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  1. #1
    Join Date
    Apr 2012
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    Unhappy Mitsi pipes problems


    I have been invited to install a VRF system in a large apartment. During the visit to site I have seen that the pipes and cables have already been laid down. The pipes were mostly laid out in pairs of 1/4 - 3/8". i usually work with Mitsubishi Electric which has all of its indoor units with liquid/gas lines 1/4 - 1/2". I really like to perform this job with Mitsy since they are very good customers but I dont know if I can use their piping. Any suggestions?



  2. #2
    Join Date
    Feb 2012
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    Bolivia
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    Re: Mitsi pipes problems

    You know diameters depend on thermal loads and equivalent lengths, so you should calculate the suggested diameters. Not doing this is a mistake.

    If there is a discrepancy you should check whether the higher pressure drop will cause the equipment to operate outside its envelope, there’s a high chance a VRF will still comply.

    If it does not, sometimes a small design change can let you operate in that condition, for example improve condensation to prevent higher discharge temperatures or use a desuperheater.

    Surely Mitsu people can help you with this.

  3. #3
    Join Date
    Oct 2003
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    Belgium
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    Re: Mitsi pipes problems

    Some Mitsubishi types have the tubes you mention, not all. You can reduce size many times with R410a. Which indoor units you want to install?
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  4. #4
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    Dec 2011
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    Re: Mitsi pipes problems

    All Mitsu indoor up to at least 3.5KW are 3/8 + 1/4 if I'm not mistaking. Maybe different for VRFs. Can't say I've fitted units that small on a VRF system.

  5. #5
    Join Date
    Oct 2003
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    Re: Mitsi pipes problems

    HeavyT, looked once in the Mitsu manual and you are right for the VRF range: even the smallest one is 1/4 - 1/2. Sorry, my mistake.
    20 m 3/8 gives a Dp of 0.63 bar at 2.5 kW
    10 m gives 0.3 bar or 1.26 K.
    So you will be limited at +/- 2 to 2.5 kW for a 3/8 tube, depending on the length.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  6. #6
    Join Date
    Apr 2012
    Location
    Albania
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    Red face Re: Mitsi pipes problems

    Most of the indoor units will be either hidden floor types or normal floor types. Most of them are also between 2.2 and 2.5, expect for maybe one which is 2.8kW. So I think i might be ok over all. Thank you all for the support.

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