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Solar thermochemical hydrogen production is a promising pathway for producing sustainable fuels and chemicals. One of the main challenges in the development of these processes is their low steam conversion extent, dictated by its restrictive thermodynamics requiring extremely high temperatures over 1500 °C and low oxygen partial pressure to obtain a steam conversion over 10%. While condensing the unreacted steam is technically simple, the latent heat is thus rendered useless for the process. In many cases, this lost heat can be larger than the higher heating value of the produced hydrogen. We propose a new separation method based on a mechanical vapor recompression cycle, enabling the recovery of the latent heat by compressing the steam–hydrogen mixture prior to the condensation process, thus creating a temperature difference between the hot exhaust and cold inlet streams. We show that this separation method can recover the latent heat and keep its quality in relevant operating conditions while requiring less than 14% of the recovered heat for compression work, resulting in a coefficient of performance over 7. This method increases the viability of solar thermochemical hydrogen production cycles, especially under limited steam conversion conditions. • A new method for hydrogen–steam separation based on mechanical vapor recompression. • Coefficient of performance can achieve value over 10 for low steam conversion cases. • At higher conversion additional heat is needed to complete the boiling of the fresh steam. • Applications in solar thermochemical hydrogen production can increase overall system efficiency. [ABSTRACT FROM AUTHOR]

In this paper, we present the development of a gray-box model for unitary air conditioning equipment that can be trained with as little as 5 data points with higher accuracy on test data. The model utilizes the same model inputs as is typical in building energy simulation, and is accurate. While black-box models require large data sets to deliver accurate results, white-box models require higher computational and engineering efforts along with detailed knowledge of the system, and are often difficult to obtain. The model presented here addresses a hybrid solution that is a steady-state, component-based, gray-box model that requires inputs from the source and sink fluids and rated performance of the specific piece of equipment, only. The basic physics of a vapor compression cycle are captured in individual component models for the heat exchangers, compressor, and expansion valve. These components are generalized to eliminate refrigerant-side inputs. A key addition is the development of correlations for the overall heat transfer coefficient times surface area (UA) obtained from Symbolic Regression (SR). The model successfully predicts the cooling capacity, coefficient of performance (COP), and sensible heat ratio (SHR) for three state-of-the-art variable speed, split-system, air conditioning systems with capacities of 12.3(3.5), 14(4), and 17.6(5) kW(tons), achieving a mean absolute percentage error (MAPE) of less than 3.4%. These results suggest that the gray-box model can be useful in predicting the performance of similar systems in the future, which could be valuable for energy management and optimization purposes. • Development of a component-based gray-box model of a unitary air conditioner using symbolic regression. • Genetic algorithm used to formulate overall heat transfer coefficient correlation. • The model exhibits robustness and generalization, even with minimal training data. • Novel model utilizes only ambient temperatures and operational inputs, facilitating seamless integration into existing BEMs. [ABSTRACT FROM AUTHOR]

• The dynamic model for VCRS based on the Switched Moving-Boundary method is built. • The impact of environmental disturbances on the refrigeration performance is studied. • A hybrid paradigm combining online identification and adaptive control is proposed. • The overshoot performance is optimized at 10–4 magnitude in uncertain environments. • Adaptive control's IAE by 2–3 orders of magnitude compared to traditional control. Vapor compression refrigeration systems (VCRS) occupy a crucial position in modern society and in the field of thermal sciences. However, the operation of VCRS is subjected to both external disturbances (dynamic-changing environment) and inherent system characteristics (coupling or nonlinear features), leading to issues like reduced refrigeration efficiency and significant fluctuations in cooling capacity. To address these challenges and enhance the adaptability of VCRS in dynamically changing environments, this study establishes a dynamic simulation model for VCRS based on the Switched Moving-Boundary method. The impact of external environmental disturbances on refrigeration performance is investigated, and continuous online identification methods are employed to elucidate its internal coupling characteristics and nonlinear features. The adaptive temperature control method is introduced, benefiting from the developed recursive least squares method with a forgetting factor for online identification, achieving precise model identification which facilities the real-time parameters tuning of adaptive controller. The results indicate that the hybrid paradigm of online identification and adaptive control algorithm not only effectively handles various disturbances but also reduces overshoot and IAE by 2–3 orders of magnitude compared to traditional PID controllers. Adaptive PID control maintains overshoot in the 10–4 order of magnitude and IAE in the 10–5 order of magnitude. [Display omitted] [ABSTRACT FROM AUTHOR]

Development and calibration of first-principles dynamic models of vapor compression cycles (VCCs) is of critical importance for applications that include control design and fault detection and diagnostics. Nevertheless, the inherent complexity of models that are represented by large systems of differential–algebraic equations leads to significant challenges for model calibration processes that utilize classical gradient-based methods. Bayesian optimization (BO) is a sample-efficient and gradient-free approach using a probabilistic surrogate model and optimal search over a feasible parameter space. Despite the benefits of BO in reducing computational costs, challenges remain in dealing with a high-dimensional calibration task resulting from a large set of parameters that have significant impacts on system behavior and need to be calibrated simultaneously. This paper presents a reduced-dimension BO framework for calibrating transient VCCs models where the calibration space is projected to a low-dimensional subspace for accelerating convergence of the solution algorithm and consequently reducing the number of transient simulations. The proposed approach was demonstrated via two case studies associated with different VCC applications where 10 parameters were calibrated in each case using laboratory measurements. The reduced-dimension BO framework only required 1 / 8 th of the iterations associated with a standard BO method that deals with high-dimensional calibration parameters for converged solutions and yielded comparable accuracy. Furthermore, both calibrated models revealed significant accuracy improvements compared to uncalibrated models. [ABSTRACT FROM AUTHOR]

In light of the intensifying global climate crisis and the increasing demand for efficient electricity and cooling systems, the exploration of advanced power generation technologies has become crucial. This paper presents a comprehensive analysis of Organic Rankine Cycle–Vapor Compression Cycle (ORC-VCC) systems utilizing low-grade waste heat for the dual purpose of electricity and cooling production. The study focuses on systems that harness waste heat below 90 °C with thermal inputs up to 500 kW. An in-house Python code was developed to calculate cycle parameters and perform multi-objective optimization targeting the maximization of both ORC-VCC efficiency and power output. The optimization was conducted for 10 different cases by evaluating five working fluids across two different ambient temperatures. The analysis reveals that the optimized system achieved an impressive overall cycle efficiency exceeding 90%, demonstrating the significant potential of ORC-VCC technology in waste heat recovery applications. The Non-Dominated Sorting Genetic Algorithm II (NSGA-II) multi-objective optimization approach was found to be particularly effective at navigating the multi-dimensional solution space and identifying the global optimum. This study provides valuable insights into system performance across a range of operating conditions and design parameters. Sensitivity analyses highlight key factors influencing cycle efficiency and power output. These findings have important implications for the development and deployment of ORC-VCC systems as a sustainable and efficient solution to meet growing energy needs while reducing greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

A novel heat-driven ejector refrigeration machine for an onboard air-conditioning system of a merchant ship was conceptualized and analyzed. The source of waste heat is low-pressure steam from the exhaust gas boiler (0.5-0.7 MPa). However, the steam from auxiliary boilers is used in port. It was proposed to include a thermal energy storage unit in the ejector refrigeration machine design to reduce fuel consumption by auxiliary boilers in the port. A phase change material with a melting point of 142 °C was proposed for use as thermal energy storage material. It was admitted for the TES unit to replace half of the generator load for 1 day of operation. For such conditions the volume and mass of the thermal energy storage unit were 16.5 tons and 125 m3 at an ejector refrigeration machine cooling capacity of 174 kW. It was shown that ejector refrigeration machine with thermal energy storage unit inherent the lower fuel consumption for its operation compared to the vapor-compression refrigeration machine: 53916 vs. 80567 kg of fuel per year. It is advisable to use the proposed ejector refrigeration machine with a thermal energy storage unit on ships that have short voyages and frequent stays in port. The problems in the TES unit design that need to be studied further have been noted in the paper. [ABSTRACT FROM AUTHOR]

