Thermodynamic Performance Assessment of R32 and R1234yf Mixtures as Alternatives of R410A

Transcription

1 Thermodynamic Performance Assessment of R32 and R1234yf Mixtures as Alternatives of R410A May 2017 Nan Zheng a, Yunho Hwang b * a Department of Process Equipment & Control Engineering Xi an Jiaotong University b Center for Environmental Energy Engineering Department of Mechanical Engineering University of Maryland College Park, MD

2 R410A Applications Self-contained system Small-capacity splits Roof tops VRV systems Centralized systems Air Conditioning Chillers Low-capacity volumetric chillers (P<50 kw) Medium-capacity volumetric chillers (50<P<350 kw) High-capacity volumetric chillers (P>350 kw) Air conditioning system for trains: locomotive, wagons Mobile Air Conditioning Residential Heat Pumps Air-to-water heat pumps (Glycol) Water-to-water heat pumps Ground-to-floor heat pumps Ground-to-water heat pumps 2

3 R410A Consumption and Emissions Projected R410A consumption and emissions under the BAU scenario of China's RAC [2] 3 [2] Wang et al., Atmospheric Environment 2016,132:30-5

4 R410A Alternative Refrigerants GWP=2,088 R22 R410A? Need to consider many factors: Environmental property: low GWP Hazard: no toxicity, no or low flammability Thermophysical properties: equivalent or better efficiency Cost McLinden et al. (2014) screened 56,000 chemicals. AHRI s AREP experimentally investigated some pure and mixture refrigerants. No replacement candidate finalized yet. Most candidates are flammable. HFC/HFO mixtures are open suggested. 4

5 HFC/HFO Mixtures Alternatives HFC/HFO mixtures alternatives evaluated by the AHRI s AREP Program Mixture R125 R134a R32 R744 R1234yf R1234ze ARM-70a 10% 50% 40% D2Y60 40% 60% DR % 27.5% R-454B 69% 31% DR-55 (R452B) 7% 67% 26% HPR1D 60% 6% 34% L41 3.5% 68% 28.5% L41z (R-447B) 8% 68% 24% 5

6 Characteristics of Base Refrigerants R125 R134a R32 R744 R1234yf R1234ze Molecular mass (g mol -1 ) NBP (ºC) Critical T (ºC) Critical P (bar) H lg (kj kg -1 )* GWP 100-yr Safety class A1 A1 A2L A1 A2L A2L * Calculation is based on T r =0.8 High GWP: R125 and R134a High pressure: R744 Latent heat: R32=R744>R1234yf 6

7 Comparison of T-s Envelope T [ C] R410A R32 R1234yf s [kj/kg-k] Latent heat: R32>R410A>R1234yf Vapor curve slope: R1234yf (+)>R410A (-) >R32 (-) Sat. vapor slope contributes to reduction in compressor discharge temperature Benefits of mixing R32 and R1234yf: Compromise in GWP, flammability and discharge temperature 7

8 Comparison of Heat Transfer Coefficients Heat Transfer Coefficient [kw/m 2 k] mm,t sat =15 C mm,t sat =15 C mm,t sat =10 C mm,t sat =20 C mm,t sat =10 C mm,t sat =20 C 3 Vapor Quality [-] Li et al., International Journal of Heat and Mass Transfer 2012, 55: Long et al., International Journal of Refrigeration 2016, 61: Flow boiling heat transfer Mass velocity = 400kg m-2 s-1 Heat Flux = 12 kw m -2 For flow boiling heat transfer coefficient, R32 is slightly higher than R410A, and much higher than R1234yf. 8

9 Temperature Glide of R32/R1234yf Temperature Glide [K] x R32 =0.218 Temperature -15 C Temperature 45 C GWP 0 Mass Fraction of R32 [-] GWP= GWP 100-year [-] x R32 =0.15, maximum temperature glide of 9.8ºC and 7.9ºC, respectively. 0.05<x R32 <0.4, temperature glides are larger than 5 K x R32 =0.218, GWP reaches to upper limit (150) for application in mobile airconditioner in EU 9

10 Heat Transfer Coefficients of R32/R1234yf Heat Transfer Coefficient [kw/m 2 K] G=200 kg/m 2 s q=12 kw/m 2 D=2 mm T sat =15 C 2 Mass Fraction of R32 [-] Li et al., International Journal of Heat and Mass Transfer, 2012, 55: The variation of boiling heat transfer coefficient by the R32 mass fraction change is not linear for the R32/R1234yf mixture. x R32 =0.2, minimum value is reached. The decrease could be related to the non-linear variation in the thermophysical properties of the zeotropic mixture caused by the interactions between blend components. 10

