The hot weather can make your garage a dangerous heat box. Not only can this damage things in your garage such as electronics, but it can make it unusable space for you and your family. Keeping the garage door open and hoping for a breeze has a marginal success rate and invites debris and bugs in. Adding fans to the equation results in lots of noise and cables all over. There are better ways!
Consider add a garage door screen. These are an incredible value for the resulting usable space gained. A screen will keep the debris out while letting the breeze through. We have written about these before and our customers have had great success with them.
If you really want to tackle the heat though, you'll need to take much the same approach as when dealing with the cold as we recently blogged about. This involves replacing and enhancing seals on walk through doors and the garage door itself, installing an insulated garage door, insulating your garage's walls, and adding a "mini split" HVAC system. We didn't go into much detail about the HVAC unit before, so we'd like to ellaborate.
There are a number of different HVAC solutions suitable for a garage. If you have a window in your garage already, you may be able to fit a window unit. This is likely the most affordable approach. If you don't have a window, you may be able to utilize a portable (wheels) unit with an exhaust vent hose running through the wall, similar to a dryer vent hose. The ultimate solution is adding a "mini split" unit. This is a low profile unit that mounts to the wall near the ceiling of your garage and has a compact compressor outside. This is a full-on HVAC system like the one in your house, but in a smaller compact package.
With the right preparation, you'll see benefits in both hot and cold weather, making your garage space usable year-round.