Refrigerator Needs 100 Watt-Hours of Electricity a Day

Chest refrigerator. Photo © Tom Chalko.

If you've ever wondered how all the ice cream and french fries in supermarket freezers remain frozen even though the freezers don't have lids, well, it's because cold air is heavy and settles at the bottom.

Tom Chalko, an Australian scientist and inventor, used this property of air and some electronic apparatus to lower the energy usage of a chest freezer to just 100 watt-hours a day (pdf).

Which is the same amount of electricity a 100-watt bulb burns in an hour.

As if that weren't enough, he used the freezer as a fridge, setting it at between 4° and 7° C (39° and 45° F). Freezers typically run at 0° to -25° C (32° to -13° F).

Here's how Chalko did it.

He bought a 239-liter (8.4-cubic-foot) Vestfrost SE255 chest freezer and a battery-powered thermostat that had a digital temperature display and an internal latching relay. He took the thermostat apart and rigged it up so he could hang it on the wall and still have it cut power to the compressor when the appliance reached a certain temperature.

And then he sat back and watched his new chest refrigerator exceed his expectations. In the first 24 hours, the fridge used up 103 Wh. The compressor worked for only 90 seconds an hour.

100 Wh a day is 36.5 kWh per year. A fridge of similar size sold in the U.S.A. typically consumes about 317 kWh per year. Which makes Chalko's fridge about 9 times more efficient than an average appliance-store fridge.

Sure, it's a chest fridge, which is somewhat inconvenient, what with all the bending to retrieve food from lower shelves. There's a good reason why no manufacturer makes chest refrigerators.

But if you were set on saving energy with a chest fridge, you could put in movable shelves. Or not use the lower part of the fridge at all.

If you were paying for just 100 Wh of power a day, you could afford to use only half your fridge!