Multi-zone mini split (multi-split) questions / branch boxes

[aunsafe2015]

Let me prefix this by saying I'll be hiring a licensed HVAC tech to do this, but I just want to educate myself first.

I want to add a 6-zone ductless mini-split (one condenser, 6 indoor units) to the 2nd and 3rd floors of a house. Four bedrooms on second floor, two additional rooms on third floor. I was thinking about running the lineset from the condenser to the third floor, locating the branch boxes in an unfinished part of the third floor, and then running the individual linesets from the branch boxes to each room. For the second floor rooms, that would require going through the floor of the third floor to install the wall mounted units towards the top of the walls on the second floor.

My first question is whether it's permissible for the wall units to be located below the branch boxes? I see in a Mitsubishi manual it says that the branch box should be in the "level" between the condenser and the wall units, but I am wondering if that is requirement or suggestion. I don't see why it would be a problem for the wall unit to be below the branch box, but I know nothing.

If the branch boxes truly do need to be located vertically between the condenser and the evaporators, would it be possible to put the branch boxes on the second floor, and then run the individual linesets up to the third floor, route them to the second floor bedrooms, and then drop then back down through the floor into the bedrooms? In that scenario, the branch boxes would vertically between the condenser and the indoor units, but the linesets would go up from the branch box, horizontally through the third floor attic, and then back down to get back into the second floor bedrooms at the proper location. Not sure why that would be preferable to simply putting the branch box on the third floor, but maybe it is.

My second question is whether it's OK to have the condensate lines from the indoor units go out an exterior wall and empty onto my roof, where the water would then go to the gutters/downspouts and transferred away from my house.

Thanks in advance for any feedback!

P.S. A standard ducted split system is an option for the second floor, and ultimately I may have to do that. But I would love to have individual temperature control in each room, which is why I'm exploring this.

 

[SALIV8]

I'm far from a pro. I don't even know what a branch box is.

There are specific lengths and heights that allow the indoor units to be installed from the condenser.

Read every page of the installation manual and follow it. I'll have to google branch box as I'm used to each zone having its own Lineset.

 

[aunsafe2015]

I'm far from a pro. I don't even know what a branch box is.

There are specific lengths and heights that allow the indoor units to be installed from the condenser.

Read every page of the installation manual and follow it. I'll have to google branch box as I'm used to each zone having its own Lineset.

I think for Mitsubishi, the condensers that support up to 3 zones have a separate lineset from the condenser for each indoor unit. But the condensers that do 4, 5, or 8 indoor zones, my understanding is that branch boxes have to be used. So you have a single, larger diameter lineset from the condenser to the branch box, and the the branch box (depending on which model) supports either 3 or 5 linesets "branching" off from the branch box to serve each individual indoor unit.

I'm aware of the length and heights. I'm just seeking confirmation concerning whether an indoor unit could be placed below a branch box.

By the way, a standard ducted split system is an option for the second floor, and ultimately I may have to do that. But I would love to have individual temperature control in each room, which is why I'm exploring this.

 

[Diesel Dan]

Can't answer your questions but can comment of the branch box.

Looked into a 4/5 zone system with one condensing unit and a branch box. Ended up going with two smaller outside condensing units that were 2 zone each, no branch box. One unit per floor.

The large single condensing unit can only throttle down so far and will need to run a minimum amount of evap units. So if you only need to cool one zone others will have to be run as well. If one of my compressors fail I'll still have 50% capacity where a compressor failure on a single branch system will be total failure.

Just something to consider, best of luck!

 

[aunsafe2015]

I just discovered that the manual for the branch box (http://meus1.mylinkdrive.com/files/PAC-MKA51-31BC_Install_WG79B560H01_09-16.pdf) indicates the branch box should be installed "above the ceiling" (page 2 of the manual). That would indicate that the branch box could indeed be above the indoor unit.

Page 6 of this manual (http://meus1.mylinkdrive.com/files/MXZ-8C48NA_MXZ-4C36-5C42-8C48NAHZ_Install_RG79D595H05_03-15.pdf) says "Branch box should be placed within the level between the outdoor unit and indoor units."

Seems contradictory. I guess maybe I'll have to ask Mitsubishi.

 

[aunsafe2015]

Can't answer your questions but can comment of the branch box.

