low-GWP Refrigerants Research Articles

Transitioning to low GWP refrigerants in automobiles: A numerical simulation study on R1234yf/R152a’s heat transfer characteristics in porous microchannels

Automobile air conditioning systems significantly contribute to vehicle energy consumption. The transition to new, environmentally sustainable refrigerants in place of traditional ones is a critical trend shaping the future of this industry. The prevalent refrigerant R134a, used in automotive air conditioning, is environmentally detrimental, necessitating the development of low Global Warming Potential refrigerants as viable long-term alternatives. This study examines the flow heat transfer characteristics of the proposed refrigerant blend R1234yf/R152a in porous microchannel tubes via numerical simulation. It assesses the impact of heat flux, mass flow rate, saturation temperature, and wall superheat on the Jakob number, vaporization core density, and boiling heat transfer coefficient. Furthermore, it compares these parameters with those of R134a and R1234yf to evaluate the potential of R1234yf/R152a as a substitute. The findings indicate that the Jakob number differences among the three refrigerants are negligible. Notably, R1234yf/R152a consistently exhibits higher vaporization core density and the highest boiling heat transfer coefficient, coupled with the lowest pressure drop, thereby affirming its suitability as a heat transfer-efficient alternative. These insights could inform the enhancement and gradual transition from R134a in automotive air conditioning systems.

4E assessment of ejector-enhanced R290 heat pump cycle with a sub-cooler for cold region applications

Currently, the worldwide implementation of the Montreal Protocol has accelerated the development of low GWP refrigerants. R290 as an alternative refrigerant with low GWP has great advantages over R134a for heat pump applications. However, the use of expansion valve throttling in the heat pump cycle has a large irreversible loss. Therefore, an ejector-enhanced sub-cooler vapor injection heat pump cycle (ESVIC) with R290 for water heating is proposed in this paper to improve the energy efficiency by applying ejector. The thermodynamic models are established based on the 4E (energy, exergy, economic and environmental) analysis to compare its performance with the basic ejector-enhanced heat pump cycle (BEEC) and the sub-cooler vapor injection heat pump cycle (SVIC). The energy analysis results show that compared with the BEEC and SVIC, the volumetric heating capacity of the ESVIC is improved by 42.0 % and 21.2 %, and the heating coefficient of performance (COPh) of the ESVIC is improved by 27.6 % and 5.3 %, respectively. The exergy analysis results indicate that in BEEC, SVIC and ESVIC the exergy destruction of the expansion valves is 0.3 %, 13.5 % and 0.8 %, respectively. It is indicated that the adoption of ejector can significantly decrease the exergy destruction of expansion valves. Moreover, the environmental analysis results reveal that the carbon emissions of ESVIC is 21.5 % and 5.0 % lower than those of BEEC and SVIC, respectively. Besides, for the ESVIC system, the carbon emissions of the life cycle climate performance when using R290 are 9.9 % lower than that of using R134a, indicating that the R290 is a potential substitute for R134a in heat pump applications. The economic analysis results demonstrate that the unit exergy production costs of ESVIC is 21.6 % and 5.1 % lower than BEEC and SVIC, respectively.

Pool boiling heat transfer performance of low-GWP refrigerant R-513A on smooth tube

Pool boiling heat transfer performance of low-GWP refrigerant R-513A on smooth tube

Comparative analysis of condensation heat transfer and pressure drop of low GWP near-Azeotropic mixture and R-290 in a plate heat exchanger

Downward condensation of a near-azeotropic low GWP refrigerant mixture of R290/R1270 (65%/35% wt.), named HC01, was investigated inside an offset strip-fin (OSF) flow-structured plate heat exchanger (PHE). This study tested the prototype heat exchanger with HC01 and compared the condensation heat transfer coefficient (CHTC) and pressure drop (CPD) with the pure R-290 for working conditions of refrigerant mass flux (G) = 20–50 kg/m2s, inlet vapor quality (xin) = 0.2–0.9, saturation temperature (Tsat) = 40–55 °C, and heat flux (q) = 4–13 kW/m2. It was observed that the condensation of HC01 occurred entirely within the forced convection condensation flow regime, despite a slight change in the CHTC at a lower xin as the G increased. The CHTC demonstrated an increase in response to higher values of G and q, but decreased with increasing Tsat. Similarly, the CPD exhibited an increase with higher G and a decrease with lower Tsat, whereas the q had minimal influence. Comparison results showed that the HC01 exhibited 14.2% higher average CHTC but 6.5% lower CPD than that of R-290 because of the differences in properties, such as liquid thermal conductivity, viscosity, surface tension, latent heat, and discrepancies in liquid and vapor phase densities. Correlations were generated to predict the values of the Nusselt number (Nu) and friction factor (FF) of HC01, with mean absolute errors of 12.1% and 12.7%, respectively.

Assessment of total equivalent warming impact (TEWI) of alternative refrigerants for retrofit of R22 in single split air conditioning system

Since the adoption of the Montreal Protocol in 1987, until today, there have been several amendments to reinforce and even streamline the goals, encouraging industries to develop refrigeration systems that use low GWP refrigerants. In parallel to this, there is a large number of refrigeration units in developing countries, such as Brazil, which operate with high GWP fluids, such as R22, and discarding such equipment just because of the fluid would cause great damage not only to the owners, as well as for the environment. To reuse these units, this work aimed to evaluate alternative fluids that replace the current ones with the least possible modifications to the system without significantly compromising the performance of these sets. To achieve this, a mathematical model of a refrigeration system was developed and subsequently experimentally validated for R22. After that, this model was incorporated into a thermal zone, based on the environmental conditions of Belo Horizonte from December 2022 to November 2023 (one year) and the fluids R407C, R444B, and R454C were compared to R- 22 through COP, refrigeration capacity and Total equivalent warming impact of alternative (TEWI), in addition to analyzing environmental impacts. After the analyses, it was possible to notice that R407C performs worse than R22 in both performance parameters and TEWI. R454C has a COP and refrigeration capacity 16% and 11% lower than R22, respectively, however, it has a total TEWI 55% lower than the reference due to its low GWP. Finally, R444B was identified in this study as the best replacement alternative to R22 at mild temperatures, as it has COP and cooling capacity of 15% and 9% higher and has a TEWI that is also 55% lower than the reference.

A novel approach for designing efficient and sustainable cooling cycles with low global warming potential refrigerants

With the current legislation on the phase-out of 3rd generation refrigerants, new cooling cycles are expected to operate with 4th generation refrigerants, hence, the need for optimal system performance with these new working fluids. In this study, an innovative optimization approach was applied for the design of cooling cycles with 4th generation refrigerants based on integrating statistical analysis design of experiments (DoE) with molecular modeling using the polar soft-SAFT model. First, a detailed multi-criteria assessment was applied for the selection of 4th generation refrigerants in medium–low temperature applications. Results demonstrated the potentiality of trans-1,3,3,3-tetrafluoroprop-1-ene (R1234ze(E)) or cis-1,2,3,3,3-pentafluoroprop-1-ene (R1225ye(Z)) in terms of environmental, safety, and technical criteria in basic cooling cycles under specific operating conditions. Multi-objective optimization guided using statistical analysis tools were implemented to study potential enhancement in cooling cycle performance using these promising refrigerants in terms of energy and exergy efficiency. This included evaporator and condenser temperature, fluid choice, compression yield, superheating/subcooling degrees, and cycle type. The evaporation and condenser temperature, and the compressor efficiency are shown to monopolize more than three-quarters of the cumulative contribution on system efficiency for those operated with R1234ze(E) in advanced liquid-to-suction line heat exchangers (LL/SL-IHX). Further optimization through examining the effect of heat transfer phenomena assisted in determining optimal operating conditions for new systems operating with low GWP refrigerants, instilling annual cost savings of $1.59 K and reduction in CO2 emissions by 1.02 tCO2-eq compared to the baseline system.

