In the Colombian city of Medellin, a new headquarters is being constructed for the Empresa de Desarrollo Urbano (Urban Development Company), combining optimal thermal performance with local urban regeneration. The new EDU headquarters is the result of a three-part collaboration between the public company, the private sector, and Professor Salmaan Craig from the Harvard Graduate School of Design who has family roots in the Colombian capital.
Constructed on the site of the former EDU headquarters on San Antonio Park, the scheme aims to act as a benchmark for sustainable public buildings in Medellin, embracing the mantra of “building that breath."
As a specialist in materials, thermal design, and building physics, Professor Craig (EngD) voluntarily offered his service to the scheme’s realization. Below, he explains the thermodynamic challenges behind the building’s conception.
The design represents a serious commitment to innovation towards the generation of sustainable buildings in Medellín, through prefabricated façade system, solar panels, solar chimney, temperature calibration, thermal buoyancy, and an absence of air conditioning.
The purpose of this project is to use innovation as a tool for the renovation and revitalization of downtown Medellin, creating a socially safe territory through a healthy mix of building functions and public activity. In this dynamic, the project aims to stimulate the transformation of the city center to promote a sustainable habitat and guarantee public freedom - a dual strategy of social urbanism, and a culture of sustainability.
Its conceptualization is based on "a building that breathes", thinking of "simple materials, intelligent geometries”. An external skin composed of high-quality prefabricated elements allows the external cold air to be directed towards an external chimney, generating and influencing thermal mass. Thermodynamic concepts, such as convection and thermal forces, generate a constant flow of air by a change of temperature, from cold to hot, creating comfortable air currents in employee workspaces.
The building is located within an area of a strategic development, the Macro Project of Rio Centro. The building has a total area of 2,983 m2, including 1,968 m2 of common areas. Its slender quadrangular massing reaches a height of 37 meters starting from platform level, following the same perimeter as the demolished existing building.
The building has two basements where there are utility areas for water storage, parking, technical rooms, recycling, trash, maintenance, and storage rooms. The first floor is catered to the community with a payment center, reception, gallery of projects, community services and filing area.
The new headquarters has ten floors with an average height of 3.70 meters, distributed as follows: from the 2nd to the 4th floor are offices; on the 5th are the common areas, a kitchenette and a terrace; Offices from 6th to 8th; the 9th floor is for the general management office, while on the 10th, utility and work areas are distributed, in addition to the elevator maintenance room.
A new type of ventilation, a new type of experiment
The way we sense heat is more complex than we like to admit. Thermal comfort standards define what is acceptable in buildings, and these standards evolve as we learn more about thermal sensation. Most people will agree when it is far too hot or far too cold. But in between, it’ s harder to predict how people will react. What will they tolerate? What will they enjoy? Any number of physiological, psychological, cultural and climatic differences could tip the balance.
At first, the purpose of thermal comfort standards was to define a universal range of temperatures that would apply to all people in all buildings in all climates at all times. These standards developed alongside air-conditioning technology and modernist architecture. Together they gave rise to the International Style. But new thermal comfort standards signal a change in approach. They acknowledge important subtleties in thermal sensation, such our tendency to adapt to seasonal changes, or our tendency to tolerate warmer temperatures if we know we can open a window..
It’ s hard to overstate the importance of these revisions. The target comfort range is the starting-point or closing door to all conversations on passive design. Medellín is a case in point. On a typical day, the temperature will oscillate between 18°C and 28°C in the shade, and there is very little variation throughout the year.
Most people will instinctively say that the upper part of this range is too hot, leading to the conclusion that air-conditioning is necessary. But according to the new standards, this temperature range is okay for office activities, so long as there is sufficient air movement .This raises an important question: If we can’t design buildings without air-conditioning inThe Eternal Spring, where else can we?
One of the major challenges of natural ventilation is the unpredictable frequency, direction, and strength of the wind. In Medellín, the direction of the wind is reliable, but it is only strong enough for about 40% of the year. Thankfully, in the last decade, progress has been made in understanding a more reliable driving force — buoyancy. Buoyancy ventilation is a different kind of natural ventilation. It isn't powered by the wind. It’ s powered by the waste heat from occupants, computers and other internal heat gains.
Hot air rises, as every paisa who ever made a globo knows. We have designed our building to exploit this effect. A chimney connects to all the office floors. Heated by occupants and computers, the interior air rises naturally up the chimney. Asit escapes at the top, fresh air is pulled in from the windows and across the floor plates.
With wind-driven ventilation, the fresh air is pushed in from the sides. But with buoyancy ventilation, the fresh air is sucked in from the sides—by the warm air column rising up the chimney. So the action is different. And it’ s also more reliable. On a hot day, when the occupancy is high, there may not be enough wind to flush out the interior. But buoyancy ventilation is different: as the occupancy increases so does the driving force. In other words, buoyancy is a force you can engineer. By design, we can reliably sustain a ‘ breeze’ in the absence of wind.
How does one know how to size the chimney and the windows? If the openings are incorrectly sized, there will not be enough air flow, and the interior will overheat. This used to be a difficult problem, especially for multistory buildings. But new research has provided new insights. We now have simple mathematical models that retain the most important physics. Now design teams can easily decide if buoyancy ventilation is feasible, early on in the design process.
