kinetic solar pavilion - wordpress.com · 04/04/2013  · kinetic solar pavilion introduction- the...

Kinetic Solar PavilionIntroduction- The assignment was to make a kinetic geometry with a skin

that at least can be used to let photovoltaic cells follow the sun. Also the structure must be easily transportable, erectable and it must not be too heavy. The span has to be approximately 10 meters.

The problem with most geometries is that most of the surface area is not perpendicular to the sun, which makes the use of photovoltaic cells on the structure very inefficient. Especially when a curved façade is used, only a very small amount of surface area can be perpendicular to the sun.

Ideal would be when all the surface area would be perpendicular to the sun all time during the day. Because all the PV-cells are orientated perpendicular to the sun, they can deliver more electricity.When we look in nature, we can find good examples in plants. During the day sunflowers track the sun, because this increases the reproductive success of the plant. Also many plants have an internal clock which makes the flowers close at night. This has to do with protection of their pollen and eggs. These phenomena are taken into account for the concept development. A closed structure is preferred during the night and when there is no direct sunlight. When the structure is closed, people inside will be protected by the wind and cold. But when it comes to the structure during the day, the structure has to follow the sun. The movement of the structure has to be controlled just the way as a puppeteer controls the movement of his puppet. The space underneath doesn’t necessarily have to be closed, but can more or less serve as an umbrella.

It’s important to have a three dimensional adjustable structure, because the track of the sun changes every day. In the Netherlands the graphs of the sun elevation for each 21th day of the month can be seen in the figure. These graphs can be interpreted with the degrees azimuth

taken into account.

How does it work?

Structure- The structure consists of a central column. Around this column a tent structure is mounted, which consists of profiles and a membrane with the photovoltaic cells on top. The tent profiles have a hinged connection to the column. At the end of the profiles is a connection for the cables. The cables run from these ends to the top of the column where the adjustable ring is mounted, after the cables run inside the building to the bottom of the column, where the rotating mechanism is placed.

Rotating mechanism- The rotating mechanism makes the tent structure move in a wave pattern. In the model 8 cables are used. In the actual realisation of this concept, more cables (for example 16) can be used to get a smoother surface.The rotating mechanism consists of two main parts. First is the outer frame, which consists of in a circle positioned pulleys and a cross-shaped rails. In the model a cross-shape is cut out in wood and the pulleys are replaced by screw eyes. The frame is mounted to the column and can’t move. The rails is the track for part two, which is the rotating arm. The arm is mounted at two places, but can move free through the rails. Because each connection can move only in one rail in one dimension, the end of the arm describes an ellipse around the cross centre. This method is also called the Trammel of Archimedes. At the end of the arm a set of 8 pulleys, one pulley for each cable, is mounted on a rotating wheel. In the model 4 pulleys are used because of the limited amount of available spaceWhen the wheel with the cables is at closest to a certain pulley, the robe that goes through this pulley is loosened. The robe that goes through the opposite pulley is at the same time tightened. The cables which go through the other pulleys are somewhere in between tightened or loosened. When the arm with the wheel attached turns around, all the cables gradually gets loosened and tightened in a wave pattern. All tent profiles make one wave. When

8 cables are used, the phase differences between each profile is 1/4 π.

Adjustments- The amplitude of the wave can be adjusted with the length of the arm. A longer arm gives a higher amplitude. A higher

amplitude gives the membrane a bigger slope. To better suit the movement of the sun per day, the arm can describe an elliptical movement. The long and short radius from the ellipse can be adjusted by moving the two arm connections to each other or away from each other. So when the sun is low, a big amplitude is needed, which means a long arm. And off course when the sun is high, a small amplitude is needed, which means a small arm. This can be adjusted for each day. The maximum slope for this structure is set to 45°.To close the tent the ring in the top of the column must be lowered. When this ring through which the cables run is lowered, the cables get loosened and the tent

structure will close. The profiles can be fixated to ankers in the ground.

Technical Execution- The structure consists of a round steel column, steel profiles and steel cables. The column is ten meters in height. At 5

meters height steel plates with a hole in it are welded to the column for the hinged connection with the profiles. At 8 meters height The steel ring is fixated by fasten the robe at the proper distance down at the column. On the steel ring pulleys are welded to guide the cables from the end of the profiles down to the column. On top of the column two pulleys are welded to make it possible to lift the steel ring up or loosen it down with cables. On the profiles near the hinged junction the membrane is mounted to the profiles. On the other end this is also the case, but here are also the cables mounted, which

can be seen in the figure.

Improvements- Of course there is still room for improvement of the concept. In the current design the tent structure can be lifted by the wind.

This can be fixed by attaching a second series of cables to the end of the profiles. These cables will run underneath the roof. These cables go to a new rotating arm which is exactly the opposite of the original arm. So when one arm loosens a certain cable at a certain endpoint, the other arm tightens the cable in the other direction. Because the profiles are now always under tension, the roof is more stable and won’t be lifted by the wind.Another improvement is to decrease the size of the rotating mechanism. There are two ways of doing this. The size in the model is already decreased by a half, because of the use of pulleys in the rotating arm. The cables are mounted to the frame, go through the pulleys and go back through the pulleys on the frame. Therefor the the cable ratio between the rotating mechanism and the rest of the cables will be 2:1. So the amplitude of the rotating mechanism is half of the amplitude of the original one. When more pulleys are used, the amplitude can decrease even more. But remember that the force needed to move the rotating arm would increase with the same ratio.Another way of decreasing the arm in the rotating mechanism is to lower the ring above in the column. By doing this a smaller amplitude is needed for moving the

profiles to the same heigth. But the cables will be in a less optimal angle.

Concept- All these aspects are taken into account for the concept development. The design is a tensile structure. This structure is

closed during the night to provide protection against the weather. During the day this structure opens up to the sun and follows the sun during the day,

just like a sunflower.

E.J. van Rijbroek | 0654140Masterproject 2 Building Technology‘Free Form Dynamics’04-04-2013