Artificial neural networks (ANNs) have been considered for assessing the potential of low GWP refrigerants in experimental setups. In this study, the capability of using R449A as a lower GWP replacement of R404A in different temperature levels of a supermarket refrigeration system is investigated through an ANN model trained using field measurements as input. The supermarket refrigeration was composed of two indirect expansion circuits operated at low and medium temperatures and external subcooling. The results predicted that R449A provides, on average, a higher 10% and 5% COP than R404A at low and medium temperatures, respectively. Moreover, the cooling capacity was almost similar with both refrigerants in both circuits. This study also revealed that the ANN model could be employed to accurately predict the energy performance of a commercial refrigeration system and provide a reasonable judgment about the capability of the alternative refrigerant to be retrofitted in the system. This is very important, especially when the measurement data comes from field measurements, in which values are obtained under variable operating conditions. Finally, the ANN results were used to compare the carbon footprint for both refrigerants. It was confirmed that this refrigerant replacement could reduce the emissions of supermarket refrigeration systems.

The phase-down of hydrofluorocarbons and substitution with low global warming potential values are consequences of the awareness about the environmental impacts of greenhouse gases. This theoretical study evaluated the energy and exergy performances and the environmental impact of three vapor compression system configurations operating with the hydrocarbons R290, R600a, and R1270 as alternatives to R134a. The refrigeration cycle configurations investigated in this study include a single-stage cycle, a cycle equipped with an internal heat exchanger, and a two-stage cycle with vapor injection. According to the results, the alternative hydrocarbon refrigerants could provide comparable system performance to R134a. The analysis results also revealed that using an internal heat exchanger or a flash tank vapor injection could improve the system's efficiency while decreasing the heating capacity. The most efficient configuration was the two-stage refrigeration cycle with vapor injection, as revealed by the exergy analysis. The environmental impact analysis indicated that the utilization of environmentally-friendly refrigerants and improving the refrigeration system's efficiency could mitigate equivalent CO2 emissions significantly. The utilization of hydrocarbons reduced the carbon footprint by 50%, while a 1% to 8% reduction could be achieved using the internal heat exchanger and flash tank vapor injection.

This study provides a global warming impact analysis of environmentally friendly refrigerants used as replacements for R134a and R245fa. R290, R1234yf, R1234ze(E), R513A and R450A are considered as refrigerants to replace R134a in medium temperature applications. For R245fa, there are five alternative refrigerants, R1224yd(Z), R600, R1336mzz(Z), R1233zd(E) and R1234ze(Z), which are selected for high-temperature applications. The analysis is done considering the emission factors in Brazil, Sweden, Canada and Poland. In Sweden and Brazil, the total equivalent warming impact per heating capacity of R134a is higher than its alternative refrigerants in medium temperature application, although R134a exhibits a higher coefficient of performance than its alternatives. In high-temperature applications, R1336mzz(Z) has the lowest total equivalent warming impact per heating capacity due to its higher coefficient of performance than other tested refrigerants. The highest total equivalent warming impact per heating capacity belongs to R245fa in all countries except in Poland, where R600 exhibits a higher value due to its lower coefficient of performance and the relatively higher emission factor in Poland compared to other selected countries. These results revealed that in addition to the global warming potential, the emission factor associated with the sources of electricity generation has a crucial impact on indirect emissions.

Industry and other sectors are currently looking for solutions to decarbonize their processes, including heating, which is mainly based on fossil fuel boilers. Heat pumps can provide heating with higher performance based on their high coefficient of performance (COP). This work considers a multilevel heat pump (MTHP) for multi-source heating, based on a three-stage cascade in which excess heat in the condenser is used for external flows, that can be connected in series or parallel. Several available low GWP refrigerants have been considered, and a multi-parameter selection analysis has been carried out. For low, medium, and high-temperature stages, R1243zf, R-1224yd(Z), and R-1233zd(E) are the best refrigerants, respectively, selected. This system is able to operate between 0 and 160 degrees C, with three heating levels at 60, 110, 160 degrees C (31.75, 21.59, and 29.92 kW, respectively) at a COP of 2.181. The total cooling capacity of the system is 45.08 kW and the total heating capacity is 83.26 kW. The MTHP concept can provide a significant carbon footprint reduction compared to natural gas boilers used in European countries.

