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• Methodology to minimize the energy consumption of household refrigerators. • Convertion of the pair needle valve-capillary tube into an equivalent tube diameter. • Empirical correlation to estimate the EC based on the restriction and charge. In the first part of this work an experimental apparatus was designed and constructed to map the energy consumption of a household refrigerator subjected to several combinations of refrigerant charge and expansion restriction. In the second part, the expansion restriction imposed by the pair metering valve-capillary tube was converted into an equivalent tube diameter applying two different procedures: dry nitrogen flow and mathematical modeling. An empirical correlation to estimate the energy consumption based on the capillary tube inner diameter and refrigerant charge was also developed and used during the minimization process. Different strategies were also explored in order to reduce the amount of experiments to a minimum. It was found that at least 14 data points, collected with three different refrigerant charges, are required to ensure the convergence of the energy consumption minimization process. [ABSTRACT FROM AUTHOR]

This paper describes a quasi-steady-state simulation model for predicting the transient behavior of a two-door household refrigerator subjected to periodic door opening and evaporator frosting. A semi-empirical steady-state model was developed for the refrigeration loop, whereas a transient model was devised to predict the energy and mass transfer into and within the refrigerated compartments, and also the frost build-up on the evaporator. The key empirical heat and mass transfer parameters required by the model were derived from a set of experiments performed in-house in a climate-controlled chamber. In general, it was found that the model predictions followed closely the experimental trends for the power consumption (deviations within ±10%) and for the compartment temperatures (deviations within ±2 K) when the doors are opened periodically and frost is allowed to accumulate over the evaporator. [ABSTRACT FROM AUTHOR]

Abstract: In this work the thermodynamic behavior of a household refrigerator was experimentally studied by simultaneously varying the refrigerant charge and the expansion restriction. A special charging device was designed and constructed for this purpose comprised of a cylinder, a load cell and two solenoid valves. In addition, the original capillary tube was replaced with a larger-diameter capillary tube and installed in series with a metering valve. The expansion restriction was varied by adjusting the capillary tube–metering valve pair to settings higher and lower than that of the original system. A total of 95 energy consumption measurements were recorded with different combinations of refrigerant charge and expansion restriction. A minimum energy consumption region comprised of several combinations of refrigerant charge and expansion restriction was clearly identified. It was also observed that an improper combination of expansion restriction and refrigerant charge may increase the energy consumption by up to 30%. [Copyright &y& Elsevier]

Abstract: A simplified model to assess the energy performance of vapor compression ‘on–off’ controlled refrigerators is presented herein. The model consists of first-principles algebraic equations adjusted with experimental information obtained from the refrigeration system under study. The experimental work consisted of controlling and measuring the system and component operating conditions in order to gather key information for the development and validation of the model. The methodology showed similar accuracy to that using more sophisticated dynamic simulation codes, but with lower computational costs. When compared to experimental data, the model predicted AHAM energy consumption tests within a ±5% deviation band. A sensitivity analysis considering the number of tube rows in the condenser coil, the number of fins in the evaporator coil and the compressor stroke is also reported. The refrigeration system under study was a top-mount ‘Combi’ 600-l refrigerator, ‘on–off’ controlled by the temperature of the fresh-food compartment. [Copyright &y& Elsevier]

Abstract: A first-principles model for simulating the transient behavior of household refrigerators is presented in this study. The model was employed to simulate a typical frost-free 440-l top-mount refrigerator, in which the compressor is on–off controlled by the freezer temperature, while a thermo-mechanical damper is used to set the fresh-food compartment temperature. Innovative modeling approaches were introduced for each of the refrigerator components: heat exchangers (condenser and evaporator), non-adiabatic capillary tube, reciprocating compressor, and refrigerated compartments. Numerical predictions were compared to experimental data showing a reasonable level of agreement for the whole range of operating conditions, including the start-up and cycling regimes. The system energy consumption was found to be within ±10% agreement with the experimental data, while the air temperatures of the compartments were predicted with a maximum deviation of ±1°C. [Copyright &y& Elsevier]

