Refrigerator Energy Consumption

Refrigerators can have very different energy consumption depending on the year of manufacture and features that affect energy use such as size, automatic defrost, or side-by-side design. To estimate the energy consumption of these appliances, we use the calculation method described in the Energy Data Sourcebook (Wenzel et al. 1997). Due to changes in technology and Federal efficiency standards, refrigerators have become significantly more efficient over time. Because most consumers do not know the Energy Factor of their refrigerator(s), we use a shipment-weighted energy factor based on the year the refrigerator was purchased (Table 14). This number is the average energy factor for all units sold within a particular year weighted by the number of units in each efficiency bin (AHAM 1996). Note that for purposes of this model, all refrigerators are assumed to be combined refrigerator/freezers. We do not distinguish between refrigerator/freezers located in conditioned space vs. those located in unconditioned space (e.g. in the garage).



                              Equation 8



                        EC = Annual energy consumption (kWh/year)

                        AV = Adjusted volume (cubic feet)

                        EF = Energy Factor (cubic feet•day/kWh)

The refrigerator / freezer adjusted volume is intended to capture in a single parameter the relatively high energy intensity of the refrigerator's frozen food compartment compared to the fresh food compartment. Equation 9 is used to calculate adjusted volume (US DOE 1995), and corresponds to the definition used in specification of federal minimum efficiency standards.



               Equation 9



                        AV = Adjusted volume (cubic feet)

                                    size = "Nominal" refrigerator/freezer volume (cubic feet)                       

                        frac = Fraction of refrigerator volume devoted to fresh-food storage (0 ≤ frac ≤ 1)

For side-by-side refrigerators, a fresh-food fraction of 0.6 is used, while all other configurations use a fraction of 0.66. Note that this model does not account for refrigerator usage factors that might vary among units, such as refrigerator and freezer temperature settings, door opening frequency, food loading rates, and ambient temperatures. While these factors can have a large impact on energy consumption, their effect has not been quantified in a way that could be incorporated into a parametric model such as this.