The need to improve the efficiency of low-temperature refrigeration systems

The gap

Evidence profile

Sourced from the stated research gap and future work of the source papers, classified as general, spanning 3 journals.

Supporting evidence — 4 representative gaps

• Thermodynamic Performance Analysis and Refrigerant Evaluation of Enhanced Cascade Vapor-Injection Refrigeration Systems (2026) · Entropy · doi

  The need to improve the efficiency of low-temperature refrigeration systems, - The lack of a systematic thermodynamic investigation of enhanced two-stage cascade refrigeration systems incorporating vapor-injection technology, - The need to identify the optimal refrigerant combinations for low-temperature refrigeration applications.

  generalstated research gap
  Keywords: need improve efficiency low-temperature refrigeration systems lack systematic
• Toward Sustainable Cooling: A Perspective on Replacing Synthetic Refrigerants with Natural Refrigerants (2026) · Energies · doi

  The transition from synthetic to natural refrigerants is not without challenges. Safety considerations, performance constraints under certain operating conditions, and infras- tructural inertia continue to slow adoption. Overcoming these barriers requires an inte- grated approach that combines technological innovation, policy support, and workforce development. Several key areas will define the success and speed of the transition to sustainable cooling: • Technological hybridisation and optimisation. The next decade will likely see an increase in cascade and secondary loop systems that combine the strengths of different natural fluids. The pair NH3/CO2 in cascade systems for industrial refrigeration is a perfect example of the potentiality of hybrid systems. Further research is required to optimise transcritical CO2 cycles for extreme tropical climates, potentially through the integration of solar-assisted cooling or advanced evaporative precooling technologies. • Component standardisation and cost reduction. Currently, the higher initial capex of natural refrigerant systems remains a barrier in de- veloping economies. Future perspectives must include the mass production and standardi- sation of high-pressure CO2 components and leak-proof HC compressors. As economies of scale are achieved, the total cost of ownership will become even more favourable, making natural refrigerants the default global economic choice. • Policy and training infrastructure. The transition is not merely a matter of hardware but of human capital. There is an urgent need for globalised training and certification programmes for technicians to handle flammable (e.g., HC), toxic (e.g., NH3), and high-pressure (e.g., CO2) fluids safely. Furthermore, policy frameworks should move beyond GWP-based metrics to incorporate life cycle climate performance, which accounts for both direct emissions and the indirect emissions from energy consumption. • The role of digitalisation. The integration of artificial intelligence and the internet of things into refrigeration systems represents a promising area of development. Predictive maintenance and real- time leak detection are particularly important for managing the safety risks associated with ammonia and hydrocarbon refrigerants. In addition, AI-driven energy management, https://doi.org/10.3390/en19102299 Energies 2026, 19, 2299 20 of 24 supported by machine learning techniques, can potentially enhance the thermodynamic performance and operational efficiency of systems using natural working fluids. • Addressing the “cooling gap” sustainably. As global temperatures rise and the “cooling gap” in developing nations narrows, demand for air conditioning is expected to grow exponentially. The long-term climate outcomes will depend significantly on how ensuring that this new demand is met with nat- ural refrigerants from the outset, avoiding the “technology lock-in” of high-GWP working fluids in rapidly urbanising regions. In summary, the transition to natural refrigerants is an engineering challenge, an envi- ronmental necessity, and an economic opportunity. By prioritising natural solutions today, the industry can provide the cooling the world needs without warming the planet further. Funding: This research study received financial support from Fundação para a Ciência e a Tecnologia (FCT) via project UID/50022/2025 (https://doi.org/10.54499/UID/50022/2025). Data Availability Statement: No new data were created or analysed in this study. Acknowledgments: The author acknowledges Fundação para a Ciência e a Tecnologia (FCT) for its financial support to LAETA via project UID/50022/2025 (https://doi.org/10.54499/UID/50022/2025). Conflicts of Interest: The author declares no conflicts of interest.

  generalfuture workevidence 5/5
  Keywords: natural systems refrigerants cooling transition fluids performance policy support high https without safety technological development
• Toward Sustainable Cooling: A Perspective on Replacing Synthetic Refrigerants with Natural Refrigerants (2026) · Energies · doi

