Topic of the diploma thesis is to describe domestic hot water substation in district heating network from control point of view. Special focus is on control valve characteristics, its influence on quality of the domestic hot water temperature control and appropriate actuator speed selection to control the valve. Valve and actuator, together with heat exchanger, have key transfer functions in domestic hot water substation control loop and with understanding them we can choose the most appropriate component characteristics to achieve optimal results. Problem solving, or choosing the right control valve flow characteristic, is being approached with help of Matlab Simulink where simulation model of substation is being built. Based on that approach we can easily choose different types of control valve flow characteristics in combination with different actuator speeds. That way results are easily comparable among each other and also evaluation from requirements of domestic hot water preparation, like settling time, dynamic error and static error, can be done.
In the introduction description of district heating technologies over time and technological guidelines of the future for heating and heating industry can be found, followed by implication of domestic hot water control problem and its demands from end user and heat generation point of view. To reach the standards and quality of the domestic hot water control, the use of the right components is crucial, which are described in second chapter of the diploma thesis. Purpose of the second chapter is to introduce the reader to important characteristics and parameters of heat exchanger, valve, temperature sensor and actuator. This enables the reader to understand the basics of the simulation model, which is described in third chapter with the help of Matlab Simulink based on mathematical equations.
Third chapter brings an explanation of domestic hot water substation components modeling and conceptual approach of it. The biggest focus is dedicated to control valve, which, due to standard approach and use of linear heat transfer theory, is selected with linear flow characteristic. Presumption of the linear heat transfer approach being optimal, is discussed in fourth chapter. Influences of the substation components on the domestic hot water temperature control in combination with different actuator-valve combinations are presented, as well. Results comparison with domestic hot water standards is shown at the end of the fourth chapter, followed by some final deductions and a conclusion.