DYNAMIC MODELING OF A COMBINED SUPERMARKET REFRIGERATION AND HVAC SYSTEM

摘要

Worldwide, innumerable supermarket refrigeration systems exist, which show significant differences with respect to their construction, working fluids and most of all their efficiency. Because of the relatively high leakage rates, supermarkets do not only contribute to the indirect, but also, to a high percentage, to the direct GWP. In many supermarkets, primary energy is consumed for heating/air conditioning and cooling at the same time. The final aim of the present work is to design a concept for a coupled efficient refrigeration, heating and air conditioning system, thus reducing the overall energy consumption. Therefore, different interconnections and control systems will be investigated compared with regard to the influence on the total energy consumption of the entire supermarket. The task is part of the research project CREATIV and is to be realized within the next three years. CREATIV has had a particular focus on deliveries related to supermarket refrigeration. The natural working fluid CO_2 (R744) will be used for the refrigeration cycle investigated in the project. The refrigeration plant is a two-stage cycle, which is applied to cool the LT and MT display cabinets. To achieve an optimal overall COP, the surplus heat provided by the refrigeration cycle will be recovered, if required, for indoor heating. To fit the overall plant to different operating conditions and to keep the interior temperature fluctuations as low as possible, a central control unit will be developed. To validate the system and to compare the different approaches in the case of fast changing conditions, a dynamic model will be developed and tested. For the description of refrigeration cycles, the programming language modelica has proved value. At the Institute of Thermodynamics and the company TLK-Thermo GmbH, the model library TIL was especially developed for thermodynamic systems, which is continuously enhancing and is retrofitted by the library for data of chemical media TILMedia Suite. Extending from that, models for the different approaches will be evaluated and optimized regarding the efficiency at different conditions. For the modulation of the models, a set of measured values are available. The influence of different ambient conditions will be investigated to fit the operating parameters.