevent mold growth. These coils retain 4-8 lbs. of moisture at the end of the cooling cycle. Operating the fan for a couple hours during the partial load time of the day may reduce potiental for mold in ducts. Evaporating serval lbs. of moiture into the home raises the home 19-20%RH. If a whole house dehumidifier is used, we like to blow the dry air from the dehu into the supply side of the a/c system to slowly dry the ducts during the a/c off cycle. 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"

  5. #44
    Join Date
    Apr 2005
    Location
    Kingston Ontario Canada
    Posts
    1,210
    Quote Originally Posted by teddy bear View Post
    Good illistration. What is the &#37;RH in the ducts as the moisture evaporates of the coil during the a/c/fan off cycle. My guess is that the ducts down stream from the cooling coil are +90%RH during much of the a/c season. The a/c return and air filter will also be damp as the coil dries off. This ideal for mold growth in the supply ducts. Also during the partial a/c load time of the day/week/month, the water on the coil does slowly evaporates and migrates back to the home. This may explain the moisture/mold on grills. Personally, I feel that the ducts should be dry for several hours everyday to prevent mold growth. These coils retain 4-8 lbs. of moisture at the end of the cooling cycle. Operating the fan for a couple hours during the partial load time of the day may reduce potiental for mold in ducts. Evaporating serval lbs. of moiture into the home raises the home 19-20%RH. If a whole house dehumidifier is used, we like to blow the dry air from the dehu into the supply side of the a/c system to slowly dry the ducts during the a/c off cycle. Regards TB
    Great post, Teddy Bear!!! These are good for moldy basements, too! http://www.air-purifiers-cleaners.co...r-purifier.htm
    Bears Rule!!!

    thorton
    ________________
    A Stupid Question is the one that was never asked!

  6. #45
    Join Date
    Jul 2007
    Location
    Phoenix, AZ
    Posts
    206
    So with a 2 speed compressor, when the system is on low speed cooling the indoor coil is therefore to big and will not remove humidity from the house, but will cool the home? Two speed units are becoming more popular because of the better seer rating.

  7. #46
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,360
    Quote Originally Posted by Firebird A/C View Post
    So with a 2 speed compressor, when the system is on low speed cooling the indoor coil is therefore to big and will not remove humidity from the house, but will cool the home? Two speed units are becoming more popular because of the better seer rating.
    Yes, the indoor coil is grossly oversized for the low speed of the compressor. To offset the low speed of the compressor, the air flow is reduced to keep the temperature on the coil as low as possible. In most cases, about the same latent heat ratio is removed. This reduces the length of the off cycle which maintains same latent ratio. As the cooling load is further reduced, the a/c will over-cooler for upto 3^F. Finally the a/c short cycles with large quantities of water on the oversized a/c coil. Two speed compressors do improve latent removal compared to single speed compressors. They have complicated controls and components. They are also difficult to set-up, expensive to maintain and purchase. With all this, they are unalbe to remove moisture without considerable cooling load. It is more effective to use simple high SEER single speed a/c and a whole house dehumidifier. The whole house dehu is capable of maintaining <50%RH with little or no cooling load. 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"

  8. #47
    Join Date
    Jul 2007
    Location
    Phoenix, AZ
    Posts
    206
    TB, thanks for your time.
    Here in Phoenix we can run 100 to 110 degrees with 10% outside humidity for 3 months in the summer. The equipment manufactors are pushing these 2 stage compressors, saying you do not need your full cooling capacity most of the time. But when you do need full capacity you have it. First stage cooling I think is around 60 to 70 percent of your full cooling capacity. The furnace does run on a slower speed for first stage cooling. So the TXV should flood the indoor coil out and maintain your superheat on low speed cooling. The outdoor condensor is very simple on these two stage units. The variable speed furnace for these units do have a circuit board and more complex blower motor in it. I just put in 2- 4 ton american standard 2 stage R-410a units last week on a house. I was impressed with the units and how they ran and worked. The compressor drew 4 to 5 amps less when it was on first stage cooling over the second stage cooling. It has took a while for me to accept, but I think these 2 stage compressors are the way to go now. For higher end sales and customers.

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