Review on ozone depletion and global warming

The current electric refrigeration and air condition systems are major causes for ozone depletion and global warming. These systems consume large percent of the worldwide gross production of electricity (around 17%). Therefore, developing new refrigeration systems that are able to work using renewable sources (solar, geothermal, etc) and waste heat sources is necessary to address these problems. In this paper, an experimental investigation and heat transfer analysis of an innovative thermal-mechanical refrigeration (TMR) system are presented. The TMR system replaces the electric compressor of the conventional refrigeration systems with an expander-compressor unit (ECU). The ECU can be driven by ultra-low temperature heat sources, has simple configuration, and high flexibility for the operating conditions. A hybrid electric-compressor and ECU refrigeration experimental setup was built to investigate the performance of the ECU and compare it to the electric compressor with R134a as the working fluid. The effect of the major operating parameters (condenser and evaporator pressures and temperatures) on the performance of the electric and TMR systems are investigated and analyzed. The results show that a maximum COP is obtained at refrigerant mass of 30g in electric mode and at refrigerant mass of 60g in ECU mode. A comparison of the TMR to other existing thermal refrigeration systems showed that most of these systems have more complex configurations, lower COP, and higher capital costs.

A major current focus of refrigeration and air-conditioning research is energy usage and environmental impact (e.g., the influence of refrigerants and air-conditioning systems on ozone layer depletion and global warming). The ejector-based refrigeration system is a technology that, it is hoped, can save power while using environment-friendly refrigerants to reduce any adverse effects on nature. The reduction of compressor dependency is the first and essential aim of this study; the second is to demonstrate the replacement of R134a with the new refrigerant R1234yf in motor vehicle air-conditioning systems, establishing the benefits of employing R1234yf in conjunction with a hybrid air-conditioning system. In such a system, the engine's exhaust gases are used to operate the ejector. A numerical model has been developed which estimates the ejector entrainment ratio at a specified spindle and primary nozzle exit position. A theoretical model using energy and exergy analysis illustrates the impact of hybrid systems on performance under different operating conditions (i.e., engine exhaust, ambient air, and evaporator temperatures). At a specified exhaust temperature, a detailed comparison has been conducted between a current air-conditioning system with R134a and the hybrid system with R1234yf. It was found that the R1234yf hybrid system reduced compressor energy consumption by 44.43% and operating exhaust heat levels by 12.79%. The coefficient of performance increased by 41.42%, while the exergetic efficiency reduced from 37.14% to 13.85%. Cooling capacity dropped by 12.73%. The hybrid air-conditioning system based on R1234yf demonstrated tremendous potential for improving vehicle air-conditioning system efficiency.

Applications of refrigerant R1234yf in heating, air conditioning and refrigeration systems: A decade of researches

Assessment of a novel defrost method for PV/T system assisted sustainable refrigeration system

The phase‐out of CFC production and further regulations on HCFC are required because of their association with the depletion of stratospheric ozone. HFCs and their mixtures have evolved as long‐term replacements for CFCs and HCFCs. For air conditioning and refrigeration systems, new synthetic lubricants having miscibility with HFC refrigerants, similar to that of mineral oils with CFCs, have been developed. Data on the miscibility ofR‐32/125 and R‐125/143a with polyol ester lubricants are presented in this paper. In the temperature range of interest (−40°C to 60°C), we observed the upper immiscible region, lower immiscible region, as well as the coalescence of the two regions, for polyol ester lubricants with these HFC refrigerant mixtures. HFC‐143a is least miscible among the three pure HFC refrigerants. The stability of R‐32/125 and R‐125/143a with dry polyol ester lubricants is very good at 204° C. With high moisture content, hydrolysis of the lubricant occurs at high temperatures. The onset of significant hydrolysis of lubricant (B) takes place between 175°C and 200°C. Care must be exercised to maintain the dryness of polyol ester lubricants and refrigeration systems to prevent this occurring.