Foreword for Special Issue "Trends Towards Low-GWP Refrigerants Used in Refrigeration and Air Conditioning Equipment"

Foreword for Special Issue "Trends Towards Low-GWP Refrigerants Used in Refrigeration and Air Conditioning Equipment"

Trends in Low-GWP Next-generation Refrigerants for Environment-friendly

Trends in Low-GWP Next-generation Refrigerants for Environment-friendly

Isothermal (vapor ＋ liquid) equilibrium measurements and correlation of the binary mixture 3,3,3-trifluoropropene (R1243zf) ＋ isobutane (R600a) at temperatures from [formula omitted] to [formula omitted] K

The restrictions set by the F-gas Regulation and the Kigali Amendment to the Montreal Protocol have pushed an extensive research into alternatives for fluorinated greenhouse gases in air conditioning and refrigeration. Hydrofluoroolefins (HFOs) are emerging as promising substitutes for hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) in HVAC and refrigeration. Amongst these, R1243zf raised interests as low-GWP substitutes for R134a. The pursuit of low GWP refrigerants has also led to the examination of hydrocarbons (HCs), like propane (R290) and isobutane (R600a), due to their efficiency, low charge, and affordability, despite their flammability. The mixtures of R1243zf and isobutane could be of interest for medium temperature heat pump applications. Moreover, blending HFOs with HCs usually leads to azeotropic mixtures. While HCs benefit of a wide range of data and reliable Equations of State (EoS), HFOs, and in particular their mixtures, lack comprehensive information. This study reports vapor–liquid equilibrium (VLE) measurements for the 3,3,3-trifluoropropene (R1243zf) + isobutane (R600a) binary system in the temperature range between 283.15 K and 323.15 K. The measurements have been carried out by means of a vapor-recirculation apparatus combined with gas-chromatographic analysis. This work reports 53 experimental data with an expanded uncertainty (k=2) of 0.003 mol mol−1. The reported data, along with the data available in the literature, have been used to developed two new mixture models based on the Helmholtz free energy EoS, both leading to a significant improvement in the VLE prediction, with RMSE values lower than 0.005 mol mol−1 for both the liquid and the vapor phase composition.

The emission reduction potential and cost-effectiveness of low-GWP refrigerants in electric vehicle air conditionings

Electric vehicles play a crucial role in the carbon neutrality transformation of urban transportation, provided that they are powered by electricity generated from renewable (rather than fossil-based) generation sources. However, the substantial indirect emissions from electric vehicle air conditioning energy consumption and the significant direct emissions from HFCs (hydrofluorocarbons) refrigerants pose considerable challenges. In order to identify low-GWP (global warming potential) refrigerants -such as R1234yf, R744, and R290 - that can effectively minimize carbon emissions while maintaining certain cost-effectiveness, this paper establishes the relevant life-cycle analysis and life-cycle cost analysis models for electric vehicle air conditioning. The results obtained show that, in 2022, the total carbon emissions of China’s automotive air conditioning fleet were approximately 162 million tons CO2-eq. The nationwide average carbon emissions ranking of various refrigerant heat pumps is R290 < R1234yf < R744 < R134a. The Net Present Value (NPV) of the life cycle cost for R134a electric vehicle heat pump is estimated to be around 11,500 yuan. Among the three low-GWP refrigerants, the life cycle cost of R290 is significantly lower than that of R134a under nationwide average conditions, while R744 exhibits the best life cycle performance in certain cold cities/regions.

Theoretical Investigation of Low Global Warming Potential Blends Replacing R404A: The Simple Refrigeration Cycle and Its Modifications

Abstract R404A refrigerant is one of the most widely used hydrofluorocarbons in the commercial refrigeration industry for low and medium temperatures. However, this refrigerant contributes negatively to the environment due to its high global warming potential (GWP = 3943), and for several years, it has been labeled as one of the refrigerants that should be phased out. The present study theoretically evaluates low-GWP refrigerants as a replacement alternative to R404A, including R407H, R442A, R449A, R454A, R454C, R455A, R459B, and R465A. The analysis focuses on the comparison between relative differences in the volumetric flow in the compressor suction and the coefficient of performance for four configurations of the vapor compression cycle, such as the basic cycle, the cycle with an internal heat exchanger, the cycle with direct injection, and the cycle with a sub-cooler. According to the proposed operating conditions of evaporation temperature (−10 °C and −40 °C) and condensation temperature (40 °C and 55 °C), R454A could be the best long-term replacement option for its low GWP, energy performance, and direct fit for any configuration. R459B could also be considered a viable option, but with certain design modifications. On the contrary, the refrigerants R465A, R455A, and R454C would be discarded because they present a greater non-adaptation to the compressor in each configuration analyzed.

