High GWP Refrigerants Research Articles

Development of the National Cooling Action Plan of the Philippines

Abstract The Philippines NCAP was developed to account for the environmental impacts of energy consumption (indirect impacts) and use of high-GWP refrigerants (direct impacts) from the RAC Sector that can be mitigated by transitioning to more climate-friendly and higher-efficiency refrigerants. Utilizing the NCAP Methodology developed by the UNEP-led Cool Coalition, UN ESCAP in collaboration with Alliance for an Energy Efficient Economy (AEEE) together with and built on the expertise of the Cool Coalition’s NCAP Working Group facilitated by The Kigali Cooling Efficiency Programme (K-CEP), the Philippines NCAP was launched by the Philippines Department of Energy – Energy Utilization and Management Bureau, Department of Environment and Natural Resources, and United Nations Development Programme (Philippines Country Office). This paper presented the Reference Cooling Scenario (RCS) and the Sustainable Cooling Scenario (SCS) adopted from the business-as-usual (BAU) and Clean Energy Scenario (CES) of the Philippine Energy Outlook. With these assumptions on RCS and SCS, the domestic refrigeration sector will save 4.41 TWh while the residential cooling sector will save 12.15 TWh. There is a net effect in total emission reduction estimates of 10.68 MT CO2 equivalent which is close to 12 % of the unconditional target submitted to UNFCCC.

Electrifying Chemistry: Characterizing TEMPO-Based Electrocatalysts for Isopropanol to Acetone Conversion in Novel Heat Pumps

Heating, ventilation, and air conditioning (HVAC) systems account for more than 40% of the U.S. electricity usage, primarily utilizing vapor compression system (VCS) heat pumps, raising environmental concerns. The phase down of high GWP refrigerants, targeting an 85% reduction by 2035, prompts the exploration of novel heat pump technologies. Electrochemical looping heat pumps (ELHP) show promise by employing redox reactions for fluid compression to replace conventional compression technologies. However, energy-intensive redox interconversion necessitates catalysts to lower activation energy. Inspired by electrosynthesis principles, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) emerged as a successful homogeneous electrocatalyst for selective isopropanol oxidation to acetone for use in ELHP. HPLC and 13C NMR confirmed remarkable selectivity (~100%) at practical isopropanol concentrations.To enhance TEMPO's catalytic activity, various electron-withdrawing and donating groups were explored. TEMPO-OCH3, among seven derivatives, exhibited superior efficiency with a notable rate constant (6 M-1s-1) and turnover frequency (3.1 s-1). This study innovatively applies concepts from molecular catalysis for the development of efficient catalyst materials.

Experimental COP optimization procedure in an air-based reverse Brayton cycle for cryogenic applications

Sustainable and efficient refrigerants are essential due to increasing regulatory constraints on traditional high-GWP refrigerants. This study investigates the potential of natural refrigerants, specifically air, in Reverse Brayton Cycles (RBC) for low-temperature applications. Unlike carbon dioxide and ammonia, which pose limitations and safety concerns below -40°C, air offers a safer and more versatile solution due to its excellent thermodynamic properties and availability. An experimental RBC was constructed using automotive components like centrifugal compressors, a radial turbine, and inter-coolers. These cost-effective and accessible components shift the refrigeration paradigm. The RBC was tested to optimize the Coefficient of Performance (COP) at -100°C while dissipating 2 kW, a typical scenario for whole-body cryotherapy (WBC). Key control parameters included the pressure ratio of the centrifugal compressors and the position of the stator vanes in the variable geometry turbine (VGT). The optimization process resulted in a COP increase of up to 28%. Additionally, a 1D gas-dynamic model validated these results, suggesting that different component selections could enhance performance by 17% compared to the experimental optimum point. Air-based RBC systems using automotive components can effectively achieve temperatures below -40°C, offering a viable, eco-friendly alternative to traditional refrigerants. This advancement addresses regulatory challenges and contributes to the scientific community by providing a sustainable refrigeration solution using commercially available components and demonstrating improvements through experimental data.

