40. Building Thermal Exergy Analysis

The energy and environmental impacts due to energy consumption in the building sector are one of the main topics in the global energy field. A building is an energy system that uses energy sources in order to maintain its functionality and to ensure thermal indoor comfort for its occupants. Exergy analysis is a way to assess the impact of an energy system on the environment. This chapter introduces a model able to describe the interaction between a building and its surroundings from an exergetic point of view. The building is considered as a so-called black box, evaluating the exergy of overall energy and matter fluxes that cross the system boundaries. In this way it is possible to evaluate the exergy balance of the system and particularly the destroyed exergy. The exergy destruction percentage can be understood as a building environmental impact indicator. To illustrate the model and its operating suitability, an existing building was analyzed using the transient simulation software Trnsys. The modeling results show that about 95 % of the exergy used from the building is destroyed and that about 5 % is lost (transferred to the surroundings). This means that this building has very high impact. The model can be applied to assess the effectiveness of different building energy retrofit strategies. Through Trnsys modeling some conventional and advanced retrofit strategies, as well as on-site renewable energy utilization, are analyzed. The chapter presents the main analysis results, showing which of these strategies are able to reduce the building’s exergy demand and, hence, the building’s impact.