Fresh Food Compartment Research Articles

Energy, exergy, exergoeconomic, and exergoenvironmental analyses and multi-objective optimization of parallel two-stage compression on the domestic refrigerator-freezer

In this paper, the performance of a parallel two-stage compression (PTC) cycle on the domestic refrigerator-freezer in a laboratory according to the IEC 62552–2015 standard is investigated. The relatively large temperature difference between the fresh food compartment (FFC) and the refrigerant in the fresh food compartment evaporator (FFCE) leads to high compression and irreversible losses in the refrigeration circuit. To avoid the mentioned problems and reduce energy consumption, a PTC cycle is used. The innovation of this article is the 4E analyses (energy, exergy, exergoeconomic, exergoenvironmental) for the PTC cycle using the results obtained from the laboratory. Ultimately, the multi-objective optimization of the PTC cycle is conducted. For optimizing the PTC cycle, the total cost rate and the exergy efficiency are set as targets and the evaporator pressure and condenser pressure as variables. MATLAB and REFPROP 9.1 are used to model the system. Results showed that the highest exergy destruction rate is associated with the FFCE (0.349 kW) and compressor (0.183 kW). The highest exergy efficiency among the equipment is evaporators. The maximum exergoeconomic factor is related to the freezer compartment evaporator (FZCE) (98.70%) and then the compressor (98.62%). FZCE has the highest environmental impact (99.9%).

Investigation of a flexible triple-evaporator domestic refrigerator/freezer with R600a with integrated economization

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

Simulation of faults in domestic refrigerators of different volumetric capacity: Effect on thermal and energy behavior

The present study compares the thermal and energy performance of refrigerators with varying volumetric capacities when faults occur. Simulated faults include the malfunction of the fan attached to the evaporator and the airflow return area obstruction in the freezer. The proposal above included three intensity levels for each fault. Both refrigerators were instrumented to measure temperature conditions within the fresh food compartment and the freezer. In addition, during the test period, energy consumption was measured until thermal stability was reached in both compartments. The effect of each fault’s levels was compared with the reference condition for each refrigerator, which was without faults, as they left the factory. The results show that the fan fault caused the most significant variation in the thermal condition of both refrigerators. The temperature increased from 2°C to 4°C in the fresh food compartment, and from 1°C to 14°C in the freezer. The above causes warmer spaces compared to the reference refrigerator. Consequently, each refrigerator's energy consumption increased from 36% to 65%.

Implementation of fuzzy control in a domestic refrigerator considering the influence of the thermal load

This paper presents the development of a fuzzy control implemented in a domestic refrigerator in which the thermal load (food) is included as an input variable and a novel aspect of the control. The fuzzy control regulates the speed of the fan attached to the evaporator and the airflow to the fresh food compartment of the refrigerator according to a set of rules that incorporate the amount of thermal load and the temperature conditions of the compartments. The fuzzy control was evaluated in an empty refrigerator (without food) and with three thermal load conditions. Thus, resulting in a fuzzy control capable of maintaining thermal conditions similar to those obtained with the factory ON/OFF refrigerator controller. In addition, the total energy consumption is reduced by 1.7% when the refrigerator is empty and by a maximum of 9.53% in the presence of a low thermal load. Finally, the coefficient of performance shows increases in all the cases studied with the implementation of the fuzzy control.

Dynamic modelling of the steady state and load processing operation of a domestic refrigerator cooled through natural convection

