It’s affordable housing on an epic scale: a residential block of 242 new apartments in Salburúa, Spain (just outside Madrid). Designed by ACXT Architects, it’s also a project that takes a substantial bite out of the greenhouse gas emissions associated with running a conventionally built development of similar size and fucntion. The key? Cogeneration.

Cogeneration, or combined heat and power, works by taking energy lost during the process of burning fuel to heat space or water and turning it into electricity to power a building, essentially using the same fuel twice.  The bigger the building, the more energy goes to waste in the process of heating it, and the more electricity can be generated via that waste heat. Ecofriend reports that this affordable housing project  produces 70 kilowatts of power via cogeneration, which is more than the building actually uses, allowing excess power to be sold back to the grid.

image via Aitor Ortiz (via Gizmag)

The building is composed of  a 21-story tower and a continuous, U-shaped block with a varying height of between four and seven floors. These variations in height allow for better views for the building’s residents, as well as more access to natural daylighting, increasing energy efficiency. The project features  nine retail units at the ground floor as well as two underground levels of parking. It was completed in 2011.

Apparently the city is feeling good about the project, as ACXT currently has another public project in the works for in Salburúa this year, a civic center designed to provide the district of Vitoria-Gateiz with a venue for sports, cultural events, and administration offices.