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This work presents an energy, exergy, and environmental evaluation of a novel compound PV/T (photovoltaic thermal) waste heat driven ejector-heat pump system for simultaneous data center cooling and waste heat recovery for district heating networks. The system uses PV/T waste heat with an evaporative-condenser as a driving force for an ejector while exploiting the generated electric power to operate the heat pump compressor and pumps. The vapor compression system assessed several environmentally friendly strategies. The study compares eleven lower global warming potential (GWP) refrigerants from different ASHRAE safety groups (R450A, R513A, R515A, R515B, R516A, R152a, R444A, R1234ze(E), R1234yf, R290, and R1243zf) with the hydrofluorocarbon (HFC) R134a. The results prove that the system presents a remarkable overall performance enhancement for all investigated refrigerants in both modes. Regarding the energy analysis, the cooling coefficient of performance (COPC) enhancement ranges from 15% to 54% compared with a traditional R134a heat pump. The most pronounced COPC enhancement is caused by R515B (a 54% COPC enhancement and 49% heating COP enhancement), followed by R515A and R1234ze(E). Concerning the exergy analysis, R515B shows the lowest exergy destruction, with the highest exergy efficiency than all investigated refrigerants. Funding for open access charge: CRUE-Universitat Jaume I

A comprehensive techno-economic evaluation is evaluated based on an innovative compound ejector-heat pump system with PV/T (photovoltaic thermal) waste heat-driven. The aim of the system is simultaneous data centre cooling and waste heat recovery for district heating to reduce residential greenhouse gas emissions. The new system avoids the ejector pump by combining PV/T waste heat with an evaporative-condenser as an ejector driving force, considering several low global warming potential alternatives to R134a. The simulation indicates that the proposed system presents a remarkable diference in all investigated refrigerants’ overall system coefcient of performance (COP). Particularly, R515B presents the highest increase in COP, 54% and 49% in cooling and heating modes, respectively. It also provides the highest electricity consumption reduction, 84.1 MWh yearly. Moreover, the system improves the data centre power usage efectiveness (PUE) index from 10 to 19%. In fnancial terms, the shortest payback period (6.3 years) is obtained with R515B, followed by R515A and R1234ze(E). Funding for open access charge: CRUE-Universitat Jaume I

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.

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 CO2 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).

Several environmental protection policies have been enforced restricting working fluids with high global warming potential (GWP) values used in many types of refrigeration and heat pump systems. However, ultralow-temperature (ULT) refrigeration has not been included, which commonly uses refrigerants with very high GWP values (such as R23 and R508B). Therefore, publicly available research programs seeking low GWP alternative refrigerants do not cover this application and the transition to more environmentally friendly fluids is slowed down. This work presents a comprehensive review that summarizes and discusses the available studies about ULT refrigeration systems. The current status of the technology, system architectures and refrigerants are analyzed. Moreover, the transition towards low GWP refrigerants is proposed, presenting the most promising low GWP alternatives. The most commonly used architectures for ULT refrigeration are the two-stage cascade and auto-cascade, in which the use of ejector has recently been considered in research papers. R170 and R1150 are the available natural refrigerants suitable for ULT, but they have not yet been included in many flammability and risk assessment studies. The A2 hydrofluoroolefin R1132a has been recently proposed as a blend component to avoid problems of stability. However, more information is still necessary to start with simulation and experimental studies. R41 could be an alternative due to its low GWP and suitable normal boiling point, but it has not been thoroughly investigated yet. Overall, there is a gap in the literature in terms of developing alternative refrigerants for ULT refrigeration. This study aims at shedding light on this gap to direct future research in this field towards reliable, environmentally friendly and marketable alternative refrigerants.

High-Temperature Heat Pump (HTHP) is becoming a feasible technology for decarbonization, being proposed as an alternative to fossil fuel boilers in several industrial, commercial, and urban applications. This work presents a semi-empirical assessment of a two-stage cascade cycle for HTHP applications to produce hot water up to 150 °C from a water flow at 35 °C and 25 °C. This work uses experimental results of two single-stage heat pump prototypes (R-1234ze(E) and R-1336mzz(Z)) with different temperature lifts as baseline inputs. The energy performance of the proposed two stage cascade HTHP is evaluated through a semi-empirical model, including several novel mixtures for both stages. Up to 14% of COP increase was reached respect to the baseline when using R-152a/600 (0.08/0.92) and R-1233zd(E)/161 (0.88/0.12) for the low stage and high stage, respectively. The VHC increases 30% with the selected combinations, but the discharge temperature also rises. Direct CO2e emissions were negligible by using low GWP refrigerants. The country proposed for the two-stage cascade HTHP greatly influences greenhouse gas indirect CO2e emissions. It is estimated that in countries carbon emission factor lower than 0.35 kgCO2e kWh−1 the mixtures selected would reduce the emissions compared to fossil fuel boilers for the same heating capacity. Funding for open access charge: CRUE-Universitat Jaume I

