A Study of R134a Leaks 

Heavy Duty Vehicles

CARB Contract No. 06-342

Andrew Burnette

infoWedge

Rick Baker

Eastern Research Group
Acknowledgements

• Dr. Tao Huai, Dr. Tao Zhan, Dr. Alberto 

Dorothy Shimer (CARB)

• Dr. Denis Clodic (Center for Energy Stud

Ecole des Mines de Paris)

• Dr. Winfried Schwarz (Öko-Recherche G• Jim Baker (Delphi Corp)• Gary Hansen (Red Dot Corp)• Dr. Stephen Andersen (US EPA)• Multiple Sacramento area fleets (most o

whom requested to stay anonymous)
Outline

• Introduction• Methods – Gravimetric – Maintenance (mass-balance)• Results – Gravimetric – Maintenance (mass-balance)• Analysis/Discussion – Gravimetric – Maintenance (mass-balance)• Summary/Recommendation
Background

• Refrigerants used in mobile air 

conditioning (MAC) systems can enthe atmosphere through a number mechanisms – low-level, long-term leaks – rapid leaks caused by discrete inciden

(e.g., system failure) – regular system servicing – end-of-life losses
1,1,1,2-tetrafluoroethan

(HFC-134a)

• R134a is one of the most common 

refrigerants used in MAC systems today

• It has a global warming potential (GWP) 

1,300 (1,2)

• ARB estimated that total R134a emissio

from all MAC systems in California (inclulight-duty vehicle systems) approximatemillion metric tons of CO

2-equivalent (C

in 2004 (3)

(1) Intergovernmental Panel on Climate Change Fourth Assessment Report (AR4), 2(2) Updated GWP from AR4 is 1430, but legacy value of 1300 is used here for comp

previous inventories

(3) California Air Resources Board, Initial Statement of Reasons for Proposed Regula

Small Containers of Automotive Refrigerant, December 5, 2008, p. 4.
Generic MAC System

(vapor compression cycle

Source: Yingzhong Yu, “Generic Approach of Refrigerant HFC134a Emission Modes From Mobile Air Conditioning (MAC) Systems.” PhD Thesis, Ecole des Mines, Paris, France, October 23, 2008
MACs In Vehicles
Project Objectives

• Characterize in-use R134a emiss

from heavy-duty onroad and offrvehicles in California

– Estimate low-level, long-term leaka

from MAC systems that use R134a

– Combine with equipment populatio

estimates into an annual emission inventory for the state for those tyleaks
Target Sample for the Stu

• Heavy-duty, onroad and offroa

• Variety of MAC configurations

– Joint seal type–Amount of permeable materials–Compressor type

• Budget for about 70 vehicles
MAC Configuration Considerat

• Used SAE J2727 and industry ex

to determine MAC parameters important to leak rates

• Limited sample size and probable 

variability of field measurements dictated 1 or 2 MAC parameters investigated for impacts on estimemissions
Sample Selection

• Vehicles in professional use

• Protected, on-site garage spac

with power required

• Turn-key sample process takes 

hours to complete
Target Number of Sample

Bin ID Vehicle Type # Units

1 Full Sized Transit Bus 112 Shuttle Bus 53 MD Utility Truck/Van 184 HD Truck Tractor 185 Other HD Trucks (dump, waste, etc)

9

6 Construction Equipment 57 Agricultural Equipment 4

Total 70
Gravimetric Measurement 

Method

• Several alternatives investigated• Selected method blased upon one 

developed by Dr. Denis Clodic, Ecole Mines, Paris, France

– Originally for light-duty cars in a clima

controlled area

– Modified for application to heavy-duty 

equipment in the field

– Similar to SAE J2762 (which is also ba

upon Clodic’s method)
Gravimetric Method Overv

• Recover, evacuate and recharge MAC w

known amount of R134a

– Recover from MAC to 20 kPa with compre– Distill R134a from oil and weigh– Evacuate recovery equipment to 20 Pa wi

vacuum pump

• Release to normal operations for severa

months at least

• Recover the R134a to determine leakag

any, using same steps as above
Schematic of Gravimetric 

Method

Recover

Recharge

Heat

Heat

Heat

Temp

Temp

Temp

Press
Recovery Equipment List

Item Notes Vacuum pump, high vacuum gauge, hose 

High capacity, 2-stage vacuum pump: Mastercool model 90067 

212 LPM (7.5 CFM) capacity and 0.37 kW (0.5 HP) motor. Higvacuum gauge: For reading vacuum at 20 Pa-absolute. Resoluti0.1 Pa. 

