What is a reefer container?
The unit at one end of the box blows cold or warm air through a grooved T-floor and around the cargo. It runs on power from reefer plugs at terminals and on ships, and on the road from a generator set clipped to the container or chassis. Typical units hold set points from around −30 °C to +30 °C and also control fresh-air ventilation, and sometimes humidity or the atmosphere inside.
A reefer is built to maintain a temperature, not to cool warm cargo down, so goods must be pre-cooled to the carrying temperature before loading. Insulation makes the interior smaller than a dry box: a 40-foot high cube reefer measures about 11,583 × 2,286 × 2,554 mm inside. A non-operating reefer (NOR) is a reefer shipped as a dry container with its unit switched off.
The booking must state the set point, ventilation and any humidity setting, and the empty box should pass a pre-trip inspection before release. Load below the red load line and leave space for airflow so cold air reaches all of the cargo. Reefers usually carry extra terminal charges for power and monitoring and may get shorter free time, so plan collection carefully.