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 performance Funding for open access charge: CRUE-Universitat Jaume I

In response to the COVID-19 pandemic, some vaccines have been developed requiring ultralow-temperature refrigeration, and the number of these freezers has been increased worldwide. Ultralow-temperature refrigeration operates with a significant temperature lift and, hence, a massive decrease in energy performance. Therefore, cascade cycles based on two vapor compression single-stage cycles are traditionally used for these temperatures. This paper proposes the combination of six different cycles (single-stage with and without internal heat exchanger, vapor injection, liquid injection, and parallel compression with and without economizer) in two-stage cascades to analyze the operational and energy performance in ultralow-temperature freezers. All this leads to 42 different configurations in which the intermediate cascade temperature is optimized to maximize the coefficient of performance. Ultra-low global warming potential natural refrigerants such as R-290 (propane) and R-170 (ethane) for the cascade high- and low-temperature stage have been considered. From the thermodynamic analysis, it can be concluded that liquid and vapor injection cascade configurations are the most energy-efficient. More specifically, those containing a vapor injection in the low-temperature stage (0.89 coefficient of performance, 40 % higher than traditional configurations). Then, using an internal heat exchanger for such low temperatures is unnecessary in terms of energy performance. The optimum intermediate cascade temperature varies significantly among cycles, from -37 °C to 2 °C, substantially impacting energy performance. Parallel compression configuration improves energy performance over single-stage cycles, but not as much as multi-stage (between 20 % and 30 % lower coefficient of performance). For most of low-temperature cycles, the high-temperature stage can be based on a single-stage cycle while keeping the maximum coefficient of performance.

The fact that the popular head loss coefficient concept, may become negative in branched junctions, is a symptom that something is not correctly managed. The paper makes a review of recent works which have sought new models based on physical concepts, as a way to avoid speaking about “negative losses”. Herwing and Schmandt [1], showed that the origin of the negative sign was a diffusive shear work exchange between the two streams of a branched junction. Traditionally, the head losses at the branched junctions are neglected, but definitely it cannot be done in HVAC air-duct networks. Firstly, the paper illustrates how, by ignoring this “negative loss” contradiction, traditional duct network analysis may encounter unexpected numerical difficulties. Secondly, it shows that the Minimum Energy Dissipation Principle (MinEDP) can be successfully applied to analyze the steady-state of any flow network (not necessarily HVAC ductworks), with or without shear work at junctions. Moreover, the new method does not need to know the latter, beforehand, although the nature of the solution is very different in either case. Finally, the paper includes a practical example of an HVAC ductwork to illustrate the outcomes. The new method works smoothly and quickly and does not need any ad hoc modification to cope with an eventual “negative” head loss.

Heat pumps are gaining interest to replace fossil fuel burners with the increase of the share of renewable sources in the electricity generation mix. Moreover, low global warming potential (GWP) alternatives offer a more environmentally friendly option as refrigerants. HFO-1234ze(E) and its non-flammable mixture R-515B are experimentally investigated for the first time to replace HFC-134a in heat pump water heaters (HPWH) and moderately high temperature heat pumps (MHTHP). Tests are performed in a test rig equipped with a variable frequency compressor at evaporating temperatures of 7.5, 15 and 22.5 ◦C and condensing temperatures from 55 to 85 ◦C (65 experimental tests). HFC-134a outperforms both alternatives in heating capacity (approx. 26% higher) due to the higher mass flow rate and heating effect. However, this effect is compensated by, on average, 25% lower compressor power consumption. Therefore, the coefficient of performance (COP) is comparable or slightly higher (up to 5%) for HFO-1234ze(E) and R-515B. Considering the positive results in COP and the reduced GWP, both options decrease HFC-134a MHTHP equivalent carbon emissions down to 28%. Besides, given the 20 K lower discharge temperature reached by the alternatives, the compressor operating map can be significantly extended. Finally, it is demonstrated that R-515B is a suitable non-flammable alternative to HFO1234ze(E) that keep energetic and environmental benefits while offers a safer system operation. Funding for open access charge: CRUE-Universitat Jaume I

This paper investigates a promising low-GWP refrigerant, HCFO-1224yd(Z), as an environmentally friendly replacement for HFC-245fa in high temperature heat pumps (HTHPs). First, the thermophysical properties of both fluids were analysed, and a single-stage cycle with Internal Heat Exchanger (IHX) was modelled. Then, a semi-empirical drop-in test replacement was assessed. The low-temperature reservoir was fixed at 80 °C, whereas the high-temperature reservoir was varied from 110 to 140 °C to cover a wide range of industrial applications. The theoretical and semi-empirical results illustrate that HCFO-1224yd(Z) heating capacity becomes around 8.9% lower than HFC-245fa. However, the higher suction density of HCFO-1224yd(Z) compared to the reference fluid can compensate for this effect, reducing the compressor power consumption. Hence, HCFO-1224yd(Z) presents a COP increase up to 4.5% compared to the reference fluid. At high-temperature reservoir of 140 °C, HCFO-1224yd(Z) shows a COP of 2.33, whereas HFC-245fa only reaches 2.23. The carbon footprint assessment illustrates a significant equivalent CO2,eq emissions reduction down to 90%, depending on the country (carbon emission factor). Therefore, HCFO-1224yd(Z) can be used as an alternative to HFC-245fa in HTHP systems due to its beneficial operating, energetic and environmental characteristics.

