Refrigerant Selection Guide for Heat Exchanger Design

Refrigerant selection significantly impacts heat exchanger design, system efficiency, and environmental compliance. This guide covers key considerations for modern refrigerant selection.

Environmental Regulations

Montreal Protocol

Phased out CFCs (R-11, R-12)

Phasing out HCFCs (R-22)

Kigali Amendment targets HFCs

F-Gas Regulations (EU)

GWP limits for new equipment

Phase-down schedule for HFCs

Bans on high-GWP refrigerants

EPA SNAP Program (US)

Acceptable alternatives list

Sector-specific requirements

Safety classifications

Refrigerant Comparison

High-GWP Refrigerants (Being Phased Out)

RefrigerantGWPODPSafetyNotes

R-410A20880A1Current AC standard
R-404A39220A1Commercial refrigeration
R-134a14300A1Automotive, chillers
R-407C17740A1R-22 replacement

Low-GWP Alternatives

RefrigerantGWPODPSafetyNotes

R-326750A2LR-410A alternative
R-454B4660A2LR-410A alternative
R-290 (Propane)30A3Natural refrigerant
R-744 (CO₂)10A1Transcritical systems
R-717 (Ammonia)00B2LIndustrial

Thermodynamic Properties Impact

Latent Heat

Higher latent heat = lower mass flow for same capacity

R-717: 1370 kJ/kg (excellent)

R-290: 425 kJ/kg (good)

R-410A: 220 kJ/kg (moderate)

Volumetric Capacity

Higher = smaller compressor displacement

R-410A: High (good for residential)

R-32: Higher than R-410A

R-290: Lower (larger compressor)

Pressure Levels

Affects component design:

R-744: Very high (transcritical)

R-410A: High

R-290: Moderate

R-717: Moderate

Heat Transfer Performance

Liquid Thermal Conductivity

Higher = better heat transfer

R-717: 0.50 W/m·K (excellent)

R-290: 0.10 W/m·K (good)

R-410A: 0.09 W/m·K (moderate)

Two-Phase Heat Transfer

Typical coefficients (W/m²·K):

R-717: 4000-8000

R-290: 3500-5500

R-410A: 3000-5000

R-32: 3200-5200

Safety Considerations

ASHRAE 34 Classifications

Toxicity:

A: Lower toxicity

B: Higher toxicity

Flammability:

1: No flame propagation

2L: Lower flammability (burning velocity < 10 cm/s)

2: Flammable

3: Higher flammability

Design Implications

A1 Refrigerants (R-410A, R-134a):

No special requirements

Standard equipment design

A2L Refrigerants (R-32, R-454B):

Charge limits based on room size

Leak detection recommended

Electrical classification considerations

A3 Refrigerants (R-290):

Strict charge limits (typically < 150g)

Explosion-proof electrical

Special installation requirements

Heat Exchanger Design Impacts

Tube Sizing

Higher pressure = thicker walls

Different optimal velocities

Material compatibility

Coil Circuiting

Different pressure drops

Oil return considerations

Charge optimization

Material Selection

R-717: No copper (use steel, aluminum)

R-744: High-pressure rated materials

R-290: Standard materials OK

Transition Strategies

Drop-In Replacements

Limited options; usually require system modifications

Low-GWP Conversions

R-410A → R-32 or R-454B

R-404A → R-448A or R-449A

R-134a → R-1234yf or R-513A

New System Design

Design for low-GWP from start

Consider natural refrigerants

Future-proof selections

Conclusion

Refrigerant selection requires balancing environmental regulations, safety requirements, thermodynamic performance, and practical considerations. Work with equipment manufacturers and stay informed about regulatory changes.