Adaptive high-performance and multifunctional façade systems

Adaptive, high-performance and multifunctional façades are recognized as key contributors to the EU’s climate-neutral agenda, as outlined in Directive (EU) 2024/1275, the Renovation Wave, and Horizon Europe initiatives. These systems provide environmental control (daylight, shading), serve as an interface between indoor and outdoor environments and minimize reliance on heating, cooling and artificial lighting systems, enhancing energy efficiency and occupant comfort. In addressing this challenge, this paper presents the design and prototyping of three adaptive façade typologies aiming to combine a multifunctional role of controlling, redirecting and/or harvesting solar radiation. Designed through a performance-driven, integrated design methodology, aspects of morphology (system composition, geometrical characteristics), materiality and embedded actuation are discussed along with daylighting and irradiance analyses. To analyze their potential for visual comfort (daylight quality, glare, view to the outside) and solar harvesting, simulation studies were conducted for four distinct climatic conditions, corresponding to each case study using Climatestudio and Ladybug plug-ins for Grasshopper/Rhino 3D. Each façade is evaluated in its climatic context and the outcomes are synthesized through a cross-case comparative framework that links climate driver, performance objective, and actuation-feasible states. The first façade system uses a retroreflector’s geometry to redirect solar radiation back toward its source, potentially reducing short-wave radiative loading near the façade by redirecting incident radiation toward the sky, while cable-driven actuation allows multiple folded states. The second system reinterprets static folding geometries, the so-called “Hortenkachel” into a kinetic shading system of translucent panels. The third prototype introduces rectangular photovoltaic modules supported by a cable net and strut framework facilitating solar tracking. All case examples are based on lightweight construction principles and mechanical simplicity in their kinematics. Prototypes complement the simulation studies and provide proof-of-concept validation for the kinematic behaviour of the adaptive high-performance façade systems. The novelty lies in (i) extending retroreflective optics into a kinetically reconfigurable façade for controlled solar-radiation redirection near the façade, and (ii) extracting transferable design principles across three typologies that refer to morphology, control logic, and multi-criteria performance (daylight, glare, view, radiation/energy). The reported façade states, performance ranges, and prototype strategies provide an archival benchmark for early-stage adaptive multifunctional façade design.

1 Introduction

The origins of adaptive façades can be traced back to the 1960s, when sweeping societal shifts related to culture, technological advancement, and environmental awareness converged with the energy crisis of the 1970s, stimulated innovations in building envelope design (Moloney, 2011). During this period, cybernetic theory gained attention as a framework for conceiving the building envelope not as a static element but as an active, interactive system capable of responding dynamically to environmental stimuli and occupant needs (Fortmeyer and Linn, 2014; Kolarevic and Parlac, 2015). This theoretical foundation laid the groundwork for high-performance and multifunctional systems integrating active control mechanisms, sensors, and actuators to regulate multiple factors such as solar gain, thermal transmission, and daylight access (Fox and Kemp, 2016).

High-performance façades are building envelopes designed to optimize energy efficiency, indoor environmental quality and occupant comfort, while minimizing environmental impact and operational costs (Aksamija, 2013). In the EU context, such envelopes support the climate-neutral building agenda in Directive (EU) 2024/1275, the Renovation Wave and Horizon Europe. In parallel, the concept of multifunctionality in façades has become increasingly significant, emphasizing the integration of multiple environmental and energy-related functions within a single envelope component. These solutions combine thermal insulation, solar control, daylight control and renewable energy generation. Foundational façade-performance framing is given by Perino and Serra (2015) and Favoino (2015), while Matin et al. (2018) and Shahin (2019) provide comparative overviews of responsive/adaptive façade technologies and high-performance envelope strategies; recent work further advances multifunctional adaptive concepts through integrated actuation and performance workflows (Gonzalez et al., 2023).

The integration of photovoltaic (PV) technology with shading systems marks a significant advancement in multifunctional façade design, particularly in the context of Building-Integrated Photovoltaics (BIPV) (Zhang et al., 2018). Photovoltaic-integrated shading devices (PVSDs) evolved as multifunctional components that simultaneously generate electricity and provide solar protection strategies (Corti et al., 2023). For instance, PV louvers and brise-soleil systems not only harvest solar energy but also regulate solar heat gain and daylight penetration inside buildings, optimizing thermal comfort and energy usage (Liang et al., 2024). Through simulation studies, the research in Jafari and Salavatian (2023) demonstrates that PVSDs designed with optimized configurations can achieve energy efficiency ratings of 35.54%, providing critical evidence of their dual functionality. The study shows how PVSDs regulate sunlight penetration while saving energy and producing electricity simultaneously, making it a practical application example.

Climate change pressures and decarbonization targets further accelerate the adoption of adaptive and energy-positive façades driven by PV integration and other environmental control strategies. More broadly, such adaptive façade strategies extend their influence from the building scale to the wider urban microclimate. Adaptive façades mitigate urban heat island (UHI) impacts through multiple mechanisms, including the use of shading devices to limit solar absorption, application of reflective and high albedo materials to reduce heat retention, and incorporation of green façades to promote evapotranspiration and cooling. By dynamically modulating solar heat gain and surface temperatures in response to weather and urban conditions, adaptive façades optimize their contribution to urban thermal comfort and reduce heat load at building and district scales (Koukelli et al., 2023; Yuan et al., 2022).

Both high-performance and multifunctional façade approaches promote dynamic response and multi-criteria optimization, thereby supporting a holistic and integrated strategy in contemporary façade design (Gallo and Romano, 2017). Interdisciplinary design is fundamental to the advancement of adaptive façades, as these systems are at the intersection of architecture, engineering, material sciences and building performance. Collaborative frameworks are crucial at every stage: from early conceptual design, where requirements, sustainability targets, and operational parameters are defined, to performance simulation and digital fabrication (Voigt et al., 2023; Schultz and Wang, 2022). Such approaches facilitate lifecycle-oriented thinking, ensuring that environmental, structural, and user-centric criteria are considered from material selection to post-occupancy evaluation (Hosseini et al., 2019).

Technically, adaptive façades depend on actuation to enable dynamic responses to environmental stimuli such as solar radiation, temperature, humidity, wind and user preferences. The strategic optimization of actuator type, placement, quantity, and control logic is key to achieving high performance, while maintaining reliability and cost-effectiveness. Actuation systems where motion is enabled through geometry, smart materials, or dual behavior (structural and kinetic) can achieve comparable performance to fully actuated mechanisms, while lowering weight, cost, and control complexity (Le et al., 2016).

However, the contribution of adaptive, multifunctional façades to both building-scale performance and urban thermal resilience remains underexplored. This paper addresses this gap by demonstrating a performance-driven, integrated design-and-prototyping workflow for adaptive, multifunctional façades and by extracting some generalizable insights through a structured cross-case synthesis. The objective is to clarify how façade morphology, materiality, and actuation strategy can be co-developed with environmental performance metrics to support design decision-making for adaptive envelopes.

Specifically, we (1) develop three lightweight adaptive façade typologies kinetic retroreflective shading (Dubai), kinetic Tri-fold reinterpretation of the Hortenkachel (Stuttgart), and a dual-axis BIPV shading device (Stockholm and Nicosia); (2) evaluate them using a coherent set of visual-comfort and solar-radiation metrics (illuminance, daylight provision and view categories per EN 17037, glare risk, and solar-radiation/energy indicators); and (3) synthesize trade-offs and climate suitability into transferable guidance on adaptivity scale, control complexity, and performance robustness. The reported actuation-feasible façade states and quantified performance outcomes provide archival benchmark material for future adaptive façade research and development.

