第三代制冷剂是HFC（氢氟碳化物），它是含有氢、氟和碳原子的合成化合物。 它们的通式为C<sub>n</sub>H<sub>x</sub>F<sub>y</sub>，其中n、x和y是整数1。
最常用作制冷剂的 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 世纪 80 年代和 90 年代开发的，作为第二代制冷剂 HCFC（氢氯氟烃）的替代品，后者被发现会导致臭氧层消耗。 HFC 的臭氧消耗潜值 (ODP) 为零，但它们仍然具有较高的全球变暖潜值 (GWP) 和大气寿命3。
HFC作为制冷剂具有许多优点，如稳定性高、毒性低、不易燃、沸点低、汽化潜热高以及与润滑油和金属相容等。 它们还广泛用于其他应用，例如发泡剂、溶剂、灭火器和气溶胶推进剂。
全球氢氟碳化合物的生产和消费在 2010 年代达到顶峰，然后由于科学证据的不断增加和公众对其环境危害的认识而开始下降。 2016年，197个国家签署了《蒙特利尔议定书》基加利修正案，同意在具体期限内逐步减少氢氟碳化合物和其他强效温室气体的生产和使用。
基加利修正案被认为是全球应对气候变化的重要一步，因为它有可能在本世纪末避免全球变暖0.4°C。 根据联合国最新评估，逐步减少氢氟碳化合物还可以提高冷却系统的能源效率，减少电力需求和碳排放。
氢氟碳化合物的逐步减少还刺激了替代制冷剂的开发和采用，例如 HFO（氢氟烯烃）、天然制冷剂（如氨、二氧化碳、碳氢化合物和水）和低 GWP 混合物。 这些替代品的全球变暖潜力较低或为零，但它们可能有其他缺点，例如易燃性、毒性或效率低。
因此，制冷剂的选择和开发是一个复杂的动态过程，涉及热力学、物理、化学、安全、经济和环境等多个因素。 理想的制冷剂应该具有高性能、低环境影响、低成本和广泛的可用性。
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.
