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The study and development of miniature refrigeration and climate conditioning systems based on vapor compression for small-scale applications have received wide interest in recent years due to their advantages compared with other available technologies, both active and passive. This paper identifies different applications and areas of opportunity, including electronic components and personal cooling, where small-scale vapor compression refrigeration systems are anticipated to play a key role in technological development. This paper presents the current state of the art, including applications, component designs, operating conditions, experiments, published results, etc. to describe the current status of small-scale vapor compression refrigeration and illustrate a perspective for the future of this technology. [ABSTRACT FROM AUTHOR]

In this study, an experimental study was carried out on a heat pipe, whose evaporator is located between the compressor outlet and the condenser inlet of an industrial cooler on a vapor compression cycle (VCC). It absorbs heat from the new generation refrigerant fluid of 515B and transfers it to the outdoor air. The heat pipe is a looped thermosiphon-type heat pipe. R134a refrigerant is used as a working fluid in the heat pipe. By changing the condenser air inlet temperatures, the contribution of the heat pipe to the cooling cycle has been determined experimentally. While the evaporation pressure of the refrigeration cycle with the heat pipe remains approximately constant, the condensation pressure decreases, and the sub-cool temperature increases. For condenser air inlet temperatures of 30, 40, and 50°C, the COP of the cooler with heat pipe increases by 1.8%, 2.6%, and 2.76%, respectively. As the air temperature at the condenser inlet increases, the ratio of heat pipe power to the cooling capacity of the cycle also increases. In addition, the compressor outlet temperature is reduced by 1.5%–2.8% using of the heat pipe. [ABSTRACT FROM AUTHOR]

Seawater desalination stands as an increasingly indispensable solution to address global water scarcity issues. This study conducts a thorough exergoenvironmental analysis of a multi-effect distillation with thermal vapor compression (MED-TVC) system, a highly promising desalination technology. The MED-TVC system presents an energy-efficient approach to desalination by harnessing waste heat sources and incorporating thermal vapor compression. The primary objective of this research is to assess the system's thermodynamic efficiency and environmental impact, considering both energy and exergy aspects. The investigation delves into the intricacies of energy and exergy losses within the MED-TVC process, providing a holistic understanding of its performance. By scrutinizing the distribution and sources of exergy destruction, the study identifies specific areas for enhancement in the system's design and operation, thereby elevating its overall sustainability. Moreover, the exergoenvironmental analysis quantifies the environmental impact, offering vital insights into the sustainability of seawater desalination technologies. The results underscore the significance of every component in the MED-TVC system for its exergoenvironmental performance. Notably, the thermal vapor compressor emerges as pivotal due to its direct impact on energy efficiency, exergy losses, and the environmental footprint of the process. Consequently, optimizing this particular component becomes imperative for achieving a more sustainable and efficient desalination system. [ABSTRACT FROM AUTHOR]

In this study, a vapor compression refrigeration cycle integrated with a phase change material (PCM) storage tank has been dynamically simulated over a 24-h period. The primary objective of this system is to reduce electric energy consumption during on-peak hours (12:00–19:00) and shift it to off-peak hours (1:00–10:00). During off-peak hours, the vapor compression refrigeration system stores cooling energy in the PCM storage tank. The stored cooling energy is then reused during on-peak hours to pre-cool the condenser inlet refrigerant, enhancing the cooling system's performance and reducing electric consumption during on-peak hours. Oleic acid, eutectic mixtures of 45 % capric acid and 55 % lauric acid by weight (CL), a commercial blend of salt hydrate and paraffin wax (SP224A), and CaCl2.6H2O have been selected as the PCM mediums. The effects of weather conditions and PCM storage tank parameters on the system's performance have been investigated. The results indicate that SP224A performs the best in most weather conditions. The maximum electric peak load shaving occurred under Ramsar city weather conditions, achieving 98.85 %. Additionally, the compressor's electric energy consumption is reduced by about 23.38 %. Moreover, increasing the length of PCM storage pipes leads to a reduction in compressor energy consumption during on-peak hours, as well as electric peak load shaving, with an improvement of up to 156 %.

The air conditioning and refrigeration applications use a significant portion of the electrical energy. This research analyses a performance of refrigeration system, which comprises on different configurations of solar based organic Rankine cycle (ORC) and vapor compression refrigeration (VCR) cycles requiring low evaporation temperatures. In this research, the dry natural hydrocarbons such as n-Decane, n-Dodecane and Toluene have been chosen to serve as the working fluids in ORC. Whereas in VCR cycle natural hydrocarbons such as Ethane, Propane, isobutane, isopentane and isohexane have been used because traditional working fluids have a negative environmental impact due to high values of ozone depletion and global warming potential. The simulated results showed that the facility can be operated efficiently with the use solar thermal energy resources within the temperature range 90 to 315ºC and decreasing the need for conventional fossil fuel resources. It was also revealed that the highest efficiency was achieved by n-Dodecane in regenerative ORC, which is 35.34 % at the evaporation temperature of 315ºC and the highest overall coefficient of performance (COPoverall) in regenerative ORCCRS facility was achieved by n-Dodecane in ORC and isopentane in refrigeration cycle which is 1.017 while in case of Simple ORC–VCR facility the highest COPoverall was achieved by Toluene in ORC and isopentane in refrigeration cycle, which is 0.7174 at the evaporation temperature 315ºC.

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.

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.