High temperature heat pumps (HTHPs) have a great potential to improve industrial processes with thermal demand through industrial waste heat recovery and revalorization. Vapor compression HTHPs are very sensitive to the cycle configuration, refrigerant, components, and operating temperatures. This study compares eight advanced cycle configurations and nine low global warming potential (GWP) refrigerants from an energetic, economic, and environmental comprehensive perspective to illustrate an optimum selection for different HTHP applications. Firstly, several single-stage and two-stage compression cycles are proposed adding different components, such as the ejector, economizer, parallel compressor, flash tank, or additional evaporators and condensers. Moreover, an internal heat exchanger (IHX) has been included in all configurations to maximize the energy performance and ensure dry compression. Secondly, HC-601, HC-600, HC-600a, HFO-1336mzz(Z), HFO-1336mzz(E), R-514A, HCFO-1233zd(E), HCFO-1224yd(Z), and HFO-1234ze(Z) are considered as alternative low GWP refrigerants to replace the hydrofluorocarbon HFC-245fa. The results indicate that a two-stage cascade becomes the most appropriate configuration for high temperature lifts (60 K and above). In contrast, single-stage cycles with economizer and parallel compression are suitable for low temperature lifts (50 K and below). HCFO-1233zd(E) and HCFO-1224yd(Z) show a trade-off between coefficient of performance (COP) and volumetric heating capacity (VHC). Advanced HTHPs configurations can save up to 68% of the equivalent CO2 emissions compared to a natural gas boiler.

High-temperature heat pumps (HTHPs) based on vapour compression technology are being considered an energy-efficient possibility for low-grade waste heat recovery in industrial applications. If the HTHP technology is extended, the industrial energy efficiency would be closer to the 2050 target of decarbonisation, and consequently, it would reduce the worldwide greenhouse gas emissions. This chapter gives a comprehensive overview of the current status and future possibilities of the HTHP technology based on the working principles, working fluids, configurations, existing prototypes, and the possibility of reversible operation. Many working fluid possibilities with low Global Warming Potential are available, but there is no perfect alternative, and the selection must consider many factors. The relatively higher temperature lifts make advanced configurations feasible. Existing HTHP prototypes cover a wide range of working fluids and configurations; nevertheless, they are going to be required for developing HTHPs capable of supply increasing temperatures from higher heat sources.

This work is focused on a case study of a small-scale Organic Rankine Cycle (ORC) adopted for electricity production from low-grade industrial waste heat recovery. This kind of applications raises a great interest due to the high amount of low-grade waste heat recoverable within industrial processes, but lacks of in-depth experimental investigations on the topic. The main reason is the difficulty to reach profitable small-scale projects, so more cost-effective solutions are being explored in the literature through thermo-economic optimizations. Nonetheless, the results obtained cannot be discussed with respect to actual operating data. In light of this, this paper proposes to conduct the thermo-economic optimization on the basis of an experimental application. In this manner, a comprehensive model of the facility is developed, calibrated, and validated from actual operating data. The model is used to conduct the thermo-economic optimization, revealing the influence of the organic fluid, cycle architecture, geometric parameters of main components, or control strategy used to obtain the best cost-effective solution. The main results show that, by means of a multivariable optimization using cost-effective ratios as objective function, a cheaper and powerful solution adapted to each specific project may be designed.

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.

This study illustrates the potential of high temperature heat pumps (HTHPs) integration into district heating network (DHN) through a twofold approach, using DHN as a heat sink and source. It is used as a heat sink of HTHP that uses waste heat from the supermarket’s refrigeration system as a heat source whereas it is used as a heat source to HTHP that provides heat to industrial applications. When the DHN acts as the heat sink, the integrated system provides a coefficient of performance (COP) of the waste heat recovery (WHR) system between 3.2 and 5.4, reducing the operating costs between 50% and 100% with an average price ratio of 2.25 compared with the standard CO2 refrigeration system. If the DHN is the heat source, the integrated system provides a COP from 2.8 to 5.7 for a heat sink of 110 °C. The alternative low-GWP refrigerants assessment illustrates that HC-290, HFO-1234ze(E) and HFO-1234yf were considered the ideal candidates to replace the HFC-134a, whereas HCFO-1233zd(E) and HCFO-1224yd(Z) were the most promising low-GWP refrigerants to replace HFC-245fa. Finally, the environmental results showed that the utilisation of the DHN as the heat sink in the integrated system solution produces about 60% lower equivalent CO2 emissions than the DHN generation mix. Moreover, using DHN as the heat source, the equivalent CO2 emissions can be reduced up to 98% in Sweden compared to conventional natural gas boilers. Hence, the combination of HTHPs and the DHN represents a step forward in the mitigation of climate change through the utilisation of sustainable energy conversion technologies.

