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• Predicted power consumption and COP a chiller plant using XGBoost. • Quantified impacts of data intervals and data processing on the accuracy of models. • Improved the predictions compared to the baseline using data smoothing methods. • Demonstrated a guide to develop data-driven chiller power and COP models. In recent years, data-driven models have enabled accurate prediction of chiller power consumption and chiller coefficient of performance (COP). This study evaluates the usage of time series Extreme Gradient Boosting (XGBoost) models to predict chiller power consumption and chiller COP of a water-cooled chiller plant. The 10-second measured data used in this study are from the Intelligent Building Agents Laboratory (IBAL), which includes two water-cooled chillers. Preprocessing, data selection, noise analysis, and data smoothing methods influence the accuracy of these data-driven predictions. The data intervals were changed to 30 s, 60 s, and 180 s using down-sampling and averaging strategies to investigate the impact of data preprocessing methods and data resolutions on the accuracy of chiller COP and power consumption models. To overcome the effect of noise on the accuracy of the models of chiller power consumption and COP, two data smoothing methods, the moving average window strategy and the Savitzky-Golay (SG) filter, are applied. The results show that both methods improve the predictions compared to the baseline, with the SG filter slightly outperforming the moving average. Particularly, the mean absolute percentage error of the chiller COP and power consumption models improved from 4.8 to 4.9 for the baseline to 1.9 and 2.3 with the SG filter, respectively. Overall, this study provides a practical guide to developing XGBoost data-driven chiller power consumption and COP prediction models. [ABSTRACT FROM AUTHOR]

Spiral blast freezing is a common unit operation used in food processing facilities for rapidly freezing a variety of foodstuffs. The purpose of a blast freezer is to generate high velocity, low temperature air flow over food products being conveyed within refrigerated enclosures to accomplish the freezing process. However, air flow patterns observed within field operating blast freezers are often suboptimal, resulting in diminished system performance. This paper applies a Monte Carlo simulation technique to a food product freezing simulation in order to identify velocity profiles that optimize the freezing process. A one-dimensional food product model is used to evaluate the interplay between the time variation in the magnitude of the air velocity over food products conveyed through the freezing system and the resulting dwell time needed to achieve a target product core temperature at the blast freezer exit. Temporal heat transfer coefficients derived from field measurements made in a newly installed spiral blast freezer serve as a basis to calibrate the one-dimensional product model. The results of the Monte Carlo analysis show freezing system performance is improved when high and stable air velocities over the product are achieved early in the freezing process dwell time. Air flow patterns within a freezing system that result in high air velocity later in the freezing process dwell time are suboptimal. Field-measured data on a newly installed spiral blast freezer showed this suboptimal air flow pattern and the use of baffling within the spiral enables improved airflow leading to an estimated 10 % increase in production throughput. [ABSTRACT FROM AUTHOR]

• An enhanced ejector-subcooler CO 2 transcritical refrigeration cycle is presented. • A parametric analysis and optimization of the enhanced cycle and the baseline cycle are carried out. • The results suggest the integration of the proposed cycle could achieve more compact and reliable systems. • The maximum COP improvements are computed as 11.7%-17.5% when the gas cooler outlet temperature ranges from 35 °C to 50 °C and the evaporating temperature is -40 °C. The main drawback associated with CO 2 refrigeration systems is related to their performance reduction during transcritical operation at warm climate conditions, which may be compensated by better cycle architectures such as the split-cycle with subcooling or the flash-tank configuration, among others. Specifically, the use of standard gas-ejectors together with parallel compressors provides even better efficiency improvements, not being able to use them with low-temperature evaporators to prevent the triple point inside the ejector. This paper proposes an enhanced cycle with a gas ejector for two-stage compressor architectures with vapor injection from the flash-tank, which is able to operate at low evaporating temperatures and that provides a greater performance improvement the more severe the climate conditions are. The methodology conducted is based on a thermodynamic analysis that includes parametric evaluation and cycle optimization, comparing the results to a conventional CO 2 transcritical cycle with flash-tank and dynamic vapor injection architecture. The main results show that a maximum Coefficient of Performance improvement of 17.5% is achievable for transcritical operation at -40 °C evaporating temperature. The compressor displacement capacity required with the enhanced cycle is up to 9% lower for the same refrigeration demand, reducing the electrical consumption as well as the compressor expenditure. Moreover, greater vapor injection mass flow rates are obtained by the gas-ejector injection with discharge temperature reductions up to 18%, enhancing the system reliability. [ABSTRACT FROM AUTHOR]

• A novel variable stiffness valve based on PEEK and stainless steel was proposed. • Stress-strain behavior and operational characteristics of novel valve were studied. • Impacts of novel valve on compressor performance and noise experimentally. • Compressor performance improved by 2.6 % and noise reduced by 3–5 dB. Improving valve design is crucial for enhancing the performance of rolling piston type rotary compressor. A novel variable stiffness valve based on PEEK and stainless steel was proposed. The stress-strain behavior of the novel valve was studied, and its operational characteristics, including opening and closing angles and over-compression losses, were analyzed in a compressor. It is shown that opening and closing angle of the new-designed valve were advanced compared to that of the original cylinder by about 2∼3°, leading to a general reduction in over-compression losses, with a maximum decrease of 4.15 W. The impacts of new-designed valve on compressor performance were experimentally investigated. The cooling capacity and coefficient of performance of compressors equipped with new-designed compared to original valve were improved by 1.1–1.7 % and 1.1–2.6 %, respectively. In addition, the input electrical power required for the new valve was observed to be 0.9–1.3 % lower. The incorporation of high-damping material in the new valve design significantly reduced compressor noise by 3–5 dB at the critical frequency bands of 630–1250 Hz. These findings offer valuable insights for enhancing the energy efficiency and noise reduction in rolling piston type rotary compressors. [ABSTRACT FROM AUTHOR]

• A subcooler reduces the total mass flow rate for a given operation conditions. • Reduced evaporator superheat improves the evaporator heat transfer. • The coefficient of performance increases using a subcooling system. • Flash gas mass flow rate used to reduce the superheat at the compressor inlet. A new position of an internal heat exchanger within the thermodynamic cycle is proposed to improve the performance of CO 2 refrigeration systems in warm climates, specifically in supermarket applications. The proposed configuration uses the saturated vapor from the liquid receiver to recover the heat that is rejected by a subcooler positioned after the gas cooler. This system results in a reduced evaporator superheat. This configuration is compared with a reference system. The experimental study is conducted on a CO 2 laboratory cooling system reproducing a commercial plant. The cooling capacity of the system is 30 kW. The water inlet temperature in the gas cooler (hot source) varies from 15 °C to 35 °C, while the mono-ethylene glycol outlet temperature of the evaporator (cold source) is fixed at -8 °C. The setup is validated through an energy balance. Using a subcooler in this new position improves the coefficient of performance by 10.2 % under transcritical conditions and 6.3 % under subcritical conditions when compared with the reference system. [ABSTRACT FROM AUTHOR]

