Energy Reduction Potential of Biomimetic Building Facades for Different Building Typologies in Different Climate Zones

0000-0002-4716-7225 ABSTRACT Greenhouse gas (GHG) emissions leading to anthropogenic global warming continue to be a major issue for societies worldwide. One opportunity to reduce emissions is to improve the effectiveness of building envelope, leading to a decrease in operational energy consumption. Improving the performance of a building's thermal envelope can substantially reduce energy consumption from heating, ventilation and air conditioning while maintaining occupant comfort. In previous work, a computational model of a biomimetic building façade design was found to be effective in temperate climates in an office context. This paper tests the hypothesis that biomimetic building facades have a broader application through a case study example based on animal fur and blood perfusion. Using mathematical modelling and digital simulation methods, the energy reduction potential of the biomimetic façade was tested in a set of operational applications (office, school and aged care) and across different climate zones (tropical, desert, temperate, and cool continental). Results indicated that the biomimetic façade has potential to reduce energy consumption for all building applications, with the greatest benefit shown in residential aged care (67.1% reduction). Similarly, the biomimetic building façade showed potential to reduce operational services energy consumption in all climate zones, with the greatest energy reductions achieved in the tropical (55.4% reduction) and humid continental climates (55.1% reduction). Through these results the hypothesis was confirmed, suggesting that facades engineered to mimic biological functions and processes can improve substantially decrease building operational energy consumption and can be applied in different building classifications and different climate zones. Such facades can contribute to the further reduction of greenhouse gas emissions in a broad range of contexts. This study also exemplified a method by which other biomimetic building envelope features may be assessed. Further work is suggested to assess economic viability and constructability of the proposed


Conflicts of interest/Competing interests Not Applicable
Availability of data and material Data on results is available upon request

Code availability
Software code is not openly available, however the author is willing to discuss the modelling protocols in detail with interested parties.