The increasing global demand for energy-efficient cooling systems, combined with the need to reduce greenhouse gas emissions, has led to growing interest in using low-GWP (global warming potential) refrigerants. This study conducts a multi-objective optimization of a small-scale organic Rankine cycle–vapor compression cycle (ORC-VCC) system, utilizing refrigerants R1233zd, R1244yd, and R1336mzz, both individually and in combination within ORC and VCC systems. The optimization was performed for nine distinct cases, with the goals of maximizing the coefficient of performance (COP), maximizing cooling power, and minimizing the pressure ratio in the compressor to enhance efficiency, cooling capacity, and mechanical reliability. The optimization employed the Non-dominated Sorting Genetic Algorithm III (NSGA-III), a robust multi-objective optimization technique that is well-suited for exploring complex, non-linear solution spaces. This approach effectively navigated trade-offs between competing objectives and identified optimal system configurations. Using this multi-objective approach, the system achieved a COP of 0.57, a pressure ratio around 3, and a cooling capacity exceeding 33 kW under the specified boundary conditions, leading to improved mechanical reliability, system simplicity, and longevity. Additionally, the system was optimized for operation with a cooling water temperature of 25 °C, reflecting realistic conditions for contemporary cooling applications. [ABSTRACT FROM AUTHOR]

• The evaluation of refrigeration systems due to the presence of malfunctions in their components was conducted through thermoeconomic methodology. • This methodology used splits physical exergy into its thermal and mechanical terms, in addition to using the fictitious term of negentropy. • A prognosis of system behaviour was derived, enabling utilization in maintenance scheduling and facilitating comprehensive energetic and exergetic analyses of both the refrigeration system and its individual components. In recent years, it has been possible to observe a significant expansion of the refrigeration and air conditioning industry. Considering that food refrigeration systems (blast chilling or freezing, cold storage, retail display, etc.) and air conditioners are large energy consumers, this work presents a methodology for evaluating the performance and behaviour of these systems using the thermoeconomic diagnosis concept. The thermoeconomic model used allowed the definition of the condenser and expansion device products, which is not trivial for these components. With that, the thermoeconomic diagnosis was used to evaluate the degradation of refrigeration system components, together with the influence of individual component degradations on efficiency, cooling capacity, operating parameters, and power consumption of the whole system. Through this analysis, a prognosis of system behaviour was obtained, which can be used for maintenance scheduling, as well as for the comprehensive energetic and exergetic analysis of a refrigeration system and each of its components. [ABSTRACT FROM AUTHOR]

Magnetic refrigeration based on magnetocaloric effect (MCE) has become a promising cooling technology to replace the traditional vapor compression refrigeration. However, traditional methods for searching MCE materials require producing many different compositions, causing unbearable workload and long experimental periods. Here, 3D printed La0.7Ce0.3Fe11.65Si1.35–Fe compositionally gradient alloys (CGAs) are successfully prepared using laser powder bed fusion equipped with a powder hopper with dual‐bin structure. This CGAs accelerate the high‐throughput screening for the best composition of La(Fe, Si)13/Fe with both high MCE and mechanical properties. The good interfacial compatibility between brittle 1:13 phase and reinforcing α‐Fe improves the mechanical properties significantly. Even after hydrogenation, the compressive strength and ultimate strain of the La(Fe, Si)13/Fe hydrides are ≈220% and ≈150% higher than those of stoichiometric La(Fe, Si)13. Meanwhile, the hydrogenated composite exhibits a large MCE under low magnetic field, e.g., the magnetic entropy change |ΔSM|max of 7.6 J kg−1 K−1 under 2 T is 52% higher than that of the benchmark Gd (5.0 J kg−1 K−1). Furthermore, this La(Fe, Si)13/Fe is 3D printed into various complex shapes suitable for heat exchangers. This study provides an innovative strategy for high‐throughput screening of new materials. [ABSTRACT FROM AUTHOR]

In this study, a validated mathematical model for a composite air conditioning system was established based on onsite test data. The system consists of a refrigerant pump driven two-phase cooling loop (RPTCL) and vapor compression refrigeration (VCR) cycles. The system can be switched to refrigerant pump (RP) mode, compressor mode, or hybrid mode, according to the outdoor temperature. By analyzing, the inadequacy of the existing Internet Data center (IDC) air conditioning system operation strategy was confirmed, and subsequently, five optimization strategies were proposed. The optimization strategies took two identical composite air conditioning systems as optimization unit, and under the premise of meeting the demand for cooling capacity, maximizing the operating time of RP and hybrid mode, which with higher energy efficiency, through complementary cooling capacity, to reduce the energy consumption. Meanwhile, when the cooling supply was higher than the demand, paired with optimization unit's ON/OFF ratio control, the unit's energy consumption was further reduced. The most optimization strategy provided 525.6 MWh of cooling energy to meet demand while consuming a minimum of 182.5 MWh. The optimization strategy also achieved a minimum of 12.1% and a maximum of 52.5% energy savings for IDCs in other climate zones of China. [ABSTRACT FROM AUTHOR]

One of the promising approaches to compensate for imminent depletion of fossil energy resources and their adverse global impacts is enhancing the efficiency of systems utilizing low-temperature heat sources. The initial target of the research is to present a promising system for simultaneous production of power, refrigeration, heat, and hydrogen utilizing a combination of the absorption power cycle, the vapor compression refrigeration cycle, and a proton exchange membrane electrolyzer. On this subject, a comprehensive modeling of the energy and exergy of the proposed set-up is presented, and its thermodynamic performance is scrutinized. Furthermore, a comprehensive study of various parameters is performed to evaluate their impacts on system performance. The research aims to enhance and optimize the use of energy and various resources, contributing to the development of more sustainable efficient energy systems. Thermodynamic analysis of the multiple generation system shows that under baseline conditions and initial design, the system has the capability to produce net electrical power of approximately 17.12 kW, cooling power of about 201.5 kW, heating power of around 697.1 kW, and produce pure hydrogen at a rate of 0.153 kilograms per hour. The system exhibits an energy efficiency ratio of 1.364 and an exergy efficiency of 36.58 %. Moreover, optimization with single and multiple objectives with different weighting coefficients reveals that higher values of these parameters can be obtained. In other words, in the MOOM optimization mode, exergy efficiency increases to 7.16 %, and the energy performance ratio rises to 85.73 % compared to the BM mode. Additionally, through a parametric assessment to define the effect of input parameters on system performance, it demonstrates that increasing the temperature of the heat source may simultaneously increase the exergy efficiency and energy performance ratio of the system. The Grassmann diagram also indicates that the total exergy of the input fuel is about 196.9 kW. From this amount, approximately 121.5 kW are destroyed through the components of the system. Furthermore, about 3.39 kW are lost through the absorber coolant and waste from the hydrogen production unit. About 72.4 kW are attributed to products. [ABSTRACT FROM AUTHOR]