The organic Rankine cycle (ORC) has been growing in importance as a technology for producing electricity from low temperature waste and renewable heat sources. In small-scale applications, the most used working fluid has been HFC-245fa, although this is being substituted for low GWP alternatives. A new HCFO working fluid, HCFO-1224yd(Z), has appeared as a possible alternative for HFC-245fa. In this study, this alternative working fluid is analysed and, finally, the working fluid is experimentally tested as drop-in alternative in a commercial ORC system. The main purpose is to determine the feasibility of using HCFO-1224yd(Z) as a drop-in replacement for HFC-245fa in a real facility that was initially designed to operate with HFC-245fa. The results show how the use of HCFO-1224yd(Z) offers power output that ranges from 7.5% to 17.4% lower than that provided by HFC-245fa. Although HFC-245fa offers higher power output, the results show that HCFO-1224yd(Z) offers up to 7.7% higher cycle net efficiency; this is due to the higher input thermal rate required by HFC-245fa. Finally, HCFO-1224yd(Z) has been stated as a suitable alternative to HFC-245fa as a drop-in replacement in a small-scale, low-temperature ORC, which increases its attractiveness for heat source with higher temperatures.

A significant amount of energy in the form of heat is lost in industrial processes once it is used in specific processes. Among different technologies, high-temperature heat pumps (HTHP) are a valuable method of recovering low-temperature waste heat in the industry in a very efficient way that can be activated using clean electricity. As a recently investigated technology, they are not yet spread in industrial processes, where traditional technologies are preferred. Therefore, this work shows an HTHP computer program (named HeatPack) to be used as a simulator by the university or technical students of courses included in the area of applied thermodynamics engineering. This interactive and user-friendly platform allows the modification of different operating and design parameters and the working fluid. As outputs, the program provides the rest of the operating parameters and the energy performance of the cycle (quantified by the coefficient of performance, COP). A comparison between the proposed HTHP and a gas boiler is also performed by the program and the energetic, environmental, and economic savings are displayed. Students, as the main target of users of the program, can observe how this technology can provide very relevant emission reductions in comparison with fossil fuel-based boilers, under which situation the energy performance of the HTHP is higher, and which alternative low global warming potential (GWP) refrigerants can provide more advantages. In addition to the educational use, this software can be used to design and study the integration of HTHPs in existing industrial needs to evaluate the feasibility.

Higher Education Institutions must consider the most recently developed technologies to increase energy efficiency. A significant share of the heat used in industry is wasted while still being at usable temperature levels and hence a significant energy saving potential is present in this sector. The Organic Rankine Cycle (ORC) is a system that uses low-grade waste or renewable heat to produce electricity and lower grade heat and can be integrated into a variety of applications. In this paper, an introduction to ORCs is presented, and then, a practical example of a laboratory session using an experimental test bench based in this technology in a last year bachelor’s degree course is detailed. A commercial ORC machine was run in the laboratory session, where the students were able to explore its operation through the graphical interface. They applied the main thermodynamic concepts in the interpretation of the behavior and seen the utility of this science in recently developed environmentally friendly technologies. Then, the students simulated a real case based on the valorisation of exhaust gases from an engine installed in a wastewater treatment plant. Students agreed that the combination of both parts in this session is beneficial for their understanding and that ORC machines are a viable solution to control climate change. Las instituciones de educación superior deben considerar las tecnologías desarrolladas más recientemente para aumentar la eficiencia energética. Una parte importante del calor utilizado en la industria se desperdicia mientras se mantiene en niveles de temperatura utilizables y, por lo tanto, existe un potencial significativo de ahorro de energía en este sector. El Ciclo de Rankine Orgánico (ORC) es un sistema que utiliza residuos de bajo grado o calor renovable para producir electricidad y calor de menor grado y se puede integrar en una variedad de aplicaciones. En este documento, se presenta una introducción a los ORC y, a continuación, se detalla un ejemplo práctico de una sesión de laboratorio con un banco de pruebas experimental basado en esta tecnología en un curso de licenciatura del año pasado. Se ejecutó una máquina de ORC comercial en la sesión de laboratorio, donde los estudiantes pudieron explorar su funcionamiento a través de la interfaz gráfica. Aplicaron los conceptos termodinámicos principales en la interpretación del comportamiento y vieron la utilidad de esta ciencia en tecnologías recientemente desarrolladas amigables con el medio ambiente. Luego, los estudiantes simularon un caso real basado en la valorización de los gases de escape de un motor instalado en una planta de tratamiento de aguas residuales. Los estudiantes acordaron que la combinación de ambas partes en esta sesión es beneficiosa para su comprensión y que las máquinas ORC son una solución viable para controlar el cambio climático.

