为了因应美国地区越来越严苛的公司平均燃料经济性（CAFE）相关政策，先期已在欧洲地区开始转型的制冷剂行业也开始在美国地区加速转型。具体来说，整个行业将转而采用一种全球变暖潜能值（GWP）更低的制冷剂。汽车厂商可以通过提高车辆的燃料经济性获得大量CO2积分，美国环保署(EPA)也有计划逐步淘汰R-134a制冷剂。

根据EPA的新政策，2021年后，所有在美销售的新车和轻质卡车均不得再使用汽车行业常用的R-134a制冷剂。虽然这项政策仅限制汽车和轻质卡车，但适用于中/重载卡车的类似条款也将在今年之内出台，因此到2021年，所有在美国境内销售的车辆可能均需更换制冷剂。不过，部分用于出口的车型仍可在2025年前使用R-134a系统。

与此同时，戴姆勒(Daimler)集团也最终同意在对制冷剂有特定政策要求的市场内（比如美国），为旗下品牌梅赛德斯(Mercedes)车型搭配R-1234yf系统。不过，公司目前尚未公布任何日程。据悉，戴姆勒集团曾声称汽车行业用于替代R-134a系统的R-1234yf制冷剂存在一定消防安全隐患。为了解决这一问题，戴姆勒集团在旗下车型的发动机盖下安装了一款“灭火器”，可以直接向工程师认为存在起火隐患的部位喷射惰性氩气灭火。这里的消防安全隐患主要是指，一些部件在工作时释放的热量可能足以点燃泄露的制冷剂。

由于低GWP潜能值的R-1234yf无法直接与R-134a系统兼容，因此R-134a可能并不会立刻退出历史舞台。R-1234yf的CAFE积分为：汽车13.8g/mi，卡车17.2 g/mi。（GWP是一种度量单位，意为全球变暖潜能值，世界各地的环境管理机构可以用GWP描述单位气体对全球变暖造成的影响。GWP是一个相对值，相当于单位质量温室气体释放的热量与相同质量CO2释放热量的比值。其中，CO2的GWP潜能值定义为1。）

由于采用低GWP潜能值的制冷剂可以获得更多CAFE积分，菲亚特克莱斯勒汽车（FCA）自2014年开始进行制冷剂的改革。通用汽车旗下仅有凯迪拉克XTS采用了R-1234yf制冷剂，但公司将在今年年底前广泛推广R-1234yf系统。据报道，福特(Ford)将在今年4月开始进行制冷剂改革，第一款采用R-1234fy系统的车型为翼虎(Escape)，但目前尚无具体推广的细节。目前而言，汽车厂商完全可以为同一装配线上的不同汽车搭配不同的制冷剂，实现这一点并不困难。

保修报销

据报道，目前R-1234yf的“零售价”每千克超过220美元，批发略有优惠。网上也有各种R-1234yf的广告，售价低至每千克160美元（未经确认）。但无论如何，这仍比每千克售价通常仅要6.6美元的R-134a贵的多。

FCA所售的R-1234yf制冷剂按盎司计算，公司要求经销商仅向厂方申报额外使用的制冷剂（比如，维修结束后的制冷剂充装、开始阶段从汽车系统回收的少量制冷剂）。制冷剂回收/循环/充装（简称RRR）设备的精度可达±1盎司，而且可以打印出额外使用的制冷剂剂量，经销商在向FCA报销时，必须附上RRR设备打印的列表。

最近几年，车辆所需的制冷剂用量正在不断下降。目前，FCA公司R-1234yf制冷剂用量最少的车型为Alfa Romeo4C，仅为370克；最高的为克莱斯勒(Chrysler)300和道奇(Dodge)Charger，用量为709克；其余车型的用量多在454至510克之间。

FCA的低GWP潜能值制冷剂推广相当顺利。在最近举行的移动空调协会（Mobile A/C Society，简称MACS）大会上，FCA中西部商业中心(Midwest Business Center)技术顾问Alan McAvoy向观众表示：“我们早在3年前就推出了采用R-1234yf系统的车型，目前已累计制造了超过200万辆搭配R-1234yf的车辆。目前，针对制冷剂系统的维修服务主要局限在碰撞损伤和修复泄露等。”

虽然R-134a的性能与R-1234yf无异，但EPA平流层保护部(Stratospheric Protection Division)的Rebecca von dem Hagen在MACS大会上表示，任何修车厂如果试图将R-1234yf系统改装为R-134a系统，将面临违反排放控制法规的风险。为了预防此类情况，车辆和制冷剂容器均需针对不同制冷剂，搭配专用的阀门配置。

R-744可以继续使用

未来，EPA不会限制小罐R-1234yf制冷剂在DIY市场中的流通，但前提是这些罐子配备了自动闭合阀门，可以防止泄露。这项规定是基于加州针对R-134a的规定设定的，其中还包括每罐收取10美元押金的要求。

墨西哥化工(Mexichem)曾尝试研制一种名为R-445a的混合制冷剂，用于替代R-1234yf系统，但目前已经被叫停。同时，一系列与此相关的SAE标准修订工作也停了下来。这种混合R-445a制冷剂内含85%的R-1234ze（一种与R-1234yf同族的烯烃）、6%的二氧化碳，以及9%的R-134a。由于成分中含有将会在2021年禁用的R-134a，因此这种制冷剂是否受限于美国EPA的2021禁用规定，目前还尚无定论。

德国汽车生产商协会VDA的成员仍在继续进行R-711 CO2制冷剂的合作研发。戴姆勒的工程师希望能将这种制冷剂用于部分2017款梅赛德斯E级和S级欧洲车型。目前，SAE为将这种制冷剂进入美国市场而制定的标准尚未重新开始生效。

在使用R-744制冷剂的车型开始在美销售之前，EPA将可能需要针对 “所有制冷剂均不能排放，而必须回收（或销毁）处理”的规定进行修改。这条规定也同时适用于R-1234yf，尽管这种制冷剂的GWP潜能值很低。CO2是一种自然物，而且非常便宜，因此强制回收CO2的规定存在一定的环保方面的争议。这是由于“回收”这一行为本身就会产生排放，甚至可能超过制冷剂自身的热效应（毕竟其GWP潜能值仅为1.0）。EPA已经注意到这个问题，但目前尚未专门宣布颁发豁免条款的可能性。

与此同时，目前市场上尚无可以替换R-1234yf系统的低GWP制冷剂。戴姆勒曾经强烈质疑R-1234yf制冷剂的安全性，而且曾出示实验视频，展示轻度易燃的R-1234yf可能存在安全隐患。但这次，戴姆勒也别无他法。戴姆勒的测试曾引起了广发争议，因为也有汽车行业的其他成员表示，他们认为R-1234yf非常安全。

欧盟曾发出律师函，要求戴姆勒在“新型”汽车的设计中，遵守欧盟的低GWP规定。因此，戴姆勒最终同意使用R-1234yf系统，不过也同时搭配了上文提到的车载灭火器。


作者：Paul Weissler
来源：SAE《汽车工程杂志》
翻译：SAE 上海办公室

EPA's 2021 A/C refrigerant rules accelerate R-1234yf changeover

The industry transition to a low global-warming-potential (GWP) air conditioning refrigerant, already underway in Europe, moves into high gear in the U.S., as CAFE (Corporate Average Fuel Economy) regulations add incentives. Car manufacturers receive substantial CO₂ credits that translate to more miles per gallon, and a newEPA phaseout schedule for R-134a has been adopted.

Per new EPA regulation, the long-used R-134a cannot be installed in new cars and light trucks built for domestic sale after 2021MY. Although this rule is limited to those vehicles, similar regulations for medium/heavy-duty trucks are coming this year, so the 2021 deadline may affect all domestic vehicles by that time. Some vehicles for export will still be able to use R-134a systems until 2025MY.

In the meantime, Daimler, which had charged that the alternative refrigerant R-1234yf posed potential fire safety dangers, has finally agreed to use R-1234yf systems in its Mercedes vehicles for markets where the refrigerant either is mandated or is effectively pressed for by regulatory bodies (as in the U.S.). However, no rollout schedule has been announced. Daimler will add an underhood "fire extinguisher"—an argon gas canister with spray lines directed at all parts that its engineers say might become hot enough for a leaking refrigerant to ignite.