The video below shows an‘ app’ based on these mathematical models. I developed it so the EDU design team could size the windows and the chimney properly, and make any necessary adjustments during the life of the building.
The table shows what size the openings should be on each level, to ensure that everyone gets the same deal. If you increase the fresh air rate per person, the openings increase, while the interior temperature (relative to the exterior) falls. It turns out that, by adjusting the openings properly, we can keep the average interior temperature at no more than two degrees above the exterior, while providing three or four times the normal amount of fresh air per person .
There will be three openable windows per floor, spaced to give an even distribution of fresh air, from the least polluted and quietest sides of the building. Our current idea is to put graphics on each window, showing occupants how much they should open the window, depending on how many people are on that floor that day.
What about in the afternoon, when the exterior temperature can exceed 28°C in the shade? To tackle this, we exploit two environmental aspects. First, the chimney faces west, so it will receive a ‘ solar boost’ in the afternoon. This will increase the fresh air rate by up to a third. Second, we utilize thermal mass. The exposed concrete ceilings will cool down at night, staying relatively cool during the day. They will absorb radiant heat from occupants, making it feel cooler than the exterior for most of the time.
We see this building as a laboratory. It’ s an experiment in buoyancy design, and a test of the comfort standards. The occupants are mostly architects and city planners, working for EDU. They will experience the theory and reality of buoyancy ventilation first hand. They will get to know the successes and the failures intimately. They will see how to improve the design, and how to apply the concept to different building types across the city.
And it’ s not just an experiment for EDU. We plan to broadcast the performance of the building live on the internet. Most clients and architects are not prepared to share this kind of data, because it may reveal oversights in the design or operation. But if nobody knows how buildings actually perform, how can we as an industry collectively learn from our successes and failures?
GRC (Glass Reinforced Concrete) molding and on-site installation
The Thermal Sensation: here is a video of an old experiment that I recreated in class last year. Santiago González Serna is the Colombian volunteer. The experiment goes back to at least John Locke, the seventeenth-century philosopher, who was interested in how what perceive physically and how we perceive the world. In front of Santiago, there are three buckets of water. One of them is hot, another cold and the last at room temperature. You can see him putting one hand in the hot bucket and the other hand in the cold bucket. After your hands have acclimatized, remove them. One hand is hot and the other is cold. Then dip both hands into the bucket filled with water at room temperature. When I asked him to guess the temperature, he had trouble answering. His senses were obviously in conflict: "I can not say, because my hot hand feels cold, but my cold hand feels hot." What does this tell us? That we judge temperature - and everything that comes from the senses - in a comparative way. Whether you think the water is hot or cold depends on what you just experienced. We are deeply comparative creatures.
Multistory Buoyancy Ventilation: I developed this 'app' to help the EDU team design the chimney and windows on each floor. The buoyancy force is generated by the heat of people and computer equipment. At higher levels, the resulting suction force on the façade is proportionally less. So the window openings need to be larger to deliver the same amount of fresh air down. See: Andrew Acred and Gary R. Hunt, "Stack Ventilation in Multi-Storey Atrium Buildings: A Dimensionless Design Approach," Building and Environment 72 (February 2014): 44-52, doi: 10.1016 / j.buildenv.2013.10.007
Richard J. de Dear and Gail S. Brager, "Thermal Comfort in Naturally Ventilated Buildings: Revisions to ASHRAE Standard 55," Energy and Buildings 34, no. 6 (2002): 549-61.
Andrew Acred and Gary R. Hunt, "Stack Ventilation in Multi-Storey Atrium Buildings: A Dimensionless Design Approach," Building and Environment 72 (February 2014): 44-52, doi: 10.1016 / j.buildenv.2013.10. 007; Torwong Chenvidyakarn, Buoyancy Effects on Natural Ventilation (Cambridge, New York: Cambridge University Press, 2013).
The recommended dose for new buildings is usually 10 liters per second per person (depending on the type of activity and the particular level)
LocationCarrera 49 #44-94, Medellín, Antioquia, Colombia
Design DirectionJohn Octavio Ortiz Lopera
Design TeamVíctor Hugo García Restrepo, Gustavo Andrés Ramírez Mejía, César Augusto Rodríguez Díaz, Catalina Ochoa Rodríguez, Julián Esteban Gómez Carvajal, José Arturo Agudelo, Aurlin Cuesta Serna
PromotionEmpresa de Desarrollo Urbano (EDU) + Alcaldía de Medellín
Technical Design ConsultantJuan Fernando Ocampo Echavarría
Structural designRafael Álvarez R., Ramiro Londoño Ángel, Carlos Mario Gómez Rojas
Bioclimatic ConsultantTaller de Ingeniería y Diseño Conconcreto (Concrete Enginerring & Design studio)
Acoustic ConsultantDaniel Duplat
Social DirectorGloria Estela López
Technical Design InterventionEspacios Diseño Construcción S.A.S.
General Manager EDUJaime Bermúdez Mesa (actual), César Augusto Hernández Correa (2016), Margarita Maria Ángel Bernal (2012-2015)
PhotosAlejandro Arango , Courtesy of EDU, Courtesy of Saalman Craig