Air Conditioning a garage workshop
 

Hi guys,
Anyone have any input on portable or permanent air conditioning solutions for a 2-car, 400sqft workshop? I park my 993 in it and it gets up to 110 or so when outside temp is >100. The space has no windows.

If portable units actually work, I'd do that first. Or, I would consider mounting an AC unit in the attic above the garage, and could duct fresh outside air into the attic and vent the unit to the garage if that's the best way to go.

Looking for your experiences. I can't work out there during summer time!

Edit- I've got 110 and 220 dedicated breaker circuits to use if that makes a difference.

Thanks,
Colin

Colin,
Can you insulate the walls, ceiling and the garage door? Unless you can insulate, especially the ceiling, the cool air won't hang around very long. I use a big fan, mounted up in the corner of the garage to cool the air and it also keeps flys and mosquitos to a minimum.

I used a window unit for my dedicated shop side of the garage. Was only about 180 sqft though. With 400 sqft you will either have to use multiple window units or go with an attic AC unit. I'd probably go with the attic unit.

The only thing I have to contribute is that if you stick a plain old dehumidifier in there as well, the A/C unit will not have to work nearly as hard. This goes for houses too, assuming that you have high humidity.

The walls are fully insulated, but the ceiling isn't. I could do that.

I've already got two 52" ceiling fans permanently mounted. They help, but it's just too hot during July/August.

I wish there were a window where I could just hang a window-mount A/C!

Mitsubishi ductless. Excellent. And easy to install in most cases.

http://www.mitsubishielectric.ca/ductless/M_Series.html

Cowtown, where do you live? In the right environment, an attic mounted evaporative cooler can do wonders.

If you can get a small water line plumbed, a evaporative (swamp) cooler will move much more air at a fraction of the energy costs. More/cheaper air movement means less insulation won't be a huge issue.

Getting the garage from 110 to 80 will still seem like it's air conditioned.

I have a 1500 sf detached garage that is fully insulated and drywalled. I have a 220v window unit stuck in a wall and it cools the garage in a half hour. I only use it when I go out there so cost is unnoticeable.

If you spend lots of time in the garage - then go with a dedicated attic unit.

If you occasionally go in the garage - then a window unit is perfect.

I know you don't have a window "yet", but I have a small cheap window A/C unit in my 20 x 20 insulated workshop room with 14' ceilings and it works great even on 90+ days. If I open an interconnecting garage door into my 20 x 25 paintbooth, even it will cool somewhat if left on for a long period of time.

Home Depot,Lowes,Target and Pep Boys sell portable AC units that are on 4 wheels and vent outdoors by a hose similiar to a dryer hose. I believe they are around 9,000-10,000 BTU's which I would think can do the job for your garage. I believe they are 110 volt so installation is a snap. Just a thought seeing that you currently don't have a window.

The portables work great. It's all in BTU's/cu ft.

I have a fully-insulated 25x25x12 shop and a 10k BTU 'window' mount unit. I wish I'd run 220v instead and gone with more BTU; 10k is the biggest I can run on 110v. I'm contemplating adding a 2nd 110v unit next to the existing one.

Last summer, when it hit 115 outside, the best this little unit could do was get the shop down to 80 inside.

A ceiling fan helps, too.

I'd be a happy guy if I could get 80.

Thanks for all the replies. I think I'll pick up a portable and run the tube through a hole in the side door. Sounds like that's easy and will probably be enough for my needs.

As an A/C guy, generally 1 ton of A/C will work per 400 square feet of living space. If your walls are insulated and your ceiling is insulated well, I would frame a 2 ton window unit in the wall considering you were on a concrete slab and had good seals on your doors. The problem with going with too much tonage is that the unit will not run long enough to remove the proper amount of humidity to where it feels comfortable. You want your unit to run to remove the humidity..... If you live in a hot but dry climate then you may be able to get away with a slightly smaller unit. If you have low ceilings I would say that a 2 ton (24,000btu) unit should do okay... if you have open ceilings then you may want to try a 28-32,0000 btu unit. You should always air the space out to get rid of unwanted heat before turning on your unit, this will allow the unit to supply cooler air, will prolong compressor life, and will keep the amperage of the unit lower. And for you guys out there that think you are saving money by turning off your a/c during the day and then turning it on when you get home to a hot house you are wrong. Your unit actually runs longer trying to bring the temps down in the house than what it does trying to maintain it.... unless you have 5'x5' holes knocked in the outside walls of your house LOL.......

The portables might do the job, but it really depends on your definition of "doing the job."

If you're prepared to leave the unit on 24/7, you might get by with a smaller unit, perhaps 8000-1000 BTUs.

Consider the ductless split system. They don't require the extra labor for ductwork, particularly since you already have fans to circulate the air. I'd grab a 12000 BTU (1 ton) setup. For a few more $, 18000 BTU (1.5 ton) would be great. It would keep you really cool. You're looking at $650 for the 1 ton on eBay and a few hundred more for the 1.5 ton. A competent A/C guy could install this in a few hours.

Why suggest a 2 ton unit for 400 square feet of shop? I'd save the bucks on a smaller unit and spray cellulose in the attic. Lowes and HD have cellulose for less than $10/bag and you can rent the machine for free. Spray the attic space to joist depth + extra.




A properly designed system with proper charge won't cry about running longer.

And I cannot see how a unit will run longer when operated with a setback thermostat. When your thermostat is set to a higher setting, the BTU gain is reduced, meaning you have fewer BTUs of heat to remove when you get home. Setback thermostats are not bunk. They do save energy, and saving energy means less runtime on the unit.

I recommended a 2 ton unit because a person or person's will be using it as a WORK shop, usually doing some type of WORK...... Most people will also not want to leave this area as a air conditioned space throughout the day they would usually be turning on the unit when they get home and want to work. The extra btu's will cause a faster drop in temp and will make up for the amount of Infiltration that a work shop would have. also you have to take into account any power tools, freezers etc that may produce heat in the room.


Your second comment shows that you understand nothing about air conditioning..... sorta like my wife and cars (you turn the key and it goes He He....) yeah I was referring to a properly designed and maintained system... a hot house will cause higher head pressures and higher amp readings on your compressor.... also discharge air temp will not drop to optimum until the room cools down. What you hope to achieve with a properly designed system is a 10-20 degree drop from supply to discharge air. In this respect, if your house is 110 degrees at 5:30 when you get home from work, you can look at a discharge air temp of no cooler than 80 degree discharge air. The unit will have to run considerably to make the discharge air temp drop. If you have any larger of as split than this you risk having your evaporator freeze up. Dirty filters, clogged coils and low refrigerant will also cause these problems.....

Turbo6bar, didn't read your setback tstat part... yeah turning your a/c back a little won't hurt, but I was refering to folks that turn their a/c's off and close up the house...... The difference being OFF.... If you turn your A/C up to 84 while at work and have it drop to 76 or 78 an hour before you get home, well thats fine because there is not that much of a temperature spread.... but one thing to remember with a/c's is that you are not just cooling the air, you are exchanging heat, which means you are not only pulling the heat out of the air, but all the walls, furniture, appliances, etc..... which in itself is not an instant process...

My son and I built him 20x20 music/studio for his bands and recording ventures. We left the rafters exposed for sound dispersion but used only R-13 between the studs and above the rafters. It has a 12btu 220ac wall mount unit. Living in Texas it gets up to over 120 in there before the air is turned on. In 1 hr it will be down to 75 and in 2 you could hang beef. In the winter it only takes a little 1500 watt heater to keep it 70. I can only imagine if we'd used thicker insulation.