Red Iron Building A/C Question

[bauer0667]

Good morning,

I have an older 41ft x 32ft Red Iron Building with 10ft walls and a 12ft peak in South East Nebraska. The walls are the older 12" insulated panels that lock together. It has 6" concrete with 2" foam board insulation under it. There are two 4ftx8ft Pella windows and a glass walk in door. It also has an insulated 14ftx9ft garage door and a 9ftx7ft insulated garage door. Unfortunately it sits in full sun and gets pretty hot and humid. To help with the heat and AC bill we just put up batts of R25 insulation on the ceiling and put tin up underneath it. It has a Carrier 2.5 ton central air system in it, but the compressor is shot. I never had the A/C working so I need some advice on if I should go with something bigger, smaller, or different type of A/C all together.

 

[theoldwizard1]

R25 sounds like a lot of insulation but it is not ! R25 fiberglass batts is about 8", correct ? You really want 12" or more to lower your heating/cooling bills. What do you have for insulation on the walls ?

If you get a lot of sun through the windows and door some kind of shade/film will help.

I assume you have ductwork installed so you might as well stay with central A/C but I think you are going to need more than 2.5 tons. Pay back for a couple of high seer mini-split A/C units would probably be 5-10 years (?) depending how low of a SEER rating the central air system you choose is.

 

[matt_i]

I would think that sizing about right. There's a generalized 500sqft per ton (12kbtu) of A/C guideline that obviously doesn't fit all situations. Worst case is on a super hot day you aren't going to be able to hold 68F with the A/C running constantly. So it gets to 80...personally I can handle that.

If you wanted to round up to 3 tons/36kbtu I wouldn't think it a bad choice.

 

[abgiles]

Definitely look up the MrCool DIY installations here for mini-splits. I've got a 30x60' shop here in NE Florida, and got my install done yesterday. I've got 2" of closed cell spray foam insulation on the walls, 3" on the ceilings, and R-19 insulated garage doors. I dropped my temp from 90F and 75% humidity to 79F and 51% humidity in just 5 hours. I have a 36K unit and once I partition off my mancave (30x14) section, I'll add an 18K unit for that.