Refrigerators are common household appliances in our modern day society. There have been many advancements in fridge technology throughout the years, and many companies have even added features like AI to their products for presumed user conveniences. However, not all fridges sold on the market are energy efficient per Energy Star standards, and some are more efficient than others. What should be considered when purchasing a fridge with respect to energy consumption?
What is Energy Star?
Energy Star is a program run by the United States Environmental Protection Agency and Department of Energy. Energy Star promotes energy efficiency by providing certification to products that meet set criterion.
For example, the Energy Star criteria for refrigerators and freezers, updated September 2014, was for these appliances to reach 10% less measured energy than minimum federal efficiency standards set by the Department of Energy.
The data being examined consists of information for residential refrigerator models certified under the Energy Star requirements effective September 15, 2014. There are 192 brands of fridges and 2962 models included in the data, and from this histogram below of the top 25 refrigerator companies based on the number of certified models they have available on the market, GE and Frigidaire are the top brand names, with more than 150 fridge models.
One can also see from this histogram that most certified refrigerator models do not meet Energy Star's Most Efficient 2021 criteria. Under this criteria, standard refrigerators save 40-134 kWh/yr, which is 10-20% over the federal minimum. For compact refrigerators and freezers, 34-80 kWh/yr is saved, which is 20-25% over the federal minimum. For all of the companies in the histogram, most of their models do not satisfy this standard, which is something to keep in mind when scouring the markets. For example, while GE and Frigidaire may be well known brands for appliances, this does not necessarily means they sell the best fridges in regards to energy efficiency.
How much energy do refrigerators usually require?
The box plot of the average annual energy use of fridges suggests that the fridges range from 150 to around 800 kilowatt-hours per year in terms of energy consumption. The median annual energy use is around 325 kilowatt-hours per year, meaning there are more fridges erring towards the lower levels of consumption, as confirmed by the density plot to the right.
The density plot also contains the distribution of the United States federal energy standard for each fridge. Overall, these two density curves share the same shape, with the entire federal energy standard curve shifted towards the right. This suggests that in general, the certified refrigerator models do tend to follow the federal standards laid out as expected, considering they on average would use less energy annually than what is allowed. However, this does not necessarily mean they meet the efficiency standards specified by Energy Star.
It is important to buy a refrigerator that meets your storage needs. How exactly does size affect energy consumption though? A linear model is built to find the effect of a fridge's height, width, defrosting method, ice maker presence, and connected functionality availability upon annual energy consumption.
Height and width are both significant predictors in this model. As the height of a refrigerator increases by one inch whilst keeping the other features constant at their mean, there is an expected increase in the predicted annual energy use by 0.869 kWh. It is unsurprising that this phenomenon occurs, as more energy would be required to maintain temperatures in a larger volumed fridge! The same conclusion applies to fridge width, but the increase in annual energy use is 7.691 kWh. This may be due to the fact that a wider fridge may be indicative of a more complex fridge containing features beyond simply refrigeration and freezing, such as ice makers, that would require more energy.
From the coefficient table above, all of the features included in the model have a significant linear effect upon annual energy consumption. The effect of height and width were described above. As for the the capabilities included in the model:
- Manual defrosting is expected to consume less energy than automatic defrosting, by approximately 43.6 kWh/yr.
- Fridges that have an ice maker are expected to require more energy than those that do not have an ice maker by approximately 180 kWh/yr.
- Having connected functionalities would increase energy use consumption by approximately 77.2 kWh/yr.
While ultimately, all these refrigerator qualities do seem to directly impact annual energy use, it could be helpful to consider the interactions between the presence of the various features coming with a fridge and fridge capacity upon energy consumption, considering how fitting in a feature may force the fridge to be larger.
To the left is a directed acyclic graph of how the fridge features theoretically affect energy consumption. It would make sense that the compact design would limit a fridge's possible dimensions, which in turns affects its volume. As the volume of a fridge increases, energy consumption should increase because it would require more energy to maintain temperatures in a larger space. Ice makers take up quite a bit of volume in a fridge as well, and their use also directly increases energy consumption.
Finally, defrosting capabilities also affect how much energy is needed in operating a fridge, as well as any connected functionalities that the fridge may come with.
* Visual created on daggity.net
How do different fridge features affect energy consumption?
The interaction plots tell us that the defrosting method, presence of an ice maker, and presence of connected functionalities will result in different amounts of increases in the energy consumption of that fridge as its volume increases, while the use of the compact design does not have an interactive effect with volume (same increase in energy consumption per increase in fridge volume).
