Why Subway Tunnels Are So Damn Hot in the Summer

From WeeklyDig:

You know how Park Street Station is an airless tomb from June to August? Just like all the other underground T stations, which are also sweltering and breezeless in summer? Well, they’re not hot because of global warming or substandard building codes of generations past. The real reason the T is stuffy and hot is the fault of modern improvements, according to Gerry O’Regan, railfan and officer of the Boston Street Railway Association.

“Back before air conditioning was popular, the tunnels used to be nice and cool in the summer,” he says. “They used to be where you went to get cold in the summertime.”

Which makes sense, because they’re underground, a place where temperatures aren’t as extreme as they are on the surface. That’s why before refrigeration, people had root cellars. That’s why small animals in deserts (and people in Australia, while we’re at it) live in burrows and dugouts. Because of this, the T tunnels were designed with an average temperature of 50-60 degrees in mind, and kept breezy with a ventilation system of vents that let air from the tunnels into the cars.

So what went wrong? Why are the once-cool tunnels now sweltering doldrums of death?

“It’s because the cars are air conditioned,” O’Regan says. “It heats the air discharged back into the tunnels, and works as a heat pump. It’s hot in summer because air conditioning is on. And the electronics in the cars and tunnels give off heat, too, which means that additional heat gets pumped back into subway. And there’s nowhere it can go.”

(via Universal Hub)