Introduction
With an increasing focus on environmental consciousness and inflation raising the cost of everything, energy efficiency of appliances remains at the forefront of many Americans’ minds. The constant power draw from refrigerators and freezers mean that they are usually the most energy intensive household appliance. Many refrigerators have efficiency ratings when sold, such as that from the US EPA ENERGY STAR® program. However, these ratings are based on performance in controlled conditions for new appliances. Perhaps real-world refrigerator energy consumption differs from such projected performance data, and depends on factors not captured in such ratings, such as set-point temperatures, appliance age, or household size.
To explore these factors, we have collected anonymized data on refrigerator energy use from Penn State University students and the PSU community. With enough data, we hope to be able to provide useful guidance to questions such as:
- How does refrigerator energy consumption change with the age of the equipment? Is there a right time to replace an old appliance that has become less efficient?
- How does refrigerator energy use change with size of household, set-point temperatures, or where an appliance is installed?
- Do certain brands or models maintain their efficiency over time better than others?
If you are interested in participating in this study and contributing more data, please contact Alex.Rattner@psu.edu. We think this could be a great classroom citizen-science project, and would be happy to provide resources and test supplies to teachers and schools. Anonymized raw measurement data will be shared on request.
Methods:
To collect data, a standard electronic thermometer and plug-in Kill-A-Watt power meters (P3) were used. Before installation, the refrigerator name plate was found and make, model, model year, and other important information recorded. The power monitors were installed. Room temperature was found. Once weekly, an electronic thermometer was placed in fridge. After waiting until the temperature equilibriated, the thermometer was removed from the fridge and the temperature immediately recorded. The same process was repeated to check the temperature of the freezer. As the thermometer acclimated, usage was checked through power meter and reset for the upcoming week. All data that was affected by power outages was removed from final analysis.
Findings:
A positive trend is apparent when the age of refrigerators is plotted against the average wattage (power consumption).
A trend was also found when comparing the power draw of both full-sized refrigerators and mini-fridges. Due to the larger volume kept at a cooler temperature, a greater amount of power is used to keep the same food preserving conditions. As the data has not been split in the following trials, it is likely that the correlations will be working with respect to refrigerator temperature, freezer temperature, and number of users.
Similarly, data was analyzed for number of users, freezer temperature, and refrigerator temperature and plotted against average wattage. Although a trend appears in the plot for number of users, a trend is more difficult to extrapolate from the temperatures of refrigerators and freezers plotted against wattage. One possible explanation for this is the variation in refrigerator sizes, from large household fridges to mini fridges. As larger households (or a larger number of users in general) tend to use a larger fridge, the power draw is likely to be larger. This is less likely to be tied to the the refrigerator or freezer temperature set point.
Acknowledgements
We wish to acknowledge generous research support from the U.S. National Science Foundation (CBET-1652578).