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Glass use is increasing as a construction material; however, glass façades add little to the thermal inertia of the envelope and solar radiation causes greenhouse effect inside the building, especially in hot climates. The purpose of this work is to show how the spectral and thermal behaviour of an innovative concept of glass façade, the Active Glass system, help controlling the unwanted effects of solar radiation.

Active Glass is the result of a research programme developed in Madrid's Polytechnic University. It is based on the physical property of water being opaque to infrared radiation, thus absorbing up to 60% of solar radiation energy, without significantly absorbing the remaining of visible wavelength.

Active Glass system is based on a double -or triple- glazing with water flowing through the inner chamber: glass façade transparency is not reduced, but transmission of solar energy in the near infrared region (NIR) is lower due to the higher radiation absorption power of water over air. Also, substitution of water for air in the glazing adds thermal inertia to the envelope. The combined result is an active glazing system which is able to better manage the energy inside the building.

Disposing of the heat captured by the water can be achieved in different ways. In hot climates it can either be dissipated together with the building´s other heat loads in whatever refrigeration system is provided, or it can be stored in a tank and cooled down by evaporative refrigeration or night dissipation at a very low energy cost. Active Glass System offers a seamless integration of the product in the facade to capture the solar thermal load before it gets inside the building. Furthermore, it contributes to an improved thermal feeling inside the building as it provides a more uniform temperature. The system combines comfort with architectural values of 21st century like architectural aesthetics, natural lighting and cost advantages of glass curtain wall facades.

Comparison between predicted simulation data and actual data obtained from an existing demonstration prototype is included in the paper, which ends up with a brief description of Cuenca (central Spain) Journalism Faculty façade.