Refrigeration Plant Research Articles

كفاءة الطاقة لأنظمة التكييف التقليدية في ظل تغير المناخ

The energy used in a country's economy is very important to its development. Over the years, the electricity and ventilation consumption of buildings have increased. People's concerns about the quality of their indoor environment are also increasing. Most buildings have air conditioning and ventilation systems that are designed to provide an environment that’s comfortable and healthy for the occupants. This is done through the use of ventilation. In addition to improving the indoor air quality, it can also help prevent people from experiencing discomfort. Studies have shown that about 60% of office buildings' energy consumption is attributed to the use of air conditioning systems. These systems provide cool air to the spaces while keeping the temperature controlled. A VAV system can meet the health criterion and the IAQ by supplying enough fresh air to meet national standards. A conventional AC system requires a refrigeration plant and a network of pipes to deliver cold water to the spaces. Since air-cooled chiller systems have a flexible design, they are commonly used in commercial buildings. They can provide a cooling effect that's significantly higher than that of water-cooled units. Compared to water cooling systems, air-cooled units are more energy-efficient. This is because the head pressure control of the system ensures that the pressure is kept high. The use of air conditioning has been one of the biggest sources of electrical energy consumption worldwide. It has contributed over 10% of the total energy produced, and it contributes to the harmful effects of climate change. Climate change is a growing concern that will require the production and use of more air conditioning units. This has necessitated the development of a comprehensive research to address this issue.

Alternative CO2-based blends for transcritical refrigeration systems

The extensive use of CO2 in commercial refrigeration system has grown in the last two decade thanks to the development of new components and configurations that allows working in transcritical conditions efficiently. However, using these arrangements increases the cost and complexity of the refrigerating plant, making it challenging to implement them in medium or low-capacity systems. As an alternative, CO2-based binary mixtures report attractive improvements that allow for enhancing the COP of the system by minimising its complexity and maintaining the safety and environmental conditions of CO2. This manuscript analyses five binary mixtures of CO2 with the refrigerants R32, R152a, R1234yf, R1234ze(E) and R1270, determining the optimal mixture composition for maximising the COP of a CO2 transcritical refrigeration plant in a wide range of environmental temperatures (0 to 40°C). Fixing the operating conditions for a medium-temperature application, the binary mixtures of CO2/R32 (81/19% in mass) and CO2/R1270 (92.5/7.5% in mass) reported the best COP enhancements results with increments up to +21.4% and +8.7%, respectively, at high environmental temperatures.

Application of Natural Refrigerants in Refrigeration Plants

Application of Natural Refrigerants in Refrigeration Plants

Natural refrigerants are favored by the future

BACKGROUND: Reducing the harmful impact on the environment is a promising way to the development of low-temperature technology. According to the amendment to the Montreal Agreement, approved by the Russian Federation, the use of hydrofluorocarbons should be reduced by 85% by 2036.
 AIMS: To justify the use of hydrocarbons as refrigerants in terms of their effectiveness.
 MATERIALS AND METHODS: Here, we have studied the losses of refrigeration plants at different temperature levels (refrigerant boiling points of 25 С, 18 С, and 13 С), while working with the refrigerants R134a, R404A, R1270, and R290 using the entropy-statistical method of thermodynamic analysis.
 RESULTS: Experimental results revealed that the natural refrigerants, R1270 and R290 have higher efficiency than the conventional refrigerants R134a and R404A. The values of the cooling coefficient under adiabatic compression are higher by 16.28%, 1.81%, and 1.14% compared to R404A, R1270, and R290, respectively, for installation with a boiling point of 13 C. Similarly, for installation with a boiling point of 18 C, these values are higher by 16.84%, 1.13%, and 0.58% compared to R404A, R1270, and R290, respectively. Furthermore, for installation with a boiling point of 25 C, the values of the cooling coefficient under adiabatic compression are higher by 18.53%, 0.8%, and 0.43% compared to R404A, R1270, and R290, respectively.
 In addition, the degree of thermodynamic perfection for R290 is higher by 27.99%, 19.2%, and 14.79% compared to R134a, R404A, and R1270, respectively, for a boiling point of 13 C. Similarly, for R290 and a boiling point of 18 C, it is higher by 21.25%, 14.71%, and 9.9% compared to R134a, R404A, and R1270, respectively.Furthermore, for R290 and a boiling point of 25 C, it is higher by 27.94%, 11.44%, and 3.61% compared to R134a, R404A, and R1270, respectively.
 In this study, data on the production of hydrocarbon refrigerants, in particular R1270 and R290, under the Russian Federation are presented. Moreover, quality indicators and the main areas of application for the same are provided here.
 CONCLUSIONS: The results of the analysis showed the prospects of using natural refrigerants (R1270 and R290) and allowed us to assess different ways to improve the refrigeration plants.

