How do I stop my 2013 Macbook Air from putting the computer to sleep?
knodi was close, but pmset sleep 180 does not mean "180 x display sleep time" it simply means 180 minutes.

Before you change any of your pmset settings, I would take note of your current settings. If you enter this line in Terminal.app:

sudo pmset -g live | tee -a ~/Desktop/original-pmset.txt

it will show you the current pmset settings and it will also save a copy to ~/Desktop/original-pmset.txt so you can keep it as a reference.

Manipulating computer sleep time with pmset

If I want my MacBook Air to go to skeep after 60 minutes of idle time when it is plugged into wall/AC power, I can set that using:

sudo pmset -c sleep 60

Similarly,

sudo pmset -c sleep 0

tells my MacBook Air not to put the computer to sleep, even if the display goes to sleep.

If I wanted that same setting for when the MacBook is on battery power (not AC/wall power), then I would use

sudo pmset -b sleep 0

I can also set different sleep times for disksleep and displaysleep

(You can read more about pmset at https://developer.apple.com/library/mac/#documentation/Darwin/Reference/ManPages/man1/pmset.1.html or man pmset in Terminal.)

I would be very interested to know if sudo pmset -c sleep 60 (or whatever value you choose) actually works for a Haswell-based MacBook Air.