Influence of subcooling in R-449A supermarket refrigeration system and screening of refrigerant mixtures for its energetic and environmental improvement

Current demands of the cooling sector are focused on using refrigerants with a low Global Warming Potential (GWP) and increasing energy efficiency in vapour compression installations. The main objectives of this paperwork arise from these needs, in which the use of subcooling in an R-449A commercial refrigeration system is evaluated. In addition, eco-friendly alternative refrigerants are proposed and studied. Firstly, the effect of an integrated type of subcooling is semi-empirically analysed with Engineering Equation Solver (EES). Then, the refrigeration system’s operation is simulated using low-GWP alternative refrigerants, R-454C and R-290, which have been scarcely studied in commercial refrigeration systems due to their safety classification. Moreover, new refrigerant mixtures are searched from the binary and ternary combination of pure refrigerants using the software REFPROP. The best refrigerant with safety classification A1, A2L, and A2/A3, for both medium temperature (MT) and low temperature (LT) systems is obtained from this search. After their determination, the supermarket’s operation is simulated with these refrigerants. Finally, an environmental assessment is performed. The highest energy efficiency is obtained with R-152a for the MT system and the R-290/R-1270 mixture for the LT system. However, the highest reduction of GHG emissions is achieved by R-290, with a reduction of 73.78 % with respect to the baseline system.Funding for open access charge: CRUE-Universitat Jaume IThis scientific publication is part of the R + D + i project PID2020-117865RB-I00, funded by MCIN/AEI/10.13039/501100011033, and UJI-A2022-03, funded by Universitat Jaume I. Adrián Mota-Babiloni acknowledges contract IJC2019-038997-I, funded by MCIN/AEI/10.13039/501100011033. Cosmin Mihai Udroiu acknowledges grant PRE2021-097369 funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future”. Pau Giménez-Prades acknowledges grant CIACIF/2021/182, funded by the Generalitat Valenciana (GV) and the European Social Fund (ESF)

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.Funding for open access charge: CRUE-Universitat Jaume

Thermodynamic evaluation of CO2 for ultra-low temperature refrigeration

Carbon dioxide (CO2, R744) is the only refrigerant in the safest class by the ASHRAE 34 Standard in the group of natural refrigerants, with zero ozone depletion potential and a global warming potential of 1. It has been recently proposed for commercial refrigeration and heat pumps. Ultra-low temperature (ULT) refrigeration considers two-stage cascades with hydrofluorocarbon synthetic refrigerants (R404A/R23 high and low-temperature stages, HTS and LTS, respectively) and, lately, hydrocarbons (R290/R170). This paper examines the potential of R744 in ULT refrigeration cascade configurations in combination with other promising refrigerants. R744 is proposed in the medium temperature stage (MTS) of a three-stage cascade and the HTS of a two-stage transcritical operation (subcritical and transcritical with and without ejector, respectively). The operational and energy performance are compared with standard two- and three-stage ULT refrigeration cascades. Also, the cycles have been optimized, changing the main parameters as cascade heat changer temperatures or gas cooler pressure to maximize COP. This optimization and all the models have been made with Python, extracting the thermodynamic properties of REFPROP. The results show that in the HTS, the coefficient of performance (COP) is 39 % lower than the same two-stage cascade cycle with R290. In the MTS of a three-stage cascade, COP is 10 % lower than the same three-stage cascade cycle with R290. The ejector increases the COP by 38 % in the transcritical HTS, but remains below the hydrocarbon two-stage cascade. The choice of alternative refrigerants in the other stages does not significantly vary the COP results. Technological advancements in single subcritical and transcritical R744 configurations should be transferred to ULT refrigeration cascades to increase competitiveness and take advantage of its environmental and safety characteristics

Analyse semi-empirique de la conversion des syst`emes frigorifiques des supermarch´es aux HFC avec des configurations avanc´ees du point de vue ´energ´etique, environnemental et ´economique

