Simulation and experimental verification of an adjustable ejector for inter-building hydraulic balance in secondary heating networks

Inter-building hydraulic imbalance in secondary district heating networks is a prevalent issue that leads to significant energy waste. While conventional solutions relying on control valves can improve balance at the user level, they suffer from substantial pressure losses and limited regulation capacity at the building level. This paper proposes an innovative solution based on an adjustable ejector to achieve building-level hydraulic balance in secondary networks. The device mixes a portion of the return water into the supply flow, enabling simultaneous regulation of both supply flow rate and temperature, thus achieving precise control over the building's heat delivery. A detailed numerical model of the adjustable ejector was established and its reliability was validated experimentally. The entrainment characteristics were subsequently investigated. Simulation and experimental results demonstrate that the ejector's performance is highly sensitive to changes in both secondary fluid pressure and outlet pressure. By adjusting the needle valve opening, a wide thermal power regulation range of 8.1–20.7 kJ/s was achieved. Compared to the conventional throttling method, the proposed solution increased the supply water flow rate by 10.7 %, reduced the system electricity consumption by 15.6 %–53.2 %, and improved the hydraulic stability by 26.0 %–41.2 %. Furthermore, the study reveals the influence of the needle angle on performance, providing a theoretical basis for optimized design tailored to different application scenarios. This research lays a solid theoretical foundation for the efficient and intelligent application of adjustable ejectors in secondary heating networks.