Dynamic Modelling and Control of Thermal Energy Storage

Hector Bastida, Carlos E. Ugalde-Loo, Muditha Abeysekera, Meysam Qadrdan, Jianzhong Wu, Nick Jenkins
2019 Energy Procedia  
District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand
more » ... the heat demand -outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. Abstract Thermal energy storage (TES) is a critical element in district heating systems and having a good understanding of its dynamic behaviour is necessary for effective energy management. TES supports heat sources in achieving a steady power supply. Achieving heat and electric load demand translates into a discharging and charging control problem in terms of stored heat energy. To this end, an accurate dynamic model is essential to design effective controllers to improve district heating performance. A thermal dynamic model of a water tank, together with controllers for energy charging and discharging processes, are presented in this paper. The model is based on a computational fluid dynamics approach. It is developed using thermal stratification. The hot or cold-water stream which vertically crosses each tank section is considered to describe heat transfer. This is a non-linear process represented by partial differential equations, which are linearised to obtain a suitable model for control system design. State-space and transfer function representations of the system are obtained. The non-linear model is implemented in MATLAB/Simulink to design a linear controller that regulates the mass flow rate of cold and hot water to fill or empty the tank's energy according to performance specifications. The design of regulation and tracking controllers is explained. Simulation results show that a good performance in terms of the mass flow rate input demands is achieved with the proposed controllers. Abstract Thermal energy storage (TES) is a critical element in district heating systems and having a good understanding of its dynamic behaviour is necessary for effective energy management. TES supports heat sources in achieving a steady power supply. Achieving heat and electric load demand translates into a discharging and charging control problem in terms of stored heat energy. To this end, an accurate dynamic model is essential to design effective controllers to improve district heating performance. A thermal dynamic model of a water tank, together with controllers for energy charging and discharging processes, are presented in this paper. The model is based on a computational fluid dynamics approach. It is developed using thermal stratification. The hot or cold-water stream which vertically crosses each tank section is considered to describe heat transfer. This is a non-linear process represented by partial differential equations, which are linearised to obtain a suitable model for control system design. State-space and transfer function representations of the system are obtained. The non-linear model is implemented in MATLAB/Simulink to design a linear controller that regulates the mass flow rate of cold and hot water to fill or empty the tank's energy according to performance specifications. The design of regulation and tracking controllers is explained. Simulation results show that a good performance in terms of the mass flow rate input demands is achieved with the proposed controllers.
doi:10.1016/j.egypro.2019.01.942 fatcat:k3veumtsa5efvlpekbstkbckne