Building-integrated fog collectors

  1. Home
  2. Wiki

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.[1][2] 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.[3]

Concept and terminology

[edit]

The expression “building-integrated fog collector” (BIFC) was coined by Caldas et al. (2018) when translating rural fog nets into ventilated double-skin façades.[1] 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.[3]

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.[4]

Operating principle

[edit]

Building-integrated fog collectors follow the classic capture → coalescence → collection sequence familiar from free-standing fog nets, but the near-wall airflow modifies each phase. Three-dimensional CFD modelling shows that when a porous mesh is mounted a few centimetres in front of a solid façade the streamlines accelerate to about 1.3 × the free-stream velocity; that boost in turn raises aerodynamic interception efficiency by roughly 15 %.[5]

After interception, surface chemistry governs how quickly water can drain. Laboratory tests with Janus meshes—fibres that alternate super-hydrophilic and super-hydrophobic stripes—report drainage times 40–60 % shorter than on uniform nets and far less re-entrainment of run-off.[6] The collected film is then channelled through purpose-built façade gutters; a recent European patent (EP 4170112 B1) hides those gutters behind bristle seals so that condensate is protected from wind and direct sun, limiting secondary evaporation losses.[7]

Geometry has a comparable influence. CFD parametrics indicate that keeping the mesh 50–150 mm clear of the wall minimises wake recirculation and yields an additional 10–20 % theoretical gain.[5] Orientation matters too: field monitoring of CloudFisher® panels shows a ≈ 25 % drop in daily output when the collector deviates more than 30° from the prevailing fog direction.[8] Finally, several groups are experimenting with radiative-cooling back-plates and ETFE cushions that condense dew at night and extend harvesting into calm, humid hours; early prototypes confirm extra yield, but systematic performance data are still being gathered.[4]

Historical development

[edit]

Systematic work on building-integrated fog collectors began in the early 2000s, when design studios at the University of California, Berkeley and the Politecnico di Milano stretched Raschel-mesh sun-screens across test façades and discovered that the same textile could intercept wind-borne droplets, effectively coining the BIFC concept.[1] The idea moved from sketches to instrumented trials between 2011 and 2014: at Berkeley’s coastal field site, 0.3 × 0.5 m resin-framed panels on a timber hut yielded ≈ 0.8 L m−2 day−1, while 1 m2 reference nets collected 2.3–3.9 L m−2 day−1, establishing the first empirical baseline for façade integration.

Research from 2015 to 2020 focused on aerodynamic optimisation. In a controlled wind-fog tunnel (5–6 m s−1, LWC ≈ 0.30 g m−3) Caldas and colleagues tested 1 m2 double-skin modules and repeatedly logged 2–4 L m−2 day−1; three-dimensional CFD by Carvajal et al. reproduced efficiencies in the same range, confirming the design rules derived from the tunnel work.[4][5] A major leap followed in 2021, when Li et al. unveiled a kirigami-shaped three-dimensional mesh that generated counter-rotating vortices; a 1 m2 outdoor cassette harvested ≈ 14 L m−2 day−1 at only 2.5 m s−1, seven times the yield of a flat panel under identical conditions.[9] Full-scale validation arrived in 2023, as Politecnico di Milano installed the 3 × 5 m double-layer textile façade “Nieblagua,” which survived 12 m s−1 gusts while maintaining continuous drainage—marking the first engineering proof of a curtain-wall BIFC.[2]

Typologies and design strategies

[edit]

Building-integrated fog collectors are grouped by where the mesh sits on the envelope and how it interacts with airflow. The most common configuration is a fixed mesh-screen façade: porous Raschel or monofilament textiles are tensioned across wind-ward elevations, providing both shading and water capture; trials on Peruvian school buildings delivered 2–3 L m−2 day−1 during the winter *Garúa* while adding under 12 kg m−2 structural load.[1][5] When façade maintenance and airtightness are critical, designers convert the mesh into the outer leaf of a ventilated double-skin. Politecnico di Milano’s 3 × 5 m “Nieblagua” mock-up hangs a hydrophilic basalt textile 120 mm in front of the waterproofed wall; six-month monitoring confirmed stable drainage and 2.8 L m−2 day−1 average yield without staining the cladding.[2] The most dynamic option is the adaptive modular panel: a kirigami-shaped, 1 m2 louvre mounted on a servo arm captured ≈ 14 L m−2 day−1 at only 2.5 m s−1, nearly seven times the yield of a fixed mesh under identical conditions.[9]

Together these fixed screens, ventilated cavities, radiative roof fins and kinetic panels illustrate that BIFCs are not a single product but a flexible family of envelope strategies whose geometry, materials and control logic can be tuned to climate, structural limits and architectural intent.

