Pictures of the Future      Fall 2008

When Buildings Come to Life

Sensors are set to give buildings a spectrum of information—and scientists at Siemens are working on combining many of their functions on a single chip.

^{Sensors were long considered too expensive for building systems. Research, however, is making them smaller, cheaper, and more flexible—such as Siemens’ CO₂ measurement  sensor (bottom left)}

At Siemens Corporate Technology in Munich, Germany, when physicist Rainer Strzoda enters his work area and wants to find out if the climate control system is working properly, all he needs to do is take a look at a small device on the wall. Today, the prototype laser-optic sensor developed by Siemens scientists reads 400 ppm CO₂. "That’s a good value when you consider that our atmosphere currently contains 380 ppm CO₂," says Strzoda. "This means the room contains only a little more carbon dioxide than the outside environment." As the day progresses, and Strzoda and his colleagues work on their inventions and discuss their results, the CO₂ reading slowly climbs to 600–700 ppm—solely because the scientists are breathing.

Strzoda and his colleagues actually have it good. The air in most of the world’s offices and conference rooms has a CO₂ content in excess of 1,000 ppm, the level at which people begin to feel uncomfortable and become tired and unfocused. Most buildings still don’t have CO₂ sensors—but this will soon change, according to Dr. Maximilian Fleischer, who heads Strzoda’s research group. His team has produced many sensor-related inventions that have resulted in new products from Siemens. With around 150 patents to his name, Fleischer is one of Siemens’ most productive inventors (see Pictures of the Future, Fall 2004, Gas Sensors and Fall 2006, Innovators – Fleischer).

Sensors for measuring light and temperature are widely used today. Gas sensors—micro electrical-mechanical systems (MEMS) made of silicon chips and an oxidizing layer—are a relatively new development, however. These laser-optic sensors are still in the early stages of their development, and it will be some time before they hit the market.

In contrast, the gallium oxide sensor—Fleischer’s career breakthrough invention—has been measuring the CO content of exhaust gas in thousands of small firing systems for years, thereby making it possible to optimize their energy output and emissions.

In a completely different area of development, a new sensor from Siemens’ research labs that measures alcohol content in a person’s breath may soon go into production, and Sweden has announced that it plans to become the first country to combine it with a vehicle immobilizer to prevent intoxicated people from driving. This technology, which has been licensed from Siemens, can also be used in trains, streetcars, and in connection with potentially dangerous machinery.

Big Savings from Tiny Sensors. Until now, sensors were rarely used in buildings because they were too expensive and too difficult to install and maintain. But recent advances in developing silicon-based sensor chips equipped with their own power source and radio module have caught the attention of building operators. That’s because such sensors can yield big savings. Intechno Consulting estimates that the global annual market for gas sensor systems will be roughly € 2.9 billion in 2010.

Sensors play a key role in all scenarios involving the future of building system technologies. "Houses will no longer be empty shells; they will be intelligent systems that communicate with their occupants," says Dr. Osman Ahmed, who heads an innovation team at Siemens Building Technology in Buffalo Grove, Illinois.

As soon as wireless-capable sensor chips can be produced cheaply, it will become feasible to link thousands of them in a finely woven infrastructure in buildings. "We will eventually be able to use sensors to imitate nature," predicts Ahmed. Just as our senses and nerves constantly supply our brains with information that allows us to make decisions, processors in building management systems will be used to receive and process data from thousands of sensors, and then issue appropriate commands to a variety of subsystems.

Combined with user information, building management systems will be able to perform many new services. Building users will be able to inform such systems about when they will be arriving, which security mechanisms have to be used, and which rooms to ventilate. A variety of sensors will ensure that management systems always know when a toilet is in need of repair, where a corrosive substance has been released, or where people have gathered.