Separate sensible and latent cooling (SSLC) is a promising technology for enhancing the energy efficiency of space cooling systems. In this paper, we propose an SSLC configuration consisting of an indirect evaporative cooling (IEC) device and vapor compression cycle (VCC) for handling space sensible load, and a desiccant wheel for handling space latent load. The performance of the proposed configuration is investigated using physics-based or empirical models for each component. A year-round simulation study of the proposed SSLC system is performed for 12 different cities with diverse climatic conditions. This study considers electrical, thermal, or solar energy for desiccant wheel regeneration. Parameters governing the system performance such as the air flowrate ratio in the IEC and the DW, DW regeneration air temperature, and supply temperature are studied. The proposed SSLC configuration is superior to the conventional system in all cities. The enhancement of seasonal coefficient of performance (sCOP) ranges between 50 and 261 %, 67 and 387 %, and 60 and 2072 % with yearly electrical energy savings of 33 and 72 %, 40 and 79 %, and 38 and 95 % for electrical, thermal, and solar energy for regeneration of DW, respectively. [ABSTRACT FROM AUTHOR]

The search for environmentally friendly refrigerants for vapor compression systems has been a significant focus recently due to environmental concerns such as ozone depletion and global warming. In this study, the potential of R1224yd as an alternative refrigerant is investigated. A thermodynamic analysis of a 4-kW air conditioning system is conducted to assess the performance of R1224yd. The system is analyzed from a thermodynamic perspective, and key performance indicators such as the Coefficient of Performance and exergy efficiency. The results are then compared to R245fa and R123. Furthermore, a parametric study is performed to examine the impact of key parameters, such as evaporating and condensing temperatures, on the system's performance. This analysis provides insights into the sensitivity of the system's performance to variations in these parameters. The results indicate that R1224yd is a promising candidate as an environmentally friendly alternative refrigerant compared to R123 and R245fa. Because R1224yd has the lowest environmental impact. It has about 700 kg CO2 indirect emission, but about zero kgCO2 for direct emission. While, based on the thermodynamic results, R1224yd offers better performance compared to R245fa which has 1-3% higher in performance value and exergy efficiency, and has comparable performance to R123. This suggests that R1224yd can be a viable option for the systems, providing improved energy efficiency and lower environmental impact. [ABSTRACT FROM AUTHOR]

Refrigeration system is essential in ensuring the comfort of people, preserving food for extended periods, and supporting the functionality of technological devices. However, refrigeration system accounts for approximately 17% of global electricity consumption due to the substantial energy requirement of compression work. This high consumption rate shows the need to reduce operational and maintenance costs by monitoring the efficiency of refrigeration system using Coefficient of Performance (COP). Currently, there are two methods of monitoring COP, namely substituting actual values into theoretical formulas, and developing artificial intelligence model for COP values. Therefore, this study aimed to develop COP prediction model using Artificial Neural Network (ANN) at a room set point temperature of -25°C. The results showed that through the analysis of ANN parameters, prediction model was successfully developed with an RMSE of 0.0621, an R² value of 0.8162, and a training speed of 27.3 seconds. The developed prediction model had a CvRMSE value of 3.41 and an MBe of 0.14 which falls within the acceptable values. The prediction model was able to predict COP values of other CDUs, with the same specification, for set point temperature of -21°C. This study showed a promising strategy for monitoring COP of an on-site vapor compression refrigeration system using a data-driven method. [ABSTRACT FROM AUTHOR]

Energy and exergy performance of simple vapor compression refrigeration unit is investigated experimentally with and without coupling heat exchanger of phase change material before the condenser. The hot outside air is cooled before entering the condenser throughout the day by flowing over the cooled phase change material structure that previously solidified during nighttime. Phase change material SP24 is employed because its melting/freezing range is suitable for most selected countries' climates. An experimental set‐up of an air‐phase change material heat exchanger coupled with the unit is constructed to examine its performance, including pressure–enthalpy curve, coefficient of performance, exergy performance, and power consumption including inflow air temperatures and flow rates impacts. Results affirm that the coefficient of performance, cooling capacity, power usage, and exergy destruction are improved by using phase change material. Compared to the unmodified unit, the maximum percentage of saved power and exergy destruction enhancement for the modified refrigeration unit with phase change material is about 8.8% and 10%, respectively. The maximum coefficient of performance and exergy efficiency rise is about 15.1% and 14.2%, respectively. Increasing the temperature differential across the phase change material heat exchanger, either by increasing inlet temperature or decreasing airflow, enhances the refrigeration unit power saving. [ABSTRACT FROM AUTHOR]

In a vapor compression refrigeration system, the oil enhances the efficiency of the compressor but impairs the performance of the heat exchanger. This paper focuses on the experimental study of the influence of oil quantity on the operational stability of CO 2 air conditioning system. The operational stability of the system under different oil charge quantity and operating conditions is studied. The experimental results indicate that when the oil circulation rate increases to a certain value, the adjustment of electronic expansion valve (EXV) opening or the compressor speed will cause system fluctuation and the outlet of evaporator gets close to no superheat. The critical oil circulation rate of the experimental system is about 9.2 %. The analysis of the fluctuation shows that it becomes more severe with the increasing of the refrigerant mass flow rate. When the mass flow rate increases from 210 kg∙ h −1 to 250 kg∙ h −1 at 7000 r min−1 of compressor speed, the fluctuation frequency increases from 0.072 Hz to 0.095 Hz. The occurrence of unstable phenomena has remarkable impact on system performance, the maximum difference of this system in instantaneous cooling capacity and COP during the fluctuation period is respectively 0.5 kW and 0.13. [ABSTRACT FROM AUTHOR]

