Building-integrated fog collectors

Rendering of building-integrated fog collectors (BIFCs)

Building-integrated fog collectors (BIFCs) are façade, roof or shading elements that harvest atmospheric moisture by intercepting wind-borne fog directly on the surfaces of buildings. 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 expression “building-integrated fog collector” (BIFC) was coined by Caldas et al. (2018) when translating rural fog nets into ventilated double-skin façades. They framed a BIFC as “any cladding element that simultaneously fulfils a building-physics role (e.g. shading, weather protection) and passively intercepts atmospheric droplets.” Later reviews compare BIFCs with BIPV, arguing that water-harvesting façades can “stack” functions—solar control, water supply and architectural articulation—within the same envelope depth.

Because the collector is integral to the façade, wind-load design, fire safety and maintenance access become part of the BIFC definition. Recent literature therefore classifies BIFCs first by integration zone (façade, roof, sun-breaker) and only second by mesh type, giving rise to textile curtain walls, rotating mesh louvres and roof-top radiative fins.

Operating principle

BIFCs still rely on capture → coalescence → collection, yet the building boundary layer alters each step:

• Aerodynamic interception – 3-D CFD shows that a porous screen placed just up-wind of a solid wall experiences flow acceleration ≈ 1.3 × the freestream, lifting aerodynamic collection efficiency by ~15%.
• Coalescence & drainage – Janus meshes with alternating super-hydrophilic/super-hydrophobic stripes drain 40–60% faster than uniform surfaces, reducing re-entrainment losses.
• Collection routing – Patented façade gutters (EP 4170112 B1) embed water channels behind bristle seals, protecting condensate from wind and direct sun and thereby limiting secondary evaporation.

Additional parameters:

• Boundary-layer gap – Offsetting the mesh 50–150 mm from the wall lessens wake recirculation and raises collection efficiency by 10–20% in simulations.
• Orientation – Field data from CloudFisher nets indicate a ≈ 25% yield drop when panels deviate 30° from prevailing fog winds.
• Radiative-cooling synergy – Several authors propose coupling roof-mounted condensers or ETFE cushions with fog meshes to extend water production into calm, humid nights; quantitative performance is still under study.

Historical development

Academic interest in building-integrated fog collectors emerged in the early 2000s, when design studios at the University of California, Berkeley and Politecnico di Milano experimented with Raschel-mesh sun-screens mounted on façades. Those studio prototypes demonstrated that the same textile able to shade glazing could also capture wind-borne droplets, effectively coining the BIFC concept.

Between 2011 and 2014 the idea moved from sketches to façade-scale trials. At Berkeley’s coastal fog field site, resin-framed panels measuring 0.3 × 0.5 m were fixed to a small timber test hut and produced roughly 0.8 L m⁻² day⁻¹. Parallel tests with 1 m² reference nets yielded 2.3–3.9 L m⁻² day⁻¹, creating the first empirical baseline for later façade work.

From 2015 to 2020 research focused on aerodynamic optimisation. Caldas and colleagues evaluated 1 m² double-skin modules in a controlled wind-fog tunnel (5–6 m s⁻¹, LWC ≈ 0.30 g m⁻³) and consistently recorded 2–4 L m⁻² day⁻¹. Three-dimensional CFD published by Carvajal et al. predicted collection efficiencies in the same range, validating the design rules derived from the tunnel data.

The next leap came in 2021, when Li et al. introduced a kirigami-inspired, three-dimensional mesh that generated counter-rotating vortices. A 1 m² outdoor prototype harvested about 14 L m⁻² day⁻¹ at only 2.5 m s⁻¹ wind speed and was engineered as a cassette suitable for curtain-wall systems.

In 2023 Politecnico di Milano erected a 3 m × 5 m double-layer textile façade nicknamed “Nieblagua”. The demonstrator withstood 12 m s⁻¹ gusts while maintaining continuous drainage, providing the first full-scale engineering proof of a curtain-wall BIFC.

Typologies and design strategies

The simplest expression of a building-integrated fog collector is the mesh-screen façade, in which a porous Raschel or monofilament textile is tensioned across the wind-ward elevation like a brise-soleil. Field trials on elementary schools in northern Peru reported daily yields of 2–3 L m⁻² during winter *Garúa* while adding less than 12 kg m⁻² dead load to the curtain wall.

