Background: Increasing urbanization as well as global warming requires an investigation of the influence of different construction methods and ground surfaces on the urban heat island effect (UHI effect). The extent of the influence of the urban structure, the building materials used and their surfaces on the UHI effect can be significantly reduced already in the planning phase using a designated OpenFOAM-based solver “uhiSolver”. Results: In the first part of this research work, it is shown that inner building details and components can be neglected while still obtaining sufficiently accurate results. For this purpose, the building model was divided into two layers: a surface layer without mass, where the interaction with radiation takes place, and a component layer, which contains all relevant components and cavities of the building represented with mass-averaged material properties. It has become apparent that the three parameters—albedo, heat capacity and thermal resistance—which have a decisive influence on the interaction, have different effects on the component temperatures and the surface temperatures. In the second part of this research work, dynamic 3D computational fluid dynamics (CFD) simulations are performed with uhiSolver for a residential block in Vienna. Comparing the simulation results with measurement data collected on site, it is shown that the simplified assumption of homogeneous material data for building bodies provides very good results for the validation case investigated. However, the influence of the greening measures in the courtyard of the residential block on the air temperature is found to be negligible. Furthermore, it was observed that due to locally higher radiation density, lower air velocities and higher air humidity, the apparent temperature in the courtyard is sometimes perceived to be higher than in the adjacent streets, despite the lower air temperature. Conclusions: Simplifying the modeling process of the uhiSolver software by reducing the model complexity helps to reduce manual work for setting up appropriate boundary conditions of buildings. Compared to market competitors, good results are obtained for the validation case Kandlgasse presented in this research work, despite the simplifications proposed. Thus, uhiSolver can be used as a robust analytical tool for urban planning.

Strategies to mitigate urban heat islands are a recent issue in the Austrian capital, Vienna. In this study, the uhiSolver-v2106-0.21 software was used to evaluate the summer cooling effects and humidity production of small-scale facade greening and a green pergola located in two schools within the city. Based on on-site measurement data, the study revealed that small-scale greening measures are not able to substantially reduce ambient air temperature. On a hot summer day, at 3 p.m. local time (CEST), the maximum decrease amounted to 0.3 °C at 0.1 m from the facade greening as well as inside the green pergola. As for the apparent (perceived) temperature, a reduction of up to 4 °C was observed under the green pergola compared to the unshaded roof terrace. Hence, the simulation results show that, within urban areas, a significant improvement of thermal comfort in summer can only be achieved through large-scale greenery that provides shade for pedestrians.

In the validation of microclimate simulation software, the comparison of simulation results with on-site measurements is a common practice. To ensure reliable validation, it is crucial to utilize high-quality temperature sensors with a deviation smaller than the average absolute error of the simulation software. However, previous validation campaigns have identified significant absolute errors, particularly during periods of high solar radiation, possibly attributed to the use of non-ventilated radiation shields. This study addresses the issue by introducing a ventilated radiation shield created through 3D printing, aiming to enhance the accuracy of measurements on cloudless summer days with intense solar radiation. The investigation employs two pairs of sensors, each comprising one sensor with a ventilated and one with a non-ventilated radiation shield, placed on a south-oriented facade with two distinct albedos. Results from the measurement campaign indicate that the air temperature measured by the non-ventilated sensor is elevated by up to 2.8 °C at high albedo and up to 1.9 °C at a low albedo facade, compared to measurements with the ventilated radiation shield. An in-depth analysis of means, standard deviations, and 95% fractiles highlights the strong dependency of the non-ventilated sensor error on wind velocity. This research underscores the importance of employing ventilated radiation shields for accurate microclimate measurements, particularly in scenarios involving high solar radiation, contributing valuable insights for researchers and practitioners engaged in microclimate simulation validation processes.

Research into sustainable construction is increasingly focusing on the use of renewable materials in construction. These materials represent a promising alternative to conventional building materials as they are derived from renewable sources and are usually more environmentally friendly in terms of production, transport and end-of-life treatment. The Department of Ecological Building Technologies at the Vienna University of Technology has been investigating the hygrothermal behaviour and applicability of renewable materials for many years. Not only traditional building materials such as straw, wood, sheep’s wool and hemp have been investigated, but also innovative materials such as mushroom fabric. The research covered various aspects such as moisture protection, fire protection, thermal insulation, durability and resistance to external influences. The overall aim was to deepen the understanding of ecological building materials, overcome barriers to their use, and develop damage-tolerant constructions from them. The robust properties of wheat straw, sheep’s wool, hemp, cellulose and other materials underline their potential as efficient and environmentally friendly building materials. The data and insights gained will not only help to prove the effectiveness of these materials in the construction industry, but also to address concerns and uncertainties about their functionality.

The positive effects of green infrastructure in the urban environment are nowadays widely known and proven by research. Yet, greening, which serves to improve the indoor climate and people’s well-being, is integrated very limited in public facilities such as schools. Reasons for this are seen in a lack of knowledge and financing opportunities. A focus, among others, of the MehrGrüneSchulen research project is the interdisciplinary development of cost-effective greening solutions for schools. The designs were developed in close collaboration with students of a technical college (HTL) and a horticultural school. This study describes the development process and presents the results of the first implementations of greening systems at the HTL-building complex and at nine other schools in Austria.

Aging residential buildings in urban areas require effective thermal insulation to enhance energy efficiency and indoor comfort. In Bosnia and Herzegovina (BiH), expanded polystyrene (EPS) is the most commonly used insulation material due to its affordability, despite concerns regarding its flammability and environmental impact. While regulatory changes since 2019 have recommended rock wool for high-rise buildings, the absence of binding fire safety regulations has allowed the continued use of EPS, often driven by financial constraints. This study examines energy efficiency refurbishments in Sarajevo’s high-rise residential buildings and analyze the implications of the partial implementation of recommended measures. Using case studies, surveys, and expert interviews, this research identifies key challenges, such as limited funding, fragmented renovations, and inconsistent coordination between stakeholders. The findings indicate that facade insulation is often prioritized over comprehensive upgrades, including window replacement and heating system improvements, leading to suboptimal energy savings and minimal cost reductions for residents. Additionally, the complexity of multi-apartment ownership structures hinders uniform improvements in energy efficiency. Despite these challenges, property values tend to increase after renovation, highlighting the long-term financial benefits. To maximize energy savings and ensure sustainable urban housing, stronger interdisciplinary collaboration, improved funding mechanisms, and adherence to fire-safety standards are necessary. These measures would enhance the effectiveness of renovations and support long-term energy efficiency strategies.