Low Global Warming Potential Refrigerants Research Articles

Ionocaloric refrigeration cycle

Developing high-efficiency cooling with safe, low-global warming potential refrigerants is a grand challenge for tackling climate change. Caloric effect-based cooling technologies, such as magneto- or electrocaloric refrigeration, are promising but often require large applied fields for a relatively low coefficient of performance and adiabatic temperature change. We propose using the ionocaloric effect and the accompanying thermodynamic cycle as a caloric-based, all-condensed-phase cooling technology. Theoretical and experimental results show higher adiabatic temperature change and entropy change per unit mass and volume compared with other caloric effects under low applied field strengths. We demonstrated the viability of a practical system using an ionocaloric Stirling refrigeration cycle. Our experimental results show a coefficient of performance of 30% relative to Carnot and a temperature lift as high as 25°C using a voltage strength of ~0.22 volts.

Coordinating to promote refrigerant transition and energy efficiency improvement of room air conditioners in China: Mitigation potential and costs

Implementing the Kigali Amendment to the Montreal Protocol has imposed certain restrictions on the production and consumption of hydrofluorocarbons (HFCs). Taking this opportunity to promote the alternatives of high global warming potential (GWP) HFC refrigerants in the room air conditioner (RAC) sector as well as improve the energy efficiency can bring double benefits. With the RAC sector as an example, a demand-emissions-cost model is developed to assess the potential and costs of emission reductions in different regions of China under different scenarios. The model includes three scenarios: a business as usual (BAU) scenario, a Kigali energy efficiency (KAE) scenario with simultaneous energy efficiency improvements following the Kigali amendment, and an accelerated transition energy efficiency (ATE) scenario with accelerated HFCs reduction and energy efficiency improvements. The results show that under the KAE and ATE scenario, the GHG emissions of the RAC sector will peak in 2025 at 389.8–393.9 Mt CO2-eq and 378.8–382.8 Mt CO2-eq in China. The main contribution to this result is the alternative of low GWP refrigerants. From 2021 to 2060, the cumulative direct emission reductions are about 6.4–7.4 Gt CO2-eq and 8.5–9.5 Gt CO2-eq in KAE and ATE, and the cumulative indirect emission reductions for both scenarios are 1.6–1.8 Gt CO2-eq. The cumulative abatement costs are $286–321 billion and $288–322 billion (prices in 2020). Under the ATE scenario, direct emissions from refrigerants in the RAC sector are near zero in 2060, and indirect emissions depend on the power system structure. The RAC sector's average abatement cost varies significantly in diverse climatic environments. Given the variation in average abatement cost, it is critical to tailor mitigation policies to local conditions to ensure maximum benefits.

Experiments of advanced centrifugal heat pump with supply temperature up to 100 °C using low-GWP refrigerant R1233zd(E)

High-temperature heat pumps (HTHPs) can play an extremely important role in reducing carbon emissions in industry heating. At the same time, heat pumps with low global warming potential (GWP) refrigerants need to be developed and promoted urgently, especially after the Kigali amendment entering into force. Therefore, a HTHP with low-GWP refrigerant R1233zd(E) was evaluated under 50 °C temperature lift conditions in this study. The advanced HTHP unit equipped with high-efficiency centrifugal compressor and enhanced heat exchangers was built to achieve the performance breakthrough. Control volume method of heat exchanger model was used in the simulation model of heat pump to optimize design of heat exchanger and heat transfer temperature difference from the perspective of the overall system. Experimental tests were conducted at working conditions of heat source temperature of 30–50 °C and output temperature of 60–100 °C. At the condition of 50 °C heat source and supplying 100 °C hot water, heating capacity of 381 kW and coefficient of performance (COP) of 3.67 were achieved, which is the highest efficiency in this condition among published lab-scale and prototype-scale units. The performance breakthrough of the heat pump improves the HTHP technology and promotes the applications in industrial process heating.