Where improved maintainability and airtightness are required, the collector becomes the outer layer of a ventilated cavity, forming a double-skin façade. Politecnico di Milano’s 3 m × 5 m “Nieblagua” mock-up uses a hydrophilic basalt textile suspended 120 mm in front of the waterproofed wall; wind-tunnel and on-site measurements showed stable drainage and an average yield of 2.8 L m⁻² day⁻¹ without staining the primary façade surface.

A more recent direction treats the collector as a kinetic element. Adaptive modular panels mounted on lightweight frames rotate toward the prevailing wind under guidance from humidity sensors or edge-AI forecasts. A kirigami-shaped 1 m² panel harvested roughly 14 L m⁻² day⁻¹ at only 2.5 m s⁻¹, nearly seven times the yield of a fixed mesh.

These fixed screens, ventilated cavities, radiative roof fins and adaptive panels demonstrate that BIFCs are not a single product but a family of envelope strategies whose geometry, materials and control logic can be tuned to local climate and architectural intent.

Key performance factors

• Liquid water content (LWC) and wind speed largely determine theoretical yield; façade wakes can reduce flux by 30–40 %.
• Surface patterning with alternating super-hydrophilic and slippery stripes can raise drainage efficiency by ≈40 %.
• Orientation – Computational-fluid-dynamics studies show a 15–20 % drop when panels deviate more than 30° from the dominant wind; rotating modules mitigate the loss.

Applications

Non-potable supply for buildings – Pilot façades on elementary schools and municipal offices along the northern Peruvian coast deliver 3–8% of annual non-potable demand (toilets, cleaning, landscaping), with daily yields averaging 2.5 L m⁻² under winter Garúa conditions.

Irrigation of vertical agriculture – A community greenhouse in Bogotá retro-fitted a 15 m² mesh façade that channels up to 120L day⁻¹ of fog water to NFT hydroponic gutters during the July–September fog season, reducing tanker-truck deliveries by 52%.

Potable micro-supply – On Isla de la Plata (Ecuador), a mesh-clad rooftop water tower integrated into a visitor-centre pergola produces 25–40 L day⁻¹. After first-flush diversion and ceramic + UV treatment, the water meets WHO drinking standards and replaces bottled water for staff and tourists.

Façade cooling & solar-gain control – A double-skin BIFC on a Milan test cell routes harvested water over inner aluminium fins; measured inner-surface temperatures fell by 3–5 °C and HVAC energy demand dropped 12 % while still yielding 2 L m⁻² day⁻¹.

Emergency and off-grid resilience – Following the 2023 Atacama coastal earthquake, eight modular BIFC panels (1 m × 2 m each) erected against a prefabricated clinic wall supplied ≈ 780 L over ten days for wound cleansing and sanitation.

Advantages

Envelope multifunctionality – A BIFC collects water, provides solar shading and serves as an architectural screen on the same surface, so no extra plot area is required.

Passive cooling synergy – Routing harvested water over an inner fin array in a Milan test cell lowered interior-skin temperatures by 3–5 °C and trimmed HVAC peak demand by ~12 % while still yielding 2 L m⁻² day⁻¹.

Lightweight retrofitting – Raschel HDPE mesh plus tension-cable framing adds < 12 kg m⁻², allowing installation on existing curtain walls without major reinforcement.

Climate resilience – Following the 2023 Atacama coastal earthquake, eight modular BIFC panels (1 m × 2 m each) erected on a temporary clinic wall supplied ≈ 780 L over ten days for sanitation.

Challenges

Climate dependence – Long-term monitoring on Peru’s north coast shows seasonal yield fluctuations of ±60 %, limiting scalability in dry, non-foggy periods.

Wind-load and corrosion durability – Salt-spray ageing tests indicate up to a 30 % drop in HDPE tensile strength after a five-year coastal exposure equivalent, demanding careful material selection.

Bio-fouling and pore clogging – Dust-fog cycling cut drainage efficiency by > 40 % on uncoated nets, whereas Janus-patterned meshes retained 60% higher throughput.

Fire-safety and façade code compliance – Synthetic nets used as exterior skins must satisfy EN 13501-1 or NFPA 285 fire tests; EU guidance treats permeable mesh layers as ventilated rainscreens, triggering added cavity-barrier or sprinkler requirements.

Water-quality assurance – Fog water can carry airborne contaminants; field tests on Isla de la Plata showed that first-flush diversion plus 1 µm ceramic filtration and UV disinfection brought E. coli below detection limits before human consumption.

See also

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