Why Air Conditioning Is Necessary In An Automobile? Automobile Air Conditioning System (How It Works)

WHY AIR CONDITIONING IS NECESSARY IN AN AUTOMOBILE?

·        AUTOMOBILE AIR CONDITIONING SYSTEM –

                The air conditioning system is used to keep the occupants inside the car’s cabin comfortable during hot weather. It conditions the temperature of the air inside and also removes the humidity from it which decreases its temperature according to the condition of the air. The system used in modern automobiles is called heating, ventilating and air conditioning system or HVAC. It can cool the cabin during summers, keep it warm during winters and can also removes the humidity from the air inside.
The air conditioner for automobile involves,
a)      Temperature control
b)     Air circulation control
c)      Humidity control
d)     Air purification control
Ø NECESSITY OF AIR CONDITIONING IN AN AUTOMOBILE –
1.      During cold weather, a vehicle without a heater could becomes unfortunately even dangerously, cold.
2.      The vehicle could get unfortunately hot for a variety of reasons.
3.      A vehicle may collect heat from any of the following sources:
a)      Heat from sun which radiates through the roof and windows.
b)     Engine heat transmitted through the dash panel.
c)      Heat from exhaust system.
d)     Heat from hot pavement conducted through floor panels.
e)     Heat radiated by passengers.
4.      These heat sources combine to increase temperature of passenger compartment and cause mild to extreme discomfort.
5.      Thus, the main purpose of the automobile climate control (air conditioning) systems is to provide passenger comfort.
6.      Climate control (air conditioning) systems performs this function by circulating and cooling or warming the air in the vehicle passenger compartment to control the temperature and lower the humidity.
Ø AIR CONDITIONING PARAMETERS FOR HUMAN COMFORT –
·        Human comfort is the science of providing and maintaining comfort conditioning for human being irrespective of outdoor conditions. The human comfort varies person to person as per his individual taste or choice. As such, there is no fix condition of environment in which every human being feel comfortable.
·        American society of heating, refrigeration and air conditioning engineers (ASHRAE) has conducted survey and research for many years and concluded the comfort conditions in which most of the human being feels comfortable throughout the year, irrespective of outdoor conditions.
·        The comfort conditions are :
1.      TEMPERATURE –
Temperature is the most important factor which affects human comfort to a great extent. Most of the human being feels comfortable at a temperature 22.8⁰ to 25⁰C. generally, human being feel comfortable at relatively higher temperature in winter season and feel comfortable at relatively lower temperature in summer season. The comfort temperature of individual person depend on his body structure, eating habits, the area in which he is acquainted to live.
2.      HUMIDITY –
The control of humidity is not only necessary for human comfort but it is also important from point of view of efficiency of worker. For human comfort, relative humidity is kept within a range of 35% to 60%. In wet climate we feel laziness.
3.      AIR PURITY –
We do not feel comfortable when breathing in contaminated air even if temperature and humidity is within comfortable range. Therefore, proper filtration, cleaning and purification of air is necessary to keep it free from dust, dirt and other impurities. The proper percentage of oxygen must be maintained. Therefore, in public places like theatre, auditorium and shopping center exhaust fan must be used.
4.      AIR, MOTION AND CIRCULATION –
Even if temperature, humidity and purity of air is satisfactory, certain amount of air motion is necessary for human comfort. We do not feel comfortable in dead and still air. Moreover the air moment and circulation is required in order to ensure uniform conditions in every corner of air conditioned space.
Ø COMPONENTS OF AUTOMOBILE AIR CONDITIONING SYSTEM –
·        The main components of air conditioning system are –
A.     Compressor
B.     Condenser
C.      Receiver dryer
D.     Expansion valve
E.      Evaporator
F.      Blower
G.     Magnetic clutch control