2 Performance-driven, integrated design methodology

A performance-driven, integrated design methodology for adaptive façades combines multidisciplinary criteria and quantifiable performance metrics to guide iterative design choices rather than prescribing fixed geometric solutions. Bedon et al. (2019) propose classification rules, performance indicators, and design methods that frame adaptive façades as systems mediating energy, daylight, and user comfort through adaptive behavior rather than static construction details. In line with this systems view, adaptive façades integrate passive and active components (sensing, actuation, control, and BIPV) and are commonly evaluated using performance-based indicators for energy and solar gains, power output, illuminance and daylight availability, glare probability, and occupant comfort (e.g., Perino and Serra, 2015; Galasiu and Veitch, 2006; Sadeghi et al., 2016; Zhang et al., 2022). To deal with trade-offs when integrating multifunctional façades, designers couple the assessment of photovoltaic yield, thermal performance, and visual comfort together in one simulation workflow (Hofer et al., 2016; Mesloub et al., 2020; Biloria et al., 2023). Consequently, performance-based processes in adaptive façade design set measurable design goals from early stages to enable trade-off analysis and multi-criteria decision-making, following decision-support and simulation-based frameworks (Voigt et al., 2023; Attia et al., 2012; Nabil and Mardaljevic, 2005). Practical constraints related to manufacturability, durability, and regulatory compliance are then incorporated to prevent high-performing, yet impractical solutions (Zhang et al., 2022; Attia et al., 2012; Perino and Serra, 2015).

Figure 1 illustrates the workflow of an interdisciplinary, integrated design process that is followed in this paper. The design elements including morphology, kinematics, construction and ecology inform performance verification, which includes static/structural, kinetic/operational, and daylight/visual comfort/solar radiation. Early decisions regarding parameters such as module size, array topology, depth, and degrees of freedom are coupled to the associated system kinematics and motion analysis. Mechanical detailing defines the constraints for feasible actuation and joints. Additionally, ecological criteria such as material, embodied impacts, energy efficiency serve as boundary conditions for the design process. A bidirectional loop between numerical simulation studies and scale-model prototyping follows for kinetic model validation. Performance assessment is based on corresponding guidelines set by EN 17037 operationalized through illuminance targets, daylight availability, discomfort-glare risk, and visual-environment metrics (EN 17037; Reinhart, 2014; Reinhart, 2018). The reference room material set (walls/ceiling/floor and glazing) was held constant across all cases investigated; only the façade-layer optical properties varied per typology (e.g., PV reflectance, translucent panel transmittance). In addition, the workplane sensor grid used a spacing of 0.60 m, identical across all indoor studies following standards like EN 17037 and LEED.

Figure 1

Figure 1. Integrated design approach of adaptive kinetic façades. Source: Matheou and Phocas (2025).

To improve comparability across the three developments, performance is assessed using a consistent metric set organized into: (i) indoor visual comfort (workplane illuminance and distribution; daylight provision and view categories per EN 17037; glare risk via annual glare probability/spatial glare indicators and selected point-in-time DGP checks), (ii) solar-radiation management (incident/reflected radiation, cumulative irradiance maps, and near-façade radiation redirection indicators), and (iii) solar-energy implications (annual incident radiation converted to transmitted solar heat gains where relevant). Unless otherwise stated, indoor simulations use the same reference office geometry and sensor-plane definition to enable cross-case interpretation. The performance metrics used in each case study are as follows:

Case 3.1 (Kinetic retroreflective, Dubai): reflection efficiency (ray redirection), cumulative irradiance (near-façade domain), workplane illuminance, EN 17037 daylight provision and view, annual glare probability.

Case 3.2 (Kinetic Tri-fold, Stuttgart): point-in-time illuminance (solstice-based), worst-case glare checks, EN 17037-based view assessment, parametric sensitivity to geometry (arrangement/coverage/shape).

Case 3.3 (Dual-axis PVSD, Stockholm and Nicosia): point-in-time illuminance and DGP at seasonal extrema, annual incident radiation and transmitted solar heat gains, annual spatial glare indicator (sDG) and comparative glare interpretation.

Point-in-time simulations are used where the research question requires rapid parametric exploration across many geometric variants and actuation states (e.g., arrangement, coverage, and shape studies). Running annual climate-based simulations for every parametric permutation and every reconfigurable state would be computationally prohibitive and would obscure early-stage design trends. To avoid overgeneralization, annual or climate-based metrics are applied selectively to the final actuation-feasible variants and to those cases where annual behavior is essential to the claim (e.g., annual glare exposure or annual solar gains). Representative dates (solstices/equinoxes) and hours (midday/afternoon) are selected to capture seasonal extrema of solar altitude/azimuth and to test known critical conditions for glare and solar load on south- and west-facing façades; in Dubai, peak-radiation hours during hot-season months are emphasized to reflect worst-case solar exposure.

3 Conceptual design and experimental prototyping of kinetic façade systems

3.1 Kinetic retroreflective façade system

3.1.1 Design concept

The kinetic retroreflective façade system (Kip, 2023) addresses the complex challenge of balancing visual comfort parameters including illuminance, daylight availability, glare mitigation, and view to the outside, while simultaneously potentially reducing short-wave radiative loading near the façade by redirecting incident radiation toward the sky. The project’s innovative approach centers on a kinetic retroreflective façade system that redirects incident solar radiation back toward the atmosphere, thereby avoiding problematic redirection into urban canyons that could exacerbate the urban heat island effect.

A cube corner retroreflector is an optical device that reflects incident electromagnetic radiation, particularly in the visible spectrum, predominantly back toward its source, maintaining this directional property largely independent of the device’s orientation relative to the incident beam (Hansen and Madhu, 1972). Figure 2 illustrates this principle for August 21 at four time points (11:00, 12:00, 13:00 and 14:00). This unique characteristic has made retroreflectors indispensable in diverse applications, including road safety devices, bicycle spoke reflectors and radar systems (CIE, 2024). The extension of retroreflective concepts from static devices to kinetic architectural systems, however, introduces substantial technical challenges. These include the integration of actuation and control mechanisms, as well as the performance-based metrics (illuminance, glare etc.).

Figure 2

Figure 2. Retroreflector principle on August 21 at: (a) 11:00; (b) 12:00; (c) 13:00 and (d) 14:00. Source: M. Kip.

3.1.2 Methods of environmental performance analysis

Dubai, UAE, was selected as the case study location due to the recorded increase of 4 °C in average temperature between 2005 and 2019 (Mahanta and Samuel, 2020). Based on the global horizontal radiation map, the highest levels of solar radiation in Dubai occur between 11:00 and 14:00 during the months of May to August. Accordingly, the simulation studies for daylighting analysis were conducted for the hottest months on May 21, June 21, July 21 and August 21 using ClimateStudio plug-in (Solemma LLC, 2023) for Rhino3D/Grasshopper. Outdoor solar-radiation redirection and near-façade irradiance exposure (ray-tracing and cumulative irradiance analysis) was further evaluated using Ladybug plug-in and Honeybee Cumulative Irradiance Heat Maps (CIHM), respectively.

A preliminary comparative ray-tracing and cumulative irradiance analysis (Koukelli et al., 2023) was conducted to evaluate near-façade short-wave radiative performance of different façade configurations: baseline (glazed façade), horizontal louvers, biaxial rotation of quadratic panels (A1), monoaxial rotation of quadratic panels with a fixed horizontal axis set at 22.5° (A2), and six types of basic trihedral corner reflectors (S1, S2, S3 and T1, T2, T3) (Figure 3). The horizontal louvers were designed with a depth of 50 cm and a spacing of 50 cm. The square trihedral corner reflectors (S1, S2, S3) were analyzed in three distinct orientations facing the sky (Figure 3E), each with length of 50 cm and a row spacing of 50 cm. Specifically, the panels were oriented with their reflective surfaces tilted toward the horizon at three different angles: (i) S1 with the V-shape positioned centered symmetrically, (ii) S2 with the V-shape rotated horizontally and toward the left, and (iii) S3 with the entire unit laterally toward the left. The triangular trihedral corner reflectors (T1–T3) followed the same set of orientations. All retroreflector configurations were considered as fixed and did not track the sun path.

Figure 3

Figure 3. Case studies: (a) baseline (glazed façade); (b) horizontal louvres; (c) kinetic retroreflective façade system; (d) A1-biaxial (left) and A2-monoaxial quadrat façade module (right); (e) square trihedral corner reflectors: S1 (left), S2 (middle), S3 (right) and (f) triangular trihedral corner reflectors: T1 (left), T2 (middle), T3 (right). Source: M. Kip.

