Kurkliniken Bad Colberg 

Workshop talks given at Southern California Edison

Matthias Schuler

Matthias Schuler is a founder and managing technical director of TRANSSOLAR Energietechnik GmbH in Stuttgart, Germany. He has directed the engineering of many advanced façade buildings including the Deutsche Post Hochhaus in Bonn, Nord/ LB in Hannover, and LVA SchleswigHolstein in Lübeck. He currently lectures both at the University of Stuttgart and at the Harvard Graduate School of Design. He has published many popular press articles as well as co-authored the book “Glass Construction Manual”. Mr. Schuler holds a Masters degree in Mechanical Engineering from the University of Stuttgart. http://www.transsolar.com

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In older buildings, we had weather protection with a connection to the outside, fresh air, and external shading to control solar gains, which is now missing in buildings in North America. What we are looking for are solutions to meet thermal comfort demands and sun protection, light redirection that adapts to changing external conditions, noise protection and then a kind of rethinking of natural ventilation which was standard in buildings before they invented the fan. So if I could sum up what the façades of the future would do, they would do all of this and we could just hang a façade element when constructing a building and be done with all heating, ventilation, and cooling. This is the vision where I think façades will be in the future.

As an example, you have background research that shows that thermal comfort is more than just air temperature. It is also about radiative temperature. So if you have access to thermal mass, by getting rid of the suspended ceiling for example, you can increase or decrease the operative temperature, which is also mainly influenced by the temperature of the surrounding area. If you are able to cool the thermal mass actively or passively down, this acts as a kind of cooling supply for keeping your operative temperature down. This will then allow you to have the air temperature up at a higher level.

In terms of investments cost, however, there is a competition between a fully air-conditioned building and a naturally ventilated and naturally daylit building. With a naturally ventilated and daylit building, you are coming down from an operating cost in the range of $2.00/m² to around $0.50-$1.00/ m² . On the investment side, you can drop down to a typical investment for the mechanical system in the range of around $200/m² to around $50/m² , which means on the one hand you can save investment costs and on the other hand you can also save operating costs. I think that this is interesting; you can only be cost effective if you offset the investment you put into the façade. You have to save on the mechanical system to justify the cost of a double-façade system. You can’t first build a fully air-conditioned building and then add an advanced façade. This will never pay.

Starting with a refurbishment building, this is a building from the 1960s in downtown Stuttgart. The intention of the investor was to save the money from mechanical ventilation and go for natural ventilation. The problem was the street noise level was around 65 dBA, which with manual ventilation would not be allowed by codes in Germany. So we added this kind of single-glazed screen glass façade on the outside, permanently ventilated, which allows us to drop the noise level down to the range of 8 to 10 dB. We are collecting data on how the real building behaves and we’ll compare it to the simulation.

This is also a refurbishment, a university building in Mannheim. Originally, this was a glass-infill concrete structure, but after 20 years, the balconies were falling down and the building was condemned. This refurbishment involved just putting a single glazed screen façade in front of the original façade. The interesting thing is they kept the whole internal old façade, which increased the thermal behavior of the façade system with this kind of unheated buffer zone. You can keep the old façade and just add a screen on the outside. In this case, it allows us to go back to natural ventilation.

Another example is a building located on a heavy, noisy street just four lanes, not the twelve that one sees in Los Angeles, so on the south and north side, we have this kind of buffer façade which allows natural ventilation. In this case, it is not cross-ventilated, it uses a chimney in the middle that takes air from the south and north sides into the building.

This IRS building in Stuttgart has a natural ventilation chimney in the middle of the high-rise building. You have this two-meter wide chimney, which runs partly as a supply and partly as an exhaust chimney throughout the building. There is a wind catcher on top of the building, which supports this natural stack effect with wind pressure. This building has been used for around five years and there is no air conditioning and no cooling devices. We kept the temperature in this case below what the German code is, which is in the range of 27-28º  C.

This is a building which is realized in Shanghai, opened in last November. In this case, the façade is what we call a fifth façade, which is the roof. The single membrane roof allows daylighting in the exhibition halls during most of the year, only a part of the year are the halls really used for exhibitions. This translucent membrane gets very hot in direct sun, 50-55º C. So in this case, we developed with the manufacturer, Ferrari, a new membrane which has a low-E coating on the inside and a sort of printing on the inside which cuts the long-wave radiation.

