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  1. #1
    Join Date
    May 2009
    Location
    Waterloo Ontario
    Posts
    58

    Higher ton evap coil, with lower ton cond

    hey guys,

    I've been told that when matching up a cond and evap, if you use a larger evap coil it will increase the seer rating?

    Ive got a 2 ton lennox heat pump, and a 3 ton case coil made by lennox as well.

    How does this effect the seet rating? is it stickly because of the increased size of the evap surface area?

  2. #2
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    The saturated temperature/pressure will be higher with a larger evaporator coil, which lowers the compression ratio, so the compressor uses less energy for a similar amount of cooling.
    The total btuh capacity typically goes up slightly, but so does the sensible heat ratio, so humidity control can suffer a bit.
    If more government is the answer, then it's a really stupid question.

  3. #3
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,371
    Quote Originally Posted by mark beiser View Post
    The saturated temperature/pressure will be higher with a larger evaporator coil, which lowers the compression ratio, so the compressor uses less energy for a similar amount of cooling.
    The total btuh capacity typically goes up slightly, but so does the sensible heat ratio, so humidity control can suffer a bit.
    Add- " so humidity control can suffer a bit" unless the air is flow is slowed enough to lower the coil temperature several degrees below the desired inside dew point. Slowing the air flow will remove more moisture while maintaining a higher suction capacity. The negative factor is that more moisture is needed to get the coil to drip to the drain and retained on the larger coil which will evaporate into the home at the end the cooling cycle. This affects the muli-speed a/cs in a big way. They lower cooling capacity will very large coils. 1-2 lbs. moisdture per ton are need on a coil to start draining. At the end of the cycle, the retained moisture evaporates back into the home. Make the cooling cycle are long as possible. Using a whole house dehumidifier for maintaining <50%RH during low/no cooling loads is much more effective.
    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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