Our body is like a machine, it consumes food as fuel and converts it to power and heat. The normal body temperature is around 37 degrees Celsius, so the excessive heat should be removed from our body. Heat transfer happens from warmer object to cooler object or environment. As a result, when the ambient temperature is decreased to less than normal body temperature, the body starts to lose heat by three natural processes, called evaporation, convection, and radiation. The first process, evaporation, is directly related to relative humidity of our surrounding environment.
On the other hand, convection and radiation is related to the surrounding temperature.
Body comfort is related to three main factors: ambient temperature, relative humidity, and airflow rate. The normal temperature that body feels comfort is around 24 degree Celsius with relative humidity about %50 to %60.
The more the ambient temperature, the less the body can release extra heat to the surrounding through convection, and radiation processes. Additionally, the higher the relative humidity, the less the body can lose heat through the evaporation process.
According to the above information, the main responsibilities of an Air Conditioning system is to keep the temperature and humidity in a normal and standard range for the body comfort. As a result, determining the capacity of the system based on the usage and the heat load are of great importance. In other words, the system should run long enough to decrease both humidity and temperature to the standard range. Any oversized system can not drop down the humidity to %50 while it might decrease the temperature to 24 degrees Celsius or less.