This is a restaurant that is fully glazed and set in the middle of the woods. Their concept was to have lunch in the woods protected by glass, so not only the walls, but the roof is glass. We developed a kind of double-shell glass roof. The lower shell is not glass but a coated foil which serves a lot of functions. On one side, it is micro-perforated so it performs an acoustical function. It is low-E coated so it does not emit the radiation. It is fritted to provide shading; it also creates a buffer space to provide additional insulation during the wintertime. This is then combined with preconditioned outside air through the floor.

This is very effective because you can take long wave or short wave radiation out before it heats up the air.

Now, a little more detailed example I want to describe is a new building just under construction in Bonn. I think that when you talk about advanced façade systems you should not talk only about the architect, but the design. This team should work very early together to create this kind of integrated concept, because advanced façade systems do not stop at the façade. They go deeper and influence the ventilation system and the conditioning system. If you don’t create an integrated concept, then you build an additional system and you can never pay for the additional costs at the façade.

So in this case, there was a kind of interesting definition by the client, his first priority was work place quality. It needs to have operable windows with limited heating and cooling ventilation control. He wants the building energy use to be 25% below code. He also wants to take advantage of the natural ground energy source, which means no mechanical cooling allowed. And he wants to minimize operating costs for heating, cooling, and ventilation. Keeping this in mind, we defined several approaches. The natural ground source delivers cold water in the range of 12-15° C. Normally, with 12-15° C you cannot run an air-conditioning system – you need 6° C. In this case, we ended up with a kind of radiative system. On the other side, you have to minimize loads – minimizing solar gains, external shading with protection, etc. We used a double façade system with adjustable throttling flaps on the outside to allow for operable windows.

The entire system ended up with a double skin façade, natural cooling, which I mentioned, activation of thermal mass, which means the ceilings are uncoated, operable windows and we added a decentralized ventilation system to allow for adjustments in the ventilation. We had nearly no shafts in the building which saves a lot of space and provides additional rentable space in the building.

With wind on the façade, especially in a round building, you get areas of negative and positive pressure. With a CFD calculation, you can easily see on one half of the building you have significant negative pressure from -40 up to +100 psi. Under these circumstances, if two people open the windows and the doors are open too, you just get normally a blast of uncontrolled outside air. Using a Transsolar simulation tool combined with other tools, we showed that with adjustable flaps on the exterior glass layer, we can equalize the negative pressure and positive pressure in front of the building and create a kind of average negative pressure within the double façade.

The decentralized supply system was part of the double façade system and provided pre-heating and pre-cooling. In this case, we are controlling the supply temperature depending on the outside dew point, which means that we are always keeping in the same range so no condensation can occur with this exchange. This is important: they are not for cooling, they are just for preconditioning the outside air to come in at the same level as room temperature. Their use depends on the internal loads, you may need them or not.

We did shading and ventilation full-scale tests, of just the façade module. We also compared simulations against these measurements to identify the ventilation efficiency of our supply system. Finally, we built a one-to-one two-story mock up on site so we could compare and verify the simulations to what we measured. The building is now going up.

Finally, I will just give you an impression about a building that we finished and has now been in use for some years by the company Audi. The building has a screen façade on the south side (right side of the diagram) acting as a buffer zone and a circulation space. Automated horizontal microlouvers provide a kind of adaptive façade. Once a day, all these 400 elements try to find the zero point. They are kind of reset. Each of these 400 elements is individually controlled with a little motor driven unit which is also computerized. They are adjusted once a day typically, depending on inside temperature and on lighting level, because it works also as a lighting control for offices behind it during this five minutes of the day. During this time, the building really looks like a movie screen. The façade changes from all clear to all white, suddenly starting to open or close. You see a certain precision. When it is kind of horizontal you can easily look out through it, so it keeps a certain transparency. In this case, a lot of the offices are oriented to this circulation space and are able to look out through the façade. You can also close a part of it, the upper part or lower part. If it is open, you can easily look through the building and have a kind of visual connection through the building.

 
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