Commercial Refrigeration Systems Research Articles

Investigation of environmentally friendly new generation refrigerant R471A instead of R404A in low and medium temperature commercial refrigeration system

Hydrofluorocarbon (HFC) refrigerants (such as R134a and R404A), which are widely used in commercial refrigeration systems, contribute greatly to global warming. Because the global warming potential (GWP) values of HFC refrigerants are high. With increasing concerns about the environment (global warming, climate change, etc.) various legal regulations have been made to limit or phase out the use of refrigerants with high GWP values. To use the R471A refrigerant developed by Honeywell in 2022 as an environmentally friendly new-generation refrigerant in the commercial refrigeration system, the performance of the R471A refrigerant should be comprehensively evaluated. In this study, energy, exergy, and environmental analyses of using R471A refrigerant instead of R404A in low and medium-temperature commercial refrigeration systems were carried out and presented. Evaporator temperatures of − 30 °C, − 25 °C, − 20 °C, − 15 °C and − 10 °C and condenser temperatures of 30 °C, 40 °C, and 50 °C were selected to represent low and medium cooling temperatures and hot and cold country seasons. It was seen that R471A presents a lower mass flow rate (between 67 and 71%) and cooling capacity (between 61 and 68%) than R404A however has higher COP (between 6% and 14%) and R404A has exergy efficiency value of 6–14% lower than R471A. Also, from an environmental point of view, R471A has better environmental results than R404A.

Performance Evaluation Of Refrigerated Pickup Truck Using Hydrocarbon Refrigerants

HFCs group refrigerants are still widely used in refrigerated pickup trucks. This refrigerant is a synthetic chemical and has a high potential to cause global warming and damage the ozone layer. This study aims to obtain performance data from the use of HCs as refrigerant in refrigerated pickup trucks. The research was conducted experimentally on a pickup truck with a 1500 cc engine capacity. The size of the refrigerated room is 2300 mm long, 1500 mm wide and 1400 mm high. A commercial refrigeration system (C-250e MAX, Thermo King Europe, Belgium). The size of the evaporator, which consists of a cold air supply fan and an intake fan, is 133 mm long, 985 mm wide and 525 mm high. The cooling capacity is 2770 W. The volumetric flow rate of cold air is 1100 m3/hr. The test started at 9 am and the temperature value in a gallon of water was measured for 120 minutes. The results showed that the optimal refrigerant filling was the use of R290 (35%) and R1270 (20%). The value of the coefficient of system performance obtained from the use of the two variations of HCs is 4. Thus, refrigerant HCs R290 and R1270 can replace refrigerant HFCs in refrigerated pickup trucks with refrigerant mass variations of R290 (35%) and R1270 (20%).

Demonstration of long-term cyclic sorption of ammonia in modified expanded graphite-calcium chloride composites for practical applications

The long-term viability of the ammonia‑calcium chloride (NH3−CaCl2) pair in commercial adsorption refrigeration systems faces challenges due to the disintegration of calcium chloride (CaCl2) during multiple ammonia sorption cycles. To address this issue, we conducted a comprehensive study, starting from lab-scale investigations to experiments with full-scale commercial refrigeration systems. We prepared three calcium chloride–expanded graphite (CaCl2:EG/4:1) composite samples (labelled B1, B2, and B3) with varying water content (20–45% by weight), and also used a conventional CaCl2-activated carbon-white cement composite (CaCl2:AC:WC/16:4:1, sample A). The composites were coated over fin tubes wrapped around with wire mesh for this purpose. These composites were tested for structural integrity over 300 continuous cycles in a customized constant-volume single fin-tube adsorption/desorption bed. While all samples initially exhibited similar sorption capacity ∆χof≈0.6−0.7kgNH3/kgCaCl2, sample A experienced a significant deterioration of approximately 60% in capacity within 300 cycles due to agglomeration and volumetric expansion. In contrast, the EG-based samples demonstrated remarkable stability, with B3 maintaining ∆χ≈0.57kgNH3/kgCaCl2 even after 800 cycles. We applied B3 in a 2 TR adsorption refrigerator that uses biomass as fuel to demonstrate <15% cooling power attenuation even after prolonged operation over 800 cycles in practical scenarios. We believe these engineering interventions are necessary to encourage the broader adoption of ammonia-based adsorption refrigeration systems, which are a sustainable choice due to their zero global warming and ozone depletion potentials.

