We were completely surprised by the results of our experiment. The compressor on a full refrigerator runs more frequently than an empty one, translating into lower efficiency and higher energy use. The results disprove our hypothesis, showing the adage to be nothing more than a "wives tale". Filling all of the excess space in ones refrigerator is clearly not an economical choice.

There are a number of ways in which this investigation could be taken further:

The question arose during our analysis of whether too much water was placed in the refrigerator, impeding airflow. Comparing a full to a half full refrigerator would rule out impeded airflow as a cause for the increase in compressor run time.

Another factor we would like to see studied is whether the volume of stored material plays any role in mitigating heat flow into the body of the refrigerator. Perhaps there is a threshold amount of water that can be effective in increasing the efficiency of the refrigerator, and perhaps we exceeded this threshold. We suggest anyone who attempts a similar experiment holds several trials with various amounts of water in the fridge.

Water has a very high thermal mass, and takes significant amounts of energy to cool. Using a voluminous substance with a low thermal mass would define the difference between the effect of volume on airflow within the refrigerator compartment and the effect of thermal mass.

Lastly, we struggled to explain why the coolant ran significantly hotter when the refrigerator was full. By conducting the experiment with a temperature sensor placed in one of the jugs of water, we could determine if the water temperature fluctuated along with the air temperature inside the refrigerator. If it did, it would mean the refrigerator had to remove a greater amount of heat from the refrigerator to return it to its set operating temperature, and may explain the higher coolant temperature.