How does an air-cooler work?

Think of the cool air you enjoy every time you sit beside a lake, beach etc. Air-cooler works on the same principle – Evaporative cooling.

Molecules on the surface of water are restless! Because of their acquaintance with surrounding air molecules they are relatively more energetic (molecular collisions). The moment they gain sufficient kinetic energy, they elope (overcome the shackles of intra-molecular forces). Result is moist air which is cooler. 

Let’s apply this concept on air-cooler.

The pump circulates water through the lateral pads (the dry grass thing). When the hot air in the room comes in contact with it, the surface water evaporates and cools the air. The rotating fan blows the cool air into the room. The amount of cooling depends on the humidity of the room. Lesser the humidity better it is - Less humidity means less water content in air, so it can suck in more.

My mum was complaining that all neighbors have fixed their coolers in windows. My dad never does that for her. While I was listening to her, it suddenly struck me why it’s done. Obvious again – Continuous supply of fresh dry air for cooling. This also means that unlike the common (?) belief we should not close all doors and windows. The moist air should keep moving out ensuring that humidity in the room is not high.

Thanks to this question, I revisited few fundamentals I learnt and forgot– Evaporation, humidity etc.