Test Results from the AHRI Low GWP AREP (Alternative Refrigerant Evaluation Program) Bus Air-Conditioning System Drop-In Tests of R134a and R407C Alternative Refrigerants In Bus Air-Conditioning Units
Acknowledgements Thanks to the following companies for supplying the refrigerant samples tested: - Honeywell Mexichem Daikin To those who performed the work: - Markéta Kopecká - Michal Hegar - Prague Lab Team - Vladimír Šulc 2
Purpose Evaluate selected alternative refrigerant blends to determine their performance as drop-in replacements for R134a and R407C in bus air-conditioning systems 3
Summary Two different low GWP refrigerants were tested as possible replacements of R134a in a bus air conditioning application. Two different low GWP refrigerants were tested as possible replacements of R407C in a bus air conditioning application. Testing was run at the same combination of conditions (ambient temperature / box temperature / box air humidity/ compressor speed/evaporator fan speed) as current units charged with R134a or R407C. 4
Evaluated Refrigerants Test Refrigerants N-13a R134a/R1234yf/R1234ze 42/18/40%wt GWP 604 AC5 R32/R152a/R1234ze 12/5/83%wt GWP 92 L-20 R32/R152a/R1234ze 45/20/35%wt GWP 331 D52Y R32/R125/R1234yf 15/25/60%wt GWP 979 5
Test Setup R134a Application: Roof Mounted Bus A/C, 24 kw Cooling Capacity Under Standard Rating Conditions 6
Test Setup, Cont. R407C Application: Roof Mounted Bus A/C, 32 kw Cooling Capacity Under Standard Rating Conditions 7
Test Conditions Multiple compressor and fan speeds tested 8
Test Results R134a system 9
Test Results, Cont. R134a system 10
Test Results, Cont. R134a system 11
Test Results, Cont. R134a system 12
Test Results, Cont. R407C system 13
Test Results, Cont. R407C system 14
Test Results, Cont. R407C system 15
Test Results, Cont. R407C system 16
Conclusion Refrigerants with lower GWP values can be formulated to replace R134a and R407C in bus air-conditioning systems The refrigerants tested are not true drop-in replacements. Use of the current alternatives will require changes to the design of existing bus air-conditioning systems Several refrigerants tested are rated A2L and risk assessment work must be carried out to determine safe operation in the bus air conditioning application 17
Questions? 18
APPENDIX 19
Test Setup Units basic description: - Compressor: 4 cylinder reciprocating open shaft, 30 in 3 displacement - Lubricant: 35 cst, POE - Refrigeration system schematic diagram: 20
Test Setup, Cont. Monitored quantities: 21
Test Setup, Cont. Testing chamber: Wind tunnel with the set of nozzles, air temperature and humidity control Compressor connected with the torque sensor and driven by the electric motor Measurement uncertainty = ±5% 22
Test Evaluation Compared Variables The unit cooling capacity is determined based on the control volume energy input and output balance Cooling capacity Qo = m_air*(h_evap_in h_evap_out) Total input power P_Unit = P_Compressor + P_Fans Compressor input power P_Compressor = Torque * ω - Tq [N*m] torque - ω [s^-1] angular speed 23
Test Evaluation Compared Variables, Cont. Evaporator temperatures difference: d EVOT EVOT EVOT / Evaporator superheat difference: d ESH ESH ESH / Condensing temperatures difference: d PGOT PGOT PGOT / Suction pressures difference: d PVIP PVIP PVIP / Suction temperatures difference: d PVIT PVIT PVIT / Discharge pressures difference: d PGOP PGOP PGOP / Discharge temperatures difference: d PGOT PGOT PGOT / Diesel consumption ratio: C C C / Net cooling capacity ratio: Q Q Q / Refrigerant charge ratio: Charge Charge Charge / COP: COP COP COP / 24
Comments on results Different parameters were observed, evaluated, and compared to the same parameters obtained with R134a or R407C. - Cooling capacity: R134a - AC5 has lower capacity at all conditions except two. The two conditions are within the experimental error of the test facility. - N-13a has lower capacity at all conditions. R407C - L-20 has slightly higher or same capacity at all conditions except one. The one condition is within the experimental error of the test facility. - D52Y has lower capacity at all conditions. 25
Comments on results - Unit COP: R134a - AC5 has lower COP values at all conditions except one. - N-13a COP varies from -4% to +3%. Considering test facility accuracy, COP is similar to R134a. R407C - L-20 has slightly higher COP values at all conditions except two. - D52Y COP values are lower at all conditions. 26
Comments on results - Discharge pressure: R134a - AC5 has higher pressure at all conditions except two. The pressure differences vary from -1 psid to +15 psid. - N13a has the discharge pressure lower at all conditions. The pressure differences vary from 0 psid to -10 psid. R407C - L-20 has generally higher pressure at higher box (104 F & 120 F) and simultaneously higher ambient conditions (104 F & 120 F). The pressure differences vary from -10.8 psid to +16.3 psid. - D52Y has the discharge pressure lower at all conditions. The pressure differences vary from -2 psid to -45 psid. 27
Comments on results - Discharge temperature: R134a - AC5 has generally lower discharge temperatures (to -15 F). - N13a has lower discharge temperature at all conditions (to -26 F). R407C - L-20 has generally higher discharge temperatures, especially at the combination of lower box and ambient temperatures (to +30 F). - D52Y has generally lower discharge temperature, especially at the combination of lower box and ambient temperatures (to -38 F). 28