1.      COMPRESSOR –
The compressor is a pump driven by a belt attached to the engines crankshaft. When the air conditioning system is turned ON, the refrigerant Vapour are drawn into the compressor and it pumps refrigerant vapour to high pressure to the condenser.
The compressor also features an electrically operated magnetic clutch control, which can turn it ON or OFF as per demand of air conditioning system.
2.      CONDENSER –
The condenser is a device used to change the high-pressure refrigerant vapour to a liquid. It is mounted in front of the engine radiator, and it looks very similar to a radiator.
The refrigerant vapours at high pressure and temperature enters the condenser and due to rejection of heat it converts into liquid at high pressure. The heat of condenser is removed by air flowing over condenser. Same cooling fan can be used for radiator and condenser.
3.      RECEIVER-DRYER –
Liquid refrigerant moves to the receiver dryer. This is a small reservoir canister suiting in in-line with the outlet hose from the condenser for the liquid refrigerant, and removes any water that may have leaked into the refrigerant. Receive-dryer, removes any water that has entered the system. If the water is allowed to remain in system due to sudden reduction in pressure in expansion valve or orifice tube there is possibility of forming ice crystals, which can damage the air conditioning system.
4.      EXPANSION VALVE –
The high pressure liquid refrigerant flows from the receiver-dryer through the expansion valve, where it is allowed to expand. This expansion reduces the pressure on the refrigerant, so it can move into the evaporator. The valve senses the pressure and regulates the flow of refrigerant, which allows the system to operate steadily.
           The expansion valve serves the following two functions.
1)     The liquid refrigerant, after passing through the receiver is injected out from the expansion valve, which causes the liquid to suddenly expand and turn into the low temperature, low pressure in mist form.
2)     The expansion valve adjusts the volume of refrigerant supplied to the evaporator, according to thermal load automatically.
Some vehicles have an orifice tube rather than an expansion valve, but it serves the same purpose in allowing the refrigerant to expand and the pressure to be lowered before the liquid enters the evaporator. The orifice tube allows refrigerant to flow at a constant rate and has no moving parts, but it can become clogged with debris over time. Systems with an orifice tube automatically turn the AC system ON and OFF to regulate the flow of refrigerant to the evaporator.
If the system uses an orifice tube, there will be an accumulator between the evaporator and the compressor. An orifice tube sometimes lets too much refrigerant into the evaporator and it does not all boil. Since the compressor cannot compress liquid, only vapours, the accumulator traps any excess liquid before it can get into the compressor. Thus, accumulator allows only vapours to pass in compressor suction line.
5.      EVAPORATOR –
The evaporator is heat absorbing component that looks similar to a car radiator. It has tubes and fins and is usually mounted inside the passenger compartment below the dash board. As the low-pressure refrigerant is entered into the evaporator, it vapourize by absorbing heat from the air in the passenger compartment. The blower fan inside the passenger compartment pushes air over the coils of evaporator, so cold air is circulated inside the car through the AC vent provided on dash board. On the air-side of the evaporator, the moistures in the air is removed and the collected condensate is drained away.
6.      BLOWER –
Fresh air or re-circulated air is drawn by blower. Speed control for blower is provided o dash board with four steps. Blower speed is controlled by passing current through resistor with different resistance value to change voltage to the blower motor in four steps.
7.      MAGNETIC CLUTCH CONTROL –
When ignition switch is turned ON with blower switch in any position except OFF the heater relay goes ON.
If air conditioner switch is turned ON the magnetic clutch relay is turned ON by the A/C amplifier.
Ø REFRIGERANT –

The fluid that passes around the whole system is known as refrigerant. The refrigerant can evaporate at a low temperature, and then condense again at a higher pressure.
In the old days, R-12 was the refrigerant used in almost all cars. But it was found to be a contributor to the depletion of ozone layer as it was a chlorofluorocarbon (CFC). Therefore, refrigerants were discontinued in 1996, and started the use of a non-CFC fluid called R-134a which is eco-friendly to the environment. R-134a is used in air conditioners because it evaporates and liquefies easily, and has chemically stable and non-degenerative properties.
Ø MODERN CAR USES R-134a REFRIGERANTS INSTEAD OF R-12 BECAUSE ----
1.      Refrigerant R-134a is a hydro fluorocarbon (HFC) that has zero potential to cause the depletion of the ozone layer and very little greenhouse effect.
2.      R-134a is the non-flammable and non-explosive, has toxicity within limits and good chemical stability.
3.      It has somewhat high affinity for the moisture.
4.      The overall physical and thermodynamic properties of refrigerant R-134a closely resemble with that of refrigerant R-12.
5.      Due to all the above factors. R-134a is considered to be an excellent replacement for R-12 refrigerant.
Ø IMPORTANT PRECAUTIONS TO BE TAKEN WHILE USING A.C. SYSTEM –
1.      Operate the air conditioner periodically or at least once a week to keep the internal parts lubricated as well as prevents the hoses from hardening.
2.      Do not stick anything into the air outlet or the air inlet. As it dangerous and it can cause injury or damage.
3.      Do not switch ON the A.C at high speeds which may result in the ceasing of compressor.
4.      Avoid exposing a body directly to a continuous cool air flow for long periods. It is not good for health.
5.      Avoid placing any obstacles near the inlet or outlet, if inlet or outlet is blocked ,it may cause damage to the unit.
6.      Do not run or stop the unit frequently. If unit is run or stopped more than 4-5 times in an hour, it may cause damage to the unit.
7.      The air filter should be cleared at least once every two weeks.
8.      When the unit is cleaned, set the selector switch at OFF position.
9.      Never operate A.C. with heater ON.
10.   Do not change the refrigerant in the A.C. system before flushing.