Exergy, carbon footprint and cost lifecycle evaluation of cascade mechanical subcooling CO2 commercial refrigeration system in China

The concept of cascade mechanical subcooling is recommended to widen the application of natural working fluid CO2, improve the efficiency and reduce the carbon footprint of CO2 refrigeration system applied in commercial supermarket. Three potential configurations for CO2 system with integrated multi-stage dedicated mechanical subcooling (MS-DMS) are proposed as prospect solutions. Life cycle assessment is conducted from the viewpoint of exergy, carbon footprint and cost performance for the proposed refrigeration systems, and compared with baseline CO2 booster refrigeration system (BASE) and traditional R404A system. 8 representative cities located in diverse climatic zones across China are chosen as scenarios and discussed in detail. The results indicate the irreversible loss is efficiently reduced with the utilization of MS-DMS. The annual exergy efficiency of CO2 system integrated with triple-stage DMS (TS-DMS) is 11.92–18.48% higher than BASE. Life cycle climate performance (LCCP) is reduced by 6.87% when the TS-DMS is employed in Haikou in contrast to BASE from the perspective of carbon emissions. Additionally, the life cycle cost (LCC) is remarkably reduced by 6.8% compared with BASE. Consequently, MS-DMS CO2 systems are more suitable for the application in warm or hot regions in contrast to BASE due to its better emission reduction performance as well as lower life cycle cost.

Numerical Analysis of Using R449A Refrigerant Alternative to R404A in Cooling Systems: 3E-Analysis (Energetic, Exergetic, and Environmental)

The direct impact of refrigerants on the environment is largely dependent on the magnitude of global warming potential (GWP) values. In this regard, fluids with low GWP are very important for the environment. Commercial refrigeration accounts for about a third of the world's HFC use. R404A is a derived HFC near an azeotropic mixture. The refrigerant of R404A is widely used in commercial refrigeration systems, especially in supermarkets. As a result of the use of R404A in cooling systems with high GWP, both indirect and direct negative effects on the environment increase. In this study, the energy, exergy, and Life Cycle Climate Performance (LCCP) of R449A, which has a lower GWP value, which can be an alternative to R404A refrigerant, were investigated theoretically. Different evaporator temperatures (-30oC to -5oC) and a condenser temperature (30oC) were used in the analysis. According to the results obtained, while the mass flow rate of R449A is approximately 13% lower than that of R404A, its exergy efficiency is 5% higher. R449A was found to be approximately 5% lower than R404A in LCCP analysis.

The energy efficiency and environmental analysis of open-type commercial display cabinet with a multi-flow air curtain design

Open vertical display case refrigerators are often preferred as commercial refrigerators. This is because, despite their high energy consumption they have a higher marketing potential with the product display and offer easy access. Commercial refrigeration system accounts for half of the energy consumption in supermarkets. Air curtains of different designs are used in open vertical cabinets to reduce heat and mass transfer between the cooled air and the indoor environment. Hence, an experimental study was conducted to evaluate the multi-flow designed air curtain effects on the energy efficiencies of open display case-type commercial refrigerators. The experiments were conducted with ISO 23953:2005 standard in a controlled test room. During the trials, four different temperatures of air flowed to the refrigerator: +25 °C, +11 °C, +2°C, and 0 °C respectively through the air curtains. As a result of the experiments, a higher Coefficient of Performance COP value and lower Energy Efficiency Index (EEI) value were obtained with multi-flow air curtains. The multi-flow designed air curtain has nearly 40 % eliminated the air entrained from the outside to the indoor environment. It has ensured that the interior temperature values remain at the desired level. The second polyurethane body has reduced heat transfer through the surface by about 30 %, thereby reducing cooling load and energy consumption.

Development of a Heuristic Control Algorithm for Improving Energy Efficiency in Commercial Refrigerated Systems without Indoor Information

Despite the serious threat of global warming caused by carbon emissions, commercial refrigeration systems that generate cooling are unable to adjust their usage time. Therefore, it is essential to enhance the energy efficiency of refrigeration systems themselves. Recently developed refrigeration systems offer improved energy consumption efficiency as they utilize inverter-type outdoor units that can communicate with indoor units. However, traditional legacy refrigeration systems still suffer from poor energy efficiency because the existing indoor units cannot communicate with inverter-type outdoor units. Hence, this paper introduces a heuristic energy efficiency improvement algorithm for commercial refrigeration systems using legacy indoor units when an inverter-type outdoor unit is installed. In particular, to reduce the computational complexity of the process of selecting the optimal temperature difference and target low-pressure variables that can enhance energy efficiency, the algorithm employs the Monte Carlo method. Finally, the performance of the proposed heuristic energy efficiency improvement algorithm was evaluated in a laboratory environment to confirm its applicability.