A dynamic model of a domestic refrigerator is developed in this study and is used to analyse both the steady state (cyclic) and warm load cooling (load processing) operation. The compressor is modelled semi-empirically using loss parameters, while the capillary tube is modelled by incorporating both friction and momentum pressure drop. Heat exchangers (condenser and evaporator) are modelled as tubes divided into finite volume cells. The capillary tube-suction line heat exchanger is treated by connecting part of the capillary tube to the suction line via a heat resistor. The cabinet model consists of submodels for walls, air and shelves connected in a network to allow for thermal interaction. All the components are then arranged in a cycle, and cyclic operation is validated at 32 °C using a fixed speed compressor. A sensitivity analysis is then carried out by varying the compressor speed. In the second part of the study, the model is modified to include the effect of placing a warm load of water in the refrigerator and simulating the subsequent processing operation. This is validated using an experiment in which 20 L of water at 27 °C is placed inside the Fresh Food compartment. Results show that the power consumption value is captured well, with the average power consumption deviating less than 10% for all tests. The energy consumption is within ±5% for all tests. For load processing, the deviation in water temperature was a maximum of 1.2 °C for the whole cooling period.

A novel intelligent control method for domestic refrigerators based on user behavior

Energy consumption and food safety issues of household refrigerators have attracted considerable attention in recent years. Today, most household refrigerators use conventional controllers for adjusting the compressor speed to regulate the air temperatures inside cabinets. This research aims to design an intelligent control concept that integrates machine learning-based forecast of door opening events with fuzzy logic controllers. Firstly, bayesian neural network, logistic regression, and decision tree techniques are investigated to predict user behavior with data obtained from 18 real users of domestic refrigerators. Results show that logistic regression has the best performance in hourly predicting the door opening events after one week of training with more than 80% accuracy. Secondly, fuzzy logic controllers are designed to use the door opening predictions to regulate configuration parameters of the main refrigerator controller: maximum compressor speed, air temperature setpoint of fresh food compartment, and time offset to control the time of defrosting events. Finally, simulation studies are performed on a domestic refrigerator model developed at MATLAB Simscape. The developed model is based on an existing product in the market, and the accuracy of the model is verified by actual lab tests. Daily simulations of the household refrigerator for sample day profiles of an inactive and active user are performed for ambient temperatures of 16 °C, 25 °C, and 32 °C. Results show that the designed smart controller can achieve up to 2.5% and 4.5% of energy gain for active and passive user-profiles respectively, while maintaining the desired cabinet temperatures.

A case study on experimental and statistical analysis of energy consumption of domestic refrigerator

This paper presents the energy consumption analysis of the refrigerator and the effect of the condenser on it. According to the Bureau of Energy Efficiency (BEE), India, the energy efficiency of electric appliances is the key parameter for testing their performance before domestic use. For energy consumption analyses, the experimentation was conducted on the domestic refrigerator (165 L) top-mounted evaporator by retrofitting the refrigerator with an Elliptical Helical Coil Condenser (EHCC) and existing refrigerator with a Straight Tube Condenser (STC). Box-Behnken Design (BBD) is very significant in determining the significant factor and reducing the number of experiments. BBD has been performed to analyze the significance of factors ambient temperature, fresh food compartment temperature and the heat load in energy consumption, and the Coefficient of Performance (COP) of a refrigerator. The heat load and the ambient temperature are both very significant in determining the refrigerator's energy consumption. The most important thing is to increase the liquid content in the charge before it is supplied to the evaporator to extract more amount of heat to increase the cooling effect. The ANOVA (Analysis of Variance) results show that the ambient temperature and the heat load were more significant in increasing energy consumption and decreasing the COP and vice versa. The results of ANOVA and the experiment are very close; the R2 value 0.995 precisely matches the R2 adj. value 0.994. The statistical analysis using the Box-Behnken design produces a good fitting of the modeled and experimental data set. The present study aims to examine the effects of said factors and the condenser on the domestic refrigerator's energy consumption and COP. The study exhibits some enhancement in the COP to 2.59 contrary to 2.45 and energy consumption reduced to 1191 Wh from 1755 Wh during the trial of 24 h.

