Inner facade -- closed
Photo:Keiichi Tahara
Inner facade -- open
Photo:Keiichi Tahara
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3.The Effect and Performance of the Double-skin Facade
- Achieving Sunshading and Thermal Storage
When the solar radiation is strong, the temperature inside the double-skin rises as in a greenhouse. However, owing to the air inlets and outlets fitted to the top and bottom of each story, the air convects so as to take the heat away. An experiment using a life-size model proved that the hotter the facade became relative to the surrounding air, the more remarkable the convection effect that was achieved, so as to carry out the sunshading function. Of course, the thermal storage effect becomes vital, when there is a need to warm the room as in the winter season.
- The Effect of Natural Ventilation
The natural ventilation in a high-rise could give rise to the following fears: a very force power might be required to open the room doors; the wind might stream from the room to the corridor, blowing papers about; the wind might also make disturbing noises. But, such problems have been solved by the design specific. Namely, the power required to open the doors is some 20% less than that in a 7-8 story building with a conven- tional facade; the wind entering is regulated, so as not to blow papers about; the air inlets and outlets are designed not to make noise. During some 70% of the year, it is possible to live in the high-rise with the controlled natural ventilation, without artificial cooling or heating. Of course, as the inner facade can be freely opened up to 15cm, the individuals in the office rooms can let in the wind to satisfy their own requirements. Of course a system of mechanical ventilation is also installed, but it is operated at most twice an hour, whereas there is a need to ventilate 4-6 times hourly and to spend a lot of energy to cool or heat the air in more conventional buildings. By harnessing the natural ventilation, one can avoid ﾒsick-building syndromeﾓ which one is apt to get in full air-conditioned multi-story buildings.
- The Actual State of Energy Saving
Owing to such sunshading and thermal storage effects as well as natural ventilation, the energy consumption for air-conditioning in the RWE Tower is calculated at some half of that in conventional German buildings with single-skin facade and pair glass. In fact, Hanna-Drohomirecka Schaefer, a Hochtief AG's person in charge of the facility management of the tower, explained that the energy consumption for cooling and heating was some 30-35% less than that in other general buildings, even during the somewhat unpredictable first year of operation. The result was brought about not merely by the human operators, but also by the hi-tech information system.
This is managed by the computers in the central administration room, which controls the adjustment of sunshades and ventilators, based upon the climate data of the surroundings and the conditions in individual rooms, obtained through the built-in sensors. For example, when the wind velocity is faster than 7m/sec on the higher levels above the 16th floor and 10m/sec on the lower levels below the 16th, the buzzer sounds to warn people to shut the windows; and when a window is opened in a room, this information is transmitted to the computer, which then gives directions to turn off the convector in the room concerned.
- Sound Insulation and Other Effects
The outer facade is also effective in insulating the interior from the noises from traffic to a considerable extent. The "fish-mouths" hinder the sound transmission in the vertical direction, and the partitioning glass panels do the same horizontally. In addition, the double-skin has an unexpected effect - it solves the problem of acrophobia. There is no dado nor handrail along the glass from floor to ceiling. Although the architects had worried about it at an earlier stage of planning, they were assured by a doctor that there would be no problem, due to the structure of the double-skin. In fact, a person working in the tower remarked that she soon became accustomed to the situation though she had felt some fear at the beginning. Also, one of Nagel's relatives, who has serious acrophobia, told him that he felt no fear because there was still some distance to the actual exterior and some metal fittings were available to hold on to.
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