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This article presents an analysis of the feasibility of R454C and R455A, two new low global warming potential (GWP of 148) refrigerants, in vapor compression refrigeration systems as alternatives to R404A for warm countries. R454C and R455A can be the most viable low GWP options to perform a direct replacement of R404A because of the similar characteristics. They only present meaningful differences in flammability, critical temperature, temperature glide and vapor density. The analysis is based on an experimental comparison of R404A with R454C and R455A, using a fully instrumented experimental setup equipped with Internal Heat Exchanger (IHX) at condensation temperatures that represent operating conditions of warm countries. The experimental results show that cooling capacity of the replacements is slightly lower than R404A, being the Coefficient of Performance (COP) of the new mixtures 10–15% higher than that of R404A, especially at higher condensation temperatures. The results also show that the adoption of an IHX is not recommended with the alternatives due to the discharge temperature increase and the low energy performance benefit. [ABSTRACT FROM AUTHOR]

• ORC and compound ejector-multi evaporator vapour compression systems are combined. • Nine ultra-low global warming potential refrigerant pairs are proposed to replace R134a and R245fa. • Condenser waste heat recovery increases the overall coefficient of performance. • The pair R1234ze(Z)/R1234ze(E) results in the highest energy performance. This article evaluates the energy and exergy performance of a novel dual fluid combined organic Rankine-compound ejector multi evaporators vapour compression system (ORCEMES) for power, cooling and heating purposes. Six working fluids with ultra-low global warming potential: R1234ze(E), R1243zf, R1234yf for the CEMES and R1234ze(Z), R1336mzz(Z) and R1224yd(Z) for the ORC were selected, resulting in nine combinations. The system can work in two operating modes: power-cooling and power-heating modes. The combination of R1234ze(Z) and R1234ze(E) results in the highest overall system energy performance. The proposed system increases power generation from 21% to 75% at high geothermal and low geothermal temperatures, respectively, compared with separated basic ORC and multi-evaporator systems at the same operating conditions and cooling capacity. The proposed CEMES reduces compressor power consumption to 85% of the basic system, increasing COP remarkably. Concerning the exergy analysis, the low-temperature recapture heat exchanger shows the highest exergy destruction compared to the rest of the components, followed by the turbine. Besides, the second expansion valve presents the lowest exergy destruction percentage. [ABSTRACT FROM AUTHOR]

The IHX (internal heat exchanger) is introduced in some refrigeration systems in order to achieve higher energy performances. Results obtained vary greatly depending on the refrigerant used and working conditions. This paper describes a drop-in analysis of IHX effects on the performance of a vapour compression system using R1234ze(E) and R450A (R134a/R1234ze(E) commercial mixture) as R134a low-GWP replacements. The tests were carried out in a completely monitored vapour compression system varying the condensing and evaporating temperature, with and without a counter-current flow tube-in-tube IHX. Because the cooling capacity rises and the power consumption remains similar, the conclusion is that the IHX has a positive influence on the energy efficiency for all refrigerants tested. The COP (coefficient of performance) gain using R1234ze(E) is the highest observed (overcomes the R134a COP for the same conditions). The R1234ze(E) and R450A discharge temperature increments are lower than those of R134a so does not reach dangerous values and the IHX pressure drops are also below than that of R134a. [ABSTRACT FROM AUTHOR]

• HFO-1234ze(E) and R-515B are evaluated as low-GWP alternatives to HFC-134a. • An internal heat exchanger singularly benefits heating applications. • Heating production temperatures up to 90 °C are considered. • The alternative low-GWP refrigerants significantly reduces carbon emissions. • R-515B becomes a promising non-flammable alternative (A1) for heat pumps. This article provides a theoretical energy performance and carbon footprint analysis of the hydrofluoroolefin HFO-1234ze(E) and the mixture R-515B as low global warming potential (GWP) refrigerants to replace the hydrofluorocarbon HFC-134a in different heat pump applications. The reference configuration is a single-stage cycle with an internal heat exchanger (IHX). In this way, the impact of the IHX on medium and moderately high temperature heating applications has been investigated. HFO-1234ze(E) and R-515B result in approx. 25% lower heating capacity than HFC-134a due to a diminution of the latent heat of vaporisation and suction density. The heating capacity difference between HFO-1234ze(E) and R-515B remains below 2%. The heating coefficient of performance (COP) of the alternative low GWP refrigerants is comparable to that of the HFC-134a at the proposed conditions. The environmental analysis illustrates that HFO-1234ze(E) and R-515B can reduce down to 18% and 15%, respectively, the equivalent CO 2 emissions compared to HFC-134a in low-temperature space heating applications. In addition, this reduction arrive at 78% when compared to a natural gas boiler, considered as the conventional heating technology in moderately high temperature applications (domestic hot water, industrial processes, and radiators). Although HFO-1234ze(E) and R-515B present comparable energy and environmental performance, the latter refrigerant has an advantage in regard to installation safety requirements as a non-flammable refrigerant (A1). [ABSTRACT FROM AUTHOR]

