The compressor is the heart of the refrigeration cycle and is a critical component of transport refrigeration.
Transport refrigeration units operate with a cycle that uses an absorption system or vapour compressor to cool or dry the air. To understand the role of a transport refrigeration compressor, we first need to look at the refrigerant cycle.
The transport refrigeration cycle
In essence, the refrigeration process works by turning the refrigerant from a liquid into a gas. There are five mains steps to a refrigerant cycle:
- Evaporation – When the liquid refrigerant enters the evaporator, heat is absorbed as it evaporates and produces cooling. The refrigerant is diverted to a tank where the pressure rises until it meets the pressure in the evaporator. Once pressure is equalized, the refrigerant flow stops, and the temperature in the tank and evaporator rise to ambient.
- Compression – The compressor draws vapour away from the evaporator to maintain a lower temperature and lower pressure before sending it to the condenser.
- Condensing – The refrigerant leaves the condenser, which transfers heat from the refrigerant to either air or water. The byproduct is a gas refrigerant that condenses to a liquid.
- Receiving – The liquid receiver’s function is to store the liquid refrigerant and supply a continuous flow of refrigerant to the expansion valve where pressure is lowered to match the evaporative pressure.
- Expansion – By suddenly reducing the expansion valve’s pressure, the liquid boils and evaporates. This final step takes place in the evaporator to complete the cycle. The refrigerant then goes back to the compressor to repeat the process.
Finding the proper transport refrigeration unit
The above process becomes more complex for specific applications. The size of the transport refrigeration unit has an impact on the cycle, as deficiencies in the unit can produce poor results.
With the importance of refrigeration for many industries, including the transportation of food, flowers, medical supplies, and other temperature-sensitive products, proper insulation and material is needed to keep the unit cool.
The bottom line
For transport refrigeration, the cooling system is a multi-step process and is not a one-size-fits-all approach. Even a slight temperature change can result in products arriving at the facility frozen or not cooled enough, leading to a
significant loss for companies.
With something as complex as transport refrigeration, it’s imperative for companies to find the correct amount of cooling, insulation, and unit for their specific application.