Effect of viscosity grade (POE) on the smooth-tube pool boiling performance with R-1234ze(E) refrigerant

In this study, the nucleate boiling heat transfer performance for R-1234ze(E) subject to lubricant oil is reported. The viscosity grade ranges from low viscosity (68 cSt) to high viscosity (220 cSt) and the tested POE oils include POEA-68, POEA-170, POEC-170, POEA-220, and POEC-220 on a horizontal smooth copper tube. The 30 different refrigerant-oil mixtures were prepared by varying the oil mass concentration ranging from 1 % to 10 % and the corresponding saturation temperatures are 10 °C, 0 °C, and − 6 °C with heat flux ranging from 10 to 90 kW/m2. The results showed that all grades of POE oils are compatible and completely miscible with low GWP refrigerant R-1234ze(E) in the given test range. The present study reveals that the heat transfer characteristics of each refrigerant-oil mixture very much depend on the saturated temperature, heat flux, oil mass concentration, and operating pressure. The highest mass concentration (10 %) consistently deteriorates the heat transfer coefficient (HTC). However, the degradation of HTC with R-1234ze(E) is comparatively less severe than that of R-134a/POE mixture. It is found that a 3 % oil concentration is regarded as the threshold concentration for the highest enhancement in the HTC when compared to the pure refrigerant. The performances of other oil concentrations such as 1 % and 5 % are subject to saturation temperature, heat flux, and evaporator pressure. In terms of the influence of saturation temperature on HTC of the mixture, it was observed that among all the grades of oil, POEC-170 oil shows peculiar behavior and its performance is independent of saturation temperature.

Thermodynamic and carbon emission analysis with low GWP refrigerants in automobile air conditioning system

Thermodynamic and carbon emission analysis with low GWP refrigerants in automobile air conditioning system

Energy, exergy and environmental (3E) analysis of low GWP refrigerants in cascade refrigeration system for low temperature applications

This study presents a comparative energy, exergy, and life cycle climate performance (LCCP) analysis of various refrigerants in a cascade refrigeration system (CRS). The refrigerants analyzed in the low-temperature cycle (LTC) include R-23, R-116, R-41, R-170, R-1150, and R-1132a whereas high-temperature cycle (HTC) utilizes R-404A, R-455A, R-454C, R-459B, R-161, R-290, R-1270, and R-1234yf. For the first time for CRS, LCCP analysis is conducted and fourth generation low GWP and less flammable prospective refrigerants R-1132a, R-455A, R-454C, R-459B are analyzed. The study aims to find a refrigerant pair that outperforms R-23/R-404A in terms of thermodynamic efficiency while also considering environmental impact and safety considerations. Among the 48 refrigerant groups analyzed, the study reveals that R-170/R-161 and R-41/R-161 demonstrate superior performance in terms of thermodynamic efficiency and environmental impact assessment whereas the largest exergy destruction components are HTC/LTC compressors. However, if flammability is a major concern, the recommended refrigerant pair is R-1132a/R-1234yf, as it is a suitable alternative in terms of safety considerations while still maintaining favorable thermodynamic and environmental performance.

