Refrigerant R32 as lower GWP working fluid in residential air conditioning systems in Europe and the USA

Because air conditioning and heat pump systems contribute greatly to greenhouse gas emissions, equipment with both lower global warming potential (GWP) working fluids and a higher level of performance should be used. R32 (difluoromethane) has been proposed to substitute R410A, particularly in residential air conditioning (RAC) systems. This study collected the most relevant and recent researches into R32 as a refrigerant so as to assess its viability in RAC systems in both Europe and the USA, as compared to R410A and other lower GWP RAC alternatives. The R32 value of GWP is 677, which is below the F-gas regulation limit in RAC equipment (750). According to ASHRAE standard 34, R32 is less flammable than hydrocarbons, and the amount of charge permitted for R32 is above the necessary level in RAC equipment. It can be concluded that R32 has significantly good heat transfer characteristics and a level of performance that make it acceptable at low condensing temperatures, thereby avoiding overly high compressor discharge temperatures. Its performance is very similar to that of R410A across the entire operating range, and it is therefore believed that R32 will be utilized in RAC systems in the remaining countries that prioritize lower GWP fluids but are less strict in their security regulations. To replace R410A under extreme conditions, some system modifications can be conducted, or R32 mixtures with hydrofluoroolefins (HFOs) can be used. Such mixtures achieve a lower performance than R32, but are acceptable replacements when considering their lower GWP compared to that of R32, and similar level of flammability. Finally, other (R32-based) alternative mixtures have also been developed and their behaviours studied under a wide range of operating conditions.The authors thankfully acknowledge the Spanish Ministry of Education, Culture, and Sport for supporting this work through “Becas y Contratos de Formación de Profesorado Universitario del Programa Nacional de Formación de Recursos Humanos de Investigación del ejercicio 2012 (Grant number FPU12/02841)” and “Ayudas complementarias para beneficiarios de ayudas (FPU): Estancias Breves. Convocatoria 2015 (Grant number EST15/00154)”. The authors are also grateful to the Swedish Energy Agency for supporting this study under the “EFFSYS EXPAND P08” research program

Flow boiling heat transfer of a non-azeotropic mixture inside a single microchannel

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.This study moves from the need to study flow boiling of zeotropic mixture in microchannels. In the recent years much attention has been paid to the possible use of fluorinated propene isomers for the substitution of high-GWP refrigerants. The available HFOs (hydrofluoroolefins) cannot cover all the air-conditioning, heat pump, and refrigeration systems when used as pure fluids because their thermodynamic properties are not suitable for all operating conditions and therefore some solutions may be found using blends of refrigerants, to satisfy the demand for a wide range of working conditions. In the present paper a mixture of R1234ze(E) and R32 (0.5/0.5 by mass) has been studied. The local heat transfer coefficient during flow boiling of this mixture in a single microchannel with 0.96 mm diameter is measured at a pressure of 14 bar, which corresponds to a bubble temperature of 26.3°C. The flow boiling data taken in the present test section are discussed, with particular regard to the effect of heat flux, mass velocity and vapor quality. The heat transfer coefficients are compared against some predicting models available in the literature. Furthermore, the new experimental data are compared to flow boiling data of pure R1234ze(E) and pure R32 to analyze the heat transfer penalization due to the mass transfer resistance of this zeotropic mixture

Experimental determination of the optimum working conditions of a transcritical CO2 refrigeration plant with integrated mechanical subcooling

Subcooling methods for transcritical CO2 plants are being studied in order to improve their behavior. Among them, the Integrated Mechanical Subcooling system is one of the most promising owing that performs with high efficiency and it is a total-CO2 system. This work presents the experimental determination of the optimum working conditions of a transcritical CO2 plant working with an integrated mechanical subcooling system. The plant was tested at different pressure and subcooling conditions in order to optimize the COP of the plant and determine the optimal conditions for three ambient temperatures 25.0 °C, 30.4 °C and 35.1 °C and evaporation levels between −15.6 °C and −4.1 °C. Optimum operating conditions were determined and two correlations are proposed to determine the optimal pressure and subcooling as function the gas-cooler outlet temperature and the evaporation level

