Achieving an energy-neutral building stock by 2050 requires sustainable energy-efficient renovation of facades. Conventional renovation with thick insulation reduces heat losses, but demands large material quantities, particularly when meeting high thermal performance and low U-value standards. Sustainable solutions should combine energy efficiency with resource conservation, low-carbon material cycles, and reduced gray energy. Dynamic exterior wall temperature control offers such a solution by active heat flow management. The EnergySkin project is developing a facade module for energy-efficient renovation. This module will integrate an electrically conductive coating for heating and photovoltaic in an insulating glass unit, which will be mounted on an existing opaque facade as part of a modular system for serial installation. The configuration enables active external wall temperature control whilst generating the necessary electrical power itself, thereby minimizing the heating demand and primary energy consumption of the building without additional CO2 emissions. The system is being extensively investigated with respect to its thermal and electrical functionality, operating modes, and the integration of an electrical storage unit. Preliminary laboratory and component-scale tests have confirmed the feasibility of coupling transparent conductive coatings with insulating glass to achieve both passive insulation and active heating. Simulations demonstrate that integrated photovoltaic can cover the overall operational energy demand, enabling energy self-sufficiency. These findings highlight the potential of dynamic facade systems to surpass conventional insulation approaches by incorporating adaptability, renewable heat generation and circular design principles. Consequently, the project contributes to sustainable refurbishment strategies and supports climate-neutral building targets.
active facadedynamic systemenergy-efficient renovationexternal wall temperature controlphotovoltaicBundesministerium für Wirtschaft und Klimaschutz10.13039/100021130The author(s) declared that financial support was received for this work and/or its publication. This work was carried out as part of the research project EnergySkin funded by the Central Innovation Program for SMEs (German: Zentrales Innovationsprogramm Mittelstand, ZIM) by the Federal Ministry for Economic Affairs and Climate Protection (grant number: 16KN113621).section-at-acceptanceSustainable Design and ConstructionIntroduction
Based on the European Union’s commitment to achieve a climate-neutral building stock by 2050, as outlined in the Energy Performance of Buildings Directive (European Commission, 2024), Germany has established even more ambitious targets, aiming for carbon neutrality in the building sector by 2045. With regard to these European and national goals for achieving an energy-neutral building stock, the energy-efficient refurbishment of facades is of central importance (BMUB, 2016). The common practice involves installing thermal insulation on the outer shell of the building in order to reduce heat flow. Depending on the retrofitting measures and requirements profile, this approach results in high resource consumption due to the thickness of insulation material required. If this approach is maintained, the material required for insulation will increase steeply in the future as energy efficiency standards become more stringent. However, resource efficiency should always be considered in the context of sustainable buildings. This also goes hand in hand with the extraction of low-carbon materials and the reduction of gray energy. For this reason, research into alternative insulation solutions is increasingly being conducted in the construction industry (Almesbah and Wang, 2025; Gonçalves et al., 2024). One solution for this is dynamic external wall temperature control.
The following technologies and fundamental concepts are applied in this context:
Dynamic technologies have variable properties, while static technologies are characterized by stable properties (Michael et al., 2023). For example, thermal resistance in static systems is fixed regardless to weather conditions or user needs. Dynamic facade technologies expand the potential for reducing resource consumption, as they can have actively variable thermal resistance (Gonçalves et al., 2024). Passive systems, use material properties and associated physical effects to respond independently to weather conditions. Active systems use electrical control or controls to adjust their properties. They can be self-sufficient with integrated energy generation or draw additional energy from other systems. If a system is switchable, it has exactly two possible states, while a variable system either has several stages or can adjust its properties continuously within a range (Karanafti and Theodosiou, 2023). Finally, the systems can be distinguished by their application–heating or cooling–in which the dynamic function comes into play. They then behave like a static technology in the other operating mode or exhibit a dynamic function throughout the year (Karanafti et al., 2022).
While dynamic passive systems, like phase change materials (PCMs) are less technical complex and easier to construct they have the disadvantage that their phase transition temperature is predetermined during manufacturing and cannot be adjusted to changing climate conditions or occupancy demands, which can restrict their effectiveness under varying operating conditions. (Togun et al., 2025).