Exergy analysis of organic Rankine cycle for waste heat recovery using low GWP refrigerants

The use of exergy analysis in thermodynamic systems, as well as energy analysis, is quickly increasing. Exergy analysis is useful for identifying processes that cause exergy destruction and losses, and it may be used in conjunction with energy analysis. Due to environmental concerns, the use of waste heat has received a lot of attention in recent years. The Organic Rankine Cycle (ORC) is a promising method for converting waste heat into usable work at low temperatures. In this research, both the Basic Organic Rankine Cycle and the Regenerative Organic Rankine Cycle are considered for the analysis. Python is used for the simulation process. This investigation shows that the regenerative ORC has higher thermal and second law efficiency and a lower exergy destruction rate compared to the basic ORC. The Global Warming Potential (GWP) and Ozone Depletion Potential (ODP) of R1233zd(E), R1234ze(Z), R1234ze(E), and R1234yf are considered low. R1233zd(E) had a 1-5.66% and a maximum of 4.17% lower second law efficiency than R113 in regenerative ORC and basic ORC, respectively. On the other hand, R113 is not an eco-friendly fluid. As a result, R1233zd(E) can be used in place of R113 to assure better environmental quality by sacrificing a small portion of efficiency. The fluids which have a higher critical temperature showed better results compared to the fluids which have a lower critical temperature. Throughout the study, R1233zd(E) performed better than the rest of the three fluids. In both basic and regenerative ORC, R1233zd(E) has higher thermal and second law efficiency.

An Overview of Environment-Friendly Refrigerants for Domestic Air Conditioning Applications

Low global warming potential (GWP) refrigerants for the next-generation air conditioning systems have been investigated with target domestic applications. High-GWP refrigerants are mostly used in climate control applications such as heating, ventilation and air conditioning (HVAC) and refrigeration systems. The majority of refrigerants are responsible for significant environmental issues such as ozone layer depletion and global warming. The Montreal Protocol and the Kyoto Protocol have been implemented to address such issues. In the meantime, authorities in many countries have taken the initiative to phase out the usage of environmentally harmful refrigerants in vapor compression refrigeration systems. Following the global warming mitigation scheme by many signatory countries, research interest has been focused on finding alternative refrigerants with low or ultra-low GWP. This study considered the research trend and development of low-GWP refrigerants while examining system performance, safety issues, and the equivalent environmental impact as the critical assessment parameters. Here, the focus is primarily set on the potential of refrigerant blends (HFCs + HFOs) where the GWP value of 300 is set as the threshold value. Targeted for domestic heat pump systems, the performance of such systems using various refrigerant blends is collated and discussed. Many blends offer innovative drop-in replacements for R410A-conforming F-gas regulations. The technical difficulties and realistic remedies for the existing refrigerants are also discussed.

Solid–liquid equilibria of binary systems containing low global warming potential refrigerants

In this study, the solid–liquid equilibria of five binary systems containing refrigerants with low global warming potential, namely carbon dioxide (R744) + 1,1-difluoroethene (R1132a), R1132a + 2,3,3,3-tetrafluoropropene (R1234yf), R1132a + trans-1,3,3,3-tetrafluoropropene (R1234ze(E)), trifluoromethane (R23) + R1234yf, and R23 + R1234ze(E), was experimentally determined. Two experimental setups based on the cooling curve method were employed to measure the samples obtained from different sources. The results obtained using the two setups were in good agreement with the experimental uncertainty. In addition, the experimental data were compared with the values calculated using the Schröder equation, showing limited deviations. The accuracy of the experimental setups was tested by measuring the triple-point temperatures of the components of the studied binary systems, showing good agreement between the experimental data obtained for the pure refrigerants and the data available in the literature.

A state of art review on future low global warming potential refrigerants and performance augmentation methods for vapour compression based mobile air conditioning system

A state of art review on future low global warming potential refrigerants and performance augmentation methods for vapour compression based mobile air conditioning system

Techno-economic analysis of a PV/T waste heat–driven compound ejector-heat pump for simultaneous data centre cooling and district heating using low global warming potential refrigerants

A comprehensive techno-economic evaluation is evaluated based on an innovative compound ejector-heat pump system with PV/T (photovoltaic thermal) waste heat-driven. The aim of the system is simultaneous data centre cooling and waste heat recovery for district heating to reduce residential greenhouse gas emissions. The new system avoids the ejector pump by combining PV/T waste heat with an evaporative-condenser as an ejector driving force, considering several low global warming potential alternatives to R134a. The simulation indicates that the proposed system presents a remarkable difference in all investigated refrigerants’ overall system coefficient of performance (COP). Particularly, R515B presents the highest increase in COP, 54% and 49% in cooling and heating modes, respectively. It also provides the highest electricity consumption reduction, 84.1 MWh yearly. Moreover, the system improves the data centre power usage effectiveness (PUE) index from 10 to 19%. In financial terms, the shortest payback period (6.3 years) is obtained with R515B, followed by R515A and R1234ze(E).

