Long-distance transportation of food, many medicines and some chemicals became possible with the advent of electric refrigerators. Refrigerator trucks and vans, like home refrigerators, consist of two main parts, the compression refrigeration cycle and the cooling chamber. The beating heart of these refrigerators are the refrigeration units that are responsible for cooling the chamber. The refrigeration units of transportation and their types, whether direct drive or hybrid, are the subject of this article.
Introduction to Transportation Refrigeration Units
A compression refrigeration cycle and a container are used in the design of refrigerator vehicles, such as refrigerators and freezers. In a compression cycle, the phase change of a refrigerant is used to cool the refrigerator compartment. The general steps of the compression refrigeration cycle in Refrigerator trucks and portable cool storages include the following.
The movement of the refrigerant starts from the cycle compressor and the refrigerant is compressed in the compressor and liquefied from the gas. In fixed refrigerators or home refrigerators, the energy required to start the compressor is supplied by the city electricity, but this is not always possible in refrigerator vehicles or portable cold storages. This is the difference between direct drive and hybrid drive refrigeration units.
2. Cross the Condenser
We mentioned that the refrigerant is compressed inside the compressor and its temperature rises and immediately the refrigerant enters a heat exchanger. Air-cooled condensers are used in refrigerator vehicles, that is, the refrigerant inside is cooled by passing air through the condenser tubes.
3. Pressure Drop
The third step is for the refrigerant to pass through a pressure-reducing valve. At this stage, the fluid pressure is reduced at once. The purpose of this is to prepare the fluid for the final stage of the cycle. A sudden drop in pressure in the cycle pipeline reduces the boiling temperature of the fluid, and therefore, the effluent from the pressure-reducing valve will be a mixture of liquid form and saturated vapor refrigerant.
The stage of fluid passage through the evaporator or the cooling of the container is the last stage in the compression refrigeration cycle of refrigerated vehicles. The evaporator is designed as a heat exchanger and is installed inside the vehicle container. The refrigerant tends to evaporate after passing through the pressure-reducing valve. As a result, it absorbs the ambient temperature and cools its surroundings. The fluid returns to the compressor when it leaves the evaporator.
Different types of Refrigeration Units and their differences
Now that we know the general mechanism of refrigerated transport units, we can examine the difference between single-system and two-system refrigeration units. Note that this category has nothing to do with the below-zero or above zero of the refrigeration unit. It’s just a matter of how power is supplied to the refrigeration system of the vehicle refrigerator.
Direct drive refrigeration units
Direct drive refrigeration units supply their required power only through the vehicle engine. The compressor receives the power required for its operation using a belt used to the vehicle engine, and so that direct drive refrigeration units rely solely on the vehicle engine for power.
Hybrid refrigeration units (two systems)
Direct drive units are mostly used for non-stop or short-haul intercity transportation. Requires long distances and long stops for hybrid units. These units are designed in such a way that the compressor can supply its required energy from the city electricity if the engine is off.
Imagine a cargo that is going to go from city A to city B and the distance between these two cities is more than a thousand kilometers. Naturally, the driver will often have to stop at roadside resorts. In this case, the possibility of using electricity is an important advantage for the refrigerator.
Refrigerated vehicles are used to transport food and medicine products that are sensitive to temperature changes. The refrigerator used in Refrigerator trucks and vans consists of a cool storage compartment and a refrigeration unit. The refrigeration unit of these cars is designed and built based on the compression refrigeration cycle and is considered the beating heart of the refrigerator.
Units that supply only the power they need from the vehicle engine are called direct drive refrigeration units. But in hybrid drive units, you can also get help from electricity in addition to the driving force of the vehicle engine. This feature also makes it possible to transport products over long distances.