There is no technical difference between this and the desert cooler. Both work on the same principle water removes 0.56 kcal of heat for every gram evaporated. The amount of water that can be evaporated in any place depends on the relative humidity in that location. If it is a closed room then fairly quickly the humidity will rise to 100 and no further cooling will take place. As mentioned in the post, humidity will go up, which may not be a good thing for health for some people. Beyond a point water mist will start accumulating in a closed room leading to rusting of iron surfaces, growth of mildew on books and clothes. I for one will pass this.

@Ramani Sir - is there any evidence that increased humidity is not good for humans? I noticed a few posts on Twitter talking about it. Here in Nagpur, we use Desert Coolers every summer and at best, they drop the temperature by about 4-5 degree C (never checked though).

Most experts agree that air for breathing should be between RH 40 to 70%. Higher humidities can lead to problems , especially for asthmatics. Even for normal people the body temperature is regulated by evaporation of sweat, which decreases at high humidities. Desert coolers raise the humidity to unacceptable levels in closed spaces. Maybe acceptable in rooms with active circulation in and out.