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  1. #1

    Acceptable CFM With New A/C/ Heat Pump

    I recently had a new 3.5 ton A/C installed and when the tech was finished, I mention that the air handler was a little loud and there was too much air coming through the vents. He mentioned that since I had a variable speed air handler with a TXV, he could drop the speed down to 1080 CFM and that by doing that since I live in Florida, it would also help with the humidity. Everything seems to be working perfectly, but after reading some of the posts, I am concerned that it might be too low and may possibly damage the compressor. Is the information he gave me correct?

  2. #2
    Join Date
    Nov 2004
    Location
    Austin, TX
    Posts
    876
    The TXV should modulate the refrigerant flow where it wouldn't harm the compressor.
    I am for doing good to the poor, but...I think the best way of doing good to the poor, is not making them easy in poverty, but leading or driving them out of it. I observed...that the more public provisions were made for the poor, the less they provided for themselves, and of course became poorer. And, on the contrary, the less was done for them, the more they did for themselves, and became richer.
    ― Benjamin Franklin

  3. #3
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,060
    Quote Originally Posted by blitz468 View Post
    I recently had a new 3.5 ton A/C installed and when the tech was finished, I mention that the air handler was a little loud and there was too much air coming through the vents. He mentioned that since I had a variable speed air handler with a TXV, he could drop the speed down to 1080 CFM and that by doing that since I live in Florida, it would also help with the humidity. Everything seems to be working perfectly, but after reading some of the posts, I am concerned that it might be too low and may possibly damage the compressor. Is the information he gave me correct?
    Short of loosing over one ton of capacity and your energy bills being high you should be fine until the heat comes on.

  4. #4
    Join Date
    Mar 2012
    Location
    West Chester, PA
    Posts
    511
    If you're comfotable, it's fine. It is less than the required airflow but as stated earlier, the txv will protect the comrpessor from flood backs. It's likely that your duct is undersized and that your old unit's blower motor was unable to deliver the required cfm. The new VS blower is now delivering the required CFM but since the duct work is too small, there is noise and high air velocity. You will lose some capacity but again if your duct is too small you were likely never getting it with the old unit either. VS blowers become energy hogs when delivering CFM at high static pressures (undersized duct) so by backing it off you have prevented it from suckingup too many watts.

  5. #5
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,360
    Changing the air flow through the coil is the method to get the dew point or %RH you want during high cooling loads. The target should be 48-52%RH which is usually a 55^F dew point. To get a 55^F dewpoint, target a 48-50^F coil temp. This keeps efficiency up as much as possible.
    During low/no cooling loads and outdoor dew points, supplemental high eff. dehumidification is the most practical method to provide comfort and prevent mold/dust mites.
    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"

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