Authors' contributions Not applicable
Graphical Abstract

INTRODUCTION
There is currently an urgent need to reduce greenhouse gas emissions (GHG) to prevent the worst effects of climate change. In 2018, the International Panel on Climate Change released a special report which updated the probable consequences of global warming and stated that future climate-related risks are greater if warming exceeds 1.5°C (Hoegh-Guldberg 2018). This report also included a chapter on mitigation pathways to achieve the goal of limiting warming to 1.5°C. While it is acknowledged that renewable energy sources are crucial to reaching the 1.5°C target, the IPPC reported indicated that reducing demand in end use sectors -such as buildings -would also be important in mitigation strategies. Reductions in energy demand can lead to flexibility in choices available for emissions reduction strategies (Rogelj 2018). Buildings consume a large proportion of the energy required for human activity, and overall account for approximately 19% of the world's greenhouse gas emissions (Residential and Commercial Emissions in the United States 2017; Australian Energy Update 2020 2020; Lucon O. 2014). Historically, humanity has perceived facades as static building structures (Knaack et al. 2007). Only relatively recently (in the past half-century or so) have façade-integrated systems been recognised as important factors in reducing building operational energy consumption (Wigginton & Harris 2002).
In combination with this carbon reduction and energy efficiency imperative, modern occupant expectation of thermal comfort often requires energy-intensive heating ventilation and air conditioning (HVAC) systems. Improving the thermal performance of building envelopes is a key method to reduce building operational energy consumption without compromising comfort. Widespread adoption of better building practices through design schemes such as Passive House (Passive House 2020) as well as initiatives such as LEED (USGBC 2020), the Living Building Challenge (Living Building Challenge 2020) and Green Star in Australia (GBCA 2020) have all contributed to improvements in building energy efficiency.
Building operational energy efficiency is one aspect of a wider societal requirement to reduce carbon emissions associated with the buildings. It is a challenge that encompasses everything from sources of energy, policy and embodied energy. Studies more broadly on sustainable building include Zuo and Zhao (2014) and Hossaini, Hewage and Sadiq (2015). Net Zero Energy Buildings (NZEBs -buildings that generate sufficient renewable energy on site to meet their energy needs, with net zero greenhouse gas emissions) are an end objective for sustainable buildings. Hu and Qiu (2019) use building simulation methods to conclude that policy-based approaches could achieve net-zero buildings in three countries -China, the USA and Germany -by 2050. Du et al. (2019) present a study indicating that adoption of prefabrication technologies contribute significant potential for reducing CO2 emissions over the life cycle of residential buildings.
Focussing on building envelopes, multiple initiatives have been developed to passively and actively improve façade performance to balance the completing goals of reducing GHG emissions while providing expected levels of comfort. Examples of active and passive façade systems are described in Schittich (Ed.) et al. (2006), while Wigginton and Harris (2002) focus on active systems. Other researchers such present studies on initiatives to improve façade energy efficiency: Lee et al. (2002), reviewing high-performance commercial building facades; Al-Hazmy (2006), analysing heat transport through hollow building blocks; Liu, Wittchen and Heiselberg (2015) review control strategies for intelligent glazing systems; and He and Hoyano (2010) assess cooling effects of a passive evaporative cooling wall. Elkhayat et al. (2020) undertake a life cycle assessment of three high performance glazing systems, Kim and Olsen (2015) report on radiant systems, while Lydon et al. (2017) investigate multifunctional building elements. Porous ceramic materials were tested by He and Hoyano (2010), while novel 'breathing walls' have been proposed by (Craig & Grinham 2017). Examples of active, integrated unitised facades have been constructed, for example, in the Debitel Headquarters in Stuttgart, Germany (Knaack et al. 2007). Double skin facades have become widespread and tailored to different climates, for example see Poirazis (2006), Haase (2008), and Hamza (2008).
Alongside these developments, biomimicry -innovation through natural inspirationprovides additional opportunities for innovation and improvements to building façade performance. By studying natural adaptions, from an ever-growing body of biological knowledge, innovators can extract functional characteristics and translate these characteristics into innovative, adaptive, flexible and more efficient designs. In modern technology, biomimicry has been shown to be a successful method to engender innovation (Benyus 1997 Badarnah (2012Badarnah ( , 2015 proposed a specific conceptual framework for incorporating biomimetic initiatives into building skins including energy and comfort, but also structure, water management, materials and waste. Badarnah (Badarnah 2017) has also presented morphology-based methods for biomimetic façade design. Other researchers to propose schemes for integrating biomimicry to improve the functional performance of building facades include: Al-Obaidi et al. (2017), with a systematic quantitative literature review, Gruber and Gosztonyi (2010), comparing biological skin mechanisms with architectural analogies, Schleicher et al. (2015), conceptualising bio-inspired flexible façade shading schemes, and López et al. (2017), presenting a methodology to collection plant adaptions and guide mapping to architectural designs.
Research by Webb, Aye and Green (2013, 2015, 2018; Webb, Hertzsch and Green (2011) has shown that specific biomimetic strategies could improve the thermal performance of building envelopes. Testing of the efficacy of the biomimetic design was accomplished through digital modelling and building energy simulation. Others have used the simulation method for assessing building energy consumption. For example, Kumar, Thakur and De (2021) use energy simulation to energy performance of residential buildings applying new energy codes Kabul, while Heravi, Salehi and Rostami (2020) use simulation as part of an optimisation study into nearly zero energy building's design in developing countries. The methodology in the current study translated biomimetic principles and processes into a heat analysis and energy simulation engine.
Previously, animal fur and blood perfusion were selected as template characteristics for a biomimetic façade design (Webb 2018;Webb, Aye & Green 2018). Fur and perfusion were selected for the design based on their effectiveness as strategies evolved by homeothermic mammals to maintain steady core body temperatures in a wide range of environments (Schmidt-Nielsen 1997). Many mammals use a wide variety of hair and fur types to provide insulation, with heat transfer assessments on polar bears (Jessica A. Preciado 2002), the rock squirrel (Walsberg 1988b), wet fur (modelled) (Gebremedhin & Wu 2001), the Harris antelope squirrel and round-tailed ground squirrel (Walsberg 1988a) and a comprehensive study by Liwanag (2008) on fur and blubber in marine mammals.
Digital simulations of biomimetic facades in a unitised façade system (refer Figure 1 for façade type example) with animal fur and perfusion characteristics were constructed to test the hypothesis that these building envelope features would improve building energy efficiency while maintaining thermal comfort. Simulation results indicated that this façade, based on animal fur and blood perfusion, could be effective in reducing operational energy and peak heating and cooling loads by more than 50% in an office building in a temperate climate of Melbourne, Australia (Webb 2018;Webb, Aye & Green 2018). Other researchers have also proposed biomimetic features for building facades, which have been tested in individual climates for singular building types. For example, Fecheyr-Lippens and Bhiwapurkar (2017) using building simulation to test a high albedo façade with phase change materials for a small office building in Chicago, USA, with an estimated energy reduction of 68%. Kuru et al. (2018) tested a geometric façade based on ribs and stomatal openings of the barrel cactus on a naturally-ventilated education building in Sydney, Australia, and found a potential improvement by 51.5% for the 90% acceptability limits in the ASHRAE55-2010 Adaptive Thermal Comfort standard. Park (2016) introduced biomimetic strategies based on reflecting superposition eyes to improve functional illuminance in sports stadiums in Incheon, Korea. Craig et al. (2008) proposed a cellular structure with thermal mass as a roof cooling mechanism in Riyadh, Saudi Arabia, and employed TRNSYS simulation to calculate a 4.5°C reduction in roof temperature.
However, testing of the fur and perfusion façade, and these other case studies, have been limited to a singular test case for one building typology in individual climate zones. Research has been limited on wider application of biomimetic façade initiatives for building facades. For more widespread application, it was important to test the efficacy of biomimetic façade designs in different building types and in different climate zones. The hypothesis in this study was to assess whether biomimetic building facades, based on their energy-reduction potential, have a broader application. A case study was proposed to test whether a biomimetic building façade, based on animal fur and blood perfusion, would be as effective at improving energy efficiency in different climate zones and on different building types as it was shown for one building typology (office) in a temperate climate. The confirmation or rejection of this hypothesis would indicate whether biomimetic facades could be successful in broader applications, rather than individual projects. The study also aims to demonstrate suitable methods for assessing biomimetic initiatives through mathematical modelling and building simulation.

