Mitsubishi 3 Zone 36K Ductless Question (Branch Box Needed Or Not?)

HVAC_P

Hello,
I am currently working on an estimate for 3 Zone Mitsu Ductless heat pump (not a hyper heat). The head sizes are 9k 12k and 15k. The Outdoor Unit I am looking into is a Mitsu MXZ-4C36NA2-UI. Now on my distributors website it says a branch box is needed however when I read the installation manual a branch box is never mentioned. 

It has been a while since I have done a ductless job this big and I was wondering if anyone knows off the top of their head if this particular outdoor unit requires a branch box? Thanks in advance I greatly appreciate it.

GW

no BB on a 4 zone non hyper unit. If we were talking Hyper unit, then YES. Have a nice day

HVAC_P

GW said:

no BB on a 4 zone non hyper unit. If we were talking Hyper unit, then YES. Have a nice day

Thank you very much sir. I was hoping you would chime in with your Mitsu expertise. Thanks again

TAG

GW -- is this to get full output?

I ran into the output issue with the multi-head systems on my current project ... Glad I stumbled on the proper pages of the application guide before I moved forward.

Boy -- w/o a branch box you have to really look at the head output. I have only done the 3 head hyper. I did two 30k units.

But -- a friend did a 4 w/o a box?

HVAC_P

TAG said:

GW -- is this to get full output? I ran into the output issue with the multi-head systems on my current project ... Glad I stumbled on the proper pages of the application guide before I moved forward. Boy -- w/o a branch box you have to really look at the head output. I have only done the 3 head hyper. I did two 30k units. But -- a friend did a 4 w/o a box?

Do you think I would be alright doing a 3 zone (9K,12K,15K) on a non hyper heat as far as output goes?

TAG

HVAC_P ... you have to look at the tables. I have no experience with the non-Hyper.

Also -- all the points bellow are w/o a branch box.

I happen to come across all the tables where Mitsubishi shows the different multi head configurations w/ different outside units. Everybody assumes that the 15k head is a 15k head and it's going to give you the same output on a multi as a single .. well it does not.

In my new build I was doing three heads and the one head was going into a kitchen where I wanted extra AC capacity. Doing a three head was a question mark in my mid as the one was far away .. Doing a two head -- my kitchen was going to be linked to a small loft room that will only get occasional use. When I started to look at the tables you start to understand the how and why of the matching -- where you can have more head BTU vs the compressor. It's because the head is never going to give you the same as a single.

I did a 3 head hyper 5+ years ago -- 2 x 12k Cassettes and one 12k wall. 30k outside unit. I was rebuilding part of my beach house -- Cassettes did two upper bedrooms of a cape and the 12k wall did a rebuilt sun porch. These were newish back then and my diamond dealer went beyond the distributer level and we actually had quite a few discussion with Mitsubishi direct.

It worried me at the time as the sizing confused me -- as did the 36 load on the 30 compressor. My installer did not understand either ... but we followed what they said and it's worked flawlessly. I remember him saying match the compressor to the load not the heads and pick the head based on the table ... except we were looking at the wrong tables. People size these thing sometimes with extra capacity in mind ... as I was going to do on my current project. You have to be careful with the multi head.

Now -- using a branch box changes everything. There is a whole other table for that and I could have made a 3 head work in my new build if I had used the Branch box -- there you get more capacity. I ended up using 3 singles. It was a cleaner install and I had no way of hiding the two fan unit that was going to be required.

Not to scare you .. just make sure you look at the correct tables for what you are putting together and the loads have been done.

Maybe GW will chime back in -- being in MA and doing many he must understand

GW

TAG said:

GW -- is this to get full output? I ran into the output issue with the multi-head systems on my current project ... Glad I stumbled on the proper pages of the application guide before I moved forward. Boy -- w/o a branch box you have to really look at the head output. I have only done the 3 head hyper. I did two 30k units. But -- a friend did a 4 w/o a box?

Yes TAG that would be the general reason to size these systems if you really need to blow lots of BTU. The engineering gets even more in-depth. The longer the line the fewer BTU.  

GW

Here is a 3 zone hyper sheet just for example sake