Keywords

1 Introduction

Responsive architecture underpins the physical objective of buildings. It reconfigures the needs of variable mobility, location, or geometry [1]. Responsive facade refers to a façade—main or additional ones—reconfigured in response to certain variables based on the building's context. The purpose of using this responsive facade system is to answer specific geographic or climate issues, one of which is climates with a prominent level of solar exposure.

Currently, many buildings implement a responsive facade. In Dubai, the Al-Bahar Tower is knowingly famous for its responsive facade that takes Mashrabiya cultural elements [2]. This facade membrane can open and close automatically when the sun passes through one side of the building. A facade system like this has also been implemented at the Syddansk Universitet in Denmark with a triangular shape made of perforated metal that regulates the amount of light entering [3]. Simple buildings, such as houses, also use a responsive facade. An example is the tropical cave house in Vietnam, whose facade can rotate simultaneously with a manual system [4].

Most responsive facades are designed in a modular form arranged in a grid (vertical or horizontal multiplied). This modular is due to facilitate the development of the module and its operation when applied to the building [5]. In the development of the module, the exploration process was greatly assisted by Parametric Design and Digital Fabrication. The parametric approach makes the design exploration process easier by providing specific indicators such as shape, dimension, and thickness, then modifying these parameters according to context needs [6]. This parameter can create a module for a responsive facade based on the given performance, thus creating a design that responds to need and adapt other contexts only by adjusting to specific parameters. Using the parametric design also describes the opening and closing process on the responsive facade, which becomes more manageable and well described. Modelling that uses precise measurement gives an idea of how the mechanism will work in the real world. However, minor adjustments are applied at the realization stage to respond to material characteristics that are not described in the parametric design.

To realize the design into a physical form, Digital Fabrication provides various conveniences and adds value in the development of a responsive facade. One of the advantages is to ease of production in a short or predictable time [7]—cutting various patterns with laser cutting machine or making objects with 3d printing machine. At the same time, precise product results can also be generated through data input, adapted to digital model data [8]. In addition, digital fabrication also provides options with various several types of materials by adjusting the fabrication machine used.

It is established that a responsive facade can create dynamic protection in the building against the surrounding environment. Then, in the design development process, several architects have applied a parametric approach to get data from the context such as sun exposure, wind, other values that affect design results. However, few have explored the relationship between design and prototyping processes in developing responsive facades. Furthermore, further processes are needed, namely re-checking the results of the design and prototyping, whether they are following the needs of the building.

Therefore, the study aims to explore the hexagonal responsive façade system that responds to sunlight and works as a second skin for architectural buildings; it focuses on design, mechanism, and fabrication processes. Few objectives of this study: (1) we identify the excessive sun exposure that goes through interior space, then analyze the requirement for covering the window area. (2) We investigate responsive façade systems in design, kinetic mechanism, and its construction details using the digital modelling and parametric approach. (3) After finalizing each component's design of the responsive façade system, we carry out the prototyping process using digital fabrication techniques to test the kinetic mechanism in modular scale. (4) based on digital modelling and fabrication processes, we evaluate the limitations and potential of the hexagonal responsive façade for the sun shading.

2 Literature Studies

2.1 Responsive Façade in Tropical Architecture

A responsive façade is a skin of a building that actively reacts or change toward specific climate and environmental aspects (light, wind, and temperature) to suit the daily user needs inside a building [9]. Its commonly regulated by mechanical, passive, or electro-mechanical system that consist of sensing (perceive environmental data), control (translate), actuating (movement), and structural components. Mechanical system generates motions in a simple machine like a kinetic façade and can be operated by hand hence easily adapt to the user’s preferences and needs. This system offers a relatively long lifespan but tends to subside more shortly than those made of non-mechanical parts [10].