To evaluate the near-façade outdoor radiative performance of the basic trihedral corner reflectors (A1, A2, A3, S1, S2, S3, T1, T2 and T3) relative to the baseline and horizontal louvres, the simulation environment modeled an outdoor test space of 10 × 10 m, with a 5 × 4 m south-facing façade and a corresponding sensor grid at ground level to capture radiation exposure. This analysis quantifies radiation redirection and near-façade cumulative irradiance within a 10 × 10 m domain; it does not include coupled urban microclimate modeling (e.g., airflow, long-wave exchange, or temperature fields). Therefore, outcomes are interpreted as potential near-façade radiative effects, not as direct quantification of urban heat island mitigation. The glazed façade was assigned by visible transmittance (Tvis) of 54.6% and high reflectivity (R:1, G:1, B:1), with a Solar Heat Gain Coefficient (SHGC) of 0.52. All the trihedral reflectors are considered as double face textile material with a high reflectance on the outer side and high absorbance on the inner side to prevent reflection from the glass to the façade modules. The key performance metric for this study is the reflection efficiency (R [%]), defined as the percentage of reflected rays (R_p) with an angular deviation of 0°–45° relative to incident rays, normalized to the total number of rays (R_t). This metric ensures that solar radiation is redirected toward the sky rather than into the urban canyon, adjacent buildings, or pedestrian areas.

Following the cumulative irradiance analysis, illuminance analysis was conducted for all basic types (Figure 4). As a next step, the best performing type was selected for further geometric investigations, such as size and depth gradation along the façade’s height. An office model was considered for the daylighting analysis with 13.6 m in length, 10.9 m in width, and 4.0 m in height, covering an area of approximately 115 m² with south orientation (Solemma LLC, 2023). Lighting Materials (LM) have been assigned for walls, floor and ceiling, and glazing with a U-value of 0.82 W/m²K and Visible Transmittance (Tvis) of 59%. Sensor points were placed 0.75 m above the floor level to evaluate the work plane illuminance distribution. For visual comfort, metrics include illuminance (target range: 500–1,000 lux for office spaces), daylight availability in accordance with EN 17037 (four compliance levels: Fail, Minimum, Medium, High), horizontal view angle analysis (14°, 28°, and 54° thresholds for compliance levels) and annual glare probability. To ensure consistency across outdoor and indoor performance assessments, a cumulative irradiance analysis was conducted considering the geometrically improved reflector (T60-40).

Figure 4

Figure 4. Basic types of trihedral corner reflectors (S1, S2, S3 and T1, T2, T3) for the office model. Source: M. Kip.

3.1.3 Simulation results

As shown in Table 1, S1 and S3 exhibit reflectance performance exceeding 80%, with S1 reaching an average of 88% over the examined hours and S3 achieving 81% over the same period. The triangular trihedral corner reflector variants (T1, T2, T3) generally maintain high reflectance, with the T2 and T3 reaching overall performance above 75% for the majority of the time. CIHM values indicate that the radiation load decreases slightly (Table 2). On average, values are reduced by approximately 0.4 kWh/m² compared to a glass façade without shading, showing that all reflector types reduce reflected radiation toward the urban canyon. This effect arises because all façade types are oriented roughly orthogonally to the façade, which limits direct reflection of solar radiation toward the ground. Among the variants, the greatest reduction in reflected radiation is achieved by T3, with reductions of 42.9% on May 21 and June 21% and 50.0% on July 21 and August 21, and was therefore selected for the daylighting analysis.

Table 1

Table 1. Ray trace analysis on May 21, June 21, July 21 and August 21 for S1, S2, S3 and T1, T2, T3 in Dubai.

Table 2

Table 2. Results of the cumulative irradiance heat map in Dubai.

The illuminance levels were within the acceptable range (Table 3); however the results revealed a pronounced gradient, with high values near the façade, and much lower values toward the rear of the room, indicating insufficient light uniformity. To address this issue, further variations of T3 were analysed considering two different façade module sizes (60 cm and 80 cm) and depth gradient from 80 cm at the top row to 40 cm at the bottom row (T60-40 and T80-40) to allow more daylight admission by decreasing the depth.

Table 3

Table 3. Illuminance mean values of S1, S2, S3 and T1, T2, T3 in Dubai.

The illuminance levels for T60-40 range between 456 lux, 482 lux, 428 lux and 404 lux, while for T80-40 range, between 438 lux, 465 lux, 412 lux, and 386 lux in May 21, June 21, July 21 and August 21, respectively. Overall, these deviations are small and can be considered negligible in terms of illuminance performance. The analysis of light uniformity further indicated that improvements were only marginal and not sufficient to achieve a fully satisfactory distribution, leading to the conclusion that reflectors are not suitable to function as light shelves. The variation T60-40 was selected for further investigation on daylight availability, glare, and view, instead of T80-40 due to the size.

The T60-40 variation with fully open modules achieves the minimum daylight availability threshold of 100 lux across 95% of the floor area, while an improved daylight level is expected when the modules are folded (Figure 5). In terms of view analysis, the proportion classified as “failing” is limited to 7.3% at 1.20 m and 4.0% at 1.70 m (Figures 5C,D). By contrast, 91.5% (1.20 m) and 93.9% (1.70 m) of the area fall within the highest category “High.” Therefore, it can be concluded that the T60-40 variant ensures a consistently good view to the outside. The red areas in Figure 5E indicate 1.6% of views with disturbing glare, occurring between October and February from 16:00 to 18:00.

Figure 5

Figure 5. S60-40 in Dubai: (a) illuminance; (b) daylight availability; (c) view analysis at eye height 1.20 m; (d) view analysis at eye height 1.70 m; (e) annual share of disturbing glare. Source: M. Kip.

Following the improvement of indoor daylighting conditions through adjustments to the geometrical characteristics of the façade module, a further analysis of the cumulative irradiance map was conducted comparing the baseline with T60-40. As shown in Table 4, reflected radiation is reduced by 42.9% on May 21 and June 21 and by 50% on July 21 and August 21, behaving the same as T3 (Table 2). A visual assessment further confirms that radiation decreases significantly in the immediate vicinity of the façade, where red discolorations shift to yellow and, in some cases, even to blue (Table 4). At greater distances from the façade, however, no major changes are observed.

Table 4

Table 4. Cumulative irradiance heat map for the baseline and the S60-40 in Dubai.

3.1.4 Façade construction, actuation and prototyping

The system comprises seven rows of triangular trihedral corner reflectors (74 units) with a height of 45 cm and a width of 90 cm supported by a cable net system. To follow the daylighting performance criteria, the modules in the top row have a depth of 60 cm, while those in the bottom row measure 40 cm. The wings of the modules are connected to an elastic steel sheet at an angle of 45°, and to ensure optimal bending capacity of the elastic steel sheet, a clearance of 50 mm is maintained between the folding axis of the bar and the attached wing. Each module can be folded or unfolded (Figure 6) via two running cables. Since cable-driven actuation occurs horizontally in rows, individual rows can also be controlled independently. This enables, for example, the selective closure of rows at eye level to maintain outward visibility, following a clustered actuation strategy. A double-sided textile membrane is integrated into the wings’ frame, featuring high reflectance on the interior surface and high absorption on the exterior surface.

Figure 6

Figure 6. Indoor visualization with unfolded (left) and folded (right) trihedral corner reflectors and birds’ eye view with unfolded (left) and folded (right) trihedral corner reflectors. Source: M. Kip.

To experimentally assess the kinetic behaviour of the façade modules, a 1:3 scale prototype was fabricated to verify the kinetic behavior of the proposed system (Figure 7). The black elements were printed from Polyethylene Terephthalate Glycol (PETG) filament, while the elastic steel sheet was represented by an elastic joint fabricated from Thermoplastic Polyurethane (TPU) filament. The prototype provided insights into the actuation mechanism of the wings. By pulling the cables, the wings could be folded with minimal applied force; upon release, the wings returned to their initial position, demonstrating the elastic restoring capacity of the system.

Figure 7

Figure 7. Prototype in 1:3 scale with the stepwise reconfiguration. Source: M. Kip.

3.2 Kinetic tri-fold façade system

3.2.1 Design concept

The design project, developed by Jiuyuan Liu, Simon Göbel and Tobias Steiger, introduces an adaptive kinetic façade system inspired by the Hortenkachel geometry, originally designed by Helmut Rhode and later developed by Egon Eiermann. The Hortenkachel is a distinctive façade system used in the Horten department stores, consisting 50 × 50 cm tiles, initially made of ceramic and later of aluminum, each featuring a stylized “H” for Horten. The system comprises two main components: (a) the egg-crate frame of individual wings, and (b) the wings within the frame. Its application to the reference office model is illustrated in Figure 8. Technically, the original Hortenkachel was not conceived as a shading device. Therefore, the objective of this study was first to identify and optimize the geometric parameters of the Hortenkachel for solar shading aligned with user controllability (Figure 9a), and then to design a lightweight kinetic shading system using recyclable materials and a minimal number of actuators through module clustering.