In the present work, a thermo-economic evaluation of the low global warming potential fluids HCFO-1233zd-E, HFO-1336mzz-Z and HFO-1234ze-Z as alternatives to HFC-245fa in organic Rankine cycle systems for low temperature heat sources is carried out. A thermodynamic organic Rankine cycle model is extended with the overall cost of the system, and it is used to identify the system parameter values for each working fluid considered that minimize the specific investment cost at a given set of the heat source and sink inlet temperatures. Thereby, the results show that HCFO-1233zd-E and HFO-1336mzz-Z present higher efficiencies than HFC-245fa, while HFO-1234ze-Z presents lower efficiency than HFC-245fa. The low global warming potential working fluids result in lower specific investment cost values than HFC-245fa. HFO-1336mzz-Z presents the lowest specific investment cost and highest efficiency values among the working fluids of interest throughout the range of operating conditions studied.

This paper compares the predicted organic Rankine cycle performance of two low global warming potential working fluids, R1234yf and R1234ze, alternatives to R134a over a wide range of evaporating temperatures and condensing temperatures for a given thermal power input. The results show that R1234yf would require 18.3% to 25.8% higher pump power and would enable up to 13.9% lower net cycle efficiencies than R134a over the range of cycle conditions examined in this work. In the other hand, R1234ze would require 15.7% to 20.2% lower pump power and would enable up to 13.8% higher net cycle efficiencies than R134a, over the range of cycle conditions analyzed. Both alternative fluids net cycle efficiency is benefitted substantially by a recuperator. The differences with R134a in net cycle efficiency are accentuated for high evaporating and condensing temperatures.

Supermarkets are recognized worldwide as great energy consumers, especially in developed countries. Typically, energy consumptions are due to cold, heat and electricity requirements. So a Combined Cold, Heat and Power (CCHP) system (also called trigeneration system) can be used to reduce energy demands and, hence, greenhouse gas emissions to the atmosphere. In this way, this work proposes a small-scale Organic Rankine Cycle (ORC) CCHP application in a supermarket. The ORC has been designed to be used with a biomass boiler, and to produce electricity and useful heat at two different temperature levels related to an absorption chiller and supermarket heating demand. With this in mind, this work conducts the experimental characterization of the CCHP system in a test bench. Thereby, the experimental results obtained are used to predict the expected performance of the system under the supermarket conditions, as well as to quantify the energy, environmental and economic benefits of the application.

The GWP limitations are being progressively introduced in Europe through Regulation EU No 517/201, phasing out R134a in most of its refrigeration and air conditioning applications. Pure hydrofluoroolefins are proposed to substitute this fluid, however generally system modifications are needed to achieve a good performance. In the case of R1234ze(E), the cooling capacity is always much below that of R134a in drop-in or light retrofit substitutions. This work performs an experimental comparison using R1234ze(E) and R134a under different refrigeration operating conditions. R1234ze(E) is tested considering the use or not of an internal heat exchanger, and R134a at the same or lower compressor rotation speed. Results show that the use of R1234ze(E) with an open-type compressor 43% larger and an internal heat exchanger of 25% effectiveness, leads to a cooling capacity augmentation, enough to reach R134a cooling capacity in the different conditions tested. For R450A, it is sufficient only with the IHX activation.

Este artículo se encuentra disponible en la página web de la revista en la siguiente URL: https://www.mdpi.com/1996-1073/12/19/3652 Phase change materials (PCMs) can be used in refrigeration systems to redistribute the thermal load. The main advantages of the overall system are a more stable energy performance, energy savings, and the use of the off-peak electric tariff. This paper proposes, models, tests, and analyzes an experimental water vapor compression chiller connected to a PCM thermal energy storage (TES) tank that acts as an alternative heat sink. First, the transient model of the chiller-PCM system is proposed and validated through experimental data directly measured from a test bench where the PCM TES tank is connected to a vapor compression-based chiller. A maximum deviation of 1.2 C has been obtained between the numerical and experimental values of the PCM tank water outlet temperature. Then, the validated chiller-PCM system model is used to quantify (using the coeffcient of performance, COP) and to analyze its energy performance and its dependence on the ambient temperature. Moreover, electrical energy saving curves are calculated for different ambient temperature profiles, reaching values between 5% and 15% taking the experimental system without PCM as a baseline. Finally, the COP of the chiller-PCM system is calculated for di erent temperatures and use scenarios, and it is compared with the COP of a conventional aerothermal chiller to determine the switch ambient temperature values for which the former provides energy savings over the latter.