Exergy and exergoeconomic analyses of serial and bypass two-stage compression on the household refrigerator-freezer and replacement of R436A refrigerant

In this research, the performance of serial two-stage compression (STC) cycle and bypass two-stage compression (BTC) cycle on the household refrigerator-freezers is tested in the laboratory. Then, based on the results of the experiments, exergy, exergoeconomic analyses, and cycle optimization are carried out. Considering that replacing refrigerants in household refrigerator-freezers is one of the approaches to increase the performance and environmental impact of these systems, R436A refrigerant (46% Isobutene and 54% Propane mixture) is used and analyzed to replace previous refrigerants. Finally, the multi-objective optimization of the mentioned cycles is performed with both refrigerants. For analyses, two models of refrigerator-freezers with different cycles are used (STC cycle with R134a refrigerant and BTC cycle with R-600a refrigerant). In both models, two evaporators for refrigerator-freezer compartments are used. International standards (IEC 62552) are used to test refrigerator-freezers. MATLAB and REFPROP 9.1 software are used to model the systems. According to the results of the analyses, the STC cycle with R436A refrigerant has more total exergy destruction rate (0.727 kW) compared to R134a refrigerant. In the BTC cycle, in which the fresh food compartment (FFC) and freezer compartment (FZC) operate, the total exergy destruction rate with R-600a refrigerant (0.422 kW) is less than with R436A refrigerant. In the case of the BTC cycle in which only the FZC operates, the total exergy destruction rate with R-600a refrigerant (0.455 kW) is less than with R436A refrigerant. The most exergoeconomic factor among cycle equipment is related to the compressor (about 98%). The highest COP value between cycles is related to the STC cycle with R134a refrigerant.

A novel condenser with offset strip fins on a mini channel flat tube for reducing the energy consumption of a household refrigerator

The aim of the study is to reduce the amount of refrigerant and energy consumption of a household refrigerator by conserving the desired temperature inside the fresh food and freezer compartments. In this study, two novel condensers with different offset strip fin configurations on a mini-channel flat tube are used instead of a conventional wire-on-tube condenser. The impact of this novel application on the performance of the refrigerator is investigated experimentally by following the norms defined by IEC 62552:2015. The tests are conducted in a wide range of refrigerant charges (48–64 g) with three different capillary lengths (2800, 3300, and 3800 mm). Alternative couples of refrigerant charge and capillary length for the novel condensers are determined to decrease the daily energy consumption under the level of the original system with the wire-on-tube condenser. One of the aims of the study is achieved by 5.7% of energy-saving when one of the novel condensers is coupled with a 3300 mm length capillary tube and 50 g of refrigerant. The other aim of the study related with the environmental effect is achieved by reducing 10.7% of the refrigerant amount with the application of the novel condenser with offset strip fins on a mini channel flat tube.

Experimental study of a novel cool-storage refrigerator with controllable two-phase loop thermosyphon

Cool storage has been considering an efficient and cost-effective means to enhance the behavior of a refrigerator. However, its drawback in temperature control of the refrigerator compartment has not received enough attention. The controllable two-phase loop thermosyphon has the prospect of solving this problem. In this study, a novel cool-storage refrigerator integrated with a controllable two-phase loop thermosyphon is built to investigate its precise temperature control capacity. The phase change material is optimized by the orthogonal experiment method. The controllable two-phase loop thermosyphon presents the optimal cooling performance for the fresh food compartment when the filling ratio is 27.0%. As the average temperature of the fresh food compartment increases, the one on–off cycle of the controllable two-phase loop thermosyphon maintains at 32.0 min, and the operation ratio varies from 86.3% to 13.6%. The temperature control accuracy can be improved from 2.1 °C to 0.6 °C and the overall time of one on-off cycle decreases from 49.8 min to 22.4 min. The operation ratio gradually increases from 7.2% to 38.6% as the ambient temperatures increase. The results demonstrate that the controllable two-phase loop thermosyphon is a feasible and effective way to improve the temperature control performance of the cool-storage refrigerator.