Retrofit of lower GWP alternative R449A into an existing R404A indirect supermarket refrigeration system

R404A is going to be phased out from most of the commercial refrigeration systems due to its high GWP value of 3943. R449A (GWP of 1282) has been proposed to replace R404A with only minor system modifications in supermarkets. This paper presents the measurements of a light retrofit replacement of R404A using R449A in a medium temperature indirect refrigeration system (secondary fluid temperature at the evaporator outlet between −9 and −4 °C). It has been demonstrated that with a slight expansion device adjustment and 4% increase of refrigerant charge, R449A can be used in this refrigeration system designed for R404A because of its suitable thermodynamic properties and acceptable maximum discharge temperature. At a secondary fluid temperature at condenser inlet of 30 °C, the COP of R449A nearly matches that of R404A (both were between 1.9 and 2.2), despite having approximately 13% lower cooling capacity. As a conclusion, attending to the GWP reduction and similar energy performance, it was demonstrated using the TEWI methodology that the use of the recently developed refrigerant R449A in these applications can reduce the total CO2 equivalent emissions of an indirect supermarket refrigeration system designed for R404A refrigerant.This research is funded by the Swedish Refrigeration Cooperation Foundation, KYS (project “Utvärdering av en potentiell R404A-ersättare – fältprov med R449A”) and Swedish Energy Agency (EFFSYS Expand P08) with the support of Bosch Thermoteknik AB, Danfoss Värmepumpar AB, Nibe AB, Nowab, Energi & Kylanalys AB and Svenska Kyltekniska Föreningen

Acoustic determination of thermophysical properties and critical parameters for R410A and critical line of x CO2+(1− x) R410A

The thermophysical properties and critical parameters for the alternative refrigerant R410A (a near azeotropic refrigerant mixture containing difluoromethane (R32) and pentafluoroethane (R125) (50 wt % of each)) were investigated using two different acoustic techniques. The critical behavior of the system xCO2 + (1 - x)R410A was also investigated. Experimental data of speed of sound in liquid R410A from (253 to 338) K and pressures up to 65 MPa were measured using a pulse-echo method. Derived thermodynamic properties were calculated, combining our experimental data with density and isobaric heat capacity values published by other authors. Measurements of the critical temperature Tc and pressure pc on (R410A) and mixtures of xCO2 + (1 - x)R410A were performed using another simple ultrasonic time-delay technique. The binary critical line was determined over the whole composition range, showing that this system deviates only slightly from ideality since the critical line is a continuous line. The Peng-Robinson equation of state with conventional mixing and combining rules was used to correlate the binary experimental data.info:eu-repo/semantics/publishedVersio

Combining molecular modelling approaches for a holistic thermophysical characterisation of fluorinated refrigerant blends

After Montreal Protocol, hydrofluorocarbons (HFCs) appeared to be a permanent solution for replacing previous ozone-depleting substances. However, their utilisation has now progressively decreased following the Kigali Amendment application in 2016 due to their high global warming potential (GWP). Unsaturated HFCs, such as hydrofluoroolefins (HFOs), are considered feasible alternatives due to their high reaction rates and low atmospheric lifetimes, resulting in very low GWP. However, available data on their physicochemical behaviour still needs to be improved, even with the recent increase in the amount of new experimental data for these systems. In this direction, computational tools provide a quick pathway to screen their properties and complete the information obtained from experimental work. In this contribution, two different molecular modelling tools, molecular dynamics (MD) simulations and the soft-SAFT equation of state (EOS), are combined to compute the coexistence densities, vapour pressure, heat capacity, interfacial tension, and dynamic viscosity of several refrigerant blends based on 3rd and 4th generation compounds, in order to provide a thermodynamic analysis of the properties of these mixtures, addressing them for drop-in replacement purposes. Results from MD are compared with REFPROP data and those from soft-SAFT, where the capacities of both modelling methods are addressed. In general, quantitative agreement is achieved using the two approaches, offering a framework to screen these properties for new mixtures.info:eu-repo/semantics/publishedVersio

