Optimising community energy supply with exergy principles

The building sector is characterised by a wide range of heating and cooling energy demands. This energy is mainly provided by the combustion of fossil fuels, which is responsible for greenhouse gas (GHG) emissions. While much has already been achieved in energy efficiency, there are still large potentials in providing heating and cooling energy with lower or without CO2 emissions. At the community level, different energy sources are available that do not involve combustion processes. These energies are often characterised by high fluctuations and different exergy levels or 'qualities': e.g. electricity (high-exergy) from photovoltaics or low temperature (low-exergy) heat e.g. from solar energy or waste heat sources. Low energy qualities are of particular interest, because these can supply most heating and cooling demands very efficiently. The application of exergy principles is especially important, allowing the detection of different available energy-quality levels and the identification of optimal contribution to an efficient supply. From this, appropriate strategies and technologies with great potential for the use of lowvalued energy sources (LowEx) and a high share of renewable energies for heating and cooling of entire cities can be derived. An additional task is to develop and test appropriate business models for the implementation on energy systems based on low exergy principles. For this reason, it is important to demonstrate the potential of low exergy thinking on a community level as energy and a cost efficient solution in achieving 100% renewable and GHG emission-free energy systems. The paper presents the key ideas of the international co-operative work in the general framework of the International Energy Agency (IEA), the EBC Annex 64 on "LowEx Communities - Optimised Performance of Community Energy Supply Systems with Exergy Principles"