Influence of subcooling in R-449A supermarket refrigeration system and screening of refrigerant mixtures for its energetic and environmental improvement

Current demands of the cooling sector are focused on using refrigerants with a low Global Warming Potential (GWP) and increasing energy efficiency in vapour compression installations. The main objectives of this paperwork arise from these needs, in which the use of subcooling in an R-449A commercial refrigeration system is evaluated. In addition, eco-friendly alternative refrigerants are proposed and studied. Firstly, the effect of an integrated type of subcooling is semi-empirically analysed with Engineering Equation Solver (EES). Then, the refrigeration system’s operation is simulated using low-GWP alternative refrigerants, R-454C and R-290, which have been scarcely studied in commercial refrigeration systems due to their safety classification. Moreover, new refrigerant mixtures are searched from the binary and ternary combination of pure refrigerants using the software REFPROP. The best refrigerant with safety classification A1, A2L, and A2/A3, for both medium temperature (MT) and low temperature (LT) systems is obtained from this search. After their determination, the supermarket’s operation is simulated with these refrigerants. Finally, an environmental assessment is performed. The highest energy efficiency is obtained with R-152a for the MT system and the R-290/R-1270 mixture for the LT system. However, the highest reduction of GHG emissions is achieved by R-290, with a reduction of 73.78 % with respect to the baseline system.

A Review of Sensing Technologies for New, Low Global Warming Potential (GWP), Flammable Refrigerants

Commercial refrigeration systems currently utilize refrigerants with global warming potential (GWP) values ranging from 1250 to 4000. The advent of low GWP alternatives (GWP &lt;150) is expected to significantly curtail direct emissions from this segment and greatly influence the ongoing electrification and decarbonization efforts. Most of the low GWP alternatives exhibit flammability risk and hence require robust sensing solutions for a reliable and safe operation of the equipment. This review article aims to provide an overview of different sensing mechanisms suitable for potential applications in systems employing flammable refrigerants, particularly those designated as A2L class. A summary of different A2L refrigerants and their properties is provided followed by a broad review of different classes of sensors, their working principle, transduction method, features, advantages, and limitations. Additionally, key performance characteristics of accuracy, selectivity, sensitivity, dynamic characteristic, and durability among other properties are discussed. Finally, areas of improvement and corresponding approaches are suggested for potential sensors in the successful adoption of A2L class refrigerants.

Flow boiling heat transfer coefficient and pressure drop of R448A inside various multiport tubes: An experimental investigation and correlation assessment

R448A, a safety class A1 a-zeotropic refrigerant blend with a GWP of 1390, is considered an efficient and environmentally friendly substitute for R404A in direct-expansion commercial refrigeration systems. Herein, we experimentally investigate the flow boiling heat transfer and pressure drop of R448A inside a multiport mini-channel tube. The experimental ranges of mass flux and heat flux are 100–500 kg/m2s and 3–15 kW/m2, respectively, and they cover the entire quality range at three different saturation temperatures of 3, 6, and 10°C. Three different test tubes are utilized in this study to evaluate the effect of tube geometry on the heat transfer, and their diameters range from 0.831 to 1.14 mm. The results show that mass flux has favorable effects on the heat transfer coefficient and pressure drop, while heat flux has a favorable effect on the heat transfer coefficient at low mass fluxes. As the saturation temperature decreases when the mass flux is high, the heat transfer coefficient and pressure drop increase. The tube with largest perimeter but the smallest hydraulic diameter has the highest heat transfer coefficient under the low mass flux condition. Heat transfer coefficient and pressure drop experimental data were compared with the models in literature, and the results of our statistical assessment indicate that the pure fluid model modified to account for the mixture effect produces the best results. Meanwhile, most pressure drop models produce reasonably good predictions. Additionally, a new correlation is proposed to predict the heat transfer coefficient in practical applications.

Experimental study and analysis of an air-cooled condenser with the fouling on the heat exchange surface for small-scale commercial refrigeration systems

The paper presents the results of a theoretical and experimental study aimed at improving the efficiency of commercial refrigeration systems and taking into account the external negative impact on heat transfer and aerodynamics of an air-cooled condenser. The issues of the impact of solid fouling on the outer heat transfer surface of the air-cooled condenser as a factor that worsens its energy efficiency and operational reliability have been studied. A small-scale commercial refrigeration machine has been used for carrying out the study. To create external real conditions in the experimental bench, a climatic chamber and a thermostatic chamber are provided. Three types of solid fouling have been used: dust, fluff, and sand. The fouling has been collected from real operating air-cooled condensers which are identical to the experimental heat exchanger. The experimental study has been carried out with a variable mass of fouling, which made it possible to simulate various real operating conditions for the air-cooled condenser. As a result of the experiment, it has been found that out of a set of fouling roadsides, the dust has the greatest negative impact on the characteristics of the refrigeration machine as a whole, and sand has the greatest negative effect on the internal characteristics of the air-cooled condenser. Recommendations are made to determine the moment of cleaning the surface of the air-cooled condenser based on energy-saving parameters. It is proposed to fix the moment of cleaning using computer software using the permissible air mass velocity as a key parameter and the refrigeration machine operation interval under this condition.