A Review of Energy-Efficient Technologies and Decarbonating Solutions for Process Heat in the Food Industry

Heat is involved in many processes in the food industry: drying, dissolving, centrifugation, extraction, cleaning, washing, and cooling. Heat generation encompasses nearly all processes. This review first presents two representative case studies in order to identify which processes rely on the major energy consumption and greenhouse gas (GHG) emissions. Energy-saving and decarbonating potential solutions are explored through a thorough review of technologies employed in refrigeration, heat generation, waste heat recovery, and thermal energy storage. Information from industrial plants is collected to show their performance under real conditions. The replacement of high-GWP (global warming potential) refrigerants by natural fluids in the refrigeration sector acts to lower GHG emissions. Being the greatest consumers, the heat generation technologies are compared using the levelized cost of heat (LCOH). This analysis shows that absorption heat transformers and high-temperature heat pumps are the most interesting technologies from the economic and decarbonation points of view, while waste heat recovery technologies present the shortest payback periods. In all sectors, energy efficiency improvements on components, storage technologies, polygeneration systems, the concept of smart industry, and the penetration of renewable energy sources appear as valuable pathways.

Thermodynamic, environmental, and exergoeconomic analysis of multi-ejector expansion transcritical CO2 supermarket refrigeration cycles in different climate regions of Türkiye

Restrictions on high-GWP refrigerants have made the use of transcritical CO2 refrigeration systems widespread. Using transcritical booster refrigeration cycle in warm climates is unsatisfactory due to its high energy consumption. This paper presents theoretical analysis and performance comparison of three different transcritical CO2 supermarket refrigeration cycle configurations with ejector expansion in Türkiye, which has different climatic regions. Bin-hour data were derived using hourly dry-bulb temperature values for provinces from 7 different regions in Türkiye. The applicability of multi-ejectors to each modeled cycle was also investigated. Annual energy consumption and environmental impact reductions of up to 17% were obtained using ejector expansion cycle compared to booster cycle. Ejector expansion cycles achieved higher performance than booster cycle up to 46% in terms of exergy efficiency at investigated ambient temperatures. Unit product exergy costs of the ejector cycles were found up to 28% lower than booster cycle.

Experimental analysis into the effect of heat exchanger sizing on charge optimization in an R410A chiller with a dedicated subcooler

There is an increased focus on the amount of refrigerant used in the HVAC&R systems due to the ongoing phase-down of high GWP refrigerants. In the current work, charge optimization is conducted with a variable speed compressor in an R410A chiller having a nominal cooling capacity of 8 kW, which is installed with a condenser, receiver and dedicated subcooler. This study also provides for the first time insights into how a receiver and a dedicated subcooler can be used to not only obtain optimum subcooling but also account for any potential refrigerant leaks by holding additional charge in the receiver. Results indicate that an ideal charge optimization curve can be achieved by sizing the condenser and subcooler to ensure only the optimum subcooling happens in the subcooler. The impact of dedicated subcooler and condenser sizing on charge optimization as well as the system, and seasonal performance is also studied. This analysis helps in understanding how these components should be sized and when the diminishing returns occur from oversizing. This work also shows that when the system is operating with enough refrigerant to fill the receiver with saturated liquid refrigerant, using a dedicated subcooler decouples the cooling capacity increment from power consumption increase typically observed with increasing subcooling. Results show that for the current system investigated increasing the dedicated subcooler area beyond 8 % of the total available heat rejection area will not yield any additional seasonal performance improvement.

