DYNAMIC MODELING OF A COMBINED SUPERMARKET REFRIGERATION AND HVAC SYSTEM

摘要

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