PRINEVILLE, Ore. — The newest addition to Facebook’s data center campus is all about cold storage.

But it has nothing to do with temperature.

For Facebook, cold storage means data that’s no longer in high demand. Think billions of photos added around the world, since Facebook created the photo upload feature in October 2005.

Many of them haven’t been accessed in months or years. But they have to go somewhere.

Last week, the social media giant started operating a cold storage facility next to its two 338,000-square-foot Prineville data centers.

The cold storage building will allow Facebook to store old photos and data from its 1.15 billion users on separate servers from hot data, new photos and tags being added daily and accessed frequently. The result is far lower energy costs for Facebook at its Prineville site.

Facebook users upload 350 million photos every day, Michael Kirkland, a communications manager for the company, said during a tour of the cold storage building Tuesday. Users have added about 250 billion photos since Facebook started allowing photo uploads, he said.

More than 80 percent of Facebook’s online traffic centers around just 9 percent of the total photos being stored, said Chuck Goolsbee, site director for the Prineville data centers.

That makes separate storage for older photos crucial.

“Our whole focus here is on minimizing the use of energy,” Goolsbee said.

Shifting old photos to the cold storage servers frees up its other servers to handle the new photos uploaded daily.

Less than a week into its operation, the cold storage facility is already storing nine petabytes of user data. That’s equal to nearly 9.7 billion megabytes. A typical uploaded photo ranges from 2 to 10 megabytes.

When it’s full, the 16,000-square-foot cold storage building would be able to hold thousands of petabytes of data, Goolsbee said. Getting it to capacity should take several years, he said.

The company could also add two additional wings to the cold storage building as the first wing nears capacity, adding 32,000 square feet of space for servers in the coming years.

Facebook officials declined to disclose the total cost of the cold storage project. Permits issued by Crook County put the project cost for the first wing at $6.8 million, including mechanical and electrical work.