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A simplified numerical model for rainwater runoff on building facades: Possibilities and limitations

Blocken, B. and Carmeliet, J.
2012
Building and Environment, Volume 53, July 2012, Pages 59-73
Wind-driven rain; Driving rain; Building wall; Numerical simulation; Wind flow; Heat-air-moisture transfer modelling

Blocken, B. and Carmeliet, J., (2012), "A simplified numerical model for rainwater runoff on building facades: Possibilities and limitations", Building and Environment, Volume 53, July 2012, Pages 59-73.
Abstract:
A simplified numerical model for rainwater runoff on building facades is presented, evaluated and discussed. The variation of runoff film thickness is described by a first-order hyperbolic partial differential equation. This equation is derived from the continuity equation, to which the wind-driven rain (WDR) intensity and the capillary absorption flux by the wall are added as source/sink terms, and from the adoption of the parabolic velocity profile of the Nusselt solution for a simplified representation of thin film flow. Two major model simplifications are the adoption of the Nusselt solution for (1) statistically-steady, developed films, in spite of actual wave behaviour, and for (2) transient, developing films, in spite of the actual moving contact line complexity. Both simplifications are directly related to surface tension effects. Concerning the first simplification, a selective review of the literature, including experimental laboratory data, confirms the validity of the Nusselt solution for representing the time-averaged properties of thin film flow, up to film Reynolds numbers of 1000, in spite of the actual wave behaviour. Concerning the second simplification, the runoff model is evaluated by a comparison with available on-site measurements of rainwater runoff from a building facade exposed to WDR, indicating a fair qualitative and quantitative agreement. Specific attention is given to a discussion of the possibilities and limitations of the runoff model. The runoff model can easily be integrated into 2D and 3D building envelope heat-air-moisture transfer (BE-HAM) models, but further research on the simplifications and assumptions of the runoff model is required.

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Author Information and Other Publications Notes
Blocken, B.
Laboratory of Building Physics, Department of Civil Engineering, Katholieke Universiteit, Leuven, Belgium. http://perswww.kuleuven.ac.be/~u0008129/
  1. A review of wind-driven rain research in building science
  2. Conservative modelling of the moisture and heat transfer in building components under atmospheric excitation
  3. Driving rain on building envelopes II: representative experimental data for driving rain estimation
  4. Pedestrian wind environment around buildings: literature review and practical examples
  5. Quantification of driving rain as a boundary condition for water flow modelling in building parts
  6. Rainwater runoff from building facades: A review
  7. Spatial and temporal distribution of driving rain on a low-rise building
  8. Spatial and temporal distribution of driving rain on buildings: numerical simulation and experimental verification
  9. Validation of external BES-CFD coupling by inter-model comparison
  10. Wind, rain and the building envelope: studies at the Laboratory of Building Physics, KULeuven
  11. Wind-driven rain as a boundary condition for HAM simulations: Analysis of simplified modelling approaches  
Carmeliet, J.
Department of Civil Engineering Laboratory of Building Physics, Catholic University of Leuven, Belgium
  1. A comparison of different techniques to quantify moisture content profiles in porous building materials
  2. A multiscale network model for simulating moisture transfer properties of porous media
  3. A review of wind-driven rain research in building science
  4. Conservative modelling of the moisture and heat transfer in building components under atmospheric excitation
  5. Description of the moisture capacity of building materials
  6. Determination of the isothermal moisture transport properties of porous building materials
  7. Determination of the liquid water diffusivity from transient moisture transfer experiments
  8. Determination of the moisture capacity of porous building materials
  9. Driving rain on building envelopes II: representative experimental data for driving rain estimation
  10. Microscopic analysis of imbibition processes in oolitic limestone
  11. Modeling fluid flow in fractured media using continuum, network and discrete aproaches
  12. Pedestrian wind environment around buildings: literature review and practical examples
  13. Performance prediction for masonry walls with EIFS using calculation procedures and laboratory testing
  14. Position paper on material characterization and HAM model benchmarking
  15. Rainwater runoff from building facades: A review
  16. Simulating non-isothermal water vapour transfer: an experimental validation on multi-layered building components
  17. Spatial and temporal distribution of driving rain on a low-rise building
  18. The influence of soil moisture in the unsaturated zone on the heat loss from buildings via the ground
  19. Wind, rain and the building envelope: studies at the Laboratory of Building Physics, KULeuven
  20. Wind-driven rain as a boundary condition for HAM simulations: Analysis of simplified modelling approaches  


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