Air conditioning is vital for indoor comfort but traditionally relies on vapor compression systems, which raise electricity demand and carbon emissions. This study presents a novel thermo-mechanical vapor compression system that integrates an ejector with a conventional vapor compression cycle, incorporating a thermally driven second-stage compressor powered by solar energy. The goal is to reduce electricity consumption and enhance sustainability by leveraging renewable energy. A MATLAB® model was developed to analyze the energy and exergy performance using R1234yf refrigerant under steady-state conditions. This study compares four solar collectors—evacuated flat plate (EFPC), evacuated tube (ETC), basic flat plate (FPC), and compound parabolic (CPC) collectors—to identify the optimal configuration based on the collector area and costs. The results show a 31% reduction in mechanical compressor energy use and up to a 44% improvement in the coefficient of performance (COP) compared to conventional systems, with a condenser temperature of 65 °C, a thermal compression ratio of 0.8, and a heat source temperature of 150 °C. The evacuated flat plate collectors performed best, requiring 2 m2/kW of cooling capacity with a maximum exergy efficiency of 15% at 170 °C, while compound parabolic collectors offered the lowest initial costs. Overall, the proposed system shows significant potential for reducing energy costs and carbon emissions, particularly in hot climates. [ABSTRACT FROM AUTHOR]

Barocaloric cooling as an emerging cooling technology offers an eco‐friendly alternative to traditional vapor compression refrigeration. Research on barocaloric materials primarily concentrates on solid–solid phase change materials (PCMs), among which plastic crystals exhibit colossal barocaloric effect. Solid‐liquid PCMs such as paraffin also exhibit giant barocaloric effect, however, their potential is often overshadowed by leakage issues. In this work, a strategy is demonstrated by encapsulating solid‐liquid PCMs into porous carbon matrixes to generate a large family of colossal barocaloric materials. In practice, by orthogonally combining paraffins with encapsulation matrixes like graphene foam, carbon nanotube foam, and carbon foam, it can be obtained composites that work without leakage issues. The significant advantage is their colossal barocaloric effect with the highest entropy value up to 570 J K−1 kg−1 in paraffin‐20@graphene foam. Moreover, the composites possess thermal conductivity up to 89.9 W m−1 K−1 in paraffin‐20@carbon foam, and tunable working temperature in the range of 270—330 K. Most importantly, this strategy, demonstrated with 5 solid‐liquid PCMs and 3 encapsulation matrixes in this work, is just the beginning. Further exploration with more materials can develop a huge family of encapsulated solid‐liquid PCMs with colossal barocaloric performance for modern cooling technology. [ABSTRACT FROM AUTHOR]

There is an enormous amount of water vapor in ambient air that can be converted into liquid water by several methods. A method that is capable of producing a large amount of water is a vapor compression system. However, this method requires significant power input, which may cause the cost of producing water to be prohibitive. In this paper, it is proposed that a vapor compression refrigeration system that is used to cool air in a combined cycle power plant has the potential to be a viable method of atmospheric water generation. This system produces saturated air by mixing atmospheric air with water, and reduces air temperature and humidity using a mechanical chiller. The reduction in inlet air temperature enables the combined cycle power plant to generate more power output, which is used to operate the air cooling system. Therefore, the air cooling system can harvest atmospheric water without requiring external power input. This concept is proven by simulating system performance in various atmospheric air conditions using system models of mass and energy balances. [ABSTRACT FROM AUTHOR]

Postharvest losses and spoilage of agricultural products are a major problem for tropical countries, and it is even more challenging for countries encountering fluctuating power shortages, such as Pakistan. Therefore, this study focused on the energy and economic analysis of cold storage to store three products (potatoes, pomegranates, and potatoes) according to the season and storage span throughout the year. The cooling load of the cold store was supported by a LiBr‐H2O vapor absorption and vapor compression refrigeration system to maintain the desired temperature for each product during cold storage. A solar thermal PV system is installed to operate cold storage refrigeration systems. Cold storage performance was analyzed by developing thermal models of integrated systems using the ambient conditions of Lahore, Pakistan. A parametric study was also conducted to analyze the impact of various working parameters on integrated system performance, and it was found that the maximum peak cooling load of 91 kW inside cold storage is attributed to pomegranates owing to high ambient conditions during its loading month. The product loading rate significantly affects the cooling load of cold storage and varies directly with it, as observed for an increase in the product loading rate from 0 to 50 000 kg/day cooling load also increases from 34 to 87 kW. To meet the thermal demand of the generator of the vapor absorption system, parabolic troughs were installed to operate cold storage, and it was found that a minimum of four PTC were needed to support the peak cooling load at the maximum product loading rate and minimum DNI value. To meet the electrical demand of cold storage electrical equipment and the compressor of the vapor compression system, solar photovoltaic panels were installed, and it was found that a minimum of 618 panels was required at a minimum tilted radiation value. To validate the viability of proposed design system economic analysis was also conducted which revealed a payback period of 12 years for Kinnow and potatoes and 16 years for pomegranates. [ABSTRACT FROM AUTHOR]

While forced-air convective systems remain the predominant method for heating and cooling worldwide, radiant cooling and heating systems are emerging as a more efficient alternative. Current radiant cooling systems primarily rely on hydronic chilled water systems. This study introduces direct-expansion radiant cooling as a novel technique that could enhance the efficiency of radiant cooling and reduce its environmental impact. Water (R-718) has been tested as a refrigerant due to its favorable thermodynamic properties and environmental advantages; however, to the author's knowledge, it has yet to be tested in direct-expansion radiant cooling. This research investigated several refrigerants, including water (R-718), ammonia (R-717), R-410a, R-32, R-134a, and R-1234yf, for this application. The findings indicate that water demonstrates efficiency comparable to other non-natural refrigerants, making it a promising candidate, given its favorable thermodynamic properties and substantial environmental benefits. Despite challenges such as a high compression ratio necessitating multi-stage compression, a high compressor discharge temperature exceeding 300 °C and requiring specialized blade materials, and a high suction volume flow rate, direct-expansion radiant cooling operates within a different temperature range. Consequently, the compressor discharge temperature can be reduced to 176 °C, and the compression ratio can be lowered to approximately 3.5, making water a more viable refrigerant option for this application. [ABSTRACT FROM AUTHOR]

• Developed a dynamic model of a triple-evaporator domestic refrigerator/freezer. • Dynamic model validated within a 2 % deviation in average power consumption. • Implemented a two-stage economized cycle and its control scheme. • Achieved 12.9 % and 80 kWh/year reduction in power and energy consumption, respectively. • Estimated 18 TWh/year in global energy savings by 2030 with 10 % market penetration. Domestic refrigerator/freezers account for approximately 6 % of all energy consumption around the globe and mainly rely on vapor compression cycles to operate. Researchers have investigated alternative cycle architectures such as dual-loop cycles and parallel circuit cycles to improve their efficiencies. Despite the demonstrated energy saving potential of these advanced cycles, additional implementation costs are often not justifiable. However, to meet forthcoming stricter energy standards while ensuring flexible multi-temperature operation of domestic refrigerator/freezers, advanced cycle architectures are needed. In this paper, a state-of-the-art bypass circuit cycle triple-evaporator domestic refrigerator freezer with R-600a and a reciprocating compressor has been used as the baseline cycle investigate an alternative cycle configuration. Specifically, this work presents a two-stage vapor-injected cycle with a multi-evaporator system to enable energy savings and cost-effectiveness. The cycle establishes two separate evaporation temperatures to better match the cabinet temperature of fresh food and freezer compartment. The reduced difference between cabinet temperature and its evaporation temperature decreases the irreversibilities in the heat exchanger and improves overall system efficiency. Moreover, the addition of the economization line from the medium temperature evaporator reduces the compressor work. To capture the complex transient behavior of both the baseline system and proposed cycle architecture with their control strategies, a dynamic model has been developed and validated with experimental data. The validated dynamic model with the baseline cycle was modified to consider the two-stage vapor-injected cycle and its control logic, and simulation results yielded up to 13 % energy consumption reduction with respect to the baseline system. [ABSTRACT FROM AUTHOR]

