Three MXZ-5cNAHZ vs two MXZ-8cNaHZ
Hi all. We are building a “multi-generational” home for the brood here in Massachusetts. HERS rater shows 70,000 BTUs for heating load with my intended Insulation, windows, etc. Manual J from my own access to free software and results from a few installers shows roughly 90,000. I will be using Mitsubishi Mini-Splits and will expand into Attic and Basement as Family continues to grow, and those numbers above are reflective of end state full usage.
From installer, three MXZ-5cNAHZ vs two MXZ-8cNaHZ are about the same install cost with the various zones/heads we’ll have at an end state. He says since they are variable motors, it should be a wash from an electricity usage. When I look at the submittals per unit at the different design temperatures, its difficult for me to be confident. Is it likely that there is a minimum electrical load drawing power even in mild days that would make 2 larger units better than 3 smaller units? I’m seeing a 24000 minimum BTU for the 5c and 27000 BTU for the 8c at 47F.
Summary of Watts listed on the Submittals are below along with efficiency stats per unit:
|Heating at 47°F* (rated)||4220||4800||3430||4140|
|Heating at 17°F* (rated)||4130||4650||3350||4230|
|Heating at 5°F* (Max)||7910||8790||7030||7070|
|COP at 47f||3.75||3.3||4.1||3.4|
|COP at 17 f||2.3||1.8||2.3||1.9|
|cop at 5f||2||1.8||2||1.9|
Thanks in advance for advice. Definitely learned a lot in last month or so, but still a novice. Your help is always appreciated.
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