Comparative numerical study of R134a and low global warming potential refrigerants during condensation inside a smooth and dimpled tube

Comparative numerical study of R134a and low global warming potential refrigerants during condensation inside a smooth and dimpled tube

Experimental investigation of R600a as a low GWP substitute to R134a in the closed-loop two-phase thermosyphon of the mini thermoelectric refrigerator

Various energy efficiency and environmental regulations around the world, such as the European Union's (EU) F-Gas regulation, are pushing refrigerator manufacturers to replace halogenated refrigerants with environmentally-friendly alternatives with low Global Warming Potential (GWP) without energy efficiency decrease. In this respect, increasing energy conversion performance by using a low GWP refrigerant in the mini thermoelectric refrigerators (MTERs) gains important for revealing sustainable and environmentally friendly refrigerators. To make this possible, the paper provides a comprehensive examination of the effect of climate-friendly refrigerant replacement in the closed-loop two-phase thermosyphon (CLTPT) on the performance of the MTER. This study treats the experimental investigation of the R600a as a low GWP substitute to R134a in the CLTPT of the MTER. Different from the other study in the literature, an extensive performance evaluation of the commercial MTER in terms of exergy as well as energy was performed and the various filling ratios (FR) of the R600a from 19% to 78% were analyzed for the best performance. The results showed that the MTER with a 46% and 32% FR of R600a had the highest exergy efficiency with 8.55% and 8.11%, respectively while reference MTER with R134a had 5.27%. It is concluded that 32% and 46% FR of the R600a enhanced the MTER energy conversion performance according to the 19% FR of the R134a, in line with the F-Gas regulation. The 32% and 46% FR of the R600a for MTER are the best refrigerant replacement, both from thermal performance and environmental points of view.

Thermodynamic Performance and Flammability Studies of Hydrocarbon Based Low Global Warming Potential Refrigerant Mixtures

Thermodynamic Performance and Flammability Studies of Hydrocarbon Based Low Global Warming Potential Refrigerant Mixtures

Searching for Sustainable Refrigerants by Bridging Molecular Modeling with Machine Learning.

We present here a novel integrated approach employing machine learning algorithms for predicting thermophysical properties of fluids. The approach allows obtaining molecular parameters to be used in the polar soft-statistical associating fluid theory (SAFT) equation of state using molecular descriptors obtained from the conductor-like screening model for real solvents (COSMO-RS). The procedure is used for modeling 18 refrigerants including hydrofluorocarbons, hydrofluoroolefins, and hydrochlorofluoroolefins. The training dataset included six inputs obtained from COSMO-RS and five outputs from polar soft-SAFT parameters, with the accurate algorithm training ensured by its high statistical accuracy. The predicted molecular parameters were used in polar soft-SAFT for evaluating the thermophysical properties of the refrigerants such as density, vapor pressure, heat capacity, enthalpy of vaporization, and speed of sound. Predictions provided a good level of accuracy (AADs = 1.3–10.5%) compared to experimental data, and within a similar level of accuracy using parameters obtained from standard fitting procedures. Moreover, the predicted parameters provided a comparable level of predictive accuracy to parameters obtained from standard procedure when extended to modeling selected binary mixtures. The proposed approach enables bridging the gap in the data of thermodynamic properties of low global warming potential refrigerants, which hinders their technical evaluation and hence their final application.

Flow condensation heat transfer and pressure drop of R134a alternative refrigerants R513A and R450A in 0.95-mm diameter minichannels