Start-up characteristics of a R290 rotary compressor for an air source heat pump under low ambient temperature condition

Due to its excellent thermodynamic properties, low GWP refrigerant R290 is found to be promising alternative refrigerant. However, due to its special physical properties, high oil discharge rate and throttle valve blockage may occur for the R290 heat pump system under low temperature start-up conditions. In this paper, the transient characteristics, including the temperature, heat exchange rate, phase change rate, oil discharge rate and the liquid level of the oil sump, of a R290 rotary compressor used in the heat pump system under low temperature conditions are theoretically and experimentally studied. A transient heat and mass transfer model in the compressor is proposed, which considers the phase change of refrigerant in the shell. The experiment was carried out on the start-up characteristics of the compressor and the mathematical model was verified. The results show that high rotation speed and low temperature are the main reasons for the condensation of R290 in the shell. The excessive liquid refrigerant in the shell leads to a high oil discharge rate of up to 22 %. This paper will provide guidance for the use of R290 refrigerant under low temperature conditions.

An experimental data-driven charge model for round-tube-plate-fin heat exchangers using low-GWP refrigerants

Heat pumps can be switched between cooling and heating mode, requiring accurate charge modeling capabilities to enable the design of heat exchangers for near optimum efficiency in both operating modes. The charge modeling tools also require high-fidelity experimental validation data to tune their predictions. However, little experimental charge validation data is available in the open literature. This study addresses this need by providing complete, high-fidelity, experimental charge data of Round-Tube-Plate-Fin Heat Exchangers (RTPF) with ±2.2% of relative charge-measurement uncertainty and 0.8% of charge-measurement repeatability. In addition to R410A, charge data on two low-Global Warming Potential (GWP) refrigerants, R1234yf and R468C, is additionally collected. Furthermore, an accurate data-driven charge model is developed, tuned by the high-fidelity experimental charge data, with 12.3%, 12.8%, and 12.9% of the Mean Absolute Percentage Error (MAPE) based on the Taitel–Barnea, the Zivi, and the Baroczy void-fraction model, respectively. This experimentally validated charge model can contribute to enabling effective designs of heat pumps with high-accuracy charge predictions.

On falling film evaporator – A review of mechanisms and critical assessment of correlation on a horizontal tube bundle with updated development

Optimization of the energy efficiency and reduction of the greenhouse gas emission for the heat pump system is imperative to meet the net-zero goals at 2050. Chillers with falling film evaporator design not only possess better system performance but also contain less refrigerant inventory. Hence, accurate prediction of the evaporator performance is pivotal especially when charged with low-GWP refrigerant. The present study reviews the correlations for falling film evaporator with a horizontal tube bundle configuration. The major efforts of this study include four tasks: (a) literature review of the experimental studies and available empirical correlations; (b) comprehensive discussion of the falling film evaporation heat transfer mechanism; (c) development of a new rationally based correlation based on available literature; and (d) comparison of different correlations based on the existing data. The collected data includes 4114 data points from 8 sources, 6 refrigerants (R-600a, R-290, R-245fa, R-134a, R-1234ze(E), R-123), 5 types of the tubes (Plain, Turbo-GII-HP, GEWA-B, Low-fin, High-Flux), liquid Weber number from 2.2 × 10−6 to 0.7, imposed vapor Weber number from 0 to 37.2, heat flux from 2.5 to 151.5 kW/m2, and film Reynolds number from 1 to 3159.8. The new correlation gives a MAD of 28.3%, and an R2 of 0.86. Yet, the developed correlation considers various heat transfer mechanisms, including the transition point from falling film evaporation to the nucleate boiling, local evaporation, dry-out, mist flow, imposed flow, and enhanced tube effects.

Study of vapor compression refrigeration system with suspended nanoparticles in the low GWP refrigerant.

