Ducted Mini Split Trunk/Branch Question

jb9

Hello,

I am having trouble visualizing how to use a slim duct mini split with a trunk and 3 branches (each branch going to a room). What is the name of the fitting that would come off the supply on the slim duct unit? Or is the fitting that comes off the indoor unit typically just fabricated to fit each install? I am hoping I can drive air into 3 bedrooms and then use each door's passive return to bring air back to a hallway/entry and back up to the unit in the ceiling.

Thanks in advance.

bulldoglax

It won't be a standard fitting either going to be a junction box with supplys right off the box or a trunk and supply. Either way it will be custom fabricated. I saw a Panasonic that had one as part of the unit. I am not familiar with the brand just saw the equipment.

http://business.panasonic.com/26PEF1U6.html#sc_sp=business-category_featuresAd_products-hvac-heatingairconditioning_Professional%20Series&start=1&cgid=products-hvac-heatingairconditioning-professional-series

jb9

Does this look like a reasonable way to run the duct work? The returns would come back passively via the doors.

njtommy

I Honestly would pull a return from each bead room. Just in case of closed doors at night. Also watch your static pressure on the duct.

Jamie Hall

Also you would be well advised to have dampers on the outlets; the ductwork won't balance the flow all by itself.

Jack

First step is to understand the static capability of your air handler. that is going to determine what you can do. Some of the mishap air handlers have very limited static, and the ductwork has to be spot on and properly sealed for it to work.

Jack

Autocorrect. That "mishap" is supposed to be "mshp", mini-split heat pump.

jb9

Ok. This is helpful. Is the static capability of the ducted mini-split "air handler" going to be a value in CFM? Also, I oriented the duct work to split the flow but I agree it might create a bit of static resistance. The runs of each branch are about 4 feet. I am hoping a passive return (e.g. Tamarack) installed at the bottom of each door will help everything flow but I agree a proper return would be best. Thanks njtommy for that recommendation. What would a damper do? And is a damper part of the ducted mini-split system or would that be an additional component?

jb9

Also, I just took a look at the Fujitsu ARU12RLF mini-split "slim" ducted unit and saw this listed as capacity:

Static Pressure in W.C. --> 0 ~ 0.36
High 383
Medium 353
Low 324
Quiet 283

The above appears to be CFM. How do I reconcile these capabilities with my space?

Techman

What prevents the hallway air from getting sucked in from different parts of the hallway(Liv Rm) and not necessarily from the bedrooms .The room air will be colder and closer to the floor and the hallway air by the ceiling will be warmer and coming from EVERYWHERE.

ChrisJ

I had considered doing one return in the hallway, but didn't like what would happen when any doors were closed so I'm doing separate returns.

For me, warmer air by the ceiling, and the hallway being warmer doesn't matter. It won't be anywhere near as bad as outside.

njtommy

I would also look at the warranty on all the equipment your considering. If you go with Fujitsu look to see if you have an elite dealer in the area. The warranty is then extended. Daikin has a good warranty right off the bat.

jb9

Thanks njtommy. I will definitely make sure to find an elite dealer if possible. One of the questions I have about some of the feedback is that if the ceiling return in the hallway presumably has a lot of warm air, won't it simply be redistributed into the bedrooms if the ducted mini split/handler ingests it? Also, I am completely comfortable with bedrooms that are a couple degrees cooler so I am wondering if I shouldn't be too concerned. The house will be a tight envelope, so I am hoping this solution might work with a fresh air duct coming into the ducted unit.

jb9

One additional note I need to add about the site is that the two adjacent bedrooms shown above on the left side of the air handler rendering will be on the West side of the house. I just returned from a site visit and those rooms will more than likely be warmer than colder. I concluded this from talking to a local architect, other folks who live in the area and visibly noticing how everyone keeps their shades drawn on the West windows. My mitigation strategy for the summer will be to probably plant a couple deciduous trees. Even though I started this thread as a heating question, I wanted to share the site details as well.

njtommy

@jb9 I would imagine if the units pulling hot air it will just run longer to cool the space. Assuming these units work like the regular ductless ones. Their will be a return air sensor and supply air sensor to help control the operations of the equipment. The T-stat generally just gives these units a set point.