1. Energy and Weather Interactions in the Built Environment - Exploring options for Urban Energy Sustainability International Workshop on Urban Weather & Climate 12-15 July, 2011 Beijing David J. Sailor, Ph.D. Professor, Mechanical & Materials Engineering Portland State University sailor@pdx.edu Climate impacts energyEnergy impacts climate Solutions and Surprises

2. Weather Sensitivity of Urban Energy Consumption 2 SUPPLY DEMAND Climate impacts energyEnergy impacts climate Solutions and Surprises

3. Energy Use Across the Sectors Low/Mod Temp. sensitivity Mod/High Temp. sensitivity Climate impacts energyEnergy impacts climate Solutions and Surprises

4. Building Energy Use In U.S. and Europe buildings represent ~40% of total energy use and CO 2 emissions. Heating, Cooling, and Ventilation is responsible for about 1/3 of energy use in U.S. buildings Energy use ≠ Waste heat – Environmental loads – COP of cooling equipment (3 to 4 ) – Sensible vs. latent systems 4 Climate impacts energyEnergy impacts climate Solutions and Surprises

5. depends upon season/climate (~5% / o C) affects capacity requirements impacts power plant waste emissions of heat, pollutant & CO 2 (some in cities, some outside) Utility Scale Response to Temperature Climate impacts energyEnergy impacts climate Solutions and Surprises

6. Weather Sensitivity Urban Energy Generation 66 SUPPLY DEMAND Climate impacts energyEnergy impacts climate Solutions and Surprises

7. 7 Traditional Power Plants  ~ O(1%/ o C) Transmission losses (0.4%/km) Waste heat (only 35-45% efficient) Erdem and Sevilgen, 2005 Climate impacts energyEnergy impacts climate Solutions and Surprises

8. 8 Solar Power (thermal & PV) Atmospheric attenuation and Urban Heat Island (power reduction of ~13%, Wang, 2006) Particle deposition (> 5% reduction in power; Kaldellis et al., 2011) Feedback: PV can increase sensible heating of urban areas Climate impacts energyEnergy impacts climate Solutions and Surprises

9. 9 Urban Wind Power P ~  U 3 Humidity (humid air is less dense) Wind speed (10%  U  30%  P) Turbulence undesirable Climate impacts energyEnergy impacts climate Solutions and Surprises

10. Energy Use Impacts Climate through the Urban Energy Balance Solar radiation Evaporative cooling Long-wave radiation (LW) Waste heat (Q f ) Sensible heat (S) Thermal storage (G) 10 Climate impacts energyEnergy impacts climate Solutions and Surprises

11. Magnitude depends upon scale of interest – City scale ~ 10’s W/m 2 – Urban core ~ 100’s W/m 2 – Downtown building scale ~ 1000’s W/m 2 Length Scale of Analysis (m) Q f (W/m 2 ) 1001,00010,000 10 100 1,000 Climate impacts energyEnergy impacts climate Solutions and Surprises

12. Building Sector Waste Heat Houston Texas, USA, AUGUST – WEEK DAY (1600 LST), 200m grids Heiple and Sailor, 2008 Climate impacts energyEnergy impacts climate Solutions and Surprises

13. Vertical Distribution of Waste Heat from Energy Use Waste heat (Q f ) 13 Climate impacts energyEnergy impacts climate Solutions and Surprises

14. Kimura and Takahashi, Atmos. Env., 1991 Tokyo, Japan ~ 100 W/m 2 within 4km 2 cells  T Qf ~ 2 to 3 o C Climate impacts energyEnergy impacts climate Solutions and Surprises

15. Kikegawa et al., Appl. Energy, 2003 Tokyo, (Ootemachi) (Temp @ 100m) Simple 1-D Canopy model coupled with a simple BEM submodel. MM:No Q f Case-1:Q f rooftop Case-2: Q f at 3m Case-3: Q f subsurface  T Qf ~ 2 to 3 o C Climate impacts energyEnergy impacts climate Solutions and Surprises

16. City-wide Q f exceeded 60 W/m 2 in summer and 90 W/m 2 in winter Case 1: With Q f Case 2: No Q f Impacts on summer air temperature < 0.5 o C during day ~ 1 o C during night Impacts on winter air temperature ~ 1 o C during day 2 to 3 o C during night Summer Winter Fan and Sailor, Atmos. Env. 2004 Philadelphia, PA USA Climate impacts energyEnergy impacts climate Solutions and Surprises

17. Strategies for Sustainable Urban Development EnergyAirWaterCarbon High albedo surfaces Transportation Vegetation Pervious surfaces Building energy efficiency Green roofs Urban form Building-integrated renewable energy Bioswales Ecodistricts Climate impacts energyEnergy impacts climate Solutions and Surprises

18. Cool Roofs - bigger impact on sensible fluxes than building energy use

19. 110 deg F (43 C) 150 deg F (65 C) Climate impacts energyEnergy impacts climate Solutions and Surprises

20. Atmos. Chem. k i Transport/diffusion Mixing depth Fluxes/emissions: Heat, moisture, and pollutants Deposition Climate impacts energyEnergy impacts climate Solutions and Surprises UHI Mitigation Impacts Mixing…

21. Student Union, Univ. Central Florida. J. Sonne, FSEC Temperature Heat Flux 21 Green roof is warmer by ~20 o F at night Green roof is ~30-40 o F cooler during a summer day. Green Roofs Climate impacts energyEnergy impacts climate Solutions and Surprises

22. 22 Roof Design and Sensible Fluxes Scherba et al., Building and Environment 2011 Daily peak, summer

23. Cool Surfaces at Ground Level Impact Buildings Low surface albedo results in warmer ground surface Total thermal load on building (via windows) - reflected SW is replaced with emitted LW radiation Example: AT study by Yaghoobian et al., 2010 JAMC 23 LW SW High albedo Low Albedo SW LW 40-70% ~ 0 % Window glass Climate impacts energyEnergy impacts climate Solutions and Surprises

24. Building Efficiency Technologies Climate impacts energyEnergy impacts climate Solutions and Surprises

25. Urban form/morphology Mean radiant temperature is an important metric for thermal comfort, and “…density enhancement is a viable UHI mitigation option in built-up areas of warm climate cities” 25 Emmanuel and Fernando, 2007. Climate impacts energyEnergy impacts climate Solutions and Surprises

26. Final thoughts… Sustainable design strategies interact, produce feedbacks and can have far-reaching unintended consequences. Urban heat island mitigation itself is not the right target. Rather, policy makers and planners need to consider the whole suite of environmental, social, and economic goals… as well as the full suite of impacts of any technology. 26

27. Questions? sailor@pdx.edu 27