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Dropped Ceilings Soffits Will Cool Buildings Down and Save Energy


Using computer simulation, the University Centre of Energy-Efficient Buildings of the CTU carried out development and evaluation of thermally active dropped ceilings that contain materials capable of changing their phase. Their cooling performance was modeled at various geometric configurations and their behavior was also monitored from the point of view of architectural acoustics.

Dropped soffits for office buildings are designed primarily in accordance with the requirements of standards, ordinances and regulations of the government regarding the indoor environment (operative temperatures, air temperatures, air velocities, concentrations of chemical substances, dustiness, lighting and acoustics). The main reason for using materials capable of changing their phase (PCM, Phase Change Materials) is the improvement of the indoor environment in buildings. The aim is to decrease the cooling output that is needed during the summer season.

PCM is a designation for materials that change their phase at temperatures which are usable in real life. For the indoor environment in buildings located in the mild climate zone, this is the range of about 20 to 25 °C. Thermal energy is transferred when stage change takes place which is when the PCM is heated to the temperature that it melts at. At that point, it absorbs a lot of heat without an increase of its temperature and, consequently, it behaves as an ordinary material. If, on the other hand, the ambient temperature drops to the point of solidification of the PCM, it releases the heat stored. It is capable of storing or releasing as much as fourteen times more heat per a volume unit than common masonry or stone. Common use includes PCM applications in glass, facades, floors and dropped ceilings.

Our team had to consider a lot of sometimes contradictory requirements formulated from the point of view of quality of indoor environment and acoustics. Moreover, they had to be combined with other limits, for example production possibilities, standard clearances of offices and other technical as well as technological restrictions. Example: From the point of view of heat transmission, metal grid would be the most suitable packaging material for PCMs while mineral wool would be optimum from the point of view of acoustic absorbability.

After many give-and-take solutions and optimizations, we came to a conclusion, that the most suitable materials for dropped soffits with PCMs seem to be perforated plasterboard in the bottom part and thin-walled metal sheet in the upper part. This combination should conveniently balance all requirements regarding materials, spatial possibilities of buildings, geometry, and spatial arrangement with the influence on air flow as well as acoustics in rooms.