物理問題關於空氣流動

在一間密室冇開冷氣既時侯,人體的熱能會因為熱平衡散失到四周,但由於大部份熱能都不能離開密室,因此密室會變熱,至於有眼訓既感覺,唔係因為密,而係因為呼吸會產生二氧化碳,二氧化碳無法離開密室,令室內積聚大量二氧化碳,當人類吸入二氧化碳,身體會向腦部發出眼訓的訊息.

開左冷氣之後,由於冷氣內置抽風系統,令空氣得以流通,二氧化碳便會離開密室.

In building physics, 'thermal comfort' depends on 4 main factors. They are:

1. temperature
2. relative humidity
3. wind speed (or air movement)
4. radiant temperature (i.e. temperature of the surrounding environment)

The person feels uncomfortable, if the air conditioner is not turned on, is because the both the temperature and relative humidity inside the room would increase due to body heat and sweating. Also, the person is in a room with stagnant air, which slows down the evapouration of sweat from his body that makes him to have an uncomfortable feeling.

After the air conditioner is turned on, the temperature could be mainained at a lower value. The same applies to relative humidity. The operation of the air conditioner causes air movement to take place inside the room. This speeds up evapouration of sweat from the body and the person feels comfortably cool and dry.

Note: the fourth factor, radiant temperature, depends on the temperature of the walls of the room. Its value would be lowered after switching on the air conditioner, adding to a better degree of comfort to the person.