AC plan for a big building

[protegeV]

Building isn't up yet. Concrete work starts next week. I had previously thought about just doing fans and waiting for the future to do AC but my wife is pushing me to just do it right off the bat.

It's a 40x60x16. r10 faced batt insulation and 2 insulated doors. I'm wondering do I need to go with a full ducted system and 5ton unit or could i get away with two 24K minisplits. If going with a ducted system I'm thinking it would make sense to close off the attic area and blow in a bunch of insulation up there. The ac itself would be a big $$$ hit, so that might have to wait for the future.

 

[CarGuyX]

I just faced a similar situation. Of my 40' by 60' building, only 1,800 is heated and air conditioned. I basically had a residential 3.5 ton propane furnace and ac installed with one large return and one exit that diverted the air three ways. I have a 8' ceiling fan constantly going to evenly distribute the air. So far it has worked great.

 

[u3b3rg33k]

My #1 recommendation - Texas is hot. go bigger than R10 insulation. the more insulation you have, the smaller the AC you need to install, which will save you money every day all summer long.

 

[hippie2cams]

I have a 30x40 metal building with 1 16x8 door, 1 8x8 door, and 1 man door, 10 ft. walls. r19 in walls and r19 wfoil insulation on roof. I have a 3.5t heat pump that works wonders in the Houston area. It runs all summer and all winter for about 1/2 what my house runs and its a little smaller.

 

[protegeV]

I have a 30x40 metal building with 1 16x8 door, 1 8x8 door, and 1 man door, 10 ft. walls. r19 in walls and r19 wfoil insulation on roof. I have a 3.5t heat pump that works wonders in the Houston area. It runs all summer and all winter for about 1/2 what my house runs and its a little smaller.

so half the size, double the insulation?

Doesn't sound promising for me.

 

[Jackfre]

R-10 is not sufficient. Add more. How are you treating the roof insulation, or attic as you call it. A bit more detail on that would help. As described I think two 24's would be undersized by about half in the cooling mode. Heating with a 16' ceiling...don't know. I would give more thought to creating that attic space and insulate the hell out of it. That would help you bring your load back. Fujitsu makes a 24 and 36RSLX Ceiling suspended unit that I had good luck with. Not nearly as efficient as the smaller btu ranges but it might do you well. For a ducted system I run a either a single or a couple pieces of spiral the length of the space.

 

[protegeV]

R-10 is not sufficient. Add more. How are you treating the roof insulation, or attic as you call it. A bit more detail on that would help. As described I think two 24's would be undersized by about half in the cooling mode. Heating with a 16' ceiling...don't know. I would give more thought to creating that attic space and insulate the hell out of it. That would help you bring your load back. Fujitsu makes a 24 and 36RSLX Ceiling suspended unit that I had good luck with. Not nearly as efficient as the smaller btu ranges but it might do you well. For a ducted system I run a either a single or a couple pieces of spiral the length of the space.

The roof and walls are all getting the same rolls of r10. I didn't even realize how expensive insulation was.

 

[u3b3rg33k]

The roof and walls are all getting the same rolls of r10. I didn't even realize how expensive insulation was.

yeah, but you only pay for insulation once. you pay for AC every day!

 

[bobbyjean]

red steel...metal building?

 

[protegeV]

red steel...metal building?

Yes.

 

[bobbyjean]

ok...makes sense on the insulation.....with a 16 foot ceiling you have some options
how about a catwalk on one end for a ducted system with some spiral ductwork in an open type setting.....down the center if that fit your interior plan's....the catwalk also provides storage . Will the building have gable vent's?
As for the sizing .....what temp. would you be looking for 68-78.....?

 

[protegeV]

ok...makes sense on the insulation.....with a 16 foot ceiling you have some options
how about a catwalk on one end for a ducted system with some spiral ductwork in an open type setting.....down the center if that fit your interior plan's....the catwalk also provides storage . Will the building have gable vent's?
As for the sizing .....what temp. would you be looking for 68-78.....?

I'd be happy with 75-77. Dont need an icebox of a workshop.

 

[bobbyjean]

yep....living in new york so based on 500 sq. ft per ton it works...going a little bigger with some type of staging of compressor should keep you cool in texas

 

[u3b3rg33k]

I really like the true variable speed gear - got a friend to go from a 2.5 ton single stage to a 3 ton VS, and once a month he raves about how comfortable it is and how quiet it is. it's safer to add another ton "just in case" with a system like that (so long as your ducts are adequate), because if you never need it, who cares?

in texas, i'd probably do something like the Ultra-Aire SD12 Split Dehumidifier - condenser goes outside, but it's purpose is dehumidification, not cooling - you just get cool dry air instead of warm dry air.

 

[minytrker]

My shop is 26x68x15 all spray foam insulation and 26x42 is AC with a single minisplit and I can get it down to 60. I have it set on 75 and its 73-74 in the shop. Closed cell spray foam was the best money I spent besides AC. Part of my house is set on 73 and my shop feels way cooler.

 

[theoldwizard1]

The roof and walls are all getting the same rolls of r10. I didn't even realize how expensive insulation was.

You pay for insulation once, you pay for the electricity to run the A/C every time the thermostat request it !

Fort Worth ? You need at least 12" in the ceiling.

 

[protegeV]

So the concensus is to not skimp on insulation. I checked with my guy and it's only $1200 to upgrade to r19 in the ceiling. From what Ive been reading the ceiling insulation makes a much bigger difference than the walls, especially since the walls will be a light color. Am I right on that train of thought and is r19 good for the ceiling or do I need to go even thicker?

 

[Fixin'Stuff]

So the concensus is to not skimp on insulation. I checked with my guy and it's only $1200 to upgrade to r19 in the ceiling. From what Ive been reading the ceiling insulation makes a much bigger difference than the walls, especially since the walls will be a light color. Am I right on that train of thought and is r19 good for the ceiling or do I need to go even thicker?

