By Gary Goms
There has been a lot of discussion lately about the future of automotive refrigerants and their impact on the environment. Ozone depletion is no longer the main concern; now it’s global warming. Last year was the warmest year on record. Average temperatures all across the globe are on the rise, as are ocean temperatures. Arctic and Antarctic areas that are normally covered with ice during winter months are becoming ice-free. The frequency and intensity of hurricanes has reached an all-time high, and glaciers are retreating. Scientists also say the concentration of carbon dioxide in the atmosphere is at its highest level in recorded history, and that the level corresponds to the rise in temperature because CO2 retains heat.
Something is obviously going on, but there is still debate about whether the changes we are seeing are man-made or the result of a long-term global climate cycle. There’s no question that the burning of fossil fuels and slash-and-burn agricultural practices in so much of the Third World are releasing megatons of CO2 into the atmosphere. The loss of rain forest is also a factor because trees absorb CO2 out of the atmosphere as they grow and convert it into wood fiber. Consequently, there is growing concern that industrialized nations (and Third World countries) should all do more to reduce their CO2 emissions.
Part of this effort involves reducing the release of automotive refrigerants into the atmosphere. That’s why the U.S. Environmental Protection Agency requires all refrigerants to be recovered from vehicles before the vehicle is serviced or scrapped.
Unlike R-12 (freon) that was used for many years in automotive A/C systems, R-134a does not contain any chlorine and will not cause ozone depletion (ozone high in the atmosphere helps shield the earth from the sun’s harmful ultraviolet radiation). So some people wonder why the EPA insists on recovering R-134a instead of simply venting it when servicing an A/C system. The reason is because R-134a is a potent “greenhouse” gas that retains heat and contributes to global warming.
Scientists assign “global warming potential” (GWP) numbers to a range of gases that vary according to how much heat a particular gas retains. For a base reference point, CO2 has a GWP rating of 1. By comparison, R-134a refrigerant has a GWP of 1,300. In other words, one pound of R-134a that escapes into the atmosphere has the same effect on global warming as the release of 1,300 lbs. of CO2. That’s why the EPA discourages venting, and encourages recovery and recycling of R-134a, as well as all other automotive refrigerants.
Yet when you look at the big picture, the impact of automotive refrigerants compared to all the other sources of man-made CO2 is practically nothing. At the most, refrigerants represent maybe two-tenths of a percent (0.02%) of all the global warming gases released by burning fossil fuels and from deforestation. Even so, there seems to be an ongoing legislative obsession with reducing refrigerant emissions, or eliminating them altogether.
Europe on Alert
The Europeans have decided R-134a is bad for the environment and are moving forward with plans to start phasing it out in January 2011. European automakers have until 2017 to completely eliminate R-134a. The new rules will require all European vehicles equipped with A/C to use a refrigerant with a global warming potential rating of 150 GWP or less. Currently that leaves few choices: R-744 (carbon dioxide with a GWP of 1), HFC-152a (a flammable refrigerant with a GWP of 150) or possibly some blended refrigerants with a GWP rating under 150.
The Europeans like R-744 (CO2) because if it escapes from an A/C system, it will have minimal impact on global warming.
Currently, North American vehicle manufacturers have no plans to phase-out R-134a. But they are looking at ways to reduce the refrigerant capacity of A/C systems so they contain less R-134a. Some of today’s new cars require only a refrigerant charge of 13 oz. not even a full 14-oz. can of refrigerant.
There is also an ongoing effort called “I-MAC” (Improved Mobile Air Conditioning) that is aimed at reducing R-134a emissions in a number of ways. One of the goals of the I-MAC program is to reduce by half the leakage of R-134a from A/C systems by using improved seals and hoses.
Current Society of Automotive Engineer standards state refrigerant leakage should be less than 0.5 oz. (14 grams) per year. New upcoming SAE standards will reduce that amount to only 0.25 oz. (7 grams) a year.
Another goal of I-MAC is to reduce indirect emissions (tailpipe CO2) by making A/C systems 30% more energy efficient. This is being accomplished with better compressor designs and controls. The latest compressors require about 15% less energy to operate than those of only a few years ago. Better electronic control of compressor cycling and the growing use of variable displacement compressors have also yielded improvements on the order of 25% or more in reduced energy usage.
I-MAC also aims to reduce refrigerant loss during service and recovery procedures by 50%. New SAE standards are coming for next-generation recovery machines that will increase the amount of refrigerant that is actually pulled out of the vehicle. Currently, only about 80% to 95% of the refrigerant is actually recovered by most machines. The goal is to increase that number to 98% or more.
New SAE standards will also call for increased sensitivity in electronic leak detectors. Some detectors today that use heated diode or infrared sensor technology can already sniff leaks as small as 0.1 oz. (3 grams) per year. But older detectors with corona discharge sensors are less sensitive (0.5 oz./year) and often give false positive readings.
Cooling with CO2
Carbon dioxide has long been used as a refrigerant in commercial refrigeration, but it’s not a drop-in substitute for R-134a. The main reason is because it requires a much higher operating pressure: up to 2,000 psi, which is 10 times higher than a typical R-134a A/C system. Such extremely high operating pressures require much stronger hoses and a stronger evaporator and gas cooler (instead of a condenser because CO2 does not go through a phase change from vapor to liquid).
