This high-profile, International event on innovative building envelopes for architects, engineers, scientists and the construction industry, brought together experts in façade engineering from around the globe, who demonstrated many innovative and sustainable building skin designs.

BGBC was represented by dipl.eng. Kiril Velkovsky who presented the unique combination of technology solutions, used in the creation of the Sopharma Litex towers office buildings ensemble, DGNB certified by the BGBC. The office buildings opened doors back in 2011.

The presentation was titled: "The power of a responsive building skin after 10 years monitoring; Passive and cost effective solutions for the future; New vision to a hi-tech building skins with endless comfort due to natural daylight."

Our presentation showed results from 10 years monitoring of a unique "breath/semi-close cavity" double skin facade with built-in retro-optical sun protection system and adaptive functionalities for energetic and daylight transmission properties. Тhe presentation showed the results of the 10 years of monitoring of the unique "breath/semi-close cavity" double skin facade with build in retro-optical sun protection system and highly adaptive functionalities in energetic and daylight transmission properties.

The introduced façade system is installed back in 2009-2010 on an ensemble of office buildings in Sofia, Bulgaria, consistent of 3 office buildings with 15, 18 and 22 floors, connected on the first and second floors by a trade section of shops, restaurants and other services. The ensemble is named Sopharma Business Towers and Litex tower.

The project is joint initiative of two Bulgarian companies and a 100% private investment. Two of the towers are managed by Sopharma properties, co-investors in the joint project and the third office building is owned and invested by Litex Tower Ltd. The architectural decision is after arch. Dimitar Paskalev, Architectonica studio, Sofia. Façade, daylight and building physic consultant of the project is arch. Helmut Koester, Koester Lichtplanung DE in cooperation with dipl. Eng. Kiril Velkovsky, Sofia, Bulgaria. The solar protection features of the glasses and sun protection system in combination have been produced, tested and confirmed by IFT Rosenheim. Report provided by RetroSolar GmbH. The spectral glass features have been confirmed by a report of the producer AGC Flat Glass.

The project is conceived in the early years of this century and as realization dates back to 2006. It was commissioned in November 2011 and has been operating successfully ever since. Since its inception, it became a flagship of energy efficient construction in the country in the office building segment and remained as such for more than 10 years. Recipient of numerous awards, the project has been certified under the DGNB system with a gold certificate with the help of BGBC.

For a facade design technology is crucial to investigate and determine the local climate conditions at the earliest stage of building design in order to achieve a high energy efficiency. Façades in particular, as active elements having a significant influence on building physics, have an essential role to play in this respect and have to be tailored to the specific climate conditions of the area. This alows a better understanding of the necessary building physics in line with the set objectives for the façade concept which should ensure the highly set objectives of comfort, environmental friendliness and energy efficiency.

The concept of adaptive façade is based in the principle of effective providing of the best possible conditions for energy, heat and light transmission for the needs of the interior in accordance to the external conditions. It can be briefly illustrated as following:

• During the warm seasons with strong sunlight, which implies a high thermal load in the interior, the conceptual solution should enable the minimization of radiative fluxes to the interior and efficient realization of cooling power savings while providing a comfortable interior.

• During the cold seasons optimization of the radiation flows that penetrate the interior in combination with excellent thermal insulation properties leads to savings in heating power.

• In both of the preceding regimes, the façade must ensure a sufficient amount of soft diffuse light passing deep into the interior, resulting in impressive savings from interior lighting and additional savings from additional cooling power during warm seasons.

 As a result of the adaptive factor of the façade, all influenced spheres of impact by the building physics in combination lead to high energy efficiency, achieved in regard to the heating, cooling and interior lighting. In addition are also affected other sectors of the buildings energy consumption.

In terms of benefits this results in effective energy savings while maintaining comfort and a healthy environment, respectively CO2 emissions saved on a large scale. The energy saved is over 40% compared to another office building in the same area with the same purpose, constructed for the same period of time as the Sopharma -Litex office ensemble.