• A compression-assisted absorption refrigeration cycle using R32/DMAC is developed. • Enable the implementation of solar absorption refrigeration in refrigerated warehouses. • Using 60∼80 °C solar hot water obtains a low evaporation temperature of −20∼0 °C. • There is an 18.2 % reduction in electricity consumption compared to traditional method. Solar absorption refrigeration technology is considered an ideal alternative to energy-intensive refrigerated warehouses due to its decarbonization and environmental friendliness. However, it faces challenges in competing with vapor compression refrigeration, such as high driving heat source temperature (>100 °C) and a long payback period. In this paper, we address these challenges by focusing on cycle structure and working pair, and propose a compression-assisted absorption refrigeration cycle (CARC) using R32/dimethylacetamide (DMAC) as working pair. The aim is to significantly reduce driving heat source temperature by adjusting absorption pressure utilizing an auxiliary compressor, enabling the cycle to be connected to low-cost and efficient non-concentrating solar collectors, thereby effectively shortening its payback period. This cycle includes two operating modes: CARC mode powered by solar energy during the daytime and vapor compression refrigeration cycle mode driven by off-peak electricity at night, ensuring 24-hour cooling capacity for refrigerated warehouses. The results indicate that this cycle can flexibly utilize 60∼80 °C solar hot water easily obtained as driving heat source and its evaporation temperature decreases to -20 °C. To assess its performance benefits, a compression-assisted absorption refrigeration system is developed and implemented. By utilizing the limited roof area of a refrigerated warehouse, it can achieve an 18.2 % reduction in electricity consumption and a 24.2 % reduction in carbon emissions compared to the vapor compression one annually. Additionally, during peak electricity demand periods in summer, the system exhibits significant energy-saving effects, and its payback period is about 4.2 years. Ultimately, this cycle provides a viable solution for energy-saving and emission reduction in refrigerated warehouses. [ABSTRACT FROM AUTHOR]

The current small passenger car vapor compression refrigeration systems use high global warming potential (GWP) refrigerants causing the greenhouse gas effect. In the present work, the low GWP of two pure refrigerants, R1234yf and R1234ze (E), and 16 blends of R134a, R1234yf, and R1234ze (E) are analyzed numerically. The experiments were conducted with R134a refrigerant to validate the numerical results. The experiments were conducted at the compressor speed of 600–1500 rpm and the condensing air at 30–40°C, relative humidity of 85%, and velocity of 1–3 m/s. The simulation and experimental results for R134a are deviated by a minimum of 10% and a maximum of 15%. It is found that the latent heat of vaporization of the two refrigerant mixtures with 80% R134a–20% R1234yf and the three refrigerant blends of 50% R134a–10% R1234yf–40% R1234ze (E) are the highest among 16 combinations. The other blends show a moderate difference of latent heat with R134a, but for maximum cooling capacity, the blends with 80% R134a–20% R1234yf and 50% R134a–10% R1234yf–40% R1234ze (E) are found to be more suitable for practical applications. [ABSTRACT FROM AUTHOR]

Improvement of vapor-compression refrigeration systems taking into account ecological requirements will undoubtedly lead to the use of modern ozone-safe and non-greenhouse effect refrigerants. Increase of heat transfer and thermodynamic efficiency in general has raised the problem of selection of material and concentration of nanoparticles in the working mixture of refrigerant with mineral oil of compression refrigeration systems. The purpose of this study is to determine the influence of TiO2 and Al2O3 nanoparticles on the energy efficiency of refrigeration systems. Research methods: The study of operational and energy characteristics of compressor operation on the investigated mixtures was carried out on the experimental unit. Isobutane R600a refrigerant was used for the study. Efficiency is determined by power consumption, cooling capacity and efficiency. The refrigerant flow rate and nanoparticle concentration are varied during the experiment. Results: The experimental results concluded that Al2O3 nanoparticles with a mass concentration of 0.5% maximized the performance of the compressor refrigeration system. The addition of nanoparticles resulted in a significant increase in the cooling capacity, especially when compared to the original refrigeration-oil mixture with the cooling capacity parameter of 70 W. This parameter is about 79 W with the addition of TiO2 nanoparticles regardless of their concentration. When Al2O3 nanoparticles are added at concentrations of 0.1 and 0.5 wt.%, respectively, these parameters are 88 W and 102 W. [ABSTRACT FROM AUTHOR]

Gravity-assisted separation heat pipes (GSHPs) are extensively utilized in telecommunications base stations and data centers. To ensure year-round cooling, integrating GSHPs directly with a vapor compression refrigeration system is a viable solution. It is unavoidable that the refrigeration system's lubricant will infiltrate the heat pipe loop, thereby affecting its thermal performance. This paper examines the performance of a GSHP, which features a water-cooled plate heat exchanger as the condenser and a finned-tube heat exchanger as the evaporator, when the working fluid (R134a) is contaminated with a lubricant (POE, Emkarate RL-46H). The findings are compared with those from a system free of lubricant. The experimental outcomes indicate that the presence of lubricant degrades the heat transfer efficiency, particularly when the filling ratio is adequate and no significant superheat is observed at the evaporator's outlet. This results in a 3.86% increase in heat transfer resistance. When the charge of the working fluid is suboptimal, the average heat transfer resistance remains relatively constant at a 3% lubricant concentration yet increases to approximately 5.27% at a 4–6% lubricant concentration, and further to 12.32% at a 9% lubricant concentration. Concurrently, as the lubricant concentration fluctuates between 3% and 9%, the oil circulation ratio (OCR) varies from 0.02% to 0.11%. [ABSTRACT FROM AUTHOR]

• For the first time, nanoparticles have been added into the cascade cycles. • An 6.37 % increase in performance was achieved with nano-refrigerant application. • With nano-refrigerant the emission of the CO 2 has decreased by 13.03 %. There is a lack of research in the literature on the application of nanoparticles to different cascade cycle configurations with environmental refrigerants in ultra-low temperature refrigeration applications. This study is the first on the use of nano-refrigerants in cascade refrigeration cycles. In this study, the effect of 2 wt.% of CuO to RE170 and R170-pure refrigerant utilization in cascade vapor compression refrigeration cycle (CVCRC), cascade ejector refrigeration cycle (CERC) and cascade ejector intercooler refrigeration cycle (CEIRC) are investigated to achieve higher performance values in ultra-low temperature applications. For CVCRC, CERC and CEIRC, the increases in terms of coefficient of performance (COP) with the use of nano-refrigerant were found to be 12.77 %, 8.20 %, and 6.37 %, respectively, and 18.55 %, 14.05 %, and 6.07 %, for exergy efficiency. Upon scrutinizing the results with nano-refrigerant in relation to the COP, the analysis revealed that the CEIRC cycle exhibited an improvement ranging from 13.43 % to 20.49 % in comparison to CERC. Additionally, with nano-refrigerant, the CEIRC cycle demonstrated an increase ranging from 42.39 % to 75.41 % when compared to CVCRC in COP. It was observed that the utilization of CEIRC led to a 13.03 % decrease in kg CO 2 emissions in compared to CERC and a reduction of 32.53 % compared to CVCRC with using nano-refrigerant. [ABSTRACT FROM AUTHOR]

Isentropic (adiabatic) compression of superheated vapor in vapor compression refrigeration cycles usually results in some discharge superheat, i.e. the discharge temperature exceeding the condensing temperature. Large discharge superheat reduces both operating range and compression efficiency. Sub-isentropic compression with heat rejection to the heat sink is therefore superior to adiabatic compression, as it results in lower discharge superheat and improved efficiency. However, significant temperature reduction by heat transfer through the working chamber walls is difficult to facilitate in common refrigeration compressors, particularly reciprocating compressors. Refrigerant and oil injection is a well-established method for reducing temperatures and increasing efficiency in screw and scroll compressors, as well as multi-stage systems. In comparison, effective methods for temperature reduction in single-stage reciprocating compressors are fairly limited. Therefore, a concept for high-pressure liquid injection is proposed. By means of a pump and injection valve, high-pressure liquid refrigerant is injected into the working chamber and atomized. The compressed gas is cooled through the evaporation of the injected liquid. The injection valve allows for control over the injection timing and quantity, enabling adjustment of the temperature profile, which is a major distinction from existing refrigerant injection methods. The coupled compression-injection process is evaluated for various refrigerants using an energetic chamber model. The injection is found to be particularly suitable for refrigerants with a large evaporation heat and a shallow dew line slope. For the example of ammonia, a theoretical reduction in compression work of 8.9% at an evaporation temperature of −10 °C and a condensing temperature of 45 °C is found. • Proposal of high-pressure liquid injection for reciprocating compressors. • Theoretical evaluation using energetic chamber model. • Potential for significant efficiency improvement compared to isentropic compression. • Increased operating range due to reduced discharge temperature. [ABSTRACT FROM AUTHOR]

