Portable swamp coolers do look very similar to portable air conditioners, which is why there is often confusion between the two appliances. However, there is a big difference in the way the two devices work.
Air Conditioners
These coolers work by using a refrigeration process that involves compressing a special gas to create the cooling effect. That's a great simplification, but I don't want to get into too much detail in this post as it's not meant as a tutorial or study matter.
Suffice it to say, AC units are very good at drying and cooling the air they pump out into a room, but they also produce a lot of hot, moist air that must be exhausted out of the room, for obvious reasons!
This is done through a flexible hose attached to a special window fixing kit and one end and the back of the AC unit at the other. AC also tends to use quite a lot of energy to produce the cool air we all know and enjoy - typically from around one kilowatt to two kilowatts or more depending on the power output rating and the size of the space being cooled.
Swamp Coolers
On the other hand, swamp or evaporative coolers create cold air by evaporating moisture in many ways similar to how your skin feels cool when you perspire and it is exposed to a breeze.
As there is no compressor or other mechanical engine n use, swamp coolers use only a fraction of the power that a comparable AC uses. Typically 100-200 watts is consumed.
As there is no heat created, there is no need to exhaust anything and so no vent is required for these coolers.
The main downside to these coolers is they don't work well in humid conditions, since they rely on dry air absorbing moisture to create the cooling effect. If you live in an area that has 50% or higher average humidity in summer, a swamp cooler in not the best choice of cooling solution.
An air conditioner would be much more effective to control the climate in that case.
Conclusion
So there you have it - the difference between AC and swamp coolers and why an AC needs that vent hose and why swamp cooler do not! Check this video for a visual explanation:
