It’s a common misconception that freezer vans (or, indeed, domestic food freezers) work by creating cold. The truth is that they don’t actually generate coldness; they work by removing the heat from an insulated environment. When you take out as much heat energy as possible from an insulated, reasonably airtight environment, then you will create cold temperatures. This is the basic science of refrigeration, and if you have powerful enough machinery and tight enough insulation you can bring the temperature down inside the insulated compartment to extremely low levels.
There are three main pieces of machinery used to remove heat from the inside of the freezer van, all working in tandem to handle the entire process. These are the compressor, the condenser and the evaporator.
The condenser is a thin, coiled pipe that is filled with coolant fluid. This is a special chemical that is designed to be an exceptional conductor of heat. It absorbs heat energy in an extremely efficient way.
This coolant fluid runs through the system, and as it absorbs the heat and becomes hot it transforms into a low-pressure gas. The compressor takes this gas, increases the pressure, then the evaporator blows air from the outside through it to turn it into a liquid again. It’s the process of blowing air from outside through the high-pressure coolant gas that removes the heat from it and dissipates it outside.
Once the coolant has turned back into a liquid, it’s pumped back into the condenser to absorb more heat. The whole system runs like a circuit, with coolant fluid continually flowing, being turned into gas, being pressurised and then being turned back into a liquid again as the heat is dissipated outside.
There are several more technical details that make the process more efficient, but this is the basic principle of how the freezer van refrigeration unit works.
Of course this is only part of the story. The other extremely important element in the freezer van construction is the insulation. Without adequate insulation the freezer van refrigeration unit would be totally useless.
The insulation works by stopping heat from entering the vehicle from the outside. If heat leaked in from the outside, then there would be far too much heat for the condenser to remove. The efficiency of the refrigeration system and the lowest temperature that it’s possible for the system to maintain in the freezer van is directly linked to the thickness and quality of the insulation. The main difference between a refrigerator van and a freezer van isn’t the type of cooling system used; it’s the thickness of the insulation.