1. VDA OEM Safety concept for R744-A/C-systems in passenger cars
working group
of VDA OEMs
Thank you very much for the welcome and the kind introduction.
I am very glad to be here and speak for our so called ad hoc working group of VDA OEMs.
This group was created and mandated by the VDA in January 2003 to develop a safety concept for the R744-A/C-system
The members of this group are Robert Mager BMW - Jürgen Wertenbach DC - Dietmar Böhme Ford - Dirk Lücke Opel - Peter Hellmann VW.
Most of them are present today, so if you should have any further questions, tonight or tomorrow, please ask them, too.
The result of our work is the following proposal for a safety concept, we want to discuss with you.
Thanks to the just heard presentation of Erin Birgfeld, you already got an idea of what a safe system has to fulfill in general.
I want to build on that and now focus on how we make the R744-A/C-System safe and avoid the just shown scenarios with maximum leaks in the evaporator.

2. Content Standard R744-air-conditioning-system Basic requirements
Safety targets
Safety barriers in the refrigerant cycle
Safety requirements for the cabin, focus on evaporator
Safety requirements engine compartment
Secondary safety measures / e.g. odorization
Summary
But first let me give you an overview of what I will show in the following.
I’ll begin the presentation by introducing the standard R744-A/C-system, which was defined by German OEMs at the HDT-meeting in Starnberg last year.
This is the starting point of our safety concept proposal.
To introduce you further into the task of developing this saf. conc. I’ll continue with - what the other basic requirements are - what operating conditions have to be considered and - what safety targets must not be violated
Then, we are prepared to go on to the saf.conc. itself, which consists of two parts.
First the barriers or installations in the ref.cyc. which have already been defined in the stand.sys. to keep the system in a safe condition.
And second the saf.requirements for the cabin, which are the core of our proposal, to protect driver and passengers.
In the end, this will lead us to the “safe evaporator”.
Tiger Team meeting 2008
St. Wiedemann BMW AG

3. Standard R134a vs. R744-A/C-system
Internal Heat
Exchanger
Combined module
Accumulator
Gascooler
Condenser
low pressure
relief device
with high pressure
relief device
Compressor
P/T
Sensor
All of you know the basic ref.cyc. with compr., cond., exp.dev. and evap.
and all of you also know the add. feature of the R744-refrigerant-cyc.
but since there are still many possibilities to specify their arrangement and their operation, we Ger. OEMs defined a uniform R744-A/C-sys.
because it is the basis of our saf. conc., I will now describe the arrangement of the components, and later I will also discuss the operating limits
the compressor, which makes the sys.running, has to be equipped with the high press.rel.dev. as today.
The press.sensor is directly positioned after the compr. Because of the very hot gas temp. at the compr.outlet, it has to be combined with a temp.sensor.
The condenser is now the gascooler because the hot gas is typically cooled and not condensed.
for better efficiency, the refr. is additionally cooled in the int.heat exchanger
after that, it is expanded with a fixed orifice or a variable valve to the low pressure level
there, the refrigerant flows from the evaporator into the accumulator, then through the int.heat.exch. back to the compressor
an additional press.rel.dev. is necessary on the low press.side for safety during standstill; its position is optional between evaporator and compr.
beside the separate arrangement of accu. and IHX, a combined module is also feasible; further options and combinations are not possible.
Expansion
device
Evaporator
Tiger Team meeting 2008
St. Wiedemann BMW AG

4. Basic requirements
Based on standardized R744-systems and components according to relevant standards (e.g. SAE J-doc)
Applicable to all car segments
Applicable from manually to automatically controlled AC-systems
As I mentioned before, this stand.sys. is basis and starting point for our safety concept and thus, our first basic requirement
because the automobile industry produces all kinds and all sizes of passenger cars, our second requirement is that the saf.conc. is applicable to all car segments
with our third requirement, it is similar.
as automatically controlled A/C-sys. will not become standard in the near future, all kinds of A/C-sys. down to completely manually controlled ones have to be considered
so as you can see: with our safety concept, we want to be as general as possible
Tiger Team meeting 2008
St. Wiedemann BMW AG

