PURPOSE.
Air conditioning is the controlled environment of an enclosed space, such as inside an auto. Air conditioning involves dehumidifying, cleaning and cooling the air inside the car. This provides comfort to the driver and passenger alike. The main purpose of air conditioning system is to transfer heat from inside the passenger's compartment, to the surrounding outside air.
Comfort affect driver responsiveness and reaction time to a given situation. Air conditioning provides greater safety by reducing driver fatigue. In addiction, interior noise level is reduced when all windows are closed and the air conditioner is on. Air conditioning also eliminates windshields fogging. This allow the driver to maintain good visibility of the road and other cars.
CONDITIONS AFFECTING BODY COMFORT.
The three main factors that effect body comfort are temperature , relative humidity and air movement.
Temperature : Cool air increases the rate of convection; warm air slow it down. Cool air lowers the temperature of the surrounding surfaces. Therefore, the rate of radiation increases. Since warm air raises the surrounding surface temperature, the radiation rate dicreases. In general, cool air increases the rate of evaporation and warm air slows it down. The evaporation rate also depend on the amount of moisture already in the air and the mount of air movement.
Humidity : Moisture in the air is measured in term of humidity. For example, 50% relative humidity means that the air contains half the amount of moisture that is capable of holding at a given temperature. A low relative humidity allows heat to be taken away from the body by evaporation. Because low humidity means the air is relatively dry, it can readily absorb moisture. A high relative humidity has the opposite affect. The evaporation process slows down in humid conditions; thus, the speed at which heat can be removed by evaporation decreases. An acceptable comfort range for the human body is from 22°C to 26.6°C at from 45% to 50% relative humidity.
Air movement : Another factor that effect the ability of the body to give off heat is the movement of air around the body. As air movement increase, the following processes occur:
- The evaporation process of removing body heat speeds up because moisture in the air near the body is carried away at a faster rate.
- The convection process increase because the layer of warm air surrounding the body is carried away more rapidly.
- The radiation process increases because the heat of the surrounding surface is removed at a faster rate. As a result, heat radiates from the body at a faster rate.
