Knowledge Building: Future Refrigerants

The quest for cool is heating up.

The world of automotive air conditioning is preparing for its second major upheaval in as many decades. The European Union has enacted a ban on R-134a refrigerant that begins with new vehicle platforms introduced in model year 2011 and expands to all new vehicles sold in Europe by model year 2017.

When introducing a new model or completely redesigning an existing one, the design must be finalized about 18 months before production begins. The choice of refrigerants will affect the design of the vehicle, so to meet the 2011 deadline, European automakers must choose their new refrigerant now.

The first time automakers faced this decision was in the early 1990s, when governments of all the industrialized nations (or enough of them to steer the market) signed a treaty banning the production of chlorofluorocarbon gases, including R-12. A new air conditioning refrigerant was developed that does not harm the ozone layer, and by 1995, almost every new air-conditioned car and truck in the world was charged with R-134a.

This time the decision to change refrigerants is being driven by the Kyoto Protocol, an international agreement that requires reductions of specific greenhouse gas emissions, particularly carbon dioxide (CO2). Not every nation has signed this agreement, but as we’ll see later, market forces will play a role in this situation too.

To make it easier to measure and calculate greenhouse gas emissions, each gas has been assigned a Global Warming Potential (GWP) number that compares its effect on global warming with that of CO2. Carbon dioxide has a GWP of 1, while R-134a has a GWP of 1,300. The new refrigerant required by the European Union must have a GWP no greater than 150.

One Alternative

Engineers in Germany have been developing mobile air conditioning systems that use CO2 refrigerant, known as R-744a. It has the lowest possible GWP, and it will be made from CO2 that’s recovered as waste product from industrial processes, reducing (or at least delaying) other industrial CO2 emissions. Carbon dioxide works well as a refrigerant in all but the hottest climates. However, since operating pressures can exceed 2000 psi–about 10 times that of current systems–all the components in the A/C system must be designed to use R744a, and the vehicle must also be designed to use that new A/C system. Additional safety items are needed too, including valves to vent pressure in a collision, CO2 detectors inside the cabin, and a system for venting the cabin if a high concentration of CO2 is detected.

It can all be done, but it will be more complex and expensive than existing low-pressure systems, and it will add cost and complexity to the vehicle.

The Market Rules

For car manufacturers, switching from R-12 to R-134a was relatively easy and inexpensive because the new refrigerant worked with most existing A/C components. However, the change wasn’t completely seamless: a different lubricant is needed with R-134a, and improved seals and hoses are needed to control gradual leakage (R-134a is a smaller molecule). But at the OEM level, the changeover itself required only minor modifications to the vehicle, such as space for a larger condenser and more airflow through the front of the vehicle.

Changing to R-744a would require new A/C components and changes to the vehicle itself. The changes are needed not just to make the system work, but also to protect the vehicle’s occupants from high-pressure component ruptures in a collision. There’s little doubt that the auto industry and its customers would welcome an easier and less expensive alternative.

Another Alternative (Maybe)

In early 2007, two major automotive suppliers, Honeywell and DuPont, announced a joint venture to develop a new refrigerant that would meet the European regulations. Work progressed quickly; by the end of that year they had announced the development of HFO-1234yf (sometimes called “twelve-thirty-four”), and by the following winter most of the lab testing had been completed.

Testing shows that HFO-1234yf poses no special sealing problems and will not harm most of the materials in existing A/C systems. It’s no more toxic than R-134a, and if released into the atmosphere, it completely decomposes after 11 days (R-134a lives for 13 years). The makers say it decomposes to natural chemicals with “no ozone depletion potential or global warming potential.” Its GWP rating is four, so it easily meets the European requirement.

There is one safety issue: it is officially classified as “mildly flammable.” For this particular chemical, “mildly” means it will burn but it isn’t easy to ignite. The refrigerant-to-air concentration must be greater than 6%, and a high-energy ignition source is needed to initiate burning. Once lit, the burn rate is very slow, meaning it doesn’t explode. The typical automotive A/C system doesn’t hold enough refrigerant to reach that concentration, even if the whole charge were to vent into the cabin. While on-vehicle safety issues are minor, refrigerant stored in containers would have to be treated as flammable material, and it might be treated as hazardous material in service shops.

Although there is still some work to be done, DuPont, Honeywell, and the U. S. Environmental Protection Agency are confident that all the major questions have been answered: HFO-1234yf can meet all the requirements and has great potential for becoming the auto industry’s next mobile A/C refrigerant.

Final Steps

In a joint presentation by DuPont and Honeywell at the 2009 Mobile Air Conditioning Society Worldwide Convention in Dallas, Tex., earlier this year, it was reported that most of the world’s OEMs “continue strong support of HFO-1234yf,” indicating there will be a market for the new refrigerant. Successful lab tests have led DuPont and Honeywell to conclude that “HFO-1234yf is safe to commercialize for use in mobile air conditioning.” The final step is to gain approval from the appropriate government agencies to use it as a refrigerant, and there is little doubt that approval will come.

New industry guidelines that regulate storage and handling will be needed. There will also be new SAE standards for recovery/recycle/recharge equipment, hoses and fittings, refrigerant identifiers, leak detectors, storage containers, and about a dozen additional items. For companies that build vehicle A/C service equipment, complying with the new standards will be relatively easy, because most of their existing machines can be modified for use with HFO-1234yf.

No matter what refrigerant the industry switches over to, there will probably not be a retrofit program. When the industry changed from R-12 to R-134a, the goal was to remove R-12 from the fleet because of the immediate risk to the planet’s ozone layer, and therefore to human health. A retrofit program was supposed to help, but engineers and regulators at the MACS Convention said that the retrofit program was not effective enough to justify the headache and expense, and it’s likely that R-134a will simply be recovered as vehicles are retired.

The automotive industry may end up with a replacement for R-134a that doesn’t require redesigning the vehicle, but maybe not soon enough to meet the European deadline. There’s also a lot of political and corporate pressure in Germany to produce R-744a air conditioning systems. If that happens, we may or may not see R-744a here in North America. If we do, independent shops will have to decide if there’s enough business to justify investing in the necessary service equipment and training. No matter which refrigerants go into production, dedicated service equipment will be required for each one. For HFO-1234yf, the new equipment and service procedures will be similar to what exists now, adding even more market pressure to the situation.

There are a lot of ifs here, but in the next few months we’ll know whether the industry will have one mobile A/C refrigerant or two. Either way, the chan
ge-over won’t be cheap, but lessons learned from the last change should help things go a lot smoother.