Impact of Bioinspired Infill Pattern on the Thermal and Energy Efficiency of 3D Concrete Printed Building Envelope

Abstract

The traditional construction industry significantly contributes to global resource consumption and climate change. Conventional methods limit the development of complex and multifunctional architectural forms. In contrast, 3D concrete printing (3DCP), an additive manufacturing technique, enables the creation of intricate building envelopes that integrate architectural and energy-efficient functions. Bioinspired design, recognized for its sustainability, has gained traction in this context. This study investigates the thermal and energy performance of various bioinspired and regular 3DCP infill patterns compared to conventional concrete building envelopes in tropical climates. A three-stage methodology was employed. First, bioinspired patterns were identified and evaluated through a literature review. Next, prototype models were developed using Rhino and simulated in ANSYS to assess thermal performance. Finally, energy performance was analyzed using Ladybug and Honeybee tools. The results revealed that honeycomb, spiral, spiderweb, and weaving patterns achieved 35–40% higher thermal and energy efficiency than solid concrete, and about 10% more than the 3DCP sawtooth pattern. The findings highlight the potential of bioinspired spiral infill patterns to enhance the sustainability of 3DCP building envelopes. This opens new avenues for integrating biomimicry into 3DCP construction as a tool for performance optimization and environmental impact reduction.

1. Introduction

The built environments contribute to 38% of total global energy-related CO2 emissions, while the total global energy share of buildings and construction stood at 35% in 2019 [1]. Sustainability in construction does not always imply the use of environmentally friendly materials. Three-dimensional concrete printing (3DCP) might make a substantial contribution in building complicated structures for the deployment of passive designs, thereby reducing the energy usage [2]. As it promotes innovation in the construction industry by enabling the creation of complex geometries and customized design, 3DCP can contribute to several United Nations Sustainable Development Goals, particularly those related to sustainable cities, innovation, and infrastructure. Moreover, nature-based solutions in buildings can increase sustainability while improving liveability. Biomimicry or bioinspired designs can solve human challenges through the elements of biology. Biomimicry is not a style of building; it is a design process to seek answers from nature [3]. The principle of mimicking nature needs to be understood and made an integral part of the architectural design principles [4]. The most crucial variable influencing building energy use is the thermal performance, which can be improved by introducing cavities or insulation materials in the building components. Modern advanced building techniques, such as 3D printing (3DP), allow designers to develop an optimum printing arrangement with cavities that can meet both structural and thermal needs [5].

The present-day modern style structures often use brick or concrete, which traps the heat in the building envelope, and is not well-suited to tropical climates. The building envelope is the most important component of a building to achieve thermal comfort, along with the cooling systems and appliances, which need to be carefully designed, especially in tropical regions [6]. Many studies have been carried out on the structural and thermal performance of regular geometric patterns, and none exist on the thermal and energy performance of bioinspired patterns. The previous studies on different infill patterns of 3DCP cavity walls conducted by Alkhalidi and Hatuqay (2020) and Suntharalingam et al. (2021) exhibited lower energy performance without the addition of insulation [5,7]. Therefore, to overcome the drawbacks of the regular geometrical infill patterns, a study on the application of bioinspired infill patterns is warranted. Hence, this study aims to evaluate and compare the thermal and energy performance of building envelopes in the tropical region with the bioinspired 3DCP wall and the conventional concrete wall. This aim provides an answer to the research question “How much efficiency can a 3D-printed building envelope in the tropical region created with complex bioinspired infill patterns attain in terms of thermal and energy performance compared to a conventional building envelope?”.

Literature Review

Numerous research papers related to the material properties, buildability, rheology, and typologies of 3D concrete printed (3DCP) construction are available. This literature review focuses on bioinspired patterns, infill patterns, thermal, and energy performance of 3D printing (3DP) and 3DCP (Table 1). Integrating biomimicry, digital design, and optimization algorithms to evaluate and develop efficient solutions for building envelope design is an effective approach to improve thermal performance. The proposed design technique, which applies biomimetic optimization algorithms to the building envelope, has demonstrated considerable optimal results in thermal performance according to the study by Abdel-Rahman (2021) [8]. The study by Webb (2021) investigates the energy-saving capabilities of the biomimetic façade in a range of commercial and residential buildings and across various climate regions using mathematical modeling and digital simulation approaches (tropical, desert, temperate, and cool continental) [9]. According to the findings, the biomimetic façade has the potential to cut energy consumption in all building applications, with the largest advantage demonstrated in residential elderly care (67.1% saving). Similarly, the bioinspired building façade demonstrated the ability to minimize operating service energy consumption in all temperature zones, with the biggest energy savings recorded in tropical (55.4% saving) and humid continental climates (55.1% saving).