Warm climates-such as tropical climates-have a primary demand for cooling in a building’s thermal comfort, and passive cooling strategies are the most effective way to respond to it. There are 4 types of passive cooling: shading, window-to-wall ratio, glazing type, and ventilation strategy. Shading and ventilation have the highest cooling savings potential in a controlled simulation out of the four. Both shown coherence on average savings on warm-dry and warm-humid climate groups from the review, but climate conditions are still crucial in their effectiveness [11].

2.2 Kinetic Mechanisms Using Aperture Morphology/Analogy

A kinetic mechanism is a synergistic kinetic movement of each part in a system that produces an effect or a response. This understanding become the basis for the development of a kinetic facade system, a façade that–for the example-can switch from an open to a closed condition [12]. Kinetic facades are innately complex systems that consist of corresponding components that work across various material domains [13].

The evolution of kinetic façade comes along with the development of its pattern and movement. Pattern development focuses on three functional aspects: aesthetic element, environmental controller, and alternative producer of renewable energy. Movement development consists of rotation, elastic, retractable, sliding, and self-adjusting [13]. Inspired by a camera’s lens movement, Aperture can be defined as the opening in a lens through which light passes to enter the camera [14]. Through its iris blade components, it can regulate the amount of light exposure and alter the condition of the system from one situation (closed) to another (opened).

2.3 Digital Fabrication: From Parametric Modelling to Fabricating Process

Digital fabrication lies under the scope of CAD (Computer-Aided Design) and CAM (Computer-Aided Manufacturing) as it utilizes computer-driven tools to build or cut parts [15]. It can be classified into five techniques namely sectioning, folding, contouring, forming, tessellation [15]. The latter are commonly used for responsive façade since it has characteristic in terms of generating form as a collection of pieces that fill the gaps in a plane or surfaces. Tessellation can be made through parametric approach, process that enables designers to define the relationship between elements or groups and to assign values or expressions to organize and control those definitions [5]. It offers opportunity to explore unexpected solutions and minimalized complicated reworking.

Ladybug tools enable simulate sun exposure and façade’s efficiency rate. It is open-source computer software that connects CAD interfaces to a host of validated simulation engines to generate an interactive 2D and 3D graphical diagram [16]. This software acts as a plugin for Grasshopper3D and can simulate both visual and energy consumption of the parametric modelling generated earlier [17]. High validity and integration with modelling software results in its wide uses ranging from architectural research to large-scale projects.

Manufacturing techniques can be classified into formative, additive, and subtractive [18]. While the formative technique shape materials and additive techniques add material, subtractive techniques cut and/or etch flat materials into custom shape patterns using laser cutting machine –thermal-based fabrication process [19]. It works well with various sheet-shaped materials (paper, wood, plastic, acrylic, and metal), able to create high precision model, and has adjustable laser modes allowing various artistic and functional possibilities. This series of benefits eventually attract its utilization in fabricating high-quality architecture models such as those for façade [5].

3 Methodologies

3.1 Parametric Design Approach

The design of a responsive facade is developed using 3D modelling software Rhinoceros and Grasshopper [20] to identify the design requirements and qualifications. We alter Eqs. (5) through parametric design such as grids, geometry, orientation, and dimension in different values as performance considerations. This visualization interrogates the feasibility of a responsive façade and calculates the proportion of design required for responding to sunlight (see Fig. 1).

Fig. 1.
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(left to right): Al-Bahar Tower, Syddansk Universitet, Tropical Cave House

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3.2 Digital Fabrication for Prototyping Process

There are five different modules in the prototyping process; each module is made based on purposes and modifications from previous modules. Thus, this research utilizes digital fabrication to generate the prototype of a responsive façade due to its affordability and efficiency. We explore both subtractive and additive manufacturing techniques to fabricate parts, including hexagonal modules, the mechanism, and the frame. We attempt to use FDM 3D printing [7] to create small parts using PLA filament materials with additive manufacturing. Meanwhile, we exercise subtractive manufacturing with laser cutting machines to cut several materials (paper, cardboard, and plywood 3 and 6 mm) and produce modules and frames (Fig. 2).