11 Viscosity and Latent Heat of R32/R1234yf Liquid Viscosity [µpas] C 45 C Latent -15 C Latent 45 C 60 Mass Fraction of R32 [-] Latent Heat [kj/kg] Mixture latent heat increases steadily with an increasing x R32. Liquid viscosity decreases and becomes flat as x R32 increases. Higher x R32 is desired for heat transfer and thermophysical properties. But what s the most desirable composition of R32/R1234yf mixture? 11

12 Thermodynamic Cycle Model Indoor HX Exp. Valve One-way Compressor Outdoor HX Four-way Single-stage Cycle (cooling mode) Refrigerant properties were calculated based on NIST REFPROP 9.0 database. Assumptions: Neglect pressure drop in HX and pipes. Constant compressor isentropic efficiency of 0.75 Isenthalpic throttling process Saturation state at HX outlet Same condensing and evaporating temperatures for all fluids. (mixtures: average value of bubble and dew temp) Cooling Mode Heating Mode Evaporating T ( C) Condensing T ( C)

13 Discharge Pressure/Temperature Comparison Condensing Pressure [kpa] Mass Fraction of R32 [-] R410A,cooling mode R410A,heating mode R32/R1234yf,cooling mode R32/R1234yf,heating mode Discharge Temperature [ C] Mass Fraction of R32 [-] R410A,cooling mode R410A,heating mode R32/R1234yf,cooling mode R32/R1234yf,heating mode x R32 < 0.3, the condensing pressure could be reduced below 2,000 kpa for both modes. x R32 > 0.5, R32/R1234yf shows higher discharge temperature. 13

14 Cooling/Heating Capacity Comparison Cooling/Heating Capacity [kw] R32/R1234yf,Q evap R32/R1234yf,Q cond R410A,Q evap R410A,Q cond 100 Mass Fraction of R32 [-] x R32 >0.5, R32/R1234yf shows higher heating capacity. x R32 >0.45, R32/R1234yf shows higher cooling capacity. x R32 =0.218, heating and cooling capacities of R32/R1234yf are lower than those of R410A by 17.6% and 13.5%, respectively. 14

15 Cooling/Heating COP Comparison R32/R1234yf R410A 4.75 R32/R1234yf R410A Heating COP [-] Cooling COP [-] Mass Fraction of R32 [-] 4.50 Mass Fraction of R32 [-] x R32 <0.4, R32/R1234yf shows lower heating COP. x R32 =0.35, R32/R1234yf shows minimum cooling COP. 15

16 Cooling COP Increment Cooling COP Increment [%] D2Y60 T evap =10 C,T cond =30 C T evap =10 C,T cond =55 C T evap =10 C, T cond =45 C DR-5 * * COP increment increases as temperature lift increases. In Adrian s calculation results, D2Y60 shows higher COP than DR-5, while in this work, D2Y60 has lower COP. -3 Mass Fraction of R32 [-] *Adrian Mota-Babiloni et al., International Journal of Refrigeration 2015, 52: Difference in model assumption may lead to the deviation. 16

17 Conclusions Lower xr32 decreases in condensing pressure and discharge temperature but also the cooling/heating capacity so that the compressor displacement volume should be increased. xr32=0.218, GWP of R32/R1234yf is reduced by 92.8% compared to that of R410A, while the cooling/heating capacity as well as heating COP is also reduced. Either higher R32 mass fraction in R32/R1234yf or pure R32 would be the choice while considering the heat transfer and COP perspectives but it requires relaxing of GWP value. Therefore, the life cycle climate performance evaluation would help in determining the proper mass fraction value without compromising the environmental impact. 17

18 Future Work Conduct system level modeling using VapCyc and CoilDesigner, to better predict the performance of R32/R1234yf mixtures. Develop advanced capacity control method on the basis of R32/R1234yf composition adjustment according to real-time conditions. Establish test rig and verify the feasibility of using R32/R1234yf mixtures as alternatives to R410A experimentally. LCCP evaluations 18

19 Acknowledgement The support of the Center for Environmental Energy Engineering (CEEE) at the University of Maryland, Key Laboratory of Efficient Utilization of Low and Medium Grade Energy at Tianjin University, and the China Scholarship Council (CSC) are gratefully acknowledged. 19