Air-conditioning and refrigeration systems are electrical appliances that use a huge amount of energy and contribute indirectly to global warming. Also, R410A which was initially developed as a substitute for ozone-depleting refrigerants in the air-conditioning systems has been phase-out due to its high global warming potential (GWP) and the resulting harmful effect on the climate. In addition to the issue of refrigerant high GWP, energy consumption is a significant issue. The energy efficiency of new refrigerants must then be considered in the search for alternative refrigerants to ensure that they do not lead to an increase in greenhouse gas generation at the power source. Therefore, this paper investigates the energy and cooling performance of four new multi-components and ecologically friendly refrigerant blends that contained carbon dioxide and hydrofluoroolefins in their compositions as substitutes for R410A in air-conditioning systems. Relevant thermodynamic equations and REFPROP software were employed for the computational analysis. The results indicated that the new blends (R445A, R455A, R470B and R470A) exhibited a desirable low compression ratio and high heat transfer for cooling applications. The blends also exhibited low compressor energy input and low specific cooling energy. R455A has an average coefficient of performance (COP) of 24.6% above that of the reference refrigerant (R410A). The cooling capacity per unit volume for R470B, R455A and R470A across a temperature range of 253 to 293 K are higher by 1.3, 6.0, and 12.6%, respectively than that of R410A. Generally, among all the four new substitute blends, the overall assessment revealed R455A as the best replacement for R410A in air-conditioning systems due to its superior performance in terms of its low compression ratio, compressor energy and specific cooling energy. R455A also has the highest COP and relatively high cooling capacity per unit volume.

The refrigeration and air-conditioning sector is now undergoing a crucial phase where all the existing conventional refrigerants are being permitted to be neither produced nor consumed. For a better future, there is an immediate demand to look for clean refrigerants which are eco-friendly. The world is now looking for the refrigerants which do not contribute to the ozone layer depletion and global warming. The use of natural refrigerants like CO2, NH3 and hydrocarbons such as R290, R600, R600a and blends of hydrocarbons are possible solution to this problem and are being used efficiently in many systems. In this paper the importance of reconsidering the use of natural refrigerants to replace the synthetic refrigerants has been discussed. A review on the different systems where natural refrigerants are being used and modifications to such systems that could ensure better efficiency has been presented.

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.

Refrigeration and air-conditioning systems are vital to the global economy but contribute significantly to greenhouse gas emissions by using high-global-warming potential synthetic refrigerants. As regulatory frameworks like the Montreal Protocol, the Kigali Amendment, and the EU’s F-gas Regulations tighten, the industry faces a mandatory transition toward environmentally benign alternatives. This perspective paper evaluates the technological and environmental implications of replacing synthetic fluids with natural refrigerants, specifically ammonia, carbon dioxide, and hydrocarbons. A comparative assessment reveals that natural refrigerants offer superior thermodynamic efficiency, zero ozone depletion potential, and ultra-low global warming potential. While technologies like transcritical CO2 and low-charge ammonia systems may involve higher initial capital costs, they increasingly achieve life cycle cost parity through improved energy performance and regulatory stability. The analysis further explores advanced cycle configurations, such as ejectors and expanders, which mitigate efficiency losses. The transition to natural refrigerants is presented as a technologically feasible and environmentally friendly strategy to mitigate the risk that rising cooling demands further accelerate climate change. Ultimately, natural refrigerants are expected to become the default global standard within the shortest feasible timeframe, with policy, industry, and research aligned to support and accelerate this transition.

Due to increasing concerns about global warming, various environmental regulations will eventually phase out refrigerants used in air conditioning and refrigeration systems (e.g., R-410A, R-404A). Several refrigerants have been proposed as replacements, offering a variety of global warming potential (GWP), levels of energy efficiency and flammability. Some of these options are synthetic HFC/HFO mixtures such as R-454C and R-455A while other are commonly called naturals such as R-290 (Propane) and R-744 (Carbon Dioxide). This study discusses the merits of the leading options for air Conditioning and refrigeration systems. The fundamental requirements (environmental, performance, safety) are employed to fairly evaluate these options. Performance data and Life Cycle analysis results for these options are presented. Overall, this study provides information needed to judge the prospects of getting adequate replacement for R-410A and R-404A in a long-term sustainable basis.