Alternative blends of CO2 for transcritical refrigeration systems. Experimental approach and energy analysis

As a natural refrigerant, Carbon Dioxide (CO2) has been extended in almost all refrigeration fields due to its environmental friendliness, high availability, and high technological development in the main components of the cycle. However, despite the benefits, CO2 is limited to high-capacity applications due to the cost of components and the complex cycle arrangements to overcome the low coefficient of performance (COP) at high ambient temperatures. A simple but effective method to solve this issue involves mixing CO2 with other refrigerants obtaining a new refrigerant mixture with higher critical points, lower working pressures and low global warming potential (GWP). Depending on the mixture percentage, the mixture flammability can be suppressed, and the performance of the refrigeration plant can be increased.Building on this, this work determines theoretically different CO2­based zeotropic blends as an alternative to pure CO2 with the restrictions of non-flammability, GWP below 150 and higher COP than pure CO2. The results suggest two blends of CO2/R1270 and CO2/R32 that have been prepared and energetically tested in a vertical display cooler using pure CO2 as a reference. The results revealed that CO2-blends reduce energy consumption by up to 17.2 % at the ambient temperature of 25 °C and up to 12.2 % at 30 °C. Moreover, the results with CO2-blends were closest to those obtained with pure R1270 and better than R134a under the same operating conditions.

Technical solutions for the recycling of thermal energy and improving the environmental efficiency of engineering systems

Objective. The article proposes design solutions aimed at the comprehensive modernization of the cold supply system of the ice palace "Puck" in Sochi, to reduce its impact on the environment.Method. A water reuse system has been created and a technology has been developed for using low-temperature heat that is released during the operation of the refrigeration machine.Result. A refrigeration plant has been developed that allows you to utilize, accumulate and direct the heat of condensation for the secondary use of thermal energy by other engineering systems at the facility, thereby reducing heat and greenhouse gas emissions into the Earth's atmosphere and increasing the technological capabilities of cooling.Conclusion. The proposed methods make it possible to make the necessary calculations and select equipment for the implementation of the developed systems in ice arenas.

Low-cost rapid-installation data monitoring and analysis system for operating status of refrigeration plant

For refrigeration plants without building automation systems (BAS), a low-cost rapid-installation data monitoring and analysis system has been developed that can be installed without affecting the normal operation of the refrigeration system. Typical installation time is two days, and the hardware and installation cost for a canonical set of systems is approximately 5600 Chinese Yuan (780 US Dollar). Temperature data were collected from low-cost wireless measurement points on the equipment and piping of the refrigeration plant and then stored, pre-processed, and analyzed to extract parameters related to the operating status of the plant. This paper describes the methods and rules for pre-processing the data and the methods for identifyingAuthor Statement the system operating state using algorithms, including algebraic operations, statistical parameter identification based on empirical rules, and curve similarity identification. The low-cost, rapid-installation data monitoring and analysis system was applied to several refrigeration plants, and the relevant data were analyzed. The rapid data monitoring and analysis system successfully calculated and identified the energy consumption, Coefficient of Performance, Water Transport Factor, ON/OFF status, and other operating status and energy efficiency-related parameters of each item of refrigeration equipment. It also identified fault information, such as frequent start-stop and water bypass, which are common in refrigeration plants. The system costs 10% less than a traditional monitoring system. It is expected to help refrigeration plants without BAS to take the first step in establishing a monitoring system, allowing operations and maintenance personnel to better understand the operating status of the refrigeration system from a remote location, discover faults and energy-consuming behaviors in a timely manner, and improve the overall energy efficiency of the system.

Mutual impact of thermal radiations and temperature dependent thermal conductivity on non-Newtonian multiple flow regimes

The transfer of thermal energy is a specialized discipline of thermal engineering and hence own practical applications in an industrial thermal systems like refineries, air-conditioning plants, automotive engines, power plants, jet engines, refrigeration, food processing, and chemical processing plants to mention just a few. Owning such importance we have reported the collective impact of thermal radiations and temperature-dependent thermal conductivity for heat transfer in stagnation point magnetized Casson fluid flow field. The thermal flow regime of Casson fluid is manifested with a viscous dissipation effect as well. The flow equations are tackled numerically by the use of the shooting method. The outcomes are debated comparatively by considering various flow regimes namely (I) Thermal flow regime with thermal radiations (II) Thermal flow regime without thermal radiations (III) Heat flow with heat generation and (IV) Heat flow in the absence of heat generation. We believe that the present thermal comparative analysis will be helpful for the preceding studies which own thermal engineering standpoints for the transfer of thermal energy by means of fluid flow.

Energy comparison based on experimental results of a cascade refrigeration system pairing R744 with R134a, R1234ze(E) and the natural refrigerants R290, R1270, R600a

Refrigeration architectures for low-temperature applications are gaining interest in the Industrial, Commercial and Health fields. One of the most classical architectures is cascade systems, where two mechanical single vapor compression cycles are thermally paired by the cascade heat exchanger (HXcc). The HXcc, acts as condenser for the low temperature cycle and as evaporator for the high temperature cycle. Each cycle is charged with a different refrigerant adapted to the operating conditions. New environmental rules make necessary to find proper refrigerant pairs to get refrigeration plants with high energy efficiency together with environmentally friendly fluids. This experimental work compares the energy performance of a cascade refrigeration system working with the pair R134a/R744 against four alternative refrigerant pairs: R290/R744, R1270/R744, R600a/R744CO2 and R1234ze(E). Laboratory tests were conducted at three heat rejection temperatures: 20, 30 and 40°C, maintaining a fixed low-temperature heat source level (−20°C). The energy analysis shows that R290/R744 and R1270/R744 improve the cooling capacity at low heat sink temperatures, and the pair R290/R744 improves the energy performance at low temperatures. The environmental analysis shows that all the refrigerant pairs achieve a reduction in CO2eq emissions.

Fabrication and characterization of RF magnetron sputtered composite MoS2 and ZrN coatings on Ti3SiC2 max phase for space applications

The lubrication effect of solid-based materials has been recognized for centuries, but their use as lubricants dates back to only about 50 years. Solid lubricants are used in applications where parts operate under severe operating conditions such as extreme temperatures and very high vacuum. Solid lubricants replace liquid based lubricants for operation under extreme environmental conditions that are beyond the capability of a liquid-based lubricant such as high or very high vacuum, high and cryogenic temperatures, radiation, corrosive gases, and fretting wear. Applications such as space mechanisms, satellites, space vehicles, turbopumps, nuclear reactors, refrigeration plants, etc are examples of such operating conditions. In this research, nano scale composite coatings of MoS2with varied proportions of ZrN (5%, 10% and 20%) were deposited on Ti3SiC2 Max phase substrate using Physical Vapour Deposition (PVD). The PVD technique used was the RF magnetron sputtering process. Material characterization was carried out using Field Emission Scanning Electron Microscope (FESEM) Spectroscopy and Energy Dispersive X-Ray Spectroscopy (EDS). Addition of ZrNis observed to reduce the porosity of the self-lubricating MoS2 coating.

