how to get more fresh air?

im growing in a shed that can not have any holes cut out i have got a fan in there at the moment but it gets a little stuffy on hot days. when i am around the house i do leave the shed door open but during the week i have to keep it shut any suggestion. ill be adding another fan soon but i still dont think that will be enough

without been able to put holes or vents in the shed i cant see how you can draw in extra air, maybe put some frozen bottle of water in front of your fans and replace when needed it may bring ya temps down slightly, other than that i have no ideas

there are gaps in the shead but nothing big enough to what i need and ill have todo that frozen bottle thing cheers