Performance evaluation of ductless ventilation system in basement space of an underground sewage treatment plant: A scaled model case study

In recent years, the number of underground sewage treatment plants has increased dramatically in densely populated cities. Mechanical ventilation system is necessary to ensure indoor air quality in the enclosed basement space of underground sewage treatment plants. Many disadvantages exist when using conventional overhead duct ventilation system. In this paper, a ductless ventilation system based on the concept of unidirectional piston flow is proposed for such flat large-space in underground sewage treatment plants. The influences of perforated plate porosity, installation of passage partitions, opening state of vehicle passage entrance doors and air supply mode on ventilation performance are investigated by using scale-model experiments. The results suggest that perforated plate porosity is recommended between 0.25 and 0.35 and partitions near vehicle passage entrance need to be installed. With a reasonable design, the unidirectional flow is formed in the whole level. No air leakage from the basement space to ambient environment happens when the pressure at vehicle passage entrance is 200 Pa higher than that at the outlets. However, serious airflow short circuit phenomenon occurs when the pressure difference reduces to -50 Pa in scale model. Present research provides a new option for the design of ventilation system in such kind of large and flat space.