5. Safety targets .
acc. Safety-Study of Risa Safety Analysis Ltd., VDA Wintermeeting 2002
To protect driver from loss of concentration and reaction
To protect all passengers from health problems
To protect persons (service personnel included) outside the vehicle from injury
Before I now can present the concept you waiting for, I have to introduce one last topic, the safety targets
These targets were already presented by the Risa Safety Analysis Ltd. two years ago in Saalfelden and last year in Phoenix
for those who don’t know the Risa which is located in Berlin, I have some details. The Risa develops safety studies for all kinds of industries, from power plants to transportation systems
The Risa also analysis for the automotive industry and conducted a first safety-study for R744 in cooperation with the VDA four years ago.
For the following saf.con.proposal, Risa assisted us to approve its feasibility by conducting an FMEA acc. int.stand., but back to the safety targets:
the saf.targets, we have to fulfill, are in order of their importance - first to protect the driver, because the earliest impact is on his concentration and reaction and - second to protect all passengers from health problems
Third, we have to protect all persons outside the car, those uninvolved like pedestrians and those involved like technicians.
the forth target is to avoid any interference on any saf.relevant systems in the car like on electronics or on brakes
because this last target is the matter of specific design and packaging of each car model, we will, in the following, focus on the first three.
I will begin with the third, the protection of people outside, and for that, I’ll define the saf.barriers in the ref.cyc.
Tiger Team meeting 2008
St. Wiedemann BMW AG

6. Safety barriers in the refrigerant cycle: Pressure and temperature limits
Max. operating temperature 165°C
short time 180°C (less 5 min.)
Max. release pressure (high side)
17 MPa below SAE J639 2 4 6 8 10 12 14 16 18 20 50
150
250
350
450
550
spec. Enthalpie h [kJ/kg]
Refrigerant pressure [MPa]
140°C
20°C
40°C
80°C
60°C
160°C
120°C
100°C
Max. release pressure (low side)
13 MPa below SAE J639
Max operating (cut off)
pressure 14 MPa
Max. working
pressure 13,3 MPa
I am aware, that the expression “barrier” could cause misunderstanding in this context, so let me give you our def. of saf.bar.:
it is a safety installation, active or passive, that keeps a system within certain limits for safety reasons.
If one saf.bar. or inst. fails, a next saf.bar. or inst. has to engage
to visualize these saf.bar. in the ref.cyc., I like us to take a look at the press-enthalpy-diagram for R744 and, as promised before, come back to the stand.sys. and its pressure and temperature limits
Before the ref.cyc. is switched on, it has to be checked if the press. is within the upper and lower press. limit to prevent start-up difficulties.
The absolute limit for the not-operating cyc. is at a max. of 13 MPa for the low press.rel.dev. to be activated at the lastest with 2 MPa tolerance downward.
Once the cycle is running, the focus is on the high pressure with a max. of 17 MPa for the activation of the high pre.rel.dev. and again 2 MPa tol. downward
To avoid the press.rel.dev. to be activated, the max.operating pressure is set at 14 MPa where the compressor is cut off
for stabile compressor control, however, we defined the max.working pressure at 13,3 MPa, where the compressor displacement is reduced, but not cut-off
additionally important for the comp.control is the discharge or outlet temp., that can become much higher compared to R134a. The limits are 175°C for permanent operation and 190°C for short periods up to 5 min..
Max. switch-on pressure 9,5 MPa
Min. switch-on pressure 2,5 MPa
Tiger Team meeting 2008
St. Wiedemann BMW AG

7. Safety barriers in the refrigerant cycle
Compressor switch-on depending on pressure and temperature
Limitation of discharge pressure and temperature
Pressure relief devices on high and low pressure side
Material strength to protect components against breaking and bursting according to SAE J639
After this illustration of press. and temp. limits, I like to derive the detailed saf.barriers or installations in the right order of their engaging:
The first barrier is the conditional compressor start, which depends on the pressure and temperatures in the not operating state.
Is everything all right and the compr. running, the comp.control is the barrier or installation to avoid high pressures and temperatures
if it fails, the press.rel.dev. on high-press.side is the next barrier.
And not to forget the press.rel.dev. on the low-pressure side, which is the barrier for the switched-off sys., specially when overfilled.
should these press.rel.dev. fail too, the minimum design or burst pressure is still twice the max.relief.press., which is 34 MPa on the high-press.side and 26 MPa on the low-press.side, according SAE J639
thus, breaking or even bursting of any cyc.component cannot occur, neither in standstill nor during operation of the ref.cyc.
And therefore, our third saf.target, the protection of persons outside, is not violated at any time.
What is left now, are the first two targets, which relate to the passenger compartment
Tiger Team meeting 2008
St. Wiedemann BMW AG