Next generation of ejector-supported R744 booster systems for commercial refrigeration at all climates

The pernicious effects of synthetic refrigerants on different environmental aspects leave natural refrigerants as the only alternative for vapour compressions systems. Among natural refrigerants, CO2 (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).

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.

A Data-Driven Approach Towards the Application of Reinforcement Learning Based HVAC Control

Refrigeration applications consume a significant share of total electricity demand, with a high indirect impact on global warming through greenhouse gas emissions. Modern technology can help reduce the high power consumption and optimize the cooling control. This paper presents a case study of machine-learning for controlling a commercial refrigeration system. In particular, an approach to reinforcement learning is implemented, trained and validated utilizing a model of a real chiller plant. The reinforcement-learning controller learns to operate the plant based on its interactions with the modeled environment. The validation demonstrates the functionality of the approach, saving around 7% of the energy demand of the reference control. Limitations of the approach were identified in the discretization of the real environment and further model-based simplifications and should be addressed in future research.

The Impact of Phase Changes of Imidazolium Based Ionic Liquids on the Solubility of Hydrofluorocarbons

Project EARTH (Environmentally Applied Research Toward Hydrofluorocarbons) is focused on developing sustainable processes for selectively separating refrigerant mixtures with high global warming potentials. The initial focus of the project is R-410A which is widely used in both commercial refrigeration systems and residential air conditioning. It is an azeotropic mixture containing 50 wt.% HFC-32 (CH2F2) and 50 wt.% HFC-125 (CHF2CF3). The separation approaches being investigated include membranes, porous media, and the use of ionic liquids as entrainers for extractive distillation.This poster will describe the work being conducted using ionic liquids and will specifically focus on the impact of phase changes of imidazolium based ionic liquids that are solid at room temperature on the solubility of HFC-32 and HFC-125. The poster will include an overview of how we use specialized equipment including a High-Pressure View Cell and Hiden Isochema IGA gravimetric microbalance to build a comprehensive understanding of these solubility differences.

Determination of defrost efficiency and energy efficiency index value using different defrost methods and refrigerants: An experimental study

In this study, open-type refrigeration cabinets were designed and manufactured using hot gas and electrical resistance defrost methods and R290, R449A and R404A refrigerants. The aim of this study is to determine the temperature increase of the products during the process, CO2 emission amount, defrost efficiency, and energy efficiency index (EEI) value with different defrost methods and refrigerants for commercial refrigeration systems. The increase in package temperatures during the defrosting process was determined as 1.33 °C in the electrical method. The results showed that the hot gas method was 7.15% more efficient in terms of defrosting efficiency. The EEI value was calculated as 78.76 with the use of R290 in the hot gas method and the energy class was determined as F and the hot gas emit 5.9% less CO2 than in the resistance experiments. In the hot gas defrost method, it was seen that 20.3% less energy was consumed compared to the total consumption. It was observed that R290 refrigerant and the hot gas defrost method were the most suitable for commercial systems in terms of defrosting process losses, total energy consumption, and temperature rise of the cooled product during defrosting.

Energetic, exergetic and financial evaluation of a solar-powered absorption chiller integration into a CO2 commercial refrigeration system

This study investigates the integration of a solar absorption chiller by means of subcooling to a CO2 booster system that serves the refrigeration needs of a supermarket refrigeration plant with an installed capacity of 80 kW and 20 kW for medium and low-temperature regimes, respectively. The proposed energy saving configuration is analyzed in an energetic, exergetic, and financial manner, using the climatic data for the city of Athens, Greece. The current approach constitutes the theoretical reference for the actual implementation of this novelty either in new plants or as a retrofit in existing ones. The proposed solution includes the employment of a single-stage absorption chiller operating with LiBr–H20 working pair, which is driven by heat produced in evacuated tube collectors installed in the store’s rooftop. The energy analysis is conducted with validated numerical models that are developed in MATLAB using the CoolProp library. The collecting area and the corresponding chiller capacity of the proposed configuration are selected through financial evaluation. More specifically, the collecting area is analyzed parametrically from 25 m2 to 200 m2. Finally, 100 m2 of collecting area with 60 kW of chiller capacity are proved to be the optimum solution financially with 8.4 years payback period and 44.57 k€ net present value. This optimum solution results in an annual power consumption decrease of 8.12% which leads to energy savings of 27.45 MWh/year.

