energy and weather interactions in the built environment - exploring options for urban energy...

Energy and Weather Interactions in the Built Environment - Exploring options for Urban

Energy Sustainability

International Workshop on Urban Weather & Climate12-15 July, 2011

Beijing

David J. Sailor, Ph.D.Professor, Mechanical & Materials Engineering

Portland State University

[email protected]

Climate impacts energy Energy impacts climate Solutions and Surprises

mailto:[email protected]

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Weather Sensitivity of Urban Energy Consumption

SUPPLY

DEMAND


Vehicles

Industry

Residential

Commercial

Energy Use Across the Sectors

Low/Mod Temp. sensitivity

Low/Mod Temp. sensitivity

Mod/High Temp. sensitivity

Mod/High Temp. sensitivity


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Building Energy Use

• In U.S. and Europe buildings represent ~40% of total energy use and CO2 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


• depends upon season/climate (~5% / oC)

• affects capacity requirements

• impacts power plant waste emissions of heat, pollutant & CO2

(some in cities, some outside)

Utility Scale Response to Temperature


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Weather Sensitivity Urban Energy Generation

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SUPPLY

DEMAND


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Traditional Power PlantsDh ~ O(1%/o C)Transmission losