AUTOMOBILEHVACSYSTEM ROLL NO :3448
What is HVAC ? H.V.A.C – Heating, Ventilation and Air Conditioning system A HVAC System consists of a chain of components designed to heat, ventilate or cool a specific area while maintaining a defined environmental cleanliness level.
Need For HVAC • Easy climate control • Increasing pollution • Ozone layer depletion • Greenhouse effect
3 2 4 1 Enthalpy kJ/kg Refrigeration Cycle • Vapor compression cycle • 1-2 :Compression • 2-3 : Condensation • 3-4 : Expansion • 4-1 : Evaporation
Working • The system must be capable of keeping a temperature of 22˚C inside a stationary black vehicle with four occupants, with an outside temperature of 40˚C. • Also, the system must be an efficient heating system, keeping an internal temperature of 15˚C with an outside temperature of 0˚C.
Sources of heat to system • Faster the car moves, the greater amount of infiltration into the car and rate of heat transfer is more. • The sun baking down on the blank road will raise the temp. up 50to 60 C and thus increases the amount of heat transferred into the car through the floor. • Because of the relatively large glass areas, metal construction and the flow of air around the moving vehicle(automobile) is very large ,so the air conditioning capacity is also large in comparison with A. C. installed at home. • Quantity of fresh air in. • Moisture movement through car. • Activity level, occupancy patterns, and make- up (male, female, child) of people. • Quantity of heat directly rejected by sun on car.
Selection Basis • Scroll Compressors – • Compact design and High Volumetric Efficiency ( around 98% ). • Refrigerant R134a – • Minimized environmental impact. • Plate-Fin Heat Exchanger- • Compact size, Higher heat transfer capability. • Simple design incorporated to minimize cost.
Compressor • Heart of the system, belt driven pump that fastened to engine. • Responsible for compressing and transferring refrigerant. • Two interleaved scrolls with involute geometry. • One scroll fixed while the other orbits eccentrically to compress fluid • Advantage: • Very high volumetric efficiency (almost 98%) • Lesser Noise and lighter compared to rotary • compressor.
Condenser • Responsible for heat dissipation • The condenser is designed to radiate heat. • Located in front of the radiator • Require good air flow when system is in operation • Plate fin type heat exchanger with micro channels used. • Very compact and better heat transfer capability. • Hot compressed refrigerant vapour cools at constant pressure to liquid. • Overall Heat Transfer Coefficient = 92 W/m2K • Area = 6.87 m2
Accumulator • Depending on the vehicle, the A/C system will either have a receiver dryer or an accumulator. • Components contain a desiccant, chemical that attracts moisture. • Prevents formation of corrosive acids on mixture of water and acid. • Also act as temporary storage for refrigerant to prevent starving of evaporator
Evaporator • Heat absorption component. • Used remove heat from the inside of vehicle. • Secondary benefit - dehumidification. • Unconditioned air passes through a filter before entering the evaporator. • Plate-fin evaporator with micro channels used.
Advantages • Travel with comfort for a long distance, In any type of atmospheric conditions without tired. • Fuel Efficiency. • Reduction Greenhouse Gas Emission. • Reduction in ozone layer depletion. • Environment Friendly.
Disadvantages • Engine speed, average and power will reduce • Initial cost of unit • Complicated system
Future Aspects • Now a days automobile HVAC system are under development and have used atmospheric carbon dioxide ( CO2 ) as a refrigerant which is compatible to R134a in performances and efficiency. This system also has advantage to reduce carbon emission which in turn results into reduce green house effect. • Also in newer cars a “computer control system” is used to control multi-zone HVAC system which can give comfort to a individual occupant as per the occupant required.