In the modern world, the vapor compression refrigeration (VCR) system is essential in various global applications, including climate control, refrigeration, and food preservation, contributing significantly to energy consumption. The significant energy demands associated with these applications highlight the urgency for sustainable and energy-efficient alternatives that can help diminish our dependence on electrical power. To reduce energy consumption and enhance energy efficiency, a dedicated mechanical subcooled (DMS) system can be integrated with a vapor compression system (VCR) system. This study aims to evaluate and optimize the dedicated mechanical subcooled-vapor compressor refrigeration system (DMS-VCR) system using refrigerant R134a for a 100 kW commercial chiller used for water cooling application. The primary objective is to assess the system from multiple angles which include energy, exergy, environmental, economic analysis (4E's) and optimizing it to enhance its overall effectiveness to reduce the system's annual cost. It is thermo-economically optimized, allowing for independent optimization of the evaporator, condenser-1, condenser-2, and sub-cooler components. The proposed system reduces electrical energy consumption by 17.24% and CO2 emissions by 12.4%. The DMS-VCR system outperforms the standalone VCR system. The DMS-VCR system's annual operating costs are 6.71% lower than an equivalent VCR system, and optimization further reduces costs by 1.88% (case-I: irate = 10%, Ny = 5 years, and toper = 4000 h) and 16.36% (case-II: irate = 2%, Ny = 10 years, and toper = 5000 h).The study underscores the importance of subcooling within the DMS-VCR system, highlighting its desirability as it varies with the recovery factor and annual operation period. As a result of the DMS-VCR system's better efficiency, design engineers are likely to find it more attractive. [ABSTRACT FROM AUTHOR]

This study proposes a simulation technique for investigating a battery thermal management system based on direct refrigerant cooling (BTMS-DRC). The main focus is to investigate the temperature uniformity and working temperature of the module housing. The simulation technique employs a finite element method for a combined conduction–convection heat transfer to predict the module housing temperature. The refrigerant side is based on two-phase flow evaporation, which is represented by the convection heat transfer under a certain refrigerant saturation temperature. The real BTMS-DRC, which is based on the dual-evaporator vapor compression refrigeration system, is constructed for experimentation with the test bench. The simulated result is validated with the experimental results to ensure correction of the modelling. Error rates of approximately 2.9–7.2% are noted throughout the specified working conditions. The BTMS can produce temperatures of less than 35 °C under conditions where 80–320 W heat is generated. The difference in the temperature of the module is around 1.7–4.2 °C. This study also investigates the impact of heat generation, the convection heat transfer coefficient (href), the refrigerant saturation temperature, and thermal conductivity on the module's temperature. The thermal conductivity ranges from 25 to 430 W/m·K, while the href ranges from 80 to 400 W/m2·K. [ABSTRACT FROM AUTHOR]

This study analyses the performance of an integrated transcritical CO2 (R-744) refrigeration system operating in winter conditions within a supermarket in Trento, north Italy. This system fulfils multiple functions, providing the heating (for domestic hot water and space heating), cooling, and freezing capabilities for the supermarket. Energy analysis reveals that the average value of the total coefficient of performance, total COP, over the entire study period is calculated at 2.47. Notably, the medium-temperature (MT) compressor rack exhibits the highest power consumption, especially in sub −5 °C conditions. The auxiliary (AUX) compressor rack and the gas cooler (GC) fan contribute significantly to the electrical power usage. The air conditioning (AC) heating load is consistently high, averaging 41.6 kW, while the domestic hot water (DHW) heating load remains stable at approximately 5 kW. The refrigeration demands include an average MT cooling load of 25.86 kW and a low-temperature (LT) freezing load of 10–15 kW, with an average of 13.76 kW. The current study also delves into exergy analysis, disclosing an overall system exergy efficiency of 22.4%. The AUX compressor rack is identified as the primary exergy destructor, followed by the GC, AC coils, MT compressor rack, and the ejector. The LT compressor rack has the highest exergy efficiency, followed by the MT and LT expansion valves. [ABSTRACT FROM AUTHOR]

This study compares the performance of dedicated mechanical subcooled vapor compression refrigeration (DMS-VCR) system and actual vapor compression refrigeration (VCR) system of same capacity (100 kW), and evaluates them on the basis of energy, exergy, and coefficient of structural bond (CSB) configuration. Results indicate that DMS-VCR system outperforms VCR system at constant condenser temperature (Tcond = 40° C) with varying evaporator temperatures (Tevap = 0 °C, 5 °C and 10 °C).The most significant results occurs at 0 °C, resulting in a coefficient of performance (COP) 4.60 % higher than actual VCR system's COP and exergetic efficiency 4.38 % higher than actual VCR system's exergetic efficiency, making it a more favourable choice for water chilling applications. Additionally, the study investigates the potential of the CSB method in improving system efficiency by reducing irreversibility rate in a specific component. It finds that improving the efficiency of a component can significantly decrease the total irreversibility rate of the system. The CSB value of condenser-1 and evaporator are observerd to be highest (i.e. 1.96 and 2.27) and hence the performance of DMS-VCR system can be greatly improved by changing the efficiency parameter of evaporator and condenser-1 of the DMS-VCR system. [ABSTRACT FROM AUTHOR]

