During the refurbishment of a large hospital, noise emissions in the piping and at the chimney stack had to be reduced due to stricter noise protection regulations. The challenge in dimensioning the sound attenuation system lay in sufficiently reducing noise levels without causing a significant reduction in flue gas volume flow through added flow resistance, ensuring continued effective flue gas extraction.
Given this conflict, FlowMotion was commissioned to simulate the flow within the entire piping system, including the chimneys. The boiler and piping system comprised four boilers. As these were used alternately for various tasks, such as heating, hot water, and laundry, the full-load case had to be assumed for each individual boiler. Furthermore, some boilers recovered exhaust gas heat using heat exchangers, leading to highly variable flue gas temperatures. The flue gas was then channelled to a four-flue chimney via four pipes of differing lengths.
The simulation examined the four pipelines from the boiler outlet to the chimney outlet. In the cases studied, flow through the boiler pipes was generated solely by the draught of the chimneys. Consequently, precisely modelling the buoyancy of warm air—and thus the temperature and density distribution—alongside flow resistance, was of critical importance.
It was demonstrated that the generated volume flow depends primarily on the boiler temperature and the shape and length of the pipe. In some instances, flow separation and rotation occurred, which increased flow resistance. Through these flow simulations, the effect of a silencer on flow conditions could be verified during the planning phase, enabling a practical and economical design.
