Air conditioning system in automobile

AIR-CONDITIONING (AC)  SYSTEM  IN AUTOMOBILE :

Airconditioning:

     Airconditioning is a branch of science which deals with conditioning of air for human comfort,irrespective of external conditions,It is known as air conditioning.

(or)

  The simultaneous control of temperature,humidity,purity,motion,cleaniness of air

Factors affecting comfort air conditioning :

v  Temperature of air

v  Humidity of air

v  Purity of air

v  Motion of air

Temperature of air :

          Maintanence of temperature with a enclosed space.generally for human comfort conditions the temperature of air is equal to 21⁰C and relative humidity is 56% irrespective of outside air.

Humidity of air :

          The percentage of decreasing (or) increasing in moisture content of air during summer (or) winter respectively to produce comfortable and healthy conditions.

----For summer air conditioning it should be not less than 60%

----For winter air conditioning  it should not be more than 40%

Purity of air :

          It has been noticed that people don’t feel comfortable when breathing the contaminated air even if it is at a acceptable temperature and humidity ranges.It is because due to presence of dust & bacterias in order to remove the dust,cleaning,filteration&purification of air must be required.

Motion of air:

                   Motion of air should be controlled in order to keep constant temperature throughout condition space. It is necessary that there should be equidistant of air through air conditioning..

Air-conditioning System :

  The system which effectively controls the temperature,humidity,purity,motion of air to produce the desired effects upon the occuptance of the space is known as air conditioning system.

Necessity of Automobile Air-Conditioning:

           Due to varying conditions of heating, ventilating, cooling, dehumidification in the atmosphere at various places, it is necessary to be conditioned the air in the automobiles. To maintain human comfort and improve internal atmosphere in an enclosed space, proper control of freshness temperature, humidity and cleanliness of air is required. For this reason Automobile air-conditioning is necessary in the vehicles.

Factors to be considered for selecting/designing of air conditioning system :

v  Ability to store the heat gain.

v  Concept of desired environment by the user

v  Necessity and capacity for pre-cooling

v  Volume of the space to be air-conditioned

v  The main purpose and total investment

v  Occurrence of the external environment of
                   ¨      Humidity
                   ¨      Temperature
                   ¨      Purity 
                         ¨      motion

v  space (or) building to be used
                  ¨      location
                  ¨      orientation (or) space
                  ¨      purpose of the use

Factors to be considered in selection of air filters :

   The selection of filters should be  based on given specifications :

v  capability of dust storage must be more at low pressure at differential levels.

v  The requirement of the filters should be disscussed with equipment manufacturers

v  The amount of air handled by the filters

v  The degree of air cleanilness required by the filters

v  Level of filteration required

v  To increase efficiency of filters and prefilters should be used.

Construction and working of Passenger car Air – Conditioning System :

The main components of Auto Air- Condition are:

1. Compressor

2. Magnetic clutch

3. Condenser

4. Receiver or dehydrator

5. Expansion valve

6. Evaporator

7. Suction on  throttling valve

Figure : Realistic arragement of air conditioning system in car

Compressor:

          The compressor in the Auto Air- Condition system is belt-driven engine crankshaft pulley. A magnetic clutch engages the compressor shaft. When the voltage is applied to the compressor clutch coil was sufficient the compressor and pulley rotates together as one unit. When the voltage is interrupted the pulley, disengages automatically, causes compressor to stop.

          The low – pressured, high temperature, vaporized refrigerant enter in to the compressor and it increases the pressure of about 20kg/cm² and 100ºc temp, and pushes into the condenser. In the compressor the refrigerant never

reaches its liquid state.

Magnetic Clutch:

          The electrically controlled magnetic clutch is housed in pulley assembly and a switch is on the controlling panel. This clutch is engaged or disengaged depending upon the temperature of the air. Bellow 40 ºF. The compressor cannot be operated. Above 55ºF this switch closes and completes the circuit to the compressor clutch.

Condenser:

          It is usually placed in front of the car and it is looks like a Fin-andtube radiator. The condenser receives heated and compressed gas from the compressor and is cooled by the air passing across the condenser. The refrigerant now in the form of high pressure liquid which is fed in to the receiver drier Unit.

Figure : Arragement of air conditioning system

Reservoir or Dehydrator:

          The refrigerant stored under pressure in the Receiver drier. The drier removes any traces of moisture present in the system to avoid freezing of moisture at low temperature and thus clogging the lines. It causes running troubles.

Expansion Valve:

          In the expansion valve high pressure liquid is converted into low pressure liquid then the refinement flow in to the evaporator

Figure :wiring arragement of air conditioning system

Evaporator:

          The evaporator unit where the cooling effect is obtained is usually located inside the passenger compartment bellow the dash board. A high capacity blower circulates the air in the in the car interior across the evaporator coils, and the drops the temperature of the air inside the passenger compartment. The heat picked by the refrigerant goes back to the compressor in the vapour form, where the refrigerant is again compressed to a high pressure and the cycle starts again.

Suction throttle valve:

           It ensures that the refrigerant the evaporator says at such a pressure that the evaporator core surface temperature does not fall bellow the freezing point of water (0°c), thus preventing ice formation in the evaporator.

Selection and supply of outlet  of air-conditioned air:

v  Quantity of delivery air flowing through the outlet is directly proportional to load in the room.

v  Location at height of the outlet

v  Uniform distribution  of air from outlet

v  All parameters must be uniform