[David]

I have a 24K btu Mitsubishi mini-split heat pump in my 22' x 43' insulated garage and it works great. I've had it for a few years and it still works great. I had a 24k btu window unit before that and it just couldn't cool unless I let it run a long time.

There's a built in filter but I don't know how well it would keep sawdust out. The wall unit is pretty easy to open so perhaps a periodic coil cleaning would keep it working well.

For your size, in a climate similar to mine in Houston, I'd go with a 24k btu mini-split heat pump like mine but with 2 wall units for the 2 garage areas.

I installed it myself and it was pretty easy. A plain flair tool is all you need for the copper lines and a vacuum pump to evacuate the lines before you open the refrigerant valve to charge the system. My local HVAC supply had a mini-split installation kit in stock for about $100 that had the copper lines and I bought the system online.