• Ejector and parallel compression configurations are proposed for high temperature heat pumps. • Internal heat exchanger analysis is included in the proposed configurations. • Alternative sustainable refrigerant assessment is performed to replace HFC-245fa. • Multi-objective analysis evaluates the compromise between volumetric heating capacity and COP. • Advanced high temperature heat pump configurations are promoted. Climate change evolution urges us to take action to reduce greenhouse gas emissions. As one of the main contributors, the industrial sector requires cleaner methods of heat production, such as high temperature heat pumps (HTHP) with the highest energy efficiency. Facing this challenge, this paper provides a performance comparison of the ejector and economizer with parallel compression configurations in HTHPs for low-grade waste heat recovery. A single-stage cycle has been used as a reference configuration to compare the proposed options. The internal heat exchanger (IHX) is included in all the configurations to extend the analysis and illustrate the influence of this component in high temperature applications. Moreover, alternative low-GWP refrigerants have been analyzed in order to replace the reference working fluid HFC-245fa. Ejector and economizer with parallel compression configurations with IHX provide a coefficient of performance (COP) improvement of up to 36% and 72.5%, respectively, using HFC-245fa for a heating temperature production of 140 °C. Moreover, the volumetric heating capacity (VHC) increases around 36% for the ejector cycle and 80% for the economizer with parallel compression cycle with IHX. HC-601, HFO-1336mzz(Z), and R-514 have the most significant COP improvement compared to HFC-245fa, along with the highest VHC drop. Multi-objective evaluation illustrates that single-stage and ejector configurations with IHX have similar results, whereas the economizer with parallel compression cycle with IHX presents a significant COP and VHC improvement. HCFO-1233zd(E) and HCFO-1224yd(Z) presents the proper trade-off between COP and VHC. [ABSTRACT FROM AUTHOR]

Abstract High-temperature heat pumps (HTHPs) based on vapour compression can be used for industrial low-grade waste heat valorisation, which can aid in mitigating climate change. Currently, the performance of HTHPs operating at high-temperatures lifts is limited; therefore, advanced configurations become an opportunity for their utilisation. This paper presents an HTHP cascade with configurations of internal heat exchangers (IHXs) that uses low GWP refrigerants in both high-stage (HS) (HCFO-1233zd(E), HFO-1336mzz(Z), HCFO-1224yd(Z), and pentane) and low-stage (LS) (HFO-1234yf, HFO-1234ze(E), butane, isobutane, and propane) cycles. Prior to the analysis and presentation of results, an optimisation of the operating conditions is performed based on intermediate temperature and IHX effectiveness in both stage cycles. Results indicate that butane and isobutane appear to be the most convenient working LS fluids from the point of view of coefficient of performance (COP). The highest system performance is obtained using pentane and HFO-1336mzz(Z) in the HS cycle. Compared to third-generation refrigerants (HFC-245fa/HFC-134a), a slight COP improvement is obtained using HCFO-1233zd(E), and HCFO-1224yd(Z). A comparable or even lower volumetric flow rate at the HS compression suction is also observed. The use of pentane/butane achieved maximum COP (3.15), which is a 13% improvement compared to COP obtained when HFC-245fa/HFC-134a is employed. Highlights • A high-temperature heat pump cascade with the IHXs is proposed and optimised. • Synthetic and natural refrigerants with low GWPs are proposed for both stages. • The higher effectiveness of both IHXs in similar proportions increases total COP. • Pentane/butane presents maximum COP and minimum HCFO-1224yd(Z)/HFO-1234yf. • A few refrigerant pairs are comparable with HFC-245fa/HFC-134a in the stages of V ˙ s u c . [ABSTRACT FROM AUTHOR]