PERFORMANCE CHARACTERISATION OF TRANSPORT TEMPERATURE CONTROL UNITS IN HEAT MODE A NEW TEST METHOD

摘要

A recent study has shown that transport temperature control (TTC) units used for the transport of perishable foodstuffs, can operate in heat mode for up to 60% of the year in regions north of the 55° latitude [1]. Despite the clear importance of heat mode during the transportation of perishable foods, current test methods used to evaluate heating capacity lack accuracy. As a result, this paper presents a new test method for accurately measuring the heating capacity of TTC units operating in low ambient temperatures, below -10°C. Existing test methods allow heating capacity to be evaluated to an accepted accuracy of ±10%, based on either measurement of airflow rate through the evaporator and air inlet outlet temperature difference across the evaporator, or refrigerant flow rate and refrigerant temperature difference across the evaporator. However, the new method proposed in this paper is based on electrical heat input that can be measured to an accuracy of ±1%. The new test method was performed on a truck TTC unit, positioned within a test facility capable of generating controlled low ambient air temperatures and the results are compared with those obtained using existing methods. In contrast with the existing test methods, this new heating capacity test procedure is based on the measurement of electrical power input from electric heaters and can provide results that account for additional heat influence from the evaporator's fans and non-uniform airflow through the evaporator. The test procedure described is generic and can be applied to determine heating capacity of any TTC unit that employs hot gas as a working fluid.