Nature is an art form; it produces patterns by organizing itself in a systematic way. These natural patterns and shapes emerge from the fundamental principle of evolution: that organisms and structures evolve to their most optimal form. Spirals, in particular, exhibit remarkable uniformity, curving around themself in a perfectly regular manner. The inner surface of a spiral is shorter and compressed, while the outer surface is longer and stretched, an arrangement that enhances its strength and ability to withstand higher pressures [10]. A notable example is the Sydney Opera House in Australia, which demonstrates the application of the logarithmic spiral in architecture. This concept of logarithmic spiral not only contributes to the building’s aesthetic, but also improves its structural integrity, thermal efficiency, and energy performance.

In nature, tessellation patterns are categorized as edge-to-edge, non-edge-to-edge, and overlapping [11]. The honeycomb pattern represents an edge-to-edge tessellation, the sunflower head is a non-edge-to-edge tessellation, and fish scales or pangolin skin illustrate overlapping tessellation. The honeycomb structure has been explored for over a thousand years and found beyond traditional awareness of high mechanical strength to an understanding of multifunctional principles of honeycomb structure [12]. The study by Regassa et al. (2021) reported that spider webs exhibit compressive and tensile strength, toughness, and robustness [13]. Similarly, the baya weaverbird weaves its nest using fibrous materials, resulting in one of the strongest natural nest structures [14].

The poor thermal and energy performance of 3DCP walls, as highlighted in some of the literature, has motivated the integration of the bioinspired patterns with 3DCP to evaluate their performance and compare it with solid concrete structures. Large cavities in 3DCP walls were found as a factor that adversely affects the thermal performance of the printed walls; however, existing research did not provide detailed insights into potential solutions for this issue [15]. Much research did not compare the thermal and energy performance of 3DPC structures with conventional construction systems [7].

Low thermal conductivity can be achieved by controlling the size and geometry of internal cells. Complex infill design selected for heat storage has the potential for minimal pressure drop flow and uniform energy performance [16]. Research on bioinspired patterns has primarily focused on 3D printing with ABS and PLA materials, evaluating structural performance [17]. However, there is a notable gap in the literature regarding studies that combine bioinspired patterns with 3D concrete printing to evaluate thermal and energy performance using sophisticated simulation software.

Table 1. Compilation table of the literature for different patterns.

Title	Authors	Materials and Methods	Results and Findings
Computational assessment of thermal performance of 3D-printed concrete wall structures with cavities	Marais et al., 2021 [18]	The research used the finite element method (FEM) to analyze the thermal performance of 3D-printed concrete wall structures with different cavity arrangements and materials.	The study found that the thermal performance of 3DCP walls with cavities is material dependent. The inclusion of cavities in lightweight foam concrete walls with lower thermal conductivity worsens their thermal performance, while the inclusion of cavities in high-performance concrete walls with higher thermal conductivity improves their thermal performance in summer.
Developing an integrated 3D-printed façade with complex geometries for active temperature	Sarakinioti et al., 2018 [16]	The research followed a methodology that involved the design and production of facade panels using 3DP technology. The research involved simulations to understand the thermal effects of the system on indoor spaces in different climates. The methodology was interdisciplinary, involving researchers from various fields.	The study found that integrating multiple functions for optimizing thermal performances and creating mono-material structures is possible with 3DP technology. It proved that low thermal conductivity is achievable by controlling the size and geometry of the cells, and the material is a major parameter for achieving low thermal conductivity.
Energy efficient 3D-printed buildings: Material and techniques selection worldwide study	Alkhalidi and Hatuqay, 2020 [5]	The research followed a methodology that involved designing wall configurations using Ansys Workbench to achieve a thermal transmittance that complies with national regulations for each climatic zone. The results were then plotted in Autodesk Revit and Green Building Studio energy simulation to determine the energy demand of the designed structure.	The study found that a balance between cavities and 3D-printed material should be maintained to achieve the desired U-values and structural performance. The researchers also estimated the annual energy demand for each climatic zone, indicating that the building’s annual energy demand depends mainly on the difference between the ambient air and the indoor temperatures.
Energy Performance of 3D-Printed Concrete Walls: A Numerical Study	Suntharalingam et al., 2021 [7]	The research followed a methodology that involved conducting numerical simulations and analysis to determine the U-values of different 3D-printed concrete (3DPC) wall configurations. The study included a series of 32 simulations with different 3DPC wall configurations, and the results were interpreted to draw conclusions about the energy performance of the walls.	The study found that the 3D-printed concrete cavity walls had low energy performance, as the U-values did not meet standard regulations. However, their performance improved with cavity insulation, resulting in a minimum thermal transmittance value of 0.34 W/mK. Additionally, the study proposed a suitable equation to find the U-values of 100 mm-thick cavity wall panels with different configurations.

