Refrigerator Energy Consumption

Home Energy Saver

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. In Home Energy Saver professional and consumer the energy consumption of these appliances is estimated,  using 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. 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 (based on data from AHAM collected by LBNL's Appliance Standard Group). Note that for purposes of this model, all refrigerators are assumed to be combined refrigerator/freezers. The Legacy System does not distinguish between refrigerator/freezers located in conditioned space vs. those located in unconditioned space (e.g. in the garage).

 

EC = (365 X AV) / EF                                        Equation 1

        where

                        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 2 is used to calculate adjusted volume (US DOE 1995), and corresponds to the definition used in specification of federal minimum efficiency standards.   


AV = size X (frac + (1 - frac) * 1.63                Equation 2

            where

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.

Scoring Tool

Consistent with the asset rating model the Home Energy Scoring tool does not take user or operational inputs for refrigerators, and all homes have the same energy for refrigeration. This is estimated using the same model using the values for a 20 cubic foot, top mount unit with efficiency equivalent to the shipment weighted average of a unit built in year N, as shown in equation 3.

N = Year - (0.5 * LT)                                             Equation 3

Where:

N = the year to use for the shipment weighted efficiency for the default refrigeration

Year = The current year

LT = The estimated expected unit lifetime, presently estimated at 20 years