MATERIALS AND METHODS
As indicated in Section 1, the objective of this expanded study was to determine whether the animal fur-perfusion façade design was at least as effective in a broader range of climate zones and building types as it was shown for an office building in a temperate climate.
A conventional method to distinguish climate zones is the Köppen-Geiger (K-G) climate classification, refer Figure 2  o Section 2.2, Dynamic Building Simulations. Reference and biomimetic façade models were integrated into to a conventional Building Energy Simulation (BES) software package to test the performance of the proposed biomimetic façade designs.  Section 3, Results and discussion o Section 3.1 -Extent of simulations, where the format of the simulations was described. o Section 3.2 -Results for the façade scenarios in the selected climate zones were summarised and discussed. o Section 3.3 -Results for the façade scenarios for the three selected building types were summarised and discussed. o Section 3.4 -Comparison with simulation and Energy Reduction Studies.
The results obtained in the current study were compared with a selection of alternative energy efficiency measures for different climate zones building types.  Section 4, Limitations and further work o The limitations in the methods used in this study were identified and examined. o Economic impact was discussed.  Section 5, Conclusions o The conclusions for the study were drawn, including whether the results confirmed the hypothesis described in Section 1.

Façade Model development
The façade models for conventional materials and the biomimetic fur and perfusion facades are summarised below. For full model development, refer to Webb (2018) and (Webb, Aye & Green 2018).

Reference
For the Reference Façade (Ref), a time-dependent model was developed based on the generalised 1-D heat equation through a plane wall without sources or sinks (Holman 2001). The temperature, T(x,t), was calculated as: The physical situation was represented in Figure 3. A heat balance at the inside and outside surfaces was conducted to define the internal and external boundary conditions.
For the external surface: These heat balance boundary conditions were expanded to include relevant coefficients and temperatures: Radiant heat transfer coefficients were linearized, e.g. for long wave radiation:

External Fur Layer
Multiple models and methods have been devised to calculate heat transfer through fur or, equivalently (refer Webb (2018); Webb, Hertzsch and Green (2011)). The Davis and Birkebak (1974) model was selected for translation to a fur-lined biomimetic façade design. This model related conductive energy flux across the fur layer, qf, to a temperature gradient, ∆T, and fur thickness layer, Lf, via an effective fur thermal conductivity, keff, as follows: Further development on the radiation heat transfer using an extinction coefficient and energy relationships let to the following expression: where: αf,S = bulk fur solar absorptivity, qS,skin = solar radiation absorbed by skin, FS = absorption factor at solar wavelengths, Nf,s = optical thickness for solar wavelengths (Webb, Aye & Green 2018), βh,S = hair extinction coefficient across solar wavelengths (Davis & Birkebak 1974).
Heat Transfer: With an expression for heat transfer through the fur layer, qf, the fur heat transfer was integrated into the façade model ( Figure 4). Heat transfer through the fur was then incorporated into a heat balance on the external surface of the wall:   Pennes (1948) provided a fundamental basis for the study of heat transfer in living tissue, which was selected as the basis to describe fluid perfusion in the biomimetic façade model as follows (refer Figure 5 and Webb, Aye and Green (2018)):

Perfusion Layer
Equation (10) could be solved in place of the unmodified heat equation (Equation (1)) as the basis for perfusion in the biomimetic façade design.
Heat Transfer:

Finite difference solutions
The equations in the preceding sections required suitable solution methods for adoption in a dynamic building annual energy simulation. This led to the introduction of a finite difference scheme to numerically solve the model equations (Webb 2018;Webb, Aye & Green 2018). An explicit finite difference scheme was developed for the biomimetic façade, with the nominal 0.1m thick façade split into 4 discrete steps. Accordingly, the fundamental heat equation, Equation (1), became: Here, Ti represented the temperature for the ith internal node at timestep n + 1 and the Fourier number, Fo, is: The finite difference models for the reference and biomimetic facades are shown in Figure 6.
Heat Transfer:

Dynamic Building simulations
Customised finite difference models were developed in the preceding section, representing the characteristics of both conventional and biomimetic façades. These numerical models were implemented in TRNSYS for annual dynamic energy simulation. The biomimetic design model adapted for TRNSYS software in this study was a façade that included both fur and perfusion initiatives, i.e. it included the advantages of both. TRNSYS (TRaNsient SYstem Simulation or TRNSYS) is a well-recognised method for testing building designs (refer validation standard and (ASHRAE 140-2017) and Neymark and Judkoff (2008)).

Building Simulation model
In all climates selected, a rectangular floor plate was created, containing six zones, with glazing north and south facades ( Figure 7 and Figure 8). The model assumed that the building floor was situated above another floor of identical dimensions (creating an adiabatic floor surface), while the ceiling was externally exposed above via an external roof construction.

Building fabric
Building fabric and glazing for the Type 56 model are shown in Table 1.

HVAC System
The occupied zones on the modelled building floor were assumed to be air conditioned to meet thermal comfort requirements of occupants during hours of operation, which depended upon the building type, as per Table 2. HVAC system design calculations were based on an assumption that the building would be serviced by a chilled water (CHW) and heating hot water (HHW) variable air volume (VAV) air conditioning system for both heating and cooling. Air would be cooled or heated via chilled or heating hot water. The following major components were required:  Chiller (assumed air-cooled, Integrated Part Load Value of 3.7),  Boiler (assumed gas-fired, efficiency 80%),  Fans,  Chilled water pumps,  Hot water pumps for heating.  Outside at 11 L s -1 per person (Schittich (Ed.) et al. 2006). The development of the specific pressures and capacities of HVAC equipment was as per Webb (2018). These were based, where possible, on minimum energy efficiency standards [National Construction Code BCA 2016 Volume 1 2016).

Internal loads and schedules
Three customary internal heat gains were added to the model: occupants, lighting, and electrical equipment (computers, printers, monitors, refrigerators, etc.). Lighting was specified as per the maximum lighting efficiency allowance given in the National Construction Code BCA 2016 Volume 1 2016). For offices, equipment heat gains were set to the specifications of NABERS Ratings for offices (Handbook for estimating NABERS Ratings 2019). For aged care, internal heat gains were set on the assumption that aged care facilities would have minimal equipment and account for items such as a computer terminal and TV, while school classrooms were also assumed to have minimal equipment loads (it was assumed that each student did not use a laptop).
Metabolic and clothing values were referenced from the data in the ASHRAE Handbook -Fundamentals 2009). A lower value of activity was ascribed to occupants in Aged Care buildings. Clothing was maintained consistently across all three cases and set at 0.6 clo (summer) and 0.95 clo (winter). The following table summarises these inputs.

Performance metrics
Building facades perform numerous functions, however the primary measures for evaluating the effectiveness of the biomimetic facades in this study were the minimisation of building HVAC energy consumption and minimisation of peak façade heat loss and gain, as shown in the table below. In addition to these energy-based criteria, it was also necessary to define 'thermal comfort' in measurable terms (Schittich (Ed.) et al. 2006):  Indoor Air Temperature (IAT) -20-25°C, and  Mean Surface Temperature (MST) -no more than 3°C different to air temperature.

RESULTS AND DISCUSSION
Using models for conventional and biomimetic facades described, integrated into a building model in TRNSYS (Section 2), annual simulations for the different climate zones and building typiesolog were conducted. The results for these simulations in terms of annual operational services energy and peak loads are presented herein.

Extent of simulations
For each of the four climate zones, an annual dynamic energy simulation was conducted for both the biomimetic façade ('Biom') and the reference façade ('Ref') as indicated in the following table.

