Multi-split with unit in every bedroom
JTuck
| Posted in General Questions on
I’m building a cottage style house with hip roof and dormers on the southern edge of zone 4. For the 900 sqft 2nd floor, my energy star mechanical contractor is recommending 3 6000btu multi-split units (MSZGL06NAU1) for 3 bedrooms, 1 bath, and conditioned attic behind the knee walls. I’m sure that’s overkill. What are the negatives to this setup? Will they dehumidify?
Thank you.
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Replies
Run the heating and cooling load numbers for those bedrooms using aggressive assumptions on R-values and air tightness using a freebie online Manual-J tool such as LoadCalc.net. I suspect just one GL06 covers more that 2/3 of the load.
Running them in DEHUMIDIFY mode will dehumidify, but if they're more than 50% oversized it may not cut it in normal cooling mode. Depending on your 99% ( heating) outside design temp, whole floor is probably within range of a single zone KD09 or KD12 mini-duct solution, which might be a better bet:
http://meus1.mylinkdrive.com/files/M_SEZ-KD12NA4_SUZ-KA12NA2_SUBMITTAL-en.pdf
http://meus1.mylinkdrive.com/files/M_SEZ-KD09NA4_SUZ-KA09NA2_SUBMITTAL-en.pdf
They make a KD15 and KD18 too, if necessary, but the minimum modulation levels of the bigger units are higher, resulting in more cycling/less comfort, and potentially lower efficiency.
Fujitsu's 9RLFCD ducted 3/4 tonner has more heating capacity @ +17F than a KD18, and a lower minimum modulation level (by half) and a beefier blower too, all of which would make it a better choice if there is local support for Fujitsu. (I wish Mitsubishi would put their better compressor technology in their ducted mini-splits the way Fujitsu does.)
http://www.fujitsugeneral.com/us/resources/pdf/support/downloads/submittal-sheets/9RLFCD.pdf
https://ashp.neep.org/#!/product/25309
http://meus1.mylinkdrive.com/files/M_SEZ-KD18NA4_SUZ-KA18NA2_SUBMITTAL-en.pdf
Which multi-split compressor did the proposal marry the GL06s to?