Urban Energy and Microclimate: Wind tunnel experiments and multi-scale modeling

Transcription

1 Urban Energy and Microclimate: Wind tunnel experiments and multi-scale modeling J.Allegrini 1,2, P. Moonen 1,2, S. Saneinejad 1,2, V. Dorer 1 & J. Carmeliet 1,2 1 ETHZ, Chair of Building Physics, Zürich, Switzerland 2 Empa, Laboratory for Building Science and Technology, Dübendorf, Switzerland * K. Orehounig 1 1 ETHZ, Chair of Building Physics, Zürich, Switzerland Empa Building Science and Technology ETH Chair of Building Physics

2 Urban Microclimate and Energy Wind speed: reduced Less ventilation potential and heat removal Radiation encapture Increased surface temperature heat flux Lower convective heat transfer coefficients Increased air temperatures Allegrini et al. 2012

3 Components of urban microclimate model

4 Structure of the presentation Modeling of a street canyon: 1. Air flow and Radiation (Jonas Allegrini) 2. Air flow, Radiation and Heat and Moisture (Saba Saneinejad)

5 1. Airflow + Radiation CFD Computational Fluid Dynamics Radiation Models Solar and longwave radiation Experimental Setup Interreflective and longwave radiation

6 1. Airflow + Radiation momentary flow field isothermal leeward wall heated windward wall heated 40 RPM (1.45m/s) Allegrini et al. 2012

7 main vortex second counter rotating vortex Allegrini et al. 2012

8 Windward wall heating Isothermal case main vortex & second counter rotating vortex due to buoyancy Allegrini et al. 2012

9 All surfaces heated the ventilation potential Strong increase of ventilation potential by buoyancy at low freestream velocity. No influence at high freestream velocity (forced convection) Allegrini et al. 2012

10 Structure of the presentation Modeling of a street canyon: 1. Air flow and Radiation (Jonas Allegrini) 2. Air flow, Radiation and Heat and Moisture (Saba Saneinejad)

11 2. Air flow, Radiation, Heat and Moisture Coupled-model Computational Fluid Dynamics (CFD) model + Building Envelope Heat and Moisture (BE-HAM) model + Radiation model (RAD)

12 2. Air flow, Radiation, Heat and Moisture Coupled-model Computational Fluid Dynamics (CFD) model + Building Envelope Heat and Moisture (BE-HAM) model + Radiation model (RAD)

13 2. Air flow, Radiation, Heat and Moisture Coupled-model Computational Fluid Dynamics (CFD) model + Building Envelope Heat and Moisture (BE-HAM) model + Radiation model (RAD) q m h = q c,m,w c,h,w = CMTC(p v v w p ref q = q + (L + C.T)q + q c,m,w BE-HAM ) rad

14 Evaluation of urban thermal comfort Universal Thermal Climate Index (UTCI) Equivalent ambient temperature of a reference environment providing the same physiological responses air temperature mean radiant temperature relative humidity wind speed clothing activity Surface temperatures of environment radiating to the person Direct solar radiation on person

15 Evaluation of urban thermal comfort Heat wave period Effect of: 1. High reflective surfaces 2. Shadowing 3. Evaporative cooling

16 Materials with high albedo value

17 Heat wave : white colors

18 Heat wave : white colors

19 Shadowing

20 Heat wave : 50 % shadowing

21 Heat wave : 50 % shadowing

22 Heat wave : evaporative cooling

23 Evaporative cooling Lv = 2.5x10 6 J/kg first drying phase second drying phase 100%RH surface relative humidity drying rate wet bulb temperature surface temperature time Saneinejad et al., 2011,

24 Heat wave : evaporative cooling

25 Heat wave : evaporative cooling

26 Conclusions + Outlook shadowing -> highest cooling effect The high albedo -> less efficient, and evaporative cooling is the least effective. performance of different measures greatly depends on the urban context and the local climatic conditions For high Reynolds number no strong dependency of the velocity profiles on temperature -> forced convection Importance of buoyancy on the flow in urban street canyons Outlook: From street canyon to an urban quarter Coupling of micro-climate model with meso-scale models

27 Urban Energy and Microclimate: Wind tunnel experiments and multi-scale modeling J.Allegrini 1,2, P. Moonen 1,2, S. Saneinejad 1,2, V. Dorer 2 & J. Carmeliet 1,2 1 ETHZ, Chair of Building Physics, Zürich, Switzerland 2 Empa, Laboratory for Building Science and Technology, Dübendorf, Switzerland jonas.allegrini@empa.ch * K. Orehounig ETHZ, Chair of Building Physics, Zürich, Switzerland Empa Building Science and Technology ETH Chair of Building Physics