F-gas phase-down schedules will remove most of the HFCs (hydrofluorocarbons) used in refrigeration systems in the short term. Besides refrigerant substitution, configuration modifications can be considered in existing installations to increase energy efficiency. Basic cycle, direct injection, economiser, parallel compression, and cascade configurations with internal heat exchanger have been proposed to increase the energy efficiency of a supermarket refrigeration system when replacing R-404A with R-449A at low and medium temperatures. Both systems are based on indirect expansion and are equipped with a subcooler. Their regular operation was recorded using R-404A and R-449A during a representative period. Then, a semi-empirical approach is followed to determine R-449A energy performance with each proposed configuration. Only parallel compression (PC) and basic cycle with internal heat exchanger (IHX) benefit energy performance, highlighting the medium temperature (MT) system. However, this benefit is not extended to the environmental analysis because the R-449A charge in PC significantly increases. Moreover, additional PC components extend the expected payback period, and a drop-in replacement is financially more interesting. Therefore, using R-449A with minor modifications in the MT and LT R-404A refrigeration system decreases 52% and 60% carbon footprint, respectively. The payback period of this action is below one year in both circuits. This study provides a semi-empirical methodology for existing systems to predict alternative refrigerants’ energy performanceFunding for open access charge: CRUE-Universitat Jaume

Sustitución del R-404A en un sistema de refrigeración de media y baja temperatura mediante ciclos de compresión paralela con el R-449A

Este trabajo amplía el análisis operacional de un sistema de refrigeración comercial con niveles de temperatura media (MT) y temperatura baja (LT). El objetivo es cuantificar los beneficios de un rediseño del sistema utilizando arquitecturas avanzadas de compresión de vapor. La configuración comparada con el sistema de referencia (ciclo básico con subenfriador, con R-449A) es una compresión paralela (PC) con intercambiador recalentamiento- subenfriamiento (IRS o IHX en inglés) y subenfriador. En el sistema MT se produce un beneficio apreciable con la configuración de compresión paralela (PC). En el sistema LT la configuración PC no supera los beneficios energéticos causados por un simple reemplazo del R-404A por el R-449A sin modificar la configuración. El bajo factor de emisiones de Suecia hace que las emisiones directas predominen en el análisis TEWI

Experimental results of a high-temperature heat pump prototype with R1336mzz(Z) for various production temperatures

Ponència presentada en 26th IIE International Congress of Refrigeration, Paris, august 21-25, 202

Mélanges ternaires de réfrigérants pour la réfrigération à ultra-basse température

The absence of GWP limitation for refrigerants operating in vapour compression systems with a target temperature below –50 ◦C has caused slower market development. Therefore, while typical refrigeration applications have several mixtures offering different characteristics, a few mixtures already exist for –80 ◦C refrigeration (R469A, R-472A, and R-473A). This paper explores the combination of pure fluids with varied characteristics as three-component mixtures for ultra-low temperature refrigeration. Different parameters have been considered in the theoretical screening, such as volumetric cooling capacity, coefficient of performance, global warming potential, and flammability at constant operating conditions. R-32, R-41, R-125, R-134a, R-152a, R-170, R-227ea, R-290, R-744, R-1132a, R-1150, R-1234ze(E) and RE-170 have been combined at steps of 5%. Mixtures with the lowest global warming potential and highest coefficient of performance result in high flammability, particularly at − 80 ◦C. Environmental and energy aspects would require a lower priority in trade-off selections to reduce the flammability classification.Funding for open access charge: CRUE-Universitat Jaume

Influence of subcooling in R449A supermarket low-temperature refrigeration circuit using medium temperature cooling load

Ponencia presentada en el congreso 3rd IIR Conference on HFO Refrigerants and Low GWP blends, Shanghai, China, April 5-7, 2023This work studies the impact of subcooling in supermarket refrigeration systems with medium and low-temperature requierementsbased on a vapor compression single-stage with a subcooler

Experimental Assessment of the Internal Heat Exchanger in Vapour Compression Systems With Low GWP Refrigerant R516A

Ponència presentada en: 14th International Conference of Applied Energy, Bochum, 8-12, August, 2022.Internal heat exchangers (IHX) are commonly used to improve the energy performance of vapour compression refrigeration cycles. However, the magnitude of the improvement depends on the refrigerant and operational conditions. This paper experimentally investigates the influence of a high IHX on vapour compression systems. The new low global warming potential refrigerant R516A is assessed as a drop-in replacement to R134a at different medium temperature refrigeration conditions. In the case of a 40% effectiveness IHX, R516A shows the highest cooling capacity (4.8% to 9.1%), and COP (4.9% to 11.6%) increases compared to the situation without this element. It can be concluded that the IHX always benefits the energy performance of the refrigeration system at acceptable compressor discharge temperatures