CFD analysis for predicting cooling time of a domestic refrigerator with thermoelectric cooling system

Abstract In this work, Computational Fluid Dynamics (CFD) analysis was conducted considering three different turbulence (viscous) models for a fresh food compartment of a domestic refrigerator (DR), in order to not only gain idea on cooling down time rate of fresh food compartment but also present air and temperature distribution inside the compartment when it is loaded. The refrigerator composes of three compartments: Fresh food (FFC), chill (CC) and freezer (FC). The FFC compartment is cooled by a thermoelectric/Peltier cooler (TEC) while the other compartments are handled by a vapour compression (VC) system. To measure cooling times, tests were conducted according to new IEC62552:2015 standard in climatic chambers and the cooling time was measured as 146.5 min. The predictions of developed CFD model clearly visualize the airflow and temperature fields inside the FFC. Concerning numerical predictions for the packages in the upper regions were in better agreement (below 10%) with measurements than the predictions for the packages in the lower regions mainly due to convective heat transfer behaviour.

Effect of Vacuum Insulation Panels on Energy Consumption and Thermal Load Transfer between Compartments in a Three-Temperature Frost-Free Refrigerator

The three-temperature frost-free refrigerator is popular in China currently, which adopts a single evaporator and separate air ducts to distribute cold air into all compartments, i.e., the fresh food compartment (FFC), the variable temperature compartment (VTC), and the freezer compartment (FZC). Two identical refrigerators with cyclopentane insulation are comparatively studied in this article, one with vacuum insulation panels (VIPs) in two sidewalls and the other without. Results show that VIPs reduce the steady-state energy consumption of the refrigerator by 12.4% due to smaller average power input and longer compressor-off duration. The decrease in average power input originates from a shorter FFC-damper-on duration since VIPs reduce its thermal load. However, the FFC average temperature rises unexpectedly with shorter damper-on and longer damper-off durations, and induces thermal load transfer from FFC to FZC through the mixing of return air in the evaporator chamber. Consequently, FZC-only duration increases and compensates for the decrease in FFC-damper-on duration, resulting in an overall similar compressor-on duration. Simulation results of the heat transfer process through the evaporator are also provided in both cases to obtain a full view of the thermal load transfer process.

Heat exchanger optimization of a domestic refrigerator with separate cooling circuits

In this study, the effects of evaporator type and geometry, capillary tube diameter and capillary length on the cooling system performance and energy consumption in the bypass two-circuit cycle have been examined experimentally. In the experiments, wire on tube and finned tube evaporators were used in the fresh food compartment of a 500 L top mount freezer refrigerator. 0.66 mm and 0.8 mm capillary tube diameters and 3000 mm and 3500 mm capillary tube lengths were selected as other design parameters. Experiments were performed according to IEC 62552 household refrigerating appliances standard at 25 °C ambient temperature when the average temperature of the fresh food compartment is set to 5 °C and the warmest temperature of the freezer compartment is −18 °C. The Design of Experiments (DOE) technique which is a six sigma method has been used to determine simultaneously the individual and combined effects of parameters on the refrigerator performance. General linear model method, which is a useful framework for comparing how several variables affect different continuous variables, was chosen to identify the effectiveness of the parameters. According to the experimental results, it was found that the most effective parameter of the system is the evaporator type. Finned tube evaporator with 12 tube passes were found the best option for the bypass two-circuit refrigeration cycle among the 8 different options. The optimum cooling performance and the lowest energy consumption were provided with 0.66 mm capillary tube diameter and 3500 mm capillary tube length in the experiments.

Study on the effect of graphene nanosheets refrigerant oil on domestic refrigerator performance