Table 1. Compilation table of the literature for different patterns.

Title	Authors	Materials and Methods	Results and Findings
Computational assessment of thermal performance of 3D-printed concrete wall structures with cavities	Marais et al., 2021 [18]	The research used the finite element method (FEM) to analyze the thermal performance of 3D-printed concrete wall structures with different cavity arrangements and materials.	The study found that the thermal performance of 3DCP walls with cavities is material dependent. The inclusion of cavities in lightweight foam concrete walls with lower thermal conductivity worsens their thermal performance, while the inclusion of cavities in high-performance concrete walls with higher thermal conductivity improves their thermal performance in summer.
Developing an integrated 3D-printed façade with complex geometries for active temperature	Sarakinioti et al., 2018 [16]	The research followed a methodology that involved the design and production of facade panels using 3DP technology. The research involved simulations to understand the thermal effects of the system on indoor spaces in different climates. The methodology was interdisciplinary, involving researchers from various fields.	The study found that integrating multiple functions for optimizing thermal performances and creating mono-material structures is possible with 3DP technology. It proved that low thermal conductivity is achievable by controlling the size and geometry of the cells, and the material is a major parameter for achieving low thermal conductivity.
Energy efficient 3D-printed buildings: Material and techniques selection worldwide study	Alkhalidi and Hatuqay, 2020 [5]	The research followed a methodology that involved designing wall configurations using Ansys Workbench to achieve a thermal transmittance that complies with national regulations for each climatic zone. The results were then plotted in Autodesk Revit and Green Building Studio energy simulation to determine the energy demand of the designed structure.	The study found that a balance between cavities and 3D-printed material should be maintained to achieve the desired U-values and structural performance. The researchers also estimated the annual energy demand for each climatic zone, indicating that the building’s annual energy demand depends mainly on the difference between the ambient air and the indoor temperatures.
Energy Performance of 3D-Printed Concrete Walls: A Numerical Study	Suntharalingam et al., 2021 [7]	The research followed a methodology that involved conducting numerical simulations and analysis to determine the U-values of different 3D-printed concrete (3DPC) wall configurations. The study included a series of 32 simulations with different 3DPC wall configurations, and the results were interpreted to draw conclusions about the energy performance of the walls.	The study found that the 3D-printed concrete cavity walls had low energy performance, as the U-values did not meet standard regulations. However, their performance improved with cavity insulation, resulting in a minimum thermal transmittance value of 0.34 W/mK. Additionally, the study proposed a suitable equation to find the U-values of 100 mm-thick cavity wall panels with different configurations.

Building energy demand forecasting, according to Abu Baker et al. (2015), is a good technique for improving energy efficiency and controlling energy consumption throughout the design phase of buildings [19]. They also mentioned that computer-aided modeling provides an indicator of energy use and helps to improve building energy efficiency [19]. Additionally, the study by Alkhalidi and Hatuqay (2020) gives a guideline for creating an energy-efficient, contented 3DP built environment that meets the world’s climatic zones [5].

2. Materials and Methods

This research adopted a three-stage methodology to identify and evaluate the thermal and energy performance of bioinspired 3DCP envelopes in the tropical region. In order to provide an answer to the research question mentioned in Section 1, innovative strategies are adopted to investigate the thermal performance of 3DCP walls by FEM using Ansys Workbench 2022 R2, and the energy performance was investigated using Rhino 6 + Grasshopper plug-in Honeybee and Ladybug tools 1.5.0. The main novelty in this research is the design of the bioinspired patterns for the 3DCP walls. However, the designs took inspiration from nature’s patterns identified based on their performance evaluation from the earlier studies.