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]

• Biogas energy assisted hybrid milk cooling system was experimentally investigated. • Energy consumption in the first and last milking is detected as 2.29 and 2.54 kWh. • Energy efficiency is 45.61% higher than conventional systems for the first milking. • It consumes 24.40% less energy than other hybrid systems for the last milking. Biogas energy assisted hybrid milk cooling system was investigated experimentally, in this study. The system operated in a cycle. Primarily, biogas was obtained from the residues of animals in the farm environment and an internal combustion gas engine is started with this gas. Then, the gas engine provided the power required for the compressor of the cooling system to operate. The main purpose of the study was to encounter the energy required for milk cooling only from the biomass potential of animal wastes and in this way, it was to bring a system with high energy efficiency for milk cooling process to the literature and industry. In experiments, 150 liters of milk in the first milking and 300 liters of milk in the last milking were cooled. It was determined that the energy consumption in the first and last milking is 2.29 kWh and 2.54 kWh. The results revealed that this developed system was 45.61% and 41.61% more advantageous for first and last milking, respectively, compared to conventional milk cooling systems in terms of energy consumption. When the system compared to other alternative energy source assisted milk cooling technologies with similar milk cooling capacity, It was observed that 14.55% and 24.40% more efficient with regards to energy consumption for the first and last milking. Additionally, experimental and Carnot COP values of the cooling system were determined as 4.29 and 8.26, respectively. These data revealed that the hybrid system had a higher performance of 38.4% compared to other milk cooling techniques. [ABSTRACT FROM AUTHOR]

• A novel CO 2 booster system for commercial refrigeration is presented. • The objective is to simplify ejector-supported booster systems keeping efficiency. • The system layout was experimentally validated and benchmarked. • Efficiency increased up to 40 % compared to conventional booster systems. • The novel configuration performed positively under all ambient conditions. The pernicious effects of synthetic refrigerants on different environmental aspects leave natural refrigerants as the only alternative for vapour compressions systems. Among natural refrigerants, CO 2 (R744) has become the preferred choice for commercial refrigeration at almost any location and climate. However, efficient R744 refrigeration systems for warm climates have a great level of complexity, implementing technologies such as mechanical subcooling or ejector that increase the investment costs. The goal of the novel hybrid configuration presented in this work is to simplify ejector-supported R744 commercial refrigeration systems while maintaining all the benefits of the ejector implementation in transcritical operation mode. Moreover, utilization of a low-pressure accumulator layout in the subcritical mode removes all the practical challenges related to the booster layout operating at low ambient temperatures. This solution is based on: (i) MT and LT compressor suction groups, (ii) non-superheated MT evaporation with increased evaporation temperature, and (iii) ejector utilization throughout the year. The ejector is actively operated as a high-pressure-control device at elevated ambient temperatures ('summer mode'), while it is passive and acts as a check-valve at lower ambient temperatures ('winter mode'). The experimental campaign performed proved that this novel system configuration is more energy efficient than booster systems with parallel compressors at any condition, improving the COP by around 40 % at the most extreme gas cooler outlet temperatures tested, i.e., 40 °C (summer mode) and 10 °C (winter mode). [ABSTRACT FROM AUTHOR]

This paper presents the design and application of a virtual sensor used in case of failure of the main physical sensor for temperature readings in automotive air conditioning. Using auxiliary temperature and pressure physical sensors combined with Support Vector Machine (SVM) Regression, the model of the virtual sensor is derived and prepared to be used as a redundant sensor until the broken physical sensor maintenance. Thus, enabling the system to operate continuously and maintaining its original power and thermal comfort features until the physical sensor replacement. In total, 32 h of training and test data involving different environmental conditions were used to generate the model that was further integrated. The designed virtual sensor presented a Mean Square Error (MSE) of 1 , 3 o C , a Mean Absolute Percentage Error (MAPE) of 3 , 6 % , and a Pearson Correlation Coefficient of 0,90. The results enabled the continuous and autonomous operation of the air conditioning plant respecting the designed thermal comfort guidelines even when under the physical sensor failure condition. [ABSTRACT FROM AUTHOR]

• Main refrigeration systems in fishing vessels are based on R-22 and R-717. • There are significant developments in R-744 refrigeration systems. • The number of R-744 refrigeration units in fishing vessels has been increasing. • There is a lack of scientific efforts/studies on R-744 systems in fishing vessels. Globally, most fishing vessels still use the ozone-depleting and climate-harmful R-22 in their freezing and refrigerated seawater (RSW) systems. However, in some regions, the natural refrigerant ammonia is the preferred refrigerant. Another natural refrigerant, carbon dioxide (R-744), is becoming a viable option and is increasingly used onboard. This option will not exclude ammonia, but rather will be a good alternative to it to meet the demand for different cooling/freezing needs in post-R-22 systems. There are currently major developments in R-744 refrigeration technology that are widening the potential applications of R-744. These include compressors with larger capacities, more energy-efficient components, system designs with lower freezing temperatures and integration of heat recovery and thermal storage. This paper provides a review of the development of refrigeration systems with R-744 onboard fishing vessels. It includes a description of the commonly used cooling and freezing methods and of the development in R-744 refrigeration technology, especially within the system and component design, capacity and performance. It also includes the current status of R-744 refrigeration technologies in fishing vessels. Although there are limited publications on R-744 systems for fishing vessel applications, the review shows positive prospects of utilizing R-744 and further research and innovation within this topic is recommended. [ABSTRACT FROM AUTHOR]

• We investigate R290/R600a mixtures in Vapor Compression Refrigeration System. • We present a test stand for household refrigerator compressors with small capacity. • We investigate the effect of compression ratio on the COP. • The optimum compressor speed is found close to 2100 rpm. • COP gain relative to R600a reaches up to 15 % using 60 % R290 mass weight in mixture. • 60 % of R290 mass weight exhibits a better volumetric and isentropic efficiency. This paper presents an experimental investigation of the effect of R290/R600a refrigerant mixtures on the performance of variable speed hermetic compressors used in household refrigeration. In this context, a small-capacity compressor test stand is introduced and four different compositions of R290/R600a mixtures are studied in detail. R290 composition in the refrigerant mixture varies between 40–70 % by mass weight. Performance outcomes of the mixtures are compared to baseline refrigerant R600a. The influence of R290 composition in refrigerant mixture over COP, refrigerant mass flow rate and power consumption rates are explored in the present study. Moreover, the effect of compressor speed, evaporation and condensation temperature on the compressor performance are studied via steady-state experimental tests. It has been concluded that increasing the mass weight of R290 in the mixture yields higher power consumption rates, yet it has brought a significant increase in the refrigerant mass flow rate, thus enabling a higher COP. The optimum compressor speed is found to be approximately 2100 rpm for the tested hermetic reciprocating compressor. The COP increases with the increments of evaporation temperature and decrements of the condensation temperature. The COP of the refrigeration cycle is 10–20 % greater than that of R600a depending on the composition of the refrigerant mixtures and operating conditions. [ABSTRACT FROM AUTHOR]

The combination of an ORC (Organic Rankine Cycle) with a VCC (Vapor Compression Cycle) is studied analytically. In this work, the two cycles use the same fluid and operate with a common condenser. Elementary transformations of the fluid between two consecutive points of the system are calculated using a one-dimensional thermodynamic approach considering real fluid properties, the pressure losses and irreversibilities present in the compressor, in the expander and in the pump. The performances and the recommended inlet and outlet diameters of the expander and the compressor are established for various operating conditions and 12 fluids. The system can produce a typical useful cooling capacity of 0.60 kW at 5.5 °C when using a 2 kW heating source at 65 °C and when the condenser temperature is 30 °C. The cooling capacity reaches 1.0 kW if the cold source temperature is 15.5 °C. Results show the required diameters ratios at inputs and outputs of the compressor and the expander. They indicate the situations for which the compressor is smaller than the expander and vice versa. They identify the particular cases in which the compressor and the expander have exactly the same inlet and outlet diameters. This particular case allows using two identical compressors, one working as a compressor, the second as an expander. [ABSTRACT FROM AUTHOR]

• Refrigerator modeling • Incremental capital and recurring cost of alternative designs • Energy efficient refrigerator design options • Energy efficiency – cost tradeoff • Lifecyle emissions reduction Domestic refrigeration appliances are ubiquitous consuming roughly 14% of the global residential electrical consumption. It is estimated that the global installed stock of domestic refrigerators is between 2 and 2.3 billion units. Furthermore, domestic refrigerators employ high global warming potential (GWP) refrigerants (e.g., R-134a). The global goal to limit the global warming to 1.5°C requires rapid reduction in CO 2 emissions and other greenhouse gases (GHGs). Transition towards cost-effective, efficient, and environmentally friendly refrigeration technologies is considered as one of the most effective measures to reduce GHG emissions. In this paper, we worked with 5 manufacturers in 4 developing countries to study energy efficiency (EE) design options and the associated incremental capital cost and incremental recurring cost (IRC). In our study, we have accounted for their product development capabilities, their productions volume, their relationship with original equipment manufacturers (OEMs), and the local product competition in their markets. Our detailed study showed that cost effective energy savings of 9.5 to 19.2% can be achieved while the maximum EE upgrades varied between 30.2 to 50%. Furthermore, the corresponding indirect emissions reduction varied by the local electricity production mix and the baseline technology. The cost-effective EE upgrades result in emission reduction of 65,145 to 612,959 metric tons of CO 2eq while the maximum EE upgrades result in emission reduction of 157,675 to 1,077,005 metric tons of CO 2eq. [ABSTRACT FROM AUTHOR]

• EAHE system is combined with AHU to reduce the compressor power and annual cost. • Analytical model is built to evaluate the effect of different geometry parameters. • Optimum diameter is found to be 0.35 m and length depends on the number of pipes. • Maximum power saving is 44%, and the maximum cost reduction is 16.6%. • Payback period is ranged from 0.35–9.3 years depending on the number of pipes. This paper presents a thorough parametric analysis of an earth-air heat exchanger (EAHE) that reveals optimal parameters for minimizing the cost of central air conditioning in a hot and dry climate. A mathematical model with the aid of MATLAB is developed to optimize different parameters including length, diameter, and number of pipes. The performance of the selected cooling system is evaluated in terms of compressor power consumption, overall power savings, overall cost reduction, and payback period. As a case study for our analysis, a 25-TR air-conditioning system was chosen to cool an operation room in a hospital in Egypt. The maximum reduction in compressor power consumption is estimated to be 44%. Moreover, the reduction in the annual costs is estimated to be 16.6% with a payback period that increases as the number of pipes increases. [ABSTRACT FROM AUTHOR]

• The dynamic behavior of an adjustable jet-ejector refrigeration system is assessed. • A thermal storage system is considered to cope with variable solar irradiation. • The influence of two different jet-ejector architectures is evaluated using R1234yf. • The transient response is computed under real climatic conditions. In the present paper, the mid-term performance of two different architectures of a solar-driven jet-ejector refrigeration system is numerically compared: the first one is fitted with a fixed-geometry jet-ejector while the second one is equipped with an adjustable spindle that modifies the jet-ejector area ratio. The jet-ejector behavior has been predicted with a validated computational fluid dynamics approach and the dynamic response of the overall system accounts for transient effects in a small parabolic trough collector and a hot thermal storage tank. The investigation shows that the adjustable jet-ejector allows for continuous and smooth operation in a much wider range of outdoor conditions. Additionally, it enables more efficient management of the thermal level in the hot storage system. As a result, the adjustable refrigeration system improves the performance indicators in all the warm months of the typical meteorological year under evaluation. The maximum improvement potential is found in May; the fixed-geometry system provides an average C O P th of 0.34 while the adjustable system reaches an average C O P th of 0.48 considering the same boundary conditions in both cases. [ABSTRACT FROM AUTHOR]

