Characterisation and assessment of solar reflective
pavements for urban applications
Caracterización y evaluación de pavim...
Contents of the presentation
1. Definitions
2. Introduction
3. Experimental charactersation
4. Numerical analisys
5. Concl...
Definitions
Solar reflective materials, also known as cool materials, are
characterised by:
• High solar reflectance, abil...
Cool materials (and strategies) include:
• White products
• Light coloured products
• Cool coloured products
Solar reflect...
Introduction
• Climate changes  global air
temperature increase
• More frequent and intense heat waves
• The 80% of the E...
Introduction
• Climate changes  global air
temperature increase
• More frequent and intense heat waves
• It is expected t...
A number of problems arise:
• Energy end uses for cooling
– Buildings which accounts for approximately 40% of total final ...
Cool materials for urban environment can be:
• Coatings applied on an existing substrate
• Pavements constructed using a b...
• The optical characterization with the spectrophotometer Perkin Elmer
Lambda 950, equipped with a 15 centimetres diameter...
Experimental characterisation
Numerical analysis
• ENVI-met used to evaluate the impact of
pavements on outdoor temperature.
• The software uses the met...
Numerical analysis
• Simulations were performed in spring and in summer covering the central hours of
the day, from 10 to ...
Numerical analysis
• Vertical distribution of the air
temperatures in the two receptors
• Red lines receptor in the “hot s...
Numerical analysis
• Comfort analysis based on the Thom Index
• Function of dry and wet bulb temperatures
• DI [°C] = 0.4 ...
Conclusions
• The tested products have higher solar reflectance than conventional
asphalts
• Significant air temperature r...
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EESAP4 Zinzi, Michelle

  1. 1. Characterisation and assessment of solar reflective pavements for urban applications Caracterización y evaluación de pavimentos de alta reflectancia solar para aplicaciones urbanas Michele Zinzi1, Emiliano Carnielo2, Ambra Angelini3, Gaetano Fasano1 1ENEA UTEE-ERT , 2Università of Roma Tre, 3University of Venezia EESAP, San Sebastian, 1-3 July 2013
  2. 2. Contents of the presentation 1. Definitions 2. Introduction 3. Experimental charactersation 4. Numerical analisys 5. Conclusions and next works
  3. 3. Definitions Solar reflective materials, also known as cool materials, are characterised by: • High solar reflectance, ability of the material to reject the incident solar radiation • High thermal emissivity, ability of the material to radiate away the stored heat Conventional construction materials are generally characterised by • High emissivity • Low solar reflectance (0.05 for new asphalts up to 0.25 for concrete or most tiles) • Surface temperatures can be higher up to 30°C with respect to the air temperature Cool materials minimise solar heat gain keeping the construction surfaces cooler under the sun, reducing: the cooling load in buildings and the heat released to the outdoor environment by convection.
  4. 4. Cool materials (and strategies) include: • White products • Light coloured products • Cool coloured products Solar reflectance of white coatings 0 10 20 30 40 50 60 70 80 90 100 300 500 700 900 1100 1300 1500 1700 1900 2100 2300 2500 wavelength A B C D Definitions
  5. 5. Introduction • Climate changes  global air temperature increase • More frequent and intense heat waves • The 80% of the EU population will live in urban area • Additional hazard  Urban heat island (UHI)  Increase of the air temperature in urban area respect to the surrounding country
  6. 6. Introduction • Climate changes  global air temperature increase • More frequent and intense heat waves • It is expected the 80% of the EU population will live in urban area by 2030 • Additional hazard  Urban heat island (UHI)  Increase of the air temperature in urban area respect to the surrounding country
  7. 7. A number of problems arise: • Energy end uses for cooling – Buildings which accounts for approximately 40% of total final energy consumption and 36% of CO2 emissions in Europe – Dramatic increase of cooling demand in Italy in the last ten years • The electricity bill during the peak hours • The security of energy supply (planned black out!) • Indoor and outdoor thermal comfort • Health and safety for the weaker classes – Aged people – Children – Low income people, forced to live in un-pleasant and un-safe houses Introduction Cool materials can be used for outdoor and building applications
  8. 8. Cool materials for urban environment can be: • Coatings applied on an existing substrate • Pavements constructed using a binder more reflective than tar (high absorbing) • The material tested in this study is a high porous concrete used for roads and pavements. • It is characterised by a high water draining power. • The concrete binder is treated to obtain different shades of grey. • Three colours and two different sizes of the grains were tested: 1. Off white - Grain Size 6 mm 2. Off white - Grain Size 12 mm 3. Light Grey - Grain Size 12 mm 4. Dark Grey - Grain Size 12 mm Tested materials
  9. 9. • The optical characterization with the spectrophotometer Perkin Elmer Lambda 950, equipped with a 15 centimetres diameter integrating sphere. • The integrating sphere accessory is necessary when testing diffusing materials. • 5 mesurements were carried out on each samples because of the high rugosity of the samples. • Measurements were carried out between 300 and 2500 nanometres, with a spectral resolution of 5 nm. Reflectance values [%] Experimental characterisation ρe ρNIR ρv ρe - ρe new asphalt ρe - ρe aged asphalt White - Grain Size 6 mm 45 46 46 41 29 White - Grain Size 12 mm 56 56 57 51 39 Light - Grey Grain Size 12 mm 30 31 31 26 14 Dark - Grey Grain Size 12 mm 22 23 23 18 6 New Asphalt 5 7 3 --- --- Aged Asphalt 17 20 14 --- ---
  10. 10. Experimental characterisation
  11. 11. Numerical analysis • ENVI-met used to evaluate the impact of pavements on outdoor temperature. • The software uses the method S.V.A.T. (Soil, Vegetation and Atmosphere Transfer) • It operates at micro-scale to simulate the time evolution of thermo-fluid dynamic parameters. • Portions of an urban area with buildings, roads and vegetation, including thermal and optical properties of elements. • The test was carried out in Prati, a densely urbanised district in the centre of Rome.
  12. 12. Numerical analysis • Simulations were performed in spring and in summer covering the central hours of the day, from 10 to 14. • Three different values of solar reflectance for pavements: 10% for a conventional asphalt, 32% and 56% for grey and off-white concrete pavements. • In spring the air temperature decreases by an average of 3.3(1.5)°C passing from an urban texture made up of conventional asphalts to off-white (grey) concrete. • In summer the air temperature decreases by an average of 4.4(2)°C passing from an urban texture made up of conventional asphalts to off-white (grey) concrete.
  13. 13. Numerical analysis • Vertical distribution of the air temperatures in the two receptors • Red lines receptor in the “hot spot”, green lines in the square with greens • The three curves refer to the three different pavements solutions • To be noted the cooling effect of the trees (0.5°C less) at the building height.
  14. 14. Numerical analysis • Comfort analysis based on the Thom Index • Function of dry and wet bulb temperatures • DI [°C] = 0.4 · ( Ta + Tw ) + 4.8 • Calculation in the “hot spot” R2
  15. 15. Conclusions • The tested products have higher solar reflectance than conventional asphalts • Significant air temperature reduction at urban level can be achieved (UHI mitigation) • Improvement of thermal comfort conditions, especially in extreme climatic conditions, are calculated Improvements are needed for the spectral selectivity – high NIR reflectance Calculation with more reliable thermo-fluid dynamics codes and case studies More accurate analysis with other reliable indexes for outdoor thermal comfort Thanks for the attention! Michele Zinzi Tel. +390630486256 email: michele.zinzi@enea.it skype: michele.zinzi
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