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Keeping Cool While Staying Green


3/24/2008
By Larry Carley

It’s a changing world we live in these days. Global warming is no longer a controversial theory. Many experts agree it is an undisputed fact. The question is what can we do to minimize it?
 

The crux of the global warming problem is that the amount of carbon dioxide and other man-made pollutants in the Earth’s atmosphere have been rapidly rising over the past few decades. The pollutants are a result of global industrialization, deforestation and expanding human and vehicle populations. Scientists are especially concerned over the rising levels of carbon dioxide (CO2) because even a small increase can cause the atmosphere to retain significantly more heat. It’s called the “greenhouse effect.”

How bad is it? The concentration of CO2 in the atmosphere has reached an all-time high of 383 parts per

million by volume. This is 37 percent higher than atmospheric CO2 levels at the start of the Industrial Revolution in the 1800s. The result has been higher overall average global temperatures, and some of the most extreme weather on record. The sky isn’t falling (yet), but measures are being taken that will impact all of us — and in particular, the type of automotive refrigerant that will be allowed in future cars and trucks.

OZONE DAMAGE

Back in the early 1990s, scientists discovered that R-12 refrigerant was damaging the earth’s protective ozone layer. Ozone is a special form of oxygen that contains three atoms of oxygen instead of the usual two. The extra atom makes ozone very reactive and chemically unstable, but it also allows it to absorb the shorter wavelengths of ultraviolet light. The concentration of ozone is greatest in the upper stratosphere, where it acts like a giant sunscreen to block harmful ultraviolet radiation from the sun.

Scientists discovered that the chlorine in man-made chlorofluorocarbons (CFCs), which include automotive refrigerants such as R-12, was reacting with ozone, causing it to break down faster than it could be regenerated by natural processes. So the decision was made to phase out R-12 and replace it with “ozone safe” R-134a, which contains no chlorine. By model year 1995, R-12 was history as far as new vehicle A/C systems were concerned, and many older R-12 systems were subsequently retrofitted to R-134a when major repairs were needed. At the same time, refrigerant recovery was required, and venting of any type of refrigerant during service procedures was banned. The sale of R-12 to do-it-yourselfers was also banned to discourage DIYers from recharging leaky A/C systems.

TRADING ONE PROBLEM FOR ANOTHER

The change to R-134a solved one environmental problem, but created another. At the time when R-12 was phased out and replaced with R-134a, global warming was still very controversial. But as the evidence accumulated, it became obvious that the problem was real — and that R-134a was not exactly environmentally friendly.

The thermal characteristics that make R-134a a good refrigerant also make it a bad greenhouse gas. R-134a has a global warming potential (GWP) 1,300 times that of CO2. This means one pound of R-134a that leaks into the atmosphere will have the same effect on global warming as 1,300 pounds of CO2 from any other source.

According one government report, vehicles in the US released 50.8 thousand tons of R-134a into the atmosphere, equivalent to more than 66 million tons of greenhouse gases. Though that’s only a fraction of the CO2 that vehicles pump out their tailpipes, it’s still a significant number. So engineers are looking for ways to reduce the impact of refrigerant leaks to reduce their contribution to global warming.

The two solutions that are currently being investigated are (1) to redesign R-134a A/C systems so they require a smaller charge of refrigerant, leak less and cool more efficiently, and (2) to eventually phase-out R-134a and replace it with a new refrigerant that has less of an impact on global warming.

For now, the North American and Japanese auto manufacturers are sticking with R-134a. A/C systems are being redesigned to use less refrigerant, to have better seals and hoses so they leak less, and to operate at higher efficiency so less fuel is consumed to keep the vehicle cool. Some late model A/C systems now have refrigerant charges of 12 to 14 ounces, which is much less than the 24- to 60-ounce charges that most older A/C systems require. Of course, this makes these vehicles more likely to experience cooling problems if the system develops even a tiny leak.

On the service side, changes are also being made to reduce refrigerant loss when vehicles are serviced. The latest refrigerant recovery machines do a better job of pulling all of the old refrigerant out of the vehicle. Older recovery machines may leave as much as 20 to 30 percent of the refrigerant charge in the system, which means it will escape into the atmosphere if the system is opened up to replace any parts.

In recent years, Ford, General Motors, Chrysler and Mazda have also been adding leak detection dye to the factory refrigerant charge. This allows technicians to see leaks with an ultraviolet (UV) lamp (also called a “black lamp” because of its purple-colored light).

Recharging equipment is also getting smarter and more accurate. As A/C systems are downsized and charging capacities reduced, charging accuracy becomes more important than ever before for good cooling performance.

