Have you ever wondered how your refrigerator works? Some people think that a refrigerator generates cold air but this is actually backwards. Air is naturally cold- heat is the odd thing in the universe! The temperature in space without any heat from a star is very cold (-273.15°C or -459.67°F). So the refrigerator doesn’t need to generate cold air, all it has to do is remove the heat from the air already inside. This is done with a refrigerant which is a liquid with a very low boiling point. Even gasoline can be used to build a refrigerator (but that wouldn’t be the safest option).
The refrigerator works by removing heat from the interior of the fridge and expelling it to the outside through the condenser coil. This is usually underneath the refrigerator. The basic process is:
- A refrigerant, a liquid chemical that is capable of absorbing and releasing heat, is compressed into a high-pressure gas by, you guessed it, the compressor. This raises the temperature of the gas- temperature and pressure are related. Kind of like when you have a deadline at work that you can’t quite make…
- The hot gas is then passed through a set of coils on the back or bottom of the fridge, where it releases heat to the surrounding air, causing the gas to cool and condense into a liquid. On refrigerators with the condenser coil in the bottom of the refrigerator, a condenser fan motor is used to force air through the coil and the heat is absorbed by this air and pushed into the kitchen from the back of the refrigerator and possible a louvered grill in the front.
- The liquid refrigerant then flows through an expansion valve, where it rapidly expands, causing it to evaporate into a low-pressure gas. If you picture a water hose spraying a fine mist, that is the idea.
- As the refrigerant evaporates, it absorbs heat from the interior of the freezer, cooling the air inside. The evaporator coil in the freezer section spreads the cold air to the refrigerator section with a fan motor (the evaporator fan motor). This evaporator coil tends to frost over as the moisture that comes in when the door is opened freezes to the coil. It defrosts itself with a timed defrost system using a defrost heating element, a defrost thermostat, and a defrost timer or defrost board. (If the defrost system isn’t working the passage air travels from the freezer to the refrigerator will get blocked with ice and the refrigerator section will grow warm.)
- The low-pressure gas is then drawn back into the compressor, where the cycle starts again. Once the target temperature is acheived, the refrigerator thermostat will stop the compressor until it is needed again later.
This continuous process of compressing and expanding the refrigerant allows the fridge to maintain a constant temperature inside, typically between 35-38°F (2-3°C), regardless of the temperature outside. Additionally, insulation in the walls of the fridge helps to retain the cool air and further stabilize the temperature.
If the condenser coil gets dirty (it just naturally does over time), it’s good to use a special condenser coil brush to get between the fins on the coil.
Basically, refrigerators use a cycle of compressing, condensing, and evaporating the refrigerant to remove heat from inside the freezer section. This also happens to be how an air conditioner works. I guess you could say we all live in refrigerators here in Alabama!