Exergy-based analysis of renewable multi-generation units for small scale low temperature district heating supply
One third of the world's end energy consumption is used on heating purposes in the building sector. The larger part of energy used for heating comes from high exergy sources (e.g. coal or gas). Since living spaces are usually heated up to around 20°C, application of low exergy sources (e.g. solar thermal energy or ground heat sources) is sufficient for low temperature district heating supply. The main target of the work carried out is to demonstrate the advantages of exergy-based assessment for increased efficiency of small scale district heating supply schemes. For this reason different supply scenarios, based on fossil and renewable energy sources, are investigated. The different renewable energy supply units are regarded individually or in two- or three-way combinations. In this study renewable and fossil-based supply are compared on the one hand and on the other hand the benefits of merging several renewable energy suppliers for a small building group with a high energy standard are identified. For evaluation and identification of the best supply solution, the exergetic-based assessment method is applied. Additionally simplified aspects of operational management and estimation of investment costs are used to compare the different supply solutions. The evaluation of the scenarios clearly shows that the combination of innovative supply strategies and exergetic assessment leads to a more "holistic understanding" of the energy conversion chain and offers prospects for optimized low temperature district heating supply. Furthermore economic considerations and an analysis of emissions are to be included in the evaluation. This paper represents modeling, simulation and exergetic analysis of renewable multi-generation units to low temperature district heating supply of a building group and covers a topic from IEA DHC Annex TS1.