Cold rooms used refrigerants with high global warming potential (GWP) and harmful ozone-depleting properties (ODP). As global regulations tighten and environmental awareness grows, there is an urgent need to transition toward eco-friendly refrigerants—substances that minimize environmental impact while delivering efficient cooling.

This article explores the rationale behind adopting environmentally friendly refrigerants, examines the most common options, discusses benefits and challenges, and offers guidance for implementation in cold room applications.

Why Transition to Environmentally Friendly Refrigerants?

Environmental Concerns

1. Global Warming Potential (GWP): Many conventional refrigerants (e.g., R-404A, R-507) have GWPs in the thousands, meaning that even small leaks can contribute significantly to greenhouse gas emissions.
2. Ozone Depletion Potential (ODP): Older refrigerants like chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) contribute significantly to ozone layer depletion. Although phased out under the Montreal Protocol, some HCFCs (e.g., R-22) are still in use in existing equipment.
3. Regulatory Pressure: Regions such as the European Union, North America, and parts of Asia enforce strict phase-down schedules (e.g., the Kigali Amendment to the Montreal Protocol) to eliminate high-GWP refrigerants.

Economic and Operational Factors

1. Energy Efficiency: Modern environmentally friendly refrigerants often exhibit superior thermodynamic properties, translating into lower energy consumption and reduced operating costs over time.
2. Future-Proofing: By adopting low-GWP and non-ODP refrigerants, cold room operators can avoid costly equipment retrofits or replacements when regulations tighten.
3. Corporate Sustainability Goals: Many organizations have committed to net-zero or carbon-reduction targets. Transitioning to environmentally friendly refrigerants is a tangible step toward meeting those goals.

Categories of Environmentally Friendly Refrigerants

Eco-friendly refrigerants can be broadly categorized into natural refrigerants and low-GWP synthetic refrigerants:

1. Natural Refrigerants: Substances that occur in nature or are readily derived from natural sources. Examples include:
   • Ammonia (R-717)
   • Carbon Dioxide (R-744)
   • Hydrocarbons (e.g., Propane R-290, Isobutane R-600a)
2. Low-GWP Synthetic Refrigerants: Engineered fluids designed to replace high-GWP HFCs. The most prominent class is:
   • Hydrofluoroolefins (HFOs), such as R-1234yf and R-1234ze.

Each category has distinct advantages and considerations, especially in the context of cold room applications.

Natural Refrigerants

Ammonia (R-717)

• GWP & ODP: GWP = 0; ODP = 0.
• Thermodynamic Performance: Exceptional heat absorption and transfer characteristics make ammonia one of the most energy-efficient refrigerants, particularly in large-scale installations.
• Flammability & Toxicity: Highly efficient but moderately toxic (Class B2 under ASHRAE 34) and not flammable under typical refrigeration concentrations. Proper ventilation, leak detection, and adherence to safety codes (e.g., EN 378, ASHRAE 15) are mandatory.
• Applications in Cold Rooms:
  • Industrial Food Storage: Widely used in meat and dairy processing plants.
  • Agricultural Cold Storage: Common for large, centralized facilities (e.g., fruit, vegetable, and floral storage).
• Challenges & Mitigation:
  • Safety Systems: Requires robust ammonia-resistant materials, regular maintenance, and well-trained personnel.
  • Regulatory Compliance: Local regulations may limit ammonia systems near occupied spaces; often necessitates remote machinery rooms.

Carbon Dioxide (R-744)

• GWP & ODP: GWP = 1; ODP = 0.
• Operating Pressures: Very high pressures (~8–10 MPa for medium-temperature and ~3–4 MPa for low-temperature refrigeration). Specialized high-pressure compressors and piping are necessary.
• Thermodynamic Benefits: Excellent volumetric refrigeration capacity; well suited for cascade systems (CO₂ compressors coupled with a secondary refrigerant circuit).
• Applications in Cold Rooms:
  • Cascade Systems: Often paired with ammonia (NH₃/CO₂ cascade) or a secondary refrigerant (glycol loop).
  • Transcritical CO₂ Systems: Viable in colder climates where ambient temperatures remain below ~20 °C to maintain higher cycle efficiency.
• Challenges & Mitigation:
  • High Pressure Equipment: Increased capital costs for compressors, heat exchangers, and safety relief devices.
  • Ambient Temperature Sensitivity: In hotter regions, efficiency drops unless an adiabatic gas cooler or parallel compression is employed.