R134a, which is used as a working fluid in Vapor Compression Refrigeration Systems (VCRS), is one of the refrigerants that is planned to be discontinued the usage due to the global warming. For this reason, researchers have tended to developing alternatives to R134a. In this context, in this study, the usage of R134a and its alternatives R1234yf, R450A, R513A, and R515B refrigerants were theoretically examined with the help of a theoretical model developed in the Engineering Equation Solver (EES) program using experimental data in terms of first and second laws of thermodynamics in a mechanical vapor compression refrigeration system. Analyses were performed for constant cooling capacity at various evaporation and condensation temperatures. In this study, the effects of the refrigerant type on the compressor power, heat rejection rate from the condenser, Coefficient of Performance (COP), second law efficiency, and mass flow rate of the refrigerant were determined. In addition, the results obtained under the same conditions for R134a and its alternatives were compared. As a result, compressor power increased by 5.62% for R1234yf, 2.35% for R450A, 3.41% for R513A, and 2.88% for R515B compared to R134a. Thus, it was observed that COP decreased by 5.32% for R1234yf, 2.30% for R450A, 3.30% for R513A, and 2.80% for R515B compared to R134a. Similarly, it was observed that the second law efficiency decreased by 5.32% in case of the usage of R1234yf, 2.30% in case of the usage of R450A, 3.29% in case of the usage of R513A, and 2.80% in case of the usage of R515B compared to R134a. Hence, it has been determined that the closest refrigerant to R134a in terms of the COP and the second law efficiency is R450A. [ABSTRACT FROM AUTHOR]

Nowadays, thermal comfort is becoming a major problem for people due to increasing global warming and climatic changes, but it can be resolved by the concept of Heating, Ventilation, and Air Conditioning (HVAC) systems. The purpose of HVAC is to provide occupants with a comfort zone so that they can feel comfortable according to their thermal comfort. The core objective of this study is to design and propose an HVAC system as per actual design conditions for the University Auditorium located in Karachi, Pakistan. A direct Expansion (DX - Type) system is installed in the Auditorium that has exceeded the lifespan of twenty years, refrigerant R-22 which is currently being used has been obsolete due to its high GWP (Global Warming Potential) and ODP (Ozone Depletion Potential) values which are 1810 and 0.05 respectively. To achieve the objective of this study, two approaches are employed. Cooling Load Temperature Difference (CLTD) method & Hourly Analysis Program (HAP) software. The cooling load calculated from the CLTD method is 202 kW equivalent to 57.5 Ton of Refrigeration (TR). On the other side, the cooling load calculated from HAP software is 192.8 kW equivalent to 55 TR. By considering the calculated cooling load for the University Auditorium, two different HVAC systems are proposed, based on Water cooled and Air-cooled Vapor Compression Cycle. After this study, engineers will be able to design an HVAC system for any facility as per design conditions. Also, they can propose different cost-effective and energy-efficient HVAC systems for that particular space. [ABSTRACT FROM AUTHOR]

This study presents a thermodynamic analysis of a solar-driven vapor compression refrigeration (VCR) system designed for use in the region of Ghardaïa (Southern Algeria) which is located in a desert with a semi-arid climate where the demand for cooling is high, and the solar radiation is abundant. Two working fluids are tested and compared, the HFC high GWP going to phased out, R134a and the low GWP, HFO refrigerant recently introduced R1234ze. The performance of the solar VCR system was evaluated using a numerical model developed in MATLAB software, based on thermodynamic properties of R1234ze and R134a refrigerants. The results showed that coefficient of performance (COP) and thermodynamic efficiency of the solar VCR system increased with decreasing ambient temperature due to the increase in the compressor power consumption. The COP during the 21st day of July month is obtained in the range of 4.37-5.77 for R1234ze refrigerant which are close and more than 90% of the maximum COP value, while it is in the range of 2.56-3.17 for R134a fluid. The lowest COP values are found around noon hours during 12:00 AM and 15:00 PM. In addition, the greatest amount of the PV power production for R134a and R1234ze refrigerants occurs in the middle of the day (12:00 PM) as 2.8 and 1.6 kWh, respectively. [ABSTRACT FROM AUTHOR]

A major portion of the worldwide emissions arise from mobile air-conditioning systems with hydrofluorocarbon refrigerant as working substance and which is one of major cause for the greenhouse effect. R134a refrigerant having GWP of 1400 has been extensively used in car air conditioning. To reduce greenhouse gas emissions, the current R134a refrigerant must be phase out as per Kigali Amendment. The present study deals with cooling load calculation of car model by heat balance method as per ASHRAE standard using local climate condition. Further, thermodynamic analysis of R1234yf as an alternate refrigerant to R134a has been carried out for automobile air conditioning system. The required properties of refrigerants are extracted from Engineering Equation Software. The thermodynamic analysis is carried out to study the effect of operating parameters viz. condensing temperature, evaporating temperature, degree of superheating and degree of subcooling on COP, EDR, exergy efficiency and entropy generation. The previous literature reports mainly focus on separate study of either cooling load calculation or energy analysis or exergy analysis of R1234yf and R134a for automobile air conditioning system, while this paper presents the comprehensive study of new low GWP R1234yf as an alternate refrigerant to R134a in automobile air conditioning system with cooling load calculation including the concept of energy, entropy and exergy analysis. The percentage difference in COP between R134a and R1234yf system varies from 2.44 % to 4.78 % while percentage difference in EDR varies from 6.79 % to 2.87 % when evaporating temperature varied from -10 °C to 10 °C. With 12 °C of superheating at compressor inlet, the COP of R134a is 3.9 whereas COP of R1234yf is 3.75, which makes 3.85 % lower than that of R134a. The R1234yf has 4.78 % lower value of exergy efficiency as compared to that of R134a at evaporating temperature of -10 °C and it is found that maximum exergy destruction takes place in compressor. [ABSTRACT FROM AUTHOR]

