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Manufacturers
of air conditioners for cars and trucks, such as Mitsubishi
Heavy Industries, have switched to ozone-safe coolants.
Air conditioners traditionally contained chloroflurocarbon
coolants, which damage the protective ozone layer of the
atmosphere. To prevent that damage, manufacturers have adopted
hydrofluorocarbon coolants. Those coolants, while harmless
to the ozone, present another problem: they are so-called
greenhouse gases, which contribute to global warming.
Air conditioner manufacturers therefore are
racing to develop coolants that will safeguard the ozone
without aggravating global warming. They are studying several
candidates, of which carbon dioxide is the most promising.
Mitsubishi Heavy Industries has led the industry
in research on carbon dioxide air conditioners. It has verified
the performance of carbon dioxide coolant in a working model
of an automotive air conditioner. And the company is endeavoring
to put carbon dioxide-based air conditioners into commercial
production by 2005.
Working
out the problems
Carbon
dioxide also is a greenhouse gas, but manufacturers could
obtain ample supplies of the gas from the exhaust of industrial
processes. Using carbon dioxide, therefore, would not entail
any increase in output of the gas.
The absorption and release of heat with carbon
dioxide are efficient enough to support viable air-conditioning
systems. Carbon dioxide presents vexing problems, however,
for system engineers. Most notably, it requires higher pressures
in the compression phase of the cooling cycle than hydrofluorocarbon
coolants do. That, along with carbon dioxide's chemical
properties, tends to damage seals and other system components.
Mitsubishi Heavy Industries has developed new
materials and lubricant to keep its air-conditioning system
operating smoothly with carbon dioxide coolant. Another
important feature of the company's carbon dioxide air conditioner
is the scroll compressor. The scroll configuration in the
compressor is a patented innovation. It is especially useful
in generating the high pressures required with carbon dioxide.
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