Hydrocarbons (R-290, R-600a, R-1270)

• GWP & ODP: GWP < 5 (e.g., R-290 GWP = 3; R-600a GWP = 3); ODP = 0.
• Flammability: Classified as A3 (highly flammable). Requires careful design to limit charge size and implement explosion-proof components.
• Performance Characteristics:
  • R-290 (Propane): Heat capacity and energy efficiency comparable to or better than HFCs for low- and medium-temperature applications.
  • R-600a (Isobutane): Commonly used in small commercial and residential refrigeration but less common in large cold room installations due to flammability constraints.
• Applications in Cold Rooms:
  • Small- to Medium-Sized Units: Reach-in walk-ins and reach-through cold rooms often finalized with hydrocarbon charge below regulatory thresholds (e.g., <150 g in Europe for R-290).
  • Split Systems & Condensing Units: Specialized hydrocarbon condensing units are available for modular cold rooms in small supermarkets and convenience stores.
• Challenges & Mitigation:
  • Charge Limitations: Standards like IEC 60335-2-89 restrict the allowable charge for safety.
  • Ventilation & Sensor Requirements: Must include hydrocarbon-rated components, leak detection, and adequate ventilation to avoid flammable mixtures.

Low-GWP Synthetic Refrigerants (HFOs)

R-1234yf

• GWP & ODP: GWP ≈ 4; ODP = 0.
• Flammability: Mildly flammable (A2L classification under ASHRAE 34).
• Performance: Designed primarily as a replacement for R-134a in automotive and light commercial applications. In cold rooms, it performs moderately well at medium-temperature levels (−5 °C to +10 °C), but less so at very low temperatures.
• Applications in Cold Rooms:
  • Medium-Temperature Walk-Ins: In locations where flammability risk is manageable (e.g., dedicated machinery rooms away from public areas).
  • Retrofit Potential: Existing R-134a systems can sometimes be retrofitted, though oil compatibility and minor component changes (e.g., expansion valves) may be required.
• Challenges & Mitigation:
  • Flammability Precautions: Must follow A2L guidelines—leak detection, ventilation, and use of components rated for mildly flammable refrigerants.
  • Cycle Optimization: Because R-1234yf’s thermodynamic properties differ from HFCs, system tuning (e.g., condenser and evaporator sizing) is critical.

R-1234ze

• GWP & ODP: GWP ≈ 7; ODP = 0.
• Flammability: Non-flammable (A1 classification), offering an advantage over R-1234yf in terms of safety.
• Performance: Suited for medium-temperature refrigeration; can sometimes replace R-134a or R-404A in retrofit scenarios.
• Applications in Cold Rooms:
  • Medium-Temperature Rack Systems: Ideal for supermarket walk-ins, small to medium cold storage rooms requiring −5 °C to +5 °C operation.
  • Retrofits of R-404A Plants: Lower GWP and similar operating pressures make it an appealing drop-in replacement, though moderate capacity adjustments may be necessary.
• Challenges & Mitigation:
  • Lubricant Compatibility: Requires POE oils; existing mineral-oil-based compressors may need conversion.
  • Heat Exchanger Tuning: Slightly different pressure-enthalpy curves necessitate recalibration of condensers and evaporators.

Benefits of Environmentally Friendly Refrigerants in Cold Rooms

1. Reduced Environmental Impact: Eliminating or drastically reducing GWP‐associated emissions helps achieve corporate sustainability targets and comply with international agreements like the Kigali Amendment.
2. Enhanced Energy Efficiency: Natural refrigerants (ammonia, CO₂, hydrocarbons) often exhibit superior coefficient of performance (COP) compared to HFCs, leading to lower energy bills.
3. Regulatory Compliance & Incentives: Early adopters may benefit from tax incentives, rebates, or favorable financing, depending on regional policies promoting low-GWP refrigerant use.
4. Operational Reliability: Modern eco-friendly refrigerant systems, when properly designed, can match or exceed the reliability of legacy systems, especially as manufacturers optimize equipment for these fluids.
5. Future Resilience: As international phase-down schedules for high-GWP refrigerants accelerate, equipment that runs on eco-friendly refrigerants will face fewer obsolescence risks.

Case Study: CO₂ Cascade in a Food Cold Storage Facility

A mid-sized food distribution center in northern Europe transitioned its −25 °C blast freezers and +2 °C cold rooms from R-404A to an ammonia/CO₂ cascade system. Key outcomes:

Energy Savings:

Overall energy consumption dropped by approximately 20% due to ammonia’s high efficiency at low temperatures and CO₂’s effective heat rejection.

Heat recovered from the CO₂ high-stage condenser was used for space heating during winter, further improving overall facility efficiency.

Environmental Impact:

Annual CO₂ equivalent (CO₂e) emissions from refrigerant leaks fell by over 90%, since ammonia has GWP = 0 and CO₂ has GWP = 1.

Operational Resilience:

Despite higher upfront costs (≈15% more than a conventional HFC system), the facility achieved a payback period of 4.5 years, thanks to lower energy bills, reduced refrigerant tax, and incentives from a national energy efficiency program.

Challenges Addressed:

Local safety regulations required the ammonia machinery room to be placed 50 meters away from the main building. A remote ammonia chiller with glycol loops feeding the internal CO₂ cascade mitigated this requirement.