Ventilated Facades for Low-Carbon Buildings: A Review

Abstract

The construction sector presently consumes about 40% of global energy and generates 36% of CO₂ emissions, making facade retrofits a priority for decarbonising buildings. This review clarifies how ventilated facades (VFs), wall assemblies that interpose a ventilated air cavity between outer cladding and the insulated structure, address that challenge. First, the paper categorises VFs by structural configuration, ventilation strategy and functional control into four principal families: double-skin, rainscreen, hybrid/adaptive and active–passive systems, with further extensions such as BIPV, PCM and green-wall integrations that couple energy generation or storage with envelope performance. Heat-transfer analysis shows that the cavity interrupts conductive paths, promotes buoyancy- or wind-driven convection, and curtails radiative exchange. Key design parameters, including cavity depth, vent-area ratio, airflow velocity and surface emissivity, govern this balance, while hybrid ventilation offers the most excellent peak-load mitigation with modest energy input. A synthesis of simulation and field studies indicates that properly detailed VFs reduce envelope cooling loads by 20–55% across diverse climates and cut winter heating demand by 10–20% when vents are seasonally managed or coupled with heat-recovery devices. These thermal benefits translate into steadier interior surface temperatures, lower radiant asymmetry and fewer drafts, thereby expanding the hours occupants remain within comfort bands without mechanical conditioning. Climate-responsive guidance emerges in tropical and arid regions, favouring highly ventilated, low-absorptance cladding; temperate and continental zones gain from adaptive vents, movable insulation or PCM layers; multi-skin adaptive facades promise balanced year-round savings by re-configuring in real time. Overall, the review demonstrates that VFs constitute a versatile, passive-plus platform for low-carbon buildings, simultaneously enhancing energy efficiency, durability and indoor comfort. Future advances in smart controls, bio-based materials and integrated energy-recovery systems are poised to unlock further performance gains and accelerate the sector’s transition to net-zero. Emerging multifunctional materials such as phase-change composites, nanostructured coatings, and perovskite-integrated systems also show promise in enhancing facade adaptability and energy responsiveness.

1. Introduction

The construction industry is one of the largest contributors to global energy consumption and greenhouse gas emissions, accounting for approximately 40% of total energy use and 36% of CO₂ emissions. As urbanisation accelerates and climate change becomes more urgent, sustainable design strategies have come to the forefront across architecture and engineering disciplines. Among these, VFs have emerged as an innovative and effective approach to reducing the environmental impact of buildings [1]. VFs are characterised by a layered wall assembly where an outer cladding is separated from the structural wall by an air cavity. This configuration allows for continuous air movement, facilitated by natural or mechanical ventilation. The system plays a key role in enhancing thermal insulation, managing moisture, and improving indoor comfort, while also contributing to architectural flexibility and aesthetics. Common components of a VF include external cladding, an air gap, insulation, and the main structural wall. Through the stack effect, air circulation within the cavity supports passive cooling and moisture control, reducing heat transfer and condensation risks [2]. Recent advancements have expanded the functionality of VFs through the integration of renewable energy technologies, particularly building-integrated photovoltaics (BIPVs). These hybrid systems not only enhance thermal performance but also generate electricity on-site, contributing to the energy independence and sustainability of buildings. Studies have shown that BIPV-VFs can cover a substantial portion of a building’s energy demand, with some designs achieving up to 50% electricity offset [3]. Furthermore, the development of smart and adaptive materials has added a new dimension to VF systems. Electrochromic and thermochromic technologies enable facades to react dynamically to external environmental changes, optimising daylight use and thermal comfort. Similarly, the use of eco-friendly materials such as bio-based insulators (e.g., hemp or mushroom-derived products) aligns with circular economy goals and reduces the environmental footprint of construction [4,5]. Comparative studies of facade systems reveal that VFs consistently outperform traditional and simple insulated systems in terms of energy efficiency, moisture regulation, and integration with renewable technologies. While traditional facades offer minimal environmental benefits, ventilated designs, especially those incorporating photovoltaic elements, provide a comprehensive response to the challenges of climate-responsive architecture. In light of these advantages, VFs represent a crucial strategy in the transition toward low-carbon buildings. Their multifaceted benefits, spanning energy performance, durability, indoor comfort, and environmental integration, underscore their growing relevance in contemporary architecture. Continued research into innovative materials, adaptive control systems, and performance optimisation is essential to unlocking the full potential of VFs in future building applications.

Despite the growing application and technical advancement of VFs, existing literature remains fragmented across specific facade typologies, performance metrics, and climatic contexts. There is a lack of comprehensive synthesis that bridges architectural classifications with thermodynamic performance, system adaptability, and climate-specific design strategies. Moreover, most reviews either focus narrowly on specific facade components or present generalised energy performance without cross-comparative insight into hybrid, passive-active, or multifunctional VF systems. To address these gaps, this review seeks to answer the following research questions: (i) How do different types of VFs, double-skin, rainscreen, hybrid/adaptive, and active–passive, compare in terms of energy efficiency, thermal comfort, and suitability for diverse climatic zones? (ii) What are the critical design and operational parameters that govern the thermal behaviour of these systems? (iii) How can emerging technologies such as BIPVs, PCMs, and smart materials be effectively integrated into VF systems to maximise their sustainability potential? In responding to these questions, the review offers a structured classification framework, presents detailed thermodynamic analyses, and evaluates simulation and experimental studies to provide actionable insights for researchers, architects, and policymakers. The novelty of this survey lies in its integrative approach, linking facade typologies, physical heat transfer mechanisms, simulation validation, and climate-responsiveness within a single unified narrative. By mapping out current knowledge and highlighting areas requiring further investigation, such as dynamic control systems, region-specific performance standards, and lifecycle assessments, this paper contributes a foundational reference for advancing VF research and guiding future innovation toward net-zero building design. To ensure the robustness and comprehensiveness of the review, relevant studies are identified through systematic searches of Scopus, Web of Science, and Google Scholar databases. The search strategy employed keyword combinations such as “ventilated facade”, “double-skin facade (DSF)”, “building envelope”, “active cooling”, “passive cooling”, “adaptive facade”, and “low-carbon buildings”. Priority is given to peer-reviewed journal articles published between 2010 and 2025, especially those involving experimental validation, simulation-based assessment, or climate-specific applications. Studies are selected based on their direct relevance to thermal performance, system classification, material integration, and climatic adaptability. Through this comprehensive and multi-disciplinary lens, the paper contributes a foundational reference for researchers, architects, and engineers seeking to advance facade technologies in pursuit of high-performance, net-zero buildings.

2. Types of Ventilated Facades

VF systems can be categorised into several types based on their design complexity, functionality, and degree of interaction with the internal and external environments. This section outlines the most common types of VFs used in modern low-carbon architecture [6].

VF systems can be categorised according to various criteria in the literature, depending on their physical structure, air circulation strategy, and functional control capabilities. A widely accepted and comprehensive classification approach involves organising these systems under three main dimensions: structural configuration, ventilation type, and functionality/control strategy. This framework is illustrated in Figure 1.

Structural configuration-based classification refers to the physical arrangement of facade components. Typical examples include DSFs, rainscreen cladding systems, and box window systems, which are defined by the layering of the facade and the presence or absence of an intermediate ventilated cavity. Ventilation type classification focuses on how airflow is generated and maintained within the facade system. Passive systems rely on natural forces such as buoyancy and wind pressure, whereas active systems use mechanical aids like fans or ventilators. Hybrid ventilation systems combine both methods, allowing for automatic switching depending on outdoor environmental conditions. Functionality and control-based classification consider the facade’s ability to respond to dynamic climatic factors. Passive systems are static and non-responsive, while active systems feature controllable elements such as shading devices or operable louvres. Adaptive facades go a step further, utilising sensors, actuators, and even AI-based controls to adjust their behaviour in real-time for optimal performance in daylighting, thermal comfort, and energy efficiency.

2.1. Double-Skin Facades

DSFs offer an innovative design approach that both increases energy efficiency and improves interior comfort, thanks to the ventilation gap between two independent building shells [7]. The gap, which is usually located between the main facade on the inside and the second glass or opaque layer on the outside, is controlled by natural or mechanical ventilation, undertaking functions such as regulating daylight, minimising heat transfer and providing acoustic comfort as shown in Figure 2 [8].

This system, which is preferred in modern buildings, especially in high-rise offices and mixed-use structures, provides both positive effects on energy consumption and significant contributions in terms of environmental sustainability [9]. Studies based on current literature show that DSFs can provide more optimised solutions, in addition to their contribution to energy performance, especially when adapted to climatic conditions. In this context, in the study conducted by Roig et al. [10], the effect of photocatalytic filter panels placed inside a ventilated DSF system on thermal performance was examined in detail. In the study, the ventilation cavity with photocatalytic lamellas was designed to both control solar radiation and improve indoor air quality. According to the simulation results supported by experimental measurements, the system in question reduced indoor temperatures and significantly reduced solar heat gains when integrated with natural ventilation. The authors emphasise that such systems are highly applicable, especially in hot summer and mild winter conditions similar to the Mediterranean climate. In addition, it was stated that up to a 15% reduction in heat flux transmitted to the interior surface was achieved by optimising air movements in the ventilation cavity. This reveals that DSFs not only provide passive energy efficiency but can also be supported by active comfort strategies. Moreover, to ensure the long-term durability and structural integrity of photocatalytic components, future studies could benefit from non-invasive monitoring techniques such as X-ray computed tomography (XCT), enabling the assessment of internal degradation without dismantling the facade assembly. In a study conducted by Ahriz et al. [11], the effects of different DSF configurations on energy consumption in high-rise office buildings located in regions with a Mediterranean climate were examined in detail. In simulation-based analyses, it was reported that significant energy savings could be achieved in buildings by optimising the air gap width and opening ratios. The researchers also emphasised that naturally ventilated systems work more efficiently on south-facing facades. Similarly, Naddaf and Baper [12] analysed the impact of different DSF configurations on building energy performance in Erbil, Iraq, and revealed that natural ventilation-assisted systems significantly reduced cooling loads in summer. The study showed that the positioning of openings in the ventilation shaft and the placement of sun-shade elements directly affected the system efficiency. Another study conducted specifically for the Turkish climate evaluated the thermal performance of DSFs applied in hot climate regions. This analysis, which took into account different material types, air gap thicknesses and facade ratios, indicated that systems applied in appropriate configurations both increased indoor comfort and reduced annual energy consumption by 10% to 18% [13]. Another study conducted by Aksamija [14] compared the thermal, energy and daylight performances of various DSF typologies (box-type, corridor-type and multi-storey) in different climatic conditions. Analyses using Finite Element Analysis, CFD and energy modelling methods showed that DSF systems provide better thermal performance and energy efficiency compared to single-skinned facades. Furthermore, daylight simulations revealed that these systems can reduce indoor lighting requirements. These studies clearly demonstrate that DSFs play an important role in climate-compatible design, going beyond being merely a means of visual aesthetics or passive ventilation.

2.2. Rainscreen Cladding Systems

Rainscreen cladding systems are one of the passive facade strategies that provide protection from external environmental effects and, at the same time, ensure the longevity of the building envelope thanks to the ventilated space created between the facade elements [15]. These systems generally consist of a ventilation gap positioned between a waterproof but vapour-permeable coating layer on the outside and a water-resistant main carrier surface on the inside, as shown in Figure 3 [16]. This air gap retains most of the rainwater coming to the exterior facade. It prevents it from reaching the interior structure, while at the same time contributing to the drying of the building elements by reducing condensation [17].

Rainscreen systems are widely preferred to increase the external facade strength of the building and to maintain interior comfort, especially in regions with humid and variable weather conditions [18]. The basic principle in these systems is that the incoming rainwater is kept on the outer surface of the facade, and the air circulation in the space between the facade elements evaporates and removes the moisture that may reach the inner surface [19]. Therefore, the success of the system is possible by creating a structure that is resistant to water passage while enabling air passage. The effect of rainscreen systems on energy efficiency is directly related to the optimisation of VF designs, in particular. In a study conducted in this field, the effect of different ventilation gap designs on the energy performance of rain screen wall assemblies was evaluated using CFD analysis. In the study, the effects of air gap width, panel placement and opening positions on airflow and heat transfer were analysed in detail. The results obtained revealed that a properly designed ventilation gap significantly limits heat gains from the facade surface, especially in summer, and reduces cooling loads [20]. In another study, the thermal performance of opaque VFs (OVFs) used in hot and humid climate conditions was evaluated. Simulation results revealed that designs that provide bidirectional air outlets reduce solar heat gains by 69% to 75%. This increases the effectiveness of passive cooling strategies, especially in the summer, and reduces dependence on air conditioning systems, thus saving total energy consumption [21]. In addition, in an experimental and numerical study conducted by Fantucci et al. [22], the performance of OVFs in the summer period was analysed through a simulation model calibrated with field measurements. The study showed that by effectively directing natural ventilation, overheating in interior spaces can be prevented, resulting in a significant reduction in energy consumption. These findings prove that rainscreen cladding systems are an important element in sustainable building design, not only in terms of humidity control but also in terms of energy efficiency.

2.3. Hybrid or Adaptive Facade Systems

As passive solutions reach their limits in terms of sustainability and energy efficiency, hybrid and adaptive facade systems are becoming increasingly important. These systems are hybrid structures that can respond dynamically to external environmental conditions and internal space needs, usually consisting of a combination of passive and active components [23]. Hybrid facades are created by supporting traditional DSF or VF systems with technologies such as sensors, actuators, motorised shutters, photovoltaic elements or electrochromic glass. Thus, the facade ceases to be just a static protection element and becomes an intelligent system that instantly optimises the energy performance of the building. Adaptive facade systems are characterised by the physical properties of facade components changing depending on environmental factors such as temperature, solar radiation, wind speed, and daylight levels [24]. Dynamic panels used in such facades, actuators that can manage facade openings or bio-inspired materials that can change form on their own, optimise the interaction of the system with the external environment. In this way, solar radiation is controlled by panels that move to different positions throughout the day, while interior comfort is maintained and energy consumption is minimised. Many studies in the literature show that adaptive facades significantly increase the energy performance of the building envelope, especially in climate regions where four seasons are experienced distinctly. One of the most comprehensive reviews in this field was conducted by Zhang et al. [25]. The study examined different design typologies, performance evaluation methods, and control systems of adaptive facade systems; it was stated that the systems made significant contributions to reducing energy consumption, optimising daylight use, and reducing carbon emissions. In addition, the researchers emphasised that these systems currently have limited commercial applications; however, technological developments, especially with intelligent control systems and new material technologies, have created new opportunities in this field. Another important study that addresses the general principles of adaptive facade systems from a broader perspective was published by Loonen et al. [26]. The authors systematically analysed the current status and future challenges of climate-sensitive building envelopes; in particular, they revealed that the dynamic adaptation of buildings to outdoor conditions has a direct impact on energy efficiency and indoor environmental quality. In addition, it was stated in the study that the design of adaptive systems can be made more effective by integrating multidisciplinary fields such as energy simulations and control algorithms. Another application that has come to the forefront in recent years within the scope of multifunctional solutions has been photovoltaic adaptive facade systems. These systems offer both energy production and shading functions, and have great potential, especially in the development of high-performance building envelopes [27]. It is clearly demonstrated that hybrid and adaptive facade systems play a strategic role in energy efficiency-oriented building design and offer important technological solutions that will contribute to future sustainable urbanisation goals.

2.4. Active and Passive Ventilated Systems

One of the main factors that determines the contribution of facade systems to energy efficiency is the ventilation strategy. In this context, facade systems are generally designed according to passive or active ventilation principles. Both approaches aim to increase indoor comfort by controlling air circulation in facade cavities, preventing condensation and balancing heat gains/losses. However, the main difference between these two systems is how air movement is generated and managed [28]. Passive ventilation systems work by creating airflow in the air spaces between the building and the outside environment through natural stack effects, wind direction and thermal gradients. No mechanical devices are used in such systems; therefore, there is no energy consumption. Passive ventilation offers an energy-saving and sustainable solution, especially in mild climate conditions and low wind speeds [29]. On the other hand, active ventilation systems provide air circulation with fans, motors, or mechanical ventilation devices. These systems are especially preferred in high-rise buildings, structures requiring constant and controlled airflow or areas with weak wind conditions [30]. However, active systems introduce significant operational complexities and energy overheads, particularly in tropical climates where continuous high ventilation demand coincides with elevated ambient temperatures and humidity. Mechanical components such as fans and control units must operate under sustained thermal stress, leading to increased electricity consumption and accelerated wear. Moreover, maintaining system reliability in such climates requires frequent servicing and robust corrosion-resistant materials to prevent degradation. These operational burdens can offset part of the energy savings gained from enhanced airflow control, making careful cost–benefit assessments and climate-adaptive design essential for successful deployment.

Table 1. Comparative summary of VF system types.

System Type	Key Characteristics	Advantages	Limitations	Typical Applications	Integration with Smart Materials
Double-Skin Facades [31]	Two layers (usually glazing) with a ventilated cavity in between	High thermal/acoustic insulation, solar control, and natural ventilation potential	High initial cost, complex design, risk of overheating if poorly ventilated	High-rise office buildings, cold climates	High potential for BIPV and electrochromic glass integration; suitable for active daylight and solar gain control
Rainscreen Cladding [32]	Outer cladding with ventilated cavity and inner weather barrier	Moisture control, improved durability, and passive cooling benefits	Less effective in deep energy saving unless combined with insulation	New facades and retrofit projects	Moderate integration potential; PCM panels can be embedded behind cladding; limited suitability for PV due to opaque surface
Hybrid/Adaptive Facades [33]	Integration of dynamic components (e.g., shading, PV, sensors) with responsive behaviour	Dynamic climate response, optimised comfort, and potential energy generation	High cost, maintenance requirements, complex automation	Smart buildings, research and innovation centres	Excellent integration potential with BIPV, PCM, electrochromic, and AI-driven control systems
Active and Passive Ventilation Systems [34]	Based on airflow strategy: natural (passive), mechanical (active), or both (hybrid)	Energy saving (passive), precise control (active), adaptable (hybrid)	Passive depends on climate; active increases energy demand; hybrid adds system complexity	Residential, educational, and institutional buildings	Variable; hybrid designs may integrate PCM or smart actuators, but are less suited for BIPV unless paired with other facade types

presents a comparative summary of VF systems categorised into four main types: DSFs, rainscreen cladding, hybrid/adaptive facades, and active/passive ventilation systems. Each category is evaluated based on its structural and operational characteristics, performance advantages, limitations, and common application areas. This classification supports a more informed selection of facade strategies in energy-efficient and climate-responsive building designs.