Air conditioning and refrigeration have become necessary in modern life, accounting for more than 7.8% of greenhouse gases (GHG) emitted globally. Reducing the environmental impact of these systems is crucial for meeting the global GHG emission targets. Two principal directions must be considered to reduce the environmental impact of air conditioning systems. Firstly, reducing the direct effect by looking at less harmful refrigerants and secondly, reducing the indirect effect by searching for options to improve the system efficiency. This study presents the latest developments in the vapor compression cycle and natural refrigerants, focusing on water as a refrigerant. Natural refrigerants, and especially water, could be the ultimate solution for the environmental problems associated with the operation of vapor compression cycle (VCC) cooling systems, including ozone depletion (OD) and global warming (GW). Reducing the environmental impact of building cooling systems is essential, and the recent system improvements made to enhance the system coefficient of performance (COP) are thoroughly discussed in this paper. Though the cycle improvements discussed in this work are essential and could increase the system efficiency, they still need to solve the direct environmental impact of refrigerants. Accordingly, this paper suggests that natural refrigerants, including water, are the most suitable strategic choice to replace the current refrigerants in the refrigeration and air conditioning industry. Finally, this study reviews the latest VCC system improvements and natural refrigerants in order to guide interested researchers with solutions that may reduce the environmental impact of VCC systems and suggest future research areas.

Challenges and opportunities in the management of refrigeration and air conditioning systems to reduce environmental impacts in the Colombian health sector

To reduce the expected increase in global mean temperature, the substitution of R134a as working fluid of refrigeration and air conditioning systems using refrigerants with the lowest carbon footprint possible is a priority. In this paper, the use of R1234ze(E) as pure fluid and mixed with R134a (resulting R450A) is assessed from a thermodynamic point of view. Then, these results are used to support experimental data obtained from a vapor compression system at three evaporating temperatures combined with other condensing temperatures. Regarding refrigerant main thermodynamic properties, R450A is very similar to R134a, even though the HFO R1234ze(E) is the main component of the mixture (58% compared to 42%). For both alternatives, the major differences with R134a are observed in relative molar mass, vapor density and liquid thermal conductivity. Compared with R134a, average cooling capacity obtained is lower for both alternatives (until 34% for R1234ze(E)) due to a reduction in suction density and refrigerating effect. Resulting COP of R1234ze(E) is also slightly lower even though specific compression work is significantly lower. Average R450A COP can match that of R134a at the same compression pressure ratios. Attending to the results of the drop-in tests, the main conclusion of the paper is that only R450A can be used as drop-in replacement if light reduction in system cooling capacity can be accepted.

New Technologies in Ammonia Refrigerating and Air-Conditioning Systems

Refrigerants in the evaporator have an important role in absorbing heat in the refrigeration system. However, the halocarbon refrigerants usage could damage the layer of ozone and causing global warming. Natural refrigerant is being developed to overcome the negative effects of using halocarbon refrigerants. MC-134 is one of natural refrigerant, a hydrocarbon refrigerant, that the main substances components are propane and iso-butane. This research will discuss the heat transfer coefficient value of MC-134 and the characteristics that affecting its value. The refrigerant is circulated in a heated pipe with 0.5 mm in diameter and 0.5 m in length. The result of the experiment is the variation of heat transfer coefficient between 678.42 – 5366.19 Watt/m2.°C. The value is determined by the heat flux at 149.3 – 7441.9 Watt/m2, the mass flux at 39 – 878.5 kg/m2.s, and the quality of vapor at 0.004 – 0.065. This research also shows that increasing heat flux will increase the heat transfer coefficient value.