Fig. 2.
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(Left) Parametric design for generating responsive façade (middle and right) Laser cutting process to create parts of modules

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3.3 Sun Radiation Simulation with Ladybug Tools

The purpose of this responsive façade is to tackle sun exposure pass through the openings. We perform the sun radiation simulation to verify the feasibility of responsive façade in responding sunlight. Using Ladybug Tools, an interactive visualization of climate data [16], we evaluate the responsive facade modules that block glass window from sunlight-hours (Fig. 3).

Fig. 3.
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Sun Radiation using Ladybug Tools

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We picked a two-storied conventional house situated in West Java, Indonesia. The house is located at −6.43° north (latitude) 106.78° west (longitude). It sits at the intersection of Kemang Street and Alifah Village in Sawangan District, Depok. The responsive façade is placed outside the building mass facing northeast, where it will cover a single glass window measuring 1000 × 1200 mm. The variable on this simulation is only focused on the solid area (surfaces with solid materials) and void area (the surface with glass) since Ladybug tools will not be able to calculate the material aspect (U value) (Fig. 4).

Fig. 4.
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(left) Site location ; (right) Single Glass Window as the context for the façade

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4 Result

4.1 Parametric Modelling for Creating Responsive Façade

This project is developed upon two primary concepts, a tessellation pattern known for its coverage and adjustability combined with incremental and space-saving ability of an aperture mechanism. Serves as main organizer, tessellation is firstly explored through comparison of various basic geometries. Hexagon shape is then discovered as the suitable option for several reasons including circular shape tendency, no residual space, and the dividable into smaller groups or rows. Moreover, hexagon’s 60° sides offer a fresh diagonal arrangement compared to the conventional x and y-axis (Figs. 5 and 6).

Fig. 5.
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Example of: (left) Tessellation Pattern; (right) Aperture Movement Principle

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Fig. 6.
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(left) Tessellation Grid Exploration; (right) Arrangement Possibilities

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Preliminary context analysis shows a gradient of sun exposure zones in the shape of three 30 × 100 cm long rectangles. Hexagonal pattern is then grouped into 3 rows of 5 identical modules positioned above each zone that span 30 cm wide to shade each corresponding zone individually. A single hexagonal module consists of a body, pair of arms, pair of forearms, handles, and two sets of membranes. Body serves as a platform to attach other components via a rotatable and stopper joinery. Modules are statically connected to each other and to its frame using finger joinery while a lever will collect each module’s handle to arrange simultaneous movements. Lastly, semi-transparent blades are added between forearm and body to become a radiation barrier upon activation and stay transparent when not used. Array polar calculation help set 5 pieces of membrane that rotates at a 9° angle to achieve accumulative opaqueness when fully deployed (Fig. 7).

Fig. 7.
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Sun exposure zone and hexagonal module dimension and position adjustment

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4.2 Digital Fabrication for Responsive Facade Prototype

Preliminary manual modelmaking followed by digital fabrication techniques are used in the creation of the façade that is divided into 5 stages. It starts with the creation of a paper-based prototype-1 aimed to materialize the digital concept and primary mechanisms. Suitable joinery is then explored in the second prototype that have a tiny strand of thread tied at both ends that creates a smooth rotational joint. The cardboard-made model offers proportional geometry but is too-easily bent and has loose joinery (Fig. 8).

Fig. 8.
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Manual modelmaking: (left) first prototype to materialize primary component; (right) Second prototype to find suitable joinery with proper geometry and dimension

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Digital fabrication implementation becomes the highlight of the 3rd and 4th stage that focuses on rationalizing the details. Plywood-based prototype-3 features a 3D-printed ring plate that creates consistent gap between pivoted components for a sleek and sturdy movements but still lacks tightness and has collision risk between contiguous modules. The 4th prototype sees wooden dowels replaces 3D-printed joineries-for a tighter and durable pivot-and the addition of finger joints to the sides for ease of assembly. It also features a longer lever integrated with five handle points and opposing placement of the two sets of forearms to avoid neighbouring collisions (Fig. 9).

