585-cr work to upgrade Blue Line’s tunnel ventilation & air-cooling systems starts

Kolkata: The work for modernisation of the air-conditioning and installation of tunnel ventilation system across the Blue Line's 15 underground stations was launched on Wednesday. This was the first major overhaul of India's oldest metro, which is in its 41st year. The upgrade to an energy-efficient tunnel ventilation system (TVS) and environment control system (ECS) that includes air-conditioning will cover 16-km-long Belgachhia–Rabindra Sarobar section, serving these stations.
This will add a new dimension in comfort and safety, Metro Railway general manager Subhransu Sekhar Mishra told reporters, while flagging off the Rs 585 crore project. A puja was performed to mark the occasion inside the Noapara station-cum-carshed."We would be saving a lot of energy and groundwater. The project will take four years to be completed, without impacting operations. We shall choose five stations at a time, between Begachhia and Rabindra Sarobar, as per our convenience," Mishra said."The transition from the traditional water-cooling chillers to air-cooling ones will reduce 23,000 metric tonnes of carbon footprint annually. The shift addresses the issue of drying bore wells and depletion of Kolkata's ground water level," said Asim Majumdar, Metro Railway's principal chief electrical engineer, who is leading the project.TOI reported on Sept 16, 2025, that "Metro AC set to go green with new tech". Global bids were invited, and Shinryo Suvidha Engineers India, a subsidiary of Japanese Shinryo, won the contract to replace 30 out of 46 water-cooled chillers with more energy-efficient air-cooled ones and preserve 18 crore litres of groundwater annually.Kolkata's Blue Line was the first to adopt such an air-conditioning system in a tropical climate globally along with Hong Kong. The original design made by IIT-Kharagpur in the 70s relied on an open-loop system that uses a continuous, one-way flow of water from an external source to provide cooling rather than circulating. The system required a constant water source for heat rejection. The design was modified to a semi-closed system in 2011."Now, the system moves away from energy-intensive open loops to a semi-closed methodology, where around 90 per cent of an underground station's cool air will be returned to the air handling units (AHUs), drastically reducing energy waste," an engineer said.The AC units will maintain a subsoil temperature of 28°C, facilitating the survival of thousands of microbes. "Metro operations generate heat in the tunnels, and a temperature rise could threaten microbes essential to ecological balance," explained Majumdar. Regarding the tunnel ventilation system revamp, he said, "The non-AC rakes that ran through our underground tunnels were replaced with AC ones. The system needs to be upgraded accordingly so that passengers continue to get cool air."The stations will be cooler with over-the-track exhaust. The fans will start revolving automatically if there is the slightest deviation in the standard subsoil temperature (28°C). "The advanced smoke emission feature will have fans acting as exhausts as well as fans, to release smoke in case of fire, also providing oxygen to passengers during evacuation," an engineer explained.