CO2 also requires a much stronger compressor to develop such high pressures which means a CO2 A/C system needs more horsepower in high-heat conditions to turn the compressor. Depending on how much the A/C is used, this may reduce fuel economy and performance, especially in smaller vehicles with four-cylinder engines.
Prototype CO2 systems have been in development and evaluation in a number of test vehicles worldwide, including some Humvees for the military. Critics of CO2 initially thought it would not cool very well in areas with high ambient temperatures, such as Arizona and Florida during the hottest days of summer. But so far, CO2 systems have shown they can handle the heat. In fact, some tests have revealed that CO2 actually cools down the interior of the vehicle at a faster rate than R-134a.
Even so, CO2 doesn’t measure up quite as well as R-134a in terms of overall energy efficiency at temperatures above 85° F because of its higher compressor loads. This can be offset by cycling the compressor on less often, or by minimizing the pumping capacity of a variable displacement compressor. But this also reduces the cooling output of the A/C system. For the Europeans, this isn’t a major concern because Europe has a cooler climate than North America, and less than half of European vehicles are equipped with A/C.
Compared to the other leading alternative refrigerant, HFC-152a, CO2 is considered safer. CO2 is nonflammable (unlike HFC-152a, which has a lower flammability limit of 4.8% and can explode if it mixes with air in the right proportion).
However, CO2 can be toxic to breathe in large quantities because it displaces oxygen. There is concern that a CO2 leak inside a vehicle with the windows and vents closed might impair the driver or occupants. One way to mitigate this would be to have a CO2 detector inside the vehicle that would automatically open the windows and/or vents in the event of a CO2 leak. The same sort of approach can also be used with HFC-152a.
One thing CO2 can do that other refrigerants can’t is heat. The compressor discharge temperature of a CO2 A/C system is much higher than an ordinary A/C system, so the system could also be used as a heat pump to provide quick heating during cold weather. This attribute may make CO2 an attractive alternative for “low-heat” vehicles like small diesels or diesel-hybrids that don’t produce a lot of heat, or future fuel cell vehicles that don’t have a traditional cooling system to run a heater.
Because CO2 operates at such high pressure, technicians have to be especially careful when connecting service equipment. CO2 will also require an entirely new generation of charging machines (recovery and recycling probably won’t be necessary) and leak detection equipment (dye or electronic detectors).
When European automakers start building production CO2 A/C systems, the systems will show up on imported European vehicles in the U.S., so even if domestic automakers don’t make CO2 systems, technicians will still have to be trained and equipped to handle CO2, as well as R-134a or any other alternative refrigerants that may be encountered.
The EPA’s SNAP program currently approves a number of alternative refrigerants for use in older vehicles that were originally equipped with R-12. These include various blended refrigerants that may contain mixtures of R-22, R-124, R-142b or even R-134a. Many of these products have been on the market for years, and most cool as well as, or even better than, R-12.
One thing to keep in mind about alternative refrigerants is that the EPA certifies only environmental compliance, not cooling performance. So there is no guarantee an “approved” refrigerant will perform well, or be compatible with, the seals or lubricants in an existing A/C system.
Alternative refrigerants also require unique service fittings and identification labels to be installed on the vehicle a fact that many users seem to overlook or forget, creating a cross-contamination problem the next time the vehicle is serviced. That’s why technicians should always use a “refrigerant identifier” before recovering refrigerant from a vehicle. Alternative refrigerants must also be recovered with a separate recovery machine. But most shops don’t want to buy a third recovery machine to handle alternative refrigerants because they already have one for R-12 and one for R-134a (or a combination machine with dual recovery circuits).
Yet many people use alternative refrigerants in both older and newer vehicles often improperly. Some people use it to top off or partially recharge a leaky A/C system that contains R-12 or R-134a (all the old refrigerant should be recovered first before adding a new refrigerant). They also don’t install the required service fittings or labels to warn others that a different type of refrigerant is in the A/C system which leads to the cross-contamination problems mentioned earlier. And some use flammable refrigerants such as butane, propane and other hydrocarbon mixtures, which are illegal in 19 states and are not approved by the EPA.
Flammable hydrocarbons create a potentially serious fire hazard if they leak into the passenger compartment. The gas may build up to dangerous levels and cause an explosion if ignited by a spark. Flammable hydrocarbons also pose a potential risk to technicians if there’s an underhood leak while servicing the system.
Blends that are not flammable can be used in place of R-12 or even R-134a as substitute refrigerants, or to improve cooling performance. Some blends can actually improve cooling performance 5% to 15% over R-12 or R-134a, which may provide a much-needed boost in a really hot climate. But to date, the vehicle manufacturers recommend R-134a only for retrofitting older R-12 systems, and do not approve using anything other than R-134a in newer vehicles. As for the global warming issue, some blends do have a GWP rating under 150 which makes them better suited as an alternative to R-134a than HFC-152a because HFC-152a is flammable.
Most automakers would prefer to have one universal refrigerant that could be used in every vehicle worldwide, be it R-134a, CO2, HFC-152a or a blend. For the past decade, that refrigerant has been R-134a. But now that the Europeans have indicated they are moving toward CO2, R-134a’s future isn’t certain.
If the European CO2 A/C systems work in this country, and/or individual states pass their own refrigerant legislation that is similar to the European rules (which California and some Northeastern states might do), it could force the domestic automakers to abandon R-134a in favor of CO2, HFC-152a or some blended refrigerant. Time will tell which one is ultimately the refrigerant of choice.