1. UNEP Workshop on HFC Management
Bangkok, Thailand
20, 21 April 2015
Technical Issues: Session 3 Challenges and Opportunities in addressing high GWP HFC’s in Mobile Air Conditioning (MAC) Options for Existing Systems / Equipment (Drop in / Retrofit)
SH Kapoor
Technical Chief (Climate Control)
TATA Motors Limited, India

2. Low GWP Refrigerants: Drop In / Retrofit Options?
Refrigerant Parameters for Operating Limits: 0°C Evaporating Temperature and 55°C Condensing Temperature
Parameter
HFC134a
(GWP=1430)
HFO1234yf
(GWP=4)
HFC152
(GWP=124)
R744
(GWP=1)
Suction Pressure (bar-abs)
2.9
3.2
2.6
34.9
Discharge Pressure (bar-abs)
14.9
14.6
13.3
115
Pressure Ratio
5.1
4.6
3.3
Enthalpy of Vaporization (kJ/kg)
198.6
163.3
307.1
231.3
Vapour Specific Volume (m3/kg)
0.069
0.057
0.119
0.0103
R1234 yf
R134a Cooling Performance cannot be matched with R1234yf as a ‘Drop In’
Equivalent performance and durability requirements need to be met with significant re-engineering of MAC system components
R152a
Superior Cooling Performance can be attained with R152a; cannot be ‘Drop In’ due to flammability risk in case of leak (cab/engine)
Potential Secondary Loop refrigerant with down sized MAC system components for matching R134a Cooling Performance
R744
R134a Cooling Performance cannot be matched with R744 at higher ambient temperatures (Tc=31°C)
All MAC system components require significant re-engineering due to very high system pressures and hence ‘Drop In’
is not a feasible option

3. Secondary Loop MAC: R152a, R1234yf
Parameter
Opportunity
Challenge
Design
With proper engineering design, freeze protection and optimization, secondary loop MAC’s are suitable for all climates
Complexity of integration / packaging of the additional components (small cars)
Added components, increased weight
Performance
Cabin cooling not compromised during extended idle and long idle stops (stop / start traffic)
Homogeneity of air temperatures across cooling coil due to absence of phase change
Minimizes fluctuations in vent outlet and cabin temperature
Reduce engine load during acceleration by switching off compressor (fuel economy)
Timing powered cooling – switch on compressor when engine is at high energy efficiency
Reduced MAC system noise transmitted from thermostatic expansion valve (TXV) inside passenger cabin
Increased time to ‘pull down’ temperature to comfortable levels due to thermal inertia of coolant
Development and integration of Engine Management System (EMS)
Coolant pump power consumption
Refrigerant Circuit
Absence of oil trapping issues in dual AC MAC systems particularly when rear unit is turned off

4. Secondary Loop MAC: R152a, R1234yf
Parameter
Opportunity
Challenge
Material Cost
Reduced refrigerant charge offsets cost of additional components even for dual AC MAC systems (multiple cooling points)
Reduced frequency of refrigerant recharges over a vehicles service and maintenance life
(lower ownership costs)
Environment
Use of environment friendly low GWP refrigerant R152a / R1234yf
Reduced refrigerant charge and life cycle GHG emissions
Safety
Reduced refrigerant charge lowers fire risk
Refrigerant separated from passenger compartment
Deploy refrigerant leak sensor and relief valves for quick release of refrigerant to atmosphere (thru wheel arch)
Charged components placed in wind stream and away from ignition sources

5. Summary:
Drop in / Retrofit Refrigerant Options for Existing Systems / Equipment
HFO1234yf is gaining acceptance as an alternate MAC refrigerant option due to its low GWP of 4 but is mildly flammable
HFO1234yf as a drop in refrigerant for a car already in service poses the challenge of deterioration in cooling performance and risk of cross contamination with existing PAG oil
Not all compressors are available with PAG oil compatible with HFC134a and HFO1234yf
This can lead to compressor durability issues and hence drop in is not recommended

6. Summary:
Drop in / Retrofit Refrigerant Options for Existing Systems / Equipment
HFC152a is a low GWP, slightly flammable refrigerant with superior properties and high potential of downsizing MAC system components like compressor and condenser
The flammability risk associated with HFC152a and HFO1234yf can be mitigated by reducing the refrigerant charge, deployment of a Secondary Loop (SL) and use of leak sensors and relief valves
The SL – MAC in combination with power train technologies has a high potential of improving overall energy efficiency and reducing carbon footprint
To evaluate the opportunity of using SL – MAC with HFC152a and HFO1234yf, understand the challenges related to cooling performance, safety, power train technology and cost impact, a demonstrator car project needs to be initiated by relevant stakeholders

7. End of Report
Thank You for your Attention!
Questions

8. MAC Refrigerants: Past, Present and Future
Status
Phased Out
Current
Future: Potential Alternatives
Parameter
R12 (CFC)
R22 (HCFC)
Building Air Conditioning
R134a (HFC)
R1234 yf (HFO)
R152a (HFC)
R744
Bonding
IUPAC Name
Dichloro Difluoro Methane
Chloro Difluoro
Methane
1,1,1,2 – Tetra Fluoro
Ethane
2,3,3,3 – Tetra Fluoro
Propene
1,1 – Difluoro
Carbon Dioxide
ODP
1 (2 Chlorine Atoms)
0.05 (1 Chlorine Atom)
GWP (100yr) (IPCC AR4)
10,900
1810
1430
(4 Fluorine Atoms) 4
124 (2 Fluorine Atoms) 1
Atmospheric Lifetime
100 years
12 years
14 years
0.03 years
(due to weaker double bond)
1.4 years
>100 years
Flammability (ASHRAE) A1
A2 L (Mildly)
A2 (Slightly)
Critical Temperature
111.9°C
96.14
101.06°C
92.42°C
113.26°C
31.04°C
Normal Boiling Point
-29.8°C
-40.7°C
-26.3°C
-29.4°C
-25°C
-78°C H F C C Cl F C Cl F H O C
A1 : No flame propagation
A2 : Slightly flammable- Lower flammability 60°C: > 100 g/m3 or Heat of Combustion < 19 Mega J/kg
A2L : Mildly flammable-Lower flammability 60°C: > 100 g/m3 and Heat of Combustion < 19 Mega J/kg With Maximum Burning Velocity < 10 cm/s