Unknown & surprising R152a

DFE, R152a or difluorethane is an ecological refrigerant for positive temperature refrigeration, direct replacement for R134a. Difluorethane is fully respectfull with the ozone layer, has an excellent energy efficiency and has a very low Global Warming Potencia (GWP) of just 124.

R152a is being commonly used as aerosol propellant, foaming agent, or as a component in several refrigerant blends. However, it is classified as mildly flammable by ASHRAE, and thus it has a limited use in automotion and commercial applications. However, the recent concerns about global warming, F-Gas regulation in Europe, and carbon taxes in some countries, has recovered the interest for flammable refrigerants and event highly toxic refrigerants as ammonia.

R152a features

Difluorethane is a pure fluorinated hydrocarbon with a very similar chemical formula to R134a. It has a vapor pressure curve that is equivalent to that of R134a, with small deviations of about 2K. R152a also has equivalent chemical characteristics. So it is compatible with all materials in commercial compressors and refrigeration components, thermostatic expansion valves, and lubricants.

R152a also features superior thermodynamics characteristics to those of R134a or HFOs. Heat transfer coeficients in evaporators and condensers increases in about 20% thanks to better physical properties of R152a compared to R134a. In addition a lower viscosity of gas results in a reduction of pressure drop in suction lines of aout 30%. A lower molecular weight in R152a implies a high latent heat capacity, greater volumetric compressor efficiency, and a better COP performance of the cooling cycle. Also discharge temperature increases in about 10K compared to R134a.

Prooerties of R152a vs R134a and R1234yf (REFPROP9)

R134a R1234yf R152a
Molecular weight (gr/mol) 102 114 66
Boiling temperature at standard pressure -26,1ºC – 29,5ºC – 24,0ºC
Latent vaporisation heat at -10ºC,  kJ/kg 199 163 307
Volumetric cooling capacity, kJ/m3 1293 1186 1283
GWP (IPCC AR4) 1430 4 124
Lower flammability limit %vol 6% 4%
Combustion heat, kJ/mol 428 1220 1090
Auto-ignition temperature 405ºC 454ºC
ASHARE Safety class A1 A2L A2

Thermodynamic performance

The working pressure in R152a is slightly lower (-10%) than that of R134a for a same evaporating temperature. However, it has an equivalent cooling capacity (-1% compared to R134a), and thus R152a could be used as a replacement in cooling systems operating with R134a.

In practive, the addion of all factors in a same cooling system, allowa an efficiency gain of about 20% for R152a compared to R134a, and even better in comparison to R1234yf. In a same system refrigerant load reduction in R152a is about 40% thanks to the lower molecular weight.

En el cálculo del impacto medioambiental o factor TEWI de una instalación, el R152a obtendría menor valor que el R1234yf, pues el mayor efecto directo sobre el calentamiento atmosférico debido a un mayor índice PCA, se ve ampliamente compensado por la reducción del efecto indirecto asociado al menor consumo de energía eléctrica.

Pressure (bar) – Enthalpy (kJ/kg) diagramme for some refrigerants

Chemical compatibility

The Air Conditioning & Refrigeration Technology Institute report (part of the Materials Compatibility & Lubricants research programme prepared for the US Department of Energy in 1993) examined a number of fluorocarbons at various refrigerant concentrations & lubricant viscosity grades. R152a remained miscible in all concentrations throughout the test temperature range of -50C to 90C.

The project also examined the compatibility of twenty-four hermetic motor materials with eleven pure refrigerants and seventeen refrigerant-lubricant combinations.

Elastomer samples were completely immersed in the test refrigerant. Samples exposed to R32, R125, R134a, R143a, and R152a had the least swell. Like most of refrigerants, a large swell (>35%) was found with fluorinated rubbers and silicones.

The plastics were also evaluated in pure refrigerant. HFC refrigerants seem to have the least effect on the plastics, except for the ABS plastic, which failed in most of them.

Safety requirements

R152a is classified by ASHRAE as medium safety refrigerant, class A2, non toxic but slightly flammable. Even if safety regulations in refrgieration systems will limit the use of medium safety refrigerants in commercial refrigeration DX systems, they will allow its use, with no load limit, in indirect cooling systems and DX systems in industry.

Due to the slight flammability of refrigerants in group 2, increased safety instructions will be needed, requiring specific solutions in system engineering and risk analysis. Safety regulations for explosive atmospheres would classify the cooling facilities as risk zone 2: working areas where it is not probable, under normal working conditions, that an explosive atmosphere may be formed. This classification  does not initially mean to apply ATEX measures, but rather it will help to identify which areas are likely to be unclassified by applying preventive measures (such as localised air extraction, sufficient natural ventilation, etc…).

To mitigate hazards in cold rooms it is recommended to install a leak detector isolating the evaporator and activating forced ventilation. This will avoid reaching a dangerous concentration of refrigerant is air and will prevent the explosive mix. In fact, the refrigerant load that remains inside an evaporator is usualy lower than 20gr per m3 of coldroom. This is much lower than the lower flammability limit of 0.137kg/m3.

In tehcnical rooms it is recommended to installa an automatic ventilation system that will provide sufficient ventilation air flow in case of refrigerant leak. Finally, leak-proof brazed pipes are not considered risk areas.

 

Pressure-enthalpy diagramme for R152a

Diagrama-R152a

Literature

[1] Reglamento de seguridad para instalaciones frigoríficas y sus instrucciones técnicas complementarias. Real Decreto 138/2011, de 4 de febrero. BOE núm. 57, de 8 de marzo de 2011.

[2] F-gas regulation (EU) No 517/2014 of the European Parliament and of the Council of 16 April 2014 on fluorinated greenhouse gases.

[3] Reglamento de seguridad de los trabajadores expuestos a los riesgos derivados de atmósferas explosivas en el lugar de trabajo, Real Decreto 681/2003, de 12 de junio BOE nº 145, de 18 de junio.

[4] Guía técnica para la prevención y evaluación de los riesgos derivados de atmósferas explosivas en los lugares de trabajo, RD 681/2003. Instituto Nacional de Seguridad e Higiene en el Trabajo.

[5] Mendoza, J.M. (2013). Evaluación energética de los refrigerantes R1234yf y R152a como alternativa al R134a en sistemas de refrigeración. Revista Iberoamericana de Ingeniería Mecánica. Vol 17, Nº2.

[6] Cabello, R (2015). Experimental comparison between R152a and R134a working in a refrigeration facility equipped with a hermetic compressor. International Journal of Refrigeration, 60, 92-105.

[7] Palm (2016-1). The opportunities and challenges of R152a, Part 1. (Möjligheter och utmaningar för R152a.) Department of Energy Technology. KTH Royal Institute of Technology. (Accessed on 30/07/2017)

[8] Palm (2016-2). The opportunities and challenges of R152a, Part 2. (Möjligheter och utmaningar för R152a.) Department of Energy Technology. KTH Royal Institute of Technology. (Accessed on 30/07/2017)

[9] UNE-EN 60079-10. Material eléctrico para atmósferas de gas explosivas. Parte 10: Clasificación de emplazamientos peligrosos.

[10] Godwin, D. (1993) Materials compatibility and lubricants research on CFC-Refrigerants substitutes. Air-conditioning and Refrigeration Technology Institute, Inc. The U.S. DEPARTMENT OF ENERGY.(Accessed on 30/07/2017).

[11] Bitzer Refrigerant Report (2014). Edition A-501-14. (Accessed on 30/07/2017) 

[12] BRA 2012. Guide to flammable refrigerants. British Refrigeration Association. (Accessed on 4/08/2017)