Material Considerations in HVAC design

As with any automotive design, the design engineer must consult the chemist (i.e., material engineer) about the requirements for proper functioning of the parts. Typical inputs will be temperature, pressure, friction, and chemical environment. As we have discussed, some of the components that make up a typical list can be found in Table 9.11. 

Material selection is extremely important, not only because of system requirements (i.e., temperatures, pressures, etc.) but also because of material cost considerations. In an HVAC module, the heater core and evaporator core reside within the module, which usually comprises nylon 66 or a filled polypropylene. Refrigerant flows through the evaporator core and condenser and will vary in a range from 9 to 115°C. Engine coolant flows through the heater core and reaches temperatures up to 120°C. Valves and seals within the HVAC module must withstand temperature cycling combined with pressure extremes. 

A typical module contains a mode valve, air-inlet valve, and temperature valve. The mode valve controls the various modes of the AC unit (i.e., heater, defrost, AC, blend, and bi-level). Pressure is asserted on this valve at the varying temperatures due to airflow coming from the heater and evaporator core. The temperature valve is basically a mix valve between the heater core and evaporator core and as such must endure the most extreme temperatures. Typical properties for the plastic portion used in HVAC systems are shown in Table 9.12. 

Glass fiber reinforced, Glass fiber reinforced, mineral 

Heat Exchanger Tube Material with Cladding for Brazement 

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