Looking for advice on mini-split placement in Passive House (PHIUS)
TL;DR: In a passive house, will a mini-split effectively cool the area that’s in the opposite direction of where it’s blowing? (see attachment for layout, stairs open -treads on a single steel beam stringer)
Hi again! (zone 5b, dry)
I’ve been mulling over a good location for a mini-split in our passive house and would love to get feedback from everyone here.
See the attached images of the floor plan. My primary use case for the mini-split is cooling. [Heating is also important but we’ll have towel heaters in the bathrooms for zoned heating (mini-split will still do most of the work setting temps during the day while doors are open) and we’ll also have a wood burning stove for those really cold nights (https://www.blazeking.com/products/wood-inserts/sirocco-25/).]
Here’s our cooling load requirements from our Wufi Passive analysis:
5,000 btu load with a target temp at 77º
13,000 btu load with a target temp at 72º
I’m undecided between the MSZ-FH09NA (range 1,700-12,000) and MSZ-FH12NA (range 2,500-13,300). Going up to the MSZ-FH15NA might be sized better, but it can’t module as low (range 6,450-19,000). I definitely want something that can modulate at low speeds so that temps for even mild cooling can be maintained with no short-cycling. Thoughts? Am I wrong?
Initially I’d like to try to get away with one one mini-split, but if necessary, I can install a second floor mini-split on the lower floor, possibly below the stairs or in-front of the kitchen island (which would probably be a more effective placement, but highly visible). I’d only do it if I’d need to supplement for cooling. Thought?
In terms of placement (see attachment, stairs open -treads on a single steel beam stringer), I’d like to place the mini-split where the blue arrow points with the unit facing west. I could have one vane set to blow horizontally towards the upper floor bedroom doors and the other vane set to blow down into the lower level towards the master bedroom door. Cooling bedrooms is the biggest priority. The location also seems to be the most aesthetically pleasing by being the least visible in line of site when walking around the home. My only concern is that I might not get enough cooling in the kitchen since the mini split wouldn’t be blowing in that direction, and cooking can generate a lot of heat (this is ultimately the main question/concern of the post). Thoughts? Other suggestions?
Some other notes that might be helpful:
– There will be almost no solar gain in the summer.
– I prefer a central wall unit over a central ducted horizontal minisplit with zones (via AirZone). Wall units are more efficient and can modulate lower, I don’t have to worry about dust accumulating in ducts, I also won’t have tons of vents everywhere, and I don’t have to worry about noise transfer between rooms through ducts. Each room will have some sort of sound proofing in the interior walls. The cooling season is relatively short (3 months), so I’m prioritizing sound isolation and simplicity over zoned cooling.
– If there was such a thing as ultra-low modulating wall units that can be right sized for our bedrooms, I’d put one in every room and have zoned cooling and heating while doors are closed, but that doesn’t exist. Maybe in 10 years.
P.S. This community has been pretty amazing! Congrats on your success Martin and thank you creating an online place for everyone to share with each other!
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