CH-77-01-1 -- Environmental Control of Washington Metro

The Washington metropolitan area rapid transit system is expected to have 100 miles (160.9 Km) of track with 87 stations of which 53 will be underground when the system is completed. All of the underground stations have an air-conditioning system for summer cooling because without such cooling the station temperature would rise above outside air temperature. During winter conditions, the natural piston action air flow caused by trains, plus the heat generated by the trains is expected to provide adequate fresh air and sufficient heat inside stations for the patrons, who are normally dressed for winter weather.

The ventilation for the tunnels is separate from the station environmental system. Each Metro subway station has two vent shafts, each having at least 300 square feet (27.8 m²) of cross-sectional grating area at the surface, and located about 100 feet (30.5 m) from either end of the station. Each station also has at least one entranceway which is open to the atmosphere.

One chiller plant may provide chilled water for the air-conditioning of from one to three stations. The chiller plant is located outside the subway system, on the surface; or may be located inside an equipment room within the subway system. The chilled water lines enter the tunnel via a fan or vent shaft and are run inside the tunnel to connect into the mechanical equipment rooms within the station areas.