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New build, need advice on a mini split

ReeceTucson | Posted in General Questions on

Hello, I am in the process of assisting with building a small house outside of Tucson, Az and need help selecting a mini split system. I have spent a lot of time reading this website and a lot of the mini split posts I have seen have been from the northern part of the country. We are located in Zone 2b and are more concerned with keeping the house cool than warming it up.

The house will be 800ft2 and we have decided to use a ductless mini split in order to keep initial construction costs down and reduce maintenance in the long term. I have run a Manual J analysis on CoolCalc and have divided the house into three zones. Per the advice of other posts here I am working an analysis with BEopt and LoadCalc but do not have them finished yet. The sensible cooling is aprx. 13k btu/h and the heating is aprx. 10k btu/h.

I would like to use a single outdoor heat pump with three heads in a 6k btu/h – 6k btu/h – 9k btu/h configuration. I have been looking at Mitsubishi, Gree, and Fujitsu units and while some of the compressor submittals show a range of values that match the Manual J, almost none of the heads show a variable range. The Mitsubishi FS09 series that has been mentioned before is capable of modulating lower but appears to have been discontinued or out of stock. Are there similar units capable of modulating below 2k btu/h or should we redesign the HVAC system entirely?
Thank you in advance

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Replies

  1. Kyle R | | #1

    The FS09 is still available online. https://hvacdirect.com/mitsubishi-mz-fh09na-9-000-btu-30-5-seer-ductless-mini-split-heat-pump8955.html

    You really will only need a 6k, but the turndown is the same. In order to get that 1,800 btu/hr turndown they need to be 1:1 on their own outdoor unit. The multi splits might turn down to 7 or 8k, but if only one head is calling for refrigerant all of it will flow there. I would recommend going with three 1:1 units.

    But first I would recommend putting in one ducted unit if you can figure out how to run the ducts. One register per room would be sufficient and you could put the ducts in a soffit if needed.

  2. ReeceTucson | | #2

    Thank you for the information. I will explore the ducted option but probably go with the three 1:1.

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