Graphene nanosheet have an ultra-thin sheet structure that can easily fill the contact friction surfaces and reduce friction losses. Its thermal conductivity reaches 5,300 W/mK. Therefore, a nanofluid prepared by adding graphene nanosheets to base liquid will have lower coefficient of friction and higher thermal conductivity. In this study, 1:1 mass ratio of graphene nanosheets additive to Span85 dispersant was added to SUNISO 3GS refrigerant oil, using ultrasonic oscillation dispersing and chemical methods to prepare 10 mg/L, 20 mg/L and 30 mg/L graphene nanosheets refrigerant oil. The cooling rate, freezing capacity, and energy consumption of the refrigerator using different concentrations of graphene nanosheets refrigeration oil were compared. The performance of the compressor and the refrigerator were analyzed. The results showed that during the stable refrigerator operation, adding graphene nanosheets to lubricants for the refrigerator had lower suction temperature, discharge temperature, condenser temperature, suction pressure and discharge pressure than pure oil. Both the fresh food compartment and freezer's cooling rates were increased. The increase of the concentration leaded to better freezing capacity of the freezer. The 30 mg/L graphene nanosheets refrigerant oil increased the freezing capacity of the refrigeration system by 11.1%. The on-time ratio, operating current of the compressor and energy consumption were also reduced. Compared with pure oil, the energy consumption in 24 h of the domestic refrigerator using 10 mg/L, 20 mg/L and 30 mg/L graphene nanosheets refrigerant oil dropped by 15.4%, 19.2% and 20.3%.

Experimental study on the temperature management behaviours of a controllable loop thermosyphon

The loop thermosyphon with active heat transfer control capability is a promising solution for the temperature management of the fresh food compartment of cool-storage refrigerators or other precise temperature control devices. However, the frequently start-stop operating mode of the loop thermosyphon has not received enough attention, its active temperature management behaviours still requires further investigation. In this study, a controllable loop thermosyphon used in the temperature control of a fresh food compartment is developed and its start-stop is controlled by the temperature controller with the assistance of two magnetic valves. The performances of the controllable loop thermosyphon in long-term and start-stop operating modes are tested. The controllable loop thermosyphon with 35% filling ratio present highest heat transfer rate, reliable heat transfer capability, and good stability for the varying temperatures in the fresh food compartment. Based on this filling ratio, the heat transfer rate remains higher than 40 W during the long-term operating test. When the controllable loop thermosyphon operates in the start-stop mode, the start-stop cycle decreases from 39.4 min to 27.2 min and the operating ratio increases from 12.6% to 53.7% as the temperature of the fresh food compartment rises. Particularly, when the start-stop cycle reduces from 42.6 min to 18.1 min, the temperature control accuracy is improved from 2.0 °C to 0.4 °C. The results demonstrate that the controllable loop thermosyphon is promising as a novel precise temperature management device and is qualified for the use in cool-storage refrigerators.

Energy optimization of a domestic refrigerator controlled by a fuzzy logic system using the status of the door

This paper proposes a novel fuzzy logic control system for a domestic refrigerator taking into consideration the status of the door. The goal of this system is to keep the temperature of the fresh food compartment as close as possible to the set point while saving energy. The fuzzy logic system was set up to control the speed of the compressor. The set of inference rules in this study incorporated the frequency and duration of the door opening. These rules try reducing the compressor speed at a minimum value, and therefore, reducing the number of times the compressor is turned off when the door is open. To compare and evaluate the control systems, several tests with different configuration and rules were performed. Each test ran for seventeen hours, during this time the test included three periods when the door was opened and closed several times. It was concluded that the electric current when the compressor starts was reduced and produced an overall energy saving of 3%. Thus, it is evident that the more information is incorporated into a fuzzy logic system, the more energy savings can be obtained.

Numerical analysis of a novel household refrigerator with controllable loop thermosyphons

Efficiency improvement of household refrigerators exerts extensive influences on the reduction in residential energy consumption and alleviation of environmental pollution. Controllable loop thermosyphons (CLTs) are low-cost, high-precision heat transfer control devices that can be potentially applied in refrigerators as crucial energy saving and temperature management components. A novel refrigerator with CLTs is proposed in this study. The evaporator in fresh food compartment is removed, the cold loss of the topside freezer is partly reused by the CLTs to cool the fresh food compartment in intermittent mode, and the overall cold loss of the refrigerator is efficiently reduced. The energy saving behaviour of the refrigerator is numerically studied based on tested temperature boundary conditions. The energy saving mechanism is comparatively analyzed, and the impacts of the operating condition, installation position of the CLTs, and ambient temperature are investigated. The energy saving ratio of the novel refrigerator increases from 12.9% to 19.5% when the ambient temperature rises from 17.0 °C to 31.0 °C, the operating condition varies from 1 to 4, and the locations of CLTs from the inner wall of the freezer are changed from 2.1 to 4.9 mm. Results preliminarily prove the energy saving capability of the novel refrigerator.

