Pictures of the Future    Fall 2007

Pinpointing Costs

Siemens uses the cumulative energy demand (CED) method to find ways of reducing medical devices’ energy requirements. This approach addresses the entire product lifecycle, from materials and production to operation and recycling.

When it comes to medical systems, environmentally friendly technology is a key selling point. For instance, hospitals that have environmental management systems want the major products they purchase to come with an Environmental Product Declaration. That’s because they want to know exactly how environmentally sound their production methods are, and how environmentally friendly their devices will be when in use. Such facts are provided by Dr. Franz Bömmel, Group Environmental Officer at Siemens Medical Solutions (Med), as well as product development engineers. Bömmel and others rely on the "cumulative energy demand" method or CED, which was developed principally by the Research Institute for Energy in Munich, Germany, about ten years ago. "Cumulative energy demand is the total quantity of primary energy needed to produce, use, and dispose of a device—including transportation," says Bömmel. This value reflects the energy demand related to a device over its entire lifecycle, and makes it possible to determine which phase consumes the most energy. Sometimes this quest makes Bömmel feel like a detective tracking down energy leaks.

When Bömmel’s team added up the energy demands of the Magnetom Avanto magnetic resonance imaging (MRI) system, it made a surprising discovery. The delivery of the device to the customer consumes nearly the same amount of energy as the manufacture of the components—roughly a third of the total energy used on production. In the U.S. in particular, these devices have usually been transported by air because their superconducting magnet is cooled with liquid helium and can’t be allowed to warm up. "Without a power source, all the helium evaporates in about 28 days," says Bömmel. "And cooling the magnet down again is costly. However, we found that ocean transport can be fast enough, at least on the U.S. East Coast. Several MRI systems have already been delivered that way." In fact, he adds that the coastal route requires just one-sixtieth of the energy of air transport.

"That makes a significant difference on the CED bottom line," says Bömmel. But some preliminary work had to take place before he was able to apply this method. Here, researchers at Siemens Corporate Technology (CT) provided data showing the material-specific energy demand values for 75 categories of materials that are typically used to make medical devices. These values define how much energy is consumed in the provision of an industrial material such as sheet steel—taking into account the entire value chain, from mining the ore to the finished material. Since Med generally just assembles components and manufactures few parts in-house, CT also determined CED values for a list of standard components, such as fans, computers, monitors, and keyboards.

By putting together all these pieces of the puzzle, scientists can ultimately figure out the total energy required to provide the materials that make up a product. In the Magnetom Avanto, for example, that amounts to four percent of the total energy—taking into account the complete life cycle. In this context too, Bömmel sees opportunities for improvement. That’s because 45 % of the eight-ton mass of an MRI system consists of different iron alloys and steels, while about 34 % is nonferrous metals and alloys. When considered in the CED context, however, nonferrous metals such as aluminum and copper account for substantially more energy usage than the ferrous metals. This finding suggests that in a future MRI system aluminum should be replaced by steel wherever possible to reduce the energy consumption associated with providing materials. Such a switch would also have to be accompanied by design changes to avoid a substantial increase in gross weight.

Although Avanto’s manufacturing-related energy demand has been examined, analyzing every step of this process would simply be too costly. Instead, the energy consumption of an entire production hall would be determined using electric and heat meters. If this value is divided by the total quantity in kilograms of products manufactured, you would get the specific CED value for that production hall—in kWh/kg. Such CED values can be added up to determine the CED for the entire production process of a device. An additional CED value must be determined for transportation between different factories and to the customer. With regard to the Magnetom Avanto, about 10 % of total energy demand is accounted for by this phase.

Squeezing Standby Losses. The largest chunk of energy in the lifecycle of a device is consumed during its use. Computed for a ten-year period, this amounts to about 86 % of the total kilowatt-hours—or about 460 MWh annually in the Magnetom Avanto. Here again, Bömmel foresees additional energy reduction measures. One promising area involves the different operating modes of medical devices. A principal target here will be standby losses. In the Magnetom Avanto no less than 38 % of energy is used in an unproductive state. During switch-off, the essential helium cooling guzzles up about 20 % of energy, while 18 % is used in the warm-up phase preceding a scan.

Recycling is the final phase of the CED analysis. Based on total weight, about 85 % of the material in medical devices can be recycled. About 9 %—mainly plastics—can be thermally reused. Based on the life-cycle, some 2 % of the energy can thus be credited to the CED bottom line.

Thus the CED approach can be used to calculate total energy demand for each device and, no less important, a device’s resulting environmental impact. For example, if the main energy source is known—which in medical devices is electric power—its contribution to the greenhouse effect can be estimated.

Since the calculation of all energy values in the CED method is based on primary energy demand, i.e. on the energy content of fossil fuels such as coal and oil, the energy content is first recalculated in terms of secondary energy—in this case, electric power.

A Magnetom Avanto’s average annual consumption of primary energy corresponds to about 150 MWh of electric power. Today, each kilowatt-hour of electricity produced in Germany generates about 600 g of CO₂. Thus, operating the Magnetom Avanto produces about 90 t of CO₂ annually.

Values for other pollutants, such as nitrogen oxides, can also be estimated based on energy consumption—by using the conversion tables of the German Ministry of the Environment. The CED method therefore provides an inexpensive, simplified estimate of a given device’s environmental impact.

"Of course you have to understand," says Bömmel, "that the way we use the CED method only gives you a general idea of the energy demand, since it often involves approximations. But that’s okay, because it helps us to swiftly identify energy "leaks" that we can then address. CED has helped us determine that the operation of our devices accounts for the largest share by far of their total energy consumption. So that’s the first place where we’ll take action in order to achieve further improvements."
                                                                                                                  Rolf Sterbak