Analytical modelling of food storage cooling with solar ammonia-water absorption system, powered by parabolic trough collectors. Method

The study presents a new analytical model capable to reveal the thermal behaviour of all the components of the solar ammonia-water absorption system, powered by parabolic trough collectors, serving different types of food storages: refrigeration chamber, refrigerated food storage, freezing chamber and frozen food storage. The heat inputs, that determine the total cooling load, for each food storage spaces consist of: heat gains through walls, heat gains through ventilation (fresh air), heat that must be dissipated from the stored products (technological cooling load required to cool down the products) and heat gains through operation. The influence of the number of solar parabolic trough collectors and of the storage tank size on different parameters of the refrigeration plant are investigated under low and high storage temperatures.•Food cooling with solar absorption refrigeration system.•Hourly based variation of NH3-H2O solar absorption system performances.•Long term simulation of solar absorption cooling for refrigeration and cooling.

Safe Optimization of an Industrial Refrigeration Process Using an Adaptive and Explorative Framework

Real-time optimization can play a key role for improving the performance of industrial processes, but it becomes challenging in cases where the process characteristics are uncertain, particularly when the uncertain characteristics impact safety-related constraints. In this study, we present an adaptive and explorative real-time optimization framework that can effectively learn the characteristics of an industrial refrigeration plant through externally driven changes in cooling load targets and through self-exploration. We utilize Gaussian processes (GP) to facilitate learning unknown compressor characteristics of the plant and we leverage the uncertainty quantification of the GP to drive exploration using a weighted sum term in the objective function for real-time optimization. Furthermore, the uncertainty information is used to probabilistically enforce the maximum total power consumption constraint for the compressors with high confidence at all times. Our simulated experiments demonstrate that the proposed approach safely enhances the energy efficiency of the refrigeration process, closely approximating the performance of a best-case solution that has complete information about the plant performance characteristics. We also demonstrate the impact of varying the exploration term in the solution and how the uncertainty of plant behaviour is reduced even in the absence of cooling load target changes.

Modern refrigeration solutions for maritime sector and marine refrigeration transport

New coming environmental regulations from International Maritime Organization put each involved actor from ship manager, ship owner to cargo owner into a hard situation for a short time period to change the data collection process, to determine gups considering operating needs, to create an improvement plan according to specific requirements, needs, and goals. It is one more signal, in order to reach the sustainability goal, the industry digitalization process, and available efficient and effective use of technologies should be pushed forward. From cold chain digitalization, refrigeration system maintenance, and retrofitting processes, in particular, data science, process science, and data mining can be used. Refrigeration system retrofitting process modelling is presented by data mining technology. A lack of knowledge and investment in cold chain best practices and infrastructure lead to projects failing. Efficient, controlled, and smart Refrigeration is a challenge for the sustainable refrigeration sector. The global reefer transport market will expand up to 6% from 2020 to 2027 and it is vital for countries involved in military operations as well. The results of energy, exergy, and exergoeconomic analysis of different solutions intended for marine refrigeration transport, the cascade refrigeration system with R717-R744 refrigerants is presented. It was found that the optimum condensation temperature for the refrigerant of the high-temperature circuit is 40 °C, while the boiling temperature of the lower-temperature circuit is -50 °C. The temperature mode can be considered optimal ceteris paribus. The article provides an analysis of ejector refrigeration systems that can be used to improve the energy performance of marine refrigeration plants. It is a recommended issue to consider not only industrial requests but policies, and regulations in the force and in projects development status that can change an organization’s vision and aims of a strategic packet in own turn it can be affected a project budget change for labs, research institutions, shipyards.

Cold energy storage as a solution for year-round renewable artificial ground freezing: Case study of the Giant Mine Remediation Project

In cold regions, passive thermosyphons are often employed in permafrost protection and artificial ground freezing (AGF) applications. While passive thermosyphons utilize available cold wind during cold seasons, energy-intensive refrigeration plants are sometimes needed to run thermosyphons in warmer seasons. In this study, a novel cold energy storage (CES) concept is proposed to operate thermosyphons year-round using renewable energy resources. The proposed system is based on additional energy storage ground coupled thermosyphons (ST) and heat extraction pipes (HEP). In cold seasons, the STs store wind cold energy, which is then transferred in warmer seasons using HEPs to the site of interest. The system is mathematically demonstrated using numerical models validated in our previous work against field data from the Giant Mine Remediation Project (GMRP). The results reveal that the proposed system enhances the heat extraction capacity of primary thermosyphons (located in the site of interest) by more than 15%. Further, the ground freezing process is achieved one year faster. Overall, this study presents the foundation of an innovative concept that can help run thermosyphons using renewable resources in cold regions, especially at the GMRP.

