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					HVAC System Design
 PES Institute of Technology
                      Objective
• Goal: To develop an automotive air-conditioning system
 that is smaller and lighter than with conventional technology.


• The Challenge:       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.
               H.V.A.C
• H.V.A.C – Heating, Ventilation and Air
 Conditioning system


• The HVAC regulates:
 – Room Temperature
 – Humidity
 – Air Quality
 – Air Flow
Refrigeration Cycle

    3                         2




4                         1




         Enthalpy kJ/kg




        Vapour Compression Cycle
Design Parameters & Considerations
 •   Heat Load on the HVAC        = 5.287 kW
 •   Cabin Relative Humidity      = 40%
 •   Evaporator Temperature       = 4°C
 •   Refrigerant Used             = R134a
 •   Refrigeration Cycle :          Vapour Compression


 •   Cabin design – cooling and heating requirements
 •   Temperature and Humidity range
 •   Placement of Vents and Ducts
 •   Space considerations
 •   Effect on car performance
 •   Efficiency
 •   Environmental Impact
    Cycle Analysis & Heat Load
 Assumptions:
 • Compression process is isentropic.
 • No pressure losses in piping.
 • Condenser temperature = 46°C.
 • Evaporator Temperature = 4° C.
 • Refrigerant is not sub cooled.

Heat Load Calculations:
•    Heat due to opaque surfaces   = 3598.2 W
•    Heat due to fenestration      = 1229.66 W
•    Internal Loads ( human )      = 460 W

     Total Load                    = 5.287 kW
                 Results
•   Evaporator Pressure   = 3.38 bar
•   Condenser Pressure    = 11.9 bar
•   Heat Load             = 5.287 KW
•   Condenser Cooling Load= 6.308 KW
•   Compressor Work       = 1.02 KW
•   Mass Flow Rate        = 1.94 l/min
             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.

  Weight                    5.8 kg
  Displacement              90 ml/ revolution
  Maximum Speed             12000 rpm
  Rated Voltage             12 V
                          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.


Overall heat transfer coefficient = 98 W/m2K
Area calculated                 = 3.04 m2
Fan Flow Rate                   = 90 l/s
Layout of Components
           Looking Ahead
• Finalize and validate results based on
  inputs from other teams.
• Improvise on the current design and form
  a cost effective solution.
• Documentation and reports.
Thank You !

				
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posted:2/8/2010
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