Annual energy comparison -climate zones
The following charts display annual energy results for the four climate zones for the biomimetic zone only (refer to Figure 7). This allowed the analysis to focus on the performance of biomimetic facade and to reduce complexity in the presentation of the results. Figure 9 displays results annual services energy consumption for each of the climate simulations with the biomimetic façade, including reference cases. Table 7 provides a summary of all the results across the different climate zones while Table 8 indicates the reduction that each biomimetic design achieved.   It was apparent from Figure 9 that the temperate oceanic climate zone (Cfb) -the baseline case -required least energy overall to maintain comfort conditions for occupants. As expected, more extreme climate cases required additional energy to maintain the comfort band of 20-25°C. Stockholm (Dfb), at a latitude of 56.3°N latitude, consumed the most energy, largely due to a significant proportion of heating and very limited cooling. Contrastingly, Béchar (Bwh, 31.6°N) and Manila (Aw, 14.6°N), much closer to the equator, consumed more energy that the baseline Cfb case, due primarily to an increase in cooling requirements. The cooling demand (as indicated by the chiller energy) was six times greater than the baseline Cfb case. It was observed that the greatest cooling demand occurred in the Manila simulation (Aw), which also demanded additional cooling from the perfusion pumps.
Reviewing the comparative results, biomimetic cases outperformed the reference cases in all climate zones. Physical characteristics of the fur lining to provide extra insulation and a barrier to incoming solar radiation, in combination with the water-based perfusion inside the façade, were effective in improving the building envelope energy efficiency. Absolute energy savings for the more extreme climates (Dfb and Aw) were the greatest. The reference case for Stockholm (Dfb) was 4,241 kWh greater than the biomimetic design, while in the Manila simulation, the reference was 3,112 kWh greater than the biomimetic design. The baseline Cfb case showed 928 kWh difference between reference and biomimetic designs. However, in proportional terms for total energy, the variations between biomimetic and reference cases across the climates zones were actually similar. The baseline Cfb case showed a 46% reduction in total energy savings, and all of the other three cases indicated a proportional decrease within 10% of this figure. This indicated that the biomimetic façade would have a similar affect across different climate zones (at least for those tested).
Observing individual services energy components, in all cases the biomimetic design had a lower energy consumption compared to the reference case. There was more proportional variation between cases than comparing total annual energy, For example, there was a 68% reduction in fan energy for the Aw (tropical) case, while just a 9% reduction in fan energy for the Dfb (colder humid continental) case. Conversely, chilled water pump demand in the Aw case was substantially higher than in the other climates (both biomimetic and reference simulations). This was likely due to the high, and almost continuous cooling demand requirements in a topical climate. The added insulation provided by the fur-lined façade provided a barrier to the external weather, but with small diurnal fluctuations and constant infiltration, the extra insulative effect was diminished, especially without the opportunity to obtain free cooling from cooler outside air temperatures during some parts of the day. This result pointed towards a more general trend indicating that additional energy-saving initiatives, other than improvements in the building envelope, must be considered to minimise overall building services energy consumption.
In this study, it was assumed that the energy source for heating was natural gas-fired boilers. However, given the accelerating impacts from climate change and the improvements in the technology, electric heat pumps have become more favourable as a heating source. Electric heat pumps have a COP range from 3.2-4.5. Therefore, an alternative scenario was tested where the heat source was assumed to be an electric heat pump with a COP of 3.2. In this instance the corresponding energy results appeared markedly different, as shown in Figure 10. Under these conditions, the only remaining climate with a proportionally significant heating consumption was the Dfb (humid continental) case. The tropical Aw location now consumed the greatest annual building services energy, with a large margin between the reference Aw (tropical) case and the Bwh (hot desert) case (34% difference). The difference in the biomimetic cases was not as pronounced (22% difference). Even considering these variations from the gas-fuelled heating, it was clear that the biomimetic designs provided a substantial improvement in energy efficiency.

Peak heating and cooling comparison -climate zones
Peak heating and cooling results were compiled for the biomimetic zone. These loads represented the maximum annual cooling and heating demand that was required for the space, throughout the year, normalised by floor area. The following charts indicate how the biomimetic facades performed in each of the climate zones with respect to peak heating and cooling loads. Figure 11 shows peak heating and cooling loads for the simulations with the biomimetic façade, including reference cases.

Figure 11 -Peak heating and cooling for different climates -comparison
Reviewing the results for peak loads, there were similarities and differences across climate zones. In peak cooling, simulated peaks were similar for the biomimetic zones in three of the cases (Cfb, Dfb and Bwh), while the Aw (tropical) climate showed the lowest peak cooling demand. This was despite the tropical climate having the greatest annual cooling demand and again indicated the continuous nature of the cooling requirements in tropical climates. There was greater differentiation in the heating demand across climate zones, with the Cfb and Bwh zones having a similar peak demand, while the coldest climate had a demand that was three times greater than these cases. It was important to also note that peak loads presented here represent peak system requirements to meet the dynamic cooling or heating demand for the simulated annual weather file, and would differ from the design heating and cooling loads as calculated by a mechanical design engineer.
Comparing relative differences between the biomimetic designs and reference cases in each climate, the greatest reduction achieved was for cooling in the Aw climate, which can be attributed to the effect of perfusion cooling present in the biomimetic façade. The perfusion cooling made a substantial contribution to the overall cooling supply, reducing the requirement for air-based cooling that was required in the Aw reference case. In the Aw biomimetic case, efficiencies were obtained through water-based cooling, low volumes of water required (compared to an air-based solution) plus a reduction in the fan energy required to deliver cooling to the occupied zones. In the Dfb case -a much colder climate -there was a much smaller difference between reference and biomimetic cases for heating and cooling. The heating demand for the biomimetic case was actually greater in the Dfb case. This was due to the additional heating supplied by the perfusion system in the simulation, which would have provided additional heating to the space but also lost heat to the external environment, leading to a 2% increase in peak simulated heat demand. One potential option to reduce heat loss from perfusion would be to introduce an additional layer of solid insulation beneath the external fur layer, directing greater heat flow to the internal surface.