• Experimental work on domestic refrigerators contaminated with non-condensable gases. • Energy consumption increased up to 25.9%.% • Flow visualization at the capillary tube inlet. • Compressor power oscillations during the start-up indicated contamination. This article reports an experimental study of performance degradation and expansion noise generation in a household refrigerator running with isobutane contaminated with non-condensable gases (NCGs). Controlled amounts of nitrogen were injected into the system using a purpose-built device. The refrigerant flow at the capillary inlet was visualized while an accelerometer recorded the expansion noise at the evaporator inlet. Steady-state performance tests were carried with different nitrogen contamination levels at various compressor speeds. A high sub-cooling degree and an increased discharge pressure showed to be strong evidences of the presence of non-condensable gases. Even though the thermodynamic variables reached steady-state conditions, large fluctuations were observed for the flow pattern at the capillary tube inlet and in the acceleration readings. Therefore, standardized cyclic energy consumption and pull-down tests were also conducted to evaluate the effect of NCGs on the refrigerator transients. It was noticed that the energy consumption increased up to 25.9% when the system was doped with a mass fraction of 0.43% of N 2. Also, a quasi-linear increase of the energy consumption with the N 2 mass fraction was observed. Furthermore, the system pull-down time increased by up to 10-h due to NCG contamination. A visual inspection revealed that the performance degradation was related to a partial clogging of the capillary tube that unbalanced the compressor and expansion device mass flow rates, preventing the system to reach steady-state conditions. [ABSTRACT FROM AUTHOR]

• Simulation of household refrigerators mounted with skin condensers. • Energy consumption tests with different hot-wall condenser designs. • Design guidelines focused on performance optmization. This work presents a numerical and experimental approach focused on design guidelines for hot-wall condensers applied to domestic refrigerators. To this end, seven refrigerators were manufactured with distinct condenser designs. The design parameters were the following: (i) adhesive tape (aluminum or polyethylene), (ii) tube outer diameter (4 or 4.76 mm), (iii) total length (10 or 11.5 m) and (iv) lay-out. An in-house mathematical model for hot-wall condensers was added to an in-house system simulation tool to predict the refrigerators performance. Experiments were conducted in a climate-controlled test chamber. It was found that the model predictions are close to the energy consumption measurements with deviations of the order of ±10%. It has also been found that the heat load is increased on average by 7.7% when a hot-wall condenser is added to the system. An extensive sensitivity analysis was also put forward, showing that the hot-wall condenser and thus the refrigerator performance is very much affected by the outer sheet thermal conductivity and thickness, but mainly by the tape thermal conductivity. The contact area between tube and outer sheet also plays a significant role in the heat transfer, meaning that a cheaper polymeric tape could be used if enough contact area is provided. Additionally, it has been found that there is a tube pitch which minimizes the energy consumption in despite of the condenser geometry. [ABSTRACT FROM AUTHOR]

Highlights • Experiments were carried out with 16 prototypes of the same refrigerator model. • The gathered data were correlated statistically. • A coverage area of 56% dropped the energy consumption by 21%. • The effect of the VIPs panels is higher when installed in the fresh-food compartment. • The VIP aging cannot be directly inferred from thermal conductivity measurements. Abstract In this work the thermodynamic behavior of a typical domestic refrigerator insulated in 16 distinct ways with vacuum insulation panels (VIPs) was experimentally evaluated. As expected, it was found that the energy consumption is affected by both the coverage area and the position of the panels. It was also found that samples with the same coverage area presented distinct energy consumptions and vice-versa. The gathered data were correlated statistically in order to identify the most promising regions to install the panels. It was observed that the energy consumption is reduced by approximately 6% and 11% when the doors and the rear wall are insulated with VIPs, respectively. It was also found that a coverage area of 56% drops the energy consumption by 21%. [ABSTRACT FROM AUTHOR]

Abstract: This paper outlines a simulation model for the cycling behavior of household refrigerators and, therefore, for predicting their energy consumption. The modeling methodology follows a quasi-steady approach, where the refrigeration system and also the refrigerated compartments are modeled following steady-state and transient approaches, respectively. The mass, energy and momentum conservation principles were used to put forward the equation set, whereas experimental data were collected and used to reduce the model closing parameters such as the thermal conductances and capacitances. The experiments were carried out using a controlled temperature and humidity environmental chamber. The model predictions were compared to experimental data, when it was found that the energy consumption is well predicted by the model with a maximum deviation of ±2%. A sensitivity analysis was also carried out to identify opportunities for energy savings. [Copyright &y& Elsevier]