Here at Coventry Makerspace it can get a bit warm, even with windows open the air needs to be moving for open windows to be effective..
A plan / mission is borne !
2 (or more) x Broken PC Power Supplies..
Step 1: Strip and Salvage...
First things first, be very careful when taking a PSU to bit's, there are large capacitors which could hold charge and give a large shock, possibly fatal !
Every power supply I have taken apart over the years I have found that the Fan's are plugged in rather than being hard wired, which makes it removal easier..
Most fans are held in with 4 screws, these screws normally also hold in the Guard, keep this as it can be used to prevent curious fingers exploring fans running !
Keep the circuit board, if you are a component salvager, there are plenty on there that could be useful, however, if it's a dead PSU, you may be salvaging broken parts.
I tend to keep the heat sinks, power switches, sockets, some have handy transformers which are expensive.
Step 2: Join the Fans
Using some cable ties (also known as zip ties) I thread them through the screw holes and fasten them together, ordinarily I would include the guard, but I haven't in this to make it easier to see (or, maybe I forgot ! )...
When I make these fans I build them in pairs, so I ensure the power wires are next to each other which makes it easier to join them.
Step 3: Connect and Wire
I simply strip the cables on each fan, solder and heat shrink them together to prevent an accidental shortcircuit.
Now is the time you can test your creation, you will find you don't get a gale force wind, what you do get is low pressure, but high volume, which mean in a large space you can induce air movement. The movement of the air in most places is what is lacking, with some judicious positioning of the fans, you can get good circulation and you will be in a happier place.
Step 4: Improvements....
How could this be improved...
Build a frame, mount 8 fans in switched pairs, so you can go from gentle breeze so some serious air movement !
Ensure you check the power usage of the fans, the ones in this instructable use 0.2a so we use a 12v 2a power supply, this would be enough for 10, however, I would rather power 8 and have some headway.
Add an Arduino, some Transistors, thermistors etc, and get it to switch on automatically...
Add Bluetooth or an IR controller..
Mount the frame so it can be swivelled, put a servo in and remotely adjust the direction ..
Something like this can be expanded and improved upon, all it needs is a little thought.