WHAT ARE THE ALTERNATIVES?

On the legislative forefront, the Europeans are paving the way, driving alternative refrigerant technology. The European “F-Gas” rules have declared that R-134a must be replaced with a refrigerant that has a significantly lower global warming potential (a rating no higher than 150 GWP). The phase-out on new vehicles must start in 2011 and be complete by 2017.

The European decision to phase-out R-134a does not apply to US or Asian vehicle manufacturers outside of Europe, but it does apply to any vehicle manufacturer who wants to sell cars or trucks in Europe regardless of where the vehicles are built. Consequently, if the Europeans require a new refrigerant for all of their vehicles, it will affect vehicle manufacturers worldwide — and eventually the US aftermarket.

Vehicle manufacturers don’t want to build different A/C systems for different world markets. A common refrigerant is the most economical. But it’s not as simple as it sounds. One reason is that any one of several alternative refrigerants may work. There are advantages and disadvantages for each, and it is possible that different vehicle manufacturers may come to different conclusions as to which one is the best to use.

One alternative refrigerant being considered is HFC-152a. It has a GWP rating of 140, which meets the European requirements. HFC-152a has cooling characteristics very close to that of R-134a, and could probably be used as a direct substitute for R-134a with few if any modifications. But HFC-152a has one serious drawback: it is flammable. If the refrigerant leaks into the passenger compartment, it could explode. The EPA currently bans flammable refrigerant for mobile A/C use (except in truck refer trailers), and many states also have laws that prohibit its use.

One possible solution to the flammability problem with HFC-152a is to add a leak sensor inside the vehicle to warn the passengers and open the windows if a leak occurred. Another approach is to redesign the A/C system so that it uses a “secondary loop” to keep the flammable refrigerant in the engine compartment and out of the passenger compartment. With this approach, the refrigerant circulates through an intermediate heat exchanger and chills a liquid (probably a water/antifreeze mixture) that then flows through the HVAC unit inside the vehicle. A recent report from the U.S. EPA says this approach meets its safety criteria, while also being energy efficient.

Propane is another possibility, but is considered to be much too flammable for automotive applications (though it is used in the refrigeration units on truck trailers, and even in some European household refrigerators).

Another alternative refrigerant that is currently being evaluated is HFO-1234yf. The refrigerant is being jointly developed by Honeywell and DuPont as a drop-in replacement for R-134a. It has thermal characteristics that are similar to R-134a, so no major modifications to the A/C system should be necessary. It has a low GWP rating of less than 150, which meets the European requirements. But it is mildly flammable (though less so than HFC-152a), and long term toxicology tests are still under way. Even so, Honeywell and DuPont are hoping this new refrigerant will become the front runner in the race to replace R-134a.

The other alternative refrigerant that is being seriously considered in Europe as a replacement for R-134a is R-744, which is pure carbon dioxide. C02 has a GWP rating of 1, which is the lowest of any alternative refrigerant currently under consideration. CO2 does not absorb heat as well as R-134a, R-12, HFC-152a or HFO-1234yf, so it requires much higher operating pressures (up to 2,000 psi) to cool efficiently. The operating pressure is nearly 10 times as high as R-134a, so a complete redesign of existing A/C systems would be required to use CO2 as a refrigerant.

Tests have shown that the compressor on an A/C system charged with R-744 has to pump much harder to achieve the same degree of cooling. This could increase the vehicle’s fuel consumption when running the A/C system, and more than offset any reduction in global warming from refrigerant leaks by increasing exhaust emissions out the tailpipe.

Yet proponents of R-744 say a properly designed CO2 A/C system could run as efficiently as any R-134a system today, or maybe even better.

DOWN THE ROAD

The future of R-134a will depend on several things. If the auto makers can make A/C systems more energy efficient and more resistant to refrigerant loss as the vehicle ages, there may be less political pressure to switch to one of these other alternative refrigerants. On the other hand, if Europe continues to move ahead toward R-744 and there is increasing political pressure to “do something” about global warming, domestic automakers may have no choice but to replace R-134a with HFC-152a, HFO-1234yf or even R-744.

Changes here are still years away, but changes are coming. If and when such a change occurs, it would likely involve a gradual phase-in period over a period of years. Training would be a must, and repair outlets would have to invest in new service equipment. Some type of certification for the new refrigerant(s) may also be required.

But the automotive service industry has been through this before, and we can certainly do it again. And if it is necessary to reduce the risks of global warming, it is a small price to pay.















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