Due to the Kigali amendment to the Montreal Protocol, refrigerants such as R134a are targeted for phasedown or phaseout due to their global warming potential (GWP) and lower GWP refrigerants are being considered to replace R134a. Since the condenser is typically responsible for 50% of the charge of a refrigeration system, it is vital to have a fundamental understanding of the flow condensation heat transfer performance of low GWP refrigerants such as R513A and R450A. Experimental flow condensation heat transfer coefficient data are reported for R134a, R513A, and R450A in seven parallel 0.95 mm diameter mini-channels for a range of mass fluxes (i.e., 200 – 500 kg/m2s) and qualities (i.e., 0.2 – 0.8) at a saturation temperature of 40 °C. The heat transfer coefficient uncertainties for all experiments were ± 6.3 – 21.2%, with an average of ± 9.8%. Condensation heat transfer coefficients for R134a, R513A, and R450A all increased with increasing mass flux and quality. R513A condensation heat transfer coefficients were 2.6 – 25.6% lower than R134a heat transfer coefficients and pressure drops were 4.5 – 14.0% lower than R134a pressure drops. R450A heat transfer coefficients were 2.4% higher than R134a at higher mass fluxes and qualities and up to 11.7% lower than R134a at lower mass fluxes than R134a heat transfer coefficients; R450A pressure drop were comparable to R134a pressure drop (i.e., 5.0% higher to 9.5% lower). The data were compared to three condensation correlations – Shah (2016), Kim and Mudawar (2013), and Cavallini et al. (2011); the data were predicted with mean average errors of 23.4%, 15.9%, and 23.4%, respectively.

Assessment and development of the viscosity prediction capabilities of entropy scaling method coupled with a modified binary interaction parameter estimation model for refrigerant blends

Low global warming potential (GWP) refrigerant blends have been identified that may play a role according to the gradually reduction of the baseline amount of hydrofluorocarbons (HFCs) that can be replaced on the future market. Entropy scaling theory is a potential way to describing viscosity behavior of refrigerant mixtures, which is crucial for designing and optimizing of refrigeration system. However, an important prerequisite to apply entropy scaling model to mixture is reliable binary interaction parameters (kij). To promote intensive industrialization of entropy scaling theory and avoid expensive and time-consuming experiments for kij regression simultaneously, a modified Quantitative Structure Property Relationship (QSPR) theory is proposed in this work to provide reasonable estimated kij values with an additional dispersion term. To evaluate the performance of the proposed theory systematically, five different estimation methods are considered when predicting phase behavior and viscosity. Such model shows better performances: for the non-associating mixtures including HFCs, hydrofluoroolefins (HFOs), R744 and hydrocarbons (HCS), vapor liquid equilibrium data are predicted with the deviation of 1.47%, liquid mixture viscosities are exactly reproduced with an error of 3.49%. Besides that, the modified QSPR associated with the PC-SAFT equation of state (EoS) has superior performance of kij estimation than the London’s dispersive theory and the original QSPR, especially in describing some highly nonideal systems. As a supplement, the residual entropy scaling model for viscosity by Yang et al. and the commonly used extended corresponding states model are also applied to verify the modified method.

Comprehensive experimental evaluation of R1234yf-based low GWP working fluids for refrigeration and heat pumps

This work presents an experimental comparison for low GWP refrigerants used in vapour compression cooling and heating systems. The study compares three lower global warming potential (GWP) refrigerants (R513A, R516A, and R1234yf) as drop-in refrigerants to replace the hydrofluorocarbon (HFC) R134a. Measurements are taken from a test rig at different steady-state conditions: for the cooling mode, the evaporating temperature is −5 °C, −10 °C and −15 °C, and is combined with two condensing temperatures (32.5 °C and 40 °C), and different internal heat exchanger (IHX) effectiveness. Besides, in the heating mode, the evaporating temperature is 7.5, 15 and 22.5 °C with five condensing temperatures (55 °C to 75 °C, step of 5 °C). In the cooling mode, R513A presented the highest system COP amongst the low GWP alternatives, increasing up to 8%. R516A shows the lowest system COP at the highest evaporation temperature; however, it exhibits the highest COP and capacity at the lowest evaporation temperature. The IHX positively influences the refrigerating effect for all adopted refrigerants. Regarding the heating mode, R513A presents the highest heating capacity with an average 3% increase, whereas R516A shows the lowest results. R513A shows comparable COP to R134a, especially at higher evaporating temperatures.