This research paper figures out thermal performance analysis for vapor compression refrigeration (VCR) driven by the organic Rankine cycle (ORC) implementing MATLAB software. The ORC system is powered by improved evacuated tubes and compound parabolic collectors. The paper evaluates the overall exergetic efficiency and coefficient of performance using the working fluid Pentane/R245fa. The result of the present paper indicates that optimum COP of 0.75 and exergetic efficiency of 28% is obtained at 340 K of collector output temperatures, 0.1/0.9 of fractional mass of the working fluid, and 285, 300 K for VCR condenser and evaporator temperature, respectively. Sensitivity analysis pointed out that condenser temperature was the most impactful parameter for both exergetic efficiency and COP owing to higher F-value 'of 156.06' and '89.28,' respectively. Further, collector output temperature and fractional mass of the working fluid were the least impactful parameters owing to lower F-value '1.95' and '1.02' for exergetic efficiency and COP, respectively. [ABSTRACT FROM AUTHOR]

Solar-driven ejector cooling is a potential alternative for reducing overall energy usage. Hence, a review of solar-driven ejector refrigeration cycles, along with their integration with multi-generation systems, has been conducted, and they are structured into several sections. Initially, the basics of ejector technology, the standard ejector refrigeration cycle, and its performance parameters are discussed. Concise summaries of impactful studies on solar-driven ejector refrigeration cycles containing cycle modification and hybridization, working fluid selection, and available solar collectors, alongside thermal energy storage technologies, have also been added. The solar-driven multi-generation systems with ejector refrigeration cycles, as well as various recent studies on data-driven modeling of the ejector refrigeration cycle, are effectively discussed. Apart from this, the different challenges, along with the future outlooks of the solar-driven ejector refrigeration cycle, are also analyzed. Lastly, it is concluded that developing an energy-efficient solar-driven ejector refrigeration cycle may be a potential replacement for the existing electricity-driven vapor compression refrigeration cycle. Therefore, this review would be helpful for newcomers to understand complete incite ejector refrigeration cycles along with their integration with solar energy, which is essential for the sustainable development of human civilization in the current energy scenario. [ABSTRACT FROM AUTHOR]

Room-temperature elastocaloric cooling is considered as a zero-global-warming-potential alternative to conventional vapor-compression refrigeration technology. However, the limited entropy and large-deformation features of elastocaloric polymers hinder the creation of the breakthrough in their caloric responses and device development. Herein, we report that the addition of a small amount of inorganic nanofillers into the polymer induces the aggregate of the effective elastic chains via shearing the interlaminar molecular chains, which provides an additional contribution to the entropy in elastocaloric polymers. Consequently, the adiabatic temperature change of −18.0 K and the isothermal entropy change of 187.4 J kg−1 K−1 achieved in the polymer nanocomposites outperform those of current elastocaloric polymers. Moreover, a large-deformation cooling system with a work recovery efficiency of 56.3% is demonstrated. This work opens a new avenue for the development of high-performance elastocaloric polymers and prototypes for solid-state cooling applications. In this work, inorganic nanofillers are added to SEBS polymers to induce shearo-caloric effects, enhancing the elastocaloric response. Authors design and demonstrate a double-unit cooling device with a work recovery efficiency of 56.3% and a system coefficient of performance of 8.3. [ABSTRACT FROM AUTHOR]

The present investigation focuses on enhancing the efficiency of a vapor compression refrigeration system (VCRS) by proposing a Multiple Input Multiple Output (MIMO) control strategy based on the evaporator's two-phase length and superheat temperature. A moving boundary dynamic model for the VCRS is implemented using the Thermosys Matlab Toolbox. The study analyzes the influence of actuation parameters, specifically compressor speed and expansion valve opening, on control parameters, namely two-phase length and superheat temperature. A comprehensive analysis based on the first and second laws of thermodynamics is conducted across a wide range of operating conditions. Simulation results demonstrate that two-phase length can be effectively utilized as a control parameter by selecting operating points that maximize the system efficiency. Additionally, the study reveals that extending the evaporator's two-phase length to 80–90% of its limit increases system efficiency, enabling a reduction in compressor speed while maintaining the cooling capacity. [ABSTRACT FROM AUTHOR]

This paper optimizes a variable-frequency dehumidification system (VFDS) based on the principle of vapor compression refrigeration (VCR), wherein the compressor frequency and fan speed can be changed. The effect of the compressor frequency and fan speed on the operating parameters of the VFDS, including the evaporating temperature (Te), condensing temperature (Tc), superheating (ΔTsh), and subcooling (ΔTsc), is studied experimentally under three operating conditions. The effect of variable-frequency on the dehumidification performance is analyzed at the mechanistic level through two dehumidification performance indicators, namely, the dehumidification capacity (DC) and dehumidification energy efficiency (DEE). ΔTsh is primarily controlled by the capillary throttling effect, which always starts to cross the “0” point when the fan speed is 600 rpm under different conditions. An increase in the compressor frequency leads to the opposite trend for DC and DEE, but their corresponding optimal fan speeds are relatively close. At 27 °C/60%, the optimal fan speed intervals with DC and DEE as single optimization objectives are both [600 rpm, 700 rpm]. However, at 30 °C/80%, the overall difference between the optimal fan speed intervals with DC and DEE as optimization objectives is 50–100 rpm. Importantly, the risk of frost at 18.3 °C/60% can lead to a significant extension of the optimal fan speed interval, which is [500 rpm, 900 rpm], making it more difficult to control. The concept of the dehumidification operating temperature difference (ΔT) is proposed to comprehensively evaluate the dehumidification capacity and as a control index for variable frequencies. The relationships among the optimal ΔT and the ambient dew point temperature (Td) and compressor frequency are established through response surface methodology (RSM) with a maximum deviation of 5.97%. This work can provide an optimized variable-frequency solution for the VFDS and some guidance for the control logic development of the VFDS. [ABSTRACT FROM AUTHOR]

The electrocaloric effect (ECE) is considered as an environmentally friendly refrigeration technology, which can be used to replace vapor compression refrigeration. Lead-free antiferroelectric (AFE) ceramics are promising electrocaloric materials because of large saturation polarization and polarization change with temperature, which can generate large positive or negative ECE. In this work, the lead-free Ag(Nb 1-0.8x Hf x)O 3 (x = 0, 0.001 and 0.003) AFE ceramics are fabricated through a conventional solid-state reaction method which shows a decreased the phase transition temperature of M 1 - M 2 toward room temperature (RT), and a large negative ECE (Δ T = −2.3 K under 130 kV cm−1) is obtained near the ambient temperature by using an indirect measurement in ANH0.001 AFE ceramic. The large negative ECE behavior is ascribed to dipole disordering (i.e. the anti-parallel dipoles are broken and gradually becomes disordered under an external electric field) resulting from the field-induced phase transition under a modest electric field. This work shows that AgNbO 3 -based AFE ceramics could be used in the refrigeration devices as an electrocaloric material. [ABSTRACT FROM AUTHOR]