How to achieve full liquid conditions at the capillary tube inlet of a household refrigerator

The capillary tube with a liquid-to-suction heat exchanger (CT-LSHX) is a component that is widely used in household refrigerators. Recent works have indicated that even when measuring subcooled conditions at the condenser outlet, the condition at the capillary tube inlet is a two-phase flow. The present work was dedicated to analyzing the actual refrigerant conditions at the capillary tube inlet and to investigating how full liquid conditions could be achieved.The research was performed using a typical household refrigerator with corresponding fresh food and freezer compartments, replacing the original refrigerant-to-air condenser with a refrigerant-to-water condenser. This allowed, first, the condensation conditions to be controlled and, second, the estimation of the refrigerant conditions at the condenser outlet from the heat exchanger balance. The obtained results indicated the presence of a non-equilibrium two-phase flow, composed of subcooled vapor and subcooled liquid, at the capillary tube inlet, with both liquid and vapor entering the capillary tube as a vortex with small, fast fluctuations of the liquid level. This non-equilibrium indicated that the subcooling, evaluated from the pressure and temperature of the refrigerant at the condenser outlet, was only apparent and did not allow the evaluation of the actual enthalpy.Finally, by using a smaller capillary tube diameter and increasing the compressor speed, full liquid conditions at the capillary tube inlet were achieved. Furthermore, a performance comparison between the original and the new design revealed that the COP was higher with full liquid conditions.

Numerical (CFD) and experimental analysis of hybrid household refrigerator including thermoelectric and vapour compression cooling systems

Numerical and experimental analysis of a previously investigated hybrid household refrigerator (HHR), HHR I, were conducted in this study. To determine the optimum location for the thermoelectric cooler installed in HHR I, CFD analysis was performed. As a result of the CFD predictions, two new HHRs, namely HHR II and III, were created and experimentally investigated.CFD predictions showed a more uniform air velocity and temperature distributions inside the fresh food compartments of HHR II and III compared to HHR I. Additionally, experimental measurements indicated a considerable increase in the energy efficiency of HHR II and III. Their energy consumption was nearly identical and improvements of up to 10% and 27% at the ambient temperatures of 16 °C and 32 °C, respectively, were observed when compared to HHR I. Regarding the cooling time, no effect of the relocation of the TEC was observed at the TEC's nominal voltage of 24 V.

Preliminary evaluation of the energy-saving behavior of a novel household refrigerator

The refrigerator is one of the most essential domestic appliances and causes considerable energy consumption every year. The efficiency of a normal household refrigerator is significantly affected by the heat-insulating property of the thermal barrier of the freezer due to its low inner temperature. In this study, a novel refrigerator with a loop thermosyphon is put forward to decrease the heat transfer between the freezer and ambient air. It has great potential to be popularized as a sustainable energy technology or applied in the renewable energy field considering its significant energy-saving effect, simple structure, and low cost. The energy-saving behavior of the refrigerator is preliminarily evaluated based on the theoretical calculation. The temperatures of ambient, the fresh food compartment, and the location of the heat transport component are varied; the impacts are analyzed. The total cold loss of the topside and side freezer walls is reduced from 16 W to 14 W in the normal test conditions, and the energy-saving ratio varies from 6.3% to 28.5% when the ambient temperature, the location of the heat transport component, and the fresh food compartment temperature vary. The results certificate the energy-saving capability of the novel refrigerator and its reliability in hot climate.