Recovery compressor and hose 

Compressor (Bacharach model Stinger 2000) and dedicated hos

to recover R134a from the MAC into the Recovery tank. 

Electronic scale Electronic balance: Citizen model SSH 93 with capacity of 30 k

lb) and resolution of 0.1 g (0.0035 oz). 

Recovery tank Cylinder used only to recover R134a from the MAC. After reco

R134a is transferred from this tank to the Recycling tank. 

Manifold and 3 hoses Service manifold with dedicated hoses and gauges for the low-p

and high-pressure sides of the MAC and with a hose to transfer 

from and to the MAC. 

Charging tank and hose 

Cylinder of new or recycled and purified (of air and water) R134

a dedicated hose. 

Recycling tank Cylinder used only to receive R134a distilled from the recovery Thermocouples and displays 

K-type thermocouples and readouts to monitor various temperat
Gravimetric Method 

Considerations

• Maintain MAC system tempera

• Control recovery rate to recove

only vapor (i.e., vaporize all liqrefrigerant before recovery)

• Minimize recovery hardware, 

procedural leak sources and fugitive losses
Maintain MAC Temperatur

• Warm up engine compartment

• Heat key components during 

recovery to counteract phasechange cooling

• Monitor temperatures during 

recovery (keep above 20°C)
Control Recovery Rate

• Recover only vapor (minimize liquid 

entrainment)

– Lubricating oil is dissolved in liquid R1– Oil is difficult to distill from recovered 

R134a and a source of error that can (mostly) be avoided

– Watch recovery sight glass for liquid a

recovery port temperature for rapid d(due to liquid)
Evacuation of Recovery Un

and Hose before Test
Manifold & Thermocouple

During Recovery
Weighing Recovery System 

after Recovery
Recharging MAC after R13

was Removed
Anti-tamper Measures Du

a Test
Types of Participant Fleet

• Voluntary participation

• Government and private fleets 

the Sacramento area

• Electric utilities, waste collecti

heavy construction, universitiemunicipalities, and public and private transport
Maintenance Data vs. Dire

Leak Rate Measurement

• Some fleets could only participat

supplying maintenance data

• Some of these data could be use

estimate total refrigerant consumption using a “mass balanapproach

• This approach was expanded to 

public transport fleets statewide
Issues with Mass Balance 

Approach

• Refrigerant consumption not typically tr

for each vehicle

• Useful mainly for homogenous fleets (e

large buses all using the same refrigera

• Estimates overall consumption of refrig

(accounts for all leak sources, including technician practices, faulty service equipment, theft, etc.) instead of just loterm, slow leaks from the MAC
Mass Balance Data Requireme

• Quantities and types of buses• Age range of the buses• Type of refrigerant used in eac

type of bus

• Consumption rate of R134a fo

fleet
Data Analysis

• Estimation of leak measureme

accuracy and precision

• Quality Assurance• Maintenance Data
Determining Accuracy of L

Rate Measurement

• Evacuate and recharge a new 

vehicle

• Recover R134a to determine m

balance closure

– Ideally recover 100% of recharge

• Perform on multiple vehicles• Estimate accuracy and precisio
Data Quality Assurance

• Written, step-by-step instructions and d

sheets

• NIST traceable weights to check the sca

several points during the test

• “Sanity” checks of temperature and pre

readings compared to empirical observa

• Data post-processing included comparis

previous same/similar vehicles of capactranscription error checking, etc.

• Archival of raw data sheets
Results of Measurement 

Accuracy Tests

• Performed accuracy/precision test on 4 new 

vehicles

– First one used a draft procedure

• 3 MACs tested with final procedure had mas

closure of 99% or greater (“losses” ranging 3.7 g to 14.6 g)

• Compare to results from a controlled, lab-lik

setting which achieved closure of 1 g for passenger car MACs(1)

(1) D. Clodic, “Research Study on the Definition of the Implementat

Method of Measurement of Annual Leak Flow Rates (LFRs) of MASystems”, ACEM/Armines Contract, January 2006.
Mass Based Leak Sample 

Overview

• Leak measurements occurred 

from Jan 2009 to Apr 2010

• Total of 65 samples, 3 invalid 

to servicing or failure during intervening period

• 3 converted from R12 to R13• 1 (heavy construction) had 

electric compressors
Sample Counts by Sample 

and Model Year

Sample Bin

1

2

3

4

5

6

7

Model Year

1989

1

1990

1

1991

1

1

1993

1

1995

1

1

1996

1

1997

1

1998

1

1

1

1999

1

3

1

1

1

2000

2

1

2

2

2001

2

2002

1

1

1

1

2003

2

1

1

2004

1

2

2

1

1

2005

2

1

1

2006

1

3

2007

6

2

1

2008

1

1

Sample Bin Key

1 – Full-Sized Transit Buses 2 – Shuttle Buses 3 – Medium-duty Trucks 4 – Heavy-duty Tractor Trucks 5 – Other Heavy-duty Trucks (e.g., waste haulers) 6 – Construction Equipment 7 – Agricultural Equipment 
Sample Counts by Sample 

and MAC Capacity

Sample Bin

1

2

3

4

5

6

7

Capacities (g)