The process of air entering the vapor compression refrigeration system is very common, and it can happen during installation, maintenance, or charging. Since air is a non-condensable gas compared to the refrigerant gas inside the system, it causes deterioration in the system mainly due to high condensing pressure. This experimental study contributes to verifying the negative effects that can be left by non-condensable gases in the vapor-compression refrigeration system via analyzing the performance of a chest freezer charged with R134a refrigerant without an air fraction and with three air fractions 1.7%, 2.5% and 3.3% under steady-state conditions and an ambient temperature of 32°C. The results revealed that the performance of the chest freezer deteriorated clearly with the increase in air fraction; at an air fraction of 3.3% the power consumption increased by 37.1% and the coefficient of performance decreased by 42.8% compared to without air fraction. In addition to high noise and vibration. [ABSTRACT FROM AUTHOR]

This study examined the performance of reversed Brayton cycle heat pumps to supply heat above 300 °C. The aim was to overcome the current temperature limitations faced by heat pump technology in industrial heat supply sectors by examining the viability of the reversed Brayton cycle. In particular, the effects of the operating conditions on the cycle performance, such as the waste and return heat temperatures, were analyzed through thermal performance analysis. The reversed Brayton cycle heat pumps showed improved performance over conventional vapor compression cycle heat pumps when a heat supply above 215 °C was required. Furthermore, integrating additional heat exchangers into the cycle configuration was proposed in this study as a method to enhance waste heat utilization and recover unused heat from industrial processes. By incorporating preheating and recuperated cycles, these modifications broaden the operational range under the same operating conditions. They also improve the coefficient of performance (COP) of the reference cycle by up to 23% and 27.4%, respectively. This study explored the potential of reversed Brayton cycle heat pumps to supply heat above 300 °C and provided fundamental guidelines for the efficient design and operation of reversed Brayton cycle heat pumps. The results are expected to enhance our understanding of the performance characteristics of reversed Brayton cycle heat pump technology and expand its use as an alternative to fossil-fuel-based heat supply systems. [ABSTRACT FROM AUTHOR]

Preservation of perishable food produce is a major concern in the cold chain supply system. Development of an energy-efficient on-farm cold storage facility, hence, becomes essential. Integration of thermal storage into a vapor compression refrigeration (VCR)-driven cold room is a promising technology that can reduce power consumption and act as a thermal backup. However, designing a latent heat energy storage heat exchanger encounters challenges, such as low thermal conductivity of phase change materials (PCMs) and poor heat exchanger efficiencies, leading to ineffective charging–discharging cycles. The current study investigates the effect of the integration of a Phase Change Material (PCM) in terms of the selection of the PCM, the optimal positioning of the PCM heat exchanger, and the selection of heat exchanger encapsulation material. Numerical analysis was undertaken using 3D Experience software (version: 2024x.D31.R426rel.202403212040) by creating a 3D model of a 3.4 m3 micro-cold storage unit to understand the inner temperature distribution profile. Further, the experimental setup was developed, and tests were conducted, during which the energy consumption of 1.1 kWh was recorded for the total compressor run time of 1 h. Results indicated that an improved cooling effect was achieved by positioning the PCM trays on the wall opposite the evaporator. It is seen that a temperature difference in the range of 5 to 7 °C exists between the phase change temperature of PCM and the optimal storage temperature depending on the encapsulation material. Hence, PCM selection for thermal storage applications would have an important bearing on the material and configuration of the PCM encapsulation. [ABSTRACT FROM AUTHOR]

Ammonia is a vital chemical with numerous applications. Currently, the primary methods for generating the necessary reactants for ammonia production involve steam methane reforming (SMR) and cryogenic air separation unit (CASU), while the Haber-Bosch process converts these reactants into ammonia. However, the SMR process releases substantial amounts of CO 2 , making it imperative to employ an efficient and cost-effective CO 2 capture technology to mitigate emissions. This investigation focuses on evaluating the cryogenic CO 2 capture (CCC) process for blue ammonia production and provides a thorough economic analysis, estimating both the initial investment costs and operational expenses involved in producing blue ammonia. The results indicated that the CCC process can capture 90% of the CO 2 content in the flue gas emitted by the SMR, incurring an energy penalty of 0.724 M J e / k g C O 2 while capturing CO 2 in the liquid phase with purities exceeding 99.9%. In this case, the estimated CO 2 capture costs would be 18.05, 45.1, and 16.65 USD/ton in 2021, 2022, and 2023, respectively. This represents a 40% reduction compared to the CO 2 capture costs associated with conventional amine-based technology. The results of this study indicate that the annual electricity costs for ammonia production increase by 38.5% and 64.2% when employing the CCC and amine-based processes, respectively. This investigation employed an isothermal reactor for ammonia synthesis, using the heat from the exothermic reaction in a water ammonia absorption refrigeration cycle (ARC) to condense and purify ammonia. The results show that the ARC system can effectively condense ammonia at −6 °C, producing a liquid ammonia stream with 99.3% purity. This leads to a 95% reduction in power consumption compared to a vapor compression refrigeration cycle (VCRC). Consequently, this method has the potential to decrease the annual operational costs for ammonia production by 2.92%, 2.69%, and 3.13% in 2021, 2022, and 2023, respectively. This study indicated that the hydrogen production unit incurs the highest initial investment costs, as well as operating costs, in the blue ammonia production process, followed by CASU and the Haber-Bosch process. • The performance of the CCC process for blue NH 3 production was thoroughly evaluated. • The economic impacts of CCC process were compared with those of amine-based method. • An energy efficient method for condensation of NH 3 in Haber-Bosch process is given. • Natural gas costs mainly influence the operating costs of blue NH 3 production. [ABSTRACT FROM AUTHOR]

Development and evaluation of semi-automatic controlled atmosphere storage facility for calamansi (Citrofortunella microcarpa) was developed with the application of vapor compression refrigeration engineering principles and arduino system to lengthen the fruit shelf-life for commercialization and processing purposes. The prototype's overall dimension is 210 cm in length, 120 cm in width, and 120 cm in height, and has a storage volume of 0.512 m³. It has a storage capacity of about 90-120 kilograms. Maintaining a temperature range of 8°C-10°C, CO2 of 1%-6%, O2 of 7%-12%, and N of 80%-90% atmospheric concentration inside the semi-controlled atmosphere storage facility resulted in a significant decrease in percentage (13.01%) of rotten calamansi fruit as compared to normal storage room (36.39%) from its initial weight. This demonstrates that the facility can reduce the fruits respiration rate and decrease deterioration. [ABSTRACT FROM AUTHOR]

In this study, the potential implementation of three different low-GWP refrigerants (R32, R452B, and R454B) as replacements for R410A was investigated. The study was performed using a simulation tool developed by the authors called RACHP-Lab, which is a vapor compression system simulation tool developed based on physicsbased simulation for typical mini-split air conditioners. The simulation study was carried out and validated using experimental performance data of 10 different air conditioning units available in the Egyptian market. The units included fixed-speed or variable-speed compressors and operated in cooling or heating modes. Drop-in replacement with the new refrigerants was carried out. For R32, the capacity increased between 4.9% and 13% for cooling cases, and 6.3% and 12.4% for heating cases. However, COP did not improve in all cases. For R452B and R454B with direct replacement, the capacity nearly remained the same, with an increase of COP between 1.6% and 8.0%. Soft optimization was also conducted on cooling cases where compressor suction superheat, condenser subcooling, and compressor volumetric speed were optimized to maximize COP while maintaining the original capacity of R410A. R32 showed an improvement of COP over R410A between 4.6% and 15.5%, while for R452B and R454B between 2.2% and 13.2%. [ABSTRACT FROM AUTHOR]

