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Cooling a Low-Load Home With Minisplits

albertoarriaga33 | Posted in Mechanicals on

Hey all,

What is the best way to condition a low load house with mini splits only? Horizontal ducted is out of the question as I cant get my hands on a small enough system in my market, ductwork is expensive anyways, and installing a mini split head in every room would provide double the required capacity.

Im thinking that boosted jumper ducts and a well laid out ERV could provide enough air flow to keep the home cooled with minimal temperature difference.

CZ1 hot, humid
sub 1 ACH50
R21 walls, R38 attic, double glazed windows
4 zones (first floor + 3 bedrooms)
1,800 sq ft

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  1. d_barnes | | #1

    Sounds like you have a 2 story. Have you considered a Slim Ducted mini split from Fujitsu or Mitsubishi? The air handler is approximately 9” tall, and 22”x27” and are offered down to 3/4 ton/9kbtu, and modulate down to 3k btu. You could install it in an upstairs central closet or the attic, along with a 20”x30” return and Merv13 filter, and as short as possible duct runs to registers close to interior walls. Then install a single ductless downstairs.

  2. jameshowison | | #2

    I believe there are some calculations showing how hard it is to use jumper ducts or forced air fans to distribute heat around a structure. I can't find them now, sorry! In essence you are trying to build a duct system by using rooms as part of the ducts, creating massive static pressure.

    In any case, you also have to think about ventilation, dehumidification, and point source humidity/pollutant control (bath fans and kitchen hoods).

    Perhaps this will spark some ideas, it incorporates a minisplit together with an advanced ERV, using the same duct work.

    You might also look at the SD12, a dehu with some cooling capacity. Hmmm, doesn't seem to be shown on UltraAire's site anymore. Perhaps that's discontinued?

    1. d_barnes | | #3

      James, I’ve seen similar case studies by PG&E, taking a fairly well insulated, smaller, retrofit home and adding a single ductless head in the open living area, then adding transfer fans from hallway to each bedroom. Even in mild N. California they were unable to consistently maintain a 3 degrees or less temperature difference, room to room.
      There is a high performance new build that uses a single 9k Fujitsu slim Ducted mini split, combining a ERV to the same registers that maintains near perfect temperatures, even at 115f outdoors, on approx 2500 sq ft

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