In this paper a model of Trailer Refrigeration Units, TRUs, has been developed to quantify the fuel economy and emissions benefits of alternative power systems. Trailer refrigeration units (TRUs) are refrigeration systems typically powered by a separate diesel engine, and they are used to deliver fresh and frozen food products. The products can be very sensitive to temperature variation and maintaining the proper environment is very important. The diesel engines currently used to power the refrigeration system can contribute to high amount of local emissions at the loading warehouse. 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 an unsteady thermal modeling of TRUs that is coupled to the APU. For the diesel engine a fuel and emissions map is incorporated into the model. From our simulations it was observed that the duty cycle, 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 second part of the simulation model consisted of fuel cell hybrid APU, which was also coupled to the TRU thermal model. From our simulations over typical duty cycles it was observed that the fuel cell hybrid system's energy efficiency was greater than the diesel engine; also, they have a great potential to reduce local emissions and noise which, is a great concern for TRUs. 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 will allow for better temperature and refrigeration control in future systems.