The focus of the study is the exploration of the possible efficacy and environmental advantages of nanofluids, including hybrid nanoparticles, concerning the effectiveness of the Vapor Compression Refrigeration System (VCRS). This necessitates a thorough assessment of the stability qualities, synthesis techniques, thermal conductivity, viscosity, and heat transfer efficiency of nanofluids. This research also aims to explore different Nano‐Refrigerant combinations that influence the Coefficient of Performance (COP). According to some research findings, the use of copper nanoparticles improved COP by 8.1%, while the use of alumina nanoparticles raised COP values as high as 6.71%. Moreover, studies have demonstrated that various hybrid nanoparticles like silver‐graphene oxide also greatly improve outcomes concerning amounts used, raising the system's overall performance capabilities. Finally, it can be said that there is a wide range of applications for these fluids because they can function cost‐effectively and environmentally friendly while significantly reducing energy consumption, acting as refrigerants or secondary fluid systems, and having a positive impact on performance when used in deployed VCRS configurations. [ABSTRACT FROM AUTHOR]

This study presents a novel approach that will address escalating demands for water and cooling in regions vulnerable to climate change through the proposal of an optimal integrated cooling–freshwater cogeneration system powered by renewable energy sources. Comprising three subsystems (integrated multi-effect evaporation distillation, absorption heat pump, and vapor compression refrigeration (MAV); renewable energy unit incorporating solar panels, wind turbines, batteries, and hydrogen facilities (RHP/BH); and combined heat and power (CHP)), the system aims to produce both cooling and freshwater. By recovering cooling from combined desalination and refrigeration subsystems to chill the air taken into the gas turbine compressor, the system maximizes efficiency. Through the recovery of waste heat and employing an integrated thermo-environ-economic framework, a novel objective function, termed modified total annual cost (MTAC), is introduced for optimization. Using a genetic algorithm, parametric iterative optimization minimizes the MTAC. The results reveal that under optimum conditions, the MAV, RHP/BH, and CHP subsystems account for 67%, 58%, and 100% of total annual, exergy destruction, and environmental costs, respectively. Notably, the system exhibits lower sensitivity to fuel prices than renewable energy sources, suggesting a need for future research that will incorporate dynamic product prices and greater fuel consumption to produce enhanced operational robustness. [ABSTRACT FROM AUTHOR]

The performance of a vapor compression refrigeration system (VCRS)-based residential air conditioner operating in a high-ambient temperature (HAT) country was investigated using six zero-ODP (ozone depletion potential) refrigerants as replacements to R22. The non-flammable alternative refrigerants considered in the present research were R134a, R404A, R407C, R410A, R448A, and R507A. Using the basic conservation laws, the VCRS was modeled during steady-state operation and solved using engineering equation solver (EES) software. Coefficient of performance (COP), pressures and temperatures at compressor suction and discharge, Global Warming Potential (GWP), critical pressure and temperature, compressor pressure ratio, volumetric cooling capacity (VCC) specific cooling capacity (SCC), and refrigeration effect were utilized as assessment criteria for the alternative refrigerants considered. From these refrigerants, the highest values of suction pressure, discharge temperature, and condenser pressure were attained by R410A. In addition, the discharge temperatures for all refrigerants, except R134a, were all higher than their corresponding critical values, causing a quicker drop in the VCRS's performance. As an alternative refrigerant, R407C showed the highest SCC of 141.0 kJ/kg followed directly by 139.2 and 138.0 kJ/kg for R410A and R448A, respectively. A reverse trend was found for VCC with respective values of 4722 and 3775 kJ/m3 for R410A and R448A. Lower volume flow rates and smaller-sized compressors are expected for higher VCC refrigerants. The same trend was found for the compressor's specific work input and condenser's specific heat transfer with values of (51.14, 46.82, and 45.38 kJ/kg) and (190.3, 187.8, and 183.4 kJ/kg) for R410A, R407C, and R448A, respectively. For applications in HAT countries, larger condenser's specific heat transfer makes the refrigerant more applicable. Conversely, with respect to COP, refrigerant R134a with a value of 3.075 was the superior alternative followed by R448A and R407C with respective COPs of 3.042 and 3.011. Based on the overall assessment in terms of environmental obligation, COP, compressor input power, refrigerant flow rate required, and all the evaluations made in this research, refrigerant R448A was recommended as the most appropriate substitute to R22 which can effectively be used in residential air conditioners in a HAT country. [ABSTRACT FROM AUTHOR]

Efficient detection of refrigerant leakage is of utmost importance for industrial refrigeration systems due to its potential to cause substantial impacts on system performance and the environment. Existing research on fault detection and diagnosis in refrigeration systems primarily revolves around solutions based on experimental or laboratory data. However, in the industrial use case, achieving accurate and early detection poses significant challenges. This paper reports on the development of a novel refrigerant leak detection method for industrial vapor compression refrigeration systems. Our method leverages real-world data obtained from operational installations, enabling us to assess its reliability and applicability. The proposed data-driven approach involves predicting the fault-free liquid level in the installation receiver and comparing the actual and predicted levels. In this work, we place emphasis on features and model selection. Dedicated metrics combined with a model comparison method are proposed to evaluate and compare the performance of commonly used regression models with two sets of features to determine the most effective one. Furthermore, we provide insights into the results obtained from the deployment of the proposed method in real-world industrial installations. • Refrigerant leak is detected through the receiver liquid level in the installation. • A regression model can be used to predict the fault-free liquid level. • System performance indicators were proven to be effective in long-term predictions. • Extremely randomized forest emerged as the top performer. [ABSTRACT FROM AUTHOR]

In the medical field, refrigeration systems are used to store and transport vaccines, blood, and other medical supplies that require specific temperature ranges to remain effective. As technology continues to advance, the demand for more efficient and sustainable refrigeration systems is also increasing. The freezer compartment is typically designed to maintain a temperature of −18°C to −23°C for storing frozen items. Consequently, this work aims to develop a hybrid refrigeration system that combines a thermoelectric cooler system (TEC) and a vapor compression refrigeration cycle (VCC) system to achieve lower temperatures than conventional refrigerators. Also, the performance of the proposed hybrid refrigeration system is experimentally assessed with various operating conditions, including varying the voltage delivered to the system. The experimental results exhibited that the temperature inside the freezer room reached −33°C, while the cold side temperature is −47°C. Also, the maximum coefficient of performance of the VCC system, TEC, and hybrid system is 2.07, 1.06, and 0.37, respectively, at a DC voltage applied of 6 V. Moreover, the results revealed that the hybrid system combining a TEC and a VCC system can be a valuable technology for specific applications with low temperatures and limited capacity requirements. [ABSTRACT FROM AUTHOR]

Due to the impact of global warming and climate change, more and more people are starting to have a clearer understanding and vigilance about greenhouse gases. To prevent further deterioration of the global environment, this study examines the coefficients of performance of 21 currently available refrigerants with very low global-warming potential and zero ozone-depleting potential under evaporation temperatures of 10, −20, −40, and −60 °C and condensation temperatures of 30, 40, and 50 °C, respectively. It is found that the use of pure refrigerant in a two-stage refrigeration system to replace the single-stage refrigeration system, in addition to mixing it into an appropriate mixture, can effectively improve the performance coefficient of the refrigeration system. For single-stage vapor compression refrigeration systems, R1234ze(Z), R601, and R1233zd(E) have the best refrigeration performances among the environmentally friendly refrigerants studied, while R441A performs the worst for Teva = 10 °C and −20 °C. Moreover, RE170 has the highest COP of the refrigeration system for Teva = −40 °C and −60 °C. However, R1234yf performs worse in COP when the evaporation temperature is lower, and it ranks last for Teva = −60 °C. When a double-stage vapor compression refrigeration system is employed instead, the percentage increase in the COP of the system using R1234yf becomes the largest for Teva = −40 °C and −60 °C. However, the growth rate of R717 ranks last for Teva = −60 °C. For an R717/R1234yf mixture at an optimum mass fraction of 0.25, the COP of the refrigeration system can be increased up to 25.8% despite an increase of 15.2% in operating pressure compared to R1234yf. The discharge temperature may rise; however, there will be no overheating problem for the compressor. [ABSTRACT FROM AUTHOR]

