Safety research of A2L/A3 refrigerants and risk assessment in Japan Eiji Hihara The University of Tokyo 1
Trade-off relationship between GWP and flammability To reduce the emission of greenhouse gases including HFCs from refrigerating and air-conditioning equipment, a change in refrigerants from HFCs to lower GWP refrigerants is one of the key issues. R1234yf, R32, and R290 have much lower GWPs than R410A. R410A is nonflammable, but R1234yf, R32, and R290 are flammable. Because the burning velocities of R1234yf and R32 are smaller than 10 cm/s, flammability of R1234yf and R32 is mild and it is categorized under the A2L class of the ASHRAE. Refrigerant R410A R32 R1234yf R717 R290 Boiling temperature, ºC -51.4-51.7-29.4-33.3-42.1 Critical temperature, ºC 71.3 78.1 94.7 132.4 96.7 GWP (100 years) 2088 675 4 <1 <3 Burning velocity (cm/s) - 6.7 1.5 7.2 38.7 LFL [vol %] - 13.3 6.2 15 1.8 UFL [vol %] - 29.3 12.3 28 9.5 Minimum ignition energy (mj) - 15 500 21 0.246 Flammability 1 2L 2L 2L 3 2
Research committee on risk assessment of A2L/A3 refrigerants in JSRAE For promoting the use of low-gwp refrigerants, relaxation of the legal regulation of mildly flammable refrigerants is necessary. Before relaxing regulations, risk assessment of flammable refrigerants should be carried out, and reasonable guidelines for safe design and safe use of refrigerating and air-conditioning equipment with flammable refrigerants should be formulated. A project sponsored by the New Energy and Industrial Technology Development Organization (NEDO) on the performance and safety of new refrigerants started in 2011. The Japanese Refrigeration and Air Conditioning Industry Association (JRAIA) also started the risk assessment of flammable refrigerants. To exchange knowledge of safety issues and risk assessments among researchers and manufacturers, a research committee was established by the Japan Society of Refrigerating and Air Conditioning Engineers (JSRAE). 3
Organization of the research committee for safety of A2L/A3 refrigerants Japan Society of Refrigerating and Air Conditioning Engineers, JSRAE Secretary: Fujimoto Chair: Hihara University of Tokyo Japan Automobile Manufacturers Association, JAMA Japanese Refrigeration and Air-conditioning Industry Association, JRAIA Tokyo University of Science, Suwa Kyushu University National Institute of Advanced Industrial Science and Technology, AIST Observers -NEDO -METI -KHK 4
Methodology of Risk Assessment [Probability of fire accident]=[rapid leakage] X [High concentration of refrigerant] X [Ignition source] Concentration higher than lower flammability limit Ignition Existence of an ignition source Rapid leakage 5
Numerical simulation of diffusion of refrigerant leaking in a room The University of Tokyo 6
Purpose Flammable refrigerants leakage = Risk of fire accident Risk = Flammable gas volume, presence time, and existence probability of ignition source Flammable gas volume and presence time etc are numerically analyzed when a refrigerant leaked into a living space Target refrigerants R32, R1234yf, R1234ze, R290 Target equipments RAC. for home, VRV, Chiller Located Indoor, Outdoor, Machine room 7
Leakage scenarios for split air conditioners Position of leakage No. Refrigerant Wall-mounted indoor unit Floor-standing indoor unit Outdoor unit Amount [g] Flow rate [g/min] 1 R32 1000 250 2 R1234yf 1400 350 3 R32 1000 125 4 R1234yf 1400 175 5 R32 1000 1000 6 R1234yf 1400 1400 7 R290 500 125 8 R290 200 50 9 R32 1000 250 10 R1234yf 1400 350 11 R32 1000 250 12 R1234yf 1400 350 Ventilation None None None None None 0.5 m/s 8
Result:Concentration distribution(no.1) Because the density of R32 is higher than air, R32 flows down to the floor, and is accumulated. The concentration was lower than the LFL on the floor. UFL Refrigerant:R32 Amount:1000 g Flow rate:250 g/min LFL ¼ LFL 9
Result:Combustible gas region(no.1) The combustible gas region existed just below the air outlet of the indoor unit only. The flammable gas volume was very small. After leakage, the combustible gas region vanished in less than a second. Refrigerant:R32 Amount:1000 g Flow rate:250 g/min 10
Result:Combustible gas region(no.1) The combustible gas region existed just below the air outlet of the indoor unit only. The flammable gas volume was very small. After leakage, the combustible gas region vanished in less than a second. Combustion does not occur if the ignition source does not exist inside the indoor unit. Refrigerant:R32 Amount:1000 g Flow rate:250 g/min 11
Result:Concentration distribution(no.9) There was a region where the concentration was higher than the UFL on the floor. Refrigerant:R32 Amount:1000 g Flow rate:250 g/min UFL LFL ¼ LFL 12
Result: Combustible gas region(no.9) The mixing of the refrigerant is weak, and the refrigerant concentration in the vicinity of the floor is high. In this case, not only the combustible gas volume is large, but also its duration is long. Refrigerant:R32 Amount:1000 g Flow rate:250 g/min 13
Result: Combustible gas region(no.9) The mixing of the refrigerant is weak, and the refrigerant concentration in the vicinity of the floor is high. In this case, not only the combustible gas volume is large, The leakage of flammable refrigerants from a floor-standing but also its duration indoor is long. unit has a high risk of fire. Refrigerant:R32 Amount:1000 g Flow rate:250 g/min 14
