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Question on choosing a mini split

user-7202426 | Posted in Mechanicals on

Hi all. 

I am trying to correctly size a mini-split for new construction in Santa fe NM (climate zone 5b) with an outdoor design temp of 10/91 degrees.  I have had a manual J performed and attached it below as well as the floor plans for the house. My plan as of now is to use an electric resistance heater for the bedroom and a single zone Mitsubishi(??) ductless mini-split for the rest of the house. If anyone has suggestions on sizing, placement, or a unit recommendation that would be great. 

Thanks for the help.

Noah

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Replies

  1. Expert Member
    Dana Dorsett | | #1

    Save the poor reader the work of having to figure out which rooms the mini-split would need to be covering, and the total heating and cooling loads that would add up to. Writing the load numbers for each room on the floor plan would at least be a start.

    It looks like the bedroom's heat load is 3930 BTU/hr and the whole-house load is 21635 BTU/hr, which leaves 17,705 BTU to be covered by the ductless?

    At 7200' (down town Santa Fe) the mini-split's capacity will only be ~77% of it's capacity at sea level. So when looking at specs you need something that delivers at least (17,705 / 0.77= ) 22,994 BTU/hr @ +10F. To have any margin at all for covering cold snaps ideally it's good to have a 1.2x oversize factor for the load at +10F, which brings the minimum spec to (1.2 x 22,994= )~27,600 BTU/hr

    Go to the NEEP website and start searching, using the capacity slider on the upper left:

    https://ashp.neep.org/#!/product_list/

    Setting it to 28,000 minimum comes up with only this hefty 2.5 ton Fujitsu for a single wall-unit approach:

    https://ashp.neep.org/#!/product/25343

    Backing off to 25,000 shows a few 2-ton options that might work, eg:

    https://ashp.neep.org/#!/product/25339

    https://ashp.neep.org/#!/product/25764

    (There are others.)

    It may be cheaper and better to use a pair of pretty-good 3/4 ton- 1 ton units rather than one 2-2.5 ton. A pair of Fujitsu -9RLS3 would deliver better than 30K @ +10F at sea level, a pair of Mitsubishi -FH12NA would be good for 27,200 BTU/hr:

    https://ashp.neep.org/#!/product/25332

    https://ashp.neep.org/#!/product/25895

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