Working Group III: Mitigation

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A3.2.1 Mobile Air Conditioning

HFC-134a replaced CFC-12 in virtually all vehicle air conditioners produced after 1993/94. Motor vehicle air conditioning uses HFC-134a refrigerant in an integrated system of components that provide cooling, heating, defrosting, demisting, air filtering, and humidity control. It is technically and economically feasible to significantly reduce emissions of HFC-134a refrigerants: by recovery and recycling of refrigerant during servicing and vehicle disposal; by using high quality components with low leakage rates, hoses with lower permeation rates, and improved connections; and by minimizing refrigerant charge. Efficiency improvements and smaller, lighter units can further reduce energy-related CO2 emissions. New systems using alternative refrigerants –carbon dioxide or hydrocarbons– are being developed as described below (see Section A3.2.1.3).

A3.2.1.1 Estimates of Global HFC-134a Emissions

Globally, 65%–75% of air-conditioned vehicles in service in 2000 have HFC-134a air conditioners and it is predicted that between 2000 and 2010, 70%–80% of all new vehicles will have HFC-134a air conditioners. This projection assumes a continuation of current trends of mobile air conditioning installed in vehicles in normally cool climates where air conditioning may not be necessary. When air conditioning systems were redesigned to use HFC-134a, vehicle manufacturers used a smaller refrigerant charge and reduced leakage rates. Typical direct HFC emissions over a 10-year period in the USA are 1.4 kg if recycling is undertaken during service and disposal and 3.2 kg without recycling (Baker, 2000). Estimates for HFC-134a air conditioner emissions are included in Table A3.3.

Table A3.3: Estimated global HFC-134a emissions for vehicle air conditioning
Baker (1999).
Year Vehicles w/134a A/C Recycle at service/disposal HFC-134a use HFC-134a emissions
  (million) (%) (kt) (kt)
2000 214-247 60 64-74 31-35
2010 464-530 60 58-79 37-54

A3.2.1.2 Strategies for Reducing Emissions and Improving Energy Efficiency of HFC-134a Systems

Vehicle manufacturers and their suppliers are working to increase the energy efficiency and reduce the emissions of HFC-134a systems. Typical CO2 exhaust emissions resulting from air-conditioner operation are in the range of 2% to 10% of total vehicle CO2 emissions (SAE, 2000). Comparison of reduced emissions HFC-134 systems and CO2 systems have been published (Petitjean et al., 2000; March, 1998). HFC-134a systems can be redesigned for higher energy efficiency and smaller refrigerant charge within 2–4 years, and manufacturers of replacement parts could supply high-quality components within 2–4 years (SAE, 2000). SAE (2000) estimates that improved HFC-134a systems can be introduced faster and at lower incremental cost than carbon dioxide, hydrocarbon, and HFC-152a systems.

Lowering the demand for cooling and humidity control can reduce indirect emissions from fuel consumption and could allow smaller air conditioning systems having reduced refrigerant charges. This is accomplished by increasing thermal insulation and decreasing thermal mass in the passenger compartment, by sealing the vehicle body against unwanted air infiltration, by minimizing heat transfer through window glass, and by controlling the compressor to minimize over-cooling and subsequent re-heating of air.

A3.2.1.3 Strategies for Developing Efficient Alternative Air Conditioning Systems

Considerable activity is underway to develop alternatives to HFC-134a air conditioning systems for vehicles. Prominent efforts are the European “Refrigeration and Automotive Climate Systems under Environmental Aspects (RACE) Project” (Gentner, 1998), and the Society of Automotive Engineers/US EPA/Mobile Air Conditioning Society Worldwide “Mobile Air Conditioning Climate Protection Partnership” (SAE, 1999, 2000).

Two categories of alternative refrigerant candidates have emerged for new systems: 1) transcritical carbon dioxide systems and 2) hydrocarbon or HFC-152a systems.

  1. Transcritical CO2 systems require substantial new engineering, reliability, and testing efforts. These carbon dioxide systems have potential energy efficiency that is comparable or better than HFC-134a systems and the lowest direct global warming emissions of any candidate refrigerant. Prototype systems from several European vehicle manufacturers provided comparable passenger cooling comfort in medium-sized vehicles, and one reported improved efficiency over HFC systems at the Scottsdale Symposium (SAE, 1999). A CO2 system in a small vehicle was less efficient, especially during idling (Kobayashi et al., 1998). With a higher heat rejection temperature compared to HFC-134a cycles, carbon dioxide systems can also efficiently operate in reverse mode to heat vehicle interiors. New equipment and technician training will be required to safely repair systems with operating pressures up to 6 times higher than systems with HFC-134a. The first CO2 systems could be commercially available within 4-7 years (SAE, 2000).
  2. Hydrocarbon and HFC-152a systems, with secondary cooling loops to mitigate flammability risk, are under study and development by several manufacturers in co-operation with suppliers (Baker, 2000; Ghodbane 1999; Dentis et al., 1999; SAE, 1999a). One prototype achieved a cooling performance at the 1999 Phoenix Forum comparable to HFC-134a systems (Baker, 2000; Gentner, 1998; Ghodbane, 1999; SAE, 2000). Systems using flammable refrigerants will require additional engineering and testing, development of safety standards and service procedures, and training of manufacturing and service technicians before commercialization, but would require fewer technical breakthroughs than carbon dioxide systems. If proven safe to Original Equipment Manufactures (OEMs), it is estimated that systems with flammable refrigerants could be commercially implemented in the first vehicles in as little as 4-5 years (SAE, 2000).