3. Energy Performance and Thermal Comfort

3.1. Heat Transfer Mechanisms in Facade Cavities

VF systems fundamentally alter the heat transfer pathways through a building envelope by introducing an air cavity between the outer cladding and the insulated inner wall. In this cavity, heat transfer occurs via conduction, convection, and radiation in a dynamic interplay distinct from a solid wall assembly. Conduction in a ventilated cavity is limited primarily to the solid components (cladding attachments and support brackets) rather than across the whole facade area [35]. By contrast, in a conventional insulated wall (e.g., an ETICS system), conductive heat flow spans the entire wall surface, transmitting heat inward wherever insulation or thermal mass is contiguous [36]. The ventilated cavity thus interrupts continuous conductive paths; heat must traverse the discontinuous metal fixings or thermal bridges, which occupy a small fraction of the facade area [37]. This significantly reduces the effective conductive heat gain into the building, as illustrated in Figure 4, where heat flow in a VF is largely confined to the discrete connectors instead of the whole wall plane. The thermal lag introduced by the ventilated layer further delays any residual conductive heat transfer, as the outer cladding and air gap absorb and dissipate heat before it reaches the inner wall. In essence, the ventilated cavity acts as a buffer that slows and reduces conductive heat flow. This is a key reason why VFs can keep the interior side cooler during hot periods and warmer during cold periods.

In the ventilated cavity, convection plays a dominant role in removing heat through buoyancy-driven airflow. When solar radiation heats the outer cladding and cavity air, the air’s density decreases, causing it to rise—a stack effect that induces upward airflow through the cavity [38]. This buoyancy-driven ventilation carries away a significant portion of the absorbed heat before it can conduct inward, effectively cooling the cavity. Even in the absence of wind, a VF generates airflow solely by this buoyancy effect, directly proportional to the intensity of solar heating [39]. Experiments and simulations show that the air velocity within the cavity under windless conditions is governed by the temperature difference (solar induced) between the cavity air and the outside environment [40,41]. As solar radiation increases, the buoyant flow becomes stronger, enhancing convective heat removal. In addition, any external wind will further drive convection: a wind pressure at the facade openings forces outside air into the cavity (at lower vents) and pulls heated air out (at upper vents). Studies have noted a clear correlation between external wind speed and the air speed inside the cavity [42]. At higher wind velocities, convection in the cavity transitions from pure buoyancy-driven to a mixed or forced convection regime, which can equalise the performance of different cavity designs. For instance, at roughly 5 m/s wind, both open-joint and closed-joint VFs achieve similar heat removal efficiency, and the resulting indoor wall temperatures converge (differing by merely ~0.1 °C) [43]. This indicates that beyond a certain airflow rate, convective cooling in the cavity reaches an effective maximum where additional wind offers diminishing returns.

Due to the continuous air exchange, the ventilated cavity also facilitates convective heat transfer coefficients at the interior surfaces that are higher than in a sealed air gap. According to Zhang et al. [44], an unventilated air layer within wall assemblies can exhibit a thermal resistance of about 0.15 (m².K)/W, effectively reducing heat transfer through the building envelope. This value underscores the insulating capability of unventilated air gaps in building constructions. By contrast, an open ventilated cavity sustaining moderate airflow can have an order-of-magnitude higher convective heat transfer, effectively cancelling much of the insulation effect of the air layer [45]. Field studies have shown that very high ventilation rates (on the order of 100 air changes per hour in the cavity) render the air gap’s thermal resistance nearly negligible, as the air temperature in the gap closely tracks the outdoor temperature [46].

Likewise, radiative heat exchange in the cavity is mitigated by ventilation: the moving air continuously removes hot air and replaces it with cooler air, reducing the mean radiant temperature in the gap. Nonetheless, radiation between the hot inner face of the cladding and the cooler outer face of the insulation still occurs. High-emissivity surfaces in the cavity can radiatively transfer heat across the gap, but this is partly offset by the convective cooling of those surfaces by airflow. Some VF designs use low-emissivity (low-e) coatings on the cavity-facing side of the cladding or insulation to further cut down radiative heat transfer [47]. The interplay between conduction, convection, and radiation is summarised in

Table 2. Modes of heat transfer in VF cavities.

Mode	Primary Path	Influencing Factors	Effect
Conduction	Through brackets or air	Material, gap width	Strongly reduced by discontinuities/air gap
Convection	Airflow in the cavity	Solar intensity, cavity depth, vent size/location	Dominant removal pathway
Radiation	Surface-to-surface across the gap	Surface emissivity, geometry	Reduced by ventilation or low-e coatings

, which categorises each heat transfer mode according to its pathway, influencing factors, and how it can be either enhanced or suppressed through design interventions such as cavity depth, material emissivity, and vent sizing. In summary, the cavity airflow concurrently convects heat out and cools the surfaces, while also limiting radiative exchange by lowering surface temperatures.

The stack effect in taller facades can amplify these convective processes. In multi-storey ventilated cavities, cooler air is drawn in at the bottom vent as warm air continuously rises and exits at the top, creating a self-sustaining upward airflow loop. This means the upper sections of a tall cavity often see higher air temperatures and velocities than the lower sections, especially under strong solar gain [48]. Notably, researchers found that cavity air temperatures increase with height more markedly in an open-joint VF than in a closed-joint system [49]. The open-joint configuration allows free entry of air along the height, producing a greater stack effect and thus a steeper temperature gradient up the wall. In contrast, a closed-joint (or limited inlet) design yields a more uniformly warm cavity but with less airflow, meaning heat is less effectively carried away. Paradoxically, although the closed cavity can become hotter internally, that heat is less rapidly dissipated, which can lead to slightly more heat transfer inward compared to an open joint under the same conditions [50]. Designers must therefore balance cavity openness: open-jointed facades maximise convective cooling (with cavity air speeds up to five times higher than closed systems under identical conditions, whereas closed or baffled facades reduce rain ingress and may trap some heat (which can be useful in winter but is a liability in summer). Figure 5 illustrates the airflow patterns for open- vs. closed-joint ventilated cavities. In the open-joint case, outdoor air freely enters at the base and through panel gaps, rushing upward and out, whereas in the closed-joint case, air enters only at designated vents, resulting in lower velocities and a hotter cavity air column.

Finally, the ventilated cavity introduces a thermal inertia and buffering effect, often termed thermal lag. During daytime solar exposure, part of the heat is absorbed by the cladding and cavity air, then vented out before reaching the inner wall. The inner wall experiences a delayed and reduced heat load, often peaking later in the day or not at all, compared to a wall without ventilation [51]. At night, the outer cladding cools and can even draw heat out of the cavity (if the cladding reradiates to the cold sky), sometimes resulting in a reverse flow (cool air sinking). The net result is a moderation of interior wall temperature swings over the 24 h cycle [52]. For example, Khadraoui et al. [53] experimentally and numerically demonstrated that ventilated double-wall systems significantly moderate indoor temperature fluctuations during cold periods. In a hot-arid climate, the system enhanced thermal inertia and reduced heating energy consumption by up to 15%, confirming the buffering effect of natural convection within the cavity. This demonstrates how the interplay of conduction, convection, and radiation in a ventilated cavity collectively improves the thermal performance by damping heat flow peaks and leveraging natural forces (buoyancy and wind) to eject unwanted heat. In relation to these thermal improvements, different ventilation strategies, namely natural, forced, and hybrid, offer varying levels of effectiveness depending on climatic conditions and energy goals. As shown in

Table 3. Comparison of ventilation strategies in facade cavities.

Strategy	Energy Use	Control Complexity	Performance Consistency	Peak-Load Mitigation
Natural ventilation	None	Low	Weather-dependent	Moderate
Forced ventilation	Moderate–High	Medium	Stable	High
Hybrid ventilation	Low–Moderate	High	Adaptive	Very High

, natural ventilation provides energy-free airflow but is weather-dependent, while hybrid systems deliver the highest and most adaptive performance with minimal energy input. Understanding these trade-offs helps inform smarter design decisions for low-carbon buildings.

In summary, the physics of a VF cavity can be seen as a hybrid heat transfer system: conductive paths are minimised, convective airflow actively removes heat, and radiative exchange is mitigated by lower surface temperatures and potential low-e surfaces [54]. Buoyancy-driven stack effect ventilation is the engine of heat removal in calm conditions, while wind can further augment convective cooling to the point of equalising performance across design variants at sufficient speeds. These mechanisms together explain why VFs significantly reduce heat flux entering the building, on the order of 25–30% less heat transfer compared to non-ventilated walls under summer conditions, according to multiple studies [45]. By integrating these principles into design (e.g., sizing vents, selecting cladding with suitable emissivity, and providing an adequate cavity gap), modern VFs leverage physics to passively maintain better thermal control of the building envelope. These design elements are further detailed in

Table 4. Design and operational parameters governing thermal regulation in VF systems.

Parameter	Impact on Heat Transfer
Cavity depth	Greater airflow with depth, but too deep may cause air stagnation and reduce efficiency
Vent area	Bottom-to-top ratio influences airflow rate and convective loop strength
Cladding emissivity	High-e = more radiation (beneficial in cold); Low-e = less radiation (ideal for cooling)
Air velocity	Higher velocity = stronger convective cooling; may require larger vents or wind assist
Wind exposure	Windward faces see more suction; leeward may need larger vents
PCM integration	Stores heat midday, releases it at night; moderates cavity temperatures

, which identifies key parameters such as cavity depth, vent area ratios, airflow velocity, and material emissivity. Each plays a critical role in defining the heat transfer balance, and collectively, they offer a roadmap for optimising facade thermal behaviour in both new builds and retrofits.

