Energy-efficient time-delay compensated ventilation control system for sustainable subway air quality management under various outdoor conditions

Modern subway transport has become the primary mode of travel for millions of commuters, while indoor air quality (IAQ) in subway stations is becoming a major public health concern. The IAQ management in subway stations is governed by a rule-based ventilation strategy, consisting on the introduction of fresh air from outside. However, this strategy does not consider the IAQ dynamics under time-variant outdoor conditions. Alongside, the sizeable inherent time-delay of the subway IAQ system limits the performance of feedback controllers in the ventilation system. Therefore, a time-delay compensated gain-scheduled (TDC-GS) ventilation system based on the Smith Predictor (SP) is proposed to address the time-delay of the IAQ process. This strategy was assessed for various outdoor air conditions. The performance of the control systems was analyzed under two case studies consisting of good, moderate and unhealthy outdoor air conditions. The results demonstrated that the proposed control system can maintain the IAQ at healthy levels in both cases. Under good and moderate outdoor conditions, the TDC-GS system achieved an energy savings of 10.33% compared to the rule-based ventilation system, representing an emission reduction of 132.9 kgCO₂/day. Additionally, a more stable control response was achieved by the implementation of the SP technique. In comparison to the stand-alone GS control system, the errors were reduced up to 67%.