Highly efficient air conditioning and heating systems are particularly important to the commercial success of electric, hybrid, fuel cell, and other low-emission vehicles to help overcome the limited power of such vehicles.

A3.2.1.4 Cost-Effectiveness of Reducing Emissions from Vehicle Air Conditioning

Recovery and Recycle
It is estimated that recycling rates can be increased from 60% to 90% within one to two years in developed countries (SAE, 2000). Recovery and recycling of HFCs can reduce emissions by more than 10 kt annually (Baker, 1999). About 50% of the global fleet of HFC-134a air conditioned vehicles are in the USA where recycling is mandatory, and 25% are in Japan, where voluntary programme achieve a substantial recycling rate. The remainder are in Europe where recycling ranges from zero in some countries to near 100% participation in others, and in developing countries, where a wide range of recovery practices is found. A UNDP survey of 1300 Brazilian garages found one-quarter of garages recycling HFC-134a (UNDP, 1999).

The current market value of HFC-134a recovered during service or disposal in the USA more than pays for the cost of labour, equipment, and maintenance for shops servicing more than 6 vehicle air-conditioning systems per week. By 2002 to 2003 it is technically feasible to reduce system charge and leakage rates significantly. Recovery of 0.33 kg of HFC-134a will cost US$0.70 in large shops and US$1.50 in small shops. For large shops, recovery costs for improved, low-charge vehicles are estimated at less than US$3.50/tCeq. Even for small shops, the cost-effectiveness per tonne of carbon equivalent can then be calculated in the range of US$1.18-12.81/tCeq depending upon the size of the charge (EPA, 1998).

Reduced Charge and Improved Containment
By 2002 to 2003, it is technically feasible to reduce system charge and leakage rates worldwide. It is estimated that the vehicle charge in the US can be reduced from 0.9kg to 0.8kg and that annual vehicle leakage could be reduced from 0.07 kg/yr to 0.04kg/yr (UNEP, 1998a; Baker, 1998; Sand et al., 1997; Wertenbach and Caesar, 1998). In Europe, refrigerant charges average about 0.7 kg per vehicle (Clodic, 1999). For the USA it is estimated (Baker, 2000) that emissions can be reduced from 8% to 5% per year for a 10-year reduction of 1.2 kg/vehicle without recovery and recycling or 1.0kg with recovery and recycling. Two studies (Harnisch and Hendriks, 2000; March, 1998) estimate that, in Europe, the cost per vehicle to reduce leakage rates from 10% to 4%-5%/yr is only US$11-US$13.

Alternative Systems
Three authors have published estimates of the cost of emission reductions achieved through alternative vehicle air conditioning using carbon dioxide as the refrigerant (March, 1998; Baker, 1999, 2000; Harnisch and Hendriks, 2000). These studies reported widely diverging results on the specific abatement costs of HFC emissions for the use of transcritical CO2 systems (from US$90 to >US$1000/tCeq). Differences in cost estimates can be traced back to a number of factors among which two are most important: (1) the use of producer-costs versus consumer costs and (2) differing assumptions about the existing degree of recovery of HFC-134a during servicing and at the end of life. Of lesser importance were differing assumptions on the average fluid charge of an HFC air conditioning system, annual leakage rates, relative differential costs, and applied discount rates. Once the results are normalized to common assumptions on the major factors, the abatement costs differ by only a factor of two or less (see Table A3.4).

As reported in Table A3.4, costs of avoiding HFC emissions through alternative air conditioning systems vary between US$20 and US$2100/tCeq depending on the emission characteristics of the reference HFC system (and on whether consumer or producer prices are used). Consequently in countries where systems already exist to ensure HFC recycling during servicing and at the end of life, alternative air conditioning systems will need to exhibit significantly reduced indirect emissions in order to be cost-effective in abating greenhouse gas emissions.

Table A3.4: Abatement costs a of avoiding HFC emissions by using alternative systems (based on CO2 or secondary hydrocarbons) relative to different baseline HFC emission scenarios
Alternative system compared against current HFC-134a systems Alternative system compared against improved HFC-134a systems with reduced leakage rate
With recycling, 1.4 kg 10-year emission baselineb
Without recycling, 3.2 kg 10-year emission baseline
With recycling, 0.4 kg 10-year emission baselineb
Without recycling, 2.0 kg 10-year emission baseline
Producer cost Consumer cost Producer cost Consumer cost Producer cost Consumer cost Producer cost Consumer cost
102-173 306-519 21-53 63-159 460-711 1380-2133 59-109 177-327
a Assuming:( i) equivalent energy efficiency for conventional and alternative systems, (ii) an increase of producer cost by US$60-90 per vehicle relative to current HFC-systems, (iii) a discount rate of 4% per year, and (iv) a factor of 3 between consumer cost and producer cost (Crain, 1999).
b Incremental costs for the improved HFC system and for establishing and enforcing a recovery system are not included but assumed to be small compared to additional costs of alternative systems.

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