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Building energy efficient cities


Building energy efficient cities

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The offices, shopping centres and homes of the future should be clean and green. Buildings should incorporate innovative and intelligent design to keep energy use to a minimum.

Ursula Eicker, the CITYNET Project Coordinator, at Stuttgart’s University of Applied Sciences is an expert in energy efficient building design:

“Today already more than half of the population lives in cities, and that will increase, which means cities and energy consumption is a central theme of the future,” she said.

Zerrin Yilmaz, a Professor at Istanbul Technical University, is working alongside Eicker in the research initiative: “Buildings consume almost half of the energy for a country, so if you solve the energy problem of buildings that means you are going to solve the energy problems of that country.”

Yilmaz and Eicker are on a mission to make the cities of the future as energy efficient as possible.

From their universities in Stuttgart and Istanbul they are collaborating on a European Union research project, mixing real-life case studies with laboratory modelling. Much of their research focuses on those symbols of city life – soaring glass-fronted office blocks. Zerrin Yilmaz says they pose problems of their own:

“Those are high rise and high tech buildings with very complicated automation systems that consume energy, but still there are so many possibilities to reduce energy consumption through different kinds of passive strategies.”

Passive systems help keep buildings the right temperature without relying on power-hungry machines. At Stuttgart Technical University fierce lamps are used to simulate the sun beating down on a test version of an office window. Keeping the small room inside the test cell cool is more difficult than keeping it warm, says Eicker:

“When you talk about heating we know how to do it well, we wrap it up well, we insulate it well, and with good windows you have no problem. Especially with offices, there are so many computers, lighting, people, and things that generate heat. But how do we keep these buildings cool in summer even in Germany where the climate is not that hot? It’s a problem.”

The artificial sun means researchers can test different types of shading systems in a controlled environment.

“We’re not just examining sun shades, but entire systems. For example here we have double facades where behind the first facade there’s a second skin, and there we examine the air flows, how much fresh air gets into the office. So we’re not just investigating thermal and optical features, but also the airflow in such systems,” Eicker explained.

German Phd student Tobias is working with his Turkish colleagues on a real-world example of urban development. In the windtunnel at Istanbul Technical University is a model of the city’s newly-built Kanyon centre, a development that includes an office tower, shopping centre and apartments. A flow of smoke helps Tobias visualise how the skyscraper is affected by its environment.

He told us how it works: “If there are other buildings in the neighbourhood they might have an influence on the building we are working on, so there might be turbulences of air depending on the wind direction. That’s why we are not static, we don’t only put this model here like it is, we turn it around and view it from all directions.”

Tiny sensors in the model can measure air pressure.

“Pressure distribution is important if you think about the ventilation of the building. On the windward side we have positive pressure and on the backward side we have negative pressure. This pressure difference of the two sides makes the air flow through the building which might be useful for ventilation issues or also for cooling the building,” Tobias added.

Professor Yilmaz’s team has been working closely with building managers at Kanyon, and modeling has already helped them to use their lighting more efficiently.

Yilmaz says further changes may be made: “Now are are looking into the possibility of energy saving through natural ventilation mostly, and also we have other research studies on this building for energy efficiency, for example photovoltaic applications for electricity production from the sun, and better shading devices for cooling energy saving, and also some parametric studies to see the relation between energy consumption and comfort.”

To have a clearer idea of how energy for cooling and heating will be used in an urban area you need a global view, and that is the job of Stuttgart’s artificial sky.

Model are placed inside to see how different surfaces would pass from light into shade over the course of a day.

The high-power lamp simulates the sun, and the luminescence of the dome can also vary to better imitate reality.

Eicker underlines how important this is for their research: “The sky is never equally bright, you usually have brighter patches just around the sun, the horizon is brighter, and we have to be able to recreate that situation realistically to be able to say that there is enough light in this building.” .

The artificial sky was used to study the Scharnhauser Park site near Stuttgart. Researchers examined how the distance between buildings affects the amount of sun they receive.

The area is full of energy-saving initiatives, including one particular office block. In its basement is an absorption chiller which transforms heat from the local biomass plant into cooling liquid piped through the floors.

It uses weather forecasts to regulate indoor temperatures. But Scharnhauser Park is unusual. Achieving energy efficiency on a large scale demands careful planning, says Yilmaz, whether that be in Germany or Turkey:

“You have to find the best solution during the design phase. And you have to test different design scenarios of the building to find the best solution of energy efficiency. If you can find the best solution there is a 50 per cent energy saving possibility for these kinds of buildings, which is a huge amount because they consume a lot of electricity and natural gas for heating, cooling, lighting and so on,” she said.

These researchers are learning how to best apply techniques such as passive cooling and natural ventilation in real-life large-scale urban situations. But energy efficiency is not simply a scientific and technical question, it is also a social challenge, argues Eicker:

“Building standards are quite high nowadays, but once they are in place their functioning is not optimal. There is hardly anyone to care about whether buildings systems, cooling systems, are switched on and off at the right times. There is a lot of energy consumed for ventilation which is unnecessary when hardly anyone is in the building, and lights are left on. It depends very much on the user and they have to become aware that they can actually save energy.”

Developing truly energy efficient city buildings also requires input from the people living and working in them.

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