A reefer (refrigerated) trailer is a truck trailer with an insulated closed body and a mechanical refrigeration unit that keeps the cargo at a set temperature. On most models the unit can cool and heat within a range of roughly −25 °C to +25 °C. It is used for temperature-sensitive products such as frozen and fresh food, pharmaceuticals, flowers and some chemicals; the temperature is recorded by a thermograph.
How does a reefer trailer work?
The refrigeration unit mounted on the front wall of the trailer works on a classic refrigerator cycle. The compressor compresses the refrigerant gas, the condenser releases heat to the outside, and the gas, after passing through the expansion valve, evaporates in the evaporator and draws heat from the air inside the trailer. Fans blow the cold air along the ceiling towards the rear; the air passes around the cargo and through the grooved floor and returns to the unit.
The unit usually runs on its own diesel engine; many models have an electric standby mode for connecting to mains power in a warehouse or on a ferry. Ice build-up on the evaporator is cleared by automatic defrosting at set intervals. In winter the unit switches to heating mode and protects cargo that is sensitive to freezing. In multi-compartment trailers, partition walls allow two or three different temperatures to be carried on the same trip.
Why do insulation and the ATP class matter?
The body is made of sandwich panels filled with polyurethane foam. The ATP Agreement, which governs the international carriage of perishable foodstuffs, was signed in Geneva on 1 September 1970; Türkiye became a party on 21 December 2012, and according to UN records there are 52 parties. Under ATP, the heat transfer coefficient (K) may not exceed 0.70 W/m²K for normally insulated equipment and 0.40 W/m²K for heavily insulated equipment.
The class marking on the trailer shows what it can do. For example, FRC is heavily insulated, mechanically refrigerated equipment that can bring the internal temperature to, and maintain it at, the desired value between −20 °C and +12 °C when the mean outside temperature is +30 °C. The first ATP certificate of a newly built trailer is issued for a period not exceeding six years; details of the certificate are in the entry on the ATP certificate. In Türkiye, the width limit for refrigerated bodies is 2.60 m instead of 2.55 m, to take account of insulation thickness.
| Product group | Typical transport temperature |
|---|---|
| Frozen food, ice cream | −18 °C and colder |
| Fresh meat, dairy products | Between 0 °C and +4 °C |
| Fruit and vegetables | Between 0 °C and +13 °C depending on the product |
| Cold chain pharmaceuticals | Between +2 °C and +8 °C |
| Pharmaceuticals stored at room temperature | Between +15 °C and +25 °C |
The values in the table are for guidance; what is binding is the product label and the manufacturer's instructions.
How should loading be done?
- Pre-cooling: The trailer is brought down to the target temperature before loading starts, and the door seals are checked.
- Cargo temperature: The product must already be at the correct temperature when it enters the trailer. The unit is designed to maintain temperature; it does not have the capacity to cool a warm load quickly. The measured product temperature is recorded on the loading document.
- Unit with doors open: If loading is done without docking at a ramp, the unit is switched off; otherwise warm, humid air is drawn in and the evaporator ices up.
- Air circulation: Pallets do not touch the front wall or the ceiling and stay below the manufacturer's marked load line. Air ducts are not blocked.
- Starting the record: The thermograph or data logger is started at the moment of loading, and the set temperature is entered identically on the unit and on the document.
How is the temperature record kept?
In the EU, devices recording air temperature during the transport of frozen food are required to comply with the EN 12830 standard. For pharmaceuticals, good distribution practice (GDP) requires continuous monitoring of temperature, retention of records and investigation of deviations. On delivery, the thermograph printout is handed to the consignee; any deviation is noted on the CMR consignment note. Device selection and reading are covered in the entry on the temperature data logger.
Common mistakes
- Dragging out loading while products wait on the ramp, allowing the cargo to warm up.
- Entering the unit setting in °F instead of °C, or not comparing the setting with the document.
- Packing pallets tightly and blocking the air ducts in the floor.
- Carrying fruit and vegetables in the same compartment as meat; they are incompatible in terms of both temperature and odour.
The whole process is explained step by step in the entry on cold chain road transport.
How does Voltim Global support this?
Voltim Global's cold chain operations are carried out together with partners holding GDP certification. The temperature range, recording frequency and steps to follow in case of a deviation are put in writing before loading.