A hybrid control method for district heating substations based on time-based room temperature demand

In China, the district heating (DH) substation serves as a large heating area and has different functions in buildings. However, the control methods of DH substations are yet to adjust the water supply temperature according to the existing outdoor meteorological parameters. Due to hydraulic imbalance, it is difficult to implement flexible control according to building functions, resulting in uneven heating in different buildings and high energy use. This study aims to implement demand heating through a hybrid control method (HCM) based on the dynamic demand of room temperatures. The HCM integrates centralized and distributed controls. First, the resistance identification and hydraulic balance calculations of the pipe network were performed according to the flow and pressure balance equation to maintain conditions close to the real working condition. Second, according to the most unfavorable loop room temperature, the secondary water supply temperature was corrected to ensure that the heat supply of the substation met the requirements. Finally, the distributed valve opening was corrected by room temperature feedback from each building to achieve accurate control of room temperature. This study considered a DH substation serving both residential and office buildings as an example. The dynamic simulation model was built for analysis. Compared with the conventional control method (CCM), the HCM can effectively overcome the uneven heating phenomenon, the fluctuation of room temperature was significantly reduced, and the thermal comfort was enhanced. The heating energy use of the DH substation was reduced by 12%. The energy use of office buildings was reduced by 27.5%-38.3%. The energy consumed by circulation pump operation was reduced by 16%. The cost-saving was approximately 2.57 RMB/m2, and the total cost-saving was 4.12 x 105 RMB. In this study, the problem of dynamic thermal balance of DH substations was solved with the proposed system, which effectively responds to the demand for heating while improving energy efficiency through a flexible control system.