Phase change materials (PCMs) are used in latent heat storage (LHS) systems to effectively store thermal energy. Compact energy storage systems prefer PCMs because they show minimal size changes and are capable of storing latent heat during phase transitions. However, longer storage and release times are required due to their slower thermal conductivity, which calls for more advanced methods. In this paper investigation, the thermal conductivity of PCM was raised by using a finned HP heat pipe. When compared to a finless pipe, ANSYS simulations demonstrated a 42.8% reduction in melt completion time (four hours) at a surface temperature of 70°C. This development creates the groundwork for the development of a large-scale thermal energy storage system that is effective and overcomes the limitations of PCM heat transfer.

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.