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
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Heat Load on the HVAC
Cabin Relative Humidity
Evaporator Temperature
Refrigerant Used
Refrigeration Cycle :
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Cabin design – cooling and heating requirements
Temperature and Humidity range
Placement of Vents and Ducts
Space considerations
Effect on car performance
Efficiency
Environmental Impact
= 5.287 kW
= 40%
= 4°C
= R134a
Vapour Compression
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
•
Heat due to fenestration
•
Internal Loads ( human )
Total Load
= 3598.2 W
= 1229.66 W
= 460 W
= 5.287 kW
Results
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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 ExchangerCompact 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 !