Self-optimizing efficiency of vapor compression cycles (VCCs) involves assigning multiple decision variables simultaneously in order to minimize power consumption while maintaining safe operating conditions. Due to the modeling complexity associated with cycle dynamics (and other smart building energy systems), online self-optimization requires algorithms that can safely and efficiently explore the search space in a derivative-free and model-agnostic manner. This makes Bayesian optimization (BO) a strong candidate for self-optimization. Unfortunately, classical BO algorithms ignore the relationship between consecutive optimizer candidates, resulting in jumps in the search space that can lead to fail-safe mechanisms being triggered, or undesired transient dynamics that violate operational constraints. To this end, we propose safe local search region (LSR)-BO, a global optimization methodology that builds on the BO framework while enforcing two types of safety constraints including black-box constraints on the output and LSR constraints on the input. We provide theoretical guarantees that under standard assumptions on the performance and constraint functions, LSR-BO guarantees constraints will be satisfied at all iterations with high probability. Furthermore, in the presence of only input LSR constraints, we show the method will converge to the true (unknown) globally optimal solution. We demonstrate the potential of our proposed LSR-BO method on a high-fidelity simulation model of a commercial vapor compression system with both LSR constraints on expansion valve positions and fan speeds, in addition to other safety constraints on discharge and evaporator temperatures. [ABSTRACT FROM AUTHOR]

The most common refrigeration system is the vapor compression refrigeration (VCR) system for a household refrigerator. The challenges for researchers are to minimize the power consumption of the compressor to improve the performance of the refrigeration system. This study aimed to assess and compare the energy and exergy analysis of VCR systems using multi-walled carbon nanotubes (MWCNT) and graphene nanosheets (GN) based hybrid nano-lubricants. The mass concentrations of each nanoparticle 0.3 g/L, 0.5 g/L, 0.7 g/L, and 0.9 g/L are mixed with 250 ml of polyolester oil (POE) separately and charged with 200 g of R134a refrigerant. Furthermore, the MWCNT and GN nanoparticles are mixed in a 50:50 proportion to prepare the same concentration of hybrid nanoparticles. The properties of refrigerants are obtained with the help of REFPROP 9.1 software. The pull-down time, compressor power, pressure ratio, exergy loss, relative irreversibility (RI), and second law efficiency (SLE) are variables that have been examined. The mass concentration of 0.7 g/L of hybrid nano-lubricants (GN-MWCNT /POE) is found to be optimal. It is noted that the pull-down time, power consumption, and pressure ratio of the refrigerator are lowered by 9.01%, 16.09%, and 5.68% respectively when compared to the pure refrigerant, whereas the actual COP and SLE improved by 11.29% and 8.22% at 0.7 g/L hybrid nano-lubricants. In addition, exergy loss and relative irreversibility are decreased for hybrid nano-lubricants. [ABSTRACT FROM AUTHOR]

CO2 has been widely used as a working fluid in power generation and refrigeration systems and multistage compression is one important process in these systems. To save energy consumption, the compression should be conducted at optimum interstage pressure. In this work, a model to find the optimum interstage pressure for two-stage CO2 compression is studied. Use of cubic equations of state in the model is investigated and compared its result with the result from using a multiparameter equation of state, called SW equation of state. The compression in a subcritical region and from a subcritical to a supercritical region are investigated. The results of this study show that the cubic equations of state, except van der Waals equation of state, can generally predict the CO2 density and thermal expansivity with satisfied accuracy. The optimum interstage pressures obtained from the model using Redlich-Kwong, Peng-Robinson, and Redlich-Kwong-Soave equations of state are close to that using SW equation of state. The average absolute percentage difference (AAPD) from the comparison showed that these three cubic equations of state have AAPD less than 0.6% and 0.9% for the subcritical and transcritical compressions, respectively. The result of the study also shows that when the optimum interstage pressure is higher than the critical pressure, the optimum interstage pressure slightly increases with increasing the outlet pressure of the second-stage compressor. [ABSTRACT FROM AUTHOR]

The rising global temperatures, attributed to the high global warming potential (GWP) of conventional refrigerants, necessitate the adoption of low-GWP alternatives in HVAC systems. However, these low-GWP refrigerants often exhibit high toxicity and flammability, limiting their usage. To address these challenges, compact heat exchangers incorporating blended refrigerants have been introduced to enhance HVAC system performance. Researchers have also made significant strides in improving HVAC system efficiency by introducing the concept of suspending nanolubricants and nanorefrigerants within the system. This review paper seeks to comprehensively assess the potential of alternative refrigerants containing suspended nanoparticles, commonly referred to as nanorefrigerants. The paper reviews various mechanisms and potential combinations of different nanorefrigerants employed to enhance refrigeration system effectiveness and efficiency. A detailed examination of key heat transfer parameters and the performance predictions of low-GWP refrigerants, including those from the hydrofluoroolefin (HFO) and hydrocarbon (HC) classes, is conducted through energy and exergy analyses. Commercial refrigerants like R-134a, R-290, R-600, R-600a, R-123, R-125, R-22, R-141b, R-152, R-11, R-113, R-404a, R-407c, R-502, R-600a, R-507a, R-1234yf, R-1234ze, 1336mzz(Z), and R-410a are evaluated in conjunction with suspended nanoparticles, considering their specific properties. The findings indicate that the utilization of nanorefrigerants leads to notable improvements in overall system performance, characterized by reduced compressor workloads and increased heat transfer rates. Consequently, the integration of blended nanoparticles into refrigerants holds significant promise for advancing the HVAC field. [ABSTRACT FROM AUTHOR]

