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  1. #1
    Join Date
    Jul 2009
    Posts
    51

    Decreased life span of unit dehumidification

    Will excessive dehumidification cause a shortened life span of a unit? I'm referring to units that only have single stage cooling. If you set a unit to maximum overcool for dehumidification, the fan would run extended periods of time on a low fan speed. The compressor could have liquid slugging or low superheat.

  2. #2
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    You raise a good point.

    The merits of good airlfow and not using restritive air filters are frequently mentioned. But on the other hand, it's recomended to slwo the blwoer down up to 20% to increase dehumidification.

    I think what needs to get mentioned here, is what total capacity, or total heat transfer is occuring at the coil when the fan speed is reduced. If we are simply reducing the sensible ratio, but not greatly affecting total capacity, then the compressor won't "know the difference". But if airlfow is reduced without a high latent load, then total capacity would decrease.

    For this reason, it's probably not adviseable to attept to lower indoor humidity below perhaps 40-45%... which at 70F... is a 44F dewpoint. That means coil temps could be are hovering around 40F or even approaching freezing. 2 things can happen. 1) the coil will begin to freeze and further reduce heat transfer and slugging occurs) or 2) total capcity drops low enough that again, slugging can occur.


    So maybe the quesiton is, how low can capacity drop from reduced heat transfer at the indoor coil before problems occur. Of course, the specifics of the system in question and indoor dry and wet bulb temps and outdoor temps will affect that.

    Perhaps, that's why it's a good idea to use a dehumidifier to address latent loads, rather than pushing the performance envelope of the A/C sytem.

  3. #3
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Quote Originally Posted by venting View Post
    Will excessive dehumidification cause a shortened life span of a unit? I'm referring to units that only have single stage cooling. If you set a unit to maximum overcool for dehumidification, the fan would run extended periods of time on a low fan speed. The compressor could have liquid slugging or low superheat.
    With the proper controls on a variable speed indoor motor, the cfms are not low enough to due any damage.

    Plus longer run times are better for motors then short on and off cycles.

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