You can use your air cooler just like a fan in a closed room by turning off its water pump.
If you are thinking of using an air cooler in a closed room then it is advisable that you use it just like a pedestal or table fan.
Using a water cooler with the water pump ON is a very bad idea inside a concealed room.
Air cooler works on the principle of evaporative cooling, in which water gets mixed with air before it comes out of the cooler.
Due to evaporation the water in liquid form turns into vapor causing cooling.
This also increases the humidity of the surrounding region.
If the room is concealed, the humidity level will keep on rising and will ultimately cross that level after which the process of evaporation will become very hard and nearly stop.
After this you will not get any cooling from the water cooler and will feel very uneasy due to high humidity.
Even though the inside temperature and the outside temperature may be the same but still you will feel very hot and uneasy inside such a room.
Because there is a difference between actual vs perceived temperature.
Whatever may be the actual temperature in the outside environment.
Your perceived temperature can differ and is dependent on actual temperature, humidity level, and wind speed.
If there is high temperature outside but humidity is low and wind speed is high then you may feel OK.
On the other hand if the outside temperature is moderate but humidity is high and there is no wind.
You may feel very hot.
That is why using an air cooler in a closed and concealed room is a bad idea as with time the humidity will keep on rising.
What is the best way to use a cooler?
You must provide proper ventilation for facilitating airflow, this will counter the increase in humidity from the cooler.
You must keep all the windows and doors open.
The ideal position for any cooler is outside of the room near a window.
This makes the outside air to circulate with the room air, outdoor air is low in humidity from the room air.
If you place the cooler inside the room, it will circulate the room air which is already humid.