Lars Oliver Grobe

Shading and daylighting systems such as textiles, louvres, and prismatic glazings are used to modulate incident solar radiation. The scattering properties of these “complex fenestration systems” (CFS) determine the temporally-variant, spatial distribution of daylight and solar radiation and thus affect the energy, global warming potential, comfort, health, and qualitative performance of buildings and the urban environment. Angle-dependent, solar-optical properties of CFS (i.e., bidirectional scattering distribution function (BSDF) data), however, are often unavailable or inaccurate, hindering simulated evaluations of environmental performance. New general methods for characterizing BSDF properties have been developed and extensively validated. This article describes the ISO/CIE 25176 initiative (launched in July 2024) that aims to standardize these methods for any arbitrary CFS. Open questions such as the limits of applicability are discussed. Standardization will have immediate implications on building performance analyses, e.g., the recent adoption of ISO/CIE 10916 for lighting energy simulations now requires use of BSDF data.

Optically complex fenestration systems (CFSs) aim to balance visual and thermal comfort with energy demand and the need for daylight as a factor for human health and wellbeing. Acquired by gonio-photometric measurements and computational methods, Bidirectional Scattering Distribution Functions (BSDFs) describe the typically irregular propagation of light through CFSs. Data-driven transmission and reflection models, that make direct use of such discrete BSDFs, were implemented in simulation software such as Radiance and became essential in matrix-based daylight simulation. One such technique, the Three-Phase-Method (3PM), is proposed by the recently revised standard ISO/CIE 10916:2024 for hourly calculations of daylight supply. This standardisation of a matrix-based simulation method is contrasted by a lack of guidance for the provision of its core element, the BSDF data. This motivated the formation of a joint working group by International Organization for Standardization (ISO) and International Commission on Illumination (CIE) in 2024, aiming at the joint standard ISO/CIE 25176 “Light and lighting – Daylight in buildings – BSDF data generation for complex fenestration systems”. The new ISO/CIE 25176 shall focus on the processing and generation of BSDF datasets to be employed in daylight simulation. It prioritizes tabular BSDFs of moderate resolution for the evaluation of integral quantities for daylight supply and solar gains to back the 3PM and its inclusion in current and future standards. For evaluation of conical-based quantities, tabular BSDFs of high resolution are included for CFSs that exhibit scattering with peaky distributions. The scope, key concepts and strategies of the future ISO/CIE 25176 are presented and its limitations are discussed.

This paper investigates the integration of thermal feedback into virtual reality (VR) environments to enhance architectural design processes. While traditional VR simulations focus primarily on visual experiences, this work expands the scope to incorporate thermal sensations, offering a more immersive and holistic design tool. The development of a “Thermal VR” system, combining heat emitters with VR goggles, allows architects to assess both the thermal and visual qualities of their designs more intuitively. The system was tested using various facade designs in a virtual office setting, specifically simulating solar radiation and its impact on indoor conditions. The results demonstrate the feasibility of integrating thermal feedback in VR and highlight its potential to enhance spatial perception and decision-making. However, challenges remain in the flexibility of generalizing the approach to different designs. This research contributes to the emerging field of climate-aware architectural design, offering valuable insights into the potential of VR as a tool for simulating combined visual and thermal experiences

Computer simulation allows to study daylight conditions in the past that afforded activities in antique buildings. The Python module phos4dtools implements the efficient computation of zonal daylight metrics that are considered to indicate affordances. It was employed to solve horizontal and vertical illuminance for different orientations and elevations in the House of the Priestesses, a unit of the Hadrianic Garden Houses complex in Ostia. A reconstruction model of the unit was produced by collating an existing, detailed 3D documentation with other sources and our own survey data. The spatially and temporally resolved results of daylight simulation employing phos4dtools were imported into a GIS database. Assuming typical reflectance properties, illuminance thresholds were determined that are required for the perception of contrast detail and colour differences. Integration over temporal periods and spatial zones that are eligible for residential activities was implemented by queries to the database. First, preliminary results indicated different distributions of affordances by daylight, depending on the characteristics of the considered visual tasks. Horizontal illuminance decreases quickly with increasing distance to the aperture, suggesting that activities bound to a horizontal work plane were constraint to the immediate adjacency of windows and potentially open doors. Vertical illuminance, on the other hand, reaches deep into the building when the receiving surface is oriented to a window, particularly in the absence of exterior obstructions. The exemplary application of phos4dtools shows its potential in the interdisciplinary research on daylight and its implications on living practice in antique buildings.

The challenge of building sector decarbonization has driven an integral rethinking of the way we design and build facades. Recently, large scale 3D-printing has emerged as an alternative manufacturing technique for novel facade components aiming at high operational efficiency and low environmental impact. Focusing on translucent polymer 3D-printed facades (3DPFs), this study tackles the challenges of modeling thermal and optical effects in geometrically complex components where interactions across multiple domains and scales occur. In particular, we introduce a novel method for modeling the irregular thermo-optical properties of 3DPFs, capable of capturing relevant effects often out of the scope of traditional modeling approaches. Our model accounts for geometry-dependent physical effects ranging from millimeter-scale fabrication details that impact optical behavior to centimeter-scale geometric features influencing heat and radiation transfer, extending up to the meter-scale implications for the building application. By employing computational techniques such as ray-tracing, computational fluid dynamics, and finite element analysis, we establish a model that offers detailed thermal and optical analysis to support performance-driven design iterations. Finally, demonstrating this approach in an office building context, we show that 3DPFs can match the performance of double glazing with dynamic shading, providing effective solar and thermal management over the year. This is achieved in a single, mono-material component with no active control, suggesting 3DPFs are a promising direction for low-environmental impact facade design.

Evaluating the reflection of solar radiation by Building Integrated Photovoltaics (BIPV) with structured front-glass is challenging for two reasons. First, the resulting irregular scattering of light cannot be accounted for by simple reflection models. Second, the locations where the evaluation needs to take place cannot be predicted by simple geometric considerations, as in the case of mirror-like reflection. The detailed modelling of a BIPV module featuring a periodical, linear structure based on the scanning of its surface is described. The application of the model is demonstrated in the assessment of solar reflection by a concave array of the modules. The stochastic sampling of the BIPV modules from each location in a dense sensor grid, that is required to ensure that no local concentration of reflected solar radiation is missed, is supported by re-orienting the sensors. Rather than relying on a data-driven Bidirectional Reflectance Distribution Function (BRDF) model of limited directional resolution, the geometric structure of the front-glass is modelled by modulating the normal of a mirror-like surface. The method allows an accurate and dense simulation with moderate computational demand.

Daylight metrics that shall guide performance-driven design must be applicable to models that reflect the limited knowledge at the time of planning decisions. In particular in residential buildings, the furnishing is beyond the control of such decisions and therefore unknown in the planning phase. The impact of model detail on illuminance- and luminance-based metrics is tested on a residential unit in Singapore. At two elevations, representing a work-plane and the eye level of a standing inhabitant, the metrics are computed from a) a detailed model incorporating furniture and shading devices, b) a model with only shading devices, and c) a minimalist model representing only the design decisions of the architect. As a potential approximation to the detailed model, d) a variant of the minimalist model with wall reflectance reduced to 0.20 is tested. The results for the three levels of detail are compared and indicate the significant impact of detail on all assessed daylight metrics.