did you think that 2 unit of 2 tonner airconditioning unit is sufficient to 128 square meter library room.?

Answer 1

You size air conditioners by area of external walls, U-factor of the wall, and desired temperature difference If the room to be air conditioned is on the top floor, then you include the area of the room and the U-factor for the ceiling or roof.

4 tonnes is probably adequate, but you need to run the calculations to be sure.

Answer 2

NO, there is a better way of calculating your needs for AC, try the site below.