Annual energy comparison -building types
Similar to climate simulations, the building type comparison shows annual energy results for the biomimetic zone only. Figure 12 displays results for the annual services energy consumption for each of the building type simulations with the biomimetic façade, including reference cases. Table 9 provides a summary of all the results across the different building types and Table 10 shows the reduction that each biomimetic design had over its respective reference case for each different building type.   Following the trend of the climate simulations, biomimetic designs showed reductions in the services energy across the three building types. Compared with the varied energy reductions across climate categories, the reductions in energy for each of the services components (cooling, heating, etc) were similar between building types. There was one exception, however: the heating energy consumption for the Aged Care simulation, which showed a 7,374 kWh reduction from the reference case, compared with less than 1,000 kWh reduction in the Education and Office simulations. The main contributing factor to this result is the extended operational schedule for Aged Care facilities, which run 24 hours per day and require constant conditioning for residents -particularly for heating results in a temperate climate. Therefore, the improved insulation benefits of the fur-lined façade had a greater impact. Apart from in heating energy, the absolute reductions in energy were similar, for fans, chillers and pumps.
In terms of a proportional comparison, the reductions observed for the biomimetic cases did show some differences. For example, while all three boiler energy reductions were 80% ±10%, the chiller (cooling) reductions in the Education case was 41%, while in the Office and Aged Care cases, the reduction was around 70%. The lower reduction in cooling for the Education case was the nature of the internal loads, with the Education case having a much larger occupancy. The high occupancy of 2 m² per person resulted in internal loads being 87% higher in the Education case compared to the Office case. The additional occupancy also required air for occupant ventilation, and necessitating a higher conditioning demand for outside air. The inclusion of a high performance biomimetic façade could not affect the conditioning requirement for outside air, and this illustrated one of the limitations of the proposed design. It was apparent that the biomimetic façade would be more effective at reducing services energy consumption in building types where envelope heat loads dominated the load profile, rather than occupant loads and outside air. There was a higher proportional reduction in fan energy in the Education (28%) case compared with the Office (15%) and Aged Care (11%) cases. This result followed from the climate zone studies, which suggested that insulation building envelope strategies would have a limit to their effectiveness if internal loads and insulation were not improved as well. Figure 13 shows the peak heating and cooling loads for the building type simulations with the biomimetic façade, including reference cases. Absolute peak heating and cooling was relatively similar for the three building types, although the higher internal loads in the Education case drove a higher cooling demand. The heating demand peaks in the Education and Aged Care simulations were lower than the baseline Office case. The Education case was lower because of a later start time in the assumed schedule (09:30) compared to the office (08:30) and would operate with higher internal loads. The Aged Care case was assumed to operate continuously, and would therefore not need to start up from a cold, unoccupied building (noting again that these were dynamic peak loads and not design peak loads).

Peak heating and cooling comparison -building types
In comparing the effect of the biomimetic façade on the peak loads across the building types, it was observed that the proportional cooling reduction achieved through the biomimetic façade was similar for all three cases, with a 35% ±5% decrease in cooling when compared with the reference case. In heating, there was more of a difference in the building types, with a 17% reduction in offices, 60% reduction in the Education case and 37% reduction in the Aged Care case. The large reduction in the Education case could be attributed to the retention of internal heat from occupants due to an improved external insulation from the fur lining. In the Aged Care case, the better performance of the biomimetic façade was due to the efficiency of the perfusion system to deliver heating via hot water perfusion through the building envelope, which, once reaching the maximum allowable temperature, would have created only small ongoing demand due to losses to the external environment through a wellinsulated, fur-lined, external façade. The results for the Education and Aged Care facilities illustrated the effectiveness of the additional insulation provided by the fur layer and the efficient form of space heating achieved through perfusion through the façade. This would be especially applicable climates where heating demand is significant, such as the Cfb climate tested (Melbourne Australia) and in colder climates, such as the Dfb climate (e.g. Stockholm, Sweden).

