Repsol YPF

Refrigerants

Artificial, organochlorated refrigerants, necessary for the refrigeration cycle on which air conditioning systems are based, are condemned to disappear within the next few years, due to the fact that they contribute to the reduction of the ozone layer, in the presence of water vapour, and are by nature greenhouse gases. Artificial refrigerants have a triple effect on the environment: CFCs, and to a lesser extent HCFCs, attack the ozone layer; CFCs, HCFCs and HFC contribute directly to the increase in the greenhouse effect, as well as indirectly, through the consumption of electricity and its production of CO2, which makes the performance achieved with different refrigerants particularly important. In replacing certain refrigerants by others, the level of efficiency of the cycles should be maintained or improved.

• HCFCs
  The first step to prevent the destruction of the ozone layer was the replacement of fluorocarbons with two chlorine atoms (CFC) by fluorocarbons with one chlorine and one hydrogen atom (HCFC). These refrigerants have a lesser effect on the ozone layer due their greater stability, but have a greater effect on global warming than CFCs. However, in the latest revision of the Montreal Protocol, HCFCs were also included in the list of controlled substances and it was decided that they should stop being manufactured in 2020 and should completely disappear by 2030. Germany has brought forward the phasing out of R-22, which should be completed by the year 2000. The USA is also considering taking measures of this type. R-22 is an intermediate solution and is used to replace R-12, R-500 and R-502 in certain applications. in order to replace R-114 in high-temperature industrial processes, the following HCFCs are used: R-124, R-123 and R-141b.
  
  

• HFCs
  HFCs are coolants which do not contain chlorine, and therefore have no effect on the reduction of the ozone layer, although some do contribute considerably to the greenhouse effect. The coolants in this group are: R-134a, R-152a, R-32, R-125 and R-143a.
  
  
• Blends
  Blends are a significant possibility for the replacement of CFCs. A blend is made up of two or more coolants and can be: zeotropic, azeotropic or near-azeotropic. Azeotropic blends evaporate and condense at a constant temperature, whereas the other two do so over a certain temperature range (temprature glide). The temperature glide can be used to improve the efficiency, but the system needs to be modified. The advantage of blends is that their properties can vary depending upon the needs to  each application, varying the proportions of the components. Non-azeotropic blends can cause problems due to the different volatilities of their components. If there is a leak, it is not possible to find out what quantity has been lost of each of the refrigerants that make up the mixture, and therefore it is necessary to refill the circuit with a completely new load of refrigerant. The new generation of blends to replace the R-502 and R-22 contain no chlorine and consist principally of HFCs and hydrocarbons. Amongst others, R-407 and R-410 are used.
  
  
• Natural working fluids
  Natural working fluids are substances which exist in the biosphere in natural form. In general, they have very few disadvantages with regard to the environment (the possibility that they would contribute to the destruction of the ozone layer and global warming is zero or very close to zero). They are, therefore, long-term alternatives to CFCs. Some examples of natural working fluids are ammonia (NH3), hydrocarbons (eg. propane), carbon dioxide (CO2), air and water. Some natural working fluids are flammable or toxic. The safety implications of the use of these fluids may mean that a specific system, as well as suitable operating and maintanance routines, needs to be designed. For example, ammonia (NH3) is a good natural refrigerant, but it can be dangerous in high concentrations and at high pressure. For this reason, systems that work with ammonia are designed to work with low pressures and low quantities of NH3, being more commonly used in industrial areas than in other applications.  

Water is an excellent working fluid for high-temperature industrial heat pumps, due to its favourable thermodynamic properties and the fact that it is neither flammable nor toxic. Typical operating temperatures come into the range of between 80ºC and 150ºC. The greatest disadvantage of water as a working fluid is its low volumetric heat capacity. La mayor desventaja del agua como fluido de trabajo es su baja capacidad de calor volumétrico. This means that large and expensive compressors are required, especially at low temperatures.