Figure 8

Figure 8. Hortenkachel applied to the reference office model. Source: J. Liu, S. Göbel and T. Steiger.

Figure 9

Figure 9. Hortenkachel deconstruction: (a) hortenkachel; (b) egg-crate system; (c) wings; (d) Tri-fold: additional side wings. Source: J. Liu, S. Göbel and T. Steiger.

Initially, the egg-crate system was analysed without the wings, however, this configuration lacked flexibility (Figure 9b). Subsequently, various wing geometries were explored, testing different arrangements, sizes, coverages, shapes, and depths. When applied without the egg-crate frame, the wings alone failed to meet the target illuminance levels, particularly during winter at 12:00, when the low solar altitude allowed direct sunlight to penetrate the office room (Figure 9c). These limitations highlighted the need for a new system capable of both shading and flexibility. To address this, a single-axis Tri-fold system was developed (Figure 9d), combining modules with the primary Hortenkachel wings and additional translucent side wings to control glare and regulate indoor illuminance, while preserving outward visibility and user adaptability (Figure 10).

Figure 10

Figure 10. Outdoor (left) and indoor visualization (right) of the single-axis Tri-fold façade system. Source: J. Liu, S. Göbel and T. Steiger.

3.2.2 Methods of daylighting performance analysis

A comparative parametric analysis was conducted between the baseline (glazed façade), the original Hortenkachel, various static geometric configurations, static Tri-fold modules (50% openness) and an adaptive scenario featuring single-axis Tri-fold modules (50 × 50 cm module size arranged horizontally) to assess their influence on daylight performance. The parametric analysis examined three types with side wings arranged: (a) mixed; (b) vertical; and (c) horizontal (Figures 11a–c), where the mixed type combines both alignments, meaning that one module is vertically positioned and the adjacent module, horizontally positioned. Four module sizes were subsequently analyzed: (a) 25 cm; (b) 50 cm; (c) 75 cm; and (d) 100 cm (Figure 11d), this was followed by four coverage and shape variations: (a) façade coverage of 50%; (b) façade coverage of 75%; (c) low mid-point; and (d) high mid-point (Figure 11e). In the sun-tracking scenario (Figure 12), the Tri-Fold modules dynamically track the sun’s position and configure their openness.

Figure 11

Figure 11. Façade arrangements with side-wings grey-colored: (a) mixed; (b) vertical; (c) horizontal; (d) size variations: module 25 cm, 50 cm, 75 cm, and 100 cm; (e) coverage and shape variations: 50% covered (left); 75% covered; low mid-point; high mid-point (right). Source: J. Liu, S. Göbel and T. Steiger.

Figure 12

Figure 12. Tri-fold module tracking the solar altitude on the summer and winter solstices at 12:00 and 15:00. Source: J. Liu, S. Göbel and T. Steiger.

Daylighting simulations were performed for the summer and winter solstices at 12:00 and 15:00 in Stuttgart, Germany, using the office reference model described in Section 3.1.2, with south- and west-facing glazed façades. The analysis was conducted in Rhinoceros 3D and ClimateStudio under CIE clear sky conditions through point-in-time simulations. Opaque wood was assigned to the primary wings and polycarbonate with 30% light transmittance to the side wings.

3.2.3 Simulation results

A comparative analysis of the baseline, the Hortenkachel, the three arrangements (mixed, vertical and horizontal) and the single-axis Tri-fold system, shows significant differences in daylighting performance (Table 5). The baseline produces the highest illuminance levels (5363 lux in winter at 12:00), exceeding the target range (500–1000 lux). The Hortenkachel reduces illuminance however, the system is structurally complex for integrating adaptive feature, as it combines an egg-crate framework with additional wings, increasing material and fabrication cost. While the mixed and the vertical arrangement perform well on the winter and summer solstices at 12:00 and 15:00, mixed arrangements complicate actuation for clustering because adjacent modules have different orientations (vertical-horizontal), and vertical arrangements can lead to intolerable glare, especially in winter when the solar altitude is low. For this reason, subsequent simulations focused on the horizontal arrangement, in which the primary wings that face the sun are opaque, and the secondary wings are translucent to diffuse incoming radiation. The module-size variation had no significant effect on illuminance; however, the illuminance levels remain low and further improvement is essential. Therefore, a 50 cm module was selected as a balance between performance and human scale (Table 6). Coverage and shape studies showed that cases with high and low mid-points performed better overall, while 50% coverage yielded lower illuminance, because fully open modules already provide effective protection for south- and west-oriented surfaces (Table 7). The adaptive scenario addresses this limitation by employing a kinetic shading system that tracks the solar’s altitude to dynamically regulate illuminance. However, modules with high and low mid-points pose greater control challenges due to their asymmetrical geometry and non-uniform kinetic behavior.

Table 5

Table 5. Illuminance mean values by arrangement in Stuttgart.

Table 6

Table 6. Illuminance mean values by size in Stuttgart.

Table 7

Table 7. Illuminance mean values by coverage and shape variations in Stuttgart.

Following the parametric analysis on illuminance regarding the arrangements, size, coverage and shape variations, another comparative study was conducted for the baseline, static Tri-fold and single-axis Tri-fold. The Tri-fold solar’s altitude tracking mechanism maintains indoor illuminance within the target range, achieving a mean value of 905 lux on the summer solstice at 12:00, outperforming both the baseline (2530 lux) and the static Tri-fold (1158 lux) (Figure 13). Glare analysis was conducted for the worst-case scenario in winter solstice at 12:00 presenting intolerable glare for the baseline and the static Tri-fold (Figure 13). The single-axis Tri-fold (altitude-responsive) system demonstrates robust daylight- and glare-control behavior under seasonal variations. In summer, when the sun is higher, the modules open to permit daylight and preserve outward views while preventing glare; in winter, when the solar altitude is lower, the modules remain closed to block direct sunlight and avoid visual discomfort. View analysis (Figure 13) following EN 17037 confirms that while views towards the southern sun are occasionally obstructed for glare control in winter at 12:00, west-facing views remain accessible, reflecting the system’s adaptive and occupant-centered design. Gray zones indicate no access to views; dark blue indicates minimal access; turquoise indicates moderate access; and green indicates full access to views.

Figure 13

Figure 13. Baseline (left); static Tri-fold (middle); single-axis Tri-fold (left): (a) illuminance mean values on the summer solstice at 12:00; (b) glare probability (DGP) on the winter solstice at 12:00 (worst-case scenario); (c) view analysis on the summer solstice at 12:00 (left and middle) and on the winter solstice at 12:00 (left). Source: J. Liu, S. Göbel and T. Steiger.

3.2.4 Façade construction, actuation and prototyping

In the daylighting analysis, vertical zoning plays a crucial role in achieving optimal visual comfort. Inspired by the classical blind mechanism, the proposed adaptive shading system, Tri-fold, operates through a single actuator controlling six modules per zone (Figure 14). The actuator engages by pulling a string connected to the lower edges of the modules, causing them to fold upward in an origami-like motion. Upon release, gravity restores the modules to their original closed position. Across the entire façade, a total of 33 actuators is distributed to generate various shading patterns responsive to the sun’s position and user preferences. The side wings of the modules are supported by an aluminum frame, while the joints between the elements are made of elastic 3D-printed TPU, enabling the characteristic foldable, origami-inspired transformation of each module (Figure 15). A 1:2 scale prototype was built to experimentally demonstrate the kinematics of the system.

Figure 14

Figure 14. Cable-driven actuation method, modules clustering and module reconfiguration with 100%, 75% and 50% openness. Source: J. Liu, S. Göbel and T. Steiger.

Figure 15

Figure 15. Prototype in 1:2 scale. Source: J. Liu, S. Göbel and T. Steiger.