Gas Detectives. In their labs, Fleischer and his team are already developing sensors that can monitor air quality in buildings. "To accomplish this, we need a chip that can measure at least four parameters: temperature, humidity, gases like CO₂, and odors," says Fleischer. To this end, he and his coworkers are studying detector materials to determine which reacts best with the gases to be detected.  In a cathode sputtering facility characterized by a mysterious blue-glowing plasma, the researchers are producing sensor surfaces only a few millionths of a meter thick. And next door, in a related experiment, a small device  that uses a type of screen printing technique to detect gases is being studied. Which procedure is more suitable for gas detection depends on the materials in question. The researchers place the desired combinations of the tiny oxidation surfaces they produce side-by-side on field effect transistors (FETs) in a chip. Examples include a barium titanate-copper oxide-mixed oxide combination for detecting CO₂, and a gallium oxide with finely distributed platinum for detecting odors.

The substances being investigated in Fleischer’s lab don’t dock directly on a chip’s surface, but flow as if through a tunnel between a molecular capturing layer and the actual FET structure, causing a change in electrical resistance that the chip can read and convert into signals. If the chip is equipped with a radio module, it can wirelessly send the data to a building management system’s control units.

Although Ahmed’s vision of tomorrow’s buildings may still seem like a stretch, initial steps in that direction have already been taken. "Comfort demands are increasing," says Andreas Haas of Siemens Building Technologies in Switzer­land. He believes trends in building technologies will parallel those in cars, for which sophisticated climate control systems are now standard.

However, building operators are most interested in the savings potential that sensor systems offer. After all, sensor cost a lot less than renovating a building and, when combined with state-of-the-art optimized building automation, can produce even greater savings. Haas estimates that precise room climate sensors, and air quality and presence sensors can reduce the energy used for heating, ventilation, air conditioning, and lighting by 30 % compared to a building with conventional automation technology.

Comfort is also affected by odors. "Rooms are often aired out only because they smell unpleasant," says Fleischer. This needn’t be the case, since ambient air can be cleaned using ozone, which bonds to odor-producing molecules and neutralizes them by splitting them. This is why Siemens researchers are developing gas sensors that can recognize typical room odors. The researchers have used 18 different gases, such as ethane, propene, and acetone to produce model odors. Hexanal, for example, is used for tests of sensors designed to detect odors in carpets. The scientists are also working on developing long-lasting odor sensors. "This kind of sensor needs to function for at least ten years if it’s going to attract interest on the market," says Fleischer. If such a sensor reports a bad odor in the air to the control system, the latter will issue a command to release ozone. The sub­sequent concentration of ozone can in turn be monitored by another type of sensor in order to prevent negative side effects, such as respiratory tract irritation.

One of the main challenges in the development of gas sensors is the question of cross-sensitivities. That’s because, if false alarms are to be avoided, the detecting material on a chip must respond only to the substance being searched for.

This requirement also applies to fire alarms, of course, most of which still react optically to the presence of smoke. "But that might be too late for people near the source of a fire who have already inhaled a toxic gas," says Fleischer. This is why building operators are interested in acquiring devices that detect the specific gases typically associated with flames. Such devices would be activated long before enough smoke could be produced to set off a conventional alarm. Such detectors—especially if combined with sensors for automated climate control—are at the top of building operators’ wish lists.

Universal Experts. Siemens engineers are also working on non-chip sensors such as laser-optic devices that can remotely determine where most of a gas in a room is concentrated. Just down the hall from the laser-optic sensor lab, doctoral student Rebekka Kubisch is working with petri dishes full of a red fluid. The dishes are being used to grow cell cultures for "living" sensors that can do things such as measure water quality. "We mount these cells on chips, expose them to toxins, and then observe the types of reactions that result," she explains. At present she’s examining how the skeletal muscle cells of rats react to various waste water samples. Such living sensors offer tremendous advantages over chemical-based sensors because, while living cells react to all toxins, with chemical sensors you have to know in advance which harmful substance you want to test for.

More importantly, living sensors could be used in green buildings that save energy by setting up as many closed cycles as possible, for water and air, for example. "Highly sensitive early warning systems are critical here," says Fleischer. Looking further ahead, Ahmed adds,  "One day we’re going to have buildings that don’t require any energy from outside. We’re going to need a lot of intelligent products to get there, and multifunctional sensors are an important piece of this puzzle." Whatever the future has in store, Siemens scientists have already done a lot to take us a step closer to this vision.
                                                                                                               Katrin Nikolaus