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Condensation on minisplit louvers

this_page_left_blank | Posted in General Questions on

I’ve noticed beads of condensation on the louvers of my new mini split occasionally. Is a certain amount of this expected? I mean, you’ve got humid air in the house, there’s a cold surface, water is going to condense on it, right? Or should the dried air coming out of the unit supposed to push away ambient humid air so that it doesn’t happen? Plenty of water comes out the drain outside as well. Should I get the installer back to take a look?

The conditions during which this is happening is when the interior is around 23C, 60%RH. I didn’t think to measure the temperature of the louver.

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  1. Jon_R | | #1

    Check that the AC air isn't being over-cooled. And consider going lower on interior humidity (say 50-55%). But yes - cold ducts sweat.

    1. this_page_left_blank | | #4

      What is the criteria for over-cooled?

      1. Jon_R | | #5

        It depends on the latent/sensible ratio you want, but 20F below room air temperature is often used.

  2. Yupster | | #2

    From the manual:

    "..For efficient air conditioning, select the upper position for
    COOL/DRY, and the lower position for HEAT. If the lower
    position is selected during COOL/DRY, the vane automatically
    moves to the upward position (3) after 0.5 to 1 hour to prevent
    any condensation from dripping."

    So it seems the condensation is expected and planned for.

  3. joshdurston | | #3

    My FH09 doesn't seem to to condense on the plastic louvers, but lots of water goes down the drain. I wonder if this is related to cycling, or higher fan speed settings? I generally keep my louvers pointed more less horizontal during cooling operation.

    I started cooling at noon this past Saturday (Southern Ontario Canada), inside it was 27C 75%rh (dewpoint 22c/72f) initially, the unit never cycled once, but filled 2 5-gallon pails of condensate. Humidity came down into the 50's, within a hour.

    I measured the discharge air temp a couple times with a digital thermometer, it was around 8.7C/48f (well below the space dewpoint).

    1. kjmass1 | | #7

      How long did it take to fill up 10 gallons of condensate? That'd be quite impressive. My 12k certainly dehumidifies but it's at tops a drip or two per second, never gushing out. 80 pints over how many hours?

      1. joshdurston | | #8

        It took over 20hrs, but my house was pretty humidity soaked. I'll also admit the pails weren't totally full, when I inspected and drained them. So it may have been closer to 60 pints to be realistic. (rated moisture removal is a dismal 0.7 pints/hr).

        Interior humidity had been in the 70%rh's for a couple days. So it had lots of moisture to chew on. When it's running at low modulation levels the discharge are temp is in the 60's and it doesn't condense much, but under heavy loads the discharge drops into the high 40F range and you get lots of water.

        The only reason I mentioned it, is that the FH09 has a pretty poor rated SHR of something like 0.92. But in the real world thankfully it dehumidifies when it needs to. My FH09 is also very aggressively sized. It's the only cooling in my bungalow that somewhere between 1300-1500 sq ft in Southern Ontario. If it were oversized I suspect it would have modulated down much sooner and had a tougher time dehumidifying.
        Thanks to the variable speed compressor it can really work hard when it needs too, a conventional DX split would've seen elevated discharge temps for a quite a while until the humidity came down since it can only move so much refrigerant with a fixed speed compressor, but since the mini split compressor can hold the suction line pressure steady at a low target without freezing anything, and the LEV keeps the evaporator basically flooded (almost no superheat) it can hit well above it's weight, and handle a peak load at least one size higher. (3/4ton can actually give 1ton of capacity under the right conditions).

  4. Jon_Harrod | | #6

    I suspect that the air coming out of the unit is cooling the louvers below the dew point of the surrounding air. If this is the cause, try setting the fan speed to high, at least until the humidity comes down to the 50-55% range.

  5. this_page_left_blank | | #9

    I finally got someone to come out and look at it. Turns out that only one of the two louvers was opening, the upper one was jammed shut. It was this upper one that was collecting all the condensation. Fixed this problem and have had no condensation since.

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