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DEFRA Transport Sector

The sectoral reports on the refrigeration energy usage in transport can be downloaded from this page, the sectoral focus page.

The COP (Coefficient of Performance) of transport refrigeration systems is quite low, ranging for around 0.5 at -20°C space temperature to 1.51.75 at + 3°C space temperature and 30°C ambient temperature. Work on refrigerated transport vehicles has shown:

  • Refrigeration systems in these vehicles are invariably driven by auxiliary diesel engines.
  • Average fuel consumption of articulated vehicles (excluding the refrigeration auxiliary diesel engine) is 24 l/hr. Fuel consumption of auxiliary diesel engine is approximately 2 l/hr (8% of vehicle main engine consumption).
  • Capacity and size of vapour compression refrigeration systems can be reduced through the use of thermal energy storage (eutectics). For small journeys the vapour compression system can be eliminated completely.
  • Sufficient reject heat is available from the engine of articulated vehicles to drive sorption refrigeration systems at normal out of town driving conditions but insufficient heat will be available in town driving. This shortcoming can be overcome through the use of an auxiliary heat source or eutectic energy storage. Other issues to be addressed are the size and mounting of the sorption refrigeration system.
  • Air cycle technology is quite promising for food transport applications. Main disadvantages at present are the low COP compared to that of the vapour compression system, particularly for chilled food distribution applications, and the unavailability of off the shelf components.
  • Direct power generation from the heat in the exhaust of the engine to power refrigeration systems may be a promising technology for the future. Other technologies that need further investigation and consideration are Stirling cycle powered systems, magnetic refrigeration and solar energy driven systems.

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Refrigeration energy use in transport

Case Study: CO2 cryogenic refrigeration for food transport

This case study considers the use of CO2 based cryogenic refrigeration systems for food transport refrigeration applications and provides a comparison between these systems and conventional vapour compression systems driven by an auxiliary diesel engine. In the absence of field data the analysis was based on a spreadsheet model which was developed to analyse the thermal loads of refrigerated transport. The model takes into account the construction of the insulated container, the properties of the food cargo, the weather conditions and the operating schedule and determines the thermal loads from: i) the food product, ii) transmission and infiltration through the container walls, iii) precooling of the space, iv) infiltration due to door openings for loading and unloading.

The analysis has shown that the use of liquid CO2 for refrigerated transport applications is feasible in both large articulated vehicles and smaller rigid vehicles and such systems are already commercially available. The economics of these systems are to a large extent dependent on the relative cost of diesel fuel and the cost of liquid CO2. The uncertainty in diesel and CO2 prices makes investment in CO2 systems difficult to justify purely on economic grounds. It is therefore likely that in the short-term investment decisions on CO2 systems will be based primarily on environmental considerations.

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CO2 cryogenic refrigeration for food transport case study

Contact FRPERC

Food Refrigeration and Process Engineering Research Centre (FRPERC), Grimsby Institute (GIFHE), Nuns Corner Campus, Laceby Road, Grimsby, North East Lincolnshire. DN34 5BQ. UK.

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