Fluid phase equilibria prediction of fluorocompound-containing binary systems with the predictive E-PPR78 model

International audienceIn order to reduce the overall emissions of greenhouse gases and to be in compliance with the current environmental regulations, a new class of refrigerants, making use of fluorocompounds has appeared. Such refrigerants are often blends of alkanes, CO 2 and fluorocompounds. Consequently an equation of state (EoS) able to predict the properties of both pure compounds and multi-component systems is required to design processes involving fluorocompounds or to implement a product-design approach aimed at identifying new refrigerant mixtures. It is however well-acknowledged that the phase behavior of binary systems like, e.g., an alkane and its corresponding perfluoroalkane, show significant deviations from ideality that need to be accurately accounted for by a thermodynamic model. In this study, in order to get a predictive model applicable to fluorocompound-containing binary systems, six groups were added to the Enhanced-PPR78 model which combines the Peng-Robinson EoS and a group contribution method aimed at estimating the binary interaction parameters, () ij kT, involved in Van der Waals one-fluid mixing rules

Experimental evaluation of alternative CO2-based blends for transcritical refrigeration systems

This work presents two refrigerant CO2 blends with R32 and R1270 designed with a theoretically nonflammability and a GWP below 150. Both mixtures were tested in a small-capacity vapour compression system with and without IHX, considering the same working conditions of heat rejection temperature and demanding conditions at the evaporator. Taking the pure CO2 results as a reference in a cycle without IHX, the blend of CO2/R32 enhanced the COP up to 18.1% with an optimal pressure reduction of 19.0% and a power consumption minimization of 17.1%. The mixture of CO2/R1270 presented a COP enhancement of 8.4% with an optimal pressure reduction of 8.0% and a power consumption minimization of 7.9%. In all cases, the use of the IHX resulted positively with increments compared to the pure CO2 base cycle of 6.4% for pure CO2, 13.3% for CO2/ R1270, and 24.7% for CO2/ R32

A review of refrigerant R1234ze(E) recent investigations

[EN] Climate change is demonstrated through global surface temperatures increase in the last century. To stop this phenomenon, new regulations that ban or tax greenhouse gas fluids (HFC among them) have been approved. In the medium term, only low-GWP refrigerants will be permitted in developed countries. HFO fluids and most used HFCs as refrigerants in HVACR systems possess similar thermophysical properties. Among them, one of the most promising is R1234ze(E). This refrigerant presents good environmental properties and can be used in most of HVACR applications, pure or mixed with HFC or natural refrigerants (mainly CO2). This paper collects the most relevant research about R1234ze(E) thermophysical and compatibility properties, heat transfer and pressure drop characteristics, and vapor compression system performance; separating those works that consider R1234ze(E) pure or blended. Once the available literature is analyzed, it can be concluded that pure R1234ze(E) is a good option only in new HVACR systems. Nevertheless, if it is combined with other refrigerants, the final GWP value is also considerably reduced, maintaining efficiency parameters at levels that allow them to replace R134a, R404A or R410A in existing systems with minor modifications.The authors thankfully acknowledge the “Ministerio de Educación, Cultura y Deporte” (Grant Number FPU12/02841) for supporting this work through “Becas y Contratos de Formación de Profesorado Universitario del Programa Nacional de Formación de Recursos Humanos de Investigación del ejercicio 2012”.Mota-Babiloni, A.; Navarro-Esbrí, J.; Molés, F.; Barragán Cervera, Á.; Peris, B.; Verdú Martín, GJ. (2016). A review of refrigerant R1234ze(E) recent investigations. Applied Thermal Engineering. 95:211-222. https://doi.org/10.1016/j.applthermaleng.2015.09.055S2112229