A question of efficiency

Research in focus December 2012

What would happen if we were to run out of electricity? No lights, no heating – all our household gadgets and appliances rendered worthless. This nightmare scenario is often spun by the media when reporting on the planned phasing out of nuclear power and the shift toward using renewable energies. But exactly how we are to achieve this shift is a popular question on the lips of those following the public debate on this issue, a debate that seems to offer a stockpile of approaches and answers. The vast majority agree that the aim here is to achieve a fundamental improvement in global energy efficiency. Ultimately, a successful energy shift can only be effectuated by the efficient production and use of energy from renewable sources.

Improving energy efficiency was at the very heart of research and development activities carried out by the former department of Energy Systems at the Fraunhofer Institute for Building Physics IBP in Kassel. The members of its Low Exergy Systems research group, led by engineer Dr. Christina Sager-Klauß, were confronted every day with such fundamental questions as “What is the best way to link the various ways heat and electricity are used in buildings?” and “What part will buildings play in the future to guarantee a reliably stable grid?”

“It becomes a lot easier to resolve issues of supply efficiency when considering a wider system context. In conducting our research we tend to observe not only one building, but also factor in neighboring buildings. Depending on the application, we even extend the scope to include an entire town or city,” explains Sager-Klauß. According to Sager-Klauß, discussion of the shift in energy policy revolves around the search for an energy supply that marks a departure from centralized and conventional solutions. Most importantly, this also requires moving away from fossil fuels in favor of a decentralized energy supply based on renewable sources of energy. In describing her approach to research and development Sager-Klauß continues: “This leads us to examine just how we are to achieve the goals set by new energy policies and how we can make life in cities more sustainable.” These questions in turn inspired many exciting initiatives, including the “Grid-reactive Buildings (only German)” project. The launch of this collaborative research project, which has been funded by the German Federal Ministry of Economics and Technology (BMWi), was announced jointly by Fraunhofer IBP, the Fraunhofer Institute for Solar Energy Systems ISE and the E.ON Energy Research Center. “The aim of the  project has been to attain a comprehensive overview of buildings’ behavior within a greater energy system,” says Sager-Klauß. Over the course of the project, Sager-Klauß and her team discovered how individual or large groups of buildings behave within the smart grids of the future and how they could then contribute to such grids’ stability.

As the building sector is responsible for around 40 percent of Germany’s energy consumption, it is imperative that in addition to raising the efficiency of both buildings and grids, we optimize the demand being placed on each. It has now become possible to feed non-adjustable and fluctuating renewable energies into the grid, but this is easier said than done. Harnessing electricity from wind and solar energy production leads to local grids experiencing increased fluctuations in the surplus and shortages of electricity that are already reaching their limits. Failing to adjust grids to compensate for these fluctuations will result persistent problems in supply. “But it is possible to remedy these shortfalls. One way is to store surplus energy and another is to take measures designed to redistribute loads,” says Sager-Klauß. In any case, storing electrical energy generated by photovoltaic or wind power facilities is only possible in limited amounts and is widely considered expensive and associated with a host of technical problems.“This shows why we must continue to search for alternatives,” explains the expert. A building’s physical mass and its heating and warm water tanks offer a simple means of storing surplus electricity from renewable energy sources in the form of heat for use as and when it is needed. They also provide a distinct advantage: “As they are already present in most buildings, their potential can be tapped without any great expense,” says Sager-Klauß. “It is possible to use heat pumps to use surplus electricity at defined times in the future and to secure environmental energy more efficiently. This can all be regulated by being connected to smart grids.”
This is why the “Grid-reactive Buildings” project had focused on buildings that represent parts of a greater energy system. The first step in tackling how individual or large groups of buildings are to behave within future smart grids and how they can contribute to grid stability lies in establishing the necessary scientific foundations. To do so, the Fraunhofer researchers have characterized the interactions between buildings and building-service technologies, by performing energy analyses of a variety of building concepts on the basis of measurements collected over a period of several years. The results have been used to develop a comprehensive method with which to assess buildings as part of a greater energy system. The five assessment criteria are the individual system components, the energy supply system that governs these components, the specific building in question, the city neighborhood comprising a group of buildings, and lastly the city as a whole. In performing their quantitative assessment, Fraunhofer IBP scientists use the exergy concept (only German), which allows them to accurately describe the exergy-related qualities of heat and electricity in terms of thermodynamics. Fraunhofer researchers use dynamic models in order to integrate and evaluate these qualities to determine the level of energy efficiency on a neighborhood or city level.
At the end of the project, all three partners had compiled the complete simulation model for a city neighborhood as well as a consistent dynamic exergy-based method for evaluating settlements, which provided urban planners and decision makers with a valuable tool for the future. Sager-Klauß explains the project’s practicality: “Such simulation models are important because we can’t be sure which form the energy system of the future will take. They allow us to get a head start in testing different technology scenarios and potential solutions.”

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