Q: Is my friend Kim right when she says I鈥檒l save energy by putting bricks or polystyrene foam in the unused space of my freezer?
A: If you have an upright freezer, there is a case to be made for filling voids with material with low specific heat and low thermal conductivity. This will prevent cold air falling out when the door is opened. This lost cold air is replaced by the warmer air in the room which must subsequently be cooled when the door is closed again.
The low specific heat and thermal conductivity of the filling will minimise the heat loss caused by convection while the door is open. Obviously, adequate room must be left for air circulation when the door is closed. However, I suspect that the energy saved by filling an upright freezer with polystyrene foam is not significant. Leaving the door open as little as possible is probably a better option.
Advertisement
If you have a chest freezer, then you should put in it those things you want frozen and nothing else. The losses from a opening the lid of a chest freezer are much less those from opening the door of an upright freezer. Indeed, it is for this reason that supermarket freezers do not usually have lids.
When any freezer is closed and at its proper operating temperature, the heat loss is independent of the contents (unless they generate heat). Also, of course, reducing any object to 鈭�18 掳C from room temperature requires energy. Doing this for a pile of bricks is wasteful, unless one particularly wants very cold bricks.