8. Safety requirements for the cabin
No servicable refrigerant-side connection fitting inside the cabin
Low pressure side relief device
Mechanical fixing of the evaporator in- and outlet pipe inside the HVAC-unit
Safe evaporator
Unlike the just discussed saf.bar. in the ref.cyc., which are already defined, the following safety features for the cabin are requirements, we now and here propose
the target is to protect the driver from loss of concentration and reaction and to protect all passengers from any damage to health
to avoid such interference, the CO2-level in the cabin must remain below certain levels and therefore, our saf.requir. are:
First, because screwed connections are not as reliable as brazed or welded connections, all such connections of the ref.cyc. have to be outside the cabin.
In other words, all ref.cyc. parts that are in the HVAC-unit, like the evap. and its in- and outlet-pipes, have to be brazed.
Because once the evap. and its pipes are in the HVAC, they cannot be checked again, so specially the in- and outlet pipes need mechanical support in the HVAC to avoid any damaging impact during assembly or operation.
We think these two requirements can be handled, it just needs more planning for the HVAC
However, our third requirement is more challenging, as we want the “safe evaporator”.
Tiger Team meeting 2008
St. Wiedemann BMW AG

9. Definition of the “safe evaporator”
Fundamental safe, i.e. no breaking or bursting under any possible operating condition
Definition of leakage rates and leakage behavior
Complete and further enhanced quality assurance for - design and testing (wall thickness, material and corrosion properties) production (well known, industrialized, reliable flat tube design) storage and transport - assembly and final inspection
Before you wonder, what this could mean, I’ll give you the definition of the saf.evap. right away.
With saf.evap. we mean fundamental safe, which means no breaking or bursting under any op.cond. in the car at all
bursting in the sense of flying parts is no big deal for the evap. I think everybody can agree to that.
Breaking in the sense of longer cracks is more difficult to avoid, but doable
The real challenge arises with the leckage rates and sizes.
The saf.evap. must not have any leak during its whole life cyc., but in contrast to breaking and bursting, exceptions are possible, which I will tell you in a minute.
Just let me complete the def. of the saf.evap. and show you what is needed to guarantee this.
What we demand is a complete chain of qual.ass. for evap and HVAC
this starts with the planning of the concept for a new car, continuous with the production and ends with the final inspection at the OEM’s assembly line. I will give you more details in a minute, too, because there is one last point of our def. of the saf.evap.
It is the regular inspec. if the introduced stand.are fulfilled.
I think, this speaks for itself and needs no further explanations.
Regular inspection of fulfilling introduced production standards and worker certification
Tiger Team meeting 2008
St. Wiedemann BMW AG

10. Safe evaporator: planning and design
Material selection
Fundamental design
Robust design of the evaporator and its in- and outlet pipe
Definition of proper evaluation tests regarding increased safety aspects
Now, the decisive question is, how to achieve that?
As I already said, a complete and perfect qual.assurance is necessary, which starts with planing and design.
for the manufacturer of the evap., it already begins today with the right material selection.
Next step is the fundamental design of the evap.core, but also of its in- and outlet pipes and of the HVAC-unit.
The HVAC is important, because the evaporator has to be fixed softly inside and its pipes need mechanical support.
most important, however, are proper test procedures for evaluating the evap. and HVAC including new or at least more extensive pressure-impuls-, temperature-cycling-, vibration- or corrosion-test
These tests have to be developed together, by suppliers and OEMs.
Tiger Team meeting 2008
St. Wiedemann BMW AG

