Insulation and mini-split for metal garage

[jfw432]

I'm nearing the end of getting my concrete slab poured and trying to plan for how to configure the shop. I'm going to put a 24x35 ft metal building with 12 ft walls and I'm trying to figure out the best combo. I've looked at a bunch of different sites and Alans Factory Outlet or High Quality Steel seems like the best options with the most convenient layout. I live in middle GA so should be zone 3.

For insulation:
I looked at various types of insulation and honestly feel like spray foam may be the best option but I'm open to other suggestions. I'm a very DIY kind of guy but installing stuff over my head at 12-15ft is asking for trouble so I think I'll leave at least the ceiling to someone else. My current plan is 2" thick spray foam on the roof and 1" thick foam on the walls. I'm reaching out for other quotes but the first quote I got was around $4100 for closed cell foam at those thicknesses. That price doesn't seem too outrageous based on current research and prices. Should be around $1.25 per board foot based on my math. Alan's Factory Outlet has a quote of about $7300 to install R-17 and $3600 for double bubble but I don't think double bubble is the right choice for me.

For heat and air:
I was originally thinking of an 18k mini split unit but figure a 24k mini split would be a better option without much more money for the 840 sq ft shop just to ensure it can keep up. I figure I'll just set it at 55F in the winter and maybe 85F in the summer unless I'm in there so it's reasonable. Does this seem like a good plan? Will a single outlet in the middle of the shop be enough especially with that insulation level?

 

[Jackfre]

Your unit will have a 4 way air sweep on it. Center will be all right unless there is some reason one end will be much hotter than another and you tend to use that area a lot. The variable speed units rarely shot down. That is by design as with constant air circulation you will end up with a better balance. I agree with your choice of spray foam. Pricey, but it is the best. Insulation is one of those things the DIY’er should best avoid. In my experience the contractor can do the job for about what you can buy the material. So no gain and it is a a miserable job.

 

[American Locomotive]

24,000 BTU sounds way oversized for 840 insulated sq ft to me.

 

[pcmeiners]

Agree, run your variables in the calculator below...

Home Heat Loss Calculator

Your choice of mini split should be made with the min/max of a minisplits output, not so tied to the advertised BTUs as in.....

Fujitsu 12,000 BTU 29.4 SEER High Heat Wall Mounted Single Zone System | Got Ductless

The Fujitsu 12,000 BTU wall mounted high heat single zone system is an extremely efficient heating and cooling option for a mid-sized room. From Got Ductless, it's in stock and comes with free shipping & lift gate service. Shop for your Fujitsu 12,000 BTU wall mounted high heat system today!

gotductless.com

• Min-Max Cooling: 3,100-12,000 BTU
• Heating Capacity 12,000 BTU
• Min-Max Heating: 3,100 - 22,000 BTU

 

[jfw432]

Agree, run your variables in the calculator below...

Home Heat Loss Calculator

Your choice of mini split should be made with the min/max of a minisplits output, not so tied to the advertised BTUs as in.....

Fujitsu 12,000 BTU 29.4 SEER High Heat Wall Mounted Single Zone System | Got Ductless

The Fujitsu 12,000 BTU wall mounted high heat single zone system is an extremely efficient heating and cooling option for a mid-sized room. From Got Ductless, it's in stock and comes with free shipping & lift gate service. Shop for your Fujitsu 12,000 BTU wall mounted high heat system today!

gotductless.com

• Min-Max Cooling: 3,100-12,000 BTU
• Heating Capacity 12,000 BTU
• Min-Max Heating: 3,100 - 22,000 BTU

Ok that may all be a little over my head so I want to better understand... By running the calculator, it looks like my design loss in BTU/hr is around 16k on a 95 degree day and around 19k on a 40 degree day. So should I be finding a system that has a min-max rating where my number fall anywhere inside of the threshold?

It looks like the design loss is based on a 70 degree interior temp which is probably only shoot for during a few hours a week.

 

[Mike65]

We had a 24' x 25' metal garage built here in southern Va & had it insulated with spray foam. Here is a pic of the back wall, & the ceiling. IIRC when we had ours done it was around $4500.00.