Flammability of 2L refrigerants National Institute of Advanced Industrial Science and Technology (AIST) Research Institute for Sustainable Chemistry 15
Flammability limits of non-flammable refrigerants R-410A, R-410B, and R-134a are considered to be non-flammable. However, they become flammable under such a condition as 50%RH at 60 C. LFL UFL vol% ± vol% ± R22 non-flammable R134a 11.5 0.3 15.9 0.4 R410A 15.6 0.2 21.8 0.4 R410B 16.3 0.3 20.9 0.4 R413A 7.16 0.15 14.3 0.5 16
Dependence of humidity on flammability limit Flammability limit of R-1234yf and R-1234ze(E) LFL, HFL, vol% 15 14 13 12 11 10 9 8 7 6 5 1234yf,LFL 1234yf,UFL 1234ze,LFL 1234ze,UFL 0 20 40 60 80 100 Relative humidity at 23 C, % LFL, HFL, vol% Flammability limit of R-32 and ammonia 30 25 20 15 10 HFC-32,LFL HFC-32,UFL NH3,LFL NH3,UFL 0 20 40 60 80 100 Relative humidity at 23 C, % Flammability limits of R-1234yf and R-1234ze(E) are clearly effected by humidity. Flammable region is stretching by moisture. Flammability of R-32 and ammonia is not influence by humidity. 17
Quenching distance measurement DC spark generator - + Acrylic cylinder Electrodes with 100-mm ID plates Fan Micrometer Quenching distance (d q ), mm 25 20 15 10 5 0 1234yf 2L 2, 3 717 32 143a 152a 290 0 10 20 30 40 Burning velocity (S u0,max ), cm/s 100 10 1 ( λ c ρ S ) dq = a av p 0 32 143a 152a 290 717 0.01 0.10 1.00 1/(ρ 0 S u0,max ), 10 2 m 2 s/kg u 1234yf 2L 2, 3 The quenching distance has a strong relationship with flammability, like burning velocity. The quenching distances of 2L class refrigerants are larger than 5 mmm.. 18
Experimental Evaluation of Physical Hazard of A2L Refrigerant Assuming Actual Handling Situations Tokyo University of Science, Suwa 19
Physical Hazard evaluation assuming conceivable accident scenarios (TUSS) Background & Objective In the actual handling situation of air conditioning systems Leaked refrigerant generally has a certain degree of concentration distribution. Ignition source is very various, and ignition behavior greatly affected by the turbulence and flow of the accumulated refrigerant. We examined physical hazard by burning of A2L refrigerant under several conceivable accident situations based on these fundamental combustion behaviors. 20
Physical Hazard evaluation assuming conceivable accident scenarios (TUSS) Use with fossil-fuel heating appliance Accident scenario: A wall-mount type room air conditioner containing an A2L refrigerant is simultaneously used with a fossil-fuel heating appliance inside a general living space. Experiment 2800 観測室 Air conditioner FTIR FTIR refrigerant 2800 2100 Stove(2.4 kw) Fan heater (3.2kW) 400 BD Amp. Measurement position of refrigerant and HF concentration Refrigerants:R32, R1234yf, R410A Leak amount:800 g Leak rate:10 g/min, 60 g/min to vacuum Monitor cylinder Logger Unit: mm Heater:radiative stove (2.4 kw), oil fan heater(3.2 kw) 21
Physical Hazard evaluation assuming conceivable accident scenarios (TUSS) Use with fossil-fuel heating appliacne Results 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 R32 Concentration (vol%) Heater: radiative stove 1000 10g/min, Refrigerant 900 60g/min, Refrigerant 800 10g/min, HF 700 60g/min, HF 600 500 400 300 200 AC-ON 100 0 0 20 40 60 80 100 120 time (min) HF Concentration (ppm) HF Concentration (ppm) 2000 1800 1600 1400 1200 1000 800 600 400 200 0 10g/min, AC-OFF 10g/min, AC-ON 60g/min, AC-OFF 60g/min, AC-ON R32 R1234yf R410A Varieties of Refrigerants Refrigerant concentration (<2 vol%) was much lower than LFL. Therefore no ignition and flame propagation to A2L refrigerants were observed. Hydrogen fluoride which is generated due to the combustion or thermal decomposition was confirmed. The concentration of generated HF is more than 3 ppm which is the permissible value, even R410A. 22
Physical Hazard evaluation assuming conceivable accident scenarios (TUSS) Ignition & flame propagation by a lighter Accident Scenario: A service operative uses a portable lighter to smoke in a space in which an A2L refrigerant has leaked and accumulated. Type 1: piezo gas lighter Experiment Pneumatic cylinder Refrigerant: R1234yf, R1234ze(E), R32 Solenoid valve air Extinction Flame (1/30s passed) Push rod 1000 Lighter 300 It was predicted that the concentration of n-butane/a2l refrigerants/air mixture is within the flammable range when the concentration of A2L refrigerants close to a gas lighter is less than LFL. 23
Conclusion 1. From 2011 to 2015, the Research Committee conducted safety research and risk assessment of A2L refrigerants. A new guideline of mildly flammable refrigerants for refrigerating and air conditioning equipment was drafted in 2016. 2. New safety rules and regulations came into effect in 2016. R32, R1234yf and R1234ze(E) can be used as inactive gases for refrigerating and air conditioning equipment. 3. The Research Committee started to conduct the safety research and risk assessment of A3 refrigerants from 2016. 4. The final report on risk assessment of mildly flammable refrigerants can be freely downloaded from the following website. http://www.jsrae.or.jp/jsrae/committee/binensei/risk_eng.html 24
Thank you for your attention! 25