Using a Mine Dewatering System to Increase Cooling Capacity and Energy Recovery of Underground Refrigeration Plant: A Case Study

Heat stress in deep hot mines is a factor that often determines the possibility of technical mining of natural resources. One of the solutions enabling miners to work in such mines is air cooling. Cooling systems vary, and their selection depends on the type of mine and the mining methods used. Limited air cooling capabilities exist in electric-powered coal mines. The main solution for air cooling is based on movable spot air coolers. Such systems commonly use surface or underground refrigeration plants. An underground refrigeration plant (URP) equipped with compressor chillers does not achieve more than 2.5–3.0 MW of cooling capacity due to the limited heat rejection capacity of return air streams in a typical coal mine. The method discussed in this paper, using mine water to discharge waste heat from the underground refrigeration plant, provides a measurable benefit for optimizing the mine air cooling system. The main purpose of this research is to study the feasibility and effect of water diversion from the actual mine drainage system to the underground refrigeration plant. The water drainage system in an underground mine is called the dewatering system of the mine. The heated water in the condensers of the chillers is directed back to the mine’s central dewatering system. The recovery from water discharged to the surface contributes to optimising energy consumption for a mine air cooling and the sustainable discharge of wastewater. In addition, using the total water flow from the mine dewatering system to reject heat in compressor chillers, compared with the traditional solution, can improve the cooling capacity of URP. These findings may provide beneficial guidance for practical applications in deep hot mines with small natural water inflow.

Statistical-mathematical procedure to determine the cooling distribution of a chiller plant

This paper presents a procedure to determine the cooling capacity distribution of the chillers composing a chiller plant using a statistical analysis of the building cooling demand. The mathematical-statistical procedure uses tools such as frequency histograms, box-and-whisker plots, stem-and-leaf plots, the generalized least squares method, and finally an iterative factorial procedure to generate from the processed information. Besides the manufacturer’s data, all possible chiller plant combinations considering design constraints. The procedure was verified in a hotel facility. Eight thermal demand profiles were simulated. Statistical analysis yielded a range of individual capacities between 100–353 kW. The procedure generated 189 refrigeration plant combinations between 2 to 5 chillers, with a safety factor (SF) between 10%–20%. The highest number of combinations considered plants comprising three and four chillers, reaching 50 and 70 chiller plant options, respectively.

Performance assessment of an experimental CO[formula omitted] transcritical refrigeration plant working with a thermoelectric subcooler in combination with an internal heat exchanger

Regulations in the refrigeration sector are forcing the transition to low global warming potential fluids such as carbon dioxide in order to decrease direct greenhouse gases emissions. Several technologies have arisen over the past years to compensate the low performance of the transcritical carbon dioxide vapour compression cycle at high ambient temperatures. For low–medium power units, the inclusion of a thermoelectric subcooler or an internal heat exchanger have been proven as effective solutions for enhancing the coefficient of performance. However, the combination of a thermoelectric subcooler and an internal heat exchanger working simultaneously is yet to be explored theoretically or experimentally. This work presents, for the first time, an experimental transcritical carbon dioxide refrigeration facility that works simultaneously with a thermoelectric subcooler and with an internal heat exchanger in order to boost the cooling capacity and coefficient of performance of the refrigeration system. The experimental tests report improvements at optimum working conditions of 22.4% in the coefficient of performance and an enhancement in the cooling capacity of 22.5%. The 22.4% increase in coefficient of performance would result in a decrease of energy consumption along a reduction of the greenhouse gases emissions. The proposed combination of a thermoelectric subcooler and an internal heat exchanger outperforms each of the technologies on their own and presents itself as a great controllable solution to boost the performance and reduce the greenhouse gasses emissions of transcritical carbon dioxide refrigeration cycles.