 

[pcmeiners]

You need to read the explanation during your variable entries, for your area of Georgia , the lowest design temperature for Georgia is 10° F , found only one reference to degree days for Macon, 4354 (research google for this). I do not know your insulation variables. Put money into insulation, including insulating the slab, and a vapor barrier . You will get condensation without sufficient insulation/and a vapor barrier under the slab; you neither want your temperature dropping quickly in the early morning hours, nor do you want high air infiltration in those hours. A few thousand in foam is the way to go on a metal building, as in Mike65's garage. Once you know your insulation values, then use the calculator. Your choice of mini split is all dependent on your insulation.

In my garage (30x35) I have 2 of the above Fujitsu units, only 1 turned on. Went through the winter here in PA, got down to 7 degrees one week, the one unit was not even slightly stressed during the coldest days; it would even turn on and off during those days. I have r-13 in the walls, R-19 ceiling, 2 new large garage doors, couple windows, 1 regular door, and I have not gotten around to properly air sealing it yet. I keep my night temperature at 50-55° to keep my tools warm.

 

[My Old Tools]

My building is red iron with roll fiberglass applied over the frame before sheeting. I had an additional 8" applied to the ceiling with strapping. My shop is 30x40, 1200sf with 22' tall to the peak. I have a 36k Mr.Cool in the center of the long wall, It is overkill for my space and insulation. I have 7 large windows, man door, and 12x12 door (insulated).

 

[FL Guy]

Agree, run your variables in the calculator below...

Home Heat Loss Calculator

Your choice of mini split should be made with the min/max of a minisplits output, not so tied to the advertised BTUs as in.....

Fujitsu 12,000 BTU 29.4 SEER High Heat Wall Mounted Single Zone System | Got Ductless

The Fujitsu 12,000 BTU wall mounted high heat single zone system is an extremely efficient heating and cooling option for a mid-sized room. From Got Ductless, it's in stock and comes with free shipping & lift gate service. Shop for your Fujitsu 12,000 BTU wall mounted high heat system today!

gotductless.com

• Min-Max Cooling: 3,100-12,000 BTU
• Heating Capacity 12,000 BTU
• Min-Max Heating: 3,100 - 22,000 BTU

Can you make sense of this?

 

[Kail]

spray foam is costly, but I think what it lacks in advertised r value it makes up in sealing the building off. Batts will still bleed heat at the edges.
And metal buildings are hard to make air tight, spray foam is the most effective in my opinion

 

[pcmeiners]

Go foam.

FLguy....Design temperature is for heat not 90 degrees, more like 25 degrees in FL (January)
For a heat pump your efficency varies by SEER and HSPF eg my heat pump is a Fugitsu SEER 29, HFPS 13.8 it has an average COP of >4, meaning it is >400% efficient . Now efficiency costs, generally the more you pay the more efficient. Depending what you buy you could have a unit with an average COP of roughly 2 ( 200%) to >4 (400%). With minisplits you pay upfront with higher efficient units or you pay down the road with lower efficiency units.
The big factor with minisplits is how much you pay and expect to pay for electric costs in the future (KW rates, including taxes/surcharges). It really pays to get reasonably efficient units, maybe not super efficient like mine. With Florida, SEER (Cooling) is more important than HSPF, in most of the country/Canada, HSPF (heating) is most important.

Now the link allows you to compare minisplits with different efficiencies, I have tried other minisplit calculators, this spreadsheet calculator is in the accuracy range of others I have tried .....

https://www.energystar.gov/sites/default/files/asset/document/ASHP_Sav_Calc.xls

Agree with Kall, generally the greatest heat loss or gain is due to air infiltration, you can not seal better than foam.

"Batts will still bleed heat at the edges."

Agree, batts are not the greatest insulators. The R values manufacturers report are under perfect conditions, no air movement around or through batt material. Then fiberglass loses R value the colder the ambient temperature gets. Batts are fine only if you can stop air movement such as using plastic on the top and bottom or if a decent amount of blown cellulose is covering it or another means to enclose it air tight.