Optimization of Residential Air Source Heat Pump using Low–Global Warming Potential Refrigerants

Optimization of Residential Air Source Heat Pump using Low–Global Warming Potential Refrigerants

Optimal refrigerant mixture in single-stage high-temperature heat pumps based on a multiparameter evaluation

High-temperature heat pumps (HTHPs) are compression systems that convert residual heat to high-grade heat used in several industrial applications. Refrigerants for HTHPs are still not explored, and most studies consider only pure refrigerants. This study carries out a general screening of binary and ternary mixtures for HTHPs through a multiparameter optimization based on low global warming potential (GWP) refrigerants that are feasible for operating at higher temperatures. The proposed methodology considers several parameters such as coefficient of performance, volumetric heating capacity, flammability, GWP, and perfect glide matching. The blends were required to have a critical temperature above 150 °C and to provide high energy performance to diminish the indirect carbon footprint. No ideal mixture was found for every parameter, so a trade-off solution was required. The most critical variable was flammability, reducing the coefficient of performance significantly if the ASHRAE Std 34 A1 restriction had to be fulfilled. Finally, different mixtures are given as the bests based on the main optimizable parameter. The most promising ones which comply with the environmental restriction were R-1233zd(E) and R-1336mzz(Z) based mixtures.

Experimental study on diffusion absorption refrigerator achieving 0.2 coefficient of performance using low global warming potential refrigerant and low-grade heat source

The commercial model of diffusion absorption refrigeration operated purely via thermal energy utilizes ammonia as a refrigerant. Ammonia is not only a toxic substance but also reacts with copper; thus, most commercialized diffusion absorption refrigerator is fabricated using carbon steel instead of copper. In the previous research, copper cannot be used in the diffusion absorption refrigerator because of the ammonia. However, in this study, via the newly proposed low global warming potential refrigerant R600a, copper absorber can be employed to improve the coefficient of performance of diffusion absorption refrigerator. R600a, n-octane and helium are used as the refrigerant, absorbent, and auxiliary gas, respectively. Simultaneously, the bubble pump and absorber are fabricated from copper to improve the heat transfer rate. As a result, a high coefficient of performance is achieved despite the use of a low global warming potential refrigerant. In particular, the experimental analysis is conducted with a focus on how the effectiveness and performance of the absorber vary by comparing carbon steel and copper as the absorber material. The configuration of the two diffusion absorption refrigerators is exactly the same but the absorber material is changed. When employing copper, the effectiveness of the absorber is improved by 9.09–35.71% compared to that of carbon steel absorber under the same heat input. In addition, an experimental investigation is conducted by changing the pressure to 400 kPa, 465 kPa, 530 kPa, and 600 kPa for heat input in the range of 30–100 W to analyze the effect of heat input and operating pressure. By utilizing copper for diffusion absorption refrigerator with R600a, a coefficient of performance of 0.20 is achieved at a low generator temperature of 71.07 °C, which is the highest coefficient of performance and the lowest generator temperature with low global warming potential, so that solar energy can be utilized as the heat source in the present diffusion absorption refrigerator system.

Theoretical estimation of efficiency defect in cascade refrigeration system using low global warming potential refrigerant pair

In the presented work, researchers used Efficiency defect as a parameter for deciding the utility of refrigerants in the Cascade refrigeration system. Cascade refrigeration system’s mathematical model is created. Using the first and the second law of thermodynamics energy analysis and exergy analysis are done for different low Global warming potential refrigerant pairs like R134a/CO2, R1234yf/CO2, and R1234ze/CO2. Based on the analysis efficiency defect is calculated for every component of the cascade system individually and the whole system as well. It is found that R1234yf/CO2 has the highest value of efficiency defect, whereas R134a/CO2 has the least efficiency defect for the whole cascade system. Change of efficiency defect in various components with evaporator temperature is presented in form of graphs.

A2L low GWP HFO based refrigerant solutions in heat pump applications to drive energy efficiency, safety, and sustainability even in building restoration

Driven by energy efficiency requirements and legal restrictions like F-Gas Regulation Heat Pump OEM supplier are looking for alternative refrigerant solutions. HFO based low GWP refrigerants can help increasing the system efficiency, expanding the operating temperature range while reducing CO2 emissions. For building restoration in particular, high flow temperatures (for existing hydronic heating system) are essential for convenient and cost-and energy-efficient replacements of fossil fuel boilers. A2L classified refrigerants provide extended application range at highest safety level versus A3 classified refrigerants, but R-32 still carries a Global Warming Potential (GWP) of 675 making it a transitional solution. This paper compares different relevant parameters and points out the advantages provided by HFO A2L low GWP refrigerants (like R-454B and R-454C) for a wide capacity range of air to water and brine to water heat pumps. A special focus is put on the application of building restoration.