## 2 HFC Phase Down
### Reduction in the Dependence on HFCs  
As shown before, the dependence on refrigeration and cooling systems is expected to grow in the foreseeable future. However, considering the dramatic effects of the sector to climate change it is vital to decrease the dependence on high GWP compounds--based systems. For example, the construction of more energy efficient buildings strongly reduces the need for cooling and heating systems, and a more efficient utilization of air conditioning in buildings and vehicles reduces the energy consumption and therefore the indirect emissions of GHGs [27; 28; 29]. The reduction in F-gas emissions in the refrigeration and cooling sectors must include innovation and the development of more efficient systems with lower energy consumption, lower amounts of high GWP refrigerants, and lower leakage rates, and also profound changes in the operation and management practices. As response to the legislations imposing the HFCs' phase-down, industries quickly developed a new generation of refrigerants with lower GWP, including: (i) natural refrigerants, such as CO\({}_{2}\), ammonia and hydrocarbons, which can be efficient but with safety problems; (ii) HFCs with lower GWP, such as R-32 (GWP 677); (iii) unsaturated HFCs, known as hydrofluoroolefins (HFOs); and (iv) blends of these three types of compounds. In many cases, the utilization of non-HFC refrigerants in already existing equipment previously using HFCs is not possible or requires great modifications in the systems. In some cases, the utilization of alternative refrigerants in new equipment requires innovation in the systems, with more robust components and more specialized operation, for example, for using high pressure CO\({}_{2}\). Figure 1: Imports, production and total supply of F-gases and imports of HFCs and of unsaturated HFCs and HCFCs in the EU (2007–2019) according to the EEA Report No 15/2020 on fluorinated greenhouse gases [25]. Data in tonnes of gas (Panel (**A**)) and in million tonnes of CO\({}_{2}\)eq (Panel (**B**)). HFOs, which started to be commercialized in 2010, have no ozone depletion potential and have low GWP, being considered a more environmentally friendly alternative to HFCs for use in cooling, refrigeration and as blowing agents [30]. Due to the high reactivity of their carbon double bonds with radicals in the troposphere, they are rapidly degraded in this zone of the atmosphere [30]. Moreover, most HFOs are chemically stable and inert, nontoxic and have low flammability [20]. The best known unsaturated HFO is 2,3,3,3-tetrafluoroprop-1-ene (R-1234 yf) with a GWP of 4, which has been developed and proposed for use as a refrigerant in mobile air conditioning in passenger cars as a replacement for HFC-134a [31; 32; 33]. Another HFO, R-1234 ze (GWP 6), is also being increasingly studied for use as a blowing agent, aerosol propellant, and refrigerant [34]. Some blends of HFCs with HFOs are already replacing HFCs in commercial and industrial refrigeration [32]. Examples of those are R-448A (GWP 1273) (blend of the HFCs R-32 (GWP 677), R-125 (GWP 3170), and R-134a (GWP 1300) with the HFOs R-1234 yf (GWP 4) and R-1234 ze (GWP 6)), R-449A (GWP 1282) (blend of the HFCs R-32 (GWP 677), R-125 (GWP 3170), and R-134a (GWP 1300) with the HFO R-1234 yf (GWP 4)), and R-450A (GWP 605) and R-513A (GWP 573) (blends of the HFC R-134a with the HFOs R-1234 ze (GWP 6) and R-1234 yf (GWP 4), respectively). The HFO/HFC blends have, in most cases, clear technological advantages. However, since they are new products and are protected by industrial patents, some industrial sectors are reluctant to adopt them due to the additional costs involved. HFCs with lower GWP, such as R-32 (GWP 677), are currently being used as alternatives to HFC or HFC blends with higher GWP, such as R-410A (GWP 2088) [30].