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Minisplit in “dehumidify” mode vs. typical 70-pint dehumidifier

FluxCapacitor | Posted in General Questions on

I’m wondering which removes more moisture better and which is more efficient.  This is for a 1950’s NJ basement with bare concrete walls.

For example, how would a little 6,000 Btu  Mitsubishi MZ-FH06NA perform vs your run of the mill Home Depot 70-pint dehumidifier?

does anyone know or want to take a guess?

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Replies

  1. Jon_R | | #1

    The spec sheet for similar model numbers lists very poor moisture removal of 4.8 pints/day.

    1. joshdurston | | #2

      EDIT: I see it's a basement. Coles notes... get a dehum not a mini split.

      I suspect if you have any sort of sensible load the FH06 will technically be more efficient. But it has no means of reheat so it may overcool in the absence of a load.
      I have a FH09 which only a bit better than the FH06 in pints/hr. It's rated at 0.6pints/hr, but in dry mode I can get a bit more than a pint in 30minutes (2pints/hr, 48pints/day). My solution is to run my portable basement dehum at 60%rh, and use dry mode manually if my house is humid and over 74f.

      Based on my experience if you have a latent dominated load I would step up to the FH12 if your space has enough thermal mass to keep it from short cycling at 2500btu. The min CFM in the FH6-12 is similar but the 12 has an 1000btu min capacity which will translate into colder coil temps and a more latent capacity at min.

      This is very frustrating to me. The FH06-09 are mechanically capable of decent dehum, but there is no way to specify a max coil temperature to ensure dehum at low loads without changing to dry mode and losing space temp control. IMHO if the fan can only go down to 131cfm, then a min capacity of less than 4000 btu/hr is kinda pointless if you have any latent load. Under high latent conditions the min capacity should be matched to the min CFM or your SHR goes in the toilet.

      1. Andrew_C | | #3

        Simple separate systems -
        I understand, but I'm not sure it's something to cause frustration. Based on both personal and professional experience, simple separate systems are often cheaper to purchase, cheaper to install, less likely to fail, have less costly failures, are easier to upgrade, and are easier to maintain for both the technically inclined and the vast majority of owners/operators/maintenance staff who are not.
        Dehumidifiers fall into this category IMO. They're cheap, they work, they're portable (mostly), and you can turn them off seasonally as required.

        I suspect, without evidence, that the biggest bang for the buck energy and comfort improvements that can be made are 1) air-sealing (everywhere) and 2) dehumidification (mostly in the south, but probably 70% of the continental U.S.). I recently saw a map of %latent load versus overall cooling load for the USA, but I can't find it right now. The latent load was a LARGE percentage for a surprisingly large area.

      2. FluxCapacitor | | #4

        That’s good info. I think I’m coming to a similar conclusion (but with less thorough investigation)

        I have a FH06 and MLZ09 in my basement and my non-scientific observations (watching drains dripping) indicates the mini splits can be just as effective at moisture removal as my 15 year old dehumidifier. But then the mini splits tend to overcool the room. So I’m stuck with this ever-changing balance between running the humidifier and/or the mini split to get optimal humidity removal and maintaining desired temperature.

        Unfortunately for me the dehumidifier humidistat and mini split don’t communicate so this requires frequent adjustments.

        It’s really too bad my minisplits can’t effectively regulate temperature in dry mode....that would be magical* because I much prefer the virtually silent operation of the mini splits over the racket of the dehumidifier.

        *Did I read somewhere that Fujitsu have a model that claims to do that?

        1. Expert Member
          Dana Dorsett | | #5

          I believe all Fujitsus still follow the temperature setpoint when in DRY mode. The results in less dehumidification when there isn't much of a sensible load, but they don't overchill the place.

          From the sidebar on p. En-7 of the RLS3 manual:

          "During Cooling/Dry mode:

          Set the thermostat to a temperature
          setting that is lower than the present room
          temperature. The Cooling and Dry modes
          will not operate if the thermostat is set
          higher than the actual room temperature (in
          Cooling mode, the fan alone will operate)"

          https://www.fujitsu-general.com/data/manual/OM_9332280029-04_En.pdf

          Daikin's Quaterity series operates to independently settable temperature and humidity setpoints

          1. calum_wilde | | #6

            I can confirm that is how the Fujitsu's operate. I've been trying to passively add sensible load to my basement and I still end up with the temperature at 19°C to maintain the humidity.

  2. FluxCapacitor | | #7

    Somebody make me a dehumidifier that’s reasonable quiet, not super expensive, and can coordinate with my Mitsubishi Kumo App.

    Only then will I be happy ;-)

    1. joshdurston | | #8

      Looks like you have kumo Cloud with the remote space and humidity sensors. Any chance it unlocks any more settings having a humidity sensor? Are any of your heads running off the external sensors, or are they display only?

  3. FluxCapacitor | | #9

    Yup. I have three zones using the remote sensors.

    Activating the remote sensor will give you RH data (as you know) and will in certain situation give you more accurate thermostat control.

    I find the remote sensor useful because my head units are set to turn the fans off completely when the selected temperature is reached (as opposed to the default extra low fan setting).

    The internal temperature sensor would read erroneously in fan off on multi splits due to residual refrigerant flow through the head units.

    But doesn’t unlock anything else.

    1. joshdurston | | #10

      Thanks for the info, it's frustrating that all the pieces are there to have a more intelligent response to humidity, but the control settings and algorithms aren't, even though the hardware is.

  4. NEplumber | | #11

    MSZ-FH06NA & MUZ-FH06NA com o can remove 0.2 points per hr based off the Mitsubishi specs. That's 4.8 points in a 24hr period.
    Go with an Ultraair 70h. We installed quiet a few with happy results.
    link to a vertical one I installed for a home.
    https://www.instagram.com/p/BzRXjRMlmXD/?igshid=17k8w1gnfczp9

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