650

1

907

1

1

1080

4

2

1134

1

1

2

1

1190

1

3

2

1

1247

1

1280

1

1310

5

5

2

2

2

1360

1

1

2

2

1

1400

1

1474

2

6

1700

1

1950

2

1

2495

3

Sample Bin Key

1 – Full-Sized Transit Buses 2 – Shuttle Buses 3 – Medium-duty Trucks 4 – Heavy-duty Tractor Trucks 5 – Other Heavy-duty Trucks (e.g., waste haulers) 6 – Construction Equipment 7 – Agricultural Equipment 
“As Received” Charge Ver

Experimental Charge

-1.0-0.8-0.6-0.4-0.2

0.00.20.4

2 2 2 2 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 5 5 5 5 5 6 6 6 7

(mass found - mass recommended)

mass recommended

Sample Bin Number

"As Received" Charge Fraction

-1.0-0.8-0.6-0.4-0.2

0.00.20.4

2 2 2 2 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 5 5 5 5 5 6 6 6 7

(mass charged - mass recommended)

mass recommended

Sample Bin Number

Experimental Charge Fraction
Length of Sample Time, 

Grouped by Sample Bin

0.00.20.40.60.81.01.2

Sample Duration (yr)

Time Allowed for Leakage From MAC

shuttle

md truck

hd hwy tractor

other hd truck

construction

agriculture
Data Point, by Sample Bin

Annualized Leak Rate: Each 

38

-500

0

500

10001500200025003000

Leaked Amount (g/yr)

Annualized Leak Rate 

in Each Sample Bin

shuttle

md truck

hd hwy tractor

other hd truck

construction

agriculture

-0.5

0

0.5

1

1.5

2

2.5

Annual Leak / MAC Capacity (g/g)

Annualized Leak per MAC Capacity

shuttle

md truck

hd hwy tractor

other hd truck

construction

agriculture
Leak Rate Projection Anal

• Linear interpolation used to extrapol

from actual sample period to 12 mo

• Linear assumption probably results i

over-estimate of leak rate because rwould taper off as system working pressure decreases

– Note that several high leak rate system

projected to empty in less than 1-year
Measured Leak Rate Mode

• The measured (annualized) leak rate data w

plotted by various parameters to find obvioumodeling variables (e.g., model year, MAC capacity, etc.)

• Given the variability of the data and the sma

sample size, statistical rigor was not possible

• A model year split at 2006 was selected bec

the voluntary IMAC leak standards the onroamanufacturers agreed to follow (1)

– This is not applicable to offroad equipment, w

are assumed to have the pre-2006 leak rate

(1) Personal communication with Gary Hansen, Red Dot Corporation, April 200
Annualized Leak Rate, by 

Model Year

-500

0

500

10001500200025003000

1985 1990 1995 2000 2005 20

Leaked Amount (g/yr)

Model Year

Annualized Leak Rate vs Model Year
Average Results by Age 

Group, and for All Vehicle

306

103

257

2566

479

2566

-30 -7 -30

-500

0

500

10001500200025003000

05- 06+ All

Leak Rate (g/yr)

Model Year Bin

Average Annualized Leak Rate 

by Model Year Bin and Overall

MY-Bin Count Average Max Min StdDev

 05- 47 306 2566 -30 558

 06+ 15 103 479 -7 125

All 62 257 2566 -30 496
Analysis of Maintenance D

• Assumptions

–Accurate tracking of R134a 

purchases and recycling

–Accurate records of which 

vehicles use R134a

–Average annual R134a purch

equal average annual R134a leaks (mass balance)
Maintenance Record Leak 

Rate Sample

• Five transit bus fleets participa

• Operated all across California

– Los Angeles air basin– Northwest coastal– Northern in-land–Sacramento region–San Joaquin Valley
Maintenance Record Leak 