Compared with the single-stage compression, the two-stage compression cycle shows high efficiency and application potential under both severe heating and refrigerating conditions. Therefore, to improve the performance of the two-stage vapor-compression cycle furtherly, this study introduces three ejector-assisted two-stage compression cycles (E1, E2, and E3), and a conventional two-stage vapor-compression cycles (C1) also selected as the comparison. The energetic and exergetic efficiency of the systems using various refrigerants (R152a, R1234yf, R32 and R290) is investigated and compared based on the validated theoretical model for both the severe refrigerating and heating application. The result shows that the ejector improves the system's performance significantly. Under the refrigerating mode, System E3 using R32 is recommended to be applied. Compared with Systems C1, E1, and E2, the maximum refrigerating coefficient of performance (COPR) of System E3 using R32 is improved by 16.1, 12.4, and 9.1%, respectively, with the evaporation temperature of −40 °C and condensation of 30 °C. Systems E2 and E1 using R152a are recommended under the heating mode. Compared with Systems C1 and E3, the heating coefficient of performance (COPH) of Systems E1 and E2 using R152 is improved by 3.0 and 4.5%, respectively, with the condensation temperature of 70 °C and evaporation temperature of −5 °C. The result provides a deep understanding of the potential advantages of the ejector-assisted two-stage compression cycle applied in the refrigerating and heating field. [ABSTRACT FROM AUTHOR]

Nowadays, refrigerated food storage and transport vehicles are very common. However, with regard to the engine of vehicles, a significant amount of heat is discharged into the environment in the form of exhaust gas and jacket water. If the cooling system is used to convert this waste heat into cooling capacity, the thermal efficiency of the engine will be improved to a certain extent. Therefore, this paper uses two waste heat recovery jet refrigeration systems to recover heat from the exhaust gas and jacket water of the refrigerated vehicle. One is a conventional jet refrigeration system that uses only engine exhaust as the heat source, and the other is a system that adds a preheater upstream of the generator based on the conventional system, using engine jacket water to preheat the working fluid. This paper presents the results of comparing the impact of R141b/R123, R141b/R245fa, R142b/R134a, and R142b/R152a working fluids on system performance, and considers the effects of operating temperature and secondary flow pressure drop in the ejector receiving chamber on the system performance. The research results indicate that of the four selected working fluids, the R141b/R245fa (0.4/0.6) blend has the best overall performance. After the addition of a preheater, the system using R142b/R134a (0.6/0.4) hybrid working fluid achieves the maximum cooling capacity of 16.0994 kW and the maximum thermal efficiency of 5.45%, and the exergy loss in the generator is 1 kW lower than without the preheater. [ABSTRACT FROM AUTHOR]

Thermal characteristics of combined compressor - ejector refrigeration/heat pump systems applied in heating, ventilation, air conditioning and refrigeration (HVAC&R) of buildings are investigated. An original model for estimation of the thermal characteristics of the combined cycles is developed, to determine the influence of the evaporation, interstage, condensation, and generating temperature conditions on mechanical and thermal COP of the combined system, and to optimize the thermal parameters of the cycle. Results are presented for different temperature conditions, with R134a as a suitable refrigerant. A comparison between the thermal characteristics of the simple mechanical vapor compression cycle, the simple ejector thermocompression cycle, and the combined compressor - ejector refrigeration/heat pump cycle is given. The benefits of implementation of combined compressor - ejector refrigeration/heat pump cycles in HVAC&R systems are discussed. The temperature lift or temperature difference between condensing temperature and interstage temperature significantly influences the thermal (ejector) COP. If temperature lift is between 10 K and 20 K, high values of thermal COP can be achieved (0.5-1.0, for generating temperature equal to 80 °C; 1.0-1.8, for generating temperature equal to 120 °C). If temperature lift is between 30 K and 40 K, very low values of COPth can be obtained (0.05-0.3). High values of mechanical COP can be achieved (24.8-6.9), for compressor stage temperature lift 10-30 K. [ABSTRACT FROM AUTHOR]

• A novel R744 multi-temperature unit for last mile delivery is presented. • MT and LT ejectors are specifically designed for this application. • LT ejector allows using a single stage compressor at high ambient temperature. • Ejector cycle leads to significant increase of system efficiency. • Back-pressure cycle substantially increases flexibility in cooling power range. A novel R744 vapor-compression refrigeration system has been developed to meet the cooling needs of a medium-size refrigerated truck at two temperature levels: 4-5 kW for medium-temperature (MT) refrigeration at 0°C and 1-2 kW for low-temperature (LT) refrigeration at -20°C. This system is designed for transporting chilled and frozen goods efficiently during last-mile deliveries in urban areas. The key innovation of this system lies in its single compression stage with two different evaporation levels. Firstly, the unit incorporates an MT ejector to enhance energy efficiency by reducing the compressor pressure ratio. Furthermore, an LT ejector is employed to allow providing LT cooling with a single-stage compressor by pre-compressing vapor before it enters the compressor, avoiding excessive compression ratios. This extends the LT operational range with a single stage of compression from 34°C to 40°C ambient temperature. When the ambient temperature is not sufficient to sustain the ejector cycle, the system can switch to a back-pressure cycle. A numerical model of this refrigeration system has been developed to evaluate its steady-state and dynamic performance in both back-pressure and ejector configurations. For a specific cooling effect production (3.8 kW in MT, 1.1 kW in LT operation), the ejector cycle increases the COP by 25.8% for MT and 42.0% for LT operation compared to the back-pressure cycle. However, the back-pressure cycle offers greater flexibility in cooling power production, ranging from -32.8% to +8.2% for MT and -8.9% to +82.5% for LT, making it useful for pulldown and part-load operations. [ABSTRACT FROM AUTHOR]

As the requirement for Li-ion battery thermal management system (TMS) in electric vehicles (EVs) rises, an integrated direct cooling thermal management system with high compactness and energy efficiency has been developed. The integrated system is based on a vapor-compression refrigeration cycle, forming a dual-evaporator system, and adopts a direct cooling scheme on the battery side, which brings high coupling effects. A novel decoupling control strategy was proposed and a weight-based fuzzy logic control algorithm was applied to implement the strategy, achieving effective temperature control and reasonable refrigerant distribution between the battery side and cabin side. Experiments conducted under various scenarios demonstrated that the average temperature of both the battery pack and cabin could be stably controlled around different target values. Maximum fluctuations were effectively limited to less than 0.7 °C in different scenarios. The implementation of this decoupling control strategy has opened up new possibilities for the application of direct cooling TMS in multi-target systems. [ABSTRACT FROM AUTHOR]

Air conditioning plays a vital role in modern life, but its high energy consumption, particularly in vapor compression cycles, is a major concern. This study explores absorption cycles as an alternative, where the compressor is replaced with components powered by heat instead of electricity, potentially leading to reduce energy consuming. The study has three main approaches: theoretical analysis, experimental and validation. The theoretical analysis uses Engineering Equation Solver (EES) to model the system's performance, focusing on Coefficient of Performance (COP) and cooling capacity, for two working pairs NH3-H2O and LiBr-H2O. The experimental setup was designed to validate the theoretical model. The results from the theoretical analysis show good agreement with a maximum deviation of around 0.6%. Furthermore, the analysis indicates that the LiBr-H2O pair has better COP and cooling capacity than NH3-H2O by approximately 33%. This suggests that LiBr-H2O absorption cycles have the potential to be a more efficient and sustainable alternative for air conditioning systems. [ABSTRACT FROM AUTHOR]