An Experimental Investigation into the Effect of Thermostat Settings on the Energy Consumption of Household Refrigerators

Many household refrigerator owners do not control their thermostat settings. However, doing this could save energy consumption and also maintain the quality of stored food. This study presents the effect of regulated thermostat settings on household refrigerator energy consumption. The experiment was performed in a room chamber conditioned to temperature control at 25^oC. A household refrigerator was used as a test unit, with a cooling load placed inside the freezer component. The cooling load used was an M-package, in accordance with SNI IEC 15502: 2008. The test results reveal that household refrigerator energy consumption increases with higher thermostat settings. Increases in energy consumption range from 17.10% to 18.65%, depending on the thermostat setting.

Consumption energy; Refrigerator; Room chamber; Setting thermostat

The household refrigerator is an integral part of our life. In Indonesia, the number of household refrigerators continues to rise as the population grows. Currently, household refrigerators rank second in household energy consumption after air conditioning, partly due to the fact that household refrigerators run continuously (Khan et al., 2013). The increasing number of household refrigerator users is due to improved household economies, easy availability of electricity and cheap prices (Hasanuzzaman et al., 2011). Meanwhile, a US survey in 2009 revealed that household refrigerators consume more than 25% of household electrical energy (EIA, 2015).

Many studies have analyzed the factors that influence increases in household refrigerator energy consumption. Factors studied include the increase in energy consumption caused by ambient temperature, door openings, thermostat settings and cooling loads (Saidur et al., 2002; Hasanuzzaman, 2008). These variables combine to constitute the dominant factors that affect increases in household refrigerator energy consumption. Liu et al. (2004) conducted an experimental study on two types of household refrigerators by varying the number of door openings and ambient temperature. Their study showed that if the temperature of the unit rises due to opening of the door, then energy consumption also increases by 10% (Liu et al., 2004). Ozgun et al., performed optimization by varying the temperature and airflow into the evaporator to find household refrigerator energy efficiency (Sakalli et al., 2017).

In India, Bhatt conducted an experimental study of several brands of household refrigerators, each with a capacity of 165 liters. The tests were performed on two types of household refrigerator: single door and double door, using refrigerant HCFC 22. The thermostat settings varied with normal and maximum levels. The results showed that Specific Energy Consumption (SEC) varied between 3.23 and 4.19 kWh/y/L for single door manual defrost refrigerators, and between 3.84 and 4.78 kWh/y/L for double door auto defrost models (Bhatt, 2001). kWh/y/L is the unit of annual energy consumption to refrigerator volume, explaining the Specific Energy Consumption conditions (SEC).

Based on the experiment, an increase in energy consumption of 0.175 kWh/day was obtained when the thermostat setting was increased from point 1 to point 3. There was also a slight increase in energy consumption of 0.016 kWh/day when this setting was increased from point 3 to point 4. With the thermostat setting change from point 3 to point 4, there was no significant change in energy consumption or drop in temperature, so it can be concluded that setting the thermostat to point 3 is sufficient to keep food fresh. While even testing the energy consumption of the same refrigerator is not necessarily the same result.

The authors would like to thank the Directorate of Research and Community Service of the University of Indonesia through the "University of Indonesia Infrastructure Development Grants", under contract number 0219A/SK/R/UI/2012.

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