Through external wall temperature control, the heat flow in the building component is actively controlled and heat losses through the facade are minimized. The system helps to reduce the heating energy requirement and thus actively contributes to lowering the primary energy demand of a building and to reducing greenhouse gas emissions in the building sector.
Current dynamic façade research mainly focuses on adaptive shading or ventilation strategies rather than direct heat flow control through opaque elements (Gonçalves et al., 2024). Additionally, the amount and type of power supply for the modules has rarely been clarified, but is crucial for evaluating efficiency (Karanafti et al., 2022). While external wall heating systems exist, they remain limited in scope and integration. The LEXU II project (2022) demonstrated the feasibility of externally mounted surface heating using low-temperature water circulation coupled with heat pumps, yet required external grid electricity without photovoltaic integration. Furthermore, component demountability and end-of-life separability are absent. While the use of photovoltaic modules in façades is increasing, the electricity generated by such systems is typically fed into the building’s general electrical network or the grid and used in a decentralized manner, rather than being directly coupled to façade-integrated thermal functions (Abojela et al., 2023).
This highlights a technological gap in dynamic façade systems for renovations that combine thermal activation with system-integrated renewable energy provision, reversible mounting for fast and simple serial installation, and resource-efficient construction that enables end-of-life separation and circular material use.
EnergySkin research project addresses this gap through a demountable facade system that integrates: (1) system-integrated photovoltaics and optional battery storage for energy autonomy, (2) resistive heating coatings embedded in glazing for thin, transparent active thermal conditioning, and (3) demountable plug-and-play modules allowing full material separability at the end-of-life. For the heating layer, a contacted low-E coating is being pursued. Thermochromic coatings and advanced switchable glazing systems are not suitable as they are not delivering controllable thermal output. No existing system achieves this comprehensive integration of energy neutrality, active heat flow management, and circularity that is suitable for renovating existing facades.
Accordingly, the presented research project addresses the following question: To what extent is the development and implementation of an energy-neutral, demountable facade system integrating photovoltaic energy generation and coated glazing for active wall temperature control technically achievable for the sustainable refurbishment of existing buildings, considering its technical performance, energy balance, and material circularity?
This paper provides an overview of the EnergySkin concept and presents the objectives, design principles, and planned research activities to assess its technical feasibility and sustainability potential.
MethodologyBuilding physics
To provide the theoretical foundation for the following investigations, the underlying building physics principles are outlined below.
Heat passes through a building component from the higher to the lower temperature level. In terms of thermal insulation in winter, transmission losses occur through the building envelope from the interior to the exterior. The U-value, or heat transfer coefficient, is conventionally used as a measure of the thermal insulation quality of a building component (DIN EN ISO 6946, 2018). Under a steady-state temperature difference, Δθ, and a constant thermal transmittance, U, a constant heat flux density is established across the building component. This heat flux, q, can be described, in one dimension, as:qComponent→=U·Δθ=ΔθRTotal
For a single layer of material, the heat transfer depends on thermal conductivity, λ, layer thickness, d, and layer boundary temperatures, T1 and T2. This results in the stationary heat flow through the layer (DIN EN ISO 7345, 2018):qLayer→=T2‐T1RLayer=λT2‐T1d
According to the principle of energy conservation, the stationary heat flow through a layer is equal to the heat flow through the entire component:qComponent→=qLayer→
Formulas 1–3 result in the conventional approach to thermal insulation, which involves the application of a thick insulation layer with a low thermal conductivity.
An alternative approach may be to manipulate the heat flow by introducing additional thermal energy inside the component. The steady-state assumption according to Formula 3 therefore no longer applies. Instead, the relationship between the heat flows and the amount of heat introduced, q', can be generalized by Formula 4:qHeatsource,environment→‐qInterior,Heatsource→=q′
The heat flow from the heat source to the exterior can be described analogously to Formula 2. The decisive factor is the temperature at the location of the heat source. Increasing the introduced heat elevates the temperature at the heat source. Consequently, the introduced heat has to compensate a reduced heat flow qInterior, Heatsource simultaneous to an increased qHeatsource, Exterior, leading to a state of equilibrium described by Formula 4. Figure 1 shows the relationships between the heat flows and temperatures under stationary conditions. In this case are qInterior, Heatsource: q1 and qHeatsource, Exterior: q2.
Relationships between heat flows and temperatures under stationary conditions.