The prerequisite for the exploration and exploitation of natural gas hydrate (NGH) is ensuring that the hydrate sample does not decompose during the sampling process. In order to solve this problem, the hole-bottom freezing sampling technique (HBFS) method was proposed, which uses a cold-alcohol to reduce the temperature of the hydrate sample and prevent its decomposition. However, the low heat exchange between the cold-alcohol and the hydrate sample results in a large loss of energy, and the sample cannot be frozen to the required temperature due to the size limitations of the sampler. In this study, three different heat transfer modes were used to increase the energy efficiency, namely heat conduction (cold-alcohol), phase change heat transfer (liquid nitrogen), phase change convection (alcohol-dry ice mixture). The test results show that the freezing efficiency of the alcohol and dry-ice mixture is 11.38%, which is the highest. The alcohol-dry ice mixture can cool the average temperature of the sample from approximately -17.81 to -23.37 °C, in which the hydrate sample does not decompose rapidly under normal pressure. The alcohol–dry ice mixture is more suitable as a coolant for the HBFS. [ABSTRACT FROM AUTHOR]

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

• Dehumidifier with PEM is suitable for the humidity control in refrigerators. • Performance of PEM dehumidifier under -10~10°C conditions was experimentally investigated. • The dehumidifier has a starting voltage, which is higher at lower air temperatures. • With the increase in applied voltage, the operating current first increases and then drops. • Performance changing rate with operating parameters is much lower under sub-zero temperatures, due to possible icing and swelling inside the membrane. • The low temperature performance is not as good as normal, but the efficiency is still competitive. Dehumidifier with Polymer electrolyte membrane (PEM) is suitable for high-accuracy, limited-space humidity control in refrigerators. This study experimentally investigated the performance of PEM-based dehumidifier under the temperature range of -10~10°C. Empirical equations of PEM water content at refrigerator temperatures were developed. Results showed that although the low-temperature performance of electrolytic dehumidifier is not as good as that of room temperature, the efficiency (~1.3 × 10−2 g·J−1·m−2) is still competitive to desiccant or electrochemical methods. The dehumidifier has a starting voltage, and the voltage is higher at lower air temperatures (i.e. 1.3V for 26.1°C and 2.3 V for -3.9°C). During dehumidification, the operating current first increases significantly and then drops as the applied voltage increases, leading to a first increase and then steady dehumidification rate. The peak of current occurs at a smaller voltage as the air temperature decreases, i.e. 1.8V for 0°C and 2.5V for 26°C. Furthermore, the dehumidification rate increases as the air temperature and flow rate increases, while the changing rate with operating conditions was lower at sub-zero temperatures. Dehumidification has little effect on the oxygen concentration or temperature increment of the supply air. Characterizations also indicated that there was no obvious physical change on the PEM surface after operating at low temperatures. However, there exists a starting temperature for the dehumidifier, i.e. -9.5°C for the 3V applied voltage, which is due to the possible icing and swelling problem within the membrane. This study provided a new method, and proved its feasibility for dehumidifying at refrigerator temperatures. [ABSTRACT FROM AUTHOR]

• A novel GEHP facility for cooling and domestic hot water is developed. • A novel condenser and three thermostatic expansion valves are used in the system. • The novel GEHP facility is able to maintain expected high performance. Heat pump technologies have been widely used in air conditioning and hot water application. However, most of the heat pump systems adopt an expansion valve to complete the cooling and heating modes currently. The flaw is that as the four-way valve is switched, the expansion valve cannot be guaranteed to be very close to the inlet of the evaporator in both modes, making the performance of the cooling or heating mode worse. In addition, for gas-engine-driven heat pump (GEHP), the utilization of engine waste heat is insufficient. Based on the above two shortcomings, a novel GEHP unit with an advanced finned tube heat exchanger and three thermostatic expansion valves was built in this work. The performance was evaluated under an experimental operating range of engine speed from 1300 rpm to 2000 rpm, air temperature from 23.8°C to 27.7°C, and evaporator water inlet temperature from 13.2°C to 22.4°C. Experimental results showed that when the engine speed and ambient temperature increased, the compression ratio increased, whereas the coefficient of performance (COP), primary energy ratio with heat recovery (PER 1), and primary energy ratio without heat recovery (PER 2) of the system decreased linearly. As the evaporator water inlet temperature increased from 13.2°C to 22.4°C, the COP, PER 1 , and PER 2 had an improvement of 23.6%, 20.8%, and 27.6%, respectively. The averages of COP, PER 1 and PER 2 were 3.67, 1.57 and 0.96, respectively. The results indicated that the novel GEHP unit was able to maintain expected high performance. [ABSTRACT FROM AUTHOR]

Ammonia is a high energy efficiency refrigerant with wide-ranging utilization in industry. It is a natural refrigerant that causes no ozone depletion or global warming. The refrigerated warehouse industry has been dealing with a difficult and growing challenge due to thousands of pounds of ammonia contained within their facilities. Since ammonia is toxic and flammable in large concentrations, it is subject to numerous federal, state and local safety regulations. The current work evaluates a distributed ultra-low ammonia charge (ULC) refrigeration package that greatly reduces ammonia quantity in comparison to centralized engine room system typical in existing facilities. Using closed coupled components in a compact refrigeration package, and electronic refrigerant injection control technology, facility ammonia charge is reduced by more than 98%, and worst case release scenario reduced to less than a hundred pounds. This evaluation compares initial costs, energy efficiency, water usage, operating and maintenance costs of ULC configuration against equivalent central engine room baseline. The analysis is based on typical medium sized industrial cold storage warehouse in Sacramento, CA with freezer, cooler and dock areas. The ULC configuration shows 7% reduction in energy (kWh) and 3% reduction in water (Gal) usage. The reduction in energy and water costs, combined with other operational and maintenance related savings show that investment in ULC technology will provide a payback within 3 years. The study demonstrates ULC systems as a promising replacement technology for industrial warehouse refrigeration in terms of overall cost of ownership, human safety and environmental benefits. [ABSTRACT FROM AUTHOR]

• Current state of expanders in vapour compression refrigeration systems is reviewed. • The highest reported COP improvement in a transcritical CO 2 refrigeration system was 30%. • The highest reported COP improvement in a conventional refrigeration system was 10%. • The highest measured expander efficiency was 83%. • Knowledge gaps and challenges are identified. • Recommendations for future work are provided. This paper reviews progress reported in the open literature of the use of expanders to recover expansion power to improve the energy efficiency of vapour compression refrigeration systems. Pioneering works in the field are first discussed, and then a variety of expander mechanisms, including reciprocating piston, rolling piston, rotary vane, scroll, screw and turbine are reviewed together with their reported performance. Most of the reported works have been for transcritical CO 2 refrigeration systems, which have reported improvements in the coefficient of performance (COP) of up to 30%. In a non-CO 2 system, the maximum reported increase in the COP was 10%. The maximum reported expander efficiency (i.e. the ratio of measured power to the power available from an isentropic expansion) was 83%, obtained with a scroll expander in a CO 2 refrigeration cycle. Other expander issues including heat transfer, expansion process, internal leakage, irreversibility, control strategies, installation issues and economic analysis are also reviewed. It is noted that there are a limited number of studies in these areas. Finally, challenges and recommendations for future research in the area of refrigeration expander technology is presented. [ABSTRACT FROM AUTHOR]

• Coggins and modified coordinate descent algorithms are presented for optimization. • The optimization of mixed fluid cascade LNG process is successfully performed. • Exergy analysis is performed successfully. • The overall exergy loss is minimized to 35.91% with 25.4% energy savings. • LNG can be produced on the expense of 0.2197 kWh/kg. The mixed fluid cascade (MFC) process is considered one of the most promising candidates for producing liquefied natural gas (LNG) at onshore sites, mainly owing to its high capacity and relatively high potential energy efficiency. The MFC process involves three refrigeration cycles for natural gas precooling, liquefaction, and subcooling, making its operation more complex and sensitive. Each refrigeration cycle consists of a different mixed refrigerant, which must be optimized to change feed and ambient conditions to operate efficiently. Any sub-optimal solution can lead to high exergy losses, ultimately reducing the process energy efficiency. Operating optimally is a challenging task, mainly owing to the non-linear interactions between the constrained decision (design) variables and complex thermodynamics involved in MFC refrigeration cycles. In this context, we employ a multivariate Coggins step-up approach to reduce the exergy losses associated with the MFC process. This study reveals that the overall exergy losses can be minimized to 35.91%; resulting in 25.4% overall energy savings compared to sub-optimal MFC processes. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Integrated hybrid system combining CO 2 vapour compression cycle and adsorption chiller. • Efficient low temperature refrigeration using natural refrigerants only. • Dynamic optimisation of design and control to achieve maximum efficiency. • Energy savings up to 35% at high ambient temperatures and annual energy savings up to 22%. Sustainable refrigeration systems are of great importance to reduce greenhouse gas emissions. In particular, CO 2 vapour compression cycles are very promising due to their environmentally friendly, natural refrigerant. However, a major challenge for implementing CO 2 cycles is the low efficiency at high ambient temperatures resulting from high exergy losses in transcritical operation. To increase the efficiency, we present a hybrid system concept integrating an adsorption chiller into the CO 2 cycle. The adsorption chiller employs the natural refrigerant water and is driven by waste heat from the CO 2 cycle. The additional cooling generated by the adsorption chiller is integrated into the CO 2 cycle to increase the efficiency of the overall hybrid system. Compared to a stand-alone CO 2 cycle, we show by dynamic modelling and optimisation that the hybrid system leads to annual energy savings of 22% for a warm climate in Athens and of 16% for a moderate climate in Cologne. The results highlight the high potential of the hybrid system concept to efficiently provide refrigeration using environmentally friendly refrigerants. [ABSTRACT FROM AUTHOR]

Highlight • Our developing numerical simulation model can reproduce static and dynamic characteristics of variable refrigerant flow (VRF) systems precisely. • Our simulation model can be estimated dynamic characteristics quantitatively and can be analyzed the cause of response time difference of manipulated variables. • Interference from mutual indoor units affects the supply air temperature and superheating temperature largely, in case of manipulated each expansion valves especially. • This simulation results is expected to be applied to another VRF systems. Abstract In commercial and office buildings, it has recently become popular to install variable refrigerant flow (VRF) compression-type heat pump systems. In particular, VRF systems with multiple indoor units are being installed in large buildings because such systems have large adjustment capacity. On the other hand, because users of VRF systems can freely choose the number of indoor units to install and can turn indoor units on and off independently, operating conditions are not predictable and it is difficult to find adequate control parameters under wide changes in load. With this background, we are developing a new numerical simulation model based on the laws of physics. Because this model can easily add and delete system elements, we believe that it will be useful for VRF system analysis. In this study, we utilize a numerical simulation model to evaluate both steady and unsteady conditions in VRF systems. In this paper, we focus on the connection between manipulated variables (the expansion valve's open pulse and fan rotational speed) and controlled variables (supply air temperature and the degree of superheating at the evaporator outlet). Moreover, we compare the difference between the performance of a single indoor unit and that of multiple indoor units operating simultaneously. As a result, we can evaluate the dynamic characteristics of manipulated variables and the effect of changing the number of active indoor units, each of which has their own VRF characteristics. [ABSTRACT FROM AUTHOR]

Highlights • 2D numerical model of a device with an active electrocaloric regenerator is presented. • Material hysteresis greatly impacts the efficiency of the cooling device. • A system for energy recovery can increase the device efficiency by ten times. • The electrocaloric cooling device has a maximum specific cooling power of 16 W kg−1. Abstract This paper reports on the research and development of a cooling device with an active electrocaloric regenerator (AER) based on the bulk ceramic material (1-x)Pb(Mg 1/3 Nb 2/3)O 3 –xPbTiO 3 (PMN-100xPT). For the purposes of the study a 2D transient numerical model of the AER was developed. This model makes it possible to investigate the cooling characteristics of a device with an AER while considering the effect of the hysteresis of the electrocaloric material and the effect of the electric-energy recovery related to the polarization/depolarization process. The results of the numerical analyses show that the degree of electric energy recovery has a major impact on the efficiency of the device. By considering an idealised system for electric-energy recovery the energy efficiency (expressed by the coefficient of performance) of the device could be increased by up to ten times. A validation of the numerical model was performed through the design, construction and experiments on an improved AER cooling device. The results revealed a maximum specific cooling power of 16 W kg−1 and a maximum temperature span of 3.1 K for the new device. [ABSTRACT FROM AUTHOR]

Highlights • A new modified autocascade heat pump system for electric vehicle heating in cold climate is proposed. • Both transcritical and subcritical cycle characteristics using CO 2 -propane are theoretically evaluated. • Results show the new system has much better performance than conventional cycle. • The feasibility of the ACHP system is verified and further optimization locations in the ACHP system is pointed out with exergy analysis. Abstract Heat pump and its efficiency are of great significance to the energy saving of electric vehicle in cold climate. This paper proposes a modified autocascade heat pump (ACHP) system using natural CO 2 -propane mixture. The main purpose is to enhance the heating performance compared with that of conventional heat pump. Using a thermodynamic model of the proposed ACHP cycle, the transcritical and subcritical cycle performance under various conditions are carried out from the perspective of first and second law of thermodynamics, and the transcritical operating characteristics of ACHP system is introduced for the first time. Additionally, an exergy performance comparison has been carried out. Results indicate that the ACHP system can produce more heating capacity, lower compression pressure ratio, lower heat rejection temperature for low ambient temperature conditions and it consumes less compressor work for all the temperature range researched. For transcritical ACHP cycle, the best COP is 2.7 obtained when CO 2 mass fraction is 0.8 at −20 °C, which is 12.3% higher than that of CO 2 single stage heat pump. For subcritical ACHP cycle, the best COP is 3.97 while heating capacity is much lower than that of transcritical cycle in the same condition. Finally, the exergy analysis confirms the feasibility of the ACHP system and points out exactly the further optimization locations in the ACHP system. [ABSTRACT FROM AUTHOR]

