Page 42 - Low Temperature Energy Systems with Applications of Renewable Energy

30 Low-Temperature Energy Systems with Applications of Renewable Energy

were unsuccessful; it was impossible to eliminate leakage of these toxic substances.
Under the slogan “The refrigeration industry needs a new cooling agent, if it hopes
to use it everywhere,” a cooling agent R12 was developed by General Motors under
the direction of Charles Kettering. Industrial production of R12 began in 1931, and
of R11 in 1932. Chlorofluorocarbons (CFCs) and later hydrochlorofluorocarbons
(HCFCs) dominated in the second generation of cooling agents, especially since the
1950s, in domestic and industrial air conditioners and heat pumps. Ammonia has
been and remains the most popular cooling agent in large industrial systems, especially
in the field of production and preservation of products and beverages, and in large ice-
houses serving fishing fleets.
Third generation: Protection of the ozone layer (1997). Hypotheses regarding the
destruction of the ozone layer and the causes of the formation of “ozone holes” were
developed; e.g., the processes of cosmic radiation and the periodic growth of solar ac-
tivity, the processes of changing atmospheric circulation, etc. According to the hypoth-
esis of the influence of ultraviolet radiation, the breaking of chlorine and bromine
bonds of cooling agents makes them highly receptive to absorbing oxygen. Besides
the ozone problem, the emission of certain cooling agents has an impact on the “green-
house effect.”
The Montreal Protocol (1987) identified refrigerants that were destroying the ozone
layer and those with the potential of destroying it. The Ozone Depletion Potential
(ODP) was defined in order to classify refrigerants. As they were the worst ones,
R11 and R12 are assigned a value of unity, i.e., ODP-R11h1 and ODP-R12h1.
At present, there are the following synthetic refrigerants containing ozone-depleting
substances:
1. Refrigerants of the CFC class. CFC molecules contain chlorine, fluorine and carbon atoms;
they are greenhouse gases and ozone depleting with ODP > 0.1;
2. Refrigerants of the HCFC class. They are also greenhouse gases and ozone-depleting gases
with lower ODP of 0 < ODP < 0.1.
Fourth generation: Counteraction to global warming. The Kyoto Protocol (1997)
and “The Paris Summit on Climate” (2015) defined the possibilities of protecting the
environment from greenhouse gas emissions. The Kyoto Protocol identified sub-
stances that affect the Earth’s climate. Greenhouse gases include carbon dioxide,
methane, nitrous oxide, sulfur hexafluoride and all synthetic refrigerants. The Global
Warming Potential (GWP) was introduced. Carbon dioxide potential is taken as unity,
i.e., GWP-CO 2 h 1.
The GWP compares the amount of heat that affects global warming that is absorbed
by a certain mass of refrigerant (usually 1 kg) with the amount of heat absorbed by the
same mass of CO 2 . During the transition period, ozone-friendly refrigerants (i.e.,
ODP ¼ 0) were created. There exist the following synthetic ozone-safe cooling agents
with a high GWP:
• HFC refrigerants containing fluorine, hydrogen and carbon atoms with ODP ¼ 0.
• Refrigerants of the PFC class (perfluorocarbons), that are greenhouse- and ozone-friendly
gases containing fluorine and carbon atoms with ODP ¼ 0.