2.1. Bioinspired Patterns Identification and Shortlisting

The initial stage of the three-stage methodology is to find bioinspired patterns in the current literature. A systematic review was conducted to identify the literature relevant to the topic, and bioinspired patterns were identified from the shortlisted literature. In this study the methodology followed to finalize the patterns was a systematic framework for rating. Hence, the rating is given based on an objective method to avoid the subjectivity or personal bias of the researcher [20]. The systematic framework started with the identification stage, wherein 24 bioinspired patterns were identified from the literature, and before the screening stage, 12 patterns out of 24 patterns were eliminated by combining the patterns under the broad categories like waves, spirals, branching, etc. In the initial level of screening, two patterns are removed due to their complexity in 3DCP. Finally, four bioinspired patterns: honeycomb, spiderweb, spiral, and weaving are shortlisted based on the rating. In a similar line to study [5], the 3D-modeled bioinspired patterns in cubic form are subjected to investigation. These four bioinspired patterns in cubic form, along with the sawtooth pattern and solid concrete cube, are simulated in the Ansys simulation tool.

2.2. Thermal Performance Testing

The second stage is numerical analysis for the evaluation of the thermal performance, was carried out with the help of the Ansys 2022 R2 software. In Ansys Workbench, the steady-state thermal analysis was chosen to perform the thermal analysis of the prototype models. In steady-state thermal analysis, the heat load applied to the models and the environmental conditions remain constant over time while assessing the equilibrium state of the models. The advantage of choosing steady-state thermal analysis over transient thermal analysis is that it significantly reduces the time required to generate results, and it demands less computational power compared to the steady-state thermal analysis.

2.3. Energy Performance Testing

The third stage is energy modeling conducted in Grasshopper with the plugins Ladybug and Honeybee. Ladybug 1.5.0 is a powerful tool that enables comprehensive building environmental analysis within Grasshopper by linking to validated energy data. It allows users to work directly with EnergyPlus. Honeybee, a complementary plug-in to Ladybug, is designed for conducting more advanced environmental performance studies.

2.4. Model Validation

To ensure the reliability and accuracy of simulation results, model validation plays a crucial role in building performance analysis. A study was conducted by Henrique et al. (2017) on thermal analysis to determine the thermal transmittance value of numerous cavity designs of hollow concrete bricks [21]. Their research was validated by comparing simulated and computed findings utilizing international regulations. The findings indicate that Ansys simulations have a higher accuracy rate and are dependable, with a maximum inaccuracy of 0.99 percent [5].

Ladybug offers a wide range of 2D and 3D interactive graphics, which simplifies the process of analysis and speeds up the calculations [22]. Moreover, it allows the validated engines, like EnergyPlus and Radiance, to work with it by importing standard EnergyPlus weather files (.epw) in Grasshopper. The most widely used whole-building energy simulation engine used by many architects and engineers is EnergyPlus. EnergyPlus is an open-source software that is highly accurate and validated by many researchers [23,24]. Other simulation software tools such as IES, Ecotect, and GBS have also been employed in previous research to measure the annual overall energy usage, and they found that the GBS simulation tool was quite accurate [25], as it uses the EnergyPlus engine for the energy simulation. Similarly, Ladybug + Honeybee (L + H) also leverages the EnergyPlus engine for energy modeling. L + H is recognized as a leading building performance simulation tool for energy optimization, offering precise and quantitative results [26].

2.5. Design Criteria

The size of 200 × 200 × 200 mm was finalized for the prototype to align the size with the practical building exterior wall size of 200 mm, which is conventionally followed in most of the buildings as per IS standards IS 2212:1991 [27]. The material considered is concrete with a density of 2300 kg/m³ and a specific heat of 836.26 J/kg °K. The boundary conditions applied for the thermal simulation in Ansys are ambient temperature of 40 °C for outside and 22 °C for inside are considered for the tropical climatic region. Apart from the outer and inner surfaces of the model, the other two surfaces were considered adiabatic as these two surfaces were not exposed to the environment and considered as insulated [28]. The computational mesh size of 10 mm is used in this research, and maintains an aspect ratio closer to 1 for the transfer of information amongst the cells. Mesh size would depend on the size of the model, as smaller mesh sizes increase the computational time of the analysis [29]. However, some previous studies have shown meshing scheme hardly influences the accuracy of the thermal calculations if the aspect ratio of 1 is maintained [28].

A conceptual office room model of 3 m × 3 m × 3 m was designed using Rhino with the bioinspired patterns, sawtooth pattern, and solid concrete wall. The orientation of the building will not influence the energy performance, as the shape of the building considered was a square without any openings. The parametric environment of Rhino-3D includes geometry generation and morphing procedures with direct connection to the 3D printing process [30]. This conceptual 3DP building is simulated with the Ladybug and Honeybee (Grasshopper plugin) energy simulation software to evaluate the energy performance. The parameters set for the building program set are 0.538 people/m², 6.4 W/m² for lighting, 60.1 W/m² for electrical equipment, and a cooling setpoint of 23.9 °C for the small office [22]. The material and properties set for the construction program set are a concrete wall of 200 mm thickness with a density of 2300 kg/m³, 0.734 W/mK thermal conductivity, and 836.26 J/kg °K specific heat. Finally, for the EnergyPlus simulation, the climatic parameters established in the simulation set are for the tropical climatic region, which is taken for this study is Kuala Lumpur city, which was assigned to the model as an ‘epw’ and ‘ddy’ file downloaded from the Ladybug website.

3. Results and Findings

3.1. Thermal Performance Analysis

Conduction, convection, and radiation all contribute to heat transfer between the exterior and interior of the 3DCP walls. However, conduction is the dominant mode due to the motionless air trapped within the infill, whereas the convection and radiation of heat transfer primarily occur between the ambient air and the wall surfaces [29]. Thermal performance is assessed using various parameters, with the key indicators being thermal transmittance (U-value) and thermal resistance (R-value). A lower U-value indicates better thermal insulation, thereby reducing heat transmission through the walls. This study analyses various bioinspired patterns to identify the pattern that achieves the lowest U-value, and compares these results with those of a conventional sawtooth 3D-printed pattern and a solid concrete wall.

3.1.1. Simulation Experiment

The simulation analysis was performed using Ansys by selecting the most appropriate boundary conditions specific to the conditions, and the problems are listed in Section 2.5. In Ansys, the steady-state thermal analysis was chosen with the heat load applied, and the environmental conditions remain constant over time while assessing the equilibrium state of the models. The temperature variations at various sections of the prototype models are shown in Figure 1. The most significant aspect of Ansys simulation software is that the temperature recorded at any point of the model can be checked, and the colour swatches indicate the temperature variations at various fragments of the model.

The bioinspired patterns honeycomb, spiral, spiderweb, and weaving, along with the sawtooth pattern, and a solid concrete cube, are tested for their thermal performance. The Ansys simulation results seen in Figure 1 display 2D models of the prototype models instead of 3D models, as there is hardly any difference in the temperature variation contour between the 3D and 2D images of the model. The colour variations from red to blue show the maximum to minimum temperature recorded on the model. The models contain a uniform mesh along the entire prototype model, including the joints, with an aspect ratio of 1 for better information transfer amongst the cells.

3.1.2. Findings of Thermal Analysis

The maximum temperature recorded on the outer surface of the model for the solid concrete cube is 40.31 °C, and the minimum temperature recorded on the inner surface of the model is 29.69 °C. The temperature recording on the sawtooth pattern varied from 45.36 °C maximum to 24.46 °C minimum from the outer to inner surface of the model, respectively. The four bioinspired patterns did not show much variation between them. However, the variation in maximum temperatures recorded is between 47.62 °C in the spiderweb pattern and 47.97 °C in the spiral pattern. Similarly, the variation in minimum temperatures recorded is between 22.03 °C in the spiral pattern and 22.38 °C in the spiderweb pattern. The reason for the higher outside temperatures for the spiral, the honeycomb, the weaving, and the spiderweb patterns seen in Figure 2 is due to the heat retained on the outside of the surface, as the bioinspired patterns displayed better thermal resistance than the saw tooth pattern and solid concrete cube. Even though the temperature applied to the outside surface of all the prototype models is the same (40 °C), the increase in outside temperatures shows the thermal resistance of different patterns. The surface around the midpoint of the cavities on the inside surface of the wall, having a higher insulation effect, is seen due to the patterns and cavities, which lowers the thermal transmittance for the bioinspired patterns.

