When I told my wife that one reason our refrigerator was having trouble maintaining a low temperature was that it was overfilled, she instantly produced three household-tips books that said a refrigerator is more efficient stuffed to the gills than it is empty. This seems to contradict the first law of physics: You don’t get something for nothing. If we take Heloise and her fellow hinters at their word, it costs less to maintain a warehouse full of fish sticks than a tray of miniature ice cubes in a motel-room fridge. Given two refrigerators, one jammed tight with Jell-O molds and the other empty of everything but air, which box works harder, uses more energy, and costs more to run? –Bruce Kula, via e-mail
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You get married yesterday, Bruce? You should know that once your wife starts whipping out the helpful-hint books, magazine articles, etc, you and your half-remembered physics don’t stand a chance. While the First Law of Thermodynamics holds true even in kitchens, you forgot about the laws of heat and mass transfer–no trifling matter. If we consider only appliances that most people are likely to use on a regular basis (no pool pumps or spa heaters, please), the refrigerator arguably sucks up more electricity than anything else in the house.
It’s true that when you initially load up your fridge with room-temperature food and drinks, the motor has to chug a while to cool it down. But once the contents reach the desired temperature, the motor doesn’t have to work hard to keep them there. The fridge sees a steady transfer of heat from the room to its interior, but that doesn’t appreciably change whether it’s empty or full. Some online theorists claim that the larger thermal mass of a full fridge (as distinct from the reduced air space) increases efficiency, since the compressor will run fewer times but for longer periods–the flywheel effect, let’s call it. But my guess is that the contribution of thermal mass to energy efficiency is relatively minor. For that matter, whether the fridge is full or empty is a secondary consideration in the grand scheme. On a day-to-day basis, the main way to save energy is to keep the door shut.
Art accompanying story in printed newspaper (not available in this archive): illustration/Slug Signorino.
