Conference Year



Household refrigerator, On-off control, Energy Saving


The domestic refrigerator is responsible for 30% of the average household electricity consumption in Brazil, and the power costs regarding a single refrigerator represents up to 5% of the Brazilian minimum wage. The capacity control method employed in most of these systems consists of a thermostat used to turn on and off the compressor to maintain the temperature between the desired levels. This method of capacity control is responsible for efficiency losses as a result of the start-up and shut-down transients. The duration and the number of on/off cycles influence directly the temperature profile inside the refrigerator and the system energetic efficiency. By adjusting the thermostat, the maximum and minimum temperature achieved during the system operation are changed, and also the range between them. Having all that in mind, the aim of this study is to optimize the temperature range in a domestic refrigerator in order to make power consumption as low as possible while maintaining a given maximum temperature that cannot be exceeded in order to keep the food properly preserved. The refrigerator was modeled as a first order plus time delay system. A hysteretic relay test was used to estimate the system parameters. The system model was employed to develop mathematical relations to set the temperature amplitude inside the refrigerator, given a maximum temperature, in order to minimize the total energy consumption. Preliminary results indicated that, for the refrigerator studied in this work, the optimal amplitude should be set at approximately 7 °C, when the refrigerator is half loaded. This amplitude could save up to 15% of energy when compared to 2 °C amplitude or 35% when compared to 1 °C amplitude. Further tests will be conducted on the refrigerator to identify the system, as well as to measure the power consumption when different temperature ranges are set.Â