The present study introduces a novel cascade ejector intercooler refrigeration cycle (CEIRC) and a novel cascade ejector booster refrigeration cycle (CEBRC), which are designed to improve ultralow temperature (ULT) refrigeration system performance based on various refrigerants in terms of energy, exergy, and environment. Through the analysis conducted with eco‐friendly refrigerants for CEIRC, the refrigerant pair exhibits the highest performance that is found to consist of RE170 for high‐temperature cycles and R170 for low‐temperature cycles. These refrigerants have very low global warming potential and are eco‐friendly. The coefficient of performance (COP) reveals improvements of 3.20–9.51%, 10.55–19.12%, and 31.96–65.97% over the CEBRC, cascade ejector refrigeration cycle (CERC), and cascade vapor compression refrigeration cycle (CVCRC), respectively, resulting in corresponding exergy efficiency improvements of 3.18–9.49%, 10.48–19.12%, and 31.87–65.98%. The total compressor power and exergy destruction are also compared, indicating that the CEIRC exhibits the best performance among the four. CEIRC achieves a COP increase of 11.6% compared with the cascade refrigeration cycle, which is considered the cycle with the highest performance operating at ultralow temperatures in the literature, which is CERC. The kg CO2 effect of the CEIRC is 11.35% lower than that of the CERC. [ABSTRACT FROM AUTHOR]

In this survey, the integration of a vapor compression cycle with a phase change material (PCM) storage tank has been evaluated experimentally during the hottest days of five cities with different weather conditions: Tehran, Ramsar Hamedan, Bushehr, and Ahvaz. The temperature conditions for outdoor (condenser, compressor, etc.) and indoor (evaporator) air conditioning units are provided with the help of two separated test chambers and a controller system. The desired system has been examined based on two scenarios. In each scenario, the system is assessed for the conventional air conditioning (AC) system (with no PCM involved) and the AC plus PCM unit. Based on scenario 1 operating strategy, the results indicate that adding the PCM tank decreases the total daily COP compared to the conventional AC unit, which varies from 32.07% for Bushehr city to 17.23% for Tehran city. Whereas the AC plus PCM system’s performance enhances during on-peak hours compared to the conventional AC system, which varies from 65.99% for Hamedan city to 12.84% for Bushehr city. Based on scenario 2 operating strategy, adding the PCM storage tank to the conventional AC unit increases total electric energy consumption over 24 h, which varies from 29.35% for Bushehr city to 5.49% for Tehran city. While it leads to shaving the electric peak load from 45.11% to 67.02% in which the highest peak load shaving belongs to Tehran and the least is related to Bushehr city.

A computationally efficient but accurate dynamic modeling approach for vapor compression systems is important for many applications. Nonlinear model order reduction techniques which generate reduced order models based on high fidelity vapor compression cycle (VCC) models are attractive for the purposes. In this paper, a number of technical challenges of applying model order reduction methods to VCCs are described and corresponding solution approaches are presented. It starts with a reformulation of a standard finite volume heat exchanger model for matching the baseline model reduction structure. Reduced order models for evaporator and condenser are constructed from numerical snapshots of the high fidelity models using Proper Orthogonal Decomposition (POD). Methodologies for system stability and numerical efficiency of POD reduced order models are described. The reduced order heat exchanger models are then coupled with quasi-static models of other components to form a reduced order cycle model. Transient simulations were conducted over a wide range of operating conditions and results were compared with the full order model as well as measurements. The validation results indicate that the reduced order model can execute much faster than a high-fidelity finite volume model with negligible prediction errors.

This paper presents the thermodynamic analysis, performance assessment and working fluid selection for a novel integrated vapor compression cycle and the organic Rankine cycle system, which recovers ultra-low-temperature waste heat (50 °C) rejected by the condenser of a vapor compression cycle (VCC). The study is conducted on a vapor compression system of a 35 kW cooling capacity, followed by the component sizing of the organic Rankine cycle (ORC) based on the available waste heat in the condenser of the refrigeration system. The effect of the operational parameters of the vapor compression cycle on the overall system performance are investigated. The system performance of the integrated system is estimated in terms of coefficient of performance, cycle thermal efficiency and exergy efficiency. The novel integrated systems has been analyzed thermodynamically for 36 pairs of pure refrigerants. Results show that the working fluid pair R600a/R141b with combined coefficient of performance (3.54), ORC thermal efficiency (3.05 %), electricity saving ratio (13.34 %) and total exergy destruction (6.94 kW) is the most suitable VCC/ORC working fluid pair in full condensing method. R407c-R141b is found to be the best working fluid pair in desuperheating method for the same integrated system. The performance analysis for full condensation and desuperheating methods are also investigated. The results indicate a 12.5 % improvement in the coefficient of performance of the integrated system using the full condensation method and a 2.5 % improvement using the desuperheating method compared to the standalone air conditioning system. Additionally, the sensitivity analysis results show that there exists optimum operating condition that maximize the system performance of the integrated system.

The increasing heating demand calls for a correspondingly augmented heating capacity of the primary heating network. However, due to the restriction of existing pipes, the heating capacity can be finitely increased. Therefore, based on the organic Rankine cycle (ORC) and vapor compression cycle (VCC), a novel thermal station is proposed to realize self-augmented heating capacity. Based on laws of thermodynamics, the mathematical model is constructed, and the dynamic performances of power generation and self-augmented heating capacity are analyzed. Results show that the supply water temperature of the primary heating network greatly influences the power generation performance. The self-sufficient electricity can achieve approximately 2000 h, accounting for 61.70% of the heating period. Additionally, the proposed thermal station can flexibly reduce the return water temperature of the primary heating network to 20 °C, thereby achieving self-augmented heating capacity. The self-augmented heating capacity rate can reach 53.56%. Therefore, the proposed thermal station demonstrates excellent self-augmented heating capacity, which provides a new path for satisfying the ever-increasing heating demand.

