Stone lions guard the gates to Yale’s Central Power Plant, housed in a red brick neo-gothic structure on Tower Parkway, with the thick smoke spewing out of its towers the only sign of the activities going on inside.

But last Friday, nine curious Yale students got to explore this “Power Plant Wonderland” through a tour organized by the Student Taskforce for Environmental Partnership. The tour — led by Plant Manager Tom Starr and STEP coordinators Angel Hertslet ’08 and Anders Hsi ’08 — allowed students to see the inner workings of the power plant, which powers a large portion of the University’s campus.

After donning hard-hats and protective goggles, students followed Starr through the maze of rumbling machinery that fills the 90-year-old building, including the largest chiller in the state of Connecticut. As he guided the group past large metal compressors, chillers, boilers and gas turbines, Starr explained that the plant supplies Yale with both electricity and heat through a process called cogeneration, which is thermodynamically one of the most efficient uses of fuel.

To generate electricity, fuel is burned in a gas turbine, Starr said. The turbine turns, producing electricity. Typically, the heat generated in this process is wasted, but in cogeneration, the heat is routed to a boiler, which produces steam to power a steam turbine. The steam turbine drives chillers that can cool water. In the end, the process produces electricity, steam and chilled water.

“If you happen to be at a place where you need both electricity and steam, home run,” Starr said. “Everything we do here is about reliability, but right behind that is ensuring we’re doing it as efficiently and being as environmentally friendly as we can.”

While the power plant is designed to save energy where possible, Starr and the STEP coordinators said students also play a part in conservation by regulating their energy consumption. Reducing needless energy use is one way to cut down on carbon emissions, they said.

“You have a responsibility to be outraged when you’re in an overheated room,” Starr said.

Hsi and Hertslet pointed to Yale’s goal of reducing carbon emissions to 10 percent below 1990 levels by 2010 as a positive step towards sustainability.

“It’s a pretty aggressive commitment, and the fact that President Levin is behind it is great,” Hertslet said. “But we really want students to be behind it, too.”

The tour was incorporated into the recently launched Green Tyng contest, in which residential colleges compete to recycle and to reduce food and energy waste. Everyone who went on the tour Friday earned points for their college.

As the tour concluded, students visited the plant control room, where a staff of three operates about a dozen computers around the clock to ensure that all machines run smoothly and exhausts are properly released. The two thin exhaust towers have no visible emissions because the natural gas the plant burns is much cleaner than conventional fossil fuels, Starr said. The cloud of fumes that spills out of the cooling towers is nothing more than water vapor that is released after the chilling process, he said.

At the end of the tour, students said they were impressed by the plant.

“I know that STEP slams that information into us daily, but hearing the coordinator of a power plant tell me to stop wasting heat energy seemed to have a stronger effect,” Stanley Seiden ’10 said. “The most important thing is for students to understand that it is the responsibility of every single one of us to help Yale conserve energy.”

STEP will offer another tour sometime after spring break.