Cooling the desert

[TWX]

Hi,

I'm trying to figure out what it'll take to make this garage comfortable in the summer in Phoenix. It's block construction using those 4" tall, 8" thick, 16" wide stylized hollow blocks. The interior dimensions are 35' deep, 23'6" wide, and the lowest point the roof is 12'4" up (very, very slight downhill slope for drainage). The garage door is almost 12' by 22' on the narrow wall, and is on the east side. The north side is attached the the house almost its whole length and most of its height, the west side is somewhat shaded by trees, but the south side is exposed. The garage has a hip roof, about 2' to 2'6" eaves on all sides.

Right now I'm considering taking 4'x8' insulation panels and cutting them to 14.5" widths, 8' long, and sandwiching wood studs cut to the thickness of the insulation material between them, giving me 16" centers to mount the drywall to. I'm debating between 2" thick insulation and 1.5" thick insulation. The 2" stuff is R12.9, the 1.5" thick stuff is R9.4. If I go with the 1.5", the two-by-two, which is actually 1.5 by 1.5, will not have to be cut thinner, but if I go with 2" thick insulation I'll have to probably go with two-by-three boards (1.5" by 2.5") and rip or saw them down to 2". The cost for the 36 or so insulation panels is $26 for the 1.5" thick ones, and $33 for the 2" thick ones, which means $936 or $1188. It'll be around $325 for the 5/8" thick 4x12 drywall before tax, and I'll need about 400' of drywall tape, plus whatever else I end up doing for finishing, the fasteners to secure the insulation to the block, the fasteners to secure the studs to the block, and the fasteners to secure the drywall to the studs.

I'm then looking at a ductless-split-system around 24000BTU. I figure I'll wire for it before I install the insulation, plus all of the other electric that I want in the garage.

Anyone have any insight on something I should do differently?

 

[TWX]

Oh, btw, this is the kind of system that I've thought about for the garage...

http://www.ecoheats.com/24khs72_24_000_btu_ductless_mini_split_2413_prd1.htm

It's a Sanyo 24000btu unit with a slim compressor that won't obstruct side access too much.

 

[930dreamer]

Have you considered a evaporative cooler, In your desert location I would think it would be perfect?

 

[TWX]

I'm not 100% sold on just doing AC, but there are a couple of months each year when it's too humid for evap. The main complication with evap is that with such a high roof, it would be a pain to install, and with no windows there's no go place to put the unit/intake except the roof.

I don't know. It's going to be a lot of money regardless.

 

[930dreamer]

I'm not 100% sold on just doing AC, but there are a couple of months each year when it's too humid for evap. The main complication with evap is that with such a high roof, it would be a pain to install, and with no windows there's no go place to put the unit/intake except the roof.

I don't know. It's going to be a lot of money regardless.

I hear you, what about the evap's that attach to a garden hose and roll around. I have a beautiful place in Albuquerque,NM(second home) that has a evap cooler, when the humidity is high it *****. It was 64 degrees inside when I woke up today

 

[Gary S]

You are doing the right thing by insulating first. I don't know the R value of your block walls, but adding even the 1.5" insulation inside should get you to an R12 or so wall. That should be enough. Your wall insulation isn't nearly as critical as the ceiling is.
Do the walls like you mentioned, and then get the ceiling insulation up to at least R30 or R40.
Once you do that, you will want to add a couple of ceiling fans to move the air around.
With that setup, you might find that all you need is a single 10K or so BTU window AC unit to keep very comfortable.
I just spent the afternoon in my 24x48 garage. I have R13 walls and R40 ceiling. The outside temp is around 90 today. It was 75 degrees inside the garage when I went in there. I keep the doors closed so it can maintain the nice temp by itself. This building stays that much cooler inside just by itself with no AC.
When I went inside to work, I turned on my two ceiling fans and my 11K BTU window AC unit. As I worked, the temp slowly crept downward. It isn't enough AC to make much difference, but it gains slowly instead of losing, so it is enough for me.

 

[Kevin54]

Insulating will make a huge difference. I have R13 in the walls and R32 in the ceiling of my garage. Insulating the ceiling will make the biggest difference of keeping it cooler as it will keep the attic heat from coming down and everyone knows how hot an attic gets in the direct sun of summer. Another thing that makes a huge difference in my garage is the use of window blinds. By keeping them shut during the day it is probably 10 degrees cooler than if the blinds are open. As Gary stated above, ceiling fans help out immensely by keeping the air circulating. I had to take mine down for awhile and can really tell a difference.