The current study aims to design a new parabolic trough collector (PTC) operated polygeneration system to produce freshwater, hydrogen, cooling, and electricity in a residential society. Dowtherm A (a heat transfer fluid) is used to transfer the heat from PTC to the Organic Rankine Cycle, which is used to produce electrical power. The produced electrical power is utilized in three different ways, namely, to run the home appliances, to produce hydrogen (via water electrolysis), and to produce cooling (through a vapor compression cycle). The cooling produced by the vapor compression system is utilized to preserve the food, milk, and to operate the freezing desalination process. Effects of several factors, such as direct normal irradiance, evaporator temperature, and seawater inlet temperature, have been analyzed on the overall system behavior. Thermodynamic study results show that for a PTC area of 2000 m2, an electrical output obtained is 72 kW, the cooling rate is 112 kW, and the mass flow rate of fresh water produced is 18.4 l/day and 10.8 kg/day of hydrogen for mean solar irradiation of 700 W/m2. The energy efficiency of the system is found to be 17.5%, and the exergy efficiency of the system is around 10.9%. • A new PTC based energy system for a society in remote area is thermodynamically assessed. • Dowtherm A is used as a heat transfer fluid for PTC. • Study results show that for PTC area of 2000 m2, an electrical output obtained is 72 kW. [ABSTRACT FROM AUTHOR]

Transient response of the pinch point is crucial to the evaluations of the recuperator efficiency. A reheat and recompression cycle dynamic simulation system for supercritical CO2 is built, and a transient segmented model is developed to explore the dynamic characteristics of the recuperators. The operating conditions including inlet mass flowrate, temperature and pressure of the low temperature recuperator (LTR) change dramatically with the withdraw-mass variation, which causes different response characteristics of the pinch point. The pinch point gradually transfers from the cold end to the hot end of the LTR as the mass flowrate decreases. The higher pinch-point temperature difference leads to lower heat exchanger effectiveness, and the internal pinch point greatly weakens the recuperator performance. A new prediction model is proposed to quickly determine the pinch point location and analyze the operating conditions prone to cause internal pinch point. The range of split ratio in which the internal pinch point exists in the LTR is obtained. The lower-limit of split ratio variation is sensitive to the high- and low-pressures, the isentropic efficiency of the compressor, and the outlet temperature of the precooler, while the upper-limit of split ratio is only related to the pressures of the recuperator. [ABSTRACT FROM AUTHOR]

This paper is mainly concerned with an experimental investigation of the performance enhancement of a vapor compression refrigeration (VCR) system using nano refrigerant (R-134a + ZrO2) at steady-state conditions. The refrigeration system has become a major consumer of energy for many industrial applications. Therefore, there is a need to enhance the refrigeration systems. The performance of a refrigeration system can be improved by either reducing the compressor power or increasing the heat-absorption rate in the evaporator. The use of nano refrigerant can lead to lower power consumption, increased heat transfer capacity, and reduced (pumping, power, and particle clogging). A two-step method was prepared by dispersing ZrO2 (0.5, 1, and 1.5 % v) in PAG oil. A magnetic stirrer and an ultrasonic homogenizer were used. ZrO2 nanoparticles were selected owing to their superior thermophysical properties. Through the experiments, the discharge pressure (Pdis) varies from 11.37 bar to 7.618 bar, and the suction pressure (Psuc) changes from 1.06 to o.85 bar, which gives a VCR system pressure ratio (PR) between 6.45 and 8.32. The use of nano refrigerant reduced the compressor energy consumption by 7.68 %. Finally, the result revealed the use of (R-134a/ZrO2) nano refrigerant has also resulted in a significant increase in the cooling capacity and thermal efficiency of the system. [ABSTRACT FROM AUTHOR]

• Thermally driven cycle-based compression heat recovery systems are compared. • Effects of feed-air condition and operating parameters are investigated. • Operation optimization of the preferred system is carried out. • The optimal operating parameters of waste heat recovery system is determined. • The ORVC-ACS has 35.8% higher energy saving ratio than the ARS-ACS ones. Recovering compression heat generated in the air compression process is expected for energy saving of cryogenic air separation units. However, the effective utilization of compression heat remains a challenge due to the low-grade feature of the available heat source. Therefore, the selection of the waste heat recovery system configuration is critical to the optimum utilization of the compression heat. In this study, two waste heat recovery systems based on different thermally driven refrigeration cycles for compression heat recovery are proposed, including an organic Rankine vapor compression-based air compression system (ORVC-ACS) and an absorption refrigeration-based air compression system (ARS-ACS). A 60,000-Nm3/h scale cryogenic air separation unit is considered as a case study for assessing and comparing the energetic, exergy and economic potential of the two proposed systems. The results reveal that the ORVC-ACS is preferable to the ARS-ACS in terms of energy-saving and economic performance. Operation optimization is conducted to identify the maximum energy saving of the preferred system. The optimization results show that the ORVC-ACS is capable of saving a total electricity of 8.52 GWh/year, corresponding to 4.53% of the annual electricity consumption for air compressors, while the values are 6.43 GWh/year and 3.37% for the ARS-ACS. This work may provide guidelines for configuration selection and optimum design of waste heat recovery systems in cryogenic air separation units. [ABSTRACT FROM AUTHOR]

