Where does the heat in a fridge go?

The inside is cold, but the back can feel warm. A refrigerator does not manufacture a substance called cold; it moves heat. Follow the bright marker around the circuit to see where that energy goes.

Start with the entire pipe circuit. Refrigerant passes through four main stages and returns to the beginning. During normal operation it is reused rather than burned up. Its pressure, temperature and liquid-vapor state change along the way.

Returning vapor is at low pressure. The compressor uses electrical energy to raise its pressure and temperature. Why make it hot first? To release heat into the room, the refrigerant must be hotter than the surrounding air.

Follow the warm-colored pipe. Refrigerant releases heat to the room and gradually condenses into liquid. That rejected heat includes both what was removed from the interior and the energy supplied by the compressor.

The loop does not have one pressure everywhere. The high-pressure side releases heat to the room; the low-pressure side can absorb heat at a much lower temperature. This pressure arrangement makes the heat-moving cycle possible.

Liquid passes through a narrow capillary. The pressure drops, and some liquid flashes into vapor, leaving a cold mixture. This restriction does not produce useful shaft work, and it does not squeeze a supply of cold air into existence.

At the evaporator inside the cabinet, the remaining liquid boils. That change needs energy, supplied by the food and air inside, so they cool down. Low-pressure vapor then returns to the compressor, completing the loop.

Read the three numbers. With eighty watts of input and a coefficient of performance of two point five, two hundred watts are removed inside and two hundred eighty released outside. The machine moves existing heat as well as consuming electricity.

Increase the coefficient and watch how much heat the same input can move. A value above one does not violate conservation: the numerator is transported heat, while the denominator is added work. It is not an energy-creation efficiency.

Could leaving the door open cool the room? The absorbed heat would now come from that same room, then return at the back along with compressor work. For the room as a whole, the electrical input becomes a net heat gain.

Follow the marker once more: add work and pressure, reject heat, reduce pressure, then absorb heat inside. Colors illustrate the states, not literal molecular behavior. Real pipe layouts and operating conditions vary between refrigerators.

The next time you see a refrigerator or air conditioner, look beyond the cold side. Find where heat is absorbed, where it is rejected, and where work enters. Connect those three paths, and the mechanism becomes much clearer.