The rising global temperatures, attributed to the high global warming potential (GWP) of conventional refrigerants, necessitate the adoption of low-GWP alternatives in HVAC systems. However, these low-GWP refrigerants often exhibit high toxicity and flammability, limiting their usage. To address these challenges, compact heat exchangers incorporating blended refrigerants have been introduced to enhance HVAC system performance. Researchers have also made significant strides in improving HVAC system efficiency by introducing the concept of suspending nanolubricants and nanorefrigerants within the system. This review paper seeks to comprehensively assess the potential of alternative refrigerants containing suspended nanoparticles, commonly referred to as nanorefrigerants. The paper reviews various mechanisms and potential combinations of different nanorefrigerants employed to enhance refrigeration system effectiveness and efficiency. A detailed examination of key heat transfer parameters and the performance predictions of low-GWP refrigerants, including those from the hydrofluoroolefin (HFO) and hydrocarbon (HC) classes, is conducted through energy and exergy analyses. Commercial refrigerants like R-134a, R-290, R-600, R-600a, R-123, R-125, R-22, R-141b, R-152, R-11, R-113, R-404a, R-407c, R-502, R-600a, R-507a, R-1234yf, R-1234ze, 1336mzz(Z), and R-410a are evaluated in conjunction with suspended nanoparticles, considering their specific properties. The findings indicate that the utilization of nanorefrigerants leads to notable improvements in overall system performance, characterized by reduced compressor workloads and increased heat transfer rates. Consequently, the integration of blended nanoparticles into refrigerants holds significant promise for advancing the HVAC field.

Thermodynamic analysis of high temperature cascade heat pump with R718 (high stage) and six different low-GWP refrigerants (low stage)

Decarbonizing industrial heating globally is a significant challenge, driving the integration of high-temperature heat pumps for heat recovery and electrification in the industrial sector. However, current high-temperature heat pumps with low global warming potential refrigerants face limitations in delivering high-temperature heat due to their restricted compressor discharge temperature or require several compressors/intercoolers. To address these issues, a novel high-temperature cascade heat pump system is proposed, utilizing water (R718) in the high stage, while selecting one among six low GWP refrigerants (R1234ze(Z), R1233zd(E), R1336mzz(Z), R600, R600a, R601) in the low stage, with single compressor at each stage. To manage high discharge temperatures of high stage, liquid water injection is applied during high stage compression, modeled for both wet and dry steam. The model is validated against available experimental data with maximum error less than 5 %. Further, the effectiveness of the internal heat exchanger in low stage cycle is assessed for all investigated low stage refrigerants. Results reveal that R718 + R600 offers the optimal refrigerant working pair, achieving a maximum COP × VHC of 2895.1 kJ m−3 for delivering high temperature heat at water condensation temperature of 190 °C and recovering heat from low temperature waste energy of 50 °C.

Analysis and optimization of injection characteristics and comprehensive performance of low GWP refrigerant HP-1 in high temperature heat pump systems

In the context of low-GWP refrigerants becoming a research hotspot, the environmentally friendly refrigerant HP-1 with independent intellectual property rights in China has demonstrated significant advantages in fields such as data centers and 5G base stations. However, there are few applied studies in the field of high-temperature heat pumps (HTHPs), therefore, in this study, HP-1 was utilized in HTHP system and this process was combined with the injection technology. It has been proven to be an effective approach for performance improvement. The injection characteristics of HP-1-based HTHP were analyzed and optimized with a focus on safety, stability, and efficient operation. The application advantages of HP-1 were compared and analyzed in terms of thermodynamic performance and Total Equivalent Warming Impact. The results indicated that there were three types of characteristic injection pressures based on system performance, corresponding to the maximum coefficient of performance (COP), the lowest electronic expansion valve inlet refrigerant temperature, and the lowest exhaust temperature of the compressor. Further, the corresponding control equations for injection pressure were obtained. Based on the safety injection pressure, the optimal COP under injection pressure could effectively improve the COP of the system by 2.1–5.2 %, and the exhaust temperature also increased by 6.1–10.1 %. When the temperature of the heat source was 50 °C and the target heating temperature was 120 °C, the heating capacity of HP-1 increased by 10.8 % compared with that of R245fa, the COP of the system increased by 2.7 %, and the volume heating capacity increased by 10.3 %. Moreover, the emission reduction effect of HP-1 was significant, and the carbon dioxide emissions were reduced by 15.4–39.1 %. The analysis shows that HP-1 exhibits better performance and environmental characteristics than HFC-245fa. This study is of guiding significance to improve the thermodynamic performance of HTHP, for the safe and efficient operation and energy saving and emission reduction in the industrial field.