I'm currently installing R30 in the ceiling of my stick built garage. Attics get HOT. Everything that you can do to keep the heat out of the building, the lower your electric bills will be. My walls are R13.

 

[theoldwizard1]

You want as much insulation in your ceiling as will fit/you can afford ! R30 is NOT crazy for TX !

 

[justinjoyal]

Agreed regarding insulation. The more the better.

After you have decided, then you can size your A/C.

 

[protegeV]

You want as much insulation in your ceiling as will fit/you can afford ! R30 is NOT crazy for TX !

So what ive been reading is correct. The ceiling is the most important part to insulate. So if I went r30 in the ceiling and stuck with r10 on the walls that would be alright?

 

[u3b3rg33k]

aren't walls usually minimum R15?

 

[protegeV]

aren't walls usually minimum R15?

I think "usual" is relative. From my local research about what people actually build it's either r10 or no insulation st all.

 

[u3b3rg33k]

what I found googling for texas code:
Ceilings have gone from R-30 to R-38 but that requirement is based upon fiberglass insulation on a flat drywall ceiling and a “hot” attic above.

Walls have gone from R-13 to R-15 OR R-13+2. The +2 is referring to exterior rigid foam that can be added to a standard 2×4 wall with R-13 insulation.

referring to 2012 'code'. Code usually means minimum in my book. Personally, I'd use the thickest batts you can install in the walls without compressing them (otherwise you're paying extra for nothing).

 

[rburke65]

Ya you have to define "usual". My opinion is R-10 isn't nearly enough.

 

[JohnZ]

Our attached garage is 44' x 58' x 12' - walls were framed with 2x6's for R-22 insulation, attic insulation is R-58. Two custom-made 18' x 8' x 1-1/4" steel/foam/steel insulated sectional overhead doors, five large Andersen Low-E argon casement windows, epoxy-coated slab has a 10-mil moisture barrier and 5/8"-thick 4' x 8' sheets of tongue-and-groove closed-cell foam with heavy foil on both sides. You can only insulate PROPERLY once, when you build. Do it.

Our home was built 19 years ago (1999) - not a single crack in the slab, and the 2-part solvent-based industrial epoxy still looks like it was poured yesterday. The floor is always warm and DRY - zero moisture migration through the slab.

I had already chosen a Reznor 125,000-BTU natural gas overhead unit heater with power venting and electronic ignition - due to the effectiveness of the insulation package, we could have gone with a 75,000-BTU unit, but we didn't know that at the time.

Five years later we decided the A/C was a necessity (I restored classic Corvettes as a full-time hobby), and I had a local contractor install a Mitsubishi "Mr. Slim" 42,000-BTU (cooling only) mini-split system in 2005; it handles the load of the 2550 sq. ft. garage with no problem, both inner and outside units are scary quiet, and all it has needed in 13 years was a contactor and some wiring repairs due to mice damage. Had that contractor out last week for a checkup/tune-up, and it needed nothing.

The box in the photos below next to the Mitsubishi condenser unit is a Generac whole-house standby generator, also 13 years old.

 

[theoldwizard1]

Five years later we decided the A/C was a necessity (I restored classic Corvettes as a full-time hobby), and I had a local contractor install a Mitsubishi "Mr. Slim" 42,000-BTU (cooling only) mini-split system in 2005 ...

Any regrets going with "cooling only" ? Not that your gas bill is probably very high, but you could probably cut your annual gas bill (for the garage) by 50% or more even if you only use it for heat in spring and fall.

 

[JohnZ]

Any regrets going with "cooling only" ? Not that your gas bill is probably very high, but you could probably cut your annual gas bill (for the garage) by 50% or more even if you only use it for heat in spring and fall.

"Cooling Only" was an easy decision, as the Reznor unit heater had already been installed for five years (when we built the house) and worked fine. Don't know offhand what the garage heater contributes to the gas bill - it runs off the same meter as the house and the standby generator. The house is a 3300 sq. ft. ranch with a 2550 sq. ft. attached garage, so we're heating almost 6,000 sq. ft. for a year-round flat rate of about $165.00 per month.

 

[protegeV]

As far as insulation goes, I talked to my builder's recommended spary foam installer and was quoted $9k for 1" closed cell on the walls and 2" closed cell on the roof.
This is as opposed to $5K for r19 faced batt insulation all the way around.

From what Ive read, closed cell is only about r6 per inch. So why would I want to pay twice as much for 1/3 of the rating?!?!?!

 

[yeldogt]

Foam seals everything up -- no air movement. It's incredible stuff -- I did 2+" flash and batt on one project to meet code .. little cheaper. in a warmer climate the thickness needed is less to guard against condensation in cold weather.

Since batts leak and closed foam does not -- the effective R value of the foam is higher. I have done rehabs where you can feel the difference just walking through a building with both types.

Think how well those cheap thin foam coolers work -- same thing,

 

[protegeV]

seems slightly deceiving then, to use the same r-value scale as fiberglass if the foam supposedly works better.

It's not really an apples to apples comparison. 1" of foam has the same r-value as 2" of fiberglass

 

[webdog]

I have a similar building 40x64x12. The difference is were putting R60 in the attic and R25 I the walls because I'm in Minnesota and want to save on heating and cooling costs. My plan is to get a 5 ton AC / Gas Furnace Package unit.

I would try to jump up the insulation you have as its a one time cost, it will pay for itself every day once it's installed. For me to install the extra R6 foam in the walls was only $800 more, so far that's the only insulation I've installed and it's already cooler inside during the day. Hope to have the ceiling and walls done to full rating next week.