How to design a "breathable building": Sustainable case study - EDU Headquarters in Colombia?

In Medellin, the capital of Colombia, the Empresa de Desarrollo Urbano/Urban Development Company is building its new headquarters. It incorporates the best thermal performance for local urban regeneration. The new EDU headquarters is a tripartite collaboration between the public *** company, the private sector and Prof. Salmaan Craig from the Harvard Graduate School of Design, who has made his home in the Colombian capital.

Built on the site of the former EDU headquarters in San Antonio Park, it is intended to be a "breathing" example of sustainable public **** building in Medellín.

An expert in materials, thermal design and building physics, Professor Craig (PhD in Engineering) volunteered to help make the project a reality. Below, he explains the thermodynamic difficulties of this building concept.

This design, with its prefabricated fa?ade system, solar panels, solar chimney, temperature calibration, thermal buoyancy, and lack of air-conditioning, represents a serious commitment to sustainable building innovation in Medellín.

The concept is based on the idea of "breathing architecture", thinking about "simple materials, smart geometry". The external skin made of high-quality prefabricated elements allows the external chimney to draw in cold air directly from the outside, generating and influencing thermal mass. Thermodynamic concepts such as convection and thermodynamics, which generate a constant flow of air due to the change in temperature from cold to hot, create a comfortable airflow in the employee workspace.

The building is located within the Macro project's development strategy area in the heart of Rio. The building has a total area of 2,983 m2, including a 1,968 m2 public **** area. Its slender quadrangular volume rises 37 meters from the platform and has the same perimeter as the demolished existing building.

The building has a two-story basement that houses a multi-purpose area that includes water storage, a parking lot, a machine room room, recycling, garbage, maintenance and storage rooms. On the first floor is a payment center, front desk, project gallery, community services and filing area to meet the needs of the community.

The new headquarters has ten floors with an average height of 3.70 meters, distributed as follows: from the second to the fourth floors are offices, on the fifth floor is a public **** area, kitchen and terrace; from the sixth to the eighth floors are offices, on the ninth floor is the general management office, and on the tenth floor are distributed multi-purpose areas and workspaces, in addition to elevator maintenance rooms.

New Ventilation, New Experience

Our perception of heat is far more complex than we realize. Comfort standards define acceptable ranges within a building and gradually develop as we learn more about how heat feels. For the latter, most people can reach a ****ing understanding when it's too cold or too hot. But in the middle, predicting sensation and the degree to which it can be tolerated and felt comfortable is more complex. There is a great deal of uncertainty in physiological, psychological, cultural and climatic factors to upset this balance.

The range of so-called target comfort can serve as a starting point or dead end for conversations about passive design. Medellin is a good example: it doesn't vary much throughout the year, with temperatures in the shade fluctuating between 18?C and 28?C on a typical day.

Most people in Medellín, if asked, would instinctively respond that temperatures in the mid-to-high range are a bit too hot and therefore require air conditioning. However, according to the new standards, this temperature is perfect for the office as long as adequate air flow is ensured.

One of the biggest challenges with natural ventilation is the unpredictability of the frequency, direction and strength of the wind. In Medellín, the winds are relatively constant, but they only reach 40 percent of what's needed in a year. Fortunately, progress has been made over the past decade by understanding and integrating a more reliable force: buoyancy. Instead of wind activation, this ventilation is gained through occupants' waste heat, computers, and other heat gains inside the building.

Everyone has blown up a balloon at some point. We designed our building to take advantage of this effect: chimneys connect all the office floors. The air inside is warmed by the occupants and computer equipment and rises naturally through the chimneys. Fresh air enters the building through the windows as the hot air rises to the top.

With wind-driven air circulation, fresh air is pushed in from both sides. In buoyancy-driven ventilation, fresh air is taken from both sides. So they are different in their approach and buoyancy drives are more reliable. When it is hot, there may not be enough air to blow into the room when the building is occupied higher. However, buoyancy-driven ventilation is different: higher occupancy also drives higher power. In other words, buoyancy is a force that can be gained in design. In good design, we can maintain a "breeze" even when there is no wind.

How do you size chimneys and windows? If the openings are not the right size, there will be a lack of air flow and the room will overheat. We now have simple mathematical models that follow the most important physical principles.

There will be three windows on each floor that can be opened, spaced to give an even distribution of fresh air from the less polluted to the quieter parts of the building. The idea now is to put a chart in each window that tells users how many windows they should open, depending on how many people are on the floor that day.

What happens in the afternoon when the temperature outside in the shade can exceed 28C? To deal with this situation, we utilize two aspects of the environment: First, the chimney faces west, so in the afternoon we utilize the "solar drive".

This increases the rate of fresh air by up to a third. Secondly, we use thermal insulation: the concrete core as far as the eye can see cools down at night and keeps its temperature relatively low during the day. These absorb heat radiation from the occupants, making them feel cooler than outside most of the time.

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