Work Shop Ventilation

First, I am American and will need to advise in English units. This building is extremely large (18,000 square feet, 1.3 million cubic feet). If we look at the 2006 IMC, we have to determine whether this environment requires hazardous exhaust, or regular exhaust typical of a mechanic's garage. I recommend you look at NFPA 704 to determine if anything is hazardous. Assuming you are non-hazardous (regular sanding, welding, etc.), you will be looking a 1.5 CFM per square foot. That is 27,000 CFM of exhaust, which is huge. Your make up air can either be unconditioned, or conditioined. If it is unconditioned, you will simply have a louver(s) in the wall with a back draft damper that lets outside air in to make up the exhaust. If you need the building conditioned, you need to look at a 100% fresh air air conditioning unit(s). This unit will be enormous. The total tons of air conditioning will be in the neighborhood of 150 tons, depending on the ambient environment and the building insulation. I would recommend a ducted and dedicated exhaust hood for welding, and a paint booth with dedicated exhaust for painting. You really need a professional engineer.

Thanks for replies,but I need some more data.

With my best regards,

The dedicated exhausts are a great idea. If you are building boats, some of the locations for sanding or welding might not be accessible to booths, etc. In those cases, you might be able to run duct hoses from the individual areas to the exhaust fans, or maybe even an exhaust fan manifold or plenum.

Depending on your climate, consider too the possible heating requirements. Also, if humidity conditions are favorable (low RH), an evaporative cooler might substitute for refrigerated AC.

Some forethought will help you achieve a good solution. The OP was excellent in providing good starting information.