Highlights • HRV system was constructed to test two quasi-flow polymers heat exchanger. • The effect of the surface geometry in HRV units was evaluated experimentally. • Effects of operating parameters on HRV's performance were found. • The HRV experimental maximum COP could reach 6.6 at elevated temperature. • Empirical correlations of the experimental data were extracted. Abstract Ventilation heat recovery is a system that requires low power to operate and has a high capacity to reduce the energy consumption and increase the overall efficiency for air conditioning. This paper reports the experimental investigation of air-to-air heat exchangers employed for heat recovery ventilation in cooling mode. The two main objective of this research are to design, fabricate and testing two polymers heat exchangers of different plate geometries and to evaluate and compare the thermal performance two quasi-counter flow plate heat exchangers. The key aims were to evaluate the effect of the surface geometry of the plates heat exchanger on the performance parameters specified in ANSI/ASHRAE Standard 84 and ANSI/AHRI Standard 1060 and narrow the gap of the limited experimental comparison of polymers sensible heat exchanger in cooling mode. The experiments were conducted on two polymer heat exchangers, one with a flat plate and the other with a dimpled surface plate. The experimental results showed that the cooling capacity of the dimpled surface heat exchanger as ventilation heat recovery system in cooling mode was 50–60% better than that of the flat surface plate heat exchanger. In addition, the sensible efficiency of the dimpled surface heat exchanger was higher than that of the flat surface plates heat exchanger at lower air velocities and higher air initial temperatures. The highest COP was 6.6 achieved with dimpled surface heat exchanger under primary air operating temperature of 32.6 °C. [ABSTRACT FROM AUTHOR]

Highlights • An integrated modified-evaporator of a household refrigerator with PCMs was tested. • The average storage temperatures of the refrigerator compartments were reduced. • The average temperature of the M-packs in the evaporator increased. • The power consumption was reduced by 2% and 6% with the studied eutectic PCMs. • The compressor running time was reduced by 4% and 9% with the studied eutectic PCMs. Abstract Domestic refrigerators are among the most energy-consuming appliances. In many countries, efforts have been undertaken to enhance the thermal efficiency of domestic refrigerators, and such improvements have been focused mainly on compressor operation and electronic control. The use of phase change materials (PCMs) in domestic refrigerators decreases the cycling period of the compressor and reduces internal temperature fluctuations. Two eutectic PCMs are thermally characterised (PLUSICE E-10 and 19.5 wt% NH 4 Cl). Their phase-change temperatures and latent heat values are determined, and their thermal conductivity and density are measured at 20 °C. The main goal of the present work is to study the behaviour of an integrated modified-evaporator of a household refrigerator with two different eutectic PCMs by performing standardised tests. In general, the experimental results help enhance our understanding and improve the operation of household refrigerators in terms of the power consumption and the inner temperature variation. [ABSTRACT FROM AUTHOR]

The large datasets resulting from operating HVAC&R systems are currently scrutinized to find ways to exploit the useful information that they might contain. In this work, historical data of a centrifugal water chiller over the course of more than 1.5 years of operation is used to learn about the system and to suggest modifications to its operation scheme. The results show that principal component analysis (PCA) captures well the variance in the historical data. The first two principal components explained between 62 and 80% of the variance, depending on the cases considered. The main factors responsible for the variation of the chiller operation are found to be the weather and the cold water temperature setpoint. The effect of the sampling time step on the results is also studied. Moreover, this work demonstrates that partial least squares (PLS) regression can adequately predict an important indicator of the chiller performance, namely the coefficient of performance (COP), one time step ahead with an R² of 77.49% and root-mean square error of estimation (RMSEE) of 0.463 using a separate validation set of data. The PLS model was also able to predict future COP values up to 2 time steps (∼3 h) in advance. [ABSTRACT FROM AUTHOR]

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

Emergence of nanotechnology opens up new avenues in diverse research frontiers. Nanorefrigerants are nanotechnology based refrigerants, which are stable mixture of nanoparticles of metal, oxide, carbon and its allotropes and refrigerants. Development of nanorefrigerants provides a new research frontier in the heat transfer perspective. The studies on nanorefrigerants are still in its budding stage. The intention of the present paper is to provide a comprehensive overview of experimental studies on thermophysical and rehological properties, boiling and condensation phenomena, pressure drop characteristics, aggregation behaviour, migration and degradation characteristics of different nanorefrigerants and application of nanorefrigerants in HVAC systems. Various outlooks of future scope associated with the studies of nanorefrigerants have also been suggested. It has been recognized that addition of nanoparticles in refrigerants contributes noteworthy augment in the thermal physical and heat transfer characteristics of refrigerants. Furthermore, application of nanorefrigerants in heating, ventilation, and air conditioning systems enhance the overall performance in terms of coefficients of performance (COP) and energy efficiency. [ABSTRACT FROM AUTHOR]

The use of high temperature heat pumps (HTHPs) operating with natural fluids has been shown to be a potential environmentally friendly solution to increase energy efficiency in industrial processes. Industrial processes release a significant amount of energy as low quality waste heat to the environment. This paper reviews the research and development of efficient and cost effective HTHP technology that can utilize this waste heat. Natural fluids are of focus with consideration given to the comparable technologies using synthetic fluids. This review reveals the different challenges from fluid selection, component development to system optimization. The various innovative solutions to these challenges and promising technologies for further studies are discussed. The purpose of this paper is to serve as a start point for research by bringing together ideas, simulations and experimental results as a resource or reference tool for future development in HTHP using natural working fluids. [ABSTRACT FROM AUTHOR]