ENERGY, ENVIRONMENTAL, AND EXERGOECONOMIC (3E) ANALYSIS OF TRANSCRITICAL CO2 BOOSTER AND PARALLEL COMPRESSION SUPERMARKET REFRIGERATION CYCLES IN CLIMATE ZONES OF TÜRKİYE

Legal restrictions on high-GWP refrigerants lead to the widespread use of carbon dioxide in commercial refrigeration, where there is a high energy consumption. Although CO2 has many benefits, its lower critical temperature and higher operation pressure compared to other refrigerants lead to performance reduction. For this reason, studies have been conducted by researchers for performance enhancement. This paper presents energy, environmental impact, and exergoeconomic (3E) analysis of transcritical CO2 booster and parallel compression supermarket refrigeration cycles based on meteorological data of 11 provinces in Türkiye as samples of different climatic regions. Parallel compression cycle achieved up to 18.4% higher coefficient of performance than booster cycle between the investigated ambient temperatures. Up to 5.6% annual energy consumption and environmental impact reduction were obtained using parallel compression. Unit product costs of the parallel compression cycles were calculated between 8.2% and 18% lower than booster cycle in investigated provinces. Developing energy-efficient systems that use environmentally friendly refrigerants will contribute to a sustainable future.

Experimental study on falling film evaporation heat transfer outside a horizontal tube in refrigeration system

Experimental study on falling film evaporation heat transfer outside a horizontal tube in refrigeration system

Numerical simulation of heat transfer characteristics of falling-film evaporation of R32/R134a non-azeotropic refrigerant outside a horizontal tube

In response to the restrictions of the international community on the utilization of refrigerants with high GWP, the replacement of high-GWP refrigerants with non-azeotropic refrigerants and reduction in refrigerant charge have gradually become important research topics in academia. In this study, based on the VOF method, a 2D model of a sheet flow pattern was developed by considering the thermophysical properties and multicomponent phase change of a mixture. The falling-film evaporation of a non-azeotropic refrigerant composed of R32 and R134a outside a horizontal tube was numerically simulated. The effects of the spray height (H), tube diameter (d), inlet temperature (Tinlet), Reynolds number (Re), heat flux (q), and mass fraction of R32 in the liquid-phase mixture (MR32_liquid) on the heat transfer coefficient (HTC) were studied. The results indicate that with the increase of circumferential angle (Φ), the local HTC exhibits a trend of decreasing, increasing, decreasing, and increasing in sequence. The largest contribution to the increase in the average HTC comes from the impact and fully developed regions. An increase in H, Tinlet, and MR32_liquid is beneficial to the expansion of the fully developed region, whereas a decrease in d leads to expansion of the fully developed region. An increase in Re does not affect the extent of the fully developed region. The increase in H, Re, Tinlet, and MR32_liquid increases the average HTC, but the effect of Tinlet is not significant. Under the conditions of d = 24 mm, H = 13 mm, Re = 4000, MR32_liquid = 0.5, and q = 10 kW/m2, as the inlet temperature increases from 243.15 K to 283.15 K, the average HTC increases by 2.5%. An increase in q does not affect the average HTC, whereas an increase in d does not improve the average HTC.

A novel two-stage compression air-source heat pump cycle combining space heating, cooling, and domestic hot water production

To improve the efficiency of HVAC system, a novel air-source heat pump based on the two-stage compression cycle is proposed. The heat pump shows the multi-function of producing the domestic hot water year-round, space cooling water in summer, and space heating water in winter. The theoretical model is developed to analyze the performance of heat pump under various conditions. Four high GWP refrigerants, including R134a, R32, R407, R410A, and four low GWP refrigerants, including R1234ze(E), R600a, R152a, R290, are compared and analyzed under various conditions. Besides, the effects of environment and system operation parameters, such as domestic hot water demand ratio, evaporating and condensing temperatures, on system performance are investigated. The major results are concluded: A multi-functional air-source heat pump shows high annual efficiency by switching both the four-way valve and tee valve. The low GWP refrigerant R152a shows the best performance among the selected refrigerants, especially for summer conditions, and the COP is higher than the R1234ze(E), R134a, R600a, R32, R407C, R410a, and R290, R152a by 10.4 to 9.0 %, 8.3 to 7.9 %, 5.6 to 4.0 %, 9.1 to 13.0 %, 20.9 to 23.3 %, 29.8 to 36.5 %, and 11.0 % under the selected condition, respectively. Compared with summer conditions, R152a improves COP slightly under winter conditions, especially for R600a and R134a (less than 5 % under the selected conditions). Besides, under the summer conditions, the system performance increases first and then decreases with the increasing domestic hot water demand. The maximum COP reaches 6.7 while the summer domestic hot water load ratio (SLR) equals 0.5 and the environment air temperature equals 25 °C. The heat pump also shows a good performance under winter conditions. The minimum COP reaches 2.4 with the air temperature of −25 °C and the winter domestic hot water load ratio (WLR) of unity. The result of this study hopes to promote the further improvement of the air-source heat pump and HVAC system.

Solubility, miscibility and compatibility studies of low GWP non-flammable refrigerants and lubricants for refrigeration and air conditioning applications

Majority of currently used refrigeration and air conditioning systems utilize high GWP refrigerants such as R410A, R404A and R134a. These systems have large leak rates which leads to significant amount of release of HFC's to the environment. The growing environmental concerns are driving stringent regulations to phase out these high GWP refrigerants and move towards adoption of lower GWP refrigerants. This transition would require understanding of interaction between low GWP refrigerants and lubricating oil as well as the material compatibility with commonly used thermoplastics and elastomers. In this article, nonflammable low GWP refrigerants, R515B and R471A are introduced as the potential replacements for R410A, R404A and R134a in an air-conditioning and medium temperature refrigeration applications. Solubility and miscibility of R515B and R471A with polyol ester-based oil (POE32) is experimentally investigated over a temperature range of −20 °C to 120 °C and −30 °C to 75 °C, respectively. Further this article also presents the compatibility results of R515B and R471A (POE32) with thermoplastics and elastomers used in refrigeration and air-conditioning systems.

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.

Separation of Azeotropic Refrigerant Mixtures Using Ionic Liquids

Refrigeration and air-conditioning systems are widespread throughout modern society, from the refrigerated cold chain that provides fresh foods and storage of medicines to the air conditioning of homes and buildings. Refrigeration is viewed as one of the most transformative engineering achievements of the 20th century and the demand for cooling will continue to increase as economic conditions improve and the climate continues to warm; however, refrigerants do come with an environmental cost.In 1987, the Montreal Protocol phased out chlorofluorocarbon (CFC) refrigerants because of their high ozone depletion potential (ODP). The replacements, typically mixtures of hydrofluorocarbons (HFCs), are safe for the Earth's ozone layer, but most have high global warming potentials (GWPs). HFCs account for 7.8% of total global greenhouse gas emissions, with 63% of that from “indirect” emissions (i.e., energy for running the system). As a result, 197 countries signed the Kigali agreement in 2016 to phase out high-GWP HFCs, with the goal of reducing emissions by 80% in the next 20 years. Millions of metric tons (mts) of high-GWP refrigerants will need to be reclaimed, but there are no good methods for separating and recycling the individual components, given that many are azeotropic mixtures.Currently, there is no means of separating azeotropic HFC mixtures, and the refrigerants will ultimately have to be incinerated. The commercial HFC mixture R-410A containing 50 wt.% HFC-32 (GWP = 675) and 50 wt.% HFC-125 (GWP = 3500) is a prime example. The HFC-32 can be reused when separated in new low-GWP products such as R-454B (69 wt% HFC-32 and 31 wt% HFO-1234yf) with a 75% lower GWP than R-410A.Ionic liquids are being developed that can separate azeotropic HFC mixtures based on differences in solubility and used as entrainers in extractive distillation. This presentation will provide experimental data on the solubility of HFCs in ionic liquids that have been measured using gravimetric microbalances and modeling using the Peng-Robinson equation of state. ASPEN Plus simulations will show how a pilot process has been designed that can continuously separate azeotropic refrigerant mixtures such as R-410A.