THEORETICAL FOUNDATIONS FOR ASSESSING THE RELIABILITY OF REFRIGERATION MACHINE EQUIPMENT ON THE BASIS OF THE NEURO-FUZZY METHOD FOR IDENTIFYING THEIR STATE

In order to design modern smart enterprises such as industrial refrigerators with a high level of reliability of their operation while maintaining the proper quality of cooling, freezing and storage of various types of products, the article analyzes the current level of safety and time to failure of equipment for refrigeration equipment for refrigeration of industrial refrigerators and system analysis of the technical system of equipment of refrigeration machines to determine the requirements for the system for assessing the level of safety of equipment of enterprises – industrial refrigerators. A methodology has been developed for analyzing the state of the equipment of refrigeration machines of industrial refrigerators, as an object of malfunctions. Models of possible malfunctions are constructed with the identification of relationships between technological parameters of operability, reliability and emergency situations. A situational model of the state of the refrigeration machine as a source of malfunctions has been developed, which is distinguished by the ability to identify relationships between parameters, events – the causes of emergencies and the state of refrigeration supply of refrigeration chambers. Knowledge about fuzzy situations is structured and fuzzy reliability models are constructed that characterize the state of the equipment. The practical value of the study lies in the development of a methodology for assessing the reliability and durability of refrigeration equipment based on a neuron-fuzzy identification method, creating a knowledge base and a system for managing the refrigeration plant performance process. Thus, it is possible to manage systems for predicting and monitoring emergency situations in systems for operational monitoring of technological processes for freezing the results of eating.

Experimental validation and development of an advanced computational model of a transcritical carbon dioxide vapour compression cycle with a thermoelectric subcooling system

The inclusion of a thermoelectric subcooler as an alternative to increment the performance of a vapour compression cycle has been proved promising when properly designed and operated for low-medium power units. In this work, a computational model that simulates the behaviour of a carbon dioxide transcritical vapour compression cycle in conjunction with a thermoelectric subcooler system is presented. The computational tool is coded in Matlab and uses Refprop V9.1 to calculate the properties of the refrigerant at each point of the refrigeration cycle. Working conditions, effect of the heat exchangers of the subcooling system, temperature dependent thermoelectric properties, thermal contact resistances and the four thermoelectric effects are taken into account to increment its accuracy. The model has been validated using experimental data to prove the reliability and accuracy of the results obtained and shows deviations between the ± 7% for the most relevant outputs. Using the validated computational tool a 13.6 % COP improvement is predicted when optimizing the total number of thermoelectric modules of the subcooling system. The computational experimentally validated tool is properly fit to aid in the design and operation of thermoelectric subcooling systems, being able to predict the optimal configuration and operation settings for the whole refrigeration plant. • Transcritical CO2 vapour compression cycle with thermoelectric subcooling. • Advanced computational model to predict optimal operation settings of the system. • Validation of the model using experimental data with deviations between the ±7%. • Computational optimization of the number of modules in a thermoelectric subcooler. • 13.6% COP improvement using the hybrid solution and optimum number of modules.

Numerical Model of an Evaporative Condenser for the Food Refrigeration Industry

Evaporative condensers play a key role in refrigeration plants for industrial applications, as they are needed to dispose of the thermal and electric power required by the process. Modelling them as lumped capacitance systems is very expedient when trying to simulate e. g. the steady-state and dynamic behaviour of the whole refrigeration plant, but at the expenses of loss of information and often oversimplifying assumptions. This paper analyses two models for heat and mass transfer in cooling equipment, Poppe’s and its earlier, simpler version, Merkel’s. The two approaches are applied to describe the transport phenomena in an evaporative condenser and the predicted cooling power compared to the data declared by the manufacturer under certain operating conditions. It is demonstrated that predictions are accurate within less than 10%.