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2.2.4. Environmental issues Nowadays, for a refrigerant to be considered benign to the environment, it has to entail no harm to the ozone, and low contribution to the greenhouse effect. Two indicators need thus consideration. Firstly, the Ozone Depletion Potential (ODP) is used to evaluate the impact of the substance on the ozone layer. In fact, elements such as Chlorine and Bromine, when dispersed in the atmosphere, result in the breakdown of the ozone molecule O3, in a sequence of loop reactions that lead to the destruction of many ozone molecules by a single Cl atom. The evaluation of the ODP is made by referring the effect of a substance to the one of R11, considered having ODP=1 (IPCC, 2005). Secondly, the greenhouse effect contribution is assessed by the Global Warming Potential (GWP). The evaluation is made by comparing the ability of absorbing heat by the gas, per unit of weight, relatively to CO2, which is considered to have GWP=1. The decay rate of the gas is also taken into account, i.e. the quantity removed from the atmosphere in a given number of years. It is easily understood that the shorter the lifetime in the atmosphere of the substance, the better (Global Greenhouse Warming, 2015). For a complete evaluation of the environmental impact of the refrigerant, though, these two parameters are not sufficient. A more thorough analysis can be performed with a TEWI study. The TEWI indicator comprehends the total impact of the substance throughout the lifetime of refrigeration system, and considers not only the direct impact β due to leakages of the working fluid during the operation of the machine and during its dismissal β but also the indirect one, that is mainly due to the energy used for the functioning of the system, and is thus variable in accordance to the location and the energy sources used. The calculation of this value, expressed in kg of CO2 - equivalent emissions of GHG, can be performed as in equation (2.1). where GWP is the global warming potential of refrigerant (kgCO2/kgref), Lannual the leakage rate in the system (kgref/year), m is the refrigerant charge (kgref), N the lifetime of the system (years), πΌπππππ£πππ¦ the recycling factor, Eannual the energy consumption per year (kWh/year), Ξ² the CO2 emission factor (kgCO2/kWh) (Mohanraj, 2011) (AIRAH, 2012). 2.2.5. Policies In order to reduce the environmental impact of human activities, a number of protocols and regulations have been prepared along the years. Within the most famous are Kyoto protocol, Montreal protocol and lastly, aiming at protecting the environment by reducing emissions of fluorinated GHGs, and thus motivation behind this work, the F-gas regulation. A first version was adopted in 2006, followed by a second version to replace it, applied from the 1st January 2015. The main goal is to reduce the contribution of the refrigeration industry to the global warming, by cutting the consumption of fluorinated gases (F-gases) by 79% by 2030, with start at 2009-2012 average level ππΈππΌ=(πΊππβπΏππππ’ππ βπ)+πΊππβπβ(1βπΌπππππ£πππ¦)+(πβπΈππππ’ππ β π½) Direct: leakage Indirect: operation (2.1) -11-PDF Image | Next generation of refrigerants for residential heat pump systems
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