This paper analyses the feasibility of HCFO-1224yd(Z), HCFO-1233zd(E) and HFO-1336mzz(Z), three low global warming potential (GWP) refrigerants, as alternatives to HFC-245fa in high-temperature heat pump (HTHP) systems for low-grade waste heat recovery. HTHPs are a sustainable technology that can help to mitigate climate change through the thermal valorisation of the industrial low-grade waste heat. Before presenting and analysing the results, mapping of the minimum superheat degree requirement in the operating range, and the influence of the Internal Heat Exchanger (IHX) on each alternative are studied. The simulations were carried out at condensing temperatures from 115 to 145 °C and evaporating temperatures from 45 to 75 °C, using a single-stage cycle with and without IHX. Finally, the Total Equivalent Warming Impact (TEWI) evaluation is performed to illustrate the environmental effect of each alternative. Attending to the results, HCFO-1233zd(E) improves the COP about 27% compared to HFC-245fa, whereas HFO-1336mzz(Z) and HCFO-1224yd(Z) show an improvement of approx. 21 and 17%, respectively. Although HCFO-1233zd(E) and HCFO-1224yd(Z) present similar suction volumetric flow rate to HFC-245fa, HFO-1336mzz(Z) shows a relative increment up to 80%, and therefore, higher compressor and installation size are expected for this refrigerant. Finally, the TEWI analysis presents a significant reduction of the equivalent CO2 emissions for each low GWP alternative, between 59 and 61%. HCFO-1233zd(E) shows the highest reduction in all the simulation cases, followed by HCFO-1224yd(Z) and HFO-1336mzz(Z).

Coming refrigeration and air conditioning systems must include low GWP fluids and optimized components. An internal heat exchanger (IHX) is a common modification of the basic cycle to enhance its energy performance, and its benefits have been demonstrated with R134a and the recently developed hydrofluoro-olefin R1234yf. This paper assesses the experimental influence of a high effectiveness IHX using R134a, and the low GWP mixture R513A (a mixture of R134a and R1234yf) under different evaporating and condensing conditions (29 points tested in total). Discharge temperature has been increased up to 26 K for both fluids, and the greatest compression ratio is not feasible for R134a. The cooling capacity of the system results increased up to 5.6% for R513A whereas for R134a is around 3%. Furthermore, due to the minimum diminution of power consumption, COP also increases up to 8% for R513A and 4% for R134a. Because of the observed experimental results, high effectiveness IHX is recommended for R513A, especially for high compression ratio operations as long as the discharge temperature does not reach critical values. Finally, it has been found that Klein et al.’s and Hermes’s correlations overestimate the COP benefit and the increase in power consumption should be considered.

This paper presents a first and second law of thermodynamics study using experimental data from a medium capacity refrigeration system using R-450A, R-513A and R-134a as working fluids and an internal heat exchanger (IHX) operating in three different modes: disabled (Off), activated at 38% thermal effectiveness (Middle), and activated at 78% thermal effectiveness, which is the maximum value by design (ON). When the IHX is in the Middle mode, R-513A showed to be the best option and its coefficient of performance (COP) overcomes that of R-450A and R-134a. On the other hand, for temperatures above of −7.5 °C, both R-450A and R-134a reached the highest COP when the ON and Off modes were set, respectively.Regarding the second law study, for the Off and Middle mode, the largest exergy destruction happens in the compressor for the three refrigerants. The influence of the IHX can be observed directly in the increase of the global exergetic efficiency which passes from being 8.7% in Middle mode to 18.3% for the ON mode. Additionally, a reduction of exergy destruction ratio is seen from the Middle mode, 10.6%–22.2% in the ON mode.

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 utilization. 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.

The replacement of HFCs using lower GWP refrigerants in the coming years is a priority to reduce the predicted climate change. The exergy analysis of vapor compression systems can help to identify the feasibility of alternative fluids in existing installations and the potential to improve them. In this sense, this paper presents an exergy analysis of an experimental setup which operates with R134a and the alternative HFO/HFC mixture R513A. The evaporating temperature is ranges between −15 °C and 5 °C, while the condensing temperature is set at 30 °C and 35 °C. In this analysis, the highest amount of exergy destruction rate is obtained at the compressor, followed by the evaporator. The maximum exergy efficiencies are observed at the condenser and the thermostatic expansion device. Finally, the average global exergy efficiency of R513A when replaced R134a in this refrigeration experimental setup is 0.4% higher (absolute difference), and with respect to the components, there is only slight reduction in efficiency in the condenser using R513A. Therefore, the R513A replacement is acceptable according to the second law of thermodynamics.

