As a measure of energy “quality”, exergy is meaningful for comparing the potential for thermal storage. Systems containing the same amount of energy could have considerably different capabilities in matching a demand profile, and exergy measures this difference. Exergy stored in the envelope of buildings is central in sustainability because the environment could be an unlimited source of energy if its interaction with the envelope is optimised for maintaining the indoor conditions within comfort ranges. Since the occurring phenomena are highly fluctuating, a dynamic exergy analysis is required; however, dynamic exergy modelling is complex and has not hitherto been implemented in building simulation tools. Simplified energy and exergy assessments are presented for a case study in which thermal storage determines the performance of seven different wall types for utilising nocturnal ventilation as a passive cooling strategy. Hourly temperatures within the walls are obtained with the ESP-r software in free-floating operation and are used to assess the envelope exergy storage capacity. The results for the most suitable wall types were different between the exergy analysis and the more traditional energy performance indicators. The exergy method is an effective technique for selecting the construction type that results in the most favourable free-floating conditions through the analysed passive strategy.

Rapid urbanization and climate change are intensifying heat exposure in cities, making effective adaptation strategies essential. This study presents a streamlined digital twin modeling framework for simulating the impact of nature-based solutions (NBSs) on outdoor thermal comfort, developed within the Intelligent Communities Lifecycle (ICL) software suite. The approach automates the import of urban geometry from OpenStreetMap and integrates geolocated weather data, enabling users to efficiently test scenarios involving NBSs and surface material modifications. Outdoor thermal comfort is quantified using the Universal Thermal Climate Index (UTCI), with results visualized through an interactive cloud-based 3D platform to support participatory urban planning. The methodology is demonstrated in Meunierstraat, Leuven (Belgium), where three planning alternatives are compared across seasonal extremes. Simulations show that targeted NBS interventions, particularly temporary participatory measures, can improve thermal comfort under extreme heat. However, the benefits are seasonally dependent and spatially heterogeneous, emphasizing the value of high-resolution, scenario-based analysis. This integrated workflow enhances both technical evidence and stakeholder engagement. While the tool is capable of linking outdoor comfort improvements with building energy performance and carbon emissions, the present paper focuses solely on the outdoor thermal comfort results, leaving indoor–outdoor coupling analysis as a direction for future work.

Buildings, which are in fact ecosystems (living and inanimate organisms interacting together), are nowadays conceived and operated on the base of energy assessments underpinned by the first law of thermodynamics, and design strategies work towards energy conservation. Different approaches, based on the second law of thermodynamics, exist in research; they use the thermodynamic function called exergy - a measure of energy quality obtained from the combination of first and second law - and their scope is still centred on conservation strategies, optimised through irreversibility reduction. However, irreversibility plays a key role in nature, as entropy production dictates direction and modality of all processes and real phenomena are actually irreversible. The main problem related to the forefront of high-efficiency buildings is their high cost and complexity, which contrast stridently with the needs of the largest part of the built environment: effective low-budget sustainable solutions, easy to raise and control by non-specialised users. This research, through a pragmatic methodology, mixes practical experiences from low-budget construction sites with concepts from the relatively new discipline of non-equilibrium thermodynamics, and proposes an alternative energy design approach based on the second law of thermodynamics. Thinking of buildings as evolving ecosystems, their ability to perceive and exploit useful gradients can be enhanced through a deeper understanding of the role of irreversibility as the driving force of spontaneous processes, and imperfection as an intrinsic characteristic of architecture