Need some direction for a mini split system

[OGJordan]

So I’m wrapping up my garage build. Going to be spray foaming as next step, then drywall and I’ll be ready to move in. So question is where should I start for a mini split system ? I’m in northern Alabama, rarely below freezing. Summers are in the 90s with fairly high humidity. Will run the ac most of the time to keep it fairly reasonable in there, won’t have it as cold as a living space, but prob 78-80?

Garage is a 50x30. Bricked exterior. Will be fully spray foamed. I have a second floor over 2/3 of it. There is an open 6’ wide staircase leading to it. The upstairs room is about 25x25 with 8’ ceiling. Downstairs has 10’ ceilings where the second floor is, with my last bay being approximately 25’ ceiling (15’x30’ floor space). That’s the far bay with the single door. I’ll post some pics of the basic design and the open stair case to give you an idea what I’m dealing with as well as some pics of the height I’d the third bay. Large ceiling fan in the third bay, 2 small ones in the regular bays, one in the stair well and one upstairs.

 

[chinboys]

Manual J calculation will get you 80% of the cooling load. Then add the effect of latent cooling (the removal of the humidity) before sensible cooling load drops the temperature via a pyschrometric charting and the air leakage or exchanges per hour to really dial it in.
Too large of a system will short cycle and make you feel clamy. Too small a system and you won't be able to lower the temperature as the system struggles to drop the humidity.
Add a ceiling fan to both levels to decrease the cooling load... You will be more comfortable at higher temperatures.

 

[fitter30]

If your going to be doing woodwork or anything dusty might want to rethink mini splits. They have enhanced coils both the evaporators and condensers. Coils have little slits in the fins and the air filters are thin and don't catch the finer dirt. Also look at some YouTube videos about cleaning inside units.

 

[pcmeiners]

As to wood work dust with a minisplit in a garage, have the same situation dust wise. Plan to create an extra filter for my minisplit covering the intake area of the minisplit from woven filter media. Along with that if I raise a lot of dust I will turn off the minisplit for awhile.

As to the cooling, those fans you install will be most useful for heat distribution. Cool air sinks, so you will get a natural cooling strata above the floor during the cooling season, so the ceiling mounted fans will not provide efficiency, as it will mix the heat from above with the cold strata., just adding load to the cooling system; will not hurt but it will not help.

If you install (2) small minisplits, one on either end of the 50ft length, you will have sufficient air distribution. The loft space will need it's own split, with a means for blocking the cold area flowing down the staircase. (2) efficient 12k units downstairs, and a 12k in the loft area should be sufficient. I have an efficient 12k in my 30x36', 10 foot high garage, mounted at 9 feet, which is more than sufficient with my average insulation.

Run the electric and linesets before closing walls/ceiling behind Sheetrock. Advise mounting outside units on cement slabs, with some design to get them off ground level (8") so less dirt builds up on coils. Add surge protection to the circuits, MOVs or Transorbs between all lines(and ground) will be sufficient.

 

[OGJordan]

If your going to be doing woodwork or anything dusty might want to rethink mini splits. They have enhanced coils both the evaporators and condensers. Coils have little slits in the fins and the air filters are thin and don't catch the finer dirt. Also look at some YouTube videos about cleaning inside units.

First I’ve heard that and good to know. I build custom cars do a bit of woodwork for trunk paneling and subwoofer boxes. Thanks for bringing that up !

 

[OGJordan]

As to wood work dust with a minisplit in a garage, have the same situation dust wise. Plan to create an extra filter for my minisplit covering the intake area of the minisplit from woven filter media. Along with that if I raise a lot of dust I will turn off the minisplit for awhile.

As to the cooling, those fans you install will be most useful for heat distribution. Cool air sinks, so you will get a natural cooling strata above the floor during the cooling season, so the ceiling mounted fans will not provide efficiency, as it will mix the heat from above with the cold strata., just adding load to the cooling system; will not hurt but it will not help.

If you install (2) small minisplits, one on either end of the 50ft length, you will have sufficient air distribution. The loft space will need it's own split, with a means for blocking the cold area flowing down the staircase. (2) efficient 12k units downstairs, and a 12k in the loft area should be sufficient. I have an efficient 12k in my 30x36', 10 foot high garage, mounted at 9 feet, which is more than sufficient with my average insulation.

Run the electric and linesets before closing walls/ceiling behind Sheetrock. Advise mounting outside units on cement slabs, with some design to get them off ground level (8") so less dirt builds up on coils. Add surge protection to the circuits, MOVs or Transorbs between all lines(and ground) will be sufficient.

Yes I’ve ran two electric drops already that need to be stubbed through the wall. That’s one reason I was asking, so figure out the line sets before hand.

Don’t have any plan to isolate the upstairs, it’s mainly a storage space and I want to be able to carry anything I need up with nothing in the way.

 

[thammel]

The problem with not isolating the upstairs from the downstairs is that especially in cooling season, all the cool air from upstairs will flow down. It will make the upstairs mini-split do most of the work. I have this problem in my space. I wish I'd separated the second floor from the first. I actually made rigid foam panels that I put up in the summer time to separate the 2 zones.

 

[pcmeiners]

If it is only used for storage, with no minisplit for cooling, expect it to be uncomfortably warm up there, no cold air will reach the upstairs.

Nice sized garage, like the extra windows

 

[OGJordan]

If it is only used for storage, with no minisplit for cooling, expect it to be uncomfortably warm up there, no cold air will reach the upstairs.

Nice sized garage, like the extra windows

There will def be a mini split up there

Thanks, yeah I def need the airflow and light don’t want a closed in feel.

 

[OGJordan]

This is the flyer of our house. 4 beds, 3 baths and living room up there. The upstairs def stayed a touch warmer but it hardly “did all the work” . Open stair cases are extremely common. And with spray foam everywhere (including between floors) I think it’s hardly going to be a crisis.