11. Safe evaporator: production
Life cycle test for each evaporator design: e.g. - pressure-impulse-test - corrosion-test - leak-test burst-test
Full-automatic brazing of evaporator core, including in- and outlet pipe, in approved process
100%-leak test of evaporators in vacuum chamber at 9 MPa
The next and probably most critical part of the qual.ass. is completely the task of the suppliers, which is the production of the evap. and HVAC
It already begins with the examination of the semifinished parts by permanent non-destructive tests like ultrasonic and x-ray as well as further analysis concerning corrosion.
For best quality only full-automatic brazing of core and pipes is acceptable. Additional repair brazing cannot be allowed
to document the quality, daily tests of each production lot are necessary - starting with pressure-impulse-test - continuing with leak-test and - finishing with burst-test
a corrosion test on a daily basis would also be great
finally, the 100%-leak-test should be in the vacuum chamber, best with R744, at a pressure that is clearly above the max. low pressure for the evaporator with 13 MPa; we suggest 18 MPa
also important, but here not further discussed, the proper qualification of the employees in production, which has to be good anyway
100% leakage and functional testing of the final assembled HVAC units
Tiger Team meeting 2008
St. Wiedemann BMW AG

12. Safe evaporator: transport and assembly
Full monitoring of storing and transport - at supplier - from supplier to OEM - at OEM
Proper assembly - cockpit mounting - connection of pipes - evacuation, charge and test of the refrigerant cycle % functional test at end of line
Now once the evap. is produced and mounted into the HVAC, negative impacts are still possible until it is finally in the car.
Therefore, full and detailed monitoring is necessary for storing and transport.
During all phases of transport, else at the supplier or on the way from supplier to OEM or in the end, at the OEM, complete monitoring is quite a challenge.
Many different persons are involved in the handling of these parts, the means of transport are very manifold and thus, all kinds of incidents or even accidents are possible.
So if the evaporator, alone or mounted in the HVAC, suffers any abrupt acceleration, for example falls hard, no repairing or further use is allowed.
At the pre- and final-assembly-line, proper handling is necessary for mounting the HVAC in the cockpit and the cockpit in the car, but also for coupling the refrigerant cyc. pipes to the evaporator in the HVAC.
This very accurate care is inevitable, because the final, last check of the cycle with evacuating, charging and leak test allows no direct access to the evaporator.
Tiger Team meeting 2008
St. Wiedemann BMW AG

13. Safety requirements for the engine compartment
Service by trained personel only
Warning label to prevent DIY
Protective gear mandatory (goggles, gloves)
High pressure side relief device
Special designed refrigerant connection fittings for a safe pressure release according SAE standards
Unlike the just discussed saf.bar. in the ref.cyc., which are already defined, the following safety features for the cabin are requirements, we now and here propose
the target is to protect the driver from loss of concentration and reaction and to protect all passengers from any damage to health
to avoid such interference, the CO2-level in the cabin must remain below certain levels and therefore, our saf.requir. are:
First, because screwed connections are not as reliable as brazed or welded connections, all such connections of the ref.cyc. have to be outside the cabin.
In other words, all ref.cyc. parts that are in the HVAC-unit, like the evap. and its in- and outlet-pipes, have to be brazed.
Because once the evap. and its pipes are in the HVAC, they cannot be checked again, so specially the in- and outlet pipes need mechanical support in the HVAC to avoid any damaging impact during assembly or operation.
We think these two requirements can be handled, it just needs more planning for the HVAC
However, our third requirement is more challenging, as we want the “safe evaporator”.
R744 AC-loop components according SAE standards
Definition of maximum R744 charge on label
Service equipment and proceedings according SAE st.
Tiger Team meeting 2008
St. Wiedemann BMW AG

14. Safe system superiority to secondary safety measures
VDA OEMs prefer safe designed systems more than “state of the art” components without enhanced safety through design, process and testing improvements
Design and production of the AC-loop has to avoid any hazardous failure => components according J-SAE
In case that SAE standards and design rules cannot be guaranteed, VDA OEM recommend secondary safety measures (Several possibilities)
Now once the evap. is produced and mounted into the HVAC, negative impacts are still possible until it is finally in the car.
Therefore, full and detailed monitoring is necessary for storing and transport.
During all phases of transport, else at the supplier or on the way from supplier to OEM or in the end, at the OEM, complete monitoring is quite a challenge.
Many different persons are involved in the handling of these parts, the means of transport are very manifold and thus, all kinds of incidents or even accidents are possible.
So if the evaporator, alone or mounted in the HVAC, suffers any abrupt acceleration, for example falls hard, no repairing or further use is allowed.
At the pre- and final-assembly-line, proper handling is necessary for mounting the HVAC in the cockpit and the cockpit in the car, but also for coupling the refrigerant cyc. pipes to the evaporator in the HVAC.
This very accurate care is inevitable, because the final, last check of the cycle with evacuating, charging and leak test allows no direct access to the evaporator.
Tiger Team meeting 2008
St. Wiedemann BMW AG