Comparison with simulation and energy reduction studies
This study was undertaken to simulate the potential effect of biomimetic facades with the aim to decrease energy consumption in buildings of different type in different climate zones. To place the results of the study in context with other research, a review was conducted on other simulation studies where energy-saving initiatives have been proposed for buildings in different climate zones, with an emphasis on innovations for building envelopes or performance improvements in HVAC systems. A summary of comparative studies are indicated in Table 11 below. Bare roof compared with a green roof and innovative hybrid roof with combined effects of green roof and high albedo.
The displays results using Operational Performance Factor, which describes the relative improvement of the hybrid roof.
The results suggest that a hybrid roof would out-perform white or green roofs by a factor of 50%-100%. However, this is given in comparative terms between two initiatives and not the actual energy consumption.
The energy simulation studies noted in Table 11 may be further summarised by climate zone building type and energy reduction. This comparison was completed and compared against an equivalent summarisation of the scenarios tested in the current assessment of biomimetic facades, as shown in Table 12. Note: for additional data points, individual scenario outcomes were separated in each reference paper, where possible.  Table 12 indicates a substantial difference in energy reduction achieved through the biomimetic design compared with alternative energy efficiency initiatives. A statistical comparison of the biomimetic scenarios against the sample of alternative studies using a t-test of unequal variances suggests that there is a very low probability (<0.001) that the energy reductions from these two groups are equal, i.e. the greater magnitude achieved by the biomimetic designs may be considered statistically significant. However, it was noted that both samples sizes were relatively small and future work is recommended to extend this comparison.

LIMITATIONS AND FURTHER WORK
The basis preceding work showed the potential for biomimetic building facades as a means to reduce operational energy consumption and maintain thermal comfort for several climate zones and building types. This result was based on digital designs and modelling, which were subject to assumptions and limitations.
Building on this work, the biomimetic model could be further developed. There are opportunities to develop the model further to include additional effects and increase the accuracy of the Pennes bioheat equation, as in Cena andMonteith (1975a, 1975b), He, Wang andSun (2011), Charny (1992), Weinbaum et al. (1997) and Jiji (2009). Furthermore, the modelling of animal tissue could be varied to account for differences in tissue physiology that are apparent in different species. Potential model frameworks include Parry (1949), Ackman et al. (1975), Lockyer, McConnell andWaters (1984, 1985); Schmidt-Nielsen (1997) and Liwanag (2008).
Furthermore, there are many examples of natural adaption to acute and seasonal weather variation. Such dynamic response represents a potentially powerful direction in which to further develop the biomimetic facades. There are also opportunities to adapt and optimise fur and perfusion properties to suit specific locations. Heating optimisation would benefit the results obtained for the Dfb climate, while in tropical climates, management of air moisture content is important. Preliminary heating optimisation preliminary heating optimisation study was conducted for a fur-lined façade during winter heating in Melbourne, Australia (Webb, Hertzsch & Green 2011). Addtionally, nature-inspired initiatives to remove moisture from the air could be investigated, e.g. trees that remove fog from the air (Goldsmith, Matzke & Dawson 2013) and species of orchid that absorb moisture from a humid atmosphere (Zotz & Winkler 2013).
As highlighted in the results, it was apparent that the performance improvement achieved by the biomimetic façade was dependent upon the load balance. When building envelope loads were dominant, the greatest energy reductions were achieved. However, in situations with lower impact of building envelope heat loads, smaller energy reductions were achieved by the biomimetic facades. Additional investigation may be conducted to identify nature-inspired characteristics to improve latent heat management and ventilation heat exchange. For example, respiratory heat exchange in vertebrates Schmidt-Nielsen, Hainsworth and Murrish (1970), counter current heat exchange in elephant seals (Huntley, Costa & Rubin 1984) and brain heat flow management in Thomson's gazelles (Taylor & Lyman 1972).
The comparison between biomimetic facades and alternative energy efficiency initiatives indicated that biomimetic designs could achieve a significantly greater energy reduction. However, the sample size for alterative studies was small, and not all climate zones or building types were included. Still, the biomimetic scenarios showed similar performance results regardless of the building or climate category. This study focussed on the performance capability -energy reduction -potential for a biomimetic building skin. Further work is necessary to understand the economic feasibility of such building initiatives. While, as noted in the Introduction, there have been studies that have investigated applications of biomimicry to architecture and building skins, little emphasis has been placed on the economic feasibility and constructability. Exploration architecture have proposed a high-performance office building employing a number of biomimetic features, however the project remains at a design stage (The Biomimetic Office Building 2021). (2017) proposed a Bayesian Network as a method to organise complex decisions involved in applying biomimicry to building design, however they focussed technical requirements rather than economic considerations. Broader studies have suggested an increasing development and application of biomimetic innovation in multiple industrial sectors, however there is a gap in research on specific economic feasibility of specific biomimetic initiatives for architecture. Smith et al. (2015) identifies biomimicry as a burgeoning innovation opportunity, and identifies research, development and production in nine industrial sectors, noting that developments in carbon, water, materials, energy conversion and storage, fluid dynamics, data and computing and systems analysis all have potential application to buildings. However, these technologies, especially those currently in development or available in the market are mostly component and materials-based. The study does not investigate these technologies in the context of a construction project. In the same study, the authors site research by Fermanian Business & Economic Institute estimated that bioinspiration could account for $425 billion in US GDP and 2 million jobs. A large proportion of benefit is estimated for the building sector (approximately $70 million) however feasibility of individual technologies is not specified.

