Economical control of indoor air quality in underground metro station using an iterative dynamic programming-based ventilation system

A set-point of ventilation control system plays an important role for efficient ventilation inside metro stations, since it affects level of indoor air pollutants and ventilation energy consumption concurrently. In this study, to maintain indoor air quality (IAQ) at a comfortable range with a lower ventilation energy consumption, the optimal set-points of the ventilation control system were determined. The concentration of air pollutants inside the station shows a periodic diurnal variation in accordance with the number of passengers and subway frequency. To consider the diurnal variation of IAQ, an iterative dynamic programming (IDP) that searches for a piecewise control policy by separating whole system duration into several stages was applied. The optimal set-points of the ventilation control system in underground D-subway station, Korea were determined at every 3, 2, and 1 h, respectively. Then, according to the set-point changes, the ventilation controller was adjusted to an appropriate ventilation fan speed, correlating to the amount of outdoor PM10 that flows into the station. The results showed that the ventilation control system with the IDP-based optimal set-points has a better economical ventilation performance than manual ventilation system, with a 4.6% decrease in energy consumption, maintaining a comfortable IAQ level inside the station.