Conference Agenda

This work advances a technique for fault detection and diagnosis (FDD) in single-door refrigerating appliances based on a heuristic decision tree developed on thermodynamic grounds. Four faults were considered, namely condenser fouling, evaporator frosting, refrigerant leakage, and non-condensable gas contamination. The experiments were carried out using an ice cream display cabinet fully instrumented with pressure transducers, temperature sensors, and power meters. To ensure practical applicability in real appliances, the FDD algorithm was devised to rely on minimal instrumentation and data, therefore requiring only three additional temperature sensors in addition to the electric variables available from the compressor motor driver. Moreover, only two setup tests conducted at the minimum and maximum surrounding air temperatures with the system operating under no-fault condition were required. The approach was devised based on real time estimation of a normalized COP and validated using experimental data obtained for three different surrounding air temperatures (20°C, 25°C and 32°C) with single faults imposed. As the result, an average accuracy higher than 90% was achieved while rejecting false positives such as door openings and defrosting operations.

This paper introduces a fully automated calorimeter for testing refrigerating compressors for household applications at surrounding air temperatures of 16°C and 32°C in compliance with the newest IEC 62552 (2020) standard requirements. The rig automation included four key steps: test box and suction line temperature control, working pressures control, test run automation, and report generation. For box temperature control, an auxiliary refrigeration system with electric heaters, regulated by a PI controller, was employed to maintain the temperature references at 16°C or 32°C. A novel heat exchanger arrangement was adopted to promote suction line temperature control complying with the compressor surrounding air condition. Evaporating and condensing pressures control was achieved using two proportional electric valves with gain-scheduled PI controllers, providing a fast response to reference changes, while maintaining stability. Also, an algorithm for test automation was devised to identify steady-state condition, to change the point of operation, and to follow a pre-determined test sequence. Upon test completion, an automated report is generated, including not only of the compressor datasheet, but also the coefficients of a semi-empirical model. The calorimeter automation resulted in up to 90% reduction in total test runtime when compared to a fully manual facility.

Household refrigerators provide a convenient and safe means of food preservation and storage. More than 100 million refrigerators are used in US homes, resulting in significant primary energy consumption and carbon emissions. As a greenhouse gas with a 100-year GWP of 1430, R-134a has been banned in new U.S. domestic refrigerators and freezers since 2021, and R-600a with a GWP of 3 is widely employed as a working fluid in the current U.S. household refrigerator market. In this paper, benchmark testing was conducted for two 2023 refrigerators using R-600a. Moreover, the impact of representative customer use patterns, such as door opening and warm food storage, was studied to evaluate impact on energy consumption of the refrigerators. These results will provide background knowledge for facilitating the integration of new technologies for achieving significantly reduced greenhouse gas emissions in future efficient refrigerators.

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 previous work, a two-stage vapor-injected cycle with multi-evaporator system was investigated for its energy saving potential and cost-effectiveness. The cycle establishes two separate evaporation temperatures to better match the cabinet temperatures 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. Modeling results showed up to 13% energy consumption reduced with respect to the baseline system. In this work, a reduced-order model of a vapor-injected reciprocating compressor was integrated into a previously developed dynamic system level model to obtain more realistic and higher fidelity results. The reduced-order model considers the injection thermodynamic state and timing as well as evaporating and condensing temperatures from the system operation. By utilizing the compressor model, a control strategy was designed specifically for the two-stage vapor-injected cycle where the injection mass flow rate can change depend on the system’s load requirement. System performance improvements and the effectiveness of the control strategy are discussed along with future work. Quantitative results will be included when the manuscript is ready.

The increasing global focus on mitigating global warming has driven a change in refrigerant selection for domestic refrigerators. While most existing refrigerators use R-134a as their working fluid, there is a gradual shift towards R-600a in newly manufactured products to minimize environmental impact. In order to design a more energy-efficient isobutane refrigerator, various configurations, including both single-evaporator and dual-evaporator cycles, were investigated. The study was conducted using a high-fidelity simulation platform, the Heat Pump Design Model (HPDM), developed and experimentally validated by the US DOE/ORNL. This platform includes detailed segment-to-segment heat exchanger model, fan model, and compressor model, utilizing refrigerant properties from REFPROP 10. A quasi-steady-state approach was employed to simulate the transient behavior and performance of a domestic refrigerator. The performance of various configurations was compared, and the effects of the refrigerant properties and operating conditions were also analyzed and discussed.

Thermoelectric heat pumps (TEHPs) have found widespread use in the electronics cooling industry and portable refrigerators. However, there has been a lack of extensive research on the application of TEHPs in low-temperature refrigeration settings. To address this gap, various configurations of TEHPs were fabricated to assess their suitability for freezer applications. Key parameters such as cooling capacity and system performance of the TEHPs were crucial in evaluating these configurations. Three configurations, each with different numbers of cooling units and fan arrangements, were tested using a 300-liter freezer prototype under typical room conditions (21°C). A cooling unit is comprised of two-stage thermoelectric modules, an aluminum plate fin heat exchanger sink with fans positioned either on top or directing airflow through the center, and a cooling block with circulating icy water for heat dissipation. Across all configurations, the minimum temperature inside the freezer cabinet reached -16.0°C. The cooling capacity peaked at 74.7 W, with the thermoelectric coefficient of performance (COP) reaching a maximum of 0.45. System COP ranged from 0.23 to 0.28. Minimum TE power consumption was recorded at 138.8 W, with TE system power consumption at 174.4 W, indicating feasibility for practical residential freezer applications. This investigation lays the foundation for integrating TE freezers with ice thermal storage systems.