Sensitivity analysis and safety adjustment of the hydraulic condition in district heating networks.

• Carry out district heating network sensitivity analysis based on hydraulic model. • Sensitivity matrices in hydraulic condition are derived and validated. • Coupling characteristics of hydraulic condition are analyzed based on sensitivity. • A safety adjustment method is proposed based on sensitivity matrices. The district heating network (DHN) is an important infrastructure to meet the heating demand of residents and can become a flexible resource in integrated electricity and heating systems. When both supply temperature and flow rate are variable in DHN, i.e., quality-quantity regulation is adopted, DHN's energy efficiency can be improved, and more flexibility potential is provided for integrated electricity and heating systems to promote renewable energy consumption. However, the hydraulic condition of DHN under this situation will change more frequently, making it extremely important to effectively analyze coupling characteristics between variables in the hydraulic condition and formulate a safety adjustment strategy when state variables exceed their limits. In this paper, we establish various sensitivity matrices in the hydraulic condition that quantify control variables' impact on state variables and propose a safety management method based on sensitivity matrices. Firstly, the steady-state model of DHN's hydraulic condition is established considering the pump and motor-operated valve characteristics, and it is solved based on the Newton-Raphson method. Then, various sensitivity matrices are derived, i.e., the sensitivity matrices of node pressure and branch flow caused by the pressure of the reference node, the frequency of variable frequency pump, and the motor-operated valve opening. For the unsafe hydraulic condition where state variable overruns occur, a safety adjustment method that considers the safety of all state variables is proposed, which can avoid the problem of iterative adjustment caused by the existing sensitivity-based methods. The case study results show that sensitivity matrices can accurately describe the influence of control variables on state variables in DHN. The proposed safety adjustment method can ensure that all state variables are within their limits to the maximum extent possible. [ABSTRACT FROM AUTHOR]