Rate Analysis

• 329 buses in these fleets were 29- 

45-foot long coaches

– 181 used R134a – The rest used R22 or R407c or none

• Fleet-average leak rate (all buses u

R134a) was 1,340 grams per year

– All types of “leaks” from maintenanc

equipment, maintenance practices, recycling, slow leaks from MAC, MAC system failure, etc.
R134a Emission Inventory 

from Heavy-Duty Fleet

• Use to get an initial estimate of the 

contribution from MD and HD vehiclewhile acknowledging the uncertaintiethe method

• Estimate number of medium-duty an

heavy-duty vehicles with air-conditiocabs

• Multiply the estimated annual leak ra

per vehicle by the number of vehicle
Onroad Heavy-Duty Fleet 

2010 

• EMFAC default fleet

– About 55% of urban and “othe

buses use R134a (per fleet maestimates)

– About 100% of the rest of the 

HD fleet use R134a

• Total estimated fleet = 3,857

(2,684,000 model year 20051,173,000 model year 2006+
Offroad Heavy-Duty Fleet 

2010

• OFFROAD default fleet

– Equipment types with enclos

cab options (per ERG knowle

–Assume only equipment with 

engines 50 HP or larger wouhave MAC

• Total estimated fleet = 316
Estimate: 2010 Leaks of 

R134a directly from HD M

EMFAC Vehicle Category 

Pre-2006 Mg/yr 

(short ton/yr) 

2006+ Mg/yr 

(short ton/yr) 

All Mo

M

(short 

On-Road Equipment

[Pre-2006: 2,684,000*306=821 Mg] [2006+: 1,173,000*103=121 Mg] [All: 3,857,000 * 257=991 Mg] 

821 

(905) 

121 

(133) 

9

(1

Off-Road Equipment

[Age Basis

1: 316,600*306=97 Mg] 

[All: 316,000*257=81 Mg]

97 

(107)

(

Grand Total 1,039 (1,145) 1

(1

Note: These estimates account only for in-use leaks directly from the MAC. 

Leaks from other sources, such as maintenance procedures, are not included and are probably significant for certain vehicle types.

1 Assumes offroad MAC systems emit at the same rate as pre-2006 on-road systems. 
CO2-Equivalent Emissions 

• Assume R134a greenhouse warm

potential of 1,300 (IPCC guidelin

• 1,039 Mg/yr * 1,300 CO2E = 

1,350,000 CO2E Mg/yr from HD 

equipment

• Compare to CARB estimate of 

4,000,000 CO2E Mg/yr from all 

sources
Sources of Uncertainty in 

Estimate

• Undocumented measurement error (e.g., impact of “difficult” MAC 

not assessed in QA)

– A few systems difficult to evacuate without entraining liquids

• Linear projection for annualized leak rate (assumes no tapering of 

– Regional ambient differences may play a role here since cooler areas te

more for defogging windows, less for summer cooling, which may impatolerance of low refrigerant levels

• Only attempts to account for in-use leakage from MA

C

– Maintenance/service leaks for public transport might be significant due 

complexity and “preventative” nature (e.g., quarterly) of service

• The impact of the measurement method has not been empirically 

– Clodic has not seen adverse impacts on systems tested by Ecol des Min– Some evidence from this study indicate that impacts are possible

• Some systems may be “pushed” to leak more due to higher than normal vacu

during testing – especially older systems

• One system could not be tested due to in-leakage of air at high vacuum (high

service vacuum levels)
Summary & Main Conclusi

• MACs in heavy-duty equipment appear to be sig

in the R134a leak inventory

• This leak estimate does not account for leaks du

maintenance, equipment failure, etc

• Linear projection of leak rate to annual rate is p

an over-estimate

• Gravimetric leak measurement method accurate 

about 20 g or 2% of original MAC charge

• A possibly significant source (not accounted for 

method) is the frequent, preventative maintenalarge MACs in public transport vehicles

• Regional usage differences may impact leak rate

for defrost-only is effective at lower charges thafor comfort)
Primary Recommendation

• Survey large fleet operators and certified 

technicians to find obvious sources of leaks othan during typical MAC system operation

– Estimate leak rate ranges from sources other t

in-use MAC (e.g., maintenance) using a mass-approach (net R134a purchased = total leaked

– Compare to leak rates measured in this study 

to update the inventory

– Use results to prioritize future studies aimed a

improving the inventory
End of Presentation

Q&A
Supplementary Slides

• The following slides have some 

details behind the summaries ithe main presentation...
Supplementary Slide –

Equipment Customization

• Permanent joints wherever 

possible

• Custom hose with heavy-duty 

compression fittings

• Ball valves at hose ends• Frequent replacement of gaske

and vacuum oil
Supplementary Slide –

Evacuate-Recharge Sched
Supplementary Slide –

Data from Accuracy Tests

Vehicle 

ID 

Model 

Year 

System 

Capacity 

(g) 

Charge 

(g) 

Recovered 

(g) 

Difference

(g) 

% 

Difference 

Util2-01 2007 907 907.