In recent years, the growing needs for fulfilling the comfort cooling requirements with efficient refrigerating and air conditioning systems have gained impetus. In this work, the performance of a combined variable refrigerant volume (VRV) and cool thermal energy storage (CTES) air conditioning (A/C) system was experimentally investigated for summer and winter design conditions. Experimental results suggest that the VRV-CTES A/C system (combined A/C system) precisely maintained the indoor temperature at 24 °C for year-round operational conditions. The PCM being applied has exhibited good latent heat capacity (~160.81 kJ kg −1 ) with congruent phase transition characteristics (~9.92 °C), even after 1000 repeated thermal cycles. Furthermore, the reduced cooling capacities and reduced combined power consumption were attributed to the improved performance of the combined A/C system. In total, this system would be beneficial in terms of accomplishing comfort cooling needs for conditioning applications without sacrificing energy efficiency. [ABSTRACT FROM AUTHOR]

This paper proposes a system design of an Adaptive Food Preservation System (AFPS). It is motivated by the fact that constant storage condition in today's refrigerators has deficiency. Customized storage with fast freezing capability can better manage food quality and energy efficiency. Key components include AFPS packages and vortex tubes. Superior fast freezing capability is demonstrated by comparisons with benchmarks from refrigerator tests and regulatory standards, and experimentation with a simulated test setup at various settings of input. Theoretical and analytical models are proposed to predict package inlet and exit temperatures, freezing capacities, and freezing efficiencies. At 7 bar inlet pressure, the maximum available freezing efficiency, mean efficiencies with vacuum insulation and with ABS insulation of the AFPS Package and Vortex Tube Assembly are 6%, 4.66%, and 2.80%, respectively. AFPS technology consumes 0.18% in time and 45% in energy during fast freezing comparing with what a typical household freezer does. [ABSTRACT FROM AUTHOR]

This paper presents the results of a thermo-economic and primary-energy-factor assessment based on the field-test results for a residential air-to-water heat pump (AWHP). The AWHP experimental setup consisted of a supervisory control and data-acquisition system, which was connected to a heat meter, an electricity meter, humidity and temperature sensors, a HP control system and a computer. Based on the experimental data, the 4-year-average seasonal performance factor was determined. This information was then applied in a thermo-economic and primary-energy-factor (PEF) analysis. The results served for a comparison of the AWHP with eight different heating systems (HSs). The results reveal that the considered AWHP represents the most thermo-economically efficient system in terms of the average final costs for heat production. The results of the PEF analysis reveal that the HS with the AWHP under investigation can be characterized as the most efficient system. [ABSTRACT FROM AUTHOR]

Heat pump water heaters can increase the energy efficiency in sanitary hot water production, which is a relevant share of the final energy consumption in multiresidential and tertiary buildings. Refrigerants for these heat pumps are changing due to the F-Gas Regulation which bans high-GWP fluids. While CO 2 is an established solution, propane is a promising low-GWP alternative for heat pump water heaters serving large users in the tertiary sector, where refrigerant charge limits (due to propane's flammability) can be bypassed by installing the heat pump outdoors. Here, the components of a CO 2 and a propane air-water heat pump systems of 40 kW are sized and their COPs are compared in different climates; then, the two heat pumps are coupled to a storage tank and a user demand profile (hospital and school). For three different locations, tank size necessary to maintain users' comfort and seasonal performance factor are evaluated through simulation. [ABSTRACT FROM AUTHOR]

Lower GWP refrigerants are essential to mitigate the impact of refrigeration systems on climate change. HFO/HFC mixtures are currently considered to replace HFCs in refrigeration and air conditioning systems. The aim of this paper is to present the main operating and performance differences between R513A (GWP of 573) and R134a (GWP of 1300), the most used refrigerants for medium evaporation temperature refrigeration systems and mobile air conditioners. To perform the experimental comparison, 36 tests are carried out with each refrigerant at evaporating temperatures between −15 and 12.5°C and condensing temperatures between 25 and 35°C. The conclusion of the experimental comparison is that R513A can substitute R134a with only a thermostatic expansion valve adjustment, achieving better performance and higher cooling capacity. The discharge temperature of R513A is always lower than that of R134a. [ABSTRACT FROM AUTHOR]

CO 2 transcritical refrigeration cycles require optimization to reach the performance of conventional solutions at high ambient temperatures. Theoretical studies demonstrated that the combination of a transcritical cycle with a mechanical subcooling cycle improves its performance; however, any experimentation with CO 2 has been found. This work presents the energy improvements of the use of a mechanical subcooling cycle in combination with a CO 2 transcritical refrigeration plant, experimentally. It tested the combination of a R1234yf single-stage refrigeration cycle with a semihermetic compressor for the mechanical subcooling cycle, with a single-stage CO 2 transcritical refrigeration plant with a semihermetic compressor. The combination is evaluated at two evaporating levels of the CO 2 cycle (0 and −10 °C) and three heat rejection temperatures (24, 30 and 40 °C). The optimum operating conditions and capacity and COP improvements are analysed with maximum increments on capacity of 55.7% and 30.3% on COP. [ABSTRACT FROM AUTHOR]

This paper is devoted to the evaluation of the use of low-GWP refrigerants in marine provision plants for cruise ships. We present the state of the art of current refrigeration plants, and we identify ammonia (NH 3 ), carbon dioxide (CO 2 ), and the HFOs R1234yf and R1234ze(E) as the most promising low-GWP refrigerants adequate for the marine refrigeration systems considered in the paper. Single-stage, two-stage and cascade plant configurations are examined, and the performances of the different alternatives are evaluated through simulations. The results are analyzed, and the performances are compared with those of the current systems with R407f: in the comparisons we consider COP, volumetric capacity, safety and environmental impact. We conclude that switching from current technologies to systems using low-GWP refrigerants entails a worsening of the performances in at least one of the areas considered. Moreover, we observe that the reduction of the GWP value of the refrigerants is not an effective strategy to diminish the total environmental impact of the refrigeration systems considered. [ABSTRACT FROM AUTHOR]

Efforts to increase energy efficiency of refrigerators shall directly reduce energy consumption in residential buildings. Incorporating phase change materials (PCM) is a new approach to improve the performance of refrigerators. In this study, we have tested four different PCMs in two different refrigerator models. Compressor on/off time was optimized and better energy efficiency was achieved. Increasing condenser surface area by 20% enhanced the PCM effect. The use of only 0.95 kg of PCM has resulted in a 9.4% energy saving. Economic analyses show that using PCMs in household refrigerators is clearly a cost effective method that saves energy and reduces harmful emissions. [ABSTRACT FROM AUTHOR]

