Characteristics and efficiency of single-pipe heating systems under various imbalance models

Abstract

Hydraulic imbalance in singlepipe heating systems remains a significant issue in older multi-apartment buildings, causing uneven heat distribution, reduced occupant comfort, and increased energy consumption. This study investigates the impact of various system configurations on heat distribution, energy efficiency, and comfort. Five scenarios are analyzed: an unbalanced system without thermostats or balancing valves, a system with thermostats only, a fully balanced system with thermostats and balancing valves, a system without balancing valves and with bypasses fully closed, and a system with balancing valves, thermostats, and return temperature control. The research utilizes designing tools such as Sancom designing software and Wilo Select online configuration tool, applied to a real case study in Ukmergė, Lithuania, to evaluate energy consumption and hydraulic parameters under different configurations. The study concerns are renovation scenarios of the heating system in a multi-apartment residential building located at Anykščių g. 1, Ukmergė, Lithuania. The building consists of 30 apartments. Total heated area is 1,758.42 m². Results reveal that fully balanced systems with return temperature control significantly enhance energy efficiency, achieving up to 70% energy savings compared to unbalanced systems, while ensuring consistent temperature distribution and occupant comfort [Figure 1]. Renovating a single-pipe heating system and converting it from a constant to a variable flow regime remains a rare and insufficiently explored solution. This study investigates such a case, integrating return temperature control—an approach that is almost never applied in single-pipe configurations. The results demonstrate that even with additional hydraulic resistance introduced by balancing valves and thermostatic control valves, the system performs more efficiently. It consumes significantly less circulation energy than a constant-flow system without these components. Contrary to the common belief that additional hydraulic resistance reduces efficiency, this research shows that a well-controlled single-pipe system can operate more economically and effectively. Compared to findings by other authors—who report energy savings in the range of 10–30% by introducing thermostatic and balancing control mainly in two-pipe systems—this study provides new evidence that single-pipe systems, if properly modernized, can achieve comparable or even better energy efficiency while maintaining thermal comfort. This contributes a novel perspective to the ongoing discourse on energy optimization in old residential buildings. This study underscores the necessity of implementing balanced and regulated heating systems, demonstrating their importance in achieving energy efficiency and sustainability goals in building renovation projects.