The graphs shown in Figure 2 indicate the temperature recorded on the inner surface of the various prototype models. The inside temperature differences shown in the graphs vary from 22 °C to 30 °C based on the thermal resistance of the prototypes. The inside temperature recorded by the bioinspired patterns was the lowest, and the temperature recorded by solid concrete without any pattern was the highest among all the other prototype models. The higher outside temperature and lower inside temperature signify better thermal performance demonstrated by the bioinspired patterns. The final calculated U-value is plotted as a graph and shown in Figure 2. In the graph, the various patterns along with the solid concrete are shown on the X-axis, and the U-value is mapped on the right side of the Y-axis. The left side of the Y-axis shows the inside and outside temperature values in degrees centigrade.

Figure 3 plots the R-value, K-value, and the U-value along with the wall thickness to understand the relationships between these values. The lowest U-value of 1.2 W/m²K was recorded by most of the bioinspired patterns, and the highest U-value of 2.3 W/m²K was recorded by the solid concrete without any pattern. The lowest U-value displayed by the bioinspired patterns indicates better thermal performance than the sawtooth and solid concrete.

3.2. Energy Performance Analysis

The energy modeling simulation results display the hourly energy consumption for each month, from January to December of a year. Figure 4 shows the annual energy consumption of the building is calculated based on the daily and monthly energy utilization for the various periods of the year.

A consolidated result or a comparison table will give a better understanding of the overall performance of these patterns. Therefore, the results of the two stages of evaluation are consolidated and shown in the graph (Figure 5). The findings of the energy performance of the bioinspired 3DCP building are novel, and no previous studies have tested the energy performance of bioinspired 3DCP.

From the graph shown in Figure 4, it is evident that the energy demand of the bioinspired patterns is less than 600 KWh/year, whereas the energy demand of the sawtooth pattern is around 690 KWh/year, and for a solid concrete building, it is 965 KWh/year. Therefore, the consolidated result in Figure 5 indicates that the overall performance of the spiral, honeycomb, weaving, and spiderweb patterns surpasses that of the conventional sawtooth pattern used in 3DCP buildings and solid cast concrete structures.

4. Discussion

4.1. Thermal Analysis

The temperature recording from the Ansys simulation results shows that the spiral pattern achieved the lowest inner surface temperature of 22.03 °C among all the models. The spiral’s geometry, featuring a shorter, compressed inner surface and, longer and stretched outer surface, enhances its structural strength and enables it to act as a thermal buffer [10]. The spiral cavities slow down air movement, thereby reducing convective heat transfer, and act as a thermal buffer. The honeycomb pattern follows closely, with an inner surface temperature of 22.06 °C. These two bioinspired patterns displayed the lowest recorded temperature on the inner surfaces, suggesting slower heat transfer from the external to the internal surfaces. The pattern and the air cavities of these patterns function as insulation for the heat flow from the outer surface to the inner surface [15]. In general, heat transfer in solid materials occurs primarily through conduction, as observed in the solid concrete cube, where heat is directly conducted to the inner surface [18,31]. Despite that, the sawtooth pattern, which incorporates geometry and air cavities, has thermal performance that is inferior compared to the bioinspired patterns.

The bioinspired pattern’s performance is still higher compared to the sawtooth pattern, a common printing pattern in most of the concrete 3D printing applications. Among the bioinspired patterns, the spiral pattern displayed the best thermal performance with a lesser thickness than the honeycomb and spiderweb patterns. To overcome the differences in the thickness of the models, the U-value of these geometries is calculated, and the U-value of the spiral pattern is still lower than the other patterns, followed by the honeycomb pattern.

