Product Definition/Scope of Product Category – A refrigerator-freezer features two separate, mechanically cooled compartments for storing food. We included only units with internal storage volumes of 14 cubic feet and larger and automatic defrost. We included top mount, bottom mount, and side-by-side freezer configurations. We did not include single door units.
Market Segmentation – We included 3 size categories: medium size units (14-17.99 cu. ft.), large units (18-22.49 cu. ft.), and extra-large units (22.5 cu. ft. and larger)
Performance Criteria - In developing the list of products that are eligible for Top Ten USA we evaluated products based on the following criteria:
- Annual energy use (kWh/yr) - This is based on usage in room conditions of 90º F without door openings, which is intended to approximate usage in a 70º F room with door openings.
Test Methods – We used manufacturer reported test data using the following test method for measuring the performance criteria listed above:
DOE federal test method 10 CFR 430, Subpart B, Appendix A1 - Residential Refrigerators (and Appendix B1 -- Residential Freezers)
Data Sources and Quality Assurance - We used manufacturer reported data from the EPA ENERGY STAR website.
Market Availability - In order to be qualified the model must be currently available to consumers through retail outlets such as department stores, big box stores, independent appliance retailers and/or on-line retailers.
Families of Similar Products – For instances in which multiple models produced by the same manufacturer (under one or more brand names) were substantially the same, we listed these products as a “tie” for one place on the list. These instances could include models with different features or amenities (e.g., shelf configuration, color) that do not impact energy consumption or models produced by one manufacturer for sale under multiple brand names through distinct divisions of a parent company or under contract to other firms.
Product Ranking - We list products on the basis of a progressive efficiency curve, with the following equation:
Medium-Sized Refrigerators: Maximum qualifying energy consumption = 5.9823*Volume+273.5
Large Refrigerators: Maximum qualifying energy consumption = 19.675*Volume-1.5
Extra-Large Refrigerators: Maximum qualifying energy consumption = 10.361*Volume+217.3
This method helps balance the need for a range of sizes of refrigerator-freezers with the desire to find the lowest energy consumption. If we had simply chosen the ten lowest-energy-consuming products, they would all be the smallest size available. The coefficients in the equation were based on trial-and-error to find a regression that would include a range of product capacities. No other linear equation exists that would fulfill this criteria and also result in only 10 products.
- Average annual energy use - The average amount of energy (expressed in kWh) that a typical American household uses for a refrigerator-freezer is based on the adjusted volume of the refrigerator-freezer (cu. ft.)
- Adjusted volume (AV) - A calculation of a refrigerator-freezer’s volume used to take into account the increased energy use of a unit’s freezer compartment relative to the fresh food compartment. This measurement is used to calculate a refrigerator freezer’s average annual energy use.
Refrigerator Freezer AV = Fresh Food Storage Volume + (1.63 x Freezer Storage Volume)
- Volume - The size of a refrigerator-freezer is expressed in cubic feet.
- Top-mount - A refrigerator-freezer with the freezer compartment mounted on top of the fresh food compartment.
- Bottom-mount - A refrigerator-freezer with the freezer compartment mounted below the fresh food compartment.
- Side-by-side - A refrigerator-freezer with the freezer and fresh food compartments mounted next to each other.
- Automatic defrost - An electronic control system that runs an intermittent heating cycle to prevent frost buildup on the unit’s evaporator.
- Progressive efficiency curve - Instead of a static efficiency threshold, the progressive efficiency curve is an equation that relates efficiency (or energy consumption) to size or volume.
Further Information -
- Federal Standards - http://www1.eere.energy.gov/buildings/appliance_standards/residential/refrigerators_freezers.html
- Energy Star - http://www.energystar.gov/index.cfm?fuseaction=find_a_product.showProductGroup_code=RF
- The Consortium for Energy Efficiency - http://www.cee1.org/resid/seha/refrig/refrig-main.php3