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  1. #1
    Join Date
    Mar 2018
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    Outdoor mini split condenser unit in an insulated ventilated box indoors?

    Hey guys,

    I would need a 2 to 3 ton ductless mini split unit but unfortunately I am not able to install the outside condenser unit outside of the building. That is the reason why I need expert advice.

    I know the idea of putting an outdoor condenser unit inside was dismissed already and is a bit radical but I was thinking to put the outdoor unit into an insulated box (inside one of my rooms). This insulated box would have two fans, which are each matched with the cfm rating of the condenser unit and pull air into and out of the box (from and to outside of the building).

    I was looking at some of the mini splits and it seems that you can find outside units from mitsubishi which move around 2000 cfm.

    I was thinking about using two ec inline fans which are able to move around 2000 cfm each. Unfortunately I can't provide a link to These fans (Ruck Etamaster 355 Ruck 3320m/h) , as forum rules restrict posting of links by new users.

    Each fan uses at maximum load around 250 Watts of power. Considering a mini split has a COP rating of over 1, I think that even with the extra energy use of the fans I would come cheaper (energy wise) than anything else what would be possible in my place.

    Can I build in another room an insulated box which contains the condenser unit and this box is connected to ducting which inputs air (from outside of building) and ducting which outputs air (also to outside of the building)? I know that the condenser needs big amounts of air, so I would install two fans which are each able to move around 2000 cfm of air. I would install one fan for pulling air from outside, pushing the air into the box and then another one pulling the air out of the box and pushing them outside. The fans were chosen under the assumption that most mitsubishi condenser units (in the range of power that I need) are able to move around 2000 cfm max each.

    If I could use such a design, I would need to add 500 Watts total for the two fans. I think like that I would still be more energy efficient than other solutions. Maybe only one fan would also be sufficient, then I would only need 250 Watts extra. I am only able to use some indoor solutions and unfortunately geothermal pumps or swamp cooler are not possible. I know it is a bit problematic to find such device if you need a 2 to 3 ton unit.

    So what do you know, would such a setup work? I have not enough knowledge and experience in HVAC, that is why I need to ask a pro.

    So far I have some concerns:

    - Are the outdoor condenser units working with variable fan speeds, and is it a problem if my inline fans blow directly onto the condenser unit? Maybe the airstream of the inline fans, messes with the heating or cooling process of the condenser unit. Also has fast moving air some sort of own effect in temperature (e.g. cooling through windchill)? If it would be the case that direct air has some detrimental effect on efficiency of the unit, I probably could use some sort of wind baffle like it is offered by Mitsubishi (just google mitsubishi wind baffle for picture) . What do you think?

    - I live in a climate where in winter we can get temperatures as cold as -5 Fahrenheit. It happens rarely but it can happen. That situation means that I would need a unit which would work also in these kind of temperatures. Mitsubishi offers Hyper Heating units which work in these temperature ranges. Unfortunately it seems that the Mitsubishi 2 to 3 ton units which support Hyper Heating are almost only twin systems (have two fans), which would mean a combined airflow of 3600cfm. To provide 3600cfm of air with my inline fans to the insulated box where the condenser unit would be in, I would need to buy much stronger and much more expensive inline fans. So I only know the Mitsubishi units so far, but maybe somebody of you know the product range of the other quality brands. Does somebody know a unit which is capable to work in low temperature settings and has a cfm rating of around 2000cfm? Other option would be if somebody knows strong inline or other fans which would be able to do 3600cfm and are actually not that expensive.

    - also what do you think, would I need two or one of these inline fans? I mean suffice how much would such a condenser unit have postive influence on the static pressure. Would the outdoor unit be a resistance or an noticeable aid in pulling air for one fan in such a setup?

    So that is the situation. I hope you can answer some of my questions. Thank you very much!

  2. #2
    Join Date
    Mar 2018
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    Thread Starter
    Any knowledgeable thoughts?

  3. #3
    Join Date
    Apr 2003
    Maple Grove, MN
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    If at First You Don't Succeed, Skydiving Is Not for You.

  4. #4
    Join Date
    Jun 2014
    Dover, DE
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    I think you either need to put the units outside where they are rated to be, or explore other options.
    I havent failed. Ive just found 10,000 ways that wont work. - Thomas Edison

    Its not whether you get knocked down, its whether you get up. - Vince Lombardi

    "In this house we obey the laws of thermodynamics" - Homer Simpson

    Local 486 Instructor & Service Technician

  5. #5
    Join Date
    Jan 2004
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    Will the association allow you to make 2 big holes in your home, and to install the large grilles you will need.
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    How many times must one fix something before it is fixed?

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