Fig. 9.
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Digital Fabrication: (left) Third prototype explores digital fabrication in creating parts, (right) Fourth prototype features adjusted joinery and parts reconfiguration

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Membrane and frame integration into the modules mark the creation of final prototype. Membranes are fastened to the module via strands of yarn running through holes in its edges with a larger central hole to prevent jam. Finally, Plywood-based frame measuring 1100 × 950 × 70 mm are integrated. It can be disassembled into three main parts that each one can holds a row of modules (Fig. 10 and Table 1).

Fig. 10.
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Fifth Prototype; (top) membrane and frame integration with the module; (bottom) final assembly of the prototype

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Table 1. Prototype development
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In this development, sensing and operating aspect of the facade depend on manual user intervention. The mechanism is deployed (closed) and reversed (open) by hand-rotating a handle located in the middle of a module row. Different rows will have their own handle to achieve independent levels of shading control. Rotation of the handle will trigger the movement of the forearm and membranes through its connections with the arm and forearm. When the forearm rotates, it will pull five layers of membrane with it as they are connected by a thread and share the same pivot point. These sets of reactions will result in the facade being deployed (closed). Levers that connect all centre handles inside a single row will transfer the user's hand rotation to all adjacent modules simultaneously.

Automated sensing and rotating mechanism are one of the possible future developments of this system. A sensor will attach at the exterior side of the window and detect incoming light intensity which will be translated as an input to generate a specific row configuration (opened or closed). This scheme allows the façade to work autonomously based on weather condition and only low degree of user intervention is needed (Fig. 11).

Fig. 11.
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Opening and closing mechanism of the façade

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4.3 Shading and Sun Radiation Simulation with Hexagonal Responsive Façade

The shading performance of the facade is simulated digitally in a 3d model. Based on Fig. 12, we can see that the facade could affect the daylight that enters the interior through the translucent membranes. The intensity of daylight in every degree of openness is diverse and adjustable to suit the needs of the interior. The membrane is the main element of the diverse shading and makes it different than the facade without membranes.

Fig. 12.
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Shading diagram with and without membranes

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The façade’s performance is also simulated digitally with the help ladybug software to analyse the ability to filter sunlight by measuring sun radiation parameters in the interior. Tropical climate data of Depok, West Java, as the location is inserted into the software as a contextual situation. Preliminary simulation for full year shows a period between June and July has the highest sun radiation level in the interior, with 2–2, 4 kWh/m2. This timespan becomes a fixed variable for comparing various module phases in the most extreme radiation condition possible.

The facade has two primary phases, a fully closed module with 0 degrees rotation and a fully opened module with 45° rotation. Upon its installation into the window, a fully closed module (0° rotation) can already reduce radiation level down to 2–1.6 kWh/m2 and portrays 60% received radiation compared to the condition without the facade. It corresponds to a reduction of yellow colour shades in the sun radiation diagram that indicates a 2–2, 4 kWh/m2 radiation level.

An incrementally opened module (45° rotation) can limit incoming sun radiation decline to 1, 2–0, 4 kWh/m2 or 50% of condition without the facade. This figure can be explained visually in the radiation diagram below depicting more distribution of dark blue shades compared to the two previous tests. The dark blue colour represents sun radiation levels of 0–0, 4 kWh/m2 hence more shades of blue indicate higher façade performance (Fig. 13).

Fig. 13.
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Sun radiation diagram (left to right): without prototype, with prototype on 0°, and with prototype on 45°

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5 Discussion

5.1 Problems that Occurred in the Production Stage of the Hexagonal Module

In the process of making the final prototype, there were several obstacles that hinder the production of the hexagonal module. The first problem is the difficulty of measuring the length of the rope that connects one membrane to another. The reason is the knots that hold the ropes together on the membrane are conventionally made by hand. This can be solved by measuring and cutting the required number of strings before attaching them to the membrane assembly.

