Beware of the Heat

Three pipes run through the system, two of them 10 inches in diameter and one 12 inches wide--carrying steam hotter than 400 degrees Fahrenheit, Hawkes says.

Most areas of the tunnel itself are about 60 to 70 degrees and are heated or cooled by the ventilation system.

Some of the entrances and exits to the tunnel allow outside air to keep the tunnels quite cold. But in other areas, the heat escaping from the pipes can raise the temperature in the tunnels to over 100 degrees.

But this problem of excessive heat does not come into play for most of the tunnel system because heavy insulation minimizes the heat entering the tunnels, Hawkes says.

The function of the steam pipes is primarily to heat open space and for hot water.

The Cambridge Electric Company's power plant on Western Ave. uses either natural gas or fuel, depending on which one is cheaper to heat the water to steam, Hawkes says.

It is efficient for the University to heat the buildings by steam rather than natural gas because the University "does not need storage tanks, a boiler room or a gas main," Hawkes says.

The tunnels are not connected to every building at Harvard, but they serve virtually each one either through the walk-in tunnels or through an underground conduit, which are smaller branch pipe systems.

Hawkes says the University has three miles of pipes running through the tunnel system, and another three miles of direct buried pipes.

The tunnel system is more than half a century old. Most of the sections were built between 1927 and 1933, although the first section was built even years before, in 1914, according to documents in the University's archives.

Considering that much of the structure is relatively old, the tunnels are in fairly good condition, Hawkes says, especially in the upper section of the Yard.

He says that in the tunnels which run along Memorial Drive, the concrete was delaminating, or peeling off the walls, because of the water from the river.

Hawkes demonstrated delamination by pulling a loose piece of concrete off the tunnel wall, loosing a cloud of dust.

By walking through the tunnels, one can see the three main steam pipes lining the walls as well as a fourth pipe that carries condensate, or chilled water, back to the power plant to be reheated to steam.