|ISO 1496-2 does not specify the maximum ambient temperature at which a refrigerated container must operate correctly. The only specification is that for the purposes of testing, the cooling capacity must be 125% of the heat load that passes through the walls at an ambient temperature of 38°C and a temperature inside the container of -18°C. With the types of insulation in common use today this lies between 3 and 3.5 kW. These values are far exceeded by the refrigeration units that are available today, as can be seen from table 11. Here, the cooling capacity at -18°C is approximately 5.7 kW.
However, for practical reasons, the following applies:
Conditions of this nature are usually listed in the specifications issued by shipping companies.
- The mechanical protection mechanisms of the refrigerated circuit should not trigger when the refrigeration unit is at a standstill or as a result of sunlight. So, for example, with ambient temperatures of between 70 - 80°C it should not be possible for a pressure valve to open and release refrigerant. The Carrier Transicold 69NT40 refrigeration unit has, for example, a protection pane with a bursting pressure of 35 bar. According to the vapor pressure curve for the refrigerant R134a, this corresponds to a temperature of approximately 94°C.
- Obviously, other components of the container also should not suffer damage at a temperature of 70 - 80°C, when the refrigeration unit is at a standstill or as a result of sunlight.
- The electronics of the device should not fail when subjected to sunlight. Here also, temperatures of -80°C - 80°C may be considered realistic.
- It must be possible to operate the refrigeration unit under the ambient temperatures that occur in practice. The highest temperatures that can be expected occur when transporting refrigerated containers below deck or when operating on an asphalt surface exposed to the sun. A maximum value of 50°C is generally assumed but this is not specified in any standard.
- Values of -30°C to -40°C are considered realistic values for the lower limits for the ambient temperature. At these temperatures also, no damage should occur.
- All system components must be sufficiently protected to ensure they will operate in the rain or when exposed to salt water when stowed on deck.