Forum 2016 - Infrastructure Space - Detroit (Ruby Press)
109 108 lation. As occupancy rises, so does the driving force. With sensible spa- ce planning, buoyancy ventilation is viable when the exterior is as cool as 10°C/50°F. Plenums, buffer zones, transition spaces, common areas, or winter gardens can preheat the fresh air before it enters the occupied spa- ce proper. In hot climates, when the interi- or must be cooler than the exterior, downdraft buoyancy ventilation is a theoretical possibility. Chilled ceilings cool the space and the flow reverses. Energy is needed to cool the water in the pipes embedded in the soffit, but tepid water is sufficient because of the large cooling surface area. And there is no need for ductwork. While untested, this arrangement could be of importance in hot, dry, polluted ci- ties where the air higher up is cleaner. The influence of the Cambrid- ge group is starting to show. Some designers are starting to realize that buoyancy ventilation makes natural ventilation a more feasible prospect. For instance, a trend can be seen in the buildings of Foster+Partners. The practice’s Commerzbank Headquar- ters, completed in 1997 in Frankfurt, was branded as the world’s first eco- logical office tower. A series of stag- gered winter gardens meant openable windows could be placed near most occupants, giving free access to side ventilation. 30 St Mary Axe in London, designed for Swiss Re and comple- ted in 2004, had spiraling mini-atria, each stacked six stories high, enclo- sed by an aerodynamic form, giving occupants access to wind-driven or buoyancy ventilation, depending on conditions. It was a complex arrange- ment and its performance is unknown. The Apple Campus in Cupertino, currently under construction, is desi- gned around the simpler principles of buoyancy ventilation. The Bloomberg HQ in London, also under constructi- on, is another deep-plan office desi- gned to run on buoyancy ventilation for the major part of the year. For the first time we can cont- emplate high-density offices free of HVAC (heating, ventilation, and air-conditioning) infrastructure. At the time of writing, I am consulting on the design of a mid-rise office tower in Medellín, Colombia, a climate so perfect for natural ventilation that they call it la eterna primavera . There is litt- le wind, however, so we are applying a new model to design the building so that it is controlled by buoyancy Fig. 1: New office headquarters —with no HVAC infrastructure whatsoever—designed by and for Medellín’s urban planning department, Empresa de Desarrollo Urbano (EDU). ventilation, powered by internal gains, with a boost in the afternoon from a west-facing solar chimney. 15 There is also exposed thermal mass to re- duce the radiant temperature, and the effect of mass on stack pressure has been accounted for. The idea is that every person will receive the same twenty liters of fresh air per second, and experience the same range of operative temperatures. On each floor, 28 people will share a space of 100 square meters, but no HVAC infrastructure will be instal- led. The new headquarters is for the Urban Planning Department (EDU) of Medellín, which is willing to see it as an experiment in robust, buoyan- cy-centered design, not only for its architects but for the wider research community too. We plan to monitor the behavior of the building and the response of occupants live on the Internet. The performance of simple measures will be under the spotlight. For instance, the windows will be manually operable, with graphics on the glazing indicating by how much that window should be opened de- pending on the occupancy on that Fig. 2: The exterior shading screen is made from prefabricated Glass-fibre Reinforced Concrete (GRC). A single-glazed facade will be fitted behind the screen, on the interior side. The lack of HVAC infrastructure means double or triple glazing is unnecessary.