15. Odorized R744 as possible secondary safety measure
Odorization of non smelling hazardous gases is state of the art (e.g. natural gas, liquefied gas, CO2 for stationary fire extinguishers)
Odorization is an accepted safety measure by legislator and population since decades
Important criteria for selection: Already accepted odorant for natural gas application Approved warning agent with field experience in handling and chemical properties Odor different to any other smelling agent in car
Now once the evap. is produced and mounted into the HVAC, negative impacts are still possible until it is finally in the car.
Therefore, full and detailed monitoring is necessary for storing and transport.
During all phases of transport, else at the supplier or on the way from supplier to OEM or in the end, at the OEM, complete monitoring is quite a challenge.
Many different persons are involved in the handling of these parts, the means of transport are very manifold and thus, all kinds of incidents or even accidents are possible.
So if the evaporator, alone or mounted in the HVAC, suffers any abrupt acceleration, for example falls hard, no repairing or further use is allowed.
At the pre- and final-assembly-line, proper handling is necessary for mounting the HVAC in the cockpit and the cockpit in the car, but also for coupling the refrigerant cyc. pipes to the evaporator in the HVAC.
This very accurate care is inevitable, because the final, last check of the cycle with evacuating, charging and leak test allows no direct access to the evaporator.
Tiger Team meeting 2008
St. Wiedemann BMW AG

16. Chemical properties of odorant (Odor S-Free©)
US and German MSDS available
Type approval as warning agent according E DIN
Certified for gas application according German standard DVGW An ISO certification is expected for 2008
Main compounds are widely used acrylates (raw material in chemical industry, several tons/a)
Now once the evap. is produced and mounted into the HVAC, negative impacts are still possible until it is finally in the car.
Therefore, full and detailed monitoring is necessary for storing and transport.
During all phases of transport, else at the supplier or on the way from supplier to OEM or in the end, at the OEM, complete monitoring is quite a challenge.
Many different persons are involved in the handling of these parts, the means of transport are very manifold and thus, all kinds of incidents or even accidents are possible.
So if the evaporator, alone or mounted in the HVAC, suffers any abrupt acceleration, for example falls hard, no repairing or further use is allowed.
At the pre- and final-assembly-line, proper handling is necessary for mounting the HVAC in the cockpit and the cockpit in the car, but also for coupling the refrigerant cyc. pipes to the evaporator in the HVAC.
This very accurate care is inevitable, because the final, last check of the cycle with evacuating, charging and leak test allows no direct access to the evaporator.
Possibility to ventilate due to: Zero ODP and GWP (EPA Paper „Draft Analysis of 1999 TRI Data) Sulfur free
Tiger Team meeting 2008
St. Wiedemann BMW AG

17. Type approval and warning level for odorants
Definition: Warning level for odor is the medium odor intensity, at which every person with average possibility to smell and average physiological condition surely can detect the odorant. (Odor level 3)
Additional statistical tests: testing persons evaluated the smell impression of Odor S-Free© in comparison to THT and TBM. The smell impressions have been similar. To quote:
“ … Odor test carried out at the University of Karlsruhe proved the warning character of the sulfur-free odorant in direct competition with sulfur containing odorants and showed that this odor is well distinguishable from every day smells.“
Now once the evap. is produced and mounted into the HVAC, negative impacts are still possible until it is finally in the car.
Therefore, full and detailed monitoring is necessary for storing and transport.
During all phases of transport, else at the supplier or on the way from supplier to OEM or in the end, at the OEM, complete monitoring is quite a challenge.
Many different persons are involved in the handling of these parts, the means of transport are very manifold and thus, all kinds of incidents or even accidents are possible.
So if the evaporator, alone or mounted in the HVAC, suffers any abrupt acceleration, for example falls hard, no repairing or further use is allowed.
At the pre- and final-assembly-line, proper handling is necessary for mounting the HVAC in the cockpit and the cockpit in the car, but also for coupling the refrigerant cyc. pipes to the evaporator in the HVAC.
This very accurate care is inevitable, because the final, last check of the cycle with evacuating, charging and leak test allows no direct access to the evaporator.
Tiger Team meeting 2008
St. Wiedemann BMW AG