In real-world applications, TPU-based compliant mechanisms could be substituted with pneumatic joints which offer higher durability, scalability, and reliable performance under repeated actuation. Additionally, since the proposed system responds dynamically to the solar altitude, solar thin-film photovoltaic panels could be integrated on the primary upper wings to generate renewable energy while providing shading.

3.3 Dual-axis photovoltaic shading device

3.3.1 Design concept

An adaptive unitized building envelope system incorporating thin-film photovoltaic PV modules was developed as part of a research project conducted at the University of Cyprus. The system integrates lightweight PV modules mounted on aluminum support plates and is designed for seamless application on both new and existing building façades. A key feature of the prototype is its minimal use of actuators, which are strategically positioned outside the main structural body. The configuration reduces the number of active components within the movable structure, thereby simplifying control and minimizing mechanical complexity.

The unitized structural system comprises a primary frame of aluminum profiles, within which a pre-tensioned cable net serves as the main supporting mechanism. This cable net carries a secondary assembly consisting of aluminum struts, interconnected via continuous cables on both the front and rear sides of the system. The PV modules are rigidly attached to the front-facing struts, ensuring that any rotational movement of the struts results in a synchronized reorientation of the PV panels. The system allows for bi-axial movement, with the struts capable of rotating within both the vertical and horizontal planes. These rotations are actuated by controlled adjustments in the relative lengths of the continuous cables, enabling the PV modules to track the motion of the sun in two degrees of freedom. This capability allows for real-time adaptation to the sun’s position, maximizing energy capture throughout the day. Figure 16 illustrates a small-scale prototype of the system in its initial configuration, where the struts are aligned horizontally, and the PV modules are oriented vertically. The overall dimensions of the prototype unit in actual scale are 540 cm in width and 365 cm in height. The assembly houses 20 PV modules, each measuring 66 cm in width and 50 cm in height. Due to the rigid connection between each module and its corresponding strut, any change in the strut’s orientation directly adjusts the PV panel’s inclination, thereby enabling uniform angular realignment relative to incident sunlight.

Figure 16

Figure 16. Prototype system in 1:10 scale. Source: Phocas et al. (2024).

For synchronized movement, all cables within a plane (either horizontal or vertical) can be actuated in parallel, allowing the PV modules to reorient simultaneously and uniformly in response to changing solar angles. The continuous secondary cables are routed through a pulley system that includes a pair of counter-rotating pulleys at one end and a guiding pulley at the midpoint. This arrangement is driven by a single rotational actuator, such as a stepper motor, connected to the axis that links the paired pulleys within each row of cables. Importantly, only two actuators are employed in total, both mounted on the stationary aluminum frame and mechanically decoupled from the lightweight, movable system body. This approach maintains the low self-weight of the main structural components, ensuring efficient operation without compromising structural balance or dynamic response.

3.3.2 Methods of daylighting performance analysis

Following the initial evaluation of the dual-axis BIPV system (Phocas et al., 2024), which primarily targeted maximizing PV efficiency, while reducing the mechanical complexity (associated with dual-axis tracking), a supplementary daylighting and solar irradiance analysis was conducted.

Daylighting simulations were carried out in ClimateStudio for a CIE clear-sky condition in two distinct climatic contexts, Nicosia, Cyprus and Stockholm, Sweden, on March 20, June 21, September 22 and December 21 at 12:00, using the office reference model described in Section 3.1.2. To complement the spacing distance between the PV modules, an opaque material with a reflectance of 28% was assigned to the panels. The analysis on illuminance and glare focused on the fixed position, average optimum (static and optimized position for maximum PV power output) and sun-tracking positions for the four selected point-in-times (Figure 17). This step enables a combined evaluation of energy generation and indoor daylight quality, clarifying to what extent the dual-axis BIPV system can be redesigned to provide both high solar-energy yield and adequate daylighting and shading performance.

Figure 17

Figure 17. PVSD applied in an office model: (a) fixed position; (b) average optimum in Nicosia (left) and in Stockholm (right); (c) sun-tracking at 12:00 on March 20, June 21, September 22 and December 21 in Nicosia (from left to right); (d) sun-tracking at 12:00 on March 20, June 21, September 22 and December 21 in Stockholm (from left to right). Source: Authors.

The transmitted solar heat gain was conducted for four façade types: (a) baseline, (b) fixed vertically positioned PV, (c) average optimum for Stockholm and Nicosia (fixed position), and (d) an orientation optimized for 21 June and then applied to the entire year. The fixed vertically positioned PV and the average optimum were chosen in a previous irradiance analysis and photovoltaic system power (Phocas et al., 2024). The third configuration was defined by first determining the façade orientation that minimizes incident solar radiation for summer solstice (June 21, 12:00) and subsequently applying this single orientation to the annual simulation. This scenario reflects a summer-driven control concept and allows a direct comparison with the two other single-state strategies (vertical and annual average optimum), without introducing hourly tracking. It also quantifies the annual effect of maintaining a summer-protective façade state even during periods when passive solar gains would be desirable.

Annual incident solar radiation on the façade, obtained from ClimateStudio, was converted into transmitted solar heat gains using the common fenestration formulation:

$Q_{\text{solar}}=I_{\text{incident}}\times SHGC\times A$

where $I_{\text{incident}}$ is the solar radiation incident on the glazing $\left[{\text{kWh}/\mathrm{m}}^2·\text{yr}\right]$, $SHGC$ is the solar heat gain coefficient of the glazing (0.52 in this study), and $A$ is the glazed area (31.5 m²). This approach is consistent with the solar gain calculation methods in (ASHRAE, 2021) and with the definition of total solar energy transmittance in EN 410 and ISO 15099.

3.3.3 Simulation results

The mean illuminance values for the fixed position, average optimum and the sun-tracking system in Stockholm and in Nicosia are shown in Table 8. In Stockholm, the sun-tracking system shows a consistently lower mean illuminance than the fixed vertical position during periods of low solar altitude, with 34.9% lower (1875 vs. 2878 lux) on March 20, 29.2% lower (1992 vs. 2813 lux) on September 22, and 11.1% (786 vs. 884 lux) on December 21. The reduction is smallest on June 21 (0.36%), because the high solar altitude minimizes the kinetic feature of tracking. A comparable pattern is observed in Nicosia with the sun-tracking system, 2.5% lower (546 vs. 560 lux) on March 20, 5.0% lower (529 vs. 557 lux) on 22 September, 9.5% lower (2595 vs. 2868 lux) on 21 December and 11.6% (501 vs. 449 lux) on June 21. These results indicate that dual-axis sun tracking is most effective, in terms of differentiation from a fixed vertical system, when the solar altitude is low. In winter the difference diminishes, because the very low solar altitude combined with relatively large panel spacing allows more daylight penetration even in the fixed case.

Table 8

Table 8. Illuminance mean values of the fixed position, average optimum and the sun-tracking system in Stockholm and Nicosia.

The annual solar irradiation is 833 kWh/m²·yr in Stockholm and 1019 kWh/m²·yr in Nicosia, which corresponds (with the simulated SHGC of 0.52) to 433.2 kWh/m²·yr and 529.9 kWh/m²·yr of transmitted solar gains, respectively (Table 9). For the actual façade area of 31.5 m², this equals about 13.6 MWh/yr in Stockholm and 16.7 MWh/yr in Nicosia, confirming the expected effect of climate, with the Mediterranean location offering higher annual solar availability. The fixed vertical PV reduces annual gains by about one-third in both locations. In Stockholm, transmitted gains drop from 433.2 kWh/m²·yr to 282.4 kWh/m²·yr (34.8% reduction), which for 31.5 m² equals 8.9 MWh/yr, i.e., a reduction of roughly 4.75 MWh/yr compared to the baseline. In Nicosia, the same configuration reduces transmitted gains from 529.9 kWh/m²·yr to 348.9 kWh/m²·yr (34.2%), or from 16.7 MWh/yr to about 11.0 MWh/yr for the whole façade, a reduction of about 5.7 MWh/yr.

Table 9

Table 9. Transmitted solar heat gain values of the baseline, fixed position, adaptive optimum and the solstice-derived fixed.

