Refrigerant Selection & Properties for HVAC Engineers
Refrigerant Selection & Properties for HVAC Engineers
Refrigerant selection impacts system performance, safety, environmental compliance, and operating costs. This guide covers refrigerant classifications, properties, environmental metrics, and selection criteria per ASHRAE Standard 34.
ASHRAE Refrigerant Numbering System
Format: R-[number][letter]
Organic compounds (CFC, HCFC, HFC, HFO):
- First digit: (# carbon atoms) - 1
- Second digit: (# hydrogen atoms) + 1
- Third digit: # fluorine atoms
- Letter suffix (a, b, c): isomer designation
Examples:
- R-134a: C₂H₂F₄ (1,1,1,2-tetrafluoroethane)
- R-410A: Zeotropic blend of R-32/R-125 (50/50 wt%)
- R-407C: Zeotropic blend
Inorganic compounds:
- R-717: Ammonia (NH₃)
- R-718: Water (H₂O)
- R-744: Carbon dioxide (CO₂)
Safety Classification (ASHRAE 34)
graph TD
A[Refrigerant Safety Group] --> B[Toxicity]
A --> C[Flammability]
B --> B1[Class A: Lower Toxicity<br/>TLV ≥ 400 ppm]
B --> B2[Class B: Higher Toxicity<br/>TLV < 400 ppm]
C --> C1[Class 1: No Flame Propagation]
C --> C2[Class 2L: Lower Flammability<br/>LFL > 0.19 lb/ft³]
C --> C3[Class 2: Flammable<br/>LFL ≤ 0.19 lb/ft³]
C --> C4[Class 3: Higher Flammability]
Safety groups:
| Group | Toxicity | Flammability | Examples |
|---|---|---|---|
| A1 | Lower | None | R-134a, R-410A, R-404A, R-407C |
| A2L | Lower | Lower | R-32, R-454B, R-1234yf, R-1234ze |
| A2 | Lower | Flammable | R-152a, R-290 (propane) |
| A3 | Lower | Higher | R-290, R-600a (isobutane), R-1270 |
| B1 | Higher | None | R-123 |
| B2 | Higher | Flammable | Ammonia (R-717) |
Environmental Impact Metrics
Ozone Depletion Potential (ODP):
Relative to R-11 (CFC-11 = 1.0)
- CFCs: ODP = 0.6 to 1.0 (phased out)
- HCFCs: ODP = 0.01 to 0.1 (being phased out)
- HFCs: ODP = 0 (no chlorine)
- HFOs: ODP = 0
Global Warming Potential (GWP):
Relative to CO₂ over 100-year timeframe (CO₂ = 1)
| Refrigerant | ODP | GWP (AR5) | Status |
|---|---|---|---|
| R-11 (CFC) | 1.0 | 4,660 | Banned |
| R-12 (CFC) | 1.0 | 10,200 | Banned |
| R-22 (HCFC) | 0.055 | 1,760 | Phase-out |
| R-134a (HFC) | 0 | 1,300 | Restricted |
| R-404A (HFC) | 0 | 3,920 | Restricted |
| R-410A (HFC) | 0 | 2,088 | Current |
| R-407C (HFC) | 0 | 1,770 | Current |
| R-32 (HFC) | 0 | 677 | Low-GWP |
| R-454B (HFO blend) | 0 | 466 | Low-GWP |
| R-1234yf (HFO) | 0 | 4 | Very low-GWP |
| R-1234ze (HFO) | 0 | 7 | Very low-GWP |
| R-744 (CO₂) | 0 | 1 | Natural |
| R-717 (NH₃) | 0 | <1 | Natural |
| R-290 (propane) | 0 | 3 | Natural |
Thermophysical Properties
Common HVAC Refrigerants (at 40°F evap, 100°F cond)
| Refrigerant | P_evap (psia) | P_cond (psia) | Pressure Ratio | Discharge Temp (°F) | COP |
|---|---|---|---|---|---|
| R-134a | 37.0 | 124.3 | 3.36 | 125 | 5.2 |
| R-410A | 118.8 | 341.8 | 2.88 | 135 | 5.5 |
| R-407C | 79.4 | 228.5 | 2.88 | 130 | 5.3 |
| R-32 | 99.2 | 281.8 | 2.84 | 145 | 5.7 |
| R-454B | 100.5 | 283.0 | 2.82 | 130 | 5.6 |
| R-22 | 68.5 | 196.5 | 2.87 | 135 | 5.4 |
Volumetric Capacity
Refrigeration effect per unit volume:
$$Q_v = \frac{\dot{m}_r (h_1 - h_4)}{v_1}$$
Where $v_1$ = specific volume at compressor suction (ft³/lb)
| Refrigerant | Volumetric Capacity (Btu/ft³) | Compressor Size (relative to R-22) |
|---|---|---|
| R-22 | 52 | 1.00 (baseline) |
| R-134a | 27 | 1.93 |
| R-410A | 73 | 0.71 |
| R-407C | 50 | 1.04 |
| R-32 | 82 | 0.63 |
| R-717 (ammonia) | 213 | 0.24 |
Higher volumetric capacity = smaller compressor for same cooling
Application-Specific Selection
Residential Air Conditioning
Current standard: R-410A (A1, GWP 2088)
Replacement options:
- R-32 (A2L, GWP 677): Higher efficiency, mildly flammable
- R-454B (A2L, GWP 466): Drop-in replacement, lower pressure
Transition: New equipment moving to low-GWP A2L refrigerants
Commercial Refrigeration
Current standards:
- Supermarket racks: R-404A, R-407A (high GWP)
- Display cases: R-404A, R-134a
Replacement options:
- R-448A (A1, GWP 1273): R-404A retrofit
- R-449A (A1, GWP 1282): R-404A retrofit
- R-744 (CO₂): Transcritical systems for cold climates
- R-290 (propane): Small hermetic systems (charge limits)
Chilled Water Systems
Current standard: R-134a (A1, GWP 1300)
Replacement options:
- R-513A (A1, GWP 573): Drop-in for R-134a
- R-1234ze (A2L, GWP 7): New equipment
- R-1233zd (B1, GWP 7): Low-pressure chillers
Industrial Refrigeration
Current standard: R-717 (ammonia, B2, GWP <1)
Advantages:
- Excellent thermodynamic properties
- Zero GWP
- Low cost
Disadvantages:
- Toxic (TLV 25 ppm)
- Flammable
- Requires stringent safety measures
Alternative: R-744 (CO₂) for cascade systems
Refrigerant Regulations
Montreal Protocol (1987): Phase-out of ODP substances
- CFCs: Banned since 1996
- HCFCs (R-22): Production ban 2020
Kigali Amendment (2016): HFC phase-down
- GWP-weighted reduction schedule
- 85% reduction by 2036 (developed countries)
EPA SNAP Program: Prohibits high-GWP refrigerants in specific applications
EU F-Gas Regulation: HFC quota system, service bans for high-GWP
Refrigerant Blends
Azeotropic: Behaves as single substance (constant boiling point)
- Example: R-507A (R-125/R-143a 50/50)
Zeotropic: Temperature glide during phase change
- Example: R-407C (glide ~10°F)
- Requires careful charging (liquid only)
Temperature glide impact:
- Reduces heat transfer effectiveness
- Complicates superheat control
- Affects system design
Selection Criteria Summary
- Safety: Comply with building codes, charge limits
- Environmental: Minimize GWP, comply with regulations
- Performance: COP, capacity, operating pressures
- Compatibility: Oil type, materials, existing equipment
- Availability: Regional supply, cost
- Future-proofing: Regulatory trends
Related Technical Guides:
- Vapor Compression Refrigeration Cycle
- Compressor Selection & Performance
- Refrigeration Load Calculations
References:
- ASHRAE Standard 34: Designation and Safety Classification of Refrigerants
- ASHRAE Handbook of Refrigeration, Chapter 29: Refrigerants
- EPA Significant New Alternatives Policy (SNAP) Program
- AHRI Guideline N: Assignment of Refrigerant Container Colors