This work investigates the theoretical performance of a novel compound waste heat-solar driven ejector-solar assisted heat pump for simultaneous heating and cooling purposes. The system utilizes waste heat from three different sources, PV/T (photovoltaic thermal) with flat plate collector, milk pasteurization process, and condenser exchange heat. Real weather data is employed to determine the hourly performance of the system in three European cities, Valencia (Spain), Berlin (Germany), and Stockholm (Sweden) representing warm, middle and cold climates, respectively. Moreover, R450A and R513A alternative refrigerants are compared to the greenhouse gas R134a. The results show that the proposed system improves cooling COP by 7% using R450A in comparison with a conventional R134a vapor compression system. Furthermore, the utilization of waste heat recovery enhances the system COP from 3.7 to 4 in the absence of solar intensity. On the other hand, the results of the heating mode show that the system with PV/T and using R450A has a COP increase over the adopted solar time, ranging from 2 to 5% in Valencia; 2 to 2.5% in Berlin, and1 to 1.5% in Stockholm. However, R513A shows a COP reduction of about 5% in comparison to R134a. Regarding the heating mode with waste heat utilization from milk pasteurization, the system based on R450A results in the highest system COP, increasing COP up to 75% compared to the R134a baseline scenario. Overall, the proposed R450A systems show the highest equivalent carbon dioxide emission reduction and, therefore, it is recommended from an environmental point of view.

[EN] When retrofitting new refrigerants in an existing vapour compression system, their adaptation to the heat exchangers is a major concern. R450A and R448A are commercial non-flammable mixtures with low GWP developed to replace the HFCs R134a and R404A, fluids with high GWP values. In this work the evaporator performance is evaluated through a shell-and-microfin tube evaporator model using R450A, R448A, R134a and R404A. The accuracy of the model is first studied considering different recently developed micro-fin tube correlations for flow boiling phenomena. The model is validated using experimental data from tests carried out in a fully monitored vapour compression plant at different refrigeration operating conditions. The main predicted operational parameters such as evaporating pressure, UArp, and cooling capacity, when compared with experimental data, fit within 10% using the Akhavan-Behabadi et al. correlation for flow boiling. Results show that R450A and R404A are the refrigerants in which the model fits better, even though R448A and R134a predictions are also accurate. (C) 2015 Elsevier Ltd. All rights reserved., The authors thankfully acknowledge "Ministerio de Educacion, Cultura y Deporte" (Grant number FPU12/02841) for supporting this work through "Becas y Contratos de Formacion de Profesorado Universitario del Programa Nacional de Formacion de Recursos Humanos de Investigacion del ejercicio 2012". Finally the linguistic support of Irene I. Elias-Miranda is appreciated.

Due to the adoption of EU Regulation No 517/2014, R404A is going to be banned in Europe in most of refrigeration applications, in which is typically used, due to its very high GWP value, 3943. In this paper an experimental comparison between R404A and R448A, a non-flammable alternative with GWP of 1390, is presented. The experimental tests are intended to simulate typical freezing and conservation temperatures and different condensing conditions. Despite cooling capacity of R448A is slightly below that of R404A, R448A energy consumption is even smaller; and R448A COP is higher than that obtained using R404A. Hence, it can be concluded that R448A could be an energy efficient alternative to R404A with a GWP reduction of 70%. Compressor discharge temperature remains at non-dangerous levels., The authors thankfully acknowledge "Ministerio de Educacion, Cultura y Deporte - Gobierno de Espana" (Grant Number FPU12/02841) for supporting this work through "Becas y Contratos de Formacion de Profesorado Universitario del Programa Nacional de Formacion de Recursos Humanos de Investigacion del ejercicio 2012".

This article presents the development, validation, and comparison of two methods for modeling a reciprocating compressor. Initially, the physical mode is based on eight internal sub-processes that incorporate infinitesimal displacements according to the piston movement. Next, the analysis and modeling of the compressor through the application of artificial neural networks are presented. The input variables are: suction pressure, suction temperature, discharge pressure, and compressor rotation speed. The output parameters are: refrigerant mass flow rate, discharge temperature, and energy consumption. Both models are validated with experimental data for the refrigerants R1234yf and R134a; computer simulations show that mean relative errors are below ±10% with the physical model, and below ±1% when artificial neural networks are used. Additionally, the performance of the models is evaluated through the computation of the squared absolute error. Finally, these models are used to compute an energy comparison between both refrigerants.

The industrial sector demands novel sustainable energy systems to advance in its decarbonisation and meet the targets of the Paris Agreement for the climate change mitigation. High-Temperature Heat Pumps (HTHPs) are being investigated as a feasible energy conversion technology alternative to traditional fossil fuel boilers. This paper presents the first experimental results of an HTHP prototype equipped with a modified scroll compressor and internal heat exchanger (IHX). The elements of the main and secondary circuits are presented, as well as the test methodology and heat balances are exposed. The tests have been performed using HFC-245fa at heat source temperatures between 60 and 80 °C, and heat sink temperatures between 90 and 140 °C. The heating capacity and coefficient of performance (COP) varied between 10.9 and 17.5 kW and between 2.23 and 3.41, respectively. An exergetic analysis indicated that the expansion valve was the component with the worst second law efficiency and the compressor presented the highest potential improvement over the other cycle components. A computational analysis of low global warming potential (GWP) refrigerant alternatives was carried out, which confirmed the benefits of using an internal heat exchanger (IHX) and the good performances of the low-GWP refrigerants: HCFO-1224yd(Z), HCFO-1233zd(E), and HFO-1336mzz(Z). Finally, we proved that the proposed system can save up to 57% of the equivalent CO2 emissions of a natural gas boiler. This paper provides a reference for the high-temperature heat pump recovery of the low-grade waste heat from industrial energy processes.

