PRECis - Title

1. PRECis - Title PRECis: Assessing the Potential for Renewable Energy in Cities. The characterisation of urban microclimates, urban form and the environmental factors affecting energy use. Coordinator: The Martin Centre for Architectural and Urban Studies. Department of Architecture. University of Cambridge. Koen Steemers. Joint Director of the Martin Centre.

2. PRECis - Partners University of Cambridge Dr Koen Steemers (United Kingdom) CFD norway as. Prof. Helge Norstrud (Norway) Ecoles d’Ingénieurs de Fribourg Dr. Raphael Compagnon (Switzerland) Centre for Renewable Energy Sources Dr Argiro Dimoudi (Greece) Politecnico di Torino Prof.Mario Grosso (Italy) Municipality of Grugliasco - associated to POLITO (Italy)

3. PRECis - Objectives To demonstrate and quantify the relationships between the urban form parameters of a neighbourhood and the energy and environmental performance To assess a series of urban planning strategies and case studies, ranging from minimal intervention to complete new urban plans To develop techniques and guidelines which can assess and characterise any urban texture in terms of the potential for renewable energy

4. PRECis - Background City scale (macroscale) Urban geography City shape Transport Infrastructure Building scale Building form Envelope Fabric Materials Intermediate scale (mesoscale) Urban block / neighbourhood Public space Urban design Outside / inside relationships

5. PRECis - Background • ‘Cities of the industrial era have consciously excluded natural processes, substituting mechanical devices made possible by intensive use of fossil fuels… Thus, we might see our overwhelming problems of depletion and pollution as largely outgrowths of our ways of shaping the urban environment’. • Lyle, J.T. 'Regenerative Design for Sustainable Development', John Wiley and Sons, Inc., 1993

6. PRECis - Background • Background • The urban context by definition has the highest density of energy consumption and associated local environmental problems. • Improving the urban microclimate can bring environmental and energy benefits. • A better outdoor microclimate (cleaner, less noisy, cooler, etc.) can reduce reliance on mechanical systems in urban buildings.

7. PRECis - Potential • Potential energy savings • reduced reliance on air conditioning can halve energy use • optimising form can reduce energy further by approximately 25% • optimising glazing ratios can give an average 10% reduction in energy use

8. PRECis - Potential • Potential environmental benefits • Reduced pollution • More effective pollution dispersal • Less noise propogation • Increased daylight / sunlight availability or shade • Healthier and more pleasant outdoor environment • Increased walking and reduced reliance on transport

9. PRECis - State of the Art: Heat island Air temperature (red) measured in urban canyon H/W 5.5 in vernacular Moroccan city of Fez (hot-arid climate), in summer (top) and winter (bottom) compared with meteorological airport air temperature (black) - low during daytime and high during night-time for summer clear nights. Source: Rosenlund et al, 2000 The urban heat island (Turban-rural) Montreal on 7 March 1968 at 7am, with light wind and cloudless sky represented as isotherms or ‘island’ of higher temperature above urban areas. Source: Oke, 1986

10. PRECis - State of the Art: Temp. v. Geometry The relationship between maximum heat island intensity observed in a settlement and the canyon sky view factor (city texture) in its central area. Source: Oke, 1981

11. PRECis - State of the Art: Climate v. design Recommended urban morphological responses to major climatic regions. Source: Keplinger, 1978

12. PRECis - State of the Art: Density Would an energy-efficient environment mean great sacrifices in terms of amenity, equity or aesthetics? LEFT: Density vs. urban form - same density, different ground coverage.Source: Urban Task Force, 1999

13. PRECis - The approach

14. PRECis - Environmental and form parameters

15. Building and street specifics -Obstructions -Building depth -H/W canyon ratio -Street configuration -Building use -Envelope U-value -Façade reflectances -Façade roughness Immediate neighbourhood (effect of planted park) Directional porosity City frontal area City texture Edge effect PAD Cd Cp PRECis - Scales of investigation

16. Trondheim Cambridge Il Borgo Pathsia Pérolles Plaka PRECis - Technique Digital Elevation Model (DEM): image where each pixel has a grey-level proportional to its height. A DEM is equivalent to a full 3-dimensional description of the urban surface.

17. PRECis - Wind and pollution Computed pressure coefficient and particle streak lines for wind direction of 270 and (left) =0.14, and (right) =0.28, for a generic urban area; =0.14 represents the turbulent flow over a smooth surface, =0.28 represents the turbulent flow over medium sized vegetation and small buildings Pressure distribution on buildings superimposed with pollutant particle streak lines on the proposed scheme in the Trondheim site.

18. PRECis - Wind: simplified model Correlation between ventilation rate (red) and Cd (Coefficient of Drag) (black) for the Trondheim site (bottom right); calculations done with CFD

19. PRECis - Wind and energy use Investigating effect of urban drag coefficient Cd on airflow rates and energy loads (winter energy loss and summer cooling) and potential RE through natural ventilation CPCalc+ Cd (Coefficient of Drag) ESP-r Three-step processing of an existing urban layout with Mapping Technique to reach the Reference Model Array (RMA, right), preserving geometric properties such as Plan Area Density (PAD)

20. PRECis - Wind and planning Downwind wake core of buildings are plotted for the prevalent wind direction, representing an area of calm where wind velocity is reduced to under 50% of the upstream velocity.

21. PRECis - Vegetation and temperature Rule of thumb: As a rule of thumb, a 0.8K reduction in ambient air temperature is to be expected for a 10% increase to the ratio of green to ground surface built area

22. PRECis - Form and light

23. PRECis - Form parameters Aerial photo of LondonTotenham Court Road area London site view 400 x 400m London axonometric obtained from a DEM London Digital Elevation Model (DEM)

24. PRECis - Environmental parameters Directional porosity rose for London DEM, varying with orientation Shadow casting performed on London DEM

25. BOTTOM: comparative average sky view factors for 3 European cities - London shows higher potential for urban heat island occurrence. FAR BOTTOM: comparative average sky view factor values along the height of the street canyon, indicating potential daylighting inside buildings PRECis - Form and light

26. LT (lighting and thermal) method: manual spreadsheet method that allows the prediction of heating, lighting, ventilating and cooling energy consumption in non-domestic buildings and to help designers to determine how energy consumption of a building relates to architectural parameters at the concept design stage. PRECis - Form and energy Passive zone Façade orientation Urban Horizon Angle at 6m high Energy use (MWh/sqm/yr)

27. PRECis - Wind, light and noise

28. C - 0.45 H/W A - 2.7 H/W View factor extremes Average view factor from street to sky 0.81 0.37 D - 0.9 H/W A - 2.7 H/W Sound pressure level extremes Average sound pressure level in all streets 53.4 dB 67 dB PRECis - Light and noise

29. Trondheim Cambridge Il Borgo Pathsia London Plaka PRECis - Case studies 35% 0.14 20% 0.26 30% 0.35 51% 0.25 55% 0.21 49% 0.31 Site coverage Surface toVolume ratio ENVIRONMENTALPARAMETERS Plan area density + Surface to volume ratio Surface to volume ratio Porosity + surface to volume ratio Directionality Directional porosity + drag coefficient FORM INDICATORS Density (low - high) Grain size (coarse - fine) Compactness (compact - dispersed) Street configuration (orthogonal - organic) Skyline profile (rough - uniform) …. Design guidelines

30. PRECis THE END ‘Evolutionary approachrather than revolutionary’ ‘Remedial interventionrather than radical ‘Urban microsurgery’ Minimal interventionwith optimal environmental benefit...