Then, the joint becomes stiff after gluing the stopper and dowel which results lack of smooth rotation. The adhesive liquid blocked the stopper and the dowel hit the surface. This issue is resolved by sticking the stopper first into the join. After that, then the series of joints are installed on the body and forearm without applying any adhesive substance.

Lastly, the constraint that seriously hinders the production process of the hexagonal module is the friction between one component and another. an example of this problem occurs on the surface of the body with the forearm which makes the process of opening and closing the hexagonal module hampered. The solution to this problem lies in providing the distance between one component layer and another using the thickness of the joint to avoid friction between the forearm surface and the body and so on.

5.2 The Potential of Hexagonal Responsive Facade for Sun Shading

Environmental simulation in the previous chapter shows a 40–50% efficiency rate that is met under several situation to be considered as follow. Firstly, ladybug tools have a limitation in calculating the effects of semitransparent materials to the shading quality, leaving a slight possible shift in the overall efficiency figure. Secondly, weather data used in this simulation comes from an authorized yet open-source database (ladybug.tools/epwmap) that have a limited available weather station point, with the closest point to the site being 30 km away causing further figure shift possibility.

Regarding its application toward the multitude of architecture, hexagonal module has the potential to be used not only in residential buildings but also in the openings of a high-rise building. Constructed upon a modular system, each module can be adjusted to match existing opening properties through the parameters of dimension, number of modules, and control row or group division. Exposure simulation run through the various sizes of modules and windows shows a relatively consistent shading quality with the optimum shading performance comes from 15 to 120 cm module (Table 2).

Table 2. The potential of hexagonal responsive façade
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6 Conclusion

This study develops the hexagonal responsive façade system that responds to sunlight and works as a second skin for architectural buildings. The remaining stages include design, mechanism and fabrication processes. As a tropical country, a house in Indonesia can receive sun radiation around 2–2, 4 kWh/ m2 during the day. This excessive could generate enormous amounts of energy to set up thermal comfort in interior space. While the glass window’s purpose is for the openings and accessibility of the atmosphere to come through interior space, it is necessary to add more layers on the top of the window to block unnecessary light and heat that interferes with human comfort. Thus, a secondary façade requires incremental coverage and adjustability aspects to respond to the changing sun exposure throughout the day.

Hexagonal responsive façade has capabilities in reducing sun exposure with mechanical technology–operates by hand–which is suitable for a tropical house due to its efficiency and affordability. The tessellation configuration of the modules solves the covering areas where a dimension of 150 × 150 mm modules (in fully open condition) can cover 150–300 mm width of the sun radiation zones. The module consists of 4 distinct parts, and each part has a specific purpose: body, arm, forearm, and membrane. The levers support these modules to generate the responsive façade movement and the framework to hold modules and attach them into the primary façade. The final prototype is fabricated using laser cutting machines and plywood materials. However, it is possible to substitute the materials with the more durable ones with tropical weather (heavy rains and extreme hot season). For 1100 mm height, 950 mm width, and 70 mm thickness, the responsive façade can cover 1000 mm height and 1200 mm width windows.

A fully close hexagonal responsive façade system with 0 degrees rotation can reduce sun radiation level down to 2–1.6 kWh/m2 or 40% radiation reduction. Ones the façade is open to 45°, sun radiation decreases to 1, 2–0, 4 kWh/m2 or up to 50% radiation reduction; some areas have possibilities to completely unattached to the suns –the areas that further away from the window. In conclusion, this responsive façade could be beneficial in decreasing excessive sun radiation coming to interior space and can be implemented in several typology of buildings in tropical countries. The evaluation remains in digital simulations, in future research, it is recommended to test the prototype in practical conditions using sun radiation sensor to see the effectiveness of the responsive façade.