The average optimum fixed orientation achieves the lowest gains overall: 251.2 kWh/m²·yr in Stockholm (42.0% reduction), which is 7.9 MWh/yr for 31.5 m², and 329.2 kWh/m²·yr in Nicosia (37.9% reduction), which is 10.37 MWh/yr. The solstice-derived fixed orientation (i.e., façade position defined for 21 June and applied unchanged to the annual simulation) yields very similar results: 254.8 kWh/m²·yr in Stockholm (41.2% reduction) and 329.7 kWh/m²·yr in Nicosia (37.8% reduction), corresponding to about 8.0 MWh/yr and 10.38 MWh/yr for the full façade, respectively. This is relevant for designs that require strong solar protection in summer, but prevent over-shade in winter, when passive solar gains are desirable. It should be noted that the solstice-derived fixed orientation does not represent a continuously sun-tracking façade. A system that updates its position hourly or seasonally would be able to align the façade more closely with the incident solar vector and thus further reduce incident (and transmitted) solar gains during high-load periods. The present case therefore represents a conservative, single-state approximation of a summer-driven control strategy.

In Stockholm, the three investigated PV positioning strategies (fixed, average optimum, and sun-tracking) show that reorienting the system alone cannot eliminate glare for certain low solar altitudes. At 12:30 on March 20 all configurations reach Daylight Glare Probability (DGP) 1.00, and on December 21 the values remain clearly uncomfortable (0.79–0.81), indicating that the combination of low solar altitude and view direction creates inherently critical situations (Tables 10–12). When glare is evaluated over space and time, however, the average optimum configuration performs best (sDG = 15.1%) compared to the fixed position (19.1%) and the sun-tracking (Figure 18). This means that, relative to the fixed case, the average optimum reduces the share of views experiencing disturbing glare over the year by about 21%, while the sun-tracking case still achieves a reduction of roughly 16%. In high-latitude locations, even a limited-state adaptive façade (fixed ‘average-optimum’ or seasonal state), rather than continuous sun tracking, is more effective for visual comfort than a static vertical façade.

Table 10

Table 10. Daylight glare probability (DGP) of the fixed system at 12:30 on March 20, June 21, September 22, and December 21 in Stockholm.

Table 11

Table 11. Daylight glare probability (DGP) of the average optimum system at 12:30 on March 20, June 21, September 22, and December 21 in Stockholm.

Table 12

Table 12. Daylight glare probability (DGP) of the sun-tracking system at 12:30 on March 20, June 21, September 22, and December 21 in Stockholm.

Figure 18

Figure 18. Spatial Disturbing Glare (sDG) for the PVSD façade in Stockholm: (a) fixed position; (b) average optimum; (c–f) PVSD fixed to the sun-tracking position on: (c) March 20; (d) June 21; (e) September 21, and (f) December 21. Source: Authors.

In Nicosia, the same set of configurations results in generally lower glare levels. The fixed position already yields a relatively low annual value (sDG = 11.5%) and only moderate DGP values for the four representative dates (0.42–0.54), which implies that a static configuration is sufficient to maintain acceptable visual comfort for most of the year (Figure 19). By contrast, the more sun-facing “average optimum” and the sun-tracking drive the winter case (21 December, 12:30) up to DGP = 1.00, without providing a clear annual advantage (sDG remains around 11%–12%) (Tables 13–15). In this low-latitude, high-irradiance context, orienting the PV surface toward the solar vector increases exposure to direct high-luminance sources during the short low-solar-altitude periods, without yielding any compensatory gains in annual spatial glare.

Figure 19

Figure 19. Spatial Disturbing Glare (sDG) for the PVSD façade in Nicosia (a) fixed position; (b) average optimum; (c–f) PVSD fixed to the sun-tracking position on: (c) March 20; (d) June 21; (e) September 21, and (f) December 21. Source: Authors.

Table 13

Table 13. Daylight glare probability (DGP) of the fixed system at 12:30 on March 20, June 21, September 22, and December 21 in Nicosia.

Table 14

Table 14. Daylight glare probability (DGP) of the average optimum system at 12:30 on March 20, June 21, September 22, and December 21 in Nicosia.

Table 15

Table 15. Daylight glare probability (DGP) of the sun-tracking system at 12:30 on March 20, June 21, September 22, and December 21 in Nicosia.

A further factor that helps explain the observed DGP peaks is the spacing between PV elements. Because the array is not fully continuous, the inter-panel gaps act as apertures through which direct sunlight can penetrate when the solar altitude and azimuth align with these openings. At those moments the gap, rather than the PV surface, becomes the dominant bright element in the field of view, leading to high point-in-time DGP even though a PVSD is present. This effect is more easily triggered in low-altitude locations (such as in Stockholm in spring and winter), but it can also appear in Nicosia in December when the sun is lower. Consequently, spacing should be treated as a glare-relevant design parameter reduced or supplemented by a secondary glare layer to block these beam paths.

Comparing the two climates, Stockholm benefits most from the static average-optimum PV orientation (the yearly energy-based position), because it reduces annual spatial disturbing glare by about 21% compared to the fixed position. Nicosia, by contrast, is already well served by a fixed configuration, and additional solar-oriented positions mainly penalize the few winter hours when direct sun can enter through panel gaps. This shows that PV/façade control rules should be climate-specific: in higher latitudes the aim is to balance solar access and glare over many potentially problematic sun positions, whereas in Mediterranean conditions the priority is to shield the space from a small number of low-sun situations that sun-tracking and PV spacing would otherwise expose.

3.3.4 Façade construction, actuation and prototyping

The design of the structural components, control elements, and their interconnections follows a modular assembly logic, enabling both interchangeability of parts and facilitating straightforward assembly and disassembly processes. This modular approach supports flexibility in prototyping and potential scalability for real-world applications. In addition, a critical aspect influencing the control strategy is the configuration of the secondary cable system and its anchorage to the aluminum frame. The routing and termination points of these cables directly impact the number of actuators required for achieving the system’s adaptive motion. As such, the cable layout has been optimized to support transformability with minimal actuation, reinforcing the overall design goal of mechanical and control efficiency.

The primary design objectives include: (1) minimizing the number of actuators necessary to achieve the desired adaptability of the envelope, and (2) ensuring that the integration of control components does not interfere with the structural or gravitational behavior of the lightweight system. To this end, the actuators and associated mechanisms are deliberately decoupled from the movable body, allowing for a self-weight neutral control integration. An overview of the structural and kinematic configuration of the system is presented in Figure 20. Detailed investigations into the kinematic behavior, load-deformation response, and comparative energy performance of the integrated photovoltaic modules are provided in (Phocas et al., 2024).

Figure 20

Figure 20. Structural system with control components. Source: Phocas et al. (2024).

4 Cross-case synthesis, applicability and limits

Table 16 presents the three developments into a comparable framework, clarifying how climate drivers and dominant objectives determine the appropriate adaptivity scale and control logic. The retroreflective façade targets near-façade radiation redirection in a hot, high-irradiance context with row-level reconfiguration, whereas the Tri-fold system addresses glare/illuminance regulation in a temperate climate using zonal actuation, and the PVSD balances gains, glare, and PV orientation at the façade assembly scale across two climates. Table 16 complements this by aligning each case’s metric bundle with its objective and by making the main trade-offs explicit: (i) the retroreflective concept is effective for near-façade short-wave radiation management, yet its outcomes remain domain- and distance-dependent and should not be interpreted as coupled urban microclimate prediction; (ii) the Tri-fold device demonstrates that expressive, pattern-based shading can remain performance-robust when its motion logic is driven by climate-relevant conditions, while the point-in-time emphasis motivates targeted annual validation for final actuation-feasible states; and (iii) the PVSD highlights that energy-oriented orientations can reduce transmitted gains substantially, but glare sensitivity is often governed by panel spacing and edge conditions, meaning that geometric detailing (overlap/staggering/secondary glare layer) may be as important as tracking strategy.

Table 16

Table 16. Cross-case synthesis: design intent and implementation, assessment, key outcomes, and trade-offs.

Beyond indoor solar-gain reduction, the retroreflective configuration illustrates how a façade can be configured to manage the directionality of reflected radiation toward the exterior environment, potentially reducing re-radiation or reflected loading within an urban canyon while preserving interior visual conditions. The design intention is therefore not a single-objective reduction of incident radiation, but a redistribution strategy compatible with architectural integration and acceptable daylight levels. Its main weak point is that the demonstrated benefits are specific to near-façade short-wave radiative effects and depend on the evaluated spatial domain and distance from the façade; therefore, conclusions should remain bounded to radiation redirection unless coupled microclimate modeling is performed. The Tri-fold kinetic shading system further confirms that once a façade is made responsive, it can be steered to maintain illuminance within a target range while suppressing seasonal or orientation-driven glare peaks. This is relevant because it indicates that geometrically expressive, pattern-based devices can still perform robustly when evaluated against performance criteria, provided that their actuation logic is informed by climate-relevant simulations rather than purely geometric intent.

