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Mini-split for Phoenix, AZ duplex?

Ben Zone 2b O | Posted in Mechanicals on

Hello everybody,

I’m Ben and I’m new to GBA. Well, I’ve been reading lots of articles here and searching the Q&A, but this is my first post.

I recently purchased a duplex in downtown Phoenix, Arizona. It needs pretty much a total rehab. Most of the flooring needs to be replaced due to water and/or termite damage. This gives me the opportunity to seal the crawlspace if I want. Luckily, the exterior walls are all concrete block, so no terminte damage there.

My main question is about the cooling load for the place. It’s primarily two main rooms. One is a combined kitchen/dining/living space with no doors, and a separate bedroom with a door. I’ve run the calculator at: http://www.loadcalc.net/load.php and it says I need about 8500 btu/h cooling for each unit. Each unit is about 540SF. I used an outdoor temp of 122 and an indoor temp of 78 for the calc.

I’ve seen other calculators that give a much higher number.

If I install a 9000 btu/h unit, how do I get the conditioned air into the bedroom? I feel like I should install a 9+9 mini-split with a head in the front and one in the bedroom.

Thoughts?

Other data:
Each unit has about 80SF of windows and 38SF of exterior doors.
The west side of the building has a large shade tree shading the west wall and a good portion of the roof.

Other upgrades:
Outdoor NG on-demand hot water heater
Lots of insulation above the ceiling
PEX water lines

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Az.Guy,
    You might consider installing a ducted minisplit that directs some of its output to the bedroom, and most of its output to the main room.

  2. Expert Member
    Dana Dorsett | | #2

    The 1% outside design temp for Phoenix is 108F, not 122F. The standard test conditions at which the efficiency & capacity are specified are 95F outdoors, 80F indoors but at a higher humidity than Phoenix.

    To specify a mini-split for temps higher than 95F requires consulting the manufacturers' extended temperature capacity tables, many of which don't go as high as 122F. I suspect most 1-ton units (ducted or wall-coil mini-split, or standard split system) could handle your loads, but don't assume- check. I also suspect only a few (if any) 9000 BTU mini-splits would cover the load @ 122F.

    A 12+6 combination on a 1.5-2 ton ductless multi-split probably works.

  3. Ben Zone 2b O | | #3

    Thanks Martin and Dana,

    I put in 122 because I know it gets that hot, and I'd want to make sure the system can handle that. A ducted mini-split sounds like a decent idea.

    I'll look into a 9+9 minisplit and a 12k ducted. I've not seen a 12+6 anywhere yet.

    I'll also research the extended temperature capacity tables.

    Installation of the air conditioning is a few months away I think, but I'm trying to spec out the electrical capacity and locations for the permits.

  4. Expert Member
    Dana Dorsett | | #4

    "I've not seen a 12+6 anywhere yet."

    They're out there.

    Mitsubishi's MXZ-2B20NA multi-split compressor unit can be married to a half ton MSZ-GL06NA + 1-ton MSZ-GL12NA wall blob, and is retailed online in that configuration for ~$2500 (less mounting hardware or installation.) In competitive bidding it can probably be installed for under $5KUSD ( all-in upfront cost).

    Fujitsu's AOU18RLXFZ 1.5 ton multi can be married to (7000 BTU nominal) ASU7RLF + (12,000 BTU nominal) ASU12RLF wall coils for similar money.

    Daikin's 2MXS18NMVJU 1.5 tonner supports a combination of (7KBTU) CTXS07LVJU + (12KBTU) FTXS12LVJU wall coils, also for similar money.

    For a bit less money LG's LMU18CHV 1.5 tonner will support a (7KBTU) LMN078HVT + (12KBTU) LSN120HSV4 2 zone configuration.

    I'm sure there are others.

    The installers should have access to the extended temperature capacity tables, only some of which may be available online.

  5. Ben Zone 2b O | | #5

    Thanks Dana,

    After my reply, I researched the 6+12 units and saw several.

  6. Ben Zone 2b O | | #6

    Still working on this project... though I have purchased the mini-splits, they aren't installed yet.

    I ended up buying a 28k compressor with 3 interior units, 9+9+12. 9 for the back room, 9 for the middle room and 12 for the front room. The middle and front rooms will be mostly open to each other, but will have the option of being separated, thanks to an 8 foot by 88 inch pocket door opening.

    1. Expert Member
      Dana Dorsett | | #7

      What is the minimum modulated output of the compressor at 95F outside/80F-inside per the AHRI sheet?

      1. Ben Zone 2b O | | #8

        Thanks for the reply Dana.

        If I understand your question, I have not yet found the *minimum* output.
        I'm waiting from the manufacturer for a AHRI *sheet*. They sent me one, but it was for heating. My understanding is that the compressor (and system) might be over-sized for my cooling needs, which could cause problems.

        The AHRI *certificate* shows:
        Cooling Capacity (95F) : 28000
        EER (95F) : 12.50
        SEER : 23.00
        High Heat (47F) : 28000
        Low Heat (17F) : 17200
        HSPF : 10.30

        1. Expert Member
          Dana Dorsett | | #9

          The manufacturer's submittal sheets to the AHRI usually show minimum and maximum cooling output at +95F outdoors, +80F indoors, as well as the modulated output level at which it was tested for efficiency. eg:

          http://portal.fujitsugeneral.com/files/catalog/files/18RLXFZH3.pdf

          The 1.5 ton 2-zone cold climate Fujistu can vary between 6100 BTU/hr and 21,000 BTU/hr, but it's SEER was tested at the "nominal" 18,000 BTU/hr.

          Most manufacturers publish the submittal sheets on line, but the amount of detail on those sheets will vary.

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