4.2. Energy Analysis

The study conducted by Mahadevan et al. (2020) compared the buildings built with 3DCP environmental sustainability parameters, thermal comfort, and building energy efficiency with M25 concrete buildings and conventional brick masonry buildings [27]. Their results indicate that 3DCP building envelopes perform better in terms of thermal comfort and energy efficiency compared to M25 concrete and brick buildings. The study by Koci et al. (2014) did a computational analysis to understand the thermal performance and evaluate the energy consumption of a hollow clay brick building envelope for the European climate [32]. They have used Design Builder with EnergyPlus for energy simulation, and the obtained results showed lesser insulation layer for a hollow brick with sophisticated internal cavities used much less energy than traditional brick walls with a higher insulation layer thickness. Studies on energy performance of 3DCP are limited, and therefore, the other studies on hollow concrete blocks and hollow clay bricks are considered for discussion. Looking at the previous studies, the regular geometric patterns showed some improvement in the energy efficiency of the 3DCP buildings compared to the conventional brick or concrete buildings. However, this study showed more than 40% annual energy saving achieved by the bioinspired 3DCP building compared to the conventional concrete building, which gives the researchers hope to study further the application of bioinspired patterns in 3DCP.

In comparison to the previous research discussed above, it is evident that the energy efficiency of bioinspired patterns is significantly higher than that of conventional sawtooth 3DCP and solid concrete buildings. It is also evident that the thermal performance of these patterns directly influences energy performance due to the control of temperature by these patterns. The findings of the energy performance of the bioinspired 3DCP building are novel, as no prior studies have tested the energy performance of bioinspired 3DCP. Previous research discussed in the literature review has focused on testing the energy performance of multilayer sawtooth pattern 3DCP specimens [5] or hollow clay bricks [32].

5. Conclusions

In this study, a biomimetic approach introduced novel concepts for translating biological functions into architecture and engineering. Mimicking nature-inspired structures was successfully achieved through 3DCP, which is not possible with conventional construction. This study broadens the scope of bioinspiration, addressing gaps in mimicking natural structures within the construction industry. The thermal and energy performances of the bioinspired patterns were investigated at two stages. The following conclusions were drawn from this study:

• The spiral pattern showed strong thermal performance with a U-value of 1.22 W/m²K, over 45% more efficient than the cast concrete U-value of 2.3 W/m²K. The other three bioinspired patterns: honeycomb, weaving, and spiderweb’s thermal performance are also comparable with the spiral pattern.
• A significant reduction in the U-value of the cavity walls was observed compared to the solid concrete wall. However, the pattern of the cavity played a significant role in reducing the thermal transmittance value further.
• From the energy efficiency perspective, the spiral pattern performed well and saved energy by almost 43% compared to the conventional solid cast concrete building. Following the spiral are the other three patterns: honeycomb, weaving, and spiderweb.
• In comparison to the common sawtooth pattern, the performance of almost all the bioinspired patterns is higher in terms of thermal and energy efficiency. In thermal and energy efficiency, almost all the bioinspired patterns are nearly 15% more efficient than the common sawtooth pattern used in 3DCP buildings.
• In material saving, all the 3D-printed patterns saved 25% to 40% of material in comparison to the solid concrete, which makes it a sustainable alternative to the conventional construction system.

In the future, further research can be conducted to improve the application of bioinspired patterns in 3DCP to optimize its performance and make it more affordable. The bioinspired patterns of lobster shell and gyroid were not investigated in this study due to limitations in the 3D concrete printing. Exploring these two patterns in terms of thermal and energy performance is encouraged. Moreover, different configurations of these patterns with the variation in layer thickness, layer height, width of the wall, etc., are to be investigated to find the optimal pattern design. A real-time study on the thermal and energy performance calculation of bioinspired 3DCP building envelopes is recommended, as it will give actual results compared to the simulation studies.

This study only considers 3D-printable concrete as the material, and other materials like geopolymer concrete, clay, etc., are not considered. Optimization in terms of layer thickness and wall thickness is not explored in this study. The printing methods, printing time, and printing cost are out of the scope of this study. In practice, there are several subjects like cementitious filament pumpability, extrudability, and buildability, which are not addressed in this study. The tropical climatic region is limited to Kuala Lumpur city, Malaysia, and other tropical regions have not been explored.

This study contributes to the success of bioinspired patterns application in 3DCP construction, and further research can be performed in the future to improve or optimize its performance. Overall, this research is the first step to the application of bioinspired patterns in 3DCP, and it creates an understanding of how building envelopes can be optimally designed to improve their thermal and energy efficiency.

6. Patents

A patent application has been filed with the Intellectual Property Corporation of Malaysia (MyIPO) for this research.