Characterisation and optimisation of transport temperature control units in heat mode

Abstract

The control of air temperature within trailer food-compartment during road transportation of perishable products is critical as it influences the deterioration rate and the quality loss of food more than any other factor. As a result, this thesis focuses on temperature control during the transportation of perishable food products, particularly in cold climates, where sub-zero degree Celsius temperatures exist. Transport Temperature Control (TTC) units are designed primarily to maintain product temperature, not to reduce or increase it. Therefore, TTC units must be capable of maintaining the set-point temperature of perishable food products by automatically providing cooling and/or heating as necessary. Due to the increased importance of heat mode to the transport temperature control industry, a detailed characterization of TTC units in heating was performed. This project sought to: i) propose a test procedure and test facility capable of accurately measuring TTC unit heating capacity, ii) provide the first complete characterisation of existing standard TTC unit behaviour in heat mode, iii) highlight the problems that are encountered during food transportation in sub 0°C ambient temperature, iv) propose several original design modifications for improved heating performance with general application for all types of TTC units, and v) present the first mathematical model capable of predicting the system behaviour in heating. Based on the improvements implemented the system behaviour was significantly improved. The results show increased heating capacity by 25%, system efficiency by 30%, while the fuel consumption was reduced by 7%. The characterisation of both standard and modified TTC units was obtained through: i) a mathematical model capable of predicting the system performance to an accuracy of ±6% and ii) an experimental study based around the development of a novel test procedure and facility that reduced the measurement uncertainty from ±10% to ±1%.