I apologize for a bump...just my two cents...
ve been battling heat in my shop since I moved into my current home eight years ago. I live in SoCal, and my garage door faces west. The afternoon sun has always heated up the shop to levels that make me spend less time in the shop.
I added a mini-split HVAC, and that helped enormously. But in the summer, when the outdoor temps can get over 90 degrees (sometimes over 100), and the afternoon sun is beating on the garage door, my mini-split had no hope of keeping up, and shop temps would climb.
I insulated the walls and ceiling, and that definitely helped. But my mini-split was still no match for the summer afternoon heat.
So, I got a thermal imaging camera. I learned a few important things that have helped get the heat under control.
First, the uninsulated steel garage doors were acting as a giant radiator. I knew that, but I didn't realize just how much that contributed to the problem. On those 90 degree days with the sun beating on the door, the temp of the outside of the garage doors would get over 120 degrees. The inside of the doors would get over 110. Since my shop is a 3-car garage, that's a lot of heat! No wonder the inside of the shop kept getting so warm.
I bought those garage door insulation kits from a big box store like this https://mechanicguides.com/best-garage-door-insulation-kit/ (I think HD). That made a significant difference, but the doors were still a big radiator. Instead of the inside of the door registering 110 degrees, it would get up to the high 90s. That's a 10-15 degree drop, but my mini-split still struggled to take all that heat out of the shop.
A few months ago, I upgraded my garage doors to some of those R-18 super-insulated garage doors https://redirect.viglink.com/?format=go&jsonp=vglnk_153321046388816&key=8d1879ea4db6639656bbe1af129db4fc&libId=jkchup3w010025g3000DAk2it4yuw&loc=https%3A%2F%2Fwww.garagejournal.com%2Fforum%2Fshowthread.php%3Ft%3D235256&v=1&out=http%3A%2F%2Fwww.homedepot.com%2Fp%2FUnbranded-Thermasheath-3-R-9-6-1-1-2in-x-4ft-x-8ft-Polyiso-Rigid-Foam-Insulation-Board-W-N5150%2F100317819%3FN%3D5yc1vZbaxxZ1z0z6ja&ref=https%3A%2F%2Fwww.google.nl%2F&title=insulated%20garage%20door%20cost%20-%20The%20Garage%20Journal%20Board&txt=R%20Max%20Thermasheath%20rigid%20insulation%20 (with no windows). That has made an enormous difference. We haven't yet had any 90+ degree weather this year, but so far, the inside of my garage doors has stayed pretty close to the ambient temp in my shop. So, whatever heat the sun is putting onto the garage door's exterior is mostly not making its way into the shop.
People get fixated on seals. In some circumstances, bad seals can be the culprit. But keep in mind that the job of the seals is to keep the heat/cold in the AMBIENT air outside from getting inside. When you have a West-facing garage door and the sun is beating on your garage door in the afternoon, the ambient outside temperate is really not the problem. The problem is that the sun is super-heating the exterior surface of your garage door to a temperature that can be 20-30 degrees hotter than the outside air. That's a much bigger problem than bad seals. I'm not saying that seals don't matter; I am saying that getting as much insulation as possible on the surface of your garage door is much more critical than seals for controlling heat if you have a West-facing door and you want to keep your shop cool. At least, that has been my experience.
The thermal imaging camera also gave me some additional insights. I had extensive fluorescent lighting throughout the shop, and the camera showed just how much heat those were putting out. So, I changed to LED lighting. Enormous improvement.
