Building-integrated fog collectors

Building-integrated fog collectors (BIFCs) are architectural elements such as meshes or special panels built into facades, roofs, or shading features to harvest water from fog. These systems are especially relevant in areas where fog is frequent and can supplement non-portable water supplies while providing secondary benefits like shading and architectural interest. By embedding mesh or patterned condenser surfaces into the building envelope, BIFCs combine passive water production with shading and aesthetic functions, offering a compact alternative to ground-mounted fog nets in dense urban areas.

Concept and terminology

The concept of integrating fog-harvesting materials into building envelopes was first systematized by Caldas et al. (2018), who explored how ventilated double-skin façades could function both as architectural cladding and fog-collecting surfaces. In their work, these elements were described as multifunctional systems capable of providing shading, weather protection, and passive interception of airborne droplets. Later studies have compared such systems to building-integrated photovoltaics (BIPV), highlighting their ability to stack multiple functions—such as solar control, water harvesting, and architectural expression—within the same envelope depth. Because these collectors are physically integrated into the building skin, issues such as wind load resistance, fire safety, and maintenance accessibility become integral to their design. BIFCs are commonly categorized according to their location on the building—such as façades, rooftops, or sun-shading devices—and further differentiated by the mesh type or condensation surface employed. This has led to a variety of design solutions, including textile curtain walls, kinetic mesh louvres, and roof-mounted radiative fins.

Operating principle

Like conventional fog nets, BIFCs follow a three-step mechanism: capture → coalescence → collection. However, the proximity to a building envelope alters aerodynamic behavior. Computer Simulations suggest that placing mesh in front of building surfaces can change how air moves and help collect more fog. The actual benefit depends on the shape of the mesh, how far apart the panels are, and the local weather. Surface chemistry also plays a role in droplet behavior. Janus meshes—materials alternating super-hydrophilic and super-hydrophobic domains—demonstrate enhanced drainage and reduced droplet re-entrainment compared to uniform meshes. Harvested water is directed through embedded drainage channels in the façade, which may be protected or architecturally concealed to limit evaporation. Panel spacing and orientation are equally important. Maintaining a small offset from the wall can reduce wake recirculation, and misalignment from the fog’s prevailing direction can reduce yield. Recent experimental designs, such as kirigami-shaped meshes, have demonstrated improved interception by inducing controlled vortex structures.

Historical development

Systematic investigations into building-integrated fog collectors (BIFCs) began in the early 2010s, when researchers at the University of California, Berkeley, and the Politecnico di Milano explored the potential of Raschel-mesh shading screens to intercept wind-borne fog droplets. These initial studies established the viability of embedding fog-harvesting materials within architectural envelopes. Between 2015 and 2020, research efforts focused on improving aerodynamic performance through both physical and numerical modeling. Laboratory tests using wind tunnels examined 1 m² facade modules and found they could yield 2-4 liters of water per square meter per day. Complementary three-dimensional CFD simulations by Carvajal et al. reproduced similar efficiencies under equivalent mesh configurations, validating design rules and airflow interactions. A major innovation followed in 2021, when Li et al. introduced a kirigami-inspired, three-dimensional mesh geometry. In field trials, a 1 m² panel achieved approximately 14 L·m⁻²·day⁻¹ at a modest 2.5 m/s wind speed—about seven times the performance of a flat panel under similar conditions. In 2023, researchers at the Politecnico di Milano field-tested a 3 × 5 m textile façade mock-up known as “Nieblagua,” composed of a hydrophilic double-layer curtain system. The installation demonstrated continuous drainage under natural fog events and architectural-scale integration, marking a milestone in full-scale prototyping of BIFCs.

Typologies and design strategies

Building-integrated fog collectors (BIFCs) can be classified according to their position on the building envelope and their aerodynamic behavior. A common configuration is the fixed mesh-screen façade, where porous Raschel or monofilament textiles are tensioned across windward elevations to provide both solar shading and fog interception. In applications where façade performance criteria such as airtightness or maintainability are critical, the mesh may form the outer layer of a ventilated double-skin façade. One example is the Nieblagua prototype developed at the Politecnico di Milano, which suspends a hydrophilic basalt textile 120 mm in front of a sealed building surface; field testing over six months confirmed stable drainage and an average yield of 2.8 L·m⁻²·day⁻¹ without staining the cladding.

Since 2021, dynamic mesh modules have emerged as a high-performance alternative. Li et al. developed a kirigami-inspired 1 m² panel that generates vortex-enhanced fog capture; under 2.5 m/s wind conditions, it achieved ≈14 L·m⁻²·day⁻¹—nearly seven times the yield of conventional flat meshes under identical conditions. These diverse configurations—including fixed façades, ventilated cavities, radiative roof elements, and kinetic mesh louvres—demonstrate that BIFCs are not a singular product but a design family. Their form, materials, and control strategies can be adapted to suit specific climatic, structural, and architectural goals.

Key performance factors

Fog collector performance is influenced by both macro- and micro-scale factors. At the environmental scale, water yield depends primarily on wind speed and liquid water content in the air. Field testing of the Nieblagua façade prototype demonstrated a strong correlation between these parameters and water output, while also suggesting that collectors placed too close to turbulent wake zones may experience reduced efficiency. Panel orientation plays an equally important role: computational analyses indicate that performance drops when fog-harvesting surfaces are misaligned with the prevailing wind direction, although rotating or multi-aspect configurations can mitigate these losses. On the material side, Janus-type meshes—featuring alternating superhydrophilic and fluorinated regions—have been shown in laboratory trials to enhance drainage and accelerate droplet coalescence, improving fog capture efficiency compared to uniformly coated meshes under controlled conditions.

Applications

Building-integrated fog collectors (BIFCs) have progressed from experimental prototypes to functional components of building services in select climates. Pilot installations in coastal Peru and other fog-prone regions have demonstrated that such systems can supplement non-potable water supplies—particularly for uses like irrigation, cleaning, and toilet flushing—during the winter Garúa season. In addition to water provision, BIFCs can contribute thermal benefits. For example, a double-skin façade test cell in Milan routed harvested water over interior aluminium fins, resulting in surface temperature reductions of 3–5 °C while maintaining consistent fog water yields.

Advantages and challenges

BIFCs offer several advantages, including the integration of shading and water-harvesting functions on the same surface—eliminating the need for additional land area. Their lightweight construction, typically involving Raschel mesh and tensile cable frames, allows retrofitting onto many existing curtain walls without major structural modification.

Nonetheless, practical limitations remain. The effectiveness of fog harvesting is highly dependent on local microclimate and fog availability, with seasonal fluctuations potentially impacting reliability. Additionally, environmental exposure can degrade material performance over time. Studies on mesh durability have shown that prolonged fog–salt–dust cycling can significantly impair drainage efficiency, though engineered surfaces such as Janus meshes demonstrate improved resistance to fouling and longer-lasting performance under such conditions.

See also

• Fog collection
• Atmospheric water generator
• Building-integrated photovoltaics
• Green wall