Ageing of Mechanical Refrigerating Units for Refrigerated Transports

Some experimental data from in field measurements gave us as result a strong lowering of the performances of the refrigerating units for refrigerated transports during the service time. The question is if this lowering (ageing) is irreversible (like ageing of the insulation of the boxes) or not. The ageing of the mechanical refrigerating units is important for the evaluation of the safety coefficients to be used in coupling the units with the insulated boxes. We studied an in field measuring system to evaluate the refrigerating power of a unit: the system is based on a pulldown curve and on the extrapolation of the curve by calculation. The corrections for the evaporating temperatures are considered. The measured ageing coefficients seem to be not realistic: we investigated in order to distinguish the physiological ageing from the lack of maintenance. A further series of measurements was carried on, taking into considerations seven samples. The measurements were done on the units without any intervention and after maintenance operations. The results strength the hypothesis that the larger amount of the measured ageing is due to the lack of maintenance, while the not reversible ageing is some percents of degree of magnitude.