# Calculating the annual energy consumption for a fridge

I'm looking at a spec sheet for a fridge that I'm interested in buying:http://aegelectrolux.co.za/doc/S53420CNX2/SpecificationSheet.pdf and http://aegelectrolux.co.za/cooling/bottom-freezer-fridges/s53420cnx2-stainless-steel-bmf.html.

I was wondering how they calculate the annual energy consumption of 243kWh?

According to the spec sheet and the website , the watt / connected load is 120. If I calculate the annual energy consumption, I get:

(120W * 24 hours) * 365 days / 1000 = 1051.2kWh.

Am I doing something wrong? Quite new to doing these types of calculations so I might have missed something.

## 2 Answers

That 120W is the power while the fridge is actively working. Most of the time, the fridge isn't working - after all, it is a thermally isolated box and won't get warm by itself overly fast.

Hence, aside from marketing, the way they come up with that number is probably based on an assumption of how often the fridge needs to turn on its compressor to keep a given temperature on the inside, given a specific temperature (curve, even, maybe) on the outside.

The EU has mandatory power efficiency rating labels, the European Union energy label, which defines a calculation standard for such things. You can read its text here. I didn't do that for you, because it's not clear to me whether the method therein applies to a fridge spec sheet for the Australian market at all.

• ADDING to great answer. The number given is a relative number so you can compare model A with Model B. The number has very little bearing on how much energy it will actually use in your home. Factors such as, the fridge temperature setting, how much produce is in it, how often produce is added, how often the doors are opened, it's location, your house thermostat, your house humidity level, your local climate temperature, all act to significantly change the quoted number. – Trevor_G Mar 22 '17 at 18:42
• As @Trevor says, the main factor determining the duty cycle is the thermostat setting. The duty cycle is the run time divided by the total time. (That is if you have no broken seals or open doors. :-) – skvery Mar 22 '17 at 19:04

## DoE Rules

DoE requires all manufacturers to calculate the energy requirements. They have very specific rules. I would think they are required use the results in their documentation if sold in the US. Other countries and EU have similar

They first specify what measurements and how to do the measurements.

For example this is the formula for the Variable Defrost Control< br> Once the measurement are done then the energy is calculated

6.2 Average Per-Cycle Energy Consumption. The average per-cycle energy consumption for a cycle type, E, is expressed in kilowatt-hours per cycle to the nearest one hundredth (0.01) kilowatt-hour and shall be calculated according to the sections below.
6.2.1 All-Refrigerator Models. The average per-cycle energy consumption shall depend upon the temperature attainable in the fresh food compartment as shown below.

6.2.2 Refrigerators and Refrigerator-Freezers. The average per-cycle energy consumption shall be defined in one of the following ways as applicable.
6.2.2.1 If the fresh food compartment temperature is at or below 39 °F (3.9 °C) during both tests and the freezer compartment temperature is at or below 15°F (-9.4 °C) during both tests of a refrigerator or at or below 0°F (-17.8 °C) during both tests of a refrigerator-freezer, the average per-cycle energy consumption shall be:
E = ET1 + IET
Where:
ET is defined in 5.2.1;
IET, expressed in kilowatt-hours per cycle, equals 0 (zero) for products without an automatic icemaker, and equals 0.23 for products with an automatic icemaker; and
The number 1 indicates the test period during which the highest freezer compartment temperature was measured.
6.2.2.2 If the conditions of 6.2.2.1 do not exist, the average per-cycle energy consumption shall be defined by the higher of the two values calculated by the following two formulas:
E = ET1 + ((ET2 - ET1) × (39.0 - TR1)/(TR2 - TR1)) + IET
and
E = ET1 + ((ET2 - ET1) × (k - TF1)/(TF2 - TF1)) + IET
Where:
ET is defined in 5.2.1;
IET is defined in 6.2.2.1;
TR and the numbers 1 and 2 are defined in 6.2.1.2;
TF = freezer compartment temperature determined according to 5.1.4 in degrees F; 39.0 is the standardized temperature for fresh food compartments in degrees F; and
k is a constant 15.0 for refrigerators or 0.0 for refrigerator-freezers, each being standardized freezer compartment temperatures in degrees F.
6.2.2.3 Optional Test for Models with Two Compartments and User Operable Controls. If the procedure of section 3.3 of this appendix is used for setting temperature controls, the average per-cycle energy consumption shall be defined as follows:
E = E x + IET
Where:
E is defined in 6.2.1.1;
IET is defined in 6.2.2.1; and
E x is defined and calculated as described in AS/NZS 44474.1:2007 (incorporated by reference; see §?430.3) appendix M, section M4(a). The target temperatures t xA and t xB defined in section M4(a)(i) of AS/NZS 44474.1:2007 shall be the standardized temperatures defined in section 3.2 of this appendix.