Depending on the exact nature of your cargo and packing preparation, it may be necessary to extract heat from one or several of the following sources:

• Residual heat of the container (The container can be pre-cooled.)
  
• Heat transmitted into the container through the walls, roof, or floor. (Can be minimized with light colored or reflective exterior, which should be kept clean since dirt will reduce the effect.)
  
• Heat contained in outside air introduced for ventilation.
  
• Heat generated by the product itself. All fruits and vegetables generate heat as they "breathe."