Top-down model for dynamic simulation of cold-storage plants

A simulation model for dynamic processes in cold-storage plants is presented. It consists of interacting subsystems like the cold-store air, goods, room structures, cold-store walls, evaporator, refrigerator and environment. The mathematical description is based on mass and energy balances, coupled with simple assumptions on heat and mass transfer. Freezing of goods and frosting of the evaporator is accounted for, as well as the possibility of defrosting. A concise description of the overall dynamic behaviour is achieved by using a modular structure together with top-down modelling. An advantage of this model is its limited number of parameters, most of which can be determined from readily available information, e.g. from data sheets. Using these parameters, the transient behaviour of the most important variables in cold-store operation can be predicted. Such predictions are compared to experimental data taken in the present work in a medium-size cold store. The transient behaviour of the temperature and relative humidity in that cold store is reported for a cooling period with two different controllers and for a defrosting period. For all studied operating conditions the results of the simulation show favourable agreement with the experimental data. This shows that the simulation model is suited for studies of improved automation and control concepts for for example, at preventing losses in the quality of the goods or for energy savings.