Looked into a 4/5 zone system with one condensing unit and a branch box. Ended up going with two smaller outside condensing units that were 2 zone each, no branch box. One unit per floor.

The large single condensing unit can only throttle down so far and will need to run a minimum amount of evap units. So if you only need to cool one zone others will have to be run as well. If one of my compressors fail I'll still have 50% capacity where a compressor failure on a single branch system will be total failure.

Just something to consider, best of luck!

Thanks for the info. I may end up doing that. The 8-zone can ramp all the way down to 6000 btu cooling, 7200 btu heating. I would be using it in about 2500 sq ft of space, and all 6 of the zones would always be turned on... I'd just let some of them get pretty cool in winter and pretty warm in summer. I think it would easily be enough, though, that the 6000 btu minimum would always be satisfied such that any given zone could be running at a pretty low capacity to avoid short cycling.

 

[Ohmthis]

I’m assuming you are going to go with a hyper heat set up? I’ve installed a 4zone non hyper heat with individual line sets. After looking at the installation manual. Here’s my take. One branch box would be in the third floor ceiling to supply that floor and another in the second floor ceiling to supply that floor. Have you asked any contractors yet to get their opinions?

 

[aunsafe2015]

I’m assuming you are going to go with a hyper heat set up? I’ve installed a 4zone non hyper heat with individual line sets. After looking at the installation manual. Here’s my take. One branch box would be in the third floor ceiling to supply that floor and another in the second floor ceiling to supply that floor. Have you asked any contractors yet to get their opinions?

Thanks for the input. I haven't had a contractor come out yet, but the one I'm hoping to use is Mitsubishi Diamond Elite status, so hopefully they will know what they are doing!

 

[yeldogt]

I know you can have the branch box in the ceiling -- and drop down to do a wall. We have two different friends who installed Fujitsu systems in large Victorians and the upper branch box does three spaces ... two on the second and one on the third. Very slick system. Fujitsu was a leader with those. Mitsubishi did the multi head compressors ... but now has a full line with the boxes.

They can get down to a very low BTU output .... it's nice that manufacturers are coming out with 6k wall units.

I have done multi head Mitsubishi unit and various single systems --

If you decide on doing a conventional split system -- make sure you have it within the conditioned space and don't place it in an uninsulated attic. No matter what they say about insulated units and ductwork -- they are wasteful and working against the heat in the space. Properly done .. they work great ..especially the new 5 speed or full VS units. On a second floor you want quiet.

 

[aunsafe2015]

I know you can have the branch box in the ceiling -- and drop down to do a wall. We have two different friends who installed Fujitsu systems in large Victorians and the upper branch box does three spaces ... two on the second and one on the third. Very slick system. Fujitsu was a leader with those. Mitsubishi did the multi head compressors ... but now has a full line with the boxes.

They can get down to a very low BTU output .... it's nice that manufacturers are coming out with 6k wall units.

I have done multi head Mitsubishi unit and various single systems --

If you decide on doing a conventional split system -- make sure you have it within the conditioned space and don't place it in an uninsulated attic. No matter what they say about insulated units and ductwork -- they are wasteful and working against the heat in the space. Properly done .. they work great ..especially the new 5 speed or full VS units. On a second floor you want quiet.

Thanks for the input. The wall units can actually go down to 1600 BTU. It's the outdoor compressor that does a minimum of 6,000. But my understanding is that when it's paired with something like 6 indoor units and all of them are turned on, each indoor unit can be operating at way less than 6000 as long as the sum total of what they are operating at reaches the 6k minimum required by the outdoor unit.

In theory, very slick. In practice... Well, maybe I'll find out soon.

And yeah, the attic will be spray foamed. So whatever is up there will be in conditioned space!

 

[theoldwizard1]

Looked into a 4/5 zone system with one condensing unit and a branch box. Ended up going with two smaller outside condensing units that were 2 zone each, no branch box. One unit per floor.

A much better solution !

In general, the more branches a compressor services, the less efficient it is. Perfect would 1-to-1, but clearly NOT cost effective.

Now you know why mini-splits never really caught on in the US (big house with lots of rooms) !

 

[theoldwizard1]

Do wall mounted air handlers come with condensation pumps ?

 

[Ohmthis]

Do wall mounted air handlers come with condensation pumps ?

That’s usually an option you add on. Most in ceiling units do have them