A counter-intuitive minisplit situation
I am looking to install a single ductless mini-split system in the 2,000 cubic foot, 3rd-floor master bedroom of an Utah ski condominium (which is @ 8200 ft and climate zone 6) for COOLING. The unit has two gas-fired, forced-air furnaces that takes care of the heating, but in the summer the heat from solar gain makes the top-floor, cathedral-ceiling bedroom too warm, even with the windows open and fans going. The units were built in the 1980s without A/C, and there is no room to install a return-register duct to the 3rd floor to add AC to the forced air system. Given that the summer evenings are cool @ 8200 ft, I am assuming the mini-split should have no trouble cooling the space. The run for the refrigerant from the compressor to the head unit will be about 40 feet. I would very much like some expert input on what I need to keep in mind as I begin reaching out to local HVAC companies that install mini-split systems. Thanks in advance!
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Hey Todd.
Here are the newest and most commonly referenced GBA articles on minisplits: All About Minisplits
Have you considered better window shades/blinds to block the solar gain?
Have you considered installing an evaporative “swamp cooler”? I’m guessing from the description of your location that you’re probably in a pretty dry area with very low average humidity levels. Evaporative coolers can be even more efficient than minisplits when operated in areas with low humidity levels.
Bill
It is not clear from you question is your plan to run the mini split on the third floor and leave the window open down stairs?
What is the current R value of the ceiling?
If this is part of a large complex of similar unit how have your neighbors handled this problem?
What are the outdoor and indoor temps when you are uncomfortable?
Would the complex allow you to add an operable roof window? Or 10 inches of foam insulation on the exterior covered with a new with solar reflective shingles?
Walta
>"I am looking to install a single ductless mini-split system in the 2,000 cubic foot, 3rd-floor master bedroom of an Utah ski condominium (which is @ 8200 ft and climate zone 6) for COOLING. "
The volume of the space doesn't much affect the cooling load. Run a Manual-J.
>" Given that the summer evenings are cool @ 8200 ft, I am assuming the mini-split should have no trouble cooling the space."
Run a real Manual-J cooling load don't assume. If you want to take a stab at it DIY, either of these online freebies will produce sorta-reasonable numbers if you input that the place is completely air tight, and use generally aggressive rather than conservative numbers:
https://loadcalc.net/
https://www.coolcalc.com/
Also be sure to derate the capacity to about 75% of rated capacity given that you're at 8200':
Given that the summer evenings are cool @ 8200 ft, I am assuming the mini-split should have no trouble cooling the space.
https://s3.amazonaws.com/greenbuildingadvisor.s3.tauntoncloud.com/app/uploads/2016/09/08060512/Mitsubishi%20M%20and%20P%20series%20Altitude%20correction.pdf
(So a 1-ton rated for 12,000 BTU/hr cooling AHRI is really more like 3/4 ton unit @ 8200'.)
Odds are pretty good that any 3/4 tonner will cover this, or even the half-ton Mitsubishi FH06