Substitutes for chemicals that break down ozone

Atle Kjærvik

Working fluids that affect the ozone layer and the atmosphere, used in refrigeration systems, air-conditioning systems and heat pumps, can be replaced with natural environmentally friendly substances. Carbon dioxide (CO2), ammonia and propane are some of the fluids on which researchers at NTH/SINTEF are concentrating.

In collaboration with Hydro Aluminium, NTH and SINTEF Refrigeration Engineering have recently developed a vehicle air-conditioning system based on CO2.

"We are now going on to commercialize refrigeration and freezing systems for ships and retail stores, using ammonia and CO2," says Geir Eggen, section manager at SINTEF Refrigeration Engineering. "In line with international and Norwegian goals, we are trying to find substitutes first and foremost for CFCs (chlorofluorocarbons) that break down ozone, but we would also like to get rid of "new replacement refrigerants that also have a greenhouse effect by developing new systems based on natural fluids" says Eggen.

Environmentally friendly "air conditioning"

The new CO2-based air conditioning unit for vehicles is based on an invention made by Professor Gustav Lorentzen of NTH. Although CO2 is regarded as the most important greenhouse gas, only minute amounts of CO2 would be used as refrigerant media, and it would be produced from industrial CO2 emissions.

"Most atmospheric releases of CFCs are from vehicle air-conditioning systems," says Jostein Pettersen, a scientist at SINTEF Refrigeration Engineering. "The annual global consumption of CFC-12 for vehicles was 130,000 tons. This was about 20% of the total and air-condition world consumption of CFC, and more than 50% of all CFCs used in refrigeration systems. Around 45 million vehicles are manufactured a year, and about half of them are equipped with air-conditioning systems. HFC 134a, which is in the process of replacing CFC-12, is not a good solution, even though it does not break down ozone. Leakages of HFC 134a from air conditioning systems also increase the greenhouse effect," says Pettersen.

Old-fashioned solutions rediscovered

The use of CO2, ammonia and propane as refrigerants is by no means new to refrigeration scientists. For safety reasons, CO2 was widely used as a refrigerant on board ships until the 1950s. However, such systems had low energy efficiency and tended to become less efficient at high sea water temperatures.

New air-conditioning systems

"These problems are avoided in the new systems by means of improved gas compression and better control systems," says Pettersen. "The new commercial refrigeration systems use natural fluids as well. . They are based on ammonia as a refrigerant , with CO2 as a secondary fluid in integrated but independent loops. This is done partly for safety reasons, since ammonia is toxic and ought not to be utilized in systems from which leakages could harm people" says Jostein Pettersen.