Three side-by-side diagrams compare wall heat transfer: without external wall temperature control, with control, and using the EnergySkin system. Each shows layers, heat flow directions, temperature drops, and resistances. The first two use traditional walls; the third includes an air gap and facade module. Colored lines illustrate temperature profiles, with solid and dashed lines for different control states. Arrows indicate heat flow. Annotations define symbols for heat flow, temperature, and thermal resistance, and label each material layer and control measure for context.
The generated heat decreases the temperature difference from the interior to the position of the heat source compared to the scenario without the heat source. This effect is the external wall temperature regulation. Since the heat flow is, according to Formula 2, dependent on the temperature difference, a heat source in the building envelope therefore enables a reduction in transmission heat losses from the interior. The above considerations one-dimensional and required a heat source with a homogeneous surface area. One approach to this is the use of electrical surface resistance. An electrical conductor exhibits resistance to current flow when an electric field is applied (Ose, 2022).
The resistance of a conductor is determined not only by the material, which is taken into account by a material constant, but also by the length, and the area. If we assume that the surface resistance of a layer is that of a cuboid with a constant height made of a homogeneous material, then the aspect ratio alone determines the electrical resistance. The resistance converts electrical energy completely into heat energy (Paul and Paul, 2022).
It follows that a building envelope system is possible which extends the effect of reducing transmission heat loss from inside the building beyond insulation, by incorporating an electrical surface resistance as a heating layer for external wall temperature control.
Investigated system
The EnergySkin system adopts the proposed concept as an energy-neutral refurbishment solution. In addition to energy neutrality, the design targets resource efficiency, circularity, and disassembly, while maintaining durability and structural reliability. The system (Figure 2) comprises two principal components: the facade module and the mounting system. The facade module integrates three functional layers—photovoltaic (a), thermal insulation (b), and an active heating layer (c) whereas the mounting system provides the mechanical interface to the existing building envelope and incorporates control elements as well as electrical storage.
3D visualization of the EnergySkin facade system (Picture: Dobler Metallbau GmbH).
Exploded technical illustration of a wall section showing a facade module with insulating glass, featuring photovoltaic coating, argon-filled interspace, and active heating layer, alongside mounting system components like concealed cable routing, masonry, cover profile, EPDM seal, and boundary-dependent fixing.
The facade module is based on a double-glazed insulating unit with an argon-filled cavity, which reduces transmission heat losses through passive insulation. For the active heating, conductive transparent coatings - such as silver or transparent conducting oxides - are applied to the glazing. Such coatings are primarily used as low-emissivity (Low-E) layers in thermal insulation glazing in conventional facade constructions due to their high infrared reflectivity (Abundiz-Cisneros et al., 2020; Khaled and Berardi, 2021). When the coating is contacted and electrically powered, the resulting current flow causes heat generation within the layer due to its ohmic resistance behavior. Installed on the exterior of a facade without additional insulation, this heating layer transmits heat from the outside inwards, while the insulating glass simultaneously minimizes heat losses to the ambient environment, consequently reducing the building’s transmission losses and overall heating demand.
To ensure the desired energy neutrality, the required operating electricity must be provided in a system-integrated manner. This is achieved by integrating photovoltaic cells into the second facade layer. The use of organic photovoltaic (OPV) offers up to 89% lower life cycle impacts compared to crystalline silicon photovoltaic (c-Si PV), while also offering low non-renewable energy consumption during manufacturing (Cellura et al., 2023; Tsang et al., 2016). Additional advantages, including low production costs, high mechanical flexibility, low weight, and partial transparency are counterbalanced by low efficiency and temperature instability (Farooq et al., 2021). Battery storage is used to ensure that, in cases of insufficient photovoltaic yield, the surplus energy from periods of excess production is utilized to maintain operation.
The mounting system ensures a durable yet detachable attachment of facade modules to the existing structure, allowing for material separation at end-of-life. This design clearly distinguishes the system from conventional refurbishments using fully adhered external thermal insulation composite systems, which typically do not allow for easy disassembly. A plug-and-play principle enables efficient installation of prefabricated modules with minimal on-site effort, characterized by flexible, repositionable, and releasable dowel or screw connections. A key requirement and research subject is the avoidance of thermal bridges, which could otherwise compromise the effectiveness of the active heating.