3.2. Cooling Load Reduction and Heating Efficiency

VFs are widely recognised for their ability to reduce cooling loads in buildings while also enhancing heating efficiency in cooler seasons. By intercepting and venting out a large fraction of incident solar heat, a VF dramatically cuts down the heat gain that would otherwise penetrate the building, thereby lowering the demand on cooling systems [55]. At the same time, in cold weather or heating seasons, the ventilated cavity can be managed to improve thermal performance, for instance, by closing vents or recovering warmth from the cavity air, thus contributing to heating energy savings. This dual benefit has been demonstrated in both experimental studies and whole-building energy simulations over the past decade.

A VF acts as a passive cooling device for the building envelope. During hot periods, solar radiation that hits the outer cladding is largely dissipated by the ventilating air gap, preventing it from elevating the wall’s inner surface temperature. Empirical and simulation studies consistently report substantial reductions in the cooling energy required for buildings equipped with VFs. For example, Patania et al. [56] found that in summer, VFs achieved over 40% energy saving in cooling needs compared to identical non-ventilated walls. Similarly, Gagliano et al. [57] performed CFD analyses under summer design conditions and calculated a 47–51% reduction in heat flux through a VF relative to a non-VF. This roughly translates to nearly halving the cooling load attributable to envelope gains, a remarkable improvement.

Table 5. Reported cooling load (heat gain) reductions with VFs (selected experimental and simulation results).

Study and Climate (Source)	Facade Type and Conditions	Cooling Load Reduction (%)	Notes and Findings
Patania et al. [56]—Mediterranean summer	Ventilated vs. solid wall (Simulated)	>40%	Three VF designs all showed > 40% cooling energy savings over the unventilated wall
Gagliano et al. [57]—Temperate summer	OVF vs. unventilated (CFD)	47–51%	CFD simulation for various wind speeds; ~50% less heat flux into the building with a ventilated cavity
Gagliano and Aneli [58]—Mediterranean annual	OVF vs. conventional (Dynamic simulation)	20–55%	Comprehensive analysis winter and summer; up to 55% energy saving on the hottest summer day (East/West facade) and ~20% in winter
Maciel and Carvalho [59]—Tropical (Brazil)	Ventilated vs. cladding wall (Simulated year)	Up to 43% annual	Simulated 16 cities; the hottest climates saw ~43% yearly HVAC energy saving due to cooling load reduction
Fantucci et al. [60]—Summer test (Italy)	Ventilated clay vs. unventilated (Field experience)	~45% (Consistent with the literature)	Large-scale outdoor experiment; measured heat fluxes confirmed ~45% reduction, consistent with prior literature
Valencia case [61]—Mediterranean summer	Ventilated (open joint) vs. sealed facade	~10% AC energy saved	Field monitoring and TRNSYS simulation; ~10% less electricity for cooling with ventilated (vs. airtight) facade configuration

AC = air conditioning. Cooling load reduction values are relative improvements against a reference non-VF under comparable conditions.

summarises several key studies reporting cooling load or heat gain reductions, illustrating that savings on the order of 20–55% are often achieved across different climates and facade configurations.

From these data, it is evident that VFs can often eliminate a very large portion of the cooling load that would be imposed by solar heating of walls. The highest savings (40–55%) tend to occur in hot climates and seasons with intense solar radiation, and on facades with high sun exposure (e.g., east and west orientations, which catch low-angle sun). For instance, a study in Italy found the peak cooling energy savings were for east- and west-facing walls in summer, reaching the 50%-plus range [60]. In more moderate conditions or with some wind-driven mixing, the savings may be a bit lower (20–40%), but still significant. Even a 10% reduction in annual cooling electricity was observed in a real building in Valencia simply by using a ventilated rainscreen instead of a sealed facade, underlining that measurable gains occur in practice [61]. It should be noted that these savings are passively achieved—i.e., without any mechanical power—which makes VFs an attractive strategy for low-carbon building design.

VFs prevent heat accumulation on the exterior wall by flushing hot air out. This leads to a lower exterior wall temperature on the inside in summer, as Naboni et al. [62] observed in an experimental building in Milan. By keeping the wall’s inner surface cooler (often by several °C), the heat entering the room is delayed and diminished. Occupants or HVAC systems, therefore, face a much reduced thermal load. In many cases, the peak heat flux through the wall is shaved off and spread over a longer period (thermal lag), which also helps reduce peak cooling demand in the afternoon. In cooler seasons, a VF can be managed to improve heating performance, although the strategy differs from summer operation. If the cavity were left fully open in winter without sun, it could act as a thermal bypass, potentially increasing heat loss (since cold air would flush the cavity). However, several approaches allow VFs to benefit from heating efficiency:

• On sunny winter days, the ventilated cavity can act as an additional insulation layer, capturing solar energy to warm the air, which then reduces heat transfer from the indoor space. Masi et al. [63] conducted a year-long experimental monitoring in a Mediterranean climate and showed that an open-joint OVF system reduced winter heat fluxes by up to 85% compared to a non-insulated wall. The inner surface temperature remained close to or even higher than indoor air temperature in 18% of the winter observations, with a temperature increase of up to 2.7 °C. These findings confirm that the ventilated air cavity not only stabilises the wall surface temperature but also contributes positively to wintertime solar heat retention, effectively warming the inner wall layer and reducing the heating energy demand.
• Closing or throttling vents: Many modern VFs (or DSFs) include operable vent closures. By closing the cavity openings in cold weather, the air gap becomes an enclosed insulating layer akin to trapped air insulation. This significantly increases thermal resistance and prevents cold air from drawing heat away. An OVF in “closed mode” essentially acts like an added exterior insulating blanket during winter nights, while still allowing an open mode on sunny days for solar collection. Saber et al. [64] note that locations with low winter severity are most favourable, but even in colder climates, designers can adopt seasonal vent control to maximise benefits.
• Heat recovery and supply air preheating: Beyond passive thermal buffering, advanced VFs can actively contribute to HVAC efficiency through heat recovery from the cavity air. For instance, Sukamto et al. [65] numerically demonstrated that solar-heated air in the ventilated cavity can preheat supply air, with up to 90 W of heat exchange in winter, substantially reducing heating losses. Similarly, Rahiminejad and Khovalyg [66] evaluated heat recovery from ventilated cavities behind passive and active facades, showing that the air space can deliver thermal gains exceeding 5000 kWh/day under optimal summer conditions. These findings support the integration of VFs into mechanical ventilation systems, enabling the captured solar heat to precondition fresh air before it enters the building. Diallo et al. [67] extended this concept by simulating a hybrid facade system (E2VENT) using TRNSYS, revealing 16.5–23.5% primary energy savings across five European climates when heat recovery and latent storage are included. These results underline the significant potential of ventilated cavities as functional energy components, not merely thermal buffers, but active solar air heaters when properly coupled with HVAC systems.
• Reducing thermal bridging and infiltration: VFs play a critical role in enhancing the thermal integrity of building envelopes by relocating the waterproofing layer and cladding to the exterior, thereby protecting the insulation from moisture ingress and temperature fluctuations. Van Linden and Van Den Bossche [68] showed through hygrothermal simulations and rain infiltration tests that keeping the insulation layer dry is essential for maintaining thermal resistance; even minor water ingress can increase annual heat flux by up to 10.5% in shallow cavities. The air cavity in ventilated systems also acts as a wind pressure buffer, significantly reducing the differential pressure across the interior layers of the wall and thereby limiting air leakage and cold drafts, particularly in windy and cold climates. Furthermore, field studies by Colinart et al. [69] on a retrofitted educational building in an oceanic climate demonstrated that VFs led to higher-than-expected thermal resistance values in winter, with stable hygrothermal conditions and reduced risk of condensation. Complementarily, Azkorra-Larrinaga et al. [70] found that incorporating an open-VF increased the effective thermal resistance from 0.75 to 2.47 (°C.m²)/W, whilst also decreasing air infiltration and heat absorption under solar load. Collectively, these results validate the role of VFs in reducing thermal bridging, preventing moisture accumulation, and improving heating efficiency and occupant comfort in diverse climatic conditions.

It is important to design VFs appropriately for the climate to maximise these dual-season gains. In predominantly hot climates, the emphasis is on maximising ventilation (open joints, large vents) to dump heat in summer, accepting that in the brief cool season, the facade might simply act as a sunscreen and light insulation. In mixed or cold climates, a more adaptive approach is needed: vents that can close, or hybrid modes where the facade sometimes operates like a closed cavity or even intentionally admits solar-heated air indoors. For instance, so-called Trombe wall integrations use ventilated air spaces with thermal mass to store and slowly release heat, which can outperform a purely VF in winter [71]. The literature suggests that the most favourable climates for year-round energy benefit are those with high cooling loads and moderate winters (e.g., Mediterranean, subtropical), where the VF saves a lot in summer without incurring a big winter penalty. In very severe winter climates, VFs still provide summer savings, but designers may need to mitigate winter heat losses (through the methods above) to ensure net annual benefits [72].

In summary, VFs substantially reduce cooling loads by venting away solar heat (commonly achieving 20–50% cooling energy savings, and they can also enhance heating efficiency through solar heat capture and insulating effects (with 10–20% heating savings in many cases, and much higher if integrated with heat recovery). These improvements have been demonstrated in both experimental test cells and occupied buildings across various climates. The combination of lower cooling demand and improved heating performance makes VFs a key technology for low-carbon buildings, as they reduce HVAC energy use in all seasons while relying predominantly on passive physical processes (natural convection and solar gains) rather than active energy input. In order to facilitate a comprehensive comparison of ventilated and advanced facade configurations,

Table 6. Comparison of seasonal energy performance and suitability criteria of different facade systems.

Facade Type	Summer Performance	Winter Performance	Cooling Load Reduction	Heating Support	Indoor Comfort (PMV/PPD)	Structural Complexity	Cost	Maintenance Needs	Climate/Built Suitability
Ventilated facade [73]	Reduces solar heat via convection; natural ventilation enhances cooling	Limited passive gain; PCM can assist with heating	Medium—removes much of the solar heat naturally	Low-medium—enhanced with PCM or control strategies	Improves thermal stability; better comfort in summer	Medium—needs cavity, cladding, mounting elements	Medium—added cladding and installation	Medium—cavity cleaning and element upkeep	Warm and temperate, especially solar-exposed facades
Trombe wall [74]	Requires shading to prevent overheating; limited summer comfort	Strong passive heating; absorbs day heat, releases at night	Low—overheating possible without shading	High—acts as solar heater	Improves winter comfort; poor in summer without shade	Low–thick wall and glazing only	Low—simple mass wall construction	Low—minimal maintenance required	Cold-dry zones; passive heating needs
Double-skin facade [75]	Large air gap cuts solar load; 9–14% cooling load reduction reported	Provides insulation; solar pre-heating possible in ventilated mode	Medium-high—up to 14% reduction with optimal design	Medium—insulation and solar gains reduce heating demand	Balanced temps with correct design; minimises peaks	High—requires double glazing and control systems	High materials and labour-intensive	Medium-high—glass and system maintenance	High-rises in warm/humid zones; sun + noise control
PCM integrated facade [76]	Reduces peak indoor temps by ~2 °C; stabilises internal temperatures	Stores day heat, releases at night; supports heating	Medium—reduces cooling load via thermal mass effect	Medium—retains heat, lessens heating need	Reduces temp swings; improves PMV/PPD	Medium—PCM panels and mounts needed	High–PCM is expensive, needs a precise installation	Medium—capsule life and durability checks	Wide climate range; effective in thermal swing zones
Green facade [77]	Evapotranspiration and shading reduce surface heat; up to 75% energy savings	May block solar gain; reduces passive heating potential	High—up to 75% cooling energy reduction reported	None—blocks solar gain in winter	Summer comfort enhanced; winter comfort may drop	Medium—structure for vegetation needed	High—varies with plant type and support	High irrigation, pruning, and plant health	Hot-arid and dense cities; reduces heat island effect
Smart/Adaptive facade [33]	Actively adjusts to solar load; minimises cooling demand dynamically	Dynamic control allows solar gain; aids winter heating	High—significant reductions via responsive control	Medium—controlled gain possible for heating	Maintains optimal PMV/PPD dynamically	Very High—sensors, actuators, and moving parts	Very High—automation and tech investment	High—electronics and mechanics need frequent service	Variable climates; suitable for high-performance buildings

presents a detailed summary of their seasonal performance (in both cooling and heating modes), impact on thermal comfort, structural and economic considerations, and overall applicability across building types and climate zones. This comparative matrix serves to consolidate the various facade strategies examined in the literature, highlighting their relative strengths and limitations in an easily interpretable format.

3.3. Impact on Indoor Thermal Comfort

Beyond energy metrics, VFs have a pronounced influence on indoor thermal comfort, affecting parameters such as interior surface temperatures, temperature uniformity, and occupants’ thermal sensation indices (e.g., PMV, Predicted Mean Vote). By moderating the heat flow through external walls, VFs create more stable and comfortable indoor conditions for occupants. The study in different climates has evaluated how these facades alter the thermal environment inside buildings, finding generally positive impacts on comfort when properly implemented [78].

One key comfort benefit is the improvement in temperature uniformity within the occupied space. In a room with a conventional facade, the interior surface of an external wall can become very hot in summer or very cold in winter, leading to discomfort for occupants near the wall and uneven temperature distribution (for instance, a hot zone near a sun-exposed wall, even if the thermostat is set lower). With a VF, the interior wall surface stays significantly closer to the indoor air temperature, avoiding extreme surface temperatures. Field measurements confirm that in summer, a VF can keep the inner wall surface several degrees cooler than it would be with a non-ventilated wall. A warmer wall in winter reduces the radiant heat loss from occupants’ bodies to the surroundings, thus improving comfort without needing to raise air temperature. In essence, VFs act to diminish the radiant asymmetry between indoor surfaces, which is a crucial factor in occupant comfort. An environment where all surfaces are near the air temperature feels more comfortable than one with a very cold wall and warm air, or vice versa [79]. By maintaining wall surface temperatures closer to ideal levels, VFs help keep PMV values in the comfortable range with fewer complaints of draft or radiant discomfort [80]. Whilst current VF systems increasingly incorporate automated and sensor-based controls, there is a notable gap in user-centric approaches that integrate occupant feedback into facade operation. Future research should explore human-in-the-loop (HITL) control strategies that dynamically adjust facade parameters, such as shading, ventilation rate, or glazing properties, based on real-time input from building occupants. These systems could leverage thermal comfort feedback, mobile interfaces, or wearable sensors to personalise indoor environments on maintaining energy efficiency. Such adaptive frameworks hold promise for optimising comfort satisfaction, especially in mixed-mode or naturally ventilated buildings where occupant behaviour plays a critical role.

Studies that explicitly calculate comfort metrics have reinforced these observations. In a hot-arid climate context, Fallahpour et al. [81] employed a 3D quasi-steady CFD model and a multi-objective optimisation approach to analyse the impact of key geometric parameters of DSFs on indoor thermal conditions. By simulating airflow and temperature in a 6 × 8 × 2.8 m³ test room equipped with a DSF, the authors demonstrated that parameters such as room air outlet height, DSF air outlet height, and interior glazing height are critical for achieving optimal airflow and minimising temperature differentials between indoor and outdoor environments. The optimised configuration reduced the indoor–outdoor temperature difference to as low as 1.04 °C and nearly eliminated reverse airflow, highlighting DSF’s strong potential to maintain thermal comfort in hot-arid zones. These findings underscore the effectiveness of DSF design in passively stabilising indoor temperatures, especially when geometric interactions are fully considered. This was achieved passively, indicating how effective the ventilated cavity was at smoothing out the indoor climate. Even during the cold desert night, the VF’s buffering effect meant the indoor temperature did not plummet as much, avoiding the discomfort of very low indoor operative temperature by morning.

Another comfort aspect is the reduction in thermal stratification and drafts. By design, VFs typically include a continuous air barrier on the interior wall, which improves air tightness. The wind pressure fluctuations on the building exterior are dampened by the ventilated cavity, the air in the cavity can move independently, so the pressure that reaches the inner wall is more uniform. This means less cold outside air is sucked into the room through cracks (reducing cold drafts) and less warm indoor air is pulled out. Enhanced airtightness and stable pressures contribute to more consistent indoor temperatures from floor to ceiling and fewer localised cold spots near the wall. Occupants thus experience a more uniform environment, which correlates with higher comfort satisfaction. In naturally ventilated buildings, the VF can also help channel intentional airflow in a controlled manner when windows are opened, rather than having unpredictable infiltration paths. By providing an intermediate ventilation space, it is possible to supply outdoor air more gradually or even pre-condition it in the cavity before it enters the occupied zone (some advanced systems draw room air into the cavity and exhaust it at the top, aiding ventilation without drafts) [2]. All these effects mean that the indoor air velocity around occupants can be better managed. Typically, a ventilated opaque facade does not directly create indoor air movement (since the cavity is sealed from the room), but indirectly it prevents unwanted high-velocity infiltration jets. This is beneficial because it avoids discomfort due to cold drafts in winter, and in summer it ensures that if natural ventilation is used, it can be performed when needed for cooling rather than as an uncontrolled byproduct of wind pressure. In short, VFs contribute to a draft-free, stable environment, which is a cornerstone of thermal comfort.

It is important to note that VFs primarily address thermal comfort (temperature-based comfort). They also incidentally can contribute to better indoor air quality when integrated with ventilation systems (by providing pre-heated fresh air, or encouraging ventilation when needed), though a basic rainscreen facade by itself does not supply fresh air. Acoustically, the double-skin VF can reduce outside noise, which is another comfort facet (though outside our thermal focus) [82]. Visually, OVFs do not affect daylight, but ventilated double-skin glazed facades can reduce glare by incorporating shading in the cavity, however, that strays into a different performance area. In conclusion, VFs enhance indoor thermal comfort by stabilising interior surface temperatures, reducing radiant heat asymmetry, and preventing unwanted drafts or hot spots. Studies across climates from tropical to arid to temperate show more hours within the comfort zone and improved comfort indices (lower PPD) when VF systems are in place. These comfort improvements complement the energy savings discussed earlier: a building that requires less active cooling/heating also tends to be one where occupants feel more comfortable naturally. By leveraging passive environmental control, VFs create indoor environments that are not only energy-efficient but also healthier and more pleasant for occupants, aligning with the goals of sustainable, high-performance buildings.

3.4. Performance in Different Climate Zones

The effectiveness of VFs can vary significantly across different climate zones, and successful designs often incorporate climate-responsive strategies to optimise performance. In this subsection, the VF performance in tropical, temperate, continental, and arid climates is compared, drawing on case studies and simulations from around the world. It is also discussed how design parameters are adapted to each climate for maximum benefit, and present comparative metrics (such as energy savings and interior temperature moderation) for these zones.

Tropical Climates (Hot-Humid): In tropical regions, buildings face year-round high temperatures, intense solar radiation, and often high humidity. The primary goal of a VF here is to minimise cooling loads and prevent overheating, as heating is rarely needed. Studies consistently show that OVFs can significantly cut heat gains in tropical climates [83]. Recent investigations reinforce the effectiveness of ventilated and DSFs in tropical and subtropical regions by demonstrating significant reductions in cooling energy consumption through integrated passive and active strategies. Tognon et al. [84] assess the use of operable windows and show that natural ventilation can reduce cooling loads by up to 30% in warm climates such as Italy and by 11% even in colder climates like Finland. Shading devices within naturally ventilated DSFs (NVDSFs) are also highly effective, delivering energy savings between 24% and 76%, with simulation studies in Egypt reporting up to 76% reductions during peak summer [85,86]. Further enhancements through photovoltaic integration in NVDSFs can lower energy consumption by 50% to 84% in subtropical settings, while the application of intelligent control strategies contributes additional savings of 4.5% to 45%, depending on system complexity and climatic context [87,88,89,90]. Several region-specific studies complement these findings. In the Mediterranean, Coma et al. [91] demonstrate that green DSFs reduce annual cooling loads by approximately 33.8%. In Saudi Arabia, the application of PCMs achieves dual-seasonal benefits, cutting cooling loads by 5.6% and heating demands by 11.5% in Jeddah, and reducing heating demand by 40% in colder cities like Tabuk [92]. Chan et al. [93] find that reflective double-glazing systems in Hong Kong can cut cooling energy needs by 26% annually. In East Asian climates, Lee et al. [94] show that PV-ventilated windows reduce cooling energy by 10%, while An et al. [95] and Kang et al. [96] demonstrate that solar-driven DSFs (SDSFs) achieve 6.5% to 50.1% reductions in both heating and cooling loads. Similarly, Khabir and Vakilinezhad [97] report that optimised DSF configurations can yield up to 63% cooling energy savings in hot climate scenarios. A comprehensive case study in Dhahran by Rababa and Asfour [98] explores 224 facade retrofit combinations using genetic algorithm optimisation. The most effective solution combines external thermal insulation composite systems (ETICS) for walls, low-emissivity Argon-filled glazing, and louvred shading, resulting in a 16% reduction in annual cooling electricity use with a 14.8-year payback period. Individually, external wall retrofits reduce cooling loads by 11.1–18%, while advanced glazing and window systems offer up to 8% further savings, confirming the value of integrated, locally adapted retrofit strategies in extremely hot environments. These collective findings underscore the growing importance of climate-responsive VF systems, particularly in regions where year-round solar and thermal stress dominate building energy performance.

Design strategies for tropical VFs emphasise maximal ventilation and solar reflection. This means larger or more numerous vent openings, sometimes even operable vents, to enhance airflow when solar gain is high. External cladding materials with low solar absorptance (light-coloured or reflective finishes) are preferred to reduce solar heating of the facade [99]. Indeed, a study in a tropical climate suggests using lighter-colour claddings to further cut down cavity temperatures, especially if the facade has no insulation, the colour effect can be quite pronounced in reducing absorbed heat [83]. Additionally, tropical designs may integrate sunshades or louvres in front of the ventilated cavity to block direct sun angles, thereby reducing the load on the cavity itself.

Temperate Climates: Temperate zones have moderate summers and winters, requiring both cooling and heating over the year. VFs in these climates must provide a balance of cooling relief in summer and not significantly penalise (or even aid) heating in winter. Many European countries (e.g., much of Italy, France, and coastal regions) and parts of North America fall into this category. In temperate climates, case studies often show annual energy savings from VFs in the range of 10–60%, depending on design and operation. For example, Raji et al. [100] examined the impact of building envelope design on energy consumption in high-rise office buildings located in temperate climates. The study found that optimising parameters such as glazing type, window-to-wall ratio (around 50%), shading strategy, and roof design can reduce total energy use by up to 42%, with significant savings in heating and lighting energy. Another study in Spain (temperate/Mediterranean climate) by Peci and Ruiz [101] found that the best locations for VFs were those with mild winters and ample sun, whereas very cold, cloudy winter sites saw less net benefit. This implies temperate coastal or southern regions gain more than temperate inland or northern areas with the same facade design. In Spain’s analysis of 12 cities, the VF saved energy in all, but cities with higher solar irradiation and moderate winter temperatures (e.g., Seville, Valencia) performed the best, whereas a cooler, cloudier city still saw savings but smaller. In hot-humid climates, the absence of systematic facade design guidance may hinder performance, and early-stage integration of climate-responsive strategies is essential [102]. Moreover, naturally ventilated DSFs with hybrid or passive control systems can provide annual energy savings up to 47.9%, particularly effective in subtropical and tropical regions [55]. Meanwhile, bio-based VFs demonstrate measurable cooling benefits and lifecycle sustainability in hot-arid climates, such as Dubai [103].

Designers in temperate zones often incorporate seasonal adjustability in VFs. For instance, some systems include dampers that can partly close the cavity in winter to reduce ventilation heat losses. Others use a hybrid approach: in summer, the facade is fully ventilated; in winter, it operates like a static air layer or even a Trombe-wall-like collector if sunny. The OVF concept in temperate climates can be paired with thermal mass, e.g., a heavy inner wythe that soaks up daytime heat from the cavity when the sun is out and then releases it inward during the evening [72]. Research in Italy has suggested that adding thermal mass in contact with the ventilated air gap (either as the inner wall or within the cavity) can reduce heat transfer and improve inertia in climates with significant daily temperature swings [104]. Thus, a VF in a temperate climate might consist of an outer rain-screen (possibly glass or metal panels), a ventilated gap, and a heavy masonry inner wall: in summer the mass stays cool as heat is vented, in winter the mass can be slightly warmed by solar-heated cavity air if vents are selectively closed.

Continental Climates: These are characterised by hot summers and cold winters (large seasonal variation), typical of inland locations in mid-latitudes (e.g., Eastern Europe, Northern China, U.S. Midwest). Here, VFs face the challenge of providing strong performance in two opposite extremes. In summer, they function much like in temperate or even tropical climates, cutting down cooling loads effectively. In winter, however, if operated exactly the same (fully open), they could increase heating demand by venting away heat. Performance in continental climates thus heavily depends on management and design. The literature shows that in continental climates, VFs still yield net positive outcomes, especially if innovations are used. A climate-responsive VF system integrating PCMs and dynamic insulation was developed and validated for a continental climate with hot summers and cold winters. Simulation and prototype testing showed that the facade achieved fresh air pre-conditioning efficiencies between 60% and 75% in both heating and cooling seasons, effectively adapting to daily and seasonal thermal loads. Its thermal transmittance could be actively modulated via controlled airflow, enabling substantial cooling load reductions in summer while limiting heat loss during winter. The dual active–passive mechanism demonstrated significant potential in reducing HVAC dependence in retrofitted and new buildings alike [105]. Experimental investigations conducted in a continental climate with hot summers and cold winters demonstrated that OVFs deliver markedly different thermal benefits depending on seasonal configuration. In summer, an open-joint design with ventilated cavities reduced cooling loads by up to 11.4%, while in winter, a closed-joint, restricted-ventilation configuration achieved heating load reductions of around 6.5%. To address the contrasting requirements of both seasons, an integrated facade configuration is proposed, combining bright external cladding, a 200 mm air cavity, and ventilation openings that operate seasonally, open in summer and are sealed in winter. These findings highlight the importance of climate-responsive facade operation, where adaptive control strategies can significantly enhance annual HVAC energy performance [50].

In continental climates, climate-responsive strategies may include the following: automated vent closures based on temperature (to trap heat on cold days), integration of PCMs in the cavity to store solar heat for nighttime heating or using the cavity as a source of fresh air pre-heating on cold sunny days. Yang et al. [106] investigated a ventilated DSF integrating dual-step PCMs in a temperate continental climate, demonstrating that daytime-only ventilation (1.09 m/s) combined with PCMs (melting points at 16 °C and 28 °C) achieved up to 91.4% ventilation efficiency and significantly reduced temperature fluctuations. Curpek and Hraska [107] simulated a ventilated PV facade with PCM under continental conditions in Slovakia, showing that airflow and PCM layers reduced surface temperatures by up to 20 °C in summer and 12 °C in winter, and delayed peak thermal loads by over five hours. de Gracia et al. [108] applied reinforcement learning control to a ventilated PCM facade and achieved energy, cost, and CO₂ emission reductions of 4.3%, 7.8%, and 16.7%, respectively, highlighting the benefits of intelligent, climate-adaptive operation. Similarly, Hu et al. [109] experimentally showed that a PCM-enhanced ventilated window could reduce inlet air temperatures by 1.4 °C for 7 h (pre-cooling) and increase them by 2.0 °C for 12 h (pre-heating), achieving daily energy savings up to 1.6 MJ depending on seasonal application.

Arid Climates (Hot–Dry): Arid regions (deserts and semi-deserts) typically have very high solar gains and temperatures in the day but can have cool or even cold nights due to low humidity and clear skies (allowing radiative cooling). Examples include parts of the Middle East, North Africa, the southwest U.S., and inland Australia. VFs in these climates can be extremely beneficial for cooling during the day, while also helping with the unique diurnal swing. During the hot daytime, the ventilated cavity expels heat like a chimney, keeping the building cooler. At night, the outside air can be quite cool; a VF can either be closed to keep interior heat in (if heating is needed at night) or even continue venting to cool down the thermal mass of the building for the next day (night purging). The flexibility here is key.

Sotelo-Salas et al. [110] experimentally validated a CFD model for an evaporative OVF under hot-arid climate conditions. Their simulation identified the optimal configuration as a 0.4 m air cavity, 25 μm water droplet size, and 0.6 m nozzle spacing, achieving a maximum cooling efficiency of 64.7% and reducing the inner wall surface temperature by 9.52 °C. Unlike porous-coated facades, this system performed efficiently without increasing indoor humidity. The results highlight its potential as a passive cooling strategy in extreme climates. Meanwhile, at night, because the ventilated wall assembly had released its heat quickly at sunset, the inner wall stayed warmer than the highly heat-loaded solid wall (which tended to release heat into the interior at night). As a result, the building with a VF needed much less nocturnal heating or stayed comfortable without heating for longer [111].

Finally, architects often integrate climate-responsive facade elements in tandem with ventilation. For instance, in arid and tropical climates, combining VFs with shading devices (external louvres or greenery) yields even better performance: the shading cuts direct solar load, and the ventilated cavity handles the residual heat. In temperate and continental zones, integrating adaptive facades (that open/close, or include operable insulation or sunshades) can ensure the facade is always configured best for the season. An emerging concept is the “multi-skin adaptive VF”, which might include, say, a ventilated cavity plus a dynamic insulation layer that can slide or inflate in winter nights. These innovations point to a future where VFs are a component of a smart climate facade system, adjusting to weather in real time. In summary, VFs have demonstrated substantial performance improvements across all climate zones, but with varying emphases: tropical and arid climates reap very large cooling-focused benefits; temperate climates enjoy balanced benefits in both summer and winter with modest annual gains; continental climates can achieve good results with careful design (to maximise summer gains and mitigate winter losses). Climate-responsive design strategies, such as vent control, material choices, and integration with other passive systems, are crucial to unlocking the full potential of VFs in each climate. The versatility of this technology, able to address the extremes of a humid tropical day, a dry desert night, or a chilly continental morning, underlines why VFs are increasingly seen as a key solution for low-carbon, comfortable buildings worldwide. The comparative data and case studies confirm that, when properly tuned to their environment, VFs consistently enhance energy performance and indoor comfort across vastly different climate conditions.

Several unexpected or counterintuitive findings emerged across the reviewed literature. For instance, open-joint ventilated facades were found to outperform closed-joint systems in certain cold-weather scenarios, contradicting assumptions about airtightness and insulation. Similarly, poorly optimised ventilated cavities, especially those with insufficient depth or vent sizing, were shown to underperform even when compared to conventional insulated walls. While green facades demonstrated exceptional cooling benefits, they also caused excessive shading and underheating during colder months. In some cases, smart facades relying on automated control systems consumed more energy than passive ones due to sensor miscalibration or algorithmic inefficiencies. Likewise, Trombe wall applications, generally praised for passive heating, led to interior overheating during summer in the absence of proper shading control. These findings underscore the importance of climate-adaptive configuration, precise control strategies, and system-specific design to avoid performance setbacks and maximise the intended benefits of ventilated facade technologies.

4. Simulation and Experimental Studies

In daily life, people spend most of their time in closed environments. With the increasing work in office environments with developing technology, this situation seems to be increasing day by day. The increase in the time spent in closed environments is especially important in terms of human health and thermal comfort. Thermal comfort can be defined as being in conditions that will not create a negative physical situation in which a person feels comfortable [112]. To protect human health from negative effects, air conditioning conditions in closed environments must be suitable. This situation increases the energy consumption in buildings even more. The share of buildings in total energy consumption in Europe is approximately 40% [113]. The share of buildings in energy consumption does not only cover the production phase. The energy load of a building is expressed by Embodied energy (EE), which covers the stages of material production, construction, maintenance, repair, renovation and demolition after use [114]. However, a much more serious energy consumption occurs during use. Especially in geographies that are not climatologically suitable, the energy consumption required for heating, cooling and ventilation can cause serious energy consumption. It is a common expectation that energy consumption will decrease, and fossil fuel consumption will naturally decrease with the renovation of buildings that are constructed with traditional structures and have low energy efficiency [115]. Only 1% of the building stock in the European Union can be renewed each year. This situation makes the 2050 energy policy targets unattainable [116]. Studies carried out to reduce the energy consumption that buildings are responsible for create a wide literature. Insulation to prevent heat loss in cold climates, facade applications to benefit more from the sun, storing excess energy during the day and using it as energy input during the hours when the sun is not shining, and using innovative approaches in windows are quite effective [117]. In fact, when it is considered that insulation alone reduces the emission value caused by a residence by 5.5% in the UK, the importance of these approaches becomes clearer [118]. Walls constitute a large part of the surface of buildings. Therefore, the loss from walls is quite important. In this case, material properties and cost come into play, all of which are very important for production and after. Similarly, windows have a significant share in energy losses in buildings. 60% of the energy source in buildings occurs through windows, and this rate alone indicates that improvements in windows will significantly reduce energy consumption [119]. Not only heating loads but also cooling and ventilation activities are important in hot climate regions. Especially in regions with high solar radiation, energy consumption can be reduced with heat-retaining materials applied to the exterior facades of buildings [120]. Another method is to meet the energy need by equipping the roofs of buildings with photovoltaic (PV) systems [121]. Innovative window approaches for natural ventilation [122] and the use of solar chimneys are quite effective [123]. Providing the thermal comfort conditions required for buildings without such energy consumption is called the “Passive Building Concept” and is accepted as an innovative building approach [124]. In this section, studies evaluating energy analysis for buildings with the computational fluid dynamics (CFD) method are given, followed by experimental verification and test studies. Finally, benchmarks and case studies are given.

4.1. CFD and Building Energy Simulation Tools

The analysis of energy consumption in buildings is important. Especially considering that most of the energy consumption originates from buildings, it is inevitable to reduce this rate with innovative approaches. Since it would be quite difficult to conduct analyses experimentally for large-scale systems, it is practical to conduct analyses through computer simulations in terms of economy and time. Most of the CFD studies on energy consumption in buildings are on building elements. Researchers design different window designs to reduce heat loss from windows, which are one of the building elements. Window designs that minimise radiation effects are possible with specially coated Low-e glass technology [125]. Similarly, insulation in walls, use of special organic materials, use of PCM, and similar studies are common practices for both removing heat exposed to radiation effects and effectively utilising solar energy [111].

Table 7. Building energy simulation studies and details.

Working Details	Study Outputs	Ref.
2D CFD simulation to evaluate PCM integration in passive solar buildings. Comparison of finned vs. finless PCM housing.	Finned design improves heat transfer and reduces PCM melting time from 35 to 32 min. Triangular and rectangular fins yield different thermal effects.	[126]
3D CFD analysis on PCM thickness effect within structural elements.	PCM reduces indoor temperature by up to 5 °C. Performance varies with PCM thickness, inlet temperature, and mass flow rate.	[127]
CFD study on PV/T systems to analyse summer overheating and winter radiation gain.	Tilt angle controls solar entry. Prevents overheating in summer and allows passive heating in winter.	[128]
CFD study on BIPV system with an air duct behind PV.	45° PV inclination and 247 kg/h airflow provide the best performance. The HTC of insulation reached 5.9 W/m2K.	[129]
CFD analysis using a 2000 × 800 mm2 double-glazed window at different tilt angles and cavity widths.	Inclination of 30–60° increases heat gain by 132–146%. Larger cavity gaps increase heat gain by 106%. Larger outlet opening reduces efficiency by 127%.	[130]
CFD study on triple-glass windows (4/6/4 mm) under laminar flow, based on ISO solar standards.	CFD-derived U-values are significantly lower than standard (1.1 W/m2K). Varies with airflow.	[131]
CFD study on solar chimney performance in a 2 × 2 m room.	Circulates air but fails to meet ASHRAE temperature thresholds at high inlet temperatures.	[132]
CFD optimisation of the chimney slope for a 50 cm long solar chimney with a 4 cm gap.	Ideal slope angle: 45–60°. Performance depends on geographic and climatic factors.	[133]

provides details on energy simulations and studies conducted with CFD in buildings.

In building energy simulations, it is seen that researchers aim to prevent heat loss from building elements, ventilate indoor environments, and make effective use of the sun. The important detail at this point is to realise that these can be achieved without any energy input. Windows are responsible for many energy losses in buildings, and this creates a great handicap. However, their use is mandatory for light gain. The inevitability of using windows directs researchers to this area for innovative approaches. The use of double-glazed windows, which are widely used in the market, has been widespread compared to traditional single-glazed windows for many years. The use of insulative edge seal materials and other gases with low heat transfer coefficients instead of air as fillers in double-glazed windows offers a good option to reduce heat losses by reducing the window heat transfer coefficient to quite low figures [134]. Heat losses in windows are caused by conduction, convection, and radiation through the double glazing. To reduce these effects, heat transfer can be seriously prevented by vacuuming the air between the double glazing. The scheme of this glazing technique, called vacuum glazing, is given in Figure 6. With the vacuum glass technique, the window heat transfer coefficient can be significantly reduced [135].

Although it is possible to reduce heat loss from windows, it is unlikely to be used soon due to the initial investment costs and the prevalence of traditional production methods. Another approach that can be applied to windows is to use semi-transparent PV modules, allowing daylight to enter indoor environments and producing some of the energy required for thermal comfort conditions [137]. Buildings have large surface areas. Effective use of this surface area can be effective in terms of energy consumption. With HPV/T systems to be placed on the roof of the building or appropriate areas, the heating load of indoor environments can be reduced with the cycle to be used to remove panel heat in addition to electricity production [138]. Similarly, with PV modules and PV module-integrated hybrid systems to be placed on different surfaces, both the heating load of indoor environments can be reduced, and a significant amount of electricity can be produced [139,140]. Natural ventilation can be provided in indoor environments without energy consumption. This is possible with systems to be applied on facades and roofs. The system called solar chimney (SC) can be integrated into facades or roofs, and the air in closed spaces can be continuously discharged from the chimney, and fresh air can be taken into closed spaces without energy consumption. SC works on the principle of rising heated air and accelerates the heated air upwards through the chimney without any energy requirement [141]. With the SC concept to be applied in buildings, a warm surface is provided by placing an absorber on the other surface of the chimney, which has a glass surface. Then, natural ventilation is achieved by raising the air in contact with the surface. The schematic view of the system and two different uses are given in Figure 7. Researchers who evaluated the SC application with a CFD study claim that the optimum airflow rate will be obtained in the range of 45–70° for the chimney angle for the roof type [142].

There are many studies on SC applications for ventilation in indoor environments. Wei et al. [143] present a CFD analysis for a sloping SC to be installed on the roof of a two-story residential building. They claim that the optimum chimney inclination angle is 4° from the horizontal and that a ratio of 12:1 between the chimney length and the chimney width is the optimum ratio. Hussain and Oosthuizen [144] evaluate the use of solar energy for natural ventilation in a simple atrium building with a CFD study. They model the natural ventilation of an atrium cavity integrated with a solar chimney using buoyancy effects. They claim that the results are sufficient for thermal comfort. They state that the design parameters are the governing factor for indoor air conditions. One of the SC-like applications for natural ventilation in indoor environments without energy consumption is the Trombe wall. The system is based on the principle that the air in contact with a hot surface moves upwards with increasing temperature and provides natural ventilation. Wang et al. [145] evaluate indoor air movement with a CFD study with the addition of a Trombe wall application at a ceiling height of 2.4 m in an environment with a closed volume of 38.4 m³. They include simulation results at different entrance heights, gap widths, and solar radiation. They argue that 0.2 m is the ideal dimension for the entrance height and 0.2–0.3 m is the ideal dimension for the gap width.

4.2. Experimental Validation and Test Facilities

There are many numerical and CFD studies on thermal conditions in buildings. However, the conditions in real situations may differ from the numerical solution and simulation results. The main reason for this is that it is difficult to include all elements in the system in the analysis. Similarly, the constant change in climatic conditions and wind effects may cause differences in the results. All these reveal the importance of experimental studies. In particular, the difficulty of experimentally analysing houses and the limitations in terms of both economy and time make experimental studies difficult. Despite this, researchers have tested passive heating, cooling, and ventilation concepts in buildings with experimental prototypes they have established in laboratory or outdoor environments.

SC works on the principle of rising heated air and can continuously discharge air without additional energy input, with the continuous pressure difference it causes [146]. The system can be applied to facades in buildings and integrated into roofs. Mathur et al. [147] investigate the effectiveness of wall-type SC application on an experimental room with a volume of 1 m³. With the experimental results they obtained and the mathematical model they created, they claim that a room with a volume of 27 m³ will have 5.6 air changes per hour at 700 W/m² solar radiation. Afonso and Oliveira [148] placed 2 chimneys with a height of 2 m in a closed environment with a floor area of 12 m² to test the effectiveness of the SC experimentally. The appearance of the system is shown in Figure 8. In accordance with the SC concept, one of them makes the south-facing facade of glass. They compare the effectiveness of chimneys with a cross-sectional area of 0.2 × 1 m². They claim that SC has a solar efficiency between 10% and 22% in the reference case in the winter season. They show that insulation is a must to increase solar gain and that solar assistance efficiency will decrease by 60% in the uninsulated case.

Bouchair [149] experimentally analyses the Trombe wall effect by creating a closed environment of approximately 4.75 m³ volume. They test the airflow in a closed environment with the addition of a Trombe wall of approximately 2.2 m height. They present results with the numerical model they obtained from experimental data for 0.1–0.5 m channel opening and 0.1–0.3 m channel inlet dimensions. They present data indicating that the system will be used effectively in Algeria and regions with similar climates. Liu et al. [150] experimentally investigate the effectiveness of the Trombe wall application with a closed environment of 3.3 × 3.9 m² base area and 2.9 m height. They observe the change in the indoor temperature by opening and closing the inlet and outlet vents for the Trombe wall during daytime and evening conditions. They recommend that the ventilation vents be opened 2–3 h after sunrise and closed 1 h before sunset. They report that the heat stored in the Trombe wall is completely released, and the minimum temperature is reached by 7:30 in the morning. Hu et al. [151] present a performance critique for a Trombe wall with a DC fan integrated into a jalousie structure. The schematic view of the system is given in Figure 9. They perform an experimental setup with a width, depth, and height of 3.8, 3.9, and 2.6 m, respectively. They present results for a 1.5 × 2 m² Trombe wall integrated into the room under summer and winter climate conditions. They present the temperature distributions in the room for 0°, 45°, and 90° slat angles. They claim that the maximum temperature is obtained at a 45° slat angle value, and that a 2 °C wall temperature difference occurs when the fan is turned on at a 90° slat angle value. They emphasise that the system is promising.

4.3. Benchmarks and Case Studies

Studies on heating, cooling, and ventilation without energy consumption in buildings are also carried out regionally. Active insulation applications in cold climate regions and natural ventilation applications with the reduction in radiation effects in hot climates are common activities. Especially in applications made within the scope of natural ventilation, it is seen that geometric parameters that will provide air circulation are studied in different ways. It is seen that the importance of material type [152] as well as geometric dimensioning [153] for the Trombe wall is also studied. These natural ventilation studies carried out to reduce energy consumption in hot climate regions are promising for the zero-building approach. The commonly used Trombe wall and innovative roof-type heat recovery system diagrams are given in Figure 10.

The passive building concept attracts great attention from researchers in different climate conditions for natural ventilation. Wong and Heryanto [156] analyse the SC CFD method used to provide natural ventilation for houses in Singapore. They interpret basic design reviews by performing 32 different simulations for chimney size and chimney location indicators. They argue that the air velocity inside the house can be increased by 47% with high performance and SC in their analysis, with a wind tunnel model for 12 months. Bajc et al. [157] perform energy analysis with a 3D CFD method for a passive house with a Trombe wall for Belgrade climate conditions. The ceiling height of the 5 × 6 m² room is 3 m. The Trombe wall consists of a 0.2 m concrete wall behind a 2 mm black painted cover behind 4 mm glass. They claim that the Trombe wall, containing a 15 cm air gap, provides a great contribution in winter months and will bring additional cooling load in summer months. There are also researchers who use common construction materials to investigate the effects of using Trombe walls for Bangkok climate conditions on reducing heat transferred to houses and natural ventilation [158]. Although serious effects are obtained with a 14 cm air gap with a dark-coloured modified Trombe wall, they claim that using light-coloured ones is also sufficient for natural ventilation. Although the performance of the applications is debatable, it is important to develop studies that are suitable for the zero-building approach by reducing energy consumption. The importance of these studies increases when it is expected that buildings will meet the heating, cooling, and ventilation requirements with zero emissions and without energy consumption soon.

5. Conclusions

The vast majority of world energy consumption comes from buildings. This is particularly important in terms of controlling energy consumption and reducing emission values with innovative approaches. In this study, a general overview of the energy consumption caused by buildings is provided, and a detailed analysis is presented by including innovative approaches that will reduce energy consumption. In particular, it is discussed how the high energy consumption required to provide thermal comfort conditions after the construction of the building can be reduced with innovative designs and systems to be applied to facades and building structural elements. The effectiveness of applications suitable for the concept of self-sufficient zero building without additional energy consumption and the innovative aspects of the studies in the literature are presented from a different perspective. In order to shed light on subsequent studies, examples of energy-efficient building designs that can be used in different climate zones are included. Furthermore, recent developments in multifunctional and advanced materials provide promising pathways for boosting the energy efficiency of ventilated and building-integrated systems. Perovskite-based coatings, owing to their high photovoltaic efficiency and tuneable optical properties, are rapidly gaining attention for use in BIPV glazing and facade applications [159,160,161,162]. Likewise, bio-based solutions such as bamboo fibre-reinforced briquettes have demonstrated superior thermal resistance, aligning with sustainable construction goals [163]. Additionally, nano-engineered thin film coatings, including TiO₂ and smart glazing layers, enable dynamic control of solar gain, heat transfer, and daylighting, further contributing to the development of low or zero-carbon buildings [164,165]. These innovations offer a transformative vision for future facade systems, merging energy generation, insulation, and adaptive environmental control.