For the PVSD, the cross-climate comparison in Table 16 clarifies that “optimal” orientations are climate-dependent: in Stockholm, a static, energy-based “average optimum” orientation can mitigate low-sun glare compared to the reference fixed position, whereas in Nicosia where baseline glare levels are already low more sun-facing orientations do not necessarily improve annual glare conditions and can trigger high point-in-time DGP values in winter. This indicates that Mediterranean conditions may require protecting only a few critical low-sun hours rather than maximizing sun exposure. Across both locations, spacing between PV elements emerges as a glare-relevant parameter: panel gaps act as apertures for direct beam penetration and are responsible for glare peaks, implying that PV arrays should be detailed with overlap, staggering, or secondary glare layers when used as view-facing adaptive shading.

Across the three adaptive façade systems, a recurring design intention is to achieve transformability through lightweight construction and a minimum, strategically placed number of actuators. In the retroreflective façade, horizontal cable-driven rows enable stepwise reconfiguration; in the Tri-fold system, one actuator governs a vertical zone of modules; and in the dual-axis PV shading system, only two actuators mounted on the fixed frame drive synchronized bi-axial motion of all panels. This clustered actuation discretizes the façade’s admissible configurations. Two implications follow: first, performance evaluation should prioritize actuation-feasible states (e.g., baseline, fixed, average optimum, tracking) rather than purely geometric optima; second, a small set of robust states can offer a better performance-to-complexity ratio than continuous tracking, particularly when glare peaks are driven by a few critical low-sun hours. Embedding actuation concept early in the integrated design workflow becomes critical: module depth gradients, row/zone subdivision, and cable routing should be defined together with climatic simulations so that the façade meets illuminance targets and glare limits with minimal actuators and without adding mass to moving parts. In other words, performance assessment (illuminance, sDG, DGP) and actuation/geometry detailing (panel spacing, overlap, feasible poses) must be co-developed, because small geometric choices such as inter-panel gaps can negate glare benefits achieved through orientation alone.

The outdoor ray-tracing and cumulative irradiance analyses quantify near-façade short-wave exposure/redirection within a defined domain (10 × 10 m), and therefore indicate radiative proxies rather than coupled microclimate outcomes (air temperature, wind, long-wave exchange). A full sensitivity study of optical properties (reflectance/transmittance) was outside scope; values were fixed to representative materials and should be tested parametrically in future work. Likewise, scaled prototypes validate kinematics and assembly logic but do not replicate full-scale stiffness, friction, tolerances, actuator forces, and material optical properties; performance claims therefore rely primarily on the simulation results summarized in Table 16, while prototypes support feasibility.

5 Conclusion

This study demonstrates that adaptive façades should be assessed through a multi-criteria lens, where illuminance, daylight availability, glare control, and solar/energy performance are evaluated concurrently. Across three typologies and four climatic contexts, the results show that performance outcomes and referred control strategies are strongly climate- and objective-dependent, as synthesized in Table 16.

Quantitatively, the retroreflective system reaches reflection efficiency values up to 88% and reduces near-façade cumulative irradiance by approximately 0.4 kWh/m² relative to the unshaded baseline; the refined configuration reduces reflected radiation toward the canyon by 43%–50% at the evaluated peak-season points while maintaining EN 17037 minimum daylight provision (100 lux over 95% of the floor area) with disturbing glare limited to 1.6%. The Tri-fold system reduces extreme winter-noon illuminance from 5363 lux (baseline) and demonstrates altitude-responsive regulation, reaching approximately 905 lux at summer-solstice noon versus 2530 lux (baseline) and 1158 lux (static Tri-fold). For the PVSD, the static “average-optimum” orientation reduces annual transmitted gains by up to 42% (Stockholm) and improves annual spatial disturbing glare from 19.1% to 15.1%, confirming that robust fixed states can outperform increased control complexity under certain climatic conditions.

The findings further indicate that adaptive façade development benefits from evaluating actuation-feasible states and integrating motion logic early in the design workflow, since geometric details such as inter-panel gaps can dominate glare performance. Future work should extend validation through full-scale prototypes and, where outdoor thermal claims are central, couple near-façade radiative analyses with urban microclimate modelling while addressing standardization, lifecycle performance, and economic feasibility to support wider architectural adoption.

Data availability statement

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.

Author contributions

MM: Writing – original draft, Writing – review and editing. MP: Writing – original draft, Writing – review and editing. EC: Writing – review and editing, Writing – original draft. AM: Writing – review and editing, Writing – original draft.

Funding

The author(s) declared that financial support was received for this work and/or its publication. The project was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Project-ID 279064222—SFB 1244, and by the A.G. Leventis Foundation grant funded to the University of Cyprus, ABEPH 2022.

Acknowledgements

The authors acknowledge the work of Jiuyuan Liu, Simon Göbel, and Tobias Steiger for their commitment in the design studio “Smart Shade” held at ILEK in the winter semester 2022/23 supervised by MM, the fruitful collaboration with Matthias Kip during his Master’s thesis, and the contribution of Weifeng He to the daylighting analysis.

Conflict of interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Generative AI statement

The author(s) declared that generative AI was not used in the creation of this manuscript.

Any alternative text (alt text) provided alongside figures in this article has been generated by Frontiers with the support of artificial intelligence and reasonable efforts have been made to ensure accuracy, including review by the authors wherever possible. If you identify any issues, please contact us.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

References

Aksamija, A. (2013). Sustainable facades: design methods for high-performance building envelopes. New Jersey: John Wiley and Sons.

Google Scholar

ASHRAE (2021). ASHRAE handbook—fundamentals. Atlanta, GA: ASHRAE.

Google Scholar

Attia, S., Gratia, E., Herde, A., and Hensen, J. (2012). Simulation-based decision support tool for early stages of zero-energy building design. Energy Build. 49, 2–15. doi:10.1016/j.enbuild.2012.01.028

CrossRef Full Text | Google Scholar

Bedon, C., Honfí, D., Machalická, K., Eliášová, M., Vokáč, M., Kozłowski, M., et al. (2019). Structural characterisation of adaptive facades in Europe – part I: insight on classification rules, performance metrics and design methods. J. Build. Eng. 25, 100721. doi:10.1016/j.jobe.2019.02.013

CrossRef Full Text | Google Scholar

Biloria, N., Makki, M., and Abdollahzadeh, N. (2023). Multi-performative façade systems: the case of real-time adaptive bipv shading systems to enhance energy generation potential and visual comfort. Front. Built Environ. 9, 1119696. doi:10.3389/fbuil.2023.1119696

CrossRef Full Text | Google Scholar

Commission Internationale de l’Éclairage (CIE) (2024). CIE S 027:2024, photometry of road illumination devices, light-signalling devices and retroreflective devices for road vehicles. Vienna: CIE. doi:10.25039/S027.2024

CrossRef Full Text | Google Scholar

Corti, P., Bonomo, P., and Frontini, F. (2023). Paper review of external integrated systems as photovoltaic shading devices. Energies 16, 5542. doi:10.3390/en16145542

CrossRef Full Text | Google Scholar

Favoino, F. (2015). Assessing the performance of an advanced integrated facade by means of simulation: the actress facade case study. Façade Des. Eng. 3, 2–127. doi:10.7480/jfde.2015.2.1013

CrossRef Full Text | Google Scholar

Fortmeyer, R., and Linn, C. (2014). Kinetic architecture: designs for active envelopes. Mulgrave, VIC: Images Publishing Group.

Google Scholar

Fox, M., and Kemp, M. (2016). Interactive architecture: adaptive world. New York, NY: Princeton Architectural Press.

