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Single zone Fujitsu XLTH and Mitsubishi H2i and low temperature cutoffs

Paul_Iowa | Posted in Mechanicals on

Hey,

I live in the far northeast corner of Iowa close to the Minnesota border.  My plumber is an accommodating guy and has worked with me on my years-long house renovation.  This past fall he purchased for me and allowed me to install a Fujitsu RLS3H heat pump for my garage.  I did the install and he came and purged and vacuumed the lines.  It works great and I love it.  I purchased the equipment from him at cost and did the install.  I paid him $140 to purge and vacuum the lines and in the end spent about $2,300 for the entire setup.

He has access to either Mitsubishi or Fujitsu equipment and has agreed to do the same thing for the 2-story 1000 square foot addition I’m currently adding onto my house.  I currently have a 5.67kw solar array and will next month (once the roof of the new addition is in place) be having installed an additional 10 panels to get to 8.67kw.  The idea of heating it with electric is appealing.  My plan is to heat both floors of the new addition with separate single zone heat pumps.  I’ve done a ton of research and poured over models, specs, and outputs at low temps, and have calculated rough load requirements for both spaces.  

Given where I live and the fact we *sometimes* have temperatures that reach below -20F, how concerned should I be with the with the low cutout temperature of Mitsubishi vs Fujitsu units?  Fujitsu doesn’t specify a cutout temp, and per previous threads I’ve read on GBA, there are examples of these units running to the mid -20s and potentially lower.  The Mitsubishi models on the other hand state they have a cutout temp of -18F and won’t restart till the temperature rises to -14F.  Has this been peoples’ experiences?  

-20F is rare even in the far northeast corner of Iowa, but this past winter we did have like four consecutive (brutal) days where the temperature never made it north of about -18.  Lows bottomed out in the mid -30s.  I’d hate to be left with backup resistance heat at that temp for that time period.  Given my plumber has access to both, should the Mitsubishi cutout temperature give me pause?  I know there are a ton of factors that influence to what degree a cutout is an issue (like insulation), but generally speaking should a cutout given our climate be a cause of concern?  

Thanks for the help!

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Replies

  1. Expert Member
    Dana Dorsett | | #1

    Fujitsu units will not turn off no matter how cold it gets, and their literature implies that it's still reasonably self-protected when temps drop below the coolest temps in the capacity charts.

    Mitsubishis do in fact turn off when it's outdoor temperature sensor is out of range. The exact temperature at which that happens varies from unit to unit- it's not at precisely -18.00F, but it's usually warmer than -25F. If this is your primary heat without backup that's a good argument for going with Fujitsu if temps below -18F are an annual event. If it's only hitting those temps once or twice per decade, or if you have something like a wood stove to fire up when it's going to be ultra-cold out it matters a lot less.

    On the nights when it bottomed out in the mid-30s did it at least get up to -15F during the days?

    There are a few Chinese mini-splits that have a specified capacity at -30C/-22F, eg Midea's Premier Hyper series, Gree's Crown series. ( I have no experience with either of those vendors.) Carrier's current mini-split offerings are re-badged Mideas, all of which use Toshiba's compressor technology, but I'm not sure if Carrier is selling their cold-climate versions.

    https://th.midea.com/us/search.html?q=premier%20hyper

    I've recently been looking at their ducted cold-climate mini-splits:

    https://us.midea.com/dam/jcr:858f7d94-63a0-4042-8c35-0df96d1c3ecf/US_PP-RAC_PROD_PREMIER-DUCTED_specsheet.pdf

    The range of cold climate products from Gree is a bit narrower:

    https://www.greecomfort.com/our-products/crown/

  2. Jon R | | #2

    I'm curious - why are you concerned about a few days of resistance heat every few years? It's insignificant on an operating cost basis.

    I'd be careful about assuming that "doesn't cutout" means "doesn't suffer damage". Who knows what happens when you operate below their specified operating range (often -15F for Fujitsu)?

    1. Stephen Sheehy | | #3

      I had the same thought. What's a few days of resistance heat cost? And presumably, he'll insulate and air seal well, so even at -20, the addition isn't going to get too cold.
      In Maine, when we get mega cold temps, it's always clear and still, so during the day we get solar gain. Even if it stays below zero during the day, the house stays warm.

  3. Deleted | | #4

    Deleted

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