In the Colombian capital 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 experience heat is more complex than we care to admit. Comfort standards define what is acceptable in buildings, and evolve as we learn about thermal sensations. Most people come to a consensus about the latter when it is too cold or too hot. But in intermediate situations, it is more complicated to predict how they will feel, what they will tolerate or what they will enjoy. An uncertain number of physiological, psychological, cultural and climatic factors come into play to tip the balance.
At the outset, the goal of the standards of thermal comfort was to define a universal range of temperatures that would apply to all buildings, climates, moments and people. These were developed using modern architecture and the air conditioning technology available at the time. Together they contributed to the creation of the International Style. Making new standards of comfort indicates that important changes are coming: important subtleties will be recognized in thermal sensations, such as our tendency to adapt to seasonal changes or to tolerate higher temperatures if we know that we can open a window..
The so-called Target Comfort Range can be the starting point or the dead end in all conversations about passive design. Medellin is a good example: with very little variation throughout the year, on a typical day, the temperature oscillates between 18ºC and 28ºC in the shade.
If asked, most people in Medellin would instinctively say that the higher end of this range is too hot and that they would need air conditioning. However, according to the new standards, this temperature is suitable for offices, provided there is sufficient air movement . This raises an important question: If we can’t design buildings that don’t need air-conditioning in the “City of Eternal Spring”, where can we do it?
One of the greatest challenges of natural ventilation is the difficulty in predicting the frequency, direction, and strength of the wind. In Medellin, the direction of the wind is relatively stable, but only reaches the necessary force for 40% of the year. Fortunately, in the last decade, progress has been made to understand and incorporate a more reliable force: buoyant force, a type of ventilation not activated by the wind, but by the residual heat of the occupants, computers and other thermal gains in the interior of the building.
Everybody has blown up a balloon at some point. We designed our building to take advantage of this effect: a chimney connects all the office floors. Heated by the occupants and computers, the interior air rises naturally through the chimney. As it escapes at the top, fresh air is sucked from the windows and into the building.
With wind-driven ventilation, fresh air is pushed in from the sides. But with buoyancy-driven ventilation, fresh air is drawn from the sides. So the action is different. And it is also more reliable. On a hot day, when building occupancy is high, there may not be enough wind to blow out the indoor air. However, buoyancy-driven ventilation is different: as occupancy increases so does the driving force. In other words, buoyancy is a force that can be integrated within a design. With the right design, we can maintain a “breeze” even when there’s no wind.
How do you determine the size of the chimney and windows? If the openings are the wrong size, there will be insufficient air flow, and the interior will overheat. This used to be a difficult problem to solve, especially for multi-story buildings, but new research has provided new insights: we now have simple mathematical models that respect the most important physical principles . Now design teams can easily decide whether buoyancy-driven ventilation is feasible from the outset in the design process.
This video shows an ‘app’ based on these mathematical models. It was developed so that the EDU design team could design the size of the windows and the chimney properly, as well as make the necessary adjustments during the life of the building.
The table shows the appropriate size of the openings in each level, to ensure that they all have the same amount of fresh air. If the fresh air velocity increases per person, the openings increase, while the indoor temperature (relative to the outside) falls. By properly adjusting the openings, we can keep the average indoor temperature at no more than two degrees (+ 2 ° C) above the outside, generated three to four times the normal amount of fresh air per person.
There will be three windows per floor that can be opened, spaced out to give a uniform distribution of fresh air from the less polluted and quieter sides of the building. Our current idea is to put graphics in each window, showing the occupants how much they should open the window, depending on how many people are on that floor that day.
What about the afternoon, when the outside temperature can exceed 28 ° C in the shade? To deal with this, we exploit two environmental aspects: first, the chimney faces west, so you receive a “solar impulse” in the afternoon. This will increase the speed of fresh air by up to one third. Secondly, we use the thermal mass: the viscera of concrete in sight are cooled at night, remaining relatively cold during the day. These will absorb the radiant heat of the occupants, making them feel colder than the outside for most of the time.
We see this building as a laboratory. It is an experiment in buoyancy design and a test of comfort levels. The occupants are mostly architects and urban planners working for EDU. They will experience the theory and reality of buoyancy ventilation personally. They will recognize the successes and failures, to see how to improve the design and how to apply the concept to different types of buildings throughout the city.
This is not just an experiment for EDU. We intend to broadcast the performance of the building live on the internet. Most clients and architects are not prepared to share this type of information, as it may reveal oversights in design and operation. But if no one knows how buildings actually perform, how can we, as an industry, learn collectively 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)
- Architects: EDU – Empresa de Desarrollo Urbano de Medellín (Urban Development Company of Medellin)
- Location: Carrera 49 #44-94, Medellín, Antioquia, Colombia
- Design Direction: John Octavio Ortiz Lopera
- Design Team: Víctor Hugo García Restrepo, Gustavo Andrés Ramírez Mejía, César Augusto Rodríguez Díaz, Catalina Ochoa Rodríguez, Julián Esteban Gómez Carvajal, José Arturo Agudelo, Aurlin Cuesta Serna
- Promotion: Empresa de Desarrollo Urbano (EDU) + Alcaldía de Medellín
- Thermodynamics: Salmaan Craig
- Technical Design Consultant: Juan Fernando Ocampo Echavarría
- Structural Design: Rafael Álvarez R., Ramiro Londoño Ángel, Carlos Mario Gómez Rojas
- Construction: Constructora Conconcreto
- Bioclimatic Consultant: Taller de Ingeniería y Diseño Conconcreto (Concrete Enginerring & Design studio)
- Acoustic Consultant: Daniel Duplat
- Social Director: Gloria Estela López
- Technical Design Intervention: Espacios Diseño Construcción S.A.S.
- General Manager Edu: Jaime Bermúdez Mesa (actual), César Augusto Hernández Correa (2016), Margarita Maria Ángel Bernal (2012-2015)
- Area: 3660.0 m2
- Project Year: 2016
- Photos: Alejandro Arango , Courtesy of EDU, Courtesy of Saalman Craig