Because low GWP R-1234yf cannot be retrofitted to R-134a systems, production of R-134a will continue indefinitely for service. The R-1234yf CAFE credits are 13.8 g/mi for cars, 17.2 g/mi for trucks. (GWP, a metric used by environmental regulatory agencies worldwide, is a measure of how much a given mass of a gas contributes to global warming. It is a relative scale which compares the amount of heat trapped by greenhouse gas to the amount of heat trapped in an equal mass of CO₂. The GWP of CO₂ is by definition 1.)

The value of storing CAFE credits for a low GWP refrigerant enticed Fiat Chrysler Automobiles (FCA) into beginning its changeover in 2014MY. General Motors has had just one entry in that period, the Cadillac XTS, but GM will be virtually across the board by the end of this year. Ford reportedly will begin its changeover in April with the Escape, but no details of its rollout are available. Sending vehicles with either refrigerant down the same assembly line is not a difficult process.

Warranty payments 

The "street retail" price of R-1234yf—over $100 lb/ $220 kg has reportedly dropped slightly for volume buyers, and there are internet advertisements (of unknown validity) for as low as $72.50 lb ($160 kg). However, that's still much higher than the typical $3 lb/$6.60 kg for R-134a.

FCA's list price for R-1234yf is per ounce—because its dealers are instructed to bill the factory only for the additional amount (total refrigerant charge at the conclusion of the repair, less amount recovered from the vehicle system at the start). The recovery/recycle/recharge machines have a charge accuracy of ±1 oz and print out the amount added; the printout must be attached to a warranty claim.

Total refrigerant charges have been coming down in recent years, and those for FCA's R-1234yf systems are as low as 13 oz (370 g) on the Alfa Romeo 4C to a high of 25 oz (709 g) for the Chrysler 300 and Dodge Charger, with most in the 16-18-oz range (454-510 g).

FCA's launch of the low GWP refrigerant has gone very smoothly. At the recentMobile A/C Society (MACS) convention attended by Automotive Engineering, Alan McAvoy, technical advisor at the FCA Midwest Business Center, told the audience: "We currently have R-1234yf vehicles that have been on the road for over three years and have built over two million total. Service to this point is primarily limited to collision damage, plus a few with minor hose or fitting leakage."

Although R-134a will perform comparably to R-1234yf, EPA's Rebecca von dem Hagen, of the agency's Stratospheric Protection Division, told the MACS convention that a shop changing an R-1234yf system to R-134a would constitute the offense of tampering with an emissions control. Each refrigerant requires specific service valve fittings to discourage any attempt, both on the vehicle and the refrigerant containers.

R-744 work continues 

EPA will allow sale of small cans of R-1234yf to the do-it-yourself market, provided the cans have self-closing valves to minimize venting. This is based on California's regulation for R-134a, which includes a $10/can deposit system.

An attempt by Mexichem to develop R-445a as a lower-cost blend refrigerant alternative to R-1234yf, has been put on hold. Work on a series of enabling SAE standards has stopped, too. The blend consists of 85% R-1234ze (an olefin in the same family as R-1234yf), 6% carbon dioxide and 9% R-134a, so whether it faced the 2021 deadline for R-134a is now moot.

Members of the VDA, the German automakers association, are continuing consortium development of R-744 (CO₂) refrigerant. Daimler engineers hope for its 2017 introduction on some Mercedes E- and S-Class European models. As a result, the SAE program to develop enabling standards for a U.S. introduction has not been reactivated.

Before R-744 cars would be sold in America, EPA would be asked to modify its requirement that no refrigerants can be vented, so must be recycled (or destroyed)—a rule that includes R-1234yf despite its low GWP. CO₂ is both natural and inexpensive, and any requirement to recycle it would be environmentally questionable. Emissions would be produced by the effort, perhaps in excess of the low GWP (just 1.0) of the refrigerant itself. EPA recognizes this issue but has not specifically announced it will address an exemption.

In the meantime, there is no market-ready low GWP alternative, hence the changeover to R-1234yf. Even Daimler, which has most strongly questioned its safety and famously showed videos of a laboratory test that demonstrated potential dangers from its mild flammability, has no choice at this time. The Daimler test indications were widely disputed, as others in the industry attested to R-1234yf safety.

The European Union has initiated lawsuits to force compliance by Daimler to EU's low- GWP rule for "new type" vehicles. So the automaker has finally agreed to use R-1234yf systems, but with the on-board argon fire-suppression system noted earlier.

Author: Paul Weissler
Source: SAE Automotive Engineering Magazine