Hot enough for ya? Metro’s mystery buildings & other ways to keep riders cool

What do a historic firehouse in Petworth, a public fountain in Ballston, and a windowless brick building next to the DC Armory have in common? All three are essential components of Metrorail’s infrastructure to keep passengers cool during the region’s hot and humid summer months.

From the early days of Metrorail, planners fought for air-conditioned stations and rail cars to provide comfort to passengers and hopefully lure suburban commuters out of their automobiles. Several design features of underground Metrorail stations make a traditional air conditioning system unfeasible – the system’s iconic vaulted ceilings produce a large volume of air that would require immense energy to keep cool, while entrances leading directly to the surface and trains frequently entering and exiting make it difficult to contain conditioned air. Rather, underground stations utilize chilled water to cool stations up to six degrees from ambient temperature.

Chillers throughout the system cool water to about 40 degrees Fahrenheit, which is then circulated through pipes and coils to produce cool air within the station. Vents in the station’s coffers, escalators, and platform pylons supply cool air to passengers waiting for their train.

The Metrorail system has 52 chillers located across 31 chilled water plants throughout the region. Generally, each underground station needs one chiller for cooling. However, the three underground transfer stations (Metro Center, Gallery Place, and L’Enfant Plaza) have essentially double the volume and correspondingly require two chillers. Some stations have their own chilled water plant, while others share a plant. This is especially true downtown where stations are located close together and real estate is scarce. For a reason unclear to the author, WMATA documents indicate that chilled water plants at Bethesda and Mount Vernon Square each have two chillers, despite both plants only serving one station.

Below is a diagram of the location of the chilled water plant for each underground station, with each plant sized corresponding to the quantity of chillers at that site. WMATA names each chilled water plant sequentially based on which rail line it serves.

Metro’s chilled water plants have two primary components: indoor chillers and outdoor cooling towers. Where possible, WMATA tried to keep them closeby to each other and easily accessible for maintenance by constructing them at the surface (usually a one-story building with the cooling towers on the roof). Many of these buildings take the form of cookie-cutter brown-brick structures that are so typical of Metro architecture that many riders wouldn’t even give them a second look.

However, in some instances, WMATA made an effort to surround chilled water plants with facades that better fit into the local character of the neighborhood. The chilled water plant for Ballston and Virginia Square is hidden within a marble fountain in a public plaza and the plant for Potomac Ave and Eastern Market is surrounded by a brick facade emblematic of a Capitol Hill row house. Most notably, in 1995, WMATA incorporated a chiller plant for Georgia Ave-Petworth into the historic firehouse of DC Fire Department Engine Company No. 24.

Many underground Metrorail stations are built in neighborhoods where it would have been expensive to acquire the land to construct a freestanding chiller plant. In these instances, WMATA split the chillers from the cooling tower, with the former being located underground at the mezzanine level of the station and the latter being located on the roof of nearby buildings (often not owned by WMATA but negotiated through an agreement with a private developer). These plants are more difficult to access, hindering quick repairs during a potential malfunction. Notoriously, the chilled water plant serving Farragut North and Dupont Circle was broken for four years between 2015 and 2019, leaving passengers to wait in hot stations amid insufficient patchworks from WMATA. Although not as extreme, similar issues have recently plagued Rosslyn, Union Station, and Bethesda, all of which have their cooling towers located on nearby buildings.

What’s next for the system’s chiller infrastructure?

Like much of the Metrorail infrastructure, by the early 2010s, the system’s chilled water plants began to reach the end of their useful lives. Leaks and frequent breakdowns led to WMATA replacing the aging chilled water infrastructure with newer and more sustainable models. New chilled water plants reportedly save 400,000 gallons of water and $15,000 in electricity each year compared to the originals. Starting with Mount Vernon Square in 2011, WMATA has replaced 20 of its 31 chilled water plants, with plans currently underway to replace the plants at Van Ness, Rosslyn, Stadium/Armory, and L’Enfant Plaza.

Chilled water plants also present an unlikely opportunity for WMATA to create additional revenue streams. As discussed above, stations were built with freestanding chiller plants, since, at the time of construction, nearby land was relatively cheap to acquire. Yet, for a couple of stations, the surrounding neighborhoods have experienced a boom in development in the decades since opening.

By virtue of greatly appreciated land values, WMATA is able to lease or sell the real estate where the chiller plant is located, earning sizable revenue for the agency. In these instances, WMATA requires the property owner to incorporate the chillers and cooling towers into their new development. Recently, WMATA sold off its Navy Yard chiller plant to a developer and its Tenleytown plant to Georgetown Day School. A similar arrangement is in place for WMATA’s joint development plans at the Jackson Graham Building, the agency’s former headquarters that also contained chillers for Judiciary Square, Gallery Place, and Archives.

Despite opening 20 new Metrorail stations in the 21st century, only one (Congress Heights) is located underground and requires a chiller. However, this does not mean WMATA is moving away from chillers to provide comfort to passengers. Any expansion of underground mezzanines–such as new entrances or walkways between stations–will require additional chillers to cool the new facilities.

Conceptual designs for new entrances at Crystal City, Ballston, and Bethesda and underground walkways between Farragut North & West, and Metro Center & Gallery Place all explore the ability of existing chillers to accommodate the expansions. Although it is decades away from operation, whichever alignment is selected for the Blue/Orange/Silver Capacity and Reliability Study (such as the popular BLoop) will include over a dozen new underground platforms that will require new chilled water plants to keep passengers cool. Metrorail’s chiller infrastructure will remain a critical part of the system for decades to come.