Investigating the impact of indoor temperature on the performance of the retail commercial refrigeration system

Commercial food outlets in the UK are responsible for 3% of the UK total energy consumption, with refrigeration systems account for 29% of this total. In this paper, a validated model that simulates a commercial refrigeration system installed over 2000 sq. ft to mimic a real express store installed at the Riseholme Refrigeration Research Centre at the University of Lincoln, UK, is presented. Investigations are conducted to examine the different failures of air conditioning (AC) systems and their impacts on the indoor store temperature, and hence on the refrigeration performance and energy consumption. Three different scenarios were examined: gradual increase in store temperature caused by an AC system with reduced performance, sudden increase in store temperature caused by a drastic AC failure and fluctuations in store temperature caused by a faulty AC system. The results of the investigation for different failure scenarios of the AC system during 3 h of continual operation showed an increase in the energy consumption of the refrigeration system by 17.4% as a result of gradual AC failure, 33.6% for the sudden failure and 5.3% for the intermittent failure. It is concluded that the AC failures caused the power drawn to increase due to spending a prolonged period of time at higher temperatures than during the normal AC operation. Also, the frequency which the compressors switch on and off increases the level of wear on the compressors. Both gradual and sudden failures of the AC system show a sustained increase in temperature that leads to a greater duty cycle for the expansion valve to increase the amount of refrigerant available. It is found that the sudden failure of the AC system had the greatest impact on the system, as the temperature of the store rises quickest, the display cases are exposed to higher temperatures for a longer time; this causes the greatest demand on the system and so lead to the largest power consumption. It is notable that for all three failure types that the product temperature experiences, there are no noticeable fluctuations and they remain comfortably within the temperature boundaries between 3 and 1 °C, as the system is able to provide an adequate cooling.

ANN Modeling to Analyze the R404A Replacement with the Low GWP Alternative R449A in an Indirect Supermarket Refrigeration System

Artificial neural networks (ANNs) have been considered for assessing the potential of low GWP refrigerants in experimental setups. In this study, the capability of using R449A as a lower GWP replacement of R404A in different temperature levels of a supermarket refrigeration system is investigated through an ANN model trained using field measurements as input. The supermarket refrigeration was composed of two indirect expansion circuits operated at low and medium temperatures and external subcooling. The results predicted that R449A provides, on average, a higher 10% and 5% COP than R404A at low and medium temperatures, respectively. Moreover, the cooling capacity was almost similar with both refrigerants in both circuits. This study also revealed that the ANN model could be employed to accurately predict the energy performance of a commercial refrigeration system and provide a reasonable judgment about the capability of the alternative refrigerant to be retrofitted in the system. This is very important, especially when the measurement data comes from field measurements, in which values are obtained under variable operating conditions. Finally, the ANN results were used to compare the carbon footprint for both refrigerants. It was confirmed that this refrigerant replacement could reduce the emissions of supermarket refrigeration systems.

Comparison of compressor control strategies for energy efficient refrigerated counters

• Energy label improvements for refrigerated counters are evaluated using simulations. • Improvements are evaluated based on compressor power and product temperature. • 70% reduction of the compressor power can be attained. • Reduction of the compressor power infers higher product temperature fluctuations. • Tradeoff between power consumption and temperature fluctuation should be identified. Small scale hermetic compressors with built-in frequency converters for compressor speed adjustment are an emerging technology on the commercial market. These compressor technologies offer the ability to impose innovative compressor control strategies, such as variable speed drive or adaptive energy optimization, for small scale commercial refrigeration systems. These strategies may both reduce power consumption and increase the temperature stability of the stored goods. Both of which are a necessity for the refrigerators to abide EU regulations 2015/1095 and 2015/1094 of 5 May 2015 and thus pass the test described in EN 16825. The influence of the applied compressor control strategy was investigated in combination with improvements to the cabinet envelope and improvements to the condenser and evaporator design. The investigation was performed using a validated dynamic model of a refrigerated counter using R290 and R600a, under the EN 16825 test conditions. Both variable speed drive and adaptive energy optimization yield significant reductions in power consumption compared to the conventional On-Off control. A more constant product temperature was achieved by variable speed drive, while the product temperature fluctuated slightly more when applying adaptive energy optimization.