第三代制冷劑是HFC（氫氟碳化物），它是含有氫、氟和碳原子的合成化合物。 它們的通式為C<sub>n</sub>H<sub>x</sub>F<sub>y</sub>，其中n、x和y是整數1。
最常用作制冷劑的 HFC 是 R134a（1,1,1,2-四氟乙烷）、R125（五氟乙烷）、R32（二氟甲烷）、R410a（R32 和 R125 的混合物）、R404a（R125、R143a 和 R134a) 和 R407c（R32、R125 和 R134a 的混合物）2。
HFC 是在 20 世紀 80 年代和 90 年代開發的，作為第二代制冷劑 HCFC（氫氯氟烴）的替代品，后者被發現會導致臭氧層消耗。 HFC 的臭氧消耗潛值 (ODP) 為零，但它們仍然具有較高的全球變暖潛值 (GWP) 和大氣壽命3。
HFC作為制冷劑具有許多優點，如穩定性高、毒性低、不易燃、沸點低、汽化潛熱高以及與潤滑油和金屬相容等。 它們還廣泛用于其他應用，例如發泡劑、溶劑、滅火器和氣溶膠推進劑。
全球氫氟碳化合物的生產和消費在 2010 年代達到頂峰，然后由于科學證據的不斷增加和公眾對其環境危害的認識而開始下降。 2016年，197個國家簽署了《蒙特利爾議定書》基加利修正案，同意在具體期限內逐步減少氫氟碳化合物和其他強效溫室氣體的生產和使用。
基加利修正案被認為是全球應對氣候變化的重要一步，因為它有可能在本世紀末避免全球變暖0.4°C。 根據聯合國最新評估，逐步減少氫氟碳化合物還可以提高冷卻系統的能源效率，減少電力需求和碳排放。
氫氟碳化合物的逐步減少還刺激了替代制冷劑的開發和采用，例如 HFO（氫氟烯烴）、天然制冷劑（如氨、二氧化碳、碳氫化合物和水）和低 GWP 混合物。 這些替代品的全球變暖潛力較低或為零，但它們可能有其他缺點，例如易燃性、毒性或效率低。
因此，制冷劑的選擇和開發是一個復雜的動態過程，涉及熱力學、物理、化學、安全、經濟和環境等多個因素。 理想的制冷劑應該具有高性能、低環境影響、低成本和廣泛的可用性。
The third generation of refrigerants are HFCs (hydrofluorocarbons), which are synthetic compounds that contain hydrogen, fluorine and carbon atoms. They have the general formula of C<sub>n</sub>H<sub>x</sub>F<sub>y</sub>, where n, x and y are integers1.
The most common HFCs used as refrigerants are R134a (1,1,1,2-tetrafluoroethane), R125 (pentafluoroethane), R32 (difluoromethane), R410a (a blend of R32 and R125), R404a (a blend of R125, R143a and R134a) and R407c (a blend of R32, R125 and R134a)2.
HFCs were developed in the 1980s and 1990s as alternatives to the second generation of refrigerants, HCFCs (hydrochlorofluorocarbons), which were found to cause ozone depletion. HFCs have zero ozone depletion potential (ODP), but they still have high global warming potential (GWP) and atmospheric lifetime3.
HFCs have many advantages as refrigerants, such as high stability, low toxicity, non-flammability, low boiling point, high latent heat of vaporization and compatibility with lubricants and metals. They are also widely used in other applications, such as foam blowing agents, solvents, fire extinguishers and aerosol propellants.
The global production and consumption of HFCs peaked in the 2010s and then began to decline due to the growing scientific evidence and public awareness of their environmental hazards. In 2016, the Kigali Amendment to the Montreal Protocol was signed by 197 countries, which agreed to phase down the production and use of HFCs and other potent greenhouse gases by specific deadlines.
The Kigali Amendment is considered a major step forward in the global fight against climate change, as it has the potential to avoid up to 0.4°C of global warming by the end of the century. According to the latest assessment by the United Nations, the phase down of HFCs could also improve the energy efficiency of cooling systems and reduce the electricity demand and carbon emissions.
The phase down of HFCs has also stimulated the development and adoption of alternative refrigerants, such as HFOs (hydrofluoroolefins), natural refrigerants (such as ammonia, carbon dioxide, hydrocarbons and water) and low-GWP blends. These alternatives have lower or zero global warming potential, but they may have other drawbacks, such as flammability, toxicity or low efficiency.
Therefore, the selection and development of refrigerants is a complex and dynamic process that involves multiple factors, such as thermodynamic, physical, chemical, safety, economic and environmental aspects. The ideal refrigerant should have high performance, low environmental impact, low cost and wide availability.
