Buildings, districts and cities currently often have outdated energy systems. Homes must be made more energy-efficient and districts need to be supplied with renewable energy. In cities, the aim is to turn energy production and mobility into sustainable systems. This involves complex energy models that Kristina Orehounig is researching in her “Urban Energy Systems” department at Empa.

Kristina Orehounig, Head of the Laboratory of Urban Energy Systems at Empa

From small to large. From complicated to complex. From architecture to construction physics. Kristina Orehounig has taken this scientific path. She studied architecture at the Technical University of Vienna, received a doctorate in building simulation and has now been in charge of the “Urban Energy Systems” department at Empa for two years: energy systems of buildings, districts and even entire cities are being researched here based on an interdisciplinary and networked approach which is geared toward a sustainable future.

Ms Orehounig, buildings are the smallest units in urban energy systems. What is the biggest energy challenge in this context? Individual buildings in Switzerland are mostly already built and consume quite a lot of energy relatively speaking. Depending on the type of building and its location, we need to renovate them to make them more energy-efficient, for example by installing façade insulation, replacing windows and insulating roofs, in order to reduce their energy consumption as an initial objective.

And then? We need to integrate more energy-efficient equipment and replace heating systems fired by fossil fuels like oil and gas with systems based on renewable energy: photovoltaics to generate electricity, heat pumps, solar thermal energy, combined heat and power or district heating for heating. The aim is to stop using fossil fuels in the building and to use little or no more energy.

No energy? The right balance must be found. There are always periods of energy consumption. This can be produced ad hoc by a solar system on the roof. Or the energy required in winter is generated in summer
and then stored.

Has storage technology been fully developed? Short-term storage is not a problem. Long-term storage technologies have already been developed but are rarely integrated. This is also because there are no financial incentives as the electricity market is not open. Optimal energy management requires knowledge of the microclimate of buildings or clusters of buildings in urban areas. The step up from supplying a house to an entire district increases the complexity of the models and these become a big data project: a wealth of data from weather stations or temperatures or shading of houses must be prepared so that the energy consumption of residential units and the ideal energy mix in a district can be calculated.

“In the city of the future, decentralised, alternative energy production and energy consumption in buildings as well as electromobility must be optimally integrated into a single urban system.” Kristina Orehounig, Head of the Laboratory of Urban Energy Systems at Empa

Ms Orehounig, what concrete findings did you make based on the models you have calculated? We design the optimal energy system for a district and calculate how many heat pumps or photovoltaic cells we need to integrate, and whether storage technology or a heating network is required. We design a layout for optimal operation and show how the energy must flow. This minimises costs and CO2 emissions.

Is this the best way to create the energy-efficient city of tomorrow as a sustainable ecological space? We can now map urban districts with our models. In an entire city, the complexity is higher. We cannot map every building in detail, so simplifications are required. The future must also be included in the models, for example the effects of climate change. In this way, cooling rather than heating may become an issue. Just like urban mobility, which cannot be based on fossil fuels but rather only electric forms of transport. And alternative energy will be produced more locally, i.e. decentralised. In the future, all this must be optimally interconnected in urban areas.

The research teams reporting directly to the head of the department have worked closely with energy suppliers, cities and communes to develop their models. The resulting software is now so sophisticated that any number of urban districts can be viewed and evaluated in terms of energy efficiency. The data pool is now being continuously expanded, so that researchers can draw on empirical values for comparable urban areas where concrete measurement data is lacking.

Ms Orehounig, your research should be put into practice on a large scale. How are things progressing where this is concerned? That is also happening. Within our department, some researchers joined forces to establish the start-up “Sympheny” as an Empa spin-off. They want to further develop and commercialise our platform into an easy-to-use app. The aim is to provide energy planners with sustainable and low-cost solutions for supplying energy to suburbs, districts, specific sites, villages or even cities..