Refrigerated cargo temperature loggers usually record supply and return air temperatures.

During periods off power, circular chart recorders and some refrigeration unit recorder systems continue to operate on back up batteries, but unless USDA probes have been placed in contact with the cargo, the supply and return air probes merely record still air temperatures within the machinery plenum spaces. This may not be a true reflection of the cargo temperature when the air circulation fans are off. In circumstances where no battery back up is available there is no temperature record for the off power period.

“Censor” software has been developed principally to estimate cargo temperature in refrigerated containers during normal and abnormal operation. Problems that may occur at transfer points, following power failures, during equipment malfunction or following operator error can be assessed and analysed. Thus the program may be used both as a risk assessment tool and as an aid in cargo claims work. Custom versions of the software can be easily produced to simulate refrigerated ship cargo holds and cold stores. Censor software is used to estimate: Cargo temperature changes following loss of refrigeration. Cargo temperature changes following recovery of refrigeration. Cooling of warm cargoes. Temperatures during transport off refrigeration. Cargo temperatures during transfers at terminals. Effects of intermittent periods of refrigeration power loss and evaporator defrosting. Refrigeration unit performance and cargo cooling. Effect of variable ambient temperatures. Self heating of fruit & vegetable cargoes. Temperature change rates through freezing points.

Censor software capability is provided as an integral part of the CRT cargo claims and expert witness service.

Links:
“Temperature Prediction Software for Refrigerated Container Cargoes”
paper by J Frith presented to the Institute of Refrigeration Thursday 6th November, 2003

Software: Vissim

Examples of prediction software output:

Frozen cargo, power off for 12 hours at day 3 and day 4

Frozen cargo, power off from day 6 to day 28

Chill meat cargo, loaded warm, cooled in container, power off for 12 hours at day 6

Chilled meat cargo, temperature rise off power