6 871.7 35.9 4.0 D

Garb2-02 2006 1,190 1,217.9 1,214.2 3.7 0.3 

Priv4-1 2002 1,080 1,104.7 1,094.1 10.6 1.0 Priv5-1 2003 1,758 1,784.4 1,769.8 14.6 0.8 
Supplementary Slide 

–

Bus Fleet and R134a Maintenance Data Summa

Fleet Location Peak 

Month 

Avg. 

Daily 

High 

Avg. 

Annual 

R134a 

Purchase 

R134a Fleet Estimated 

R134a 

Leak 

Rate (per 

vehicle) 

Notes 

Fleet 1 LA Basin 32°C 

(90°F) 

27 kg (60 lb) 

40-ft coaches: 170 total; 51 use R134a, 119 use R407c 

540 g/yr (1.2 lb/yr) 

Approx. 180 lb of R134a used in 3 years for 51 buses. 150 lb purchased, 30 lb already in stock. 

Fleet 2 NW CA 18°C 

(64°F) 

2.0 kg (4.3 lb) 

40-ft coaches: 33 total; 5 w/o AC, 28 use R134a 

68 g/yr (0.15 lb/yr) 

30 lb cylinder of R134a purchased 7/18/2006. About 1⁄2 used so far. 

Fleet 3 N CA 37°C 

(99°F) 

55 kg (120 lb) 

Shuttle buses: 23 total; all use R134a 

2,400 g/yr (5.2 lb/yr) 

Purchase approx. 120 lb R134a per year for shuttle buses 

Fleet 4 Sacramento 

region 

34°C (93°F) 

Not provided 

40-ft coaches: 22 total; all use R134a 

1,100 g/yr (2.4 lb/yr) 

Maintenance records: average of 103 lb R134a per year total for 40-ft coach buses 

Fleet 4 Sacramento 

region 

34°C (93°F) 

Not provided 

Shuttle buses: 21 total; all use R134a 

2,700 g/yr (5.9 lb/yr) 

Maintenance records: average of 138 lb R134a per year total for cutaway buses 

Fleet 5 San 

Joaquin Valley 

34°C (94°F) 

180 kg (390 lb) 

Shuttle buses: 32 total; all use R134a. 29 ft to 45 ft coaches: 104 total; 80 using R134a, 24 using R22. 

1,600 g/yr (3.5 lb/yr) 

Projected “year to date” use as of Nov 4 (325.7 lb R134a & 147.1 lb R22) to end of year. 
Supplementary Slide –

Estimate of 2010 On-road HDVs with R134a

EMFAC Vehicle Category Pre-2006 Count 2006+ Count

04 - Medium-Duty Trucks (T3) 1,722,000 746,00005 - Light HD Trucks (T4) 239,000 188,00006 - Light HD Trucks (T5) 119,000 49,00007 - Medium HD Trucks (T6) 188,000 70,00008 - Heavy HD Trucks (T7) 179,000 51,00009 - Other Buses 9,000 3,00010 - Urban Buses 7,000 1,00012 - School Buses 23,000 4,00013 - Motor Homes 198,000 61,000Total 2,684,000 1,173,000
Supplementary Slide –

OFFROAD Equipment With MAC

• Rollers 

• Trenchers 

• Cranes 

• Rough Terrain Forklifts 

• Rubber Tire Loaders 

• Tractors/Loaders/Backhoes 

• Skid Steer Loaders 

• Other Construction 

Equipment 

• Forklifts 

• Sweepers/Scrubbers 

• Other General Industrial 

Equipment 

• Other Material Handling 

Equipment 

• Agricultural Tractors 

• Combines 

• Balers 

• Sprayers 

• Swathers 

• Other Agricultural 

Equipment 

• Cargo Tractor • A/C Tug, Narrow Body 

• A/C Tug, Wide Body 

• Air Conditioner (GSE) • Baggage Tug 

• Bobtail 

• Fuel Truck • Lavatory Truck 

• Maintenance Truck • Passenger Stand 

• Sweeper 

• Service Truck • Catering Truck 

• Hydrant Truck 

• Scrapers 

• Excavators 

• Graders 

• Off-highway Truc• Rubber Tire Doze

• Crawler Tractors 

• Off-Highway Tra• Skidders 

• Fellers/Bunchers • Other GSE 

• Other Workover 

Equipment 

• Drill Rig • Military Tactical 

Equipment 

• Dredger 

• Other Dredging