18. Status of testing
Oil compatibility approved (high ppm for water and odorant)
Durability and long term chemical stability of odorant approved
Approval of no chemical reaction between odorant and R744
Short term compressor tests showed no negative effects to materials of compressor
Now once the evap. is produced and mounted into the HVAC, negative impacts are still possible until it is finally in the car.
Therefore, full and detailed monitoring is necessary for storing and transport.
During all phases of transport, else at the supplier or on the way from supplier to OEM or in the end, at the OEM, complete monitoring is quite a challenge.
Many different persons are involved in the handling of these parts, the means of transport are very manifold and thus, all kinds of incidents or even accidents are possible.
So if the evaporator, alone or mounted in the HVAC, suffers any abrupt acceleration, for example falls hard, no repairing or further use is allowed.
At the pre- and final-assembly-line, proper handling is necessary for mounting the HVAC in the cockpit and the cockpit in the car, but also for coupling the refrigerant cyc. pipes to the evaporator in the HVAC.
This very accurate care is inevitable, because the final, last check of the cycle with evacuating, charging and leak test allows no direct access to the evaporator.
Compatibility between desiccant and odorant approved
Tiger Team meeting 2008
St. Wiedemann BMW AG

19. Remaining issues
Design and testing Long term compressor durability with odorized R Final material compatibility with elastomers in AC-loop - Finalized purity standard for R744 odorized
Production Infrastructure concept for R744 odorized in plant
Now once the evap. is produced and mounted into the HVAC, negative impacts are still possible until it is finally in the car.
Therefore, full and detailed monitoring is necessary for storing and transport.
During all phases of transport, else at the supplier or on the way from supplier to OEM or in the end, at the OEM, complete monitoring is quite a challenge.
Many different persons are involved in the handling of these parts, the means of transport are very manifold and thus, all kinds of incidents or even accidents are possible.
So if the evaporator, alone or mounted in the HVAC, suffers any abrupt acceleration, for example falls hard, no repairing or further use is allowed.
At the pre- and final-assembly-line, proper handling is necessary for mounting the HVAC in the cockpit and the cockpit in the car, but also for coupling the refrigerant cyc. pipes to the evaporator in the HVAC.
This very accurate care is inevitable, because the final, last check of the cycle with evacuating, charging and leak test allows no direct access to the evaporator.
Service Supply chain for aftersales supply with R744 odorized - Purity standard with container and fitting definition
Tiger Team meeting 2008
St. Wiedemann BMW AG

20. Summary
Basis is standard R744-A/C-system with safety installations to protect persons in and outside the car
“safe evaporator” to protect driver and passengers
FMEA according international standards of SAE J1739 and J2773 Safety Analysis
Applicable to - all car segments and - all A/C-systems according SAE standards
I think you now have got enough information about the safe R744-A/C-system and it is time for discussion.
But before, please let me quickly summarize the idea, motivation and intention of our proposal.
Our starting point was the standard R744-A/C-system, which required a saf.conc. and in the end, needs safety installations.
For the ref.cyc. itself, we have already defined and specified those barriers or installations. They guarantee the safe operation of the cyc. and the protection of all persons outside the car.
To protect the persons inside the car from too high CO2-concentrations, we, the adhoc working group, now propose the “safe evaporator”.
We developed this saf.conc.proposal together with the Risa, which conducted a FMEA according int.stand. and confirmed us that the safe evaporator could work.
At first glance, this concept seems to be so simple, because it needs no additional safety features, as we want it to be applicable to all car segments and all A/C-sys.
But to make the R744-A/C-system appropriately safer than today’s R134a-A/C-sys., this safe evaporator, as you all know, is quite a challenge.
Thank you very much for your attention.
Appropriately higher safety than today
Tiger Team meeting 2008
St. Wiedemann BMW AG