Cooling metal shop building

[westbrooklawn]

I have a 28 x 36 metal building with two 10x7 insulated garage doors and one walk in door. The inside is open to the peak of the roof which is about 16 high. The building is insulated with a thin foil/bubble wrap which is white on the inside and foil against the siding/roofing. I heat it with a 45k Modine heater which does fine with outside temps in the high teens.

I recently installed a 24k btu window air conditioning unit to try to cool the building... it blows a tremendous amount of cold air, but won't keep up with the task of cooling the building. With outside temps of 92, it would only get the inside down to around 85.

I am thinking about trying to get a self contained ouside ac unit, and running just a supply duct and return duct through the wall. The inside of the shop is wide open, so my thought is that just dumping the cool air into the shop would work. My questions are 1. will this work, and 2. if so, what size unit do I need (summer temps here are in the low 90's).

 

[Tscott]

Your going to have a hard time cooling a steel building with Little to no insulation. The thin radiant barrier you describe won't do much in the way of retaining heat. At the most it will help keep the heat from radiating from the metal to the inside of the building.

I would suggest that you have 2 options.

1. Install vents in the roof or a fan in the peak of one of the end walls to help pull hot air our of the top of the building and pull cool air in the from the doors. If you can get enough flow out of the peak of the building then you can get a good breeze through the doors.

2. Insulate the building better, and get an AC unit.

Chances are the first option will be the cheapest, but if you really want to cool your steel building, it can be done. I know there are insulation companies who sell pieces of insulation that fit between the existing purlins in your building.

Tom

 

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[westbrooklawn]

Back to the top.... there has to be some HVAC folks on here who can help me size a unit for this application. I don't plan on keeping the area cooled all the time, only when I am using it, maybe 3-4 hours per day, 3 or 4 days a week. I know the insulating efficiency isn't great, but it seems I should be able to flood the area with enough cool air to make it comfortable when I need to, even with the realization that there will be a large amount of loss.

 

[trythis]

Insulate with Straw Bale, cover Make the roof a green roof? Then use AC? A crazy idea, I know.

 

[hidollartoys]

You can not afford the cost of AC without insulating. The heat load will require a tremendously large AC unit.

 

[Charles (in GA)]

Building gets heat soaked. Everything in it, metal, concrete, tools, equipment, etc gets heat soaked. You walk in and want to work for three or four hours. It would take an A/C unit two or three times as big as an insulated building needs, to cool it down, as everything in it is radiating heat for hours. About the time you get done, the unit finally catches up, and the electric bill would be tremendous.

You need cross ventilation, if both garage doors are on one end, put a huge exhaust fan in the peak of the roof on the other end. Get taller garage doors, more opening, more area for air to move thru.

Charles

 

[ItBurnsWhenIPee]

I've got a 28 x 30 metal building with the same insulation you do, and I use a 20k BTU window unit to cool it. On the hottest days (like today), it'll knock it down to very bearable 78-80 degrees. I've thought about installing a second one (cut a hole in a wall because I've only got one window)...But I may just wait until this one dies and buy a bigger unit.

Have you thought about putting a second one in?

As said above though...You're not going to have a lot of luck with cooling it down, especially if you're not keeping it cool all the time. I usually turn mine on the night before I know I'm going to be out there, that way it's nice and cool when I get out there the next day.

 

[Deltarat]

I have a 30 x50 with the same bubble wrap insulation. I have 2-23k window units in mine and it stays pretty comfortable. They have delay timers on them and if I am going to work the next day, I just set them to come on a few hours before I am going to work.

 

[westbrooklawn]

Itburns and Delta -

Thanks for the encouraging information.... at least it seems feasable with the same type building. I may have to install a second unit, or go with something like a 5 ton cental AC unit. I understand Charles' point about heat soaking, but after 6 hours of overnight temps in the low 70's the interior temp of the building is also in the low 70's, so I have to assume everything inside is also cooled down to that temp. I also need to take a look at the area above the soffits... that area isn't insulated.

 

[COWBOY]

an elastomeric coating will reflect heat back off the roof

 

[slopecarver]

plant trees around the perimeter, paint the exterior white, insulate then try again with your existing AC

 

[bahamasair]

If you go with a unit thats too oversized you will end up with alot of moisture (condensation) in the building. AC units are sized to run for long enough to remove a certain % of moisture in the air. You might not have a problem in a leaky building for the short time you will be using it tho.

 

[yzair]

Here in the Hi desert area of ca I use swamp coolers they work great unless outside humidity is over about 40% which isn't very often here. I have 2 large units to cool about 2,000 sq.ft. w/10ft ceiling. usually only have to use 1 unit.

 

[mrholeshot]

I have a 3 ton heat pump in my 28X30 16 high metal building. It will cool the building despite being uninsulated and poorly sealed. It's a redneck kind of building but I don't run the A/C often. It's not insualated and I'm OK with a big fan until about 95 degrees. I try to do most stuff early in the day or at night to keep the light bill down. I'm going to get it insulated and sealed before winter. I can't stand the cold