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PPF: a tool to study solar irradiation and illuminance in urban areas

PPF is a tool developed in the PRECis project to help design "Solar Cities" by quantifying the potential for solar and daylighting applications on vertical surfaces. It uses hourly sky models and averages to obtain irradiance and luminance values. The tool also includes 3D building models and numeric data to simulate solar and daylighting potential. PPF has been used in case studies and ongoing projects, with plans for extensions for urban open space analysis.

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PPF: a tool to study solar irradiation and illuminance in urban areas

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  1. PPF: a tool to study solar irradiation and illuminance in urban areas Raphaël Compagnon (September 2002) Developed in the framework of the European project:PRECis: Assessing the Potential for Renewable Energy in Cities

  2. A method to quantify the potential for solar (passive+active ) and daylighting applications in urban areas Focus mainly on vertical surfaces (buildings facades) Goal: helping thedesign of “Solar Cities”

  3. [Final Energy] =[Urban Solar and Daylight Availability][Utilisation Factors] [Urban Solar and Daylight Availability]=[Sky][Urban form]

  4. Sky model Hourly sky models generated by gendaylit usingclimatic data from METEONORM Averaging process to obtain «average sky models » for specific applications Heating season Year 8h–18h radiance values radiance values luminance values 2 2 [W/m /sr] 2 [W/m /sr] [lm/m /sr] Active solar applications Passive solar Daylighting

  5. Average radiometric sky model computed over the heating seaso n (2299 hours): Average radiometric sky model computed over the whole year (4330 hours): False colour radiance scale: Radiometric average skiy models(solar applications)

  6. Photometric average sky model(Daylighting) Average photometric sky model computed over the whole year (4330 hours): False colour luminance scale:

  7. 3D buildings model Geometric data: • Buildings footprints at ground level • Top heights Numeric data: • Number of storeys

  8. Sky component Reflected component(1st order &2nd order)  Simulations  Using Radiance backward ray-tracing program Sky vault “virtual” pyranometer or luxmeter

  9. PPF structure

  10. Facades % with PV potential = Global solar irradiation distributions Irradiation in [kWh/m2] Threshold for PV facades systems

  11. Facades % with passive solar potential = Global solar irradiation (heating season) Irradiation in [kWh/m2] Threshold for passive solar

  12. Facades % with daylighting potential Threshold for daylighting = Illuminance distributions Mean illuminance (8h-18h) [klx]

  13. Case study site in Fribourg (CH) • Facades fractions: • for PV = 6.5 % • for passive solar = 52 % • for daylighting = 54 % Perolles areaPlot ratio = 1.2

  14. Hypothetical urban forms (plot ratio=2.0) • PV = 10 % • passive solar = 84 % • daylighting = 83 % Comb (6 storeys) • PV = 15 % • passive solar = 80 % • daylighting = 82 % Courtyards (4 & 8 storeys) • PV = 21 % • passive solar = 100 % • daylighting = 100 % Towers (15 storeys)

  15. Outdoor daylight factors (CIE overcast sky) Sky view factors (SVF) Climatically independent characteristics

  16. Perolles areaFribourg (CH) Plaka areaAthens (GR) How to define the “orientation” of an urban area ? • Count SVF-weighted facades areas facing every directions

  17. Visualisations Gray level aerial view showing annual irradiation levels on a part of the PATHSIA area in Athens

  18. Visualisations Falsecolour aerial view showing roof areas suitable for PV modules on a part of the PATHSIA area in Athens

  19. Conclusions • PPF allows to compute irradiation and illuminance distributions over large urban areas • Already used for several case studies • PPF used as a tool for ongoing projects in collaboration with EPFL • New extensions planned for urban open space analysis

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