Another Mini-Split Sizing Question

[jagnweiner]

Hello, all. Been on the forum for a month or two, but I think this is my first time posting. [edit: Turns out it's my third] I greatly appreciate the wealth of knowledge on here.

Anyhow, I am having a new steel/pole building put up where I tore down an old dilapidated garage. Dimensions are 36'x32' with 12' ceilings. I plan to insulate with fiberglass to R-19 in the walls and loose insulation to R-40ish in the ceiling. Garage doors are insulated. Inside walls and ceiling will also be steel.

I'm in northern Illinois, where summer temps don't usually get much above 90. Building is in shade almost 100% of the time. Winter temps get cold, but not usually below the teens. For heating, I plan to keep it no warmer than 45-50, unless working out there, then I'd probably heat it to about 65. In the summer, I mostly want to keep the humidity down and probably wouldn't go below 75 or so.

I decided that a DIY mini-split unit would probably be a pretty good solution. In order to figure out sizing, I used an online calculator. (tried to post the link, but I don't have enough posts to have permission to do that) It came up with a figure right around 24k BTU. Based on your experiences and superior knowledge, does a 24K BTU unit seem about right?

Thanks in advance,
Scott

 

[Wileel]

I'm not an expert, but a single 24k sounds really short for that size. I have a 24k Mr. Cool DIY in my 24x28 with 9' ceilings, but admittedly I did slightly oversize for my situation. With a building that large I think would like two, or a larger split multi system with two inside units.
I'm sure the pros will pipe in shortly

 

[jagnweiner]

Thanks for your input!

I'm sure the pros will pipe in shortly

Apparently not . . .

 

[nsula_country]

I agree, 2 tons is on the low end of capacity. Even if it was foamed. I would look at 2 heads 30k-36k. Or 2, 18k-24k systems. Mini split downfall for large areas is the lack of ducting. IMHO. I personally like a traditional split system with some form of ducting.

I recommended a friend of mine to go minimum of 24k on a 30x30x12 that is 100% foamed 3" thick.

I have standard metal building insulation, in Louisiana. In our 40x60x17, 5 Tons (60k) is adequate but marginal for the hottest and the coldest days. When 50 inside (lowest tstat will go) I can kick it up to 65-70 in reasonable amount of time. Though I have 20kw of resistive heat in addition to HP. HP will maintain. 4 ceiling fans keep air from stratifying.

I have a thread on this in signature.

CT

 

[jagnweiner]

Thanks, CT!

 

[dcg9381]

Texas. 40x60x16. I'm running 4 tons and 3-4 inches of foam. Your climate is obviously more moderate, but it can get into the 90s in the summer and your head load similiar. You'll want more HVAC... And you'll want to move air around in the building, otherwise the ducted units kinda "spot cool".

For me, doing a 2nd 2-ton unit was more cost effective than going to a 4 ton unit. And I can just run one unit during more moderate months.

 

[HotrodHR]

No professional here, but I would consider a properly sized system with two interior units, or two separate units...

 

[SALIV8]

Here’s my non pro, diy 2 cents.

Look at all the specs on the models you are thinking of. Some perform considerably better than others.

Sizing that space for heat with a mini will be a very large system or multiple large systems.

Go bigger since you will be heating.

 

[u3b3rg33k]

if you're looking at multiple heads, check the spec sheets. many single condenser multi-splits have very poor turndown ratios when compared to single head systems.

 

[nsula_country]

Another thing to consider. Is this a man cave or a shop? Filtration is another issue. Think about this. I'll post a picture later... Worth 1000 words.

CT

 

[nsula_country]

1000 words...

View media item 100604
Filtration is the key to longivity of a healthy, efficient HVAC system.

CT