Christoph Waibel

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Waibel

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Christoph

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0000-0001-6077-1411

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Publications 1 - 10 of 40

Integrating energy systems into building design with Hive: Features, user survey and comparison with Ladybug and Honeybee tools
Waibel, Christoph; Thomas, Daren; Elesawy, Amr; et al. (2022)
Building Simulation Conference Proceedings ~ Proceedings of Building Simulation 2021: 17th Conference of IBPSA (BS 2021)
We present “Hive”, a software plug-in in Rhino Grasshopper for teaching integrated building energy systems design. The purpose of Hive is to provide an easily comprehensible tool for architecture students to establish an understanding of the impact of their design decisions on building performance and (renew- able) energy systems. We enable a flexible framework allowing coupling with other third party (Grasshop- per) components by proposing a so-called simulation core, which decouples calculation modules from the input-output interface. We test Hive with architec- ture students and present results from a user sur- vey conducted. Our findings show that students find the climate and daylight analysis tools of Ladybug and Honeybee slightly more graspable for their design work, when compared to the energy tools in Hive – presumably also due to building energy being inher- ently less intuitive than daylight and climate analysis. The survey further shows that visual representation and ease-of-use appear to have priority over simu- lation accuracy and calculation time. However, we are convinced that our first version of Hive is a good starting point for accessible consideration of renew- able energy systems into architectural design, foster- ing interdisciplinary collaboration.
Do we need a saw? Carbon-based analysis of facade BIPV performance under partial shading from nearby trees
McCarty, Justin; Waibel, Christoph; Galimshina, Alina; et al. (2023)
Journal of Physics: Conference Series ~ CISBAT International Conference 2023: Renewable Energy
Building integrated photovoltaics (BIPV) are becoming more common in urban spaces. The impact of shading from nearby trees on BIPV performance and the potential conflict between the carbon sequestration benefits of trees and the carbon mitigation benefits of BIPV is not well documented in research. Therefore, this paper investigates the cost-benefit relationship of the carbon storage potential of trees vs. their shading effects on a nearby BIPV facade from the perspective of a life cycle assessment (LCA) using a high-resolution BIPV model and temporally sensitive tree growth model. The study is based on a typical Swiss residential building with adjacent vegetation and includes various BIPV facade permutations with different cell types, module orientations, inverter types, facade azimuths, grid emissions profiles, and tree planting scenarios. The results indicate that the removal of trees does not necessarily influence the overall carbon balance when considering LCA to the same degree as other features of the model space such as the grid carbon intensity or the configuration of the BIPV array. Furthermore the parametric-based analysis enables reporting on which BIPV configurations operate with the highest system efficiency under partial shading.
A parametric approach to evaluate the impact of BIPV façades on outdoor thermal comfort in different urban contexts
Duran, Ayça; Waibel, Christoph; Schlueter, Arno (2023)
Building Simulation Conference Proceedings ~ Proceedings of Building Simulation 2023: 18th Conference of IBPSA
While the promotion of Building Integrated Photovoltaics (BIPV) as a key strategy for the energy transition is widely accepted, the consequences of a large-scale BIPV deployment on the urban microclimate are not yet fully understood. Furthermore, the few existing studies addressing this issue do not lead to a consistent conclusion. This study, therefore, aims to investigate how different levels of BIPV deployment on building façades affect outdoor thermal comfort (OTC) for pedestrians in urban areas during the warmest day of the year using a parametric approach based on simulations. Computational Fluid Dynamics (CFD) simulations were conducted using Envi-met for 80 urban configurations in two climatic zones. The results indicate that the impact of BIPV on urban air temperatures can vary throughout the day, with temperature differences ranging from -0.21 to +0.46 °C for Zurich and -0.23 to +0.42 °C for Singapore, compared to scenarios without BIPV at pedestrian level in front of building façades. Among the studied parameters, ground surface material and street width were found to be the most influential, with an average increase of 1.76 and 0.37 °C in air temperature at 12 pm, respectively.
A review on artificial intelligence applications for facades
Duran, Ayça; Waibel, Christoph; Piccioni, Valeria; et al. (2025)
Building and Environment
This review applies a transformer-based topic model to reveal trends and relationships in Artificial Intelligence (AI)-driven facade research, with a focus on architectural, environmental, and structural aspects. AI methods reviewed include Machine Learning (ML), Deep Learning (DL), and Computer Vision (CV). Overall, a significantly growing interest in applying AI methods can be observed across all research areas. However, noticeable differences exist between the three topics. While CV and DL techniques are applied to image data in research on the architectural design of facades, research on environmental aspects of facades often uses numerical data with relatively small datasets and classical ML models. Research on facade structure also tends to use image data but also incorporates numerical performance prediction. A major limitation remains a lack of generalizability, which could be addressed by more comprehensive datasets and novel DL techniques. These include concepts such as Physics-Informed Neural Networks, where domain knowledge is integrated into hybrid data-driven models, and multi-modal diffusion models, which offer generative modeling capabilities to support inverse and forward design tasks. The trends and directions outlined in this review suggest that AI will continue to advance facade research and, in line with other domains, has the potential to achieve a level of maturity suitable for adoption beyond academia and into practice.
Detailed Modeling Framework for Integrated Photovoltaic in Partial Shading Conditions
McCarty, Justin; Waibel, Christoph; Schlueter, Arno (2023)
Proceedings of ECOS 2023: 36th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems
Building integrated photovoltaic (BIPV) systems are a crucial component of the transition to a low-carbon energy system. However, current simplified models of PV cells and modules used in building and urban energy simulations may not accurately capture the performance of various PV technologies under partial shading conditions. In this paper, we propose a novel framework for modeling parametric BIPV arrays using a highresolution irradiance grid and a power model that operates from the evaluation of IV-curves at the cell level to the AC to DC conversion in the inverter. This allows us to combine PV modules of varying sizes and electrical configurations based on the selected inverter type, and to capture the operative benefits of multiple types of cell technologies, module designs, and electrical layouts in building-based PV applications. We evaluate the proposed framework by comparing its performance to measurement data and to three other frameworks found in the literature through the simulation of two BIPV fac¸ades and a tilted rooftop array. The results show that the proposed framework is necessary to account for partial shading (if present) as well as provide operative details when the type of inverter to be used is in question. Overall, this paper presents a novel framework for modeling the performance of PV cells and modules in building and urban energy simulations, which has significant implications for the design and optimization of building-based PV systems.
Simulation-based Optimization in Architecture and Building Engineering - Results from an International User Survey in Practice and Research
Wortmann, Thomas; Cichocka, Judyta; Waibel, Christoph (2022)
Energy and Buildings
Although there is a substantial body of academic literature on Architectural Design Optimization (ADO), not much is known about actual ADO practices and user experiences. This paper presents results from an international user study of ADO with 186 respondents from various disciplines in architecture and building engineering. Compared to earlier user surveys from the literature, this survey employed a significantly larger sample size with active users of optimization in both industry and academia. The survey provides a comprehensive perspective on optimization in practice and highlights its utility for building design. Results can inform future developments of optimization tools to better suit needs and preferences of users, highlight a need to introduce optimization into architectural curricula, and ultimately contribute to the design of a more resource- and energy-efficient built environment. Most importantly, our survey suggests a non-ideal usage of optimization in design and research practice leading to, in the worst case, wrong conclusions drawn from optimization results. One prominent example in our survey is the potential over-reliance of (canonic) Genetic Algorithms for simulation-based problems: In the presence of low evaluation budgets, such algorithms will not converge, and modern model-based solvers would be more suitable. This demonstrates an urgent need to inform practitioners on more efficient tools suitable to the optimization task by, e.g., fostering the easy accessibility of such tools.
Image Upsampling of Low Resolution Turbulent CFD Domains with U-Net
Waibel, Christoph; Vecchiarelli, Rebekah; Duran, Ayça; et al. (2025)
Lecture Notes in Civil Engineering ~ Multiphysics and Multiscale Building Physics. Proceedings of the 9th International Building Physics Conference (IBPC 2024). Volume 4: Indoor Air Quality (IAQ), Lighting and Acoustics
The modelling of turbulent airflow with CFD is a computationally expensive task, yet vital for assessing architectural and urban ventilation concepts. Simplified airflow prediction methods exist, however at the cost of lacking accuracy and/or precision. This paper therefore proposes a hybrid simulation and deep learning approach. We utilize images of low resolution CFD domains as input to a U-Net neural network. The generated output is a high resolution upsampled image. As training data and application case, we use turbulent indoor flow with forced convection. Results are promising, as the generated flow fields can recreate higher level of details from the low resolution inputs as when compared to bicubic interpolation. However, the approach leaves room for improvement especially with respect to generated image sharpness.
Teaching architecture through an energy and climate lens
Hischier, Illias; Grobe, Lars Oliver; Waibel, Christoph; et al. (2025)
ETH Learning and Teaching Journal
Despite the increasing societal awareness of the climate crisis, considerations of outdoor and indoor climate, energy consumption and generation, and the environmental impact of material choices still represent a niche in architectural practice. Given the urgency of the issue, addressing these topics needs to be integrated in architectural design. In this work, we first describe a build-up of teaching formats and position them in view of learners’ competence development in architectural design through an energy and climate lens. We identify opportunities to refine our teaching instruments further and improve the learners' ability to independently integrate topics related to energy, emissions, climate, and comfort in the practice of design projects. We end with an outlook of an idealized build-up of these competencies across an architecture curriculum.
Impact of BIPV on Outdoor Thermal Comfort: Comparative Study of Four Urban Block Typologies
Duran, Ayça; Sogno, Rino; Buettiker, Dominic; et al. (2025)
Lecture Notes in Civil Engineering ~ Multiphysics and Multiscale Building Physics
Although building-integrated photovoltaic (BIPV) façades have been extensively researched in the context of electricity generation and carbon emission reduction, their impact on the urban microclimate is not yet fully understood. Few existing studies focus only on specific types of urban blocks or are based on generic models and do not account for climate change. This study addresses these gaps by investigating the impact of BIPV façades on outdoor thermal comfort for four urban block typologies commonly observed in Zurich, Switzerland, under current and future climate scenarios. Urban microclimate simulations were performed for a hot summer day using the Envi-met simulation software. Results show that the urban typology has a stronger influence on outdoor thermal comfort than whether BIPV has been installed or not, evidenced by the variation of average daily Universal Thermal Climate Index (UTCI) between the four typologies up to around 3 °C. Furthermore, climate change alone leads to a total increase of about 2 °C in average daily UTCI. Relative to these factors, the influence of BIPV on UTCI appears to be minimal. Depending on the time of day, BIPV facades result in a UTCI change ranging from −0.11 °C to +0.08 °C under the current climate and from −0.1 °C to +0.06 °C under the future climate scenario.
Simulation-Based Optimization of Buildings and Multi-Energy Systems
Waibel, Christoph (2018)

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