- The defrosting method of a fridge has an interactive effect with its volume upon energy consumption, as indicated by the significant interaction term - if defrosting is manual, there is less of an increase in energy consumption per unit increase in fridge volume.
- The presence of an ice maker also has a significant interactive effect with volume upon energy consumption - with an ice maker, there is a greater increase in energy consumption per unit increase in fridge volume.
- The presence vs. absence of connected functionalities in a fridge does have a legitimate interaction with its volume upon energy consumption. The interaction term is significant, and causes the connected functionality variable to no longer be a significant predictor on its own. This means the increase in annual energy consumption per unit increase in volume of the fridge is statistically different depending on the presence of connected functionalities in the fridge.
- There does not appear to be an interaction between if the fridge is a compact fridge and its volume upon annual energy use. The interaction term is not significant, and the original predictor coefficients do not vary by much. In fact, the interaction plot above confirms this finding - the increase in annual energy consumption per unit increase in volume of the fridge is essentially the same whether or not the fridge is of the compact design type.
The animation plot above suggests that refrigerators that are certified under Energy's Star 2014 criteria do not necessary satisfy the 2021 Most Efficient Standards described previously. Pretty much all fridges meet the 2014 criteria, but not all are able to meet the specified 2021 criteria; in fact, most do not. This conclusion applies to fridges of any certification year.
Once you purchase a fridge, you are likely to use it for many years going forward. Based on the moving histogram above, fridges that meet previous criterion do not necessarily continue doing so. Thus it is imperative to do the necessary research and purchase a fridge that will continue to remain energy efficient, if that is of interest.
The style type of fridge is indicative of how much energy it would require. The interactive visual of energy consumption for fridges by type suggests that the average annual energy for residential refrigerators varies based upon the type of fridge. Fridges with a bottom freezer had larger variance in their energy consumption, ranging from 300 to 800 kWh/yr. Compact fridges tended to have an annual energy use of 200 to 400 kWh/yr, although a few exceeded this range (most of the Marvel, Sub-Zero, and Galanz brands). There were fewer freezer-less and single door fridges, but their energy consumption also tended to be within 200 to 400 kWh/yr. For side-by-side style fridges, it was 600 to 800 kWh/yr, while for top freezers, their energy consumption ranged between 300 to 500 kWh/yr.
However, the energy efficiency by type of fridge also varies. In the animated line chart below, the fridges, based on type and year of Energy Star certification, on average would consume less energy than the specific federal standard per year (all positive percentages). Compact fridges on the average as a whole would require less energy than the other fridge types until 2017, when freezerless and single door fridges began performing better in terms of energy usage compared to the federal standard set for the fridge. The bottom freezer fridges and top freezer fridges performed average to the other styles, with the bottom freezer ones performing slightly better overall. Over the certification years of 2014 to 2021, the side-by-side style fridges would average the worst energy percentage less than the federal standard, although briefly doing better for fridges certified in 2015 and 2021.
While it may be impractical to directly compare energy efficiencies considering the different purposes (some contain freezers) and sizes of these fridges (compact fridges are of smaller height and width, as suggested by the boxplots to the right), it is still important to note the patterns. For example, instead of buying a side-by-side fridge, you could buy a compact fridge instead if the size were feasible for you! The previous two visuals both suggest that it would be more energy efficient.
So what should you consider when buying a fridge, in terms of energy consumption?
- Not all refrigerators are energy efficient, nor will they stay that way.
- The dimensions and type of fridge you buy plays a significant role in determining your electricity bill.
- Features such as defrosting method and ice makers also affect energy usage significantly. These features may be convenient, but there is a tradeoff between this convenience and energy consumption.
References:
- Energy Star (2021). ENERGY STAR Certified Residential Freezers. [Data set]. https://data.energystar.gov/Active-Specifications/ENERGY-STAR-Certified-Residential-Freezers/8t9c-g3tn/data
- EPA Memo ENERGY STAR Most Efficient 2021. Energy Star. https://www.energystar.gov/sites/default/files/EPA%20Memo%20ENERGY%20STAR%20Most%20Efficient%202021.pdf
- Refrigerators & Freezers Key Product Criteria. Energy Star. https://www.energystar.gov/products/appliances/refrigerators/key_product_criteria
Credits:
Created with images by LustrousTaiwan - "fruit vegetable apple" • difisher - "fridge fridge door refrigerator" • igorovsyannykov - "cola beverage brand" • RitaE - "paprika salad celery"