  As demonstrated throughout this study, the progressive evolution from CFCs and HCFCs to HFCs and more recently to HFOs has addressed specific environmental concerns but has not fully resolved the broader sustainability challenge. In this context, natural refrigerants emerge not simply as alternatives but also as structurally superior and future- proof solutions. The analysis confirms that each major natural refrigerant offers distinct advantages across application domains. Ammonia provides unmatched efficiency in industrial systems, particularly when implemented in modern low-charge configurations. Carbon dioxide has proven highly adaptable in commercial refrigeration, with technological advancements mitigating historical efficiency penalties in warm climates. Hydrocarbons offer a practical https://doi.org/10.3390/en19102299 Energies 2026, 19, 2299 19 of 24 and efficient pathway for domestic and small-scale applications, with safety risks being increasingly manageable under current standards. A key conclusion is that the transition to natural refrigerants aligns environmental performance with long-term regulatory certainty. Unlike synthetic refrigerants, which have undergone successive phase-outs, natural refrigerants are unlikely to face future restrictions due to their inherent environmental compatibility. This reduces investment risk and supports long-term planning across the sector. However, their full adoption is constrained by safety concerns, performance limitations in certain conditions, and infrastructural barriers. Addressing these challenges requires a coordinated effort in research, technological innovation, policy development, and industry transformation. By focusing on system optimisation, safety enhancement, cost reduction, and digital integration, the refrigeration sector should overcome these barriers and fully realise the potential of natural refrigerants in achieving sustainable cooling within the shortest feasible timeframe and become the default global standard of the refrigeration and air-conditioning sector.

  generalfuture workevidence 5/5
  Keywords: natural refrigerants environmental refrigeration safety sector concerns fully future across efficiency technological performance long term
• Lignin-derived carbon materials for a sustainable CO2 economy (2026) · npj Materials Sustainability · doi

  Fig. 5 | Development status and carbon management pathways of CO2-derived value-added products. (a) Current development stages of representative CO2- derived products, ranging from proof-of-concept to commercial production126–133. (b) Schematic illustration of the pathway toward carbon neutrality or carbon negativity through sorbent preparation, CO2 capture, transportation, conversion into value-added products, and utilization. or greater than the total CO2 released across all three stages of the process. Thus, the upcoming studies should focus on (a) usage of low- or zero-carbon energy generation approaches, (b) advancement of low-energy consump- tion technologies for CO2 capture, (c) advancement in conversion tech- nologies to ensure low CO2 emission, and (d) ensuring low or no CO2 is being released during the utilization of the final products. Consequently, this approach will ensure capture of carbon and its utilization to deliver meaningful climate benefits, economic growth, and fulfillment of the cir- cular economy concept. CO2 economy: challenges and outlook Addressing the escalation of atmospheric CO2 is a key aspect of environ- mental accountability. Resolving CO2 concentration is the focus of studies because CO2 is often seen as a biogenic molecule and waste. Building upon the role of lignin-derived carbon materials in CO2 capture and utilization discussed in previous sections. In reality, CO2 can be treated as a valuable resource for economic growth and is often referred to as the “CO2 economy” and this broader perspective shifts toward the opportunities and systemic challenges associated with the emerging CO2 economy. This CO2 economy can be ideally achieved by a closed-loop carbon system. In a closed-loop carbon system, the CO2 emitted from power generation, manufacturing, and chemical industries is captured and reintegrated into value chains through CCUS technologies, which were previously discussed as down- stream CO2 utilization. Forests in Finland and Sweden were once known as a carbon sink, but now they are a CO2 emitter99. Despite the emission of CO2 by land use, land-use change, and forestry (LULUCF) sector, Finland is one of the leading countries in the world that is moving towards achieving this CO2 economy through a closed-loop carbon system by focusing on three main scenarios, including (a) transformation of CO2 into energy carriers, (b) transformation of CO2 into long-lived hydrocarbon products, or (c) permanent storage of CO2. The scenario- based economic analyses demonstrated that converting biogenic CO2 into high-value products, such as synthetic aviation fuels, can significantly boost national economic output by 2.6 billion euros100. Additionally, a minimum economic gain of 1.6 billion euros can be achieved through the storage of CO2. Subsequently, as production technologies mature and profitability improves, the contribution to national value creation can increase markedly, highlighting the economic scalability of CO2-based industries. Apart from npj Materials Sustainability | (2026) 4:31 10 https://doi.org/10.1038/s44296-026-00118-7

  generalfuture workevidence 5/5
  Keywords: carbon products economic economy value utilization capture derived energy technologies closed loop system development added

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