Tall, red and green: Housing scheme sells energy back to the grid

Look up this project on the website of its architects, ACXT, and you will find that it goes by the rather understated name of 242 Affordable Housing Units in Salburúa (Salburúa being a neighborhood in the Basque city of Vitoria-Gasteiz). In many ways the downplaying of the name is in keeping with ACXT’s quiet approaches to sustainable design. Though there may be no obvious green bells and whistles such as wind turbines or photovoltaics, passive architectural methods combined with on-site generation contribute to what ACXT claims is a “considerable reduction” in the building’s carbon dioxide emissions.

Though largely a residential development the building, completed in 2011, incorporates nine shops at ground level. From there, it’s social housing all the way up: between four and seven stories for the horseshoe-shaped block that forms the building’s footprint, rising to 21 stories for the tower that rises above one end of that horseshoe.

Why the variation in height in the main block of the building? It’s all to do with daylight, or specifically sunlight – the two being subtly different things. By limiting the height of the development to the south (we’re in the northern hemisphere, needless to say), more apartments are granted a direct view of the sun. It’s an arrangement the building appears to have borrowed from its closest neighbors, and though the tower, being located at the building’s south-western corner, inevitably casts a shadow, the photographs suggest that an impressive proportion of the building’s facades are bathed in sunlight at any given time. In any case, the positioning of the tower to the south inevitably means that more apartments are granted a south-facing aspect, and though direct sunlight can be problematic, it’s also a very nice thing to have – especially at home…

More central to the building’s sustainable efforts is the cogeneration system which produces 70 kW of electricity and 109 kW of heating on site. A relatively unglamorous technology, cogeneration…is nevertheless a tremendously important weapon in a building designer’s arsenal. In this case, effectively an on-site gas-fired power station…it’s the proximity of the power generation to end use that sees CHP offering significant energy savings over grid-scale gas fired power, because a vast amount of the heat generated as a by-product can be put to use very near to where it is generated. Plus it’s heat that doesn’t have to be generated by other means, as would otherwise be the case. In a triumph of localism, cogeneration can almost be seen as putting the fuel to work twice in one go.

ACXT reports that the building is able to produce electricity to sell back to the grid, which suggests that, for some of the time at least, the cogeneration system is producing more electricity than the building needs: a good thing.

Bravo! They don’t discuss it in the article; but, I imagine the plumbing and what HVAC there is – is all home run rather than traditional right angles and elbows. You can save about 30% of the energy required to push water and air around a multi-story building.