In this work the possibilities of enhancing the energy performance of CO 2 transcritical refrigeration systems using a dedicated mechanical subcooling cycle are analysed theoretically. Using simplified models of the cycles, the modification of the optimum operating conditions of the CO 2 transcritical cycle by the use of the mechanical subcooling are analysed and discussed. Next, for the optimum conditions, the possibilities of improving the energy performance of the transcritical cycle with the mechanical subcooling are evaluated for three evaporating levels (5, −5 and −30 °C) for environment temperatures from 20 to 35 °C using propane as refrigerant for the subcooling cycle. It has been observed that the cycle combination will allow increasing the COP up to a maximum of 20% and the cooling capacity up to a maximum of 28.8%, being both increments higher at high evaporating levels. Furthermore, the results indicate that this cycle is more convenient for environment temperatures above 25 °C. Finally, the results using different refrigerants for the mechanical subcooling cycle are presented, where no important differences are observed. [ABSTRACT FROM AUTHOR]

This work presents an experimental analysis of a non-flammable R1234ze(E)/R134a mixture (R450A) as R134a drop-in replacement. While R134a has a high GWP value (1430), the R450A GWP is only 547. The experimental tests are carried out in a vapour compression plant equipped with a variable-speed compressor. The replacement suitability has been studied combining different operating conditions: evaporation temperature, condensation temperature and the use of an internal heat exchanger (IHX). The drop-in cooling capacity of R450A compared with R134a is 6% lower as average. R450A COP is even higher to those resulting with R134a (approximately 1%). The discharge temperature of R450A is lower than that of R134a, 2K as average. The IHX has a similar positive influence on the energy performance of both fluids. In conclusion, R450A can be considered as a good candidate to replace R134a. [ABSTRACT FROM AUTHOR]

R1234yf and R1234ze(E) have been proposed as alternatives for R134a in order to work with low GWP refrigerants, but this replacement results generally in a decrease of the performance. For this reason, it is interesting to explore ways to improve the system performance using these refrigerants. In this paper, a comparative study in terms of energy performance of different single stage vapour compression configurations using R1234yf and R1234ze(E) as working fluids has been carried out. The most efficient configuration is the one which uses an expander or an ejector as expansion device. On the other hand, using an internal heat exchanger in a cycle which replaces the expansion valve by an expander or an ejector could produce a detrimental effect on the COP. However, for all the configurations the introduction of an internal heat exchanger produces a significant increment on the cooling capacity. [ABSTRACT FROM AUTHOR]

This study proposes a new subcooling method for vapor compression refrigeration cycle based on expansion power recovery. In a main refrigeration cycle, expander output power is employed to drive a compressor of the auxiliary subcooling cycle, and refrigerant at the outlet of condenser is subcooled by the evaporative cooler, which makes the hybrid system get much higher COP. Various refrigerants, including R12, R134a, R22, R32, R404A, R41, R507A, R717, and R744, are considered. Thermodynamic analysis is made to discuss the effects of operation parameters (expander efficiency and inlet temperature of cooling water) on the system performance. Results show that the proposed hybrid vapor compression refrigeration system achieves much higher COP than the conventional vapor compression refrigeration system, conventional mechanical subcooling system and conventional expansion power recovery system, with maximum COP increments 67.76%, 19.27% and 17.73%, respectively when R744 works as the refrigerant in the main refrigeration cycle. It is most beneficial for R12 and R717 in the auxiliary subcooling cycle and R744, R404A and R507A in the main refrigeration cycle. [ABSTRACT FROM AUTHOR]

Abstract: Most of the existing prototype devices for magnetic refrigeration are based on a thermodynamic cycle with an active magnetic regenerator (AMR) that operates as a Brayton-type regenerative magnetic refrigeration cycle. However, there are several other cycles that may potentially influence not only the efficiency, but also the cost, compactness and simplicity of magnetocaloric devices. In this article we discuss the possibility of introducing new thermodynamic cycles. This is supported by information about, and a comparison of, the corresponding magnetic field sources. We present the results of numerical analyses and compare the characteristics of different thermodynamic cycles under different operating conditions and for different magnetic field intensities. Guidelines for future work on new magnetic thermodynamic cycles are presented. [Copyright &y& Elsevier]

Abstract: Expanders have been shown to improve the energy efficiencies of refrigeration systems. The current technology is also adequate to manufacture and integrate expanders to practical air-conditioners. In this paper, an economic analysis of the installation of expanders on to existing vapor compression cooling systems, particularly medium scale air-conditioners, is presented. Various refrigerants, including the established and the newly proposed varieties, are considered. From the investigations, it was found that when the expander efficiency is 50%, the payback periods of most conventional systems are below 3 years in high temperature countries with high electricity tariffs and are above 5 years in other countries. Expanders are especially attractive for the transcritical CO2 and the R404A systems. The payback periods are shorter for systems with highly efficient expanders, high cooling loads, high ambient temperatures and for low refrigerating temperature applications. [Copyright &y& Elsevier]

Abstract: In this paper, numerical studies on size parameters has been conducted to improve the performance of a twin-type rolling piston compressor, which has two cylinders called upper and lower cylinders with phase difference of 180°. In order to verify the computational reliability, the simulated results were compared with experimental ones. Sensitivity analysis of each parameter has been undertaken to investigate the influence of the parameters on compressor performance. Especially, size optimization has been studied to find an optimal combination of size parameters based on the sensitivity analysis of each parameter at the given operational condition and working volume. It was demonstrated that the maximum limits on the valve lift (ymax ) and the suction port diameter (D_sp) showed the highest sensitivity to the compressor performance and optimum design condition, which corresponded to an Energy Efficiency Ratio (EER) that is 2.6% higher compared to the reference condition. [Copyright &y& Elsevier]

Abstract: The paper provides results that show the impact of charge level on capacity and efficiency for several units tested in the laboratory. To evaluate the performance, capacity ratio and COP ratio were determined from measurements at various refrigerant charge levels and operating conditions. For all systems considered in this study, a refrigerant charge reduction of 25% led to an average energy efficiency reduction of about 15% and capacity degradation of about 20%. To evaluate the economic value of charge detection and correction, Seasonal Energy Efficiency Ratio (SEER) and annual cost of electricity were determined for some case studies based on the tested units. The results imply that charging inaccuracies could cause significant decreases in SEER, leading to increases in the operating costs. When the refrigerant was charged to 75% of design, the SEER value decreased by 16% and annual operating cost was increased by US$ 100 per ton of capacity. [Copyright &y& Elsevier]