Google Scholar

Galasiu, A., and Veitch, J. (2006). Occupant preferences and satisfaction with the luminous environment and control systems in daylit offices: a literature review. Energy Build. 38 (7), 728–742. doi:10.1016/j.enbuild.2006.03.001

CrossRef Full Text | Google Scholar

Gallo, P., and Romano, R. (2017). Adaptive facades, developed with innovative nanomaterials, for a sustainable architecture in the mediterranean area. Procedia Eng. 180, 1274–1283. doi:10.1016/j.proeng.2017.04.289

CrossRef Full Text | Google Scholar

Gonzalez, E., Moser, S., Krner, A., Born, L., Gresser, G. T., Weitlaner, R., et al. (2023). “Advancing solar control and energy harvesting through the use of pneumatically actuated elastic adaptive facades,” in SMART2023: 10^th ECCOMAS thematic conference on smart structures and materials, 744–756. doi:10.7712/150123.9828.444680

CrossRef Full Text | Google Scholar

Hansen, J. P., and Madhu, S. (1972). Angle scintillations in the laser return from a retroreflector. Appl. Opt. 11 (2), 233–238. doi:10.1364/AO.11.000233

PubMed Abstract | CrossRef Full Text | Google Scholar

Hofer, J., Groenewolt, A., Jayathissa, P., Nagy, Z., and Schlueter, A. (2016). Parametric analysis and systems design of dynamic photovoltaic shading modules. Energy Sci. and Eng. 4 (2), 134–152. doi:10.1002/ese3.115

CrossRef Full Text | Google Scholar

Hosseini, S. M., Mohammadi, M., Rosemann, A., Schröder, T., and Lichtenberg, J. (2019). A morphological approach for kinetic facade design process to improve visual and thermal comfort: review. Build. Environ. 153, 186–204. doi:10.1016/j.buildenv.2019.02.040

CrossRef Full Text | Google Scholar

Jafari, L., and Salavatian, S. M. (2023). Evaluation of photovoltaic performance integrated with shading system in optimizing building energy consumption in hot arid climates (case study: an office building in Shiraz). J. Renew. New Energy 10 (1), 70–85. doi:10.52547/jrenew.10.1.70

CrossRef Full Text | Google Scholar

Kip, M. (2023). An interactive origami-inspired façade system to mitigate urban heat island effects. Stuttgart: University of Stuttgart.

Google Scholar

B. Kolarevic, and V. Parlac (2015). Building dynamics: exploring architecture of change. 1st ed. (New York, NY: Routledge). doi:10.4324/9781315763279

CrossRef Full Text | Google Scholar

Koukelli, C., Prieto, A., and Asut, S. (2023). Kinetic solar envelope: performance assessment of a shape memory alloy-based autoreactive façade system for urban heat island mitigation in Athens, Greece. Appl. Sci. 12 (1), 82. doi:10.3390/app12010082

CrossRef Full Text | Google Scholar

Le, T. N., Dobashi, H., and Nagai, K. (2016). Kinematical and static force analysis on redundant drive wire mechanism with velocity constraint modules to reduce the number of actuators. Springer Nat. 3, 22. doi:10.1186/s40648-016-0057-z

CrossRef Full Text | Google Scholar

Liang, X., Zhang, H., and Sun, B. (2024). Parametric design of photovoltaic louver integrated shading devices for west facade windows of office buildings in central China. J. Asian Archit. Build. Eng. 24 (2), 924–938. doi:10.1080/13467581.2024.2320326

CrossRef Full Text | Google Scholar

Mahanta, N. R., and Samuel, A. K. (2020). “Study of land surface temperature (LST) and land cover for urban heat island (UHI) analysis in Dubai,” in 2020 8th international conference on reliability, infocom technologies and optimization (trends and future directions) (ICRITO), 1285–1288. doi:10.1109/ICRITO48877.2020.9197887

CrossRef Full Text | Google Scholar

Matheou, M., and Phocas, M. C. (2025). Improving visual comfort through integrated design in architectural education: a performance metrics analysis of adaptive kinetic facades. Archit. Civ. Eng. Environ. 18, 1–74. doi:10.2478/acee-2025-0005

CrossRef Full Text | Google Scholar

Matin, N. H., Eydgahi, A., and Shyu, S. (2018). “Comparative analysis of technologies used in responsive building facades. 2017 ASEE annual conference and exposition,” Columbus, Ohio. doi:10.18260/1-2--28052

CrossRef Full Text | Google Scholar

Mesloub, A., Ghosh, A., Touahmia, M., Albaqawy, G., Noaime, E., and Alsolami, B. (2020). Performance analysis of photovoltaic integrated shading devices (pvsds) and semi-transparent photovoltaic (stpv) devices retrofitted to a prototype office building in a hot desert climate. Sustainability 12 (23), 10145. doi:10.3390/su122310145

CrossRef Full Text | Google Scholar

Moloney, J. (2011). Designing kinetics for architectural facades: state change. 1st ed. London: Routledge. doi:10.4324/9780203814703

CrossRef Full Text | Google Scholar

Nabil, A., and Mardaljevic, J. (2005). Useful daylight illuminance: a new paradigm for assessing daylight in buildings. Light. Res. Technol. 37 (1), 41–57. doi:10.1191/1365782805li128oa

CrossRef Full Text | Google Scholar

Perino, M., and Serra, V. (2015). Switching from static to adaptable and dynamic building envelopes: a paradigm shift for the energy efficiency in buildings. J. Façade Des. Eng. 3, 143–163. doi:10.3233/fde-150039

CrossRef Full Text | Google Scholar

Phocas, M. C., Christoforou, E. G., Matheou, M., and Dimitriou, P. (2024). Concept analysis of an adaptive building envelope with thin-film photovoltaic modules. Energy Build. 311, 114150. doi:10.1016/j.enbuild.2024.114150

CrossRef Full Text | Google Scholar

Reinhart, C. F. (2014). Daylighting handbook I: fundamentals and designing with the sun. Cambridge, MA: Building Technology Press.

Google Scholar

Reinhart, C. F. (2018). Daylighting handbook II: daylight simulations and dynamic façades. Cambridge, MA: Building Technology Press.

Google Scholar

Sadeghi, S., Karava, P., Konstantzos, I., and Tzempelikos, A. (2016). Occupant interactions with shading and lighting systems using different control interfaces: a pilot field study. Build. Environ. 97, 177–195. doi:10.1016/j.buildenv.2015.12.008

CrossRef Full Text | Google Scholar

Schultz, A. C., and Wang, J. (2022). Changing perspectives: bridging design and engineering in architectural research. Technol. Archit. + Design 6, 172. doi:10.1080/24751448.2022.2114231

CrossRef Full Text | Google Scholar

Shahin, H. S. M. (2019). Adaptive building envelopes of multistory buildings as an example of high performance building skins. Alexandria Eng. J. 58 (1), 345–352. doi:10.1016/j.aej.2018.11.013

CrossRef Full Text | Google Scholar

Solemma LLC (2023). ClimateStudio (version 2.2). Cambridge, MA: Solemma, LLC. Available online at: https://www.solemma.com/ClimateStudio (Accessed October 31, 2025).

Google Scholar

Voigt, M. P., Roth, D., and Kreimeyer, M. (2023). Systematic classification of adaptive façades preparing a database. Proceed. Design Soc. 3, 3295–3304. doi:10.1017/pds.2023.330

CrossRef Full Text | Google Scholar

Voigt, M., Roth, D., and Kreimeyer, M. (2023). Decision support for defining adaptive façade design goals in the early design phase. Energies 16 (8), 3411. doi:10.3390/en16083411

CrossRef Full Text | Google Scholar

Yuan, J., Masuko, S., Shimazaki, Y., and Chai, J. (2022). Researching the design of a glass-bead retro-reflective material to reduce downward reflection for urban heat island mitigation. Mater. Today Sustainability 18, 100147. doi:10.1016/j.mtsust.2022.100147

CrossRef Full Text | Google Scholar

Zhang, X., Lau, S., Lau, S. S. Y., and Zhao, Y. (2018). Photovoltaic integrated shading devices (PVSDs): a review. Solar Energy 170, 947–968. doi:10.1016/j.solener.2018.05.067

CrossRef Full Text | Google Scholar

Zhang, X., Hao, Z., Wang, Y., and Shi, X. (2022). Adaptive façades: review of designs, performance evaluation, and control systems. Buildings 12, 2112. doi:10.3390/buildings12122112

CrossRef Full Text | Google Scholar