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Thread: Hotel Service load calc ductless heat pumps

  1. #1
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    Hotel Service load calc ductless heat pumps

    Hi Everyone, I am on the struggle bus with this one and could use some guidance. I am trying to minimize the load calculation for the HVAC on this job and not sure how to do that. I have a 120/240V single phase service. We have sixteen total one to one ductless heat pump (DHP) units. 8 of these have a MCA rating of 11A and a RLA of 8.2A for the outdoor unit and indoor unit for these shows MCA of 1A. The remaining 8 DHP's show a MCA of 12A and RLA of 6.6 for outdoor unit, indoor unit MCA is 1A.


    How can I get the lowest service calculation for all of these units? If I simply add up all of the MCA's I get 184 amps but my service is only 4/0 AL which is rated only 180 amps. Can I add up all of the RLA's plus one each of the MCA's plus all of the MCA's for the indoor units to determine load calc for these?

    8.2AX7 (RLA Outdoor units)+ 11 (MCA one outdoor unit) + 1AX7 (MCA associated with the 7 outdoor units) = 75.4A
    6.6AX7 (RLA Outdoor units) + 12 (MCA one outdoor unit) + 1AX7 (MCA associated with the 7 outdoor units) = 65.2A

    This would give me a much better service load calculation of 140.6 A if you add two lines above together. This is assuming that the MCA is the first motor at 125% and that I can add all additional motors at the RLA value plus the indoor unit MCA.

    Thanks in advance for the advice.

  2. #2
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    Minimum Circuit Ampacity = (RLA x 1.25) + Other Loads
    See-for instance:
    https://iaeimagazine.org/magazine/19...ump-equipment/
    In my opinion, MCA=1.25RLA at least then instead of 6.6 A it has to be 9A for the second group.
    If this it is about room HVAC and each room is provided with a room panel then there is other load also connected to this panel. If there are branches supplying each room then it has to be a feeder for entire hostel.

  3. #3
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    Hmm.. this will probably get deleted but... I tried to calculate this and got 206 amps but.. isnt there diversity allowances as well? Like with stoves? so with diversity, doesn't that take this to around 170 amps?

    Or am I doing the calculations all wrong.. Something that happens often to me...
    Student of electrical codes. Please Take others advice first.

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