Within the research project, industrial and academic partners collaborate to address the various tasks and complexities involved in developing the multifunctional facade system. A primary challenge lies in the integration of heating coatings and photovoltaic elements into insulating glazing while ensuring long-term compatibility, durability, and material separability. Recent research findings highlight that enabling the glass components to be removed from the insulated glass unit, recycle and even reuse them can significantly reduce the embodied carbon emissions, which supports the sustainable life cycle management of facade materials (Reshamvala et al., 2024). The system demands the incorporation of thermally and structurally effective connections between modules and the existing building envelope. These connections must be designed to prevent the formation of thermal bridges. Comprehensive investigations are carried out, ranging from numerical simulations of thermal, structural, and energy performance to laboratory and full-scale tests of material behavior and facade functionality. Additional studies address environmental performance through life cycle assessments and optimization and quality assurance throughout the development process. Additionally, a balance between functionality and resource efficiency must be achieved to ensure a sustainable and economically viable application. Improvements in thermal performance, such as a lower U-value and higher heating layer temperatures, must be carefully weighed against the reduction of raw material consumption and the minimization of environmental impacts. The research partners aim to identify and implement the optimal balance of these parameters.
DevelopmentPreliminary investigations
Preliminary experimental investigations focused on the coupling between the heating layer and the organic photovoltaic. For this purpose, a glass pane with heating layer was connected to four vertically mounted, commercially available OPV modules. The modules were connected in parallel without optimization with an MPP-tracking. The area ratio between the photovoltaic modules and heating layer was 3 to 1. To ensure that the heat generated resulted in a measurable temperature difference, the glass pane was insulated on all sides. The thermal resistance to the backside was 8.5 m2K/W, to the edges 2.3 m2K/W and to the heating layer 1.1 m2K/W. The average measured horizontal irradiation was 235 W/m2, which resulted in an average measured heating power of 10.5 W/m2. After a period of 5 h, a temperature difference of 4.4 K was measured in the center of the pane. The experiment was terminated when the photovoltaic system was completely shaded. In the event of prolonged solar exposure, a greater increase in temperature would be expected, as no state of equilibrium was detected.
Due to the high thermal resistance on the rear side of the glass pane and the small surface area of the edges, the heat flow from the heating surface is assumed to be one-dimensional and linear as a function of temperature difference. Consequently, in conjunction with the scaling of the photovoltaic output, a temperature increase of 2.5 K is assumed for a ratio of 1:1 between the heating surface and the photovoltaic system. Since this measurable temperature increase was observed, this confirms that the generated power is adequate to have an effect, justifying further, more detailed investigations.
Conducted researchLow-E coating
Various contacting techniques for low-E coated glass were investigated experimentally, as shown in Figure 3, and theoretically during the development of the glass module. The contacting techniques can be divided into cold (electroplating, conductive adhesive, digital printing of conductive inks, etc.) and hot (laser welding, ultrasonic soldering, ultrasonic welding) contacting. In hot contacting, additional heat is introduced into the process.
Examples of differently contacted low-E− coated glass.
Four close-up photographs compare electrical contact techniques: baked-in conductive silver paste, copper tape with conductive adhesive, ultrasonic soldered contacts, and bonded solder strip, each showing a metallic strip joined to a surface using the described method.
The investigations showed that successful contacting is highly dependent on the type of low-E coating. Classic low-E coatings made of silver have protective layers to prevent sulfidation and oxidation. These protective layers are not electrically conductive. Cold contacting therefore requires the removal of the protective layers. Due to the unknown exact layer structure on the glass, attempts to remove the protective layers were unsuccessful. Contacts were therefore only successfully established by ultrasonic soldering and by baking in conductive pastes. The contacts of the baked-in conductive were brittle and consequently failed mechanically due to the stresses of the measurements. In addition, they had an electric resistance of 1.4 kΩ with a diagonally contacted silver coatings of 0.2 by 0.3 m. For comparison the ultrasonic soldered contacts had an electrical resistance of 12–14 Ω. Ultrasonic contacted silver coatings revealed that strip-shaped contacts promote a more homogeneous temperature distribution. Small-area contacts or few contacts lead to the formation of hot spots.
As an alternative to low-E coatings made of silver, coatings made of aluminum-doped zinc oxide (AZO) were investigated. AZO coatings do not require additional protective layers and can therefore be contacted directly. Contact is made with conductive adhesive using copper tape. The electrical surface resistance of the AZO coating was measured at around 15 Ω. The measured temperature distribution is largely homogeneous. A drop in temperature is evident at the edges and especially in the corners. AZO coatings with strip-shaped contacts promise the best potential for the system and will be used for continued development.
Energy balance
For the calculations and simulations performed, a U-value of 1.2 W/(m2K) is assumed for the walls of existing buildings, based on the non-residential building research database of the Institute for Housing and the Environment (IWU) (Hörner and Bischof, 2022), representing the vast majority of non-residential buildings in need of renovation in Germany.
The target value after successful renovation for the entire wall structure, including the EnergySkin module, is the minimum U-value of 0.24 W/(m2K) prescribed by the German Building Energy Act (Bundesministerium für Wirtschaft und Energie, 2020). However, as long as this is feasible within the scope of a resource-saving and sustainable solution, the project aims to achieve an equivalent U-value of 0.15 W/(m2K), in line with the passive house standard.
Figure 4A shows the power requirement of the heating layer in the case of renovation. The boundary conditions were selected in accordance with DIN 4108-3 (2024) Table A.3, with 20 °C designated as the indoor temperature and −5 °C designated as the outdoor air temperature. To achieve a layer temperature of 16.5 °C, the heating layer requires a power of 26 W/m2 to reduce the heat flow from inside the room to the same level as a conventional renovation with a U-value of 0.15 W/(m2K), which is comparable to a Passive House (PH). As derived in Formula 4 the heat flow from the heating layer to the outside is the sum of the required power of the heating layer and the remaining heat flow through the existing wall from inside the room.
(A) Power requirement of the heating layer. (B) Energy balance of EnergySkin.
Line chart displays heating layer temperature and power requirement versus equivalent U-value, highlighting GEG at zero point two four and PH at zero point one five. Bar chart below shows monthly energy balance by orientation, using green for positive and red for negative values, with winter and early spring predominantly negative across north, east, south, and west orientations.
The results of simulations of crystalline and organic photovoltaic over the reference year data provided by the German weather service provide results for expected energy yields depending on the orientation of the photovoltaic at various locations throughout Germany. The annual total for a south-facing, unshaded orientation in Cologne amount to 54 kWh/m2 for OPV and 196 kWh/m2 for c-Si PV. When facing east, the energy output of the c-Si PV is 144 kW/h, when facing west it is 146 kW/h, and when facing north it is 71 kW/h. C-Si PV generates approximately four times the energy output of OPV, regardless of the respective orientation. In comparison, the OPV is characterized by higher performance in low-light conditions and at smaller angles of incidence. This characteristic makes it particularly beneficial for facade applications, as it leads to higher yields in the morning and evening hours.
Preliminary results demonstrate an energy requirement for the heating layer of approximately 25 kWh/m2 per year. These results were obtained by simulating a one-dimensional model of the thermal transmittance through the building envelope in the simulation tool IDA ICE. Selected climate boundary conditions were semi stationery and site specific. The indoor temperature of 20 degrees Celsius was assumed in accordance with DIN 4108-3and a temperature setback of 4 K between 18:00 and 7:00 h, as well as all day Saturday and Sunday, following DIN V 18599-10 (2018). The outdoor conditions were chosen as reference year data for Cologne, Germany analogous to the simulation of the photovoltaic. The temperature of the heating layer is regulated by a two-point controller with a target temperature of 3 K ± 0.5 K below the indoor temperature. The material values of the building envelope layers where set based on DIN EN ISO 10456 (2010) and DIN EN 673 (2025). Further more detailed description of the undertaken simulation as well as in depth discussion of the results are published in Stoppel et al. (2026).
For the investigated scenario the demand values of the heating layer can therefore be effortlessly met by the annual yield values of the photovoltaic. Figure 4B shows the daily energy balance when using c-SI PV. For the south-facing orientation, there are only a few consecutive days on which energy demand exceeds yield. The electrical storage system must now be designed to provide the energy at the right time, thereby enabling an energy-neutral operation of the system. The key factors influencing the potential of EnergySkin to achieve a positive energy balance are the incident solar radiation, the ambient outdoor temperature, and the setpoint temperature of the heating layer, which determines the intensity of the external wall temperature regulation.
Mounting system
The development of the EnergySkin mounting system focused on structural adaptability, thermal performance, and prefabrication. To allow installation under varying on-site conditions, the system accommodates multiple fastening methods and tolerances of ±20 mm in line with DIN 18202 (2019). This ensures reliable attachment to different substrates, including masonry with penetrations for cabling and sensors.
Two facade system approaches were investigated: unitized element facades and post-and-beam facades. The utilization of these concepts facilitates the implementation of exchangeable glass modules and scalable dimensions. Unitized systems integrate continuous thermal breaks into profiles, whereas post-and-beam solutions employ mechanically fixed separators. Numerical simulations confirmed that both configurations avoid thermal bridging and condensation in the studied system.
The mounting system was designed to hold insulating glass units of varying configurations (double, triple, stepped, or structural sealant glazing). In order to prevent damage to the glazing, proper ventilation at the rebate was incorporated. The integration of protected cable routing with plug connections facilitates the seamless integration of sensors and electrical components as part of the plug-and-play concept.
The system relies on DGNB-compliant materials that are separable and carry a verifiable CO2 footprint, with all components designed for disassembly and recycling except for the sealing compounds (DGNB, 2025). Altogether, the mounting system ensures high prefabrication potential, secure thermal separation, modular adaptability, and material circularity, thereby enabling standardized energy-neutral facade renovations.
Control and storage concept
The conceptualized electrical system essentially comprises the heating coating as a consumer, photovoltaic as a generator, and an electrical storage unit. It is intended as a stand-alone solution with direct current in the low-voltage range. Energy requirements are primarily covered directly from generation. In the event of increased demand or insufficient yield, the storage unit provides support or takes over the supply completely. If there is no demand or surplus yield, the storage unit is charged. MPP tracking increases the efficiency of the photovoltaic (Gupta et al., 2024), a bidirectional DC/DC converter maintains the constant load voltage (Alazrag and Sbita, 2023) and an battery management system protects the storage unit from overcharging or deep discharge (Rahimi-Eichi et al., 2013).
The control of the heating layer is crucial for the thermal behavior of the system and energy consumption. Two-point control of the heating layer temperature is the simplest control concept. A temperature sensor is used to measure the temperature of the heating layer. If the temperature is below the lower boundary of a specified temperature interval, the heating layer is activated via the controller; if it is above the upper boundary, it is deactivated; and if it is within the interval, the current state is maintained. Different control concepts could include the outside air temperature or room temperature, use different target variables, e.g., a temperature difference, or use different controllers like a PID controller. Due to the low complexity a two-point control is used for the first investigations as the behavior of the heating layer is easily predictable and the heat flux through the existing facade is limited to a maximum value. In terms of dynamic facades, this is therefore a switchable system with a heating function. In summer, EnergySkin behaves like a passive facade. The final selection of the control will be based on the simulation of the control loop and the resulting quality criteria like response time, accuracy and stability.
As a stand-alone solution, efficiency, operational reliability, and service life are more important than in grid-connected systems, as there is no fallback option. In addition to these system requirements, the project requirements stipulate that the storage solution should be as sustainable and scalable as possible. Various storage technologies were evaluated, with lithium-ion types (LFP, LTO, NMC) showing the greatest potential and thus are used in the development. Lithium-ion batteries have a high efficiency and long lifetimes, both are the reason they are used in 98% home storage systems and in 95% of industrial storage systems (Figgener et al., 2022). To approximate the required storage capacity per square meter the simulation results for the energy balance are used. The number of days with the depleted storage is evaluated for capacities of 0.48 kWh, 0.72 kWh, 1.20 kWh, 2.40 kWh and 4.80 kWh. For east, west or north facing facades no considered capacity is sufficient to ensure operation of the heating layer. For a south facing façade a capacity of 1.20 kWh or greater enables continuous operation, while the storages with a capacity of 0.48 kWh and 0.72 kWh are depleted 9 and 2 days respectively. Further optimization of control strategies aims to achieve feasibility of an energy storage with a capacity of 0.72 kWh.
Life cycle assessment
The objective of the research is to develop a facade system that results in a balanced or positive life cycle assessment compared to conventional reference building. All life cycle phases (modules A–D) are evaluated in accordance with DIN EN 15978 (2012). During production, the material consumption, process energy, and emissions are assessed as is the case with conventional static thermal insulation. The same applies to transport and installation. In the use phase (Module B), however, the calculation methodology differs: unlike passive insulation, the EnergySkin system has active components. Its operation requires electricity, which is intended to be supplied by the integrated photovoltaic, ensuring an energy-neutral performance. Additionally, surplus electricity can be fed back into the grid thereby improving the life cycle balance.
The integrated wall heating reduces thermal transmission losses through the facade if activated, thereby lowering the building’s heating demand. The overall results are strongly dependent on the chosen reference building and its heating system: the less sustainable the energy supply, the greater the relative benefits of EnergySkin.
At the end of its service life, the facade modules and mounting system can be dismantled. In contrast to conventional insulation, which typically is thermally utilized, EnergySkin allows for extensive material recovery and reintegration into circular material cycles. Detailed research results on life cycle analysis will be published in subsequent publications.
Summary
The goal is to develop a system that serves as an easily installable, durable, and resource-efficient alternative to conventional insulation, while offering superior adaptability to climate changes and extreme temperature fluctuations.
The initial results of the EnergySkin project highlight the potential of external wall temperature control through the integration of insulating glass with a heating coating and photovoltaic. The low-E coating was successfully contacted and heated, showing technical feasibility. Simulations demonstrated sufficient photovoltaic yield throughout the year. This allows the system to function as an alternative to conventional insulation whilst convincing with its slim and sustainable design. In addition, EnergySkin could have a positive effect on summer heat protection, as it has a lower heat capacity and higher passive thermal transmittance in comparison to conventional insulation, allowing the building to cool down at night. The conducted research indicates the site-specific factor of the climate conditions as well as the control strategy and targeted intensity of the wall temperature regulation as key for the viability from an energy perspective.
Finally, the findings of this study can be related back to the literature on adaptive façades, BIPV, and façade-integrated heating to clarify EnergySkin’s specific contribution. Transparent conductive coatings are still in use but augmented in their functionality adding the benefit of switchable heating. Facade-integrated photovoltaics satisfies the energy-demand in a sustainable way, but functions without additional connection to the building or the grid, but trusts in local energy storage. In contrast to other active thermal systems such as solar-thermal collectors or water-based façade heating, EnergySkin relies on emissive and conductive energy transfer within the glazing and avoids the use of additional transport media. This eliminates the need for pumps, piping, fluid mass, and associated seals and fittings, thereby reducing maintenance requirements and aligning the concept with a low-tech, lightweight, and materially efficient design approach.
In regards to the viability of EnergySkin from a standpoint of sustainability the key indicator is the life cycle assessment. For a final evaluation of EnergySkin the energy use has to be optimized with investigations of control strategies including energy storage. The used materials and products have to be finalized, while finding a balance between efficiency, circularity, and architectural design. Additional investigations on concise life cycle performance, diverse building geometries, different constructions, and site-specific conditions, like climate and shading scenarios will be conducted to allow an extensive assessment. At the same time, its practical feasibility is being evaluated and tested.
Data availability statement
The datasets presented in this article are not readily available because the research project is ongoing. Requests to access the datasets should be directed to clara.uhlig@tu-dresden.de.
Author contributions
CU: Conceptualization, Data curation, Formal Analysis, Funding acquisition, Investigation, Methodology, Visualization, Writing – original draft, Writing – review and editing. MS: Conceptualization, Data curation, Formal Analysis, Investigation, Methodology, Visualization, Writing – original draft, Writing – review and editing. ME: Conceptualization, Funding acquisition, Methodology, Project administration, Supervision, Writing – review and editing. PD: Conceptualization, Funding acquisition, Methodology, Project administration, Supervision, Writing – review and editing, Investigation.
Acknowledgements
The authors would like to thank the project partners Dobler Metallbau GmbH and Flachglas Sachsen GmbH for their excellent work and cooperation.
Conflict of interest
The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Generative AI statement
The author(s) declared that generative AI was not used in the creation of this manuscript.
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Edited by:Marios C. Phocas, University of Cyprus, Cyprus