Sky radiative cooling is a kind of passive cooling technology that uses the "atmospheric window" to emit the object's own heat to the low temperature of outer space; this technology has low energy consumption, no pollution, and other useful characteristics, so in recent years it has attracted widespread attention. The cooling effect of the sky radiative cooler is mainly affected by the constantly changing outdoor ambient temperature. In addition, the structure of the radiative cooler itself also means that its radiative cooling power undergoes obvious changes. Here, we utilized COMSOL simulation software to establish a numerical heat transfer model for radiative cooling, aimed at investigating the influencing factors on the sky radiative cooler and methods to enhance the structure of the radiative cooling. This study discusses outdoor ambient wind speed, the inlet flow rate of the cooler, installation angle of the cooler, and different cooler structures. Based on simulation results, it is observed that, for varying wind speeds, when the ambient radiation temperature is higher than the surface temperature of the cooler, a larger ambient wind speed leads to a poorer refrigeration effect. The maximum temperature difference in surface temperature at wind speeds of 0 m/s and 4 m/s is 0.59 °C. When the ambient temperature is lower than the surface temperature of the cooler, a smaller wind speed results in a greater net refrigeration power. The maximum temperature difference in this scenario is 0.32 °C. The net refrigeration power of the radiative cooler increases with an increase in water flow rate. As the water flow rate increases from 0 L/min to 5 L/min, the net refrigeration power increases from 25 W/m2 to 200 W/m2 and gradually stabilizes. Considering the radiative impact of the cooler on the surrounding environment, as the installation angle increases from 0° to 90°, the surface temperature of the cooler first increases and then decreases, reaching its highest temperature of 29.26 °C at 45°. The surface temperature of the cooler varies with the thickness of the air sandwich, increasing from 1 cm to 12 cm, and then decreasing. The lowest temperature of 23.4 °C is achieved at a thickness of 8 cm. The increase in the fin structure on the surface of the radiative cooler leads to a decrease in its refrigeration performance, and the difference between the inlet and outlet temperatures of the radiative cooler with a flat plate structure is always greater than that of the finned plate, and the difference in the average radiance is 23.52 W/m2. Finally, the energy-saving effect of the sky radiative cooling composite system is analyzed. Taking a typical small office building as an example, an energy consumption analysis model is set up, and the energy consumption of the composite system is simulated in four cities with different climates, using EnergyPlus software (version 8.6); the system's power consumption is the largest in hot and humid climates. Compared with the traditional vapor-compression refrigeration system, the composite system reduces air conditioning power consumption by 25.7%, 32.5%, 37.1%, and 44.8% in Guangzhou, Shanghai, Jinan, and Shenyang, respectively. The main innovations of this paper include analyzing and studying the influence of the tilt angle change of the radiative plate on the refrigeration performance of the cooler and the relationship between the surrounding buildings, adding air sandwiches and ribs to the radiative cooler to analyze the influence of convective heat transfer on the refrigeration effect, which plays a guiding role in the design and research of the sky radiative cooler. [ABSTRACT FROM AUTHOR]

In order to boost the cycles' thermal efficiency, their power generations and reduce industrial equipment costs the growing need to develop and improve the performance of power generation cycles has provided the basis for research. Currently, there are quite a few investigations aiming to consider Kalina cycles as a power generation system using low-grade heat sources. In this research, firstly KCS-11 (Kalina Cycle System11) as well as Ekalina cycle (enhanced KCS-11 with ejector) has been studied. The SEKalina cycle, which is a modification of Ekalina cycle, is introduced, examined, and simulated by EES software. In the structure of the EKalina, the throttle valve and absorber are removed and the ejector is used instead. The use of the ejector reduces pressure at the turbine's outlet and augments the difference between the enthalpy of two turbine ends, leading to enhancement of the thermal proficiency and net power output. Including an ejector and benefited from a split configuration, SEKalina cycle proposes a potential for efficiency improvement. Examining the results of the cycles, it is found that by employing the SEKalina cycle, compare to the two previously introduced cycles (EKalina and KCS-11), the thermal efficiency and net power output rise significantly. Moreover, as a result, the net power output in SEKalina cycle is 2% higher than that of EKalina cycle. [ABSTRACT FROM AUTHOR]

It is vital, following the Kyoto Protocol, to find environmentally benign and energy-efficient refrigerants, consequently boosting the coefficient of performance (COP). Refrigeration systems are used extensively in the industrial, home, and commercial sectors for cooling, heating, food preservation, and cryogenic purposes. Researchers have successfully employed the application of nanoparticles in cooling systems to achieve improved enhancement, reliability, and efficiency of refrigeration systems because of their higher heat transfer and thermophysical capabilities. The function of numerous variables, however, makes the experimental technique appear to be costly and time-consuming to carry out. This study was, therefore, designed to numerically simulate the performance assessment of a nanoparticle-enhanced Cascaded Vapor Compression Refrigeration Cycle (CVCRC). The focus of this paper is on four distinct SiO2 nanoparticle nanorefrigerants and their pure fluids: two HFCs as well as two fourth-generation refrigerants (HFOs), namely; R12, R134a, R1234yf, and R-1234ze (E). The results show that adding nanoparticles to the pure refrigerant improves COP, and the highest values were achieved with the R1234ze(E)/SiO2 mixture. Increasing the mass concentration of the nanoparticles leads to an increase in the refrigeration effect, an increase in COP, and a reduction in compressor work. Although R125 had the lowest compressor work of 47.12 kW when SiO2 nanoparticles are introduced, however, is not suitable for refrigeration because of its high GWP values. R1234ze has the second-lowest compressor work of 59.58 kW with the addition of SiO2, it is consequently more energy efficient and can be used in its place as it has a GWP of 6, among other benefits. [ABSTRACT FROM AUTHOR]