Protecting the Ozone Layer
After switching to hydrochloro fluorocarbons, or HCFCs, over a decade ago, the air conditioning equipment industry is now making chillers that use coolant with zero ozone depletion potential -- mostly...
After switching to hydrochloro fluorocarbons, or HCFCs, over a decade ago, the air conditioning equipment industry is now making chillers that use coolant with zero ozone depletion potential — mostly hydrofluorocarbons, or HFCs.
However, about 70% (down from 85% in 2000) of existing equipment continues to run on chlorofluorocarbons (CFCs). These substances were phased out years ago but are still available because of stockpiling and recycling.
“The problem as far as conversion is concerned is that the units continue to function well so owners say: Why would I disturb [things]?” says Warren Heeley, President of the Heating, Refrigeration and Air Conditioning Institute of Canada (HRAI).
The situation is about to change under new regulations that have been adopted by Alberta and B.C. and are in the cards for other provinces. Under the new rules, any CFC-containing chillers due for an overhaul must convert to HCFCs or be replaced by January 1, 2005.
Over the past decade, HCFCs have provided a convenient stopgap for air-conditioning manufacturers who were forced to eliminate CFCs under the Montreal Protocol, an international treaty signed in 1987 to protect the earth’s ozone layer. HCFCs have between 1/20th and 1/50th of the ozone-depleting potential of CFCs.
But time is running out for HCFCs too. By 2010, HCFC-22 equipment will be banned and by 2020, production and imports of HCFCs will be reduced by 99.5%.
The remaining 0.5% represents HCFC-123, which has a relatively minor impact on the ozone layer and global warming and is used exclusively in large centrifugal chillers that are expensive to replace. It has been given a 10-year grace period, to 2030, to service existing chillers.
“We’re finding a little less urgency with HCFCs to move forward because their ozone-depleting potential is much lower (than CFCs),” says Heeley. “It’s also a little more difficult to manage the HCFC transition simply because of the amount of HCFC-22 [Monochlorodifuoromethane) that’s used out there.”
But because large chillers last so long, there is an incentive for building owners to make the switch now, rather than later. Most chillers last at least 25 years, and some last up to 50 years. A plant installed today would likely outlive the deadline for the complete phase-out of HCFCs in 2030.
“Anyone who is using the low-pressure HCFC-123 refrigerant should be looking at future replacement scenarios,” advises Robert Shute, P.Eng., partner in the Mitchell Partnership. He says he has been advocating HCFC-free chillers to his clients “with great enthusiasm” for the past five years.
The alternatives to CFCs and HCFCs will help restore the ozone layer, but none are perfect. HFC-134a, the most common alternative refrigerant for large chillers in North America, has zero ozone depleting potential but is less efficient than low pressure HCFCs and contributes more to global warming.
The HFC-400 series of refrigerants are blends of other refrigerants popular in Europe but just beginning to penetrate the North American market. They may be a better alternative for high-pressure applications because they mimic the capacity and efficiency of HCFCs, but they have zero ozone depletion potential, acceptable levels of global warming potential, and low toxicity.
Another candidate is HFC-245fa, which can be used as an alternative in low-pressure HCFC-123 machines. However, because the refrigerant is flammable and has a relatively high global warming potential, its use is expected to be limited.
Ammonia is an acceptable high-pressure compression cycle refrigerant, says Shute, but it has more stringent plant safety standards. Absorption refrigeration cycles using a desiccant (lithium bromide) forced evaporation of water to generate cooling has been used for a long time and, although not as efficient as vapour compression cycles, it is an environmentally safe cooling process.
And for the truly innovative, Shute advocates looking to more environmentally friendly alternatives such as geothermal sources.CCE
* A single atom of chlorine can destroy 100,000 or more molecules of ozone.
Virginia Heffernan is a Toronto-based freelance writer.