This paper presents a model for a variable-speed liquid chiller integrating a compressor model based on Buckingham π-theorem to accurately predict the system performance when R134a is replaced with R1234yf, using a wide range of data obtained from an experimental setup. Relevant variables such as temperature, pressure, mass and volumetric flow rates, compressor power consumption and rotation speed were measured at several positions along the refrigeration and secondary circuits and were used to validate the developed model. Model results show that cooling capacity and power consumption predicted values are in good agreement with experimental data, within ±5%, being slightly higher for the deviation obtained for R134a than for R1234yf. Moreover, model results indicate that R1234yf has a reduction of coefficient of performance (COP) compared with R134a (between 2 and 11.3%), and that R1234yf COP reduction is diminished at intermediate volumetric flow rate and higher inlet temperature for the evaporator secondary fluid, respectively. On the other hand, an environmental analysis based on TEWI (total equivalent warming impact) method showed that direct emissions are almost negligible for R1234yf. However, there are no environmental benefits in terms of indirect greenhouse gas emissions using R1234yf without system modifications (as for instance the addition of internal heat exchanger or R1234yf new design components), which are required to reduce the liquid chiller climate change contribution using it as low GWP alternative in comparison with the typically used R134a refrigerant.

[EN] 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., Dr. Adrian Mota-Babiloni would like to acknowledge the funding received from the Plan for the promotion of research of the University Jaume I for the year 2016 (Grant number POS-DOC/2016/23).

The introduction of high-temperature heat pumps for waste heat recovery with low GWP refrigerants can reduce the greenhouse gas emissions in the industrial sector. This article evaluates the energy performance and the volumetric heating capacity of five vapour compression system configurations using n-Pentane, Butane, HCFO-1233zd(E) and HFO-1336mzz(Z) as HFC-245fa low GWP alternative fluids for heating production at temperatures of 110, 130 and 150 °C and different temperature lifts. The selected architectures and the equations are presented, and the most appropriate method to calculate the intermediate pressure is selected. The results of the simulation show that single-stage cycle with an internal heat exchanger (IHX) becomes the most efficient configuration at lower temperature lifts whereas two-stage cycle with IHX at higher lifts. While n-Pentane provides the highest energy performance values, Butane (only up to 130 °C) and HCFO-1233zd(E) highlight in the heating volumetric capacities. HFO-1336mzz(Z) provides intermediate values in both parameters. Consequently, the working fluid selection is highly dependent on the specifications and the energetic and installation costs.

A combined organic Rankine cycle and vapor compression cycle (ORC-VCC) system activated by low temperature heat sources was studied. Two low GWP fluids were considered as working fluids for the VCC and two different low GWP fluids for the ORC. System performance was evaluated through computational modeling over different operating conditions. The computed thermal COP of the ORC-VCC system varied between 0.30 and 1.10 over the range of operating conditions studied. The computed electrical COP of the ORC-VCC system, defined as the ratio of the rate of cooling and the ORC pump power consumption, varied between 15 and 110. The choice of VCC working fluid had only a limited influence on system thermal or electrical efficiency, with HFO-1234ze(E) presenting slightly better results. Use of HFO-1336mzz(Z) as the ORC working fluid resulted in slightly higher system thermal efficiencies and significantly higher system electrical efficiencies throughout the range of operating conditions studied. Furthermore, the system is evaluated for a typical application and the feasibility study shows good economical results., The authors thankfully acknowledge DuPont Corporation for supporting this work.

[EN] This work conducts an experimental characterization of an Organic Rankine Cycle (ORC) module along the operating conditions expected for micro Combined Heat and Power (CHP) applications. For this, a monitored test bench has been used and adapted to the planned test procedure, which consisted of varying the condensing conditions for a fixed low grade heat source. Thereby, 10 steady state points are achieved and analyzed according to thermal power input, useful heat production, gross and net electrical powers, electrical and thermal cycle efficiencies and expander effectiveness parameters. The results show the importance, for all the cited parameters, that takes to operate with a suited pressure ratio, associated with the expander built-in volume ratio, to each specific application. So, if the useful heat temperature requirements allow to operate with a moderate under-expansion in the expander, the module is optimized., The authors want to acknowledge all the invaluable cooperation of Rank (R), the ORC manufacturer, for its support in this project. Also to thank greatly the Jaume I University for its financial support under the PhD grant PREDOC/2013/28 of "Convocatoria d'ajudes predoctorals per a la formacio de personal investigador del Pla de promocio de la investigacio de la Universitat jaume I de Castello (Spain)".