The influence of the control valve characteristics on the domestic hot water temperature

Namen diplomskega dela je opisati delovanje podpostaje za pripravo tople sanitarne vode v daljinskem ogrevanju z regulacijskega vidika. Poseben poudarek je na karakteristiki regulacijskega ventila, njenem vplivu na kvaliteto regulacije temperature tople sanitarne vode in izbiri primerne hitrosti pogona za nadzor odpiranja in zapiranja ventila. Ventil in pogon imata namreč poleg toplotnega izmenjevalnika ključni prenosni funkciji v regulacijskem krogu toplotne podpostaje in z njunim poznavanjem lahko izberemo najbolj primerne karakteristike komponent za dosego najboljših končnih rezultatov. Reševanje problema oz. izbire karakteristike ventila se v diplomski nalogi lotevam s pomočjo simulacijskega modela toplotne podpostaje in njenih komponent v Matlab Simulinku, ki omogoča učinkovito primerjavo različnih tipov karakteristik ventila v kombinacijah z različnimi hitrostmi pogona. Na tak način lahko dokaj enostavno primerjamo možne rešitve med seboj in jih tudi ovrednotimo s stališča regulacijskih zahtev priprave tople sanitarne vode, kot so hitrost regulacije (regulacijski čas), dinamična napaka in statična napaka. V uvodu diplomskega dela je opisan razvoj daljinskega ogrevanja skozi čas in oči tehnoloških smernic prihodnosti ogrevanja in ogrevalne industrije, ki nakazujejo problem priprave tople sanitarne vode in njenih zahtev, tako s stališča končnih uporabnikov kot s stališča generiranja toplote v toplarnah. Za doseganje standardov in kvalitete regulacije tople sanitarne vode so ključne komponente podpostaje, ki so opisane v drugem poglavju. Namen tega poglavja je bralca seznaniti s pomembnimi karakteristikami in parametri toplotnega izmenjevalnika, ventila, temperaturnega senzorja in pogona, ter bralcu omogočiti osnovno razumevanje simulacijskega modela, ki je predstavljen v tretjem poglavju v okolju Matlab Simulink na osnovi matematičnih enačb. Namen tretjega poglavja je bralca seznaniti s konceptualnim pristopom modeliranja posamičnih komponent podpostaje za pripravo tople sanitarne vode, kjer je v največji meri opisan ventil. Zaradi standardnega pristopa in uporabe koncepta linearnega prenosa toplote v podpostajah prevladuje v industrijski praksi prepričanje, da je linearna karakteristika ventila najboljša izbira za optimalno regulacijo tople sanitarne vode. Ali je ta domneva upravičena, je tema, ki se je dotika četrto poglavje. Tu so ocenjeni vplivi posameznih komponent toplotne podpostaje na regulacijo temperature tople sanitarne vode v različnih obratovalnih pogojih in kombinacijah sklopa ventil-pogon. Primerjava rezultatov simulacije z zahtevami regulacije tople sanitarne vode je predstavljena na koncu četrtega poglavja, kateremu sledijo zaključne ugotovitve.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