Closing the hole in the ozone is seen as the world’s greatest environmantal restoration achievement but there’s a hitch …
Under the Montreal Protocol, chloroflurocarbons (CFCs) were phased out and replaced with the less damaging hydrochlorofluorocarbons (HCFCs) as an interim measure. HCFCs have now become the standard working coolant in refrigerators, air conditioners and aerosol cans.
But HCFCs are still damaging to the ozone layers and, in the longer term, hydrofluorocarbons (HFCs) were promoted as the best alternative. From January 1, 2010, the world’s developed nations must cut HCFC consumption and production by 75 percent. It will then become illegal to import, produce or sell HCFC-22 (Freon) and HCFC-142b, the ubiquitous refrigerants, for use in new equipment.
The problem is that, whereas HFCs do not destroy the ozone layer, they can be thousands of times more harmful to Earth’s climate than carbon dioxide.
The underlying problem is that the characteristics which make a good refrigerant are the ability to trap heat and durability – exactly the same characteristics that make a powerful greenhouse gas.
Ironically, the best solution may well be to use CO2 as a refrigerant. CO2 can remove heat from the air. The process starts when a refrigerator’s compressor condenses CO2 into a liquid, raising its pressure and temperature. The CO2 is then transferred to a a radiator on the back or bottom of the fridge where the heat is released. The CO2 then travels through an expansion valve, reducing the pressure and causing it to rapidly expand into vapor. As the CO2 evaporates it absorbs heat, cooling the air inside the refrigerator compartment.
The difficulty with CO2 is that it must be used at a much higher pressure than HFC refrigerants, and therefore requires stronger piping.
Coca-Cola began testing the use of CO2 as a refrigerant in vending machines and other retail refrigerators in China during the Olympics and PepsiCo is now testing these vending machines in Washington, D.C.
(Based on sources including Scientific American)