A new study from the National Academy of Sciences predicts that the growing use of so-called “green” refrigerants being phased in to replace ozone-depleting ones could contribute to the global equivalent of up to 45% in carbon-dioxide emissions by 2050. > Photo: Tudor Van Hampton Engineers prep for R-22 ban at recent HVAC conference. Related Links: View the National Academy of Sciences Study The use of hydrofluorocarbons (HFCs), such as R-404a, R-410a and HFC-134a, are set to grow exponentially as hydrochlorofluorocarbons (HCFCs), such as R-22, continue phasing out under the Montreal Protocol. In the 1990s, HCFCs replaced more-damaging chlorofluorocarbons (CFCs).
Arch dams, classically curved monoliths situated in narrow valleys, are not as common as other types of dams, such as embankment dams and gravity dams. ENR takes a look at some of the biggest arch dams in the world, both completed and under construction.