Chayaamor-Heil and Hannachi-Belkadi
Other researchers have investigated the funding, financing and policy incentives for sustainable, higher-performing buildings. For example, Diwekar (2015) suggests a more holistic perspective is required for engineering sustainability. Chen and Hong (2015) indicate that, from a Chinese perspective, subsidies do play a role in incentivising green buildings, and that improving information flow will contribute to more green building, while Staniškis and Stasiškienë (2003) presented a model for facilitating cleaner production incentives in developing countries. Finally, Muo and Azeez (2019) took a broad view of green entrepreneurship and the factors influencing businesses to maintain "business-as-usual practices", concluding that while benefits of green entrepreneurship are enormous and it has a role to creating a sustainable green economy, there are several concerns preventing more widespread adoption, such as inclusiveness and greenwashing. The authors suggest that change management should be a future focus for green entrepreneurship. The development of high performance biomimetic façades must contend with these societal and economic conditions to be a viable option in future construction. Opportunities should be sought for governmental green financing and newer investment pathways.

CONCLUSIONS
The concept of biomimicry -"innovation inspired by nature" -has been adopted in multiple technological and engineering fields as a framework for innovation and improvement. This study tested the hypothesis that the animal fur-perfusion façade design would perform at least as well to improve building services energy efficiency in different climate zones and for different building types. Results showed the biomimetic façade had strong potential to reduce energy consumption in all different climate zones and in all building types, when compared to the associated reference cases (conventional façade design) and when compared with the initial study of an office building in a temperate climate. Furthermore, with one exception (heating in the cold Dfc climate zone), the biomimetic façade showed a decrease in dynamic peak heating and cooling demand. The physical characteristics of the fur lining to provide extra insulation and a barrier to incoming solar radiation, in combination with the water-based perfusion inside the façade, were effective in improving the building envelope energy efficiency.
The observed improvements in energy efficiency and peak heating and cooling loads did vary in magnitude and proportion across the climate zones and building types. In each alternative climate zone, the percentage energy reduction achieved over a reference baseline was greater than in the original study for a Cfb climate. With colder temperatures, the Dfb climate zone had the greater absolute decrease in the services energy consumption (3,241 kWh, or 55.1%). The greatest percentage decrease was achieved in the tropical Aw climate (3,112 kWh, or 55.4%). When testing peak cooling, the tropical Aw climate also had the greatest reduction of 51%. In all of the climate zones, the magnitude of the energy decrease was greater than that for the baseline, temperate, Cfb, climate zone.
In building types, the Aged Care simulation showed the greatest potential for energy savings, with a 67.1% reduction over the reference, the Education type indicated a 42.6% reduction compared with the original Office study at 46.2%. As with the climate zones, these results indicate that the original study hypothesis was confirmed. There was a significant improvement in heating consumption in all three building types, owing to the insulative effect of the building fur and efficient water-based heat transfer from perfusion.
The proposed fur-perfusion façade was compared to other energy simulation studies focussed on building envelope energy efficiency or upgrades. This comparison indicated that the furperfusion facade performed statistically better in energy reduction that alternatives, however the sample size was limited.
These results confirmed the study hypothesis that the biomimetic façade design would perform at least equivalently in different climate zones and building types. Using this case study, the research has demonstrated the potential for biomimetic facades to have a substantial impact on the performance of building envelopes to decrease energy consumption and peak demand across multiple climate zones and building types. Additionally, the research demonstrated viable mathematical modelling and building simulation methods that could be applied for alternative biomimetic initiatives for building facades. Further work to investigate the production potential, physical validation and economic feasibility will strengthen the case for application of the fur-perfusion facades to decrease the energy footprint of buildings.