In this study, the subcooled boiling heat transfer of a Fe₃O₄/water magnetic nanofluid flowing through a vertical tube has been investigated experimentally in the presence and absence of a magnetic field. The magnetic field has been generated by quadrupole magnets. The subcooled boiling heat transfer coefficient and the boiling curves of the ferrofluid flow under the action of the magnetic field have been compared with those in the absence of magnetic field. The results showed that magnetic actuation contributes to have higher heat fluxes at the same wall superheat in comparison with heat fluxes achieved in the no magnetic field case. Therefore, the local subcooled boiling heat transfer coefficients are increased by the magnetic field. The maximum measured enhancement in local subcooled boiling heat transfer coefficient along the length of the tube by applying magnetic field is 46.58% at applied heat flux of 77,000 W m⁻² and mass flux of 270 kg m⁻² s⁻¹. Furthermore, the enhancement of local heat transfer coefficient by applying magnetic field decreases as the applied heat flux in the subcooled boiling region is increased.

The requirements of the European Union (EU) regulation on fluorinated greenhouse gases has created an incentive to reduce their amount that can be placed on the EU market (including many commonly used refrigerants) to 21% of the baseline level. This study attempts to develop a methodology to predict the future refrigerant mix in refrigeration, air conditioning, and heat pumps that will be available to the EU customers by 2021 and 2030 years. The work is based on the relevant current statistical data, refrigerant distribution, and future technology acceptance and trends in refrigerants. The study presents a refrigerant demand grow scenario and provides a basis for closer market follow up in order to facilitate decision making for refrigeration industry stakeholders. The results of the study indicate that by 2021 will be difficult to accomplish the fluorinated gas quota but by 2030 the transition is possible. By that time, the natural refrigerants will dominate the market, and a small share of lower GWP refrigerants will be necessary for specific applications.

In recognition of the impact of the refrigeration sector on climate change, global commitments are achieved to replace hydrofluorocarbon substances with more planet-friendly alternatives. In this regard, countries with high ambient temperatures (HAT) face additional problems in identifying suitable alternatives due to the impact of such temperatures on energy performance in vapor compression systems. This paper presents an experimental analysis using R134a and two lower global warming potential (GWP) mixtures in a small capacity vapor compression refrigeration system for HAT environments. The range of evaporating and condensing conditions was selected to simulate a refrigeration system working at HAT conditions. The experimental operating results show that although R450A values are acceptable, R513A shows better adaptation to the refrigeration system in terms of pressure ratio, discharge temperature, and mass flow rate. Then, attending to experimental energetic results, R450A energy performance (quantified by COP) and cooling capacity are lower than R513A and R134a. TEWI analysis of a small refrigeration unit shows CO2 equivalent emission saving when using R450A in the different condensation conditions. However, taking into account the variation of cooling capacity, R513A system results in the lowest TEWI when normalizing per unit of delivered cooling capacity.

R404A will be soon restricted from usage in commercial refrigeration in the European Union (EU) due to the requirements of the EU Regulation on fluorinated gases. Therefore, new refrigerant HFO/HFC mixtures are being developed to replace it. This paper explores the R454C and R455A as R404A alternatives and compares the characteristics that can lead their imposition in the refrigeration market. The characteristics studied are components and composition, current penetration in the market, security issues, global warming potential, energetic performance, material and lubricant compatibility and, finally, most likely applications.

Lower global warming potential (GWP) refrigerants must be used in refrigeration education to integrate the environmentallyresponsible engineering principles in class. However, most of the refrigeration educational laboratories are still usinghydrofluorocarbons (HFCs) as working fluids, which are considered as greenhouse gases. This paper shows the procedureto adapt the new refrigerant R513A in a refrigeration system used for a cooling capacity educational laboratory. First, thepaper describes the organization of the laboratory session, and the characteristics of the different methods of coolingcapacity calculation taught to the master’s degree students. Then, the benefits of including new sensors in the experimentalsetup to obtain more accurate results are explained. Later, accurate new graphics and an equation to calculate the R513Acooling capacity are provided. Finally, the educational aspects worked with the students in this session, and each coolingcapacity method are assessed. The procedure explained in this paper can be used as a guide for introducing lower GWPrefrigerants in similar educational refrigeration laboratories.

The energy performance of CO2 standard booster systems is limited in countries with high ambient temperatures to replace R404A direct expansion architectures. Therefore, cascade refrigeration systems with CO2 in the low-pressure stage can be considered. Most of the conventional cascade refrigeration systems rely on using R134a, a high global warming potential (GWP) refrigerant, in the high pressure stage. However, R134a needs to be replaced by lower GWP refrigerants to meet the targets of current environmental agreements. This study investigates R450A and R513A refrigerants as drop-in replacements to R134a in R134a/CO2 cascade refrigeration units. The experimental energy performance results suggest that both R450A and R513A can substitute R134a in cascade systems. R513A provides comparable COP and cooling capacity values to R134a, whereas the cooling capacity and COP of R450A are lower than that of the baseline R134a.