Modeling and the performance analysis of transportation refrigeration units with alternate power systems

In this research a model of Trailer Refrigeration Units (TRUs) has been developed to quantify the fuel economy and emissions benefits of potential alternative power systems. Trailer refrigeration units (TRUs) are refrigeration systems typically powered by an auxiliary diesel engine and are used to deliver temperature sensitive (fresh and frozen food) products. The products can be very sensitive to temperature variation and maintaining the proper environment is a high priority. The diesel engines currently used to power the refrigeration system can contribute to a high amount of local emissions at the loading/unloading warehouses. A promising future alternative is the use of fuel cell auxiliary power units (APUs). In this paper we have developed a MATLAB/Simulink based modeling of TRUs, and we have used the model to quantify the benefits of alternative power systems. The simulation model consists of a transient thermal modeling of TRUs that is coupled to the APU. The diesel engine emission map was developed empirically and incorporated into the model. From the simulations it was observed that the TRU duty cycles, energy consumption, and emissions are highly influenced by the ambient operating temperatures. Some of the most interesting results were observed when the ambient air temperature was very high. The simulated results were validated against the actual measured performance of the TRU.; The second part of the simulation model consisted of a fuel cell hybrid APU, which was coupled to the TRU thermal model. From our simulations over typical duty cycles it was observed that fuel cell hybrid system offers great potential to improve energy efficiency. The fuel cell hybrid system performance was found to be dependent on component size and control strategy, and we have made a study of the important parameters, such as state of battery charge, fuel cell size, and storage capacity. A fuel cell system enables a new paradigm in TRU design, since an electrical powered system allows for the use of variable rpm electrical drives such as dc motors and scroll compressors. The introduction of these more efficient and flexible systems may allow for better temperature and refrigeration control in future systems.