Intelligent Energy Efficiency Measures for Underground Metro Stations

Delhi Metro is India's first modern public transportation system and the world's 8th longest metro system with network length of 347.6 kilometers (215.9 miles) and 253 stations. The total energy consumption for running of trains and auxiliary systems was 1117 million kWh in the year 2018-19. The electrical and mechanical equipment at stations consumes about 40% of the total energy consumption of the entire network. An underground station consumes about 8 to 10 times of energy than an elevated station because of air conditioning and lighting requirements. The Environment Control System (ECS) or Ventilation, and Air-Conditioning (VAC) systems consumes approximately 70% of total energy consumption at an underground station. The Air Handling Units (AHUs) and Trackway Exhaust Fans (TEFs) which consumes about 50% of total energy consumption of VAC systems are selected on the basis of Open Mode, Close Mode and Emergency Mode operations which requires different pressure rating of the fans in different modes. During implementation of Phase-I and Phase-II of Delhi MRTS, the AHUs and TEFs were fixed speed type and consumes more power because of selection of fans at higher pressure rating. In Phase-III, all the 34 underground stations are provided with Variable Frequency Drives (VFDs) for AHUs and TEFs which resulted in the huge amount of energy savings at the underground stations as the fans can be operated with required pressure rating as per the mode. Further, Ministry of Housing & Urban Affairs, Government of India, in their publication titled 'Best Practices & Innovations in Metro Rail Systems' have acknowledged this endeavour of Delhi Metro and suggested all metros in India to provide their systems with VFDs. The actual energy savings to the tune of 35% or more are realized with the use of VFDs. This paper presents a detailed comparative study between VFD system and fixed speed system based on actual energy consumption at underground stations of Delhi Metro. The control algorithms designed to vary the speed along with the other intelligent features implemented in the station's Building Management Systems for energy savings are also presented. The paper also discusses the design basis for selection of the various equipment used in VAC systems at underground stations.