Energy analysis and performance comparison of transcritical CO2 supermarket refrigeration cycles

Using carbon dioxide as a refrigerant gains importance as a result of restrictions applied to high-GWP (Global Warming Potential) refrigerants. Although CO2 is an environment-friendly refrigerant, its low critical temperature and high operating pressure lead to high energy consumption, especially in commercial refrigeration. As a result, research and improvements are being made to reduce the energy consumption of transcritical CO2 refrigeration cycles. This paper presents thermodynamic analysis and pressure optimizations to obtain maximum performance for transcritical booster, parallel compression, and ejector expansion supermarket refrigeration cycles. Effects of different operation conditions were also investigated and cycles were compared to each other in terms of performance. It was obtained that up to 47% Coefficient of Performance (COP) improvement can be achieved using ejector expansion cycle with the help of expansion work recovery in the ejector. It was also shown that ejector expansion cycle outperforms other CO2-only cycles without ejector in all conditions.

Combined cold supply system for ship application based on low GWP refrigerants - Thermo-economic and ecological analyses

The withdrawal of popular high-GWP refrigerants will significantly affect maritime industry. Refrigeration and air conditioning systems currently used on ships are not ready to fulfil future limitations. Therefore, there is a need for system, which will operate with low-GWP refrigerants and at the same time will be efficient and reliable in difficult environmental conditions. This paper explains the concept of a cold supply system, in which refrigeration/freezing plant rejects heat not to a seawater but to a chilled water, produced by the air conditioning unit. Configuration of single stage compression with internal heat exchanger and HFO refrigerant was used in the air conditioning system, while in the refrigeration/freezing plant, two-stage compression trans-critical booster with R744 as refrigerant. Comparative thermodynamic analyses of presented concept with other configurations of thermodynamic cycles and refrigerants were performed. They were carried out in wide range of seawater temperature values and incorporated efficiency characteristics of compressors produced by a well-known manufacturers. Results confirmed ability of described system to improve energy efficiency in comparison with separated and currently used on ships cold supply systems, especially in hot climate. Economic and ecological analyses of proposed concept exhibited an additional benefit - positive environmental impact.

Energy impact evaluation of different low-GWP alternatives to replace R134a in a beverage cooler. Experimental analysis and optimization for the pure refrigerants R152a, R1234yf, R290, R1270, R600a and R744

Due to the entry into force in 2014 of the European F-Gas Regulation n° 517/2014 and the subsequent Kigali amendment, the phase-out of the medium and high-GWP refrigerants has speeded up in all refrigeration fields. The effect on the plug-in or stand-alone systems has meant that other environmentally friendly refrigerants must replace the R134a with low or ultra-low GWP maintaining the same operating conditions and reducing the energy consumption. Extended examples of these fluids are the hydrocarbons R600a and R290 and the inorganic fluid R744 (CO2). However, there are other alternatives to the HFCs R152a and R1234yf or the hydrocarbon R1270 that have hardly been analysed and can make a positive contribution to this sector. Accordingly, this work aims to evaluate the behaviour of a commercial beverage cooler experimentally when it is optimised with six alternatives to the HFC R134a: R152a, R1234yf, R290, R1270, R600a and R744. Results demonstrated that fluids R290, R1270, R152a, R744 and R600a reduce the energy of R134a in 27.5%, 26.3%, 13.7%, 3.9% and 1.2%, respectively, while the use of R1234yf increases the energy usage to 4.1%.

Trends in best-in-class energy-efficient technologies for room air conditioners

Improving the efficiency of room air conditioners (RACs) could provide significant energy and associated emissions savings, particularly in emerging economies with hot climates where the cooling demand is expected to increase dramatically. To help accelerate efficiency improvements, this study identifies “best-in-class” high-efficiency RAC components and products. The findings show that manufacturers tend to minimize manufacturing costs by using RAC designs that are readily available or standardized to their production, and they share components across various models. High-efficiency RAC models use advanced compressor technologies optimized at a low frequency, large heat exchangers with thermodynamically effective materials and designs, highly efficient direct current fan motors, advanced metering devices, and smart sensors for temperature and humidity control. Recently RAC manufacturers have been improving seasonal efficiency – better reflecting part-load operation – especially via variable-speed (inverter) drives for compressor motors. Recent highest-efficiency RAC models use low global warming potential (GWP) refrigerants, having transitioned from conventional high-GWP refrigerants, in regions where RACs that use these low-GWP refrigerants are commercially available. Recently demonstrated innovative technologies show trends toward smart hybrid designs, evaporative cooling, and solid-state materials beyond the conventional vapor-compression technology. This information could help policymakers improve their RAC market-transformation programs to align with the most-efficient global technology.

Selection and validation on low-GWP refrigerants for a water-source heat pump

Heat pumps are generally recognized as an efficient energy-saving method, and are widely used in industrial and residential applications. Due to the ratification of the Kyoto Protocol, the use of high-GWP refrigerants is gradually being restricted and they will be phased out for heat pump systems. Currently, low-GWP refrigerants, such as R718, R1234ze(Z), R600, R600a, R1233zd(E) have been evaluated for high-temperature heat pumps. However, there is still a lack of choice and research regarding low-GWP refrigerants for conventional heat pumps. Therefore, taking the system’s COP, volumetric heating capacity, pressure ratio and discharge temperature into consideration, R1234ze(E) is selected for study in this paper due to its relatively excellent system performance for wider working temperature ranges. Furthermore, a water-source heat pump using R1234ze(E) as the working fluid was simulated, built, and tested. The experimental results showed that the COP of the R1234ze(E) heat pump can reach 3.5 with a heat source varying from 10 °C to 30 °C and a water outlet temperature above 60 °C. The simulation results are in good agreement with experimental data. Moreover, the component characteristics were compared between R1234ze(E) and R134a. The results show that R1234ze(E) has apparent advantages for residential use and is economically comparable with R134a.

Understanding the market need for skills in alternative refrigerants with low global warming potential in the EU region – A comprehensive survey on Refrigerant Emissions And Leakage (REAL) alternatives programme

The widespread adoption of low GWP alternative refrigerants across Europe is critical to achieving long-term carbon reduction emissions from the Refrigeration, Air Conditioning and Heat Pump (RACHP) sector. The RACHP sector has been identified as being responsible for significant greenhouse gas emissions through direct emission (leakage of high GWP refrigerants) and indirect emissions (energy use). The changes to EU's Fluorinated greenhouse gases (F-gas) regulation No 517/2014, which came to force since 1st January 2015, has enacted restrictions on the use of halocarbon refrigerants in certain applications with the intent of reducing the F-gas associated emissions in the EU region. There are currently inconsistent levels of knowledge and awareness of how alternative refrigerants can be sustainably procured and utilised. This paper provides an understanding of the needs for skills in some European countries, specifically covering the general overview of the “as installed“ RAC use, the current training provision, the potential use and status of alternative refrigerants and recommendations on procurement process. Furthermore, the paper discusses the availability of skills and existing training materials and template in specific European countries.

Co-benefits of Energy-Efficient Air Conditioners in the Residential Building Sector of China.

Electricity demand for room air conditioners (ACs) has been growing significantly in China in response to rapid economic development and mounting impacts of climate change. In this study, we use the bottom-up model approach to predict the penetration rate of room ACs in the residential building sector of China at the provincial level, with the consideration of the urban-rural heterogeneity. In addition, we assess co-benefits associated with enhanced energy efficiency improvement of AC systems and the adoption of low-global-warming-potential (low-GWP) refrigerants in AC systems. The results indicate that the stock of room ACs in China grows from 568 million units in 2015 to 997 million units in 2030 and 1.1 billion units in 2050. The annual electricity saving from switching to more efficient ACs using low-GWP refrigerants is estimated at almost 1000 TWh in 2050 when taking account of the full technical energy efficiency potential. This is equivalent to approximately 4% of the expected total energy consumption in the Chinese building sector in 2050 or the avoidance of 284 new coal-fired power plants of 500 MW each. The cumulative CO2eq mitigation associated with both the electricity savings and the substitution of high-GWP refrigerants makes up 2.6% of total business-as-usual CO2eq emissions in China over the period 2020 to 2050. The transition toward the uptake of low-GWP refrigerants is as vital as the energy efficiency improvement of new room ACs, which can help and accelerate the ultimate goal of building a low-carbon society in China.