Optimal control of secondary side supply water temperature for substation in district heating systems

Juan Hou,Natasa Nord,Haoran Li,S.I Tanabe,P Wargocki,L Mazzarela,J Kurnitski,G Cao,H Zhang,M.C Gameiro Da Silva,I Nastase,C Inard

doi:10.1051/e3sconf/201911106015

Abstract

Low temperature is the most significant feature of the future district heating system- the 4th generation district heating (4GDH). However, a widely used control strategy for supply water temperature in substation is weather- compensated control. It is a feedforward control without any dynamic information about buildings, which can lead to higher or lower supply water temperature. This paper presents model predictive controller (MPC) applied to the supply water temperature control for substations in district heating systems. MPC is an advanced control technique, which can make full use of dynamic information of buildings to determine the optimal supply water temperature of substations. In this paper, a multiple inputs and single output dynamic model was identified by subspace methods. Two different MPC controllers were designed in Simulink. The MPC controller 1 focused on keeping indoor air temperature at reference values. The MPC controller 2 focused on both keeping indoor air temperature at reference values and tracking the minimum supply water temperature in order to find the temperature potential for the future DH systems. Both of the MPC controllers proved to have a better tracking effect for indoor air temperature and lower average supply temperatures compared to weather- compensated. The MPC controller 2 could further lower supply water temperature compared to the MPC controller 1 by tracking minimum supply water temperature in its objective function. The average supply water temperatures for the weather- compensated, the MPC controller1, and the MPC controller 2 were 52°C, 51°C and 50°C, respectively. The results showed that MPC has a great potential in the area of supply water temperature control of the district heating systems.

Highlights

In many countries around the world, the ability to heat and supply hot water to buildings is essential
Two different model predictive controller (MPC) controllers were designed in Simulink
The MPC controller 1 focused on keeping indoor air temperature at reference values

Summary

Introduction

In many countries around the world, the ability to heat and supply hot water to buildings is essential. By utilizing DH, a great improvement in energy efficiency can be achieved in the heating market. One of the most important conditions for running a DH system with high efficiency is low distribution temperatures [2]. A decrease in distribution temperatures will be essential for DH systems to play a crucial role in future sustainable energy systems [3]. Low temperature is the most significant feature of the future DH - the 4th generation district heating (4GDH). The revolutionary temperature level (50–55/25°C) will improve the efficiency of heat source, thermal storage, and distribution system, bring huge potential to renewable energies [4]

Methods

Discussion

Conclusion