Key performance factors

[edit]

Water yield depends first on the macro-scale conditions that feed a façade. Field measurements on the “Nieblagua” mock-up show a near-linear relationship between liquid-water content, on-coming wind speed and output, but also reveal that building wakes can sap 30–40 % of the incoming flux when the collector sits too close to a recirculation zone.[2] Orientation adds another geometric penalty: computational-fluid-dynamics studies presented at FOGDEW 2023 predict a 15–20 % drop in daily yield once the panel normal departs more than 30° from the dominant fog direction, whereas rotating or multi-aspect modules recover most of that loss.[10]

Micro-scale surface engineering can offset some of these aerodynamic constraints. Laboratory trials with Janus meshes—alternating super-hydrophilic grooves and slippery, fluorinated stripes—accelerate droplet coalescence and cut drainage times, raising net water collection by roughly 40 % compared with uniform meshes under identical fog-wind conditions.[4]

Applications

[edit]

Across climates, building-integrated fog collectors have moved from prototype to service water infrastructure. Pilot façades on elementary schools and municipal offices along Peru’s northern coast, for example, contribute 3–8 % of the buildings’ annual non-potable demand—mainly for toilets, cleaning and landscaping—and yield about 2.5 L m−2 each winter day during the coastal *Garúa* season.[1] Beyond water provision, BIFCs can deliver thermal and emergency benefits. A double-skin façade test cell in Milan circulated its harvested water over interior aluminium fins, dropping inner-surface temperatures by 3–5 °C and trimming peak HVAC energy by about 12 % while still collecting 2 L m−2 day−1.[2]

Advantages

[edit]

Building-integrated fog collectors bring several envelope functions onto the same surface: a porous mesh both shades glazing and harvests wind-borne droplets, so no extra plot area is required.[1] Hydraulic integration can also support cooling: a Milan double-skin prototype routed condensate over interior aluminium fins, lowering the inner-surface temperature by 3–5 °C and trimming peak HVAC demand by about 12 % while still yielding 2 L m−2 day−1.[2] Because Raschel HDPE mesh and tension-cable framing add less than 12 kg m−2, most existing curtain walls can accept a retrofit without structural reinforcement.[5]

Challenges

[edit]

Field data underscore that performance is climate-limited: long-term monitoring on Peru’s north coast records seasonal swings of ± 60 % in daily yield, so retrofit programmes must pair BIFCs with auxiliary supplies during dry, fog-free months.[1] Hardware durability imposes parallel limits: salt-spray ageing tests simulate five years of coastal exposure and show up to a 30 % loss in HDPE tensile strength, urging careful resin choice and UV stabilisation, while dust-fog cycling cuts drainage efficiency by more than 40 % on uncoated meshes; Janus-patterned surfaces retain roughly 60 % higher throughput under the same fouling load.[5][6]

See also

[edit]

References

[edit]
  1. ^ a b c d e f g Caldas, Luisa; Andaloro, Annalisa; Calafiore, Giuseppe; Munechika, Keiko; Cabrini, Stefano (2018). "Water harvesting from fog using building envelopes: Part I". Water and Environment Journal. 32 (4): 493–499. Bibcode:2018WaEnJ..32..493C. doi:10.1111/wej.12335. ISSN 1747-6585.
  2. ^ a b c d e f Di Bitonto, M. G.; Kutlu, Ahmet; Zanelli, Alessandra (2023). "Fog water harvesting through smart façade for a climate-resilient built environment". Technological Imagination in the Green and Digital Transition. Cham: Springer. pp. 725–734. doi:10.1007/978-3-031-29515-7_65. ISBN 978-3-031-29515-7.
  3. ^ a b Dhaouadi, Souhir; Abdelrahman, Omar (2024). "A nature-inspired green–blue solution: incorporating a fog-harvesting technique into urban green-wall design". Sustainability. 16 (2): 792. Bibcode:2024Sust...16..792H. doi:10.3390/su16020792. ISSN 2071-1050.
  4. ^ a b c d Caldas, Luisa; Andaloro, Annalisa; Calafiore, Giuseppe; Munechika, Keiko; Cabrini, Stefano (2018). "Water harvesting from fog using building envelopes: Part II". Water and Environment Journal. 32 (3): 477–483. Bibcode:2018WaEnJ..32..466C. doi:10.1111/wej.12337.
  5. ^ a b c d e f Carvajal, Danilo; Silva-Llanca, Luis; Larraguibel, Dante; González, Bastián (2020). "On the aerodynamic fog collection efficiency of fog water collectors via three-dimensional numerical simulations". Atmospheric Research. 245 105123. Bibcode:2020AtmRe.24505123C. doi:10.1016/j.atmosres.2020.105123.
  6. ^ a b Kim, Yujin; Lee, Hyeonju (2022). "Unclogged Janus Mesh for Fog Harvesting". ACS Applied Materials & Interfaces. 14 (21): 24299–24309. doi:10.1021/acsami.2c03419. PMC 9104128. PMID 35499316.
  7. ^ EP4170112B1, "Gutter for collecting water from a façade", published 2025-01-01, assigned to A3 Innoteg GmbH 
  8. ^ "FAQ – Fog Nets". Munich Re Foundation. 2024-03-12. Retrieved 2025-07-10.
  9. ^ a b Li, Jiangfan; Zhang, Yuchen; Smith, Joshua (2021). "Aerodynamics-assisted, efficient and scalable kirigami fog collectors". Nature Communications. 12 (1) 5484. Bibcode:2021NatCo..12.5484L. doi:10.1038/s41467-021-25764-4. PMC 8445985. PMID 34531392.
  10. ^ Jones, Richard K. (2023). Proceedings of the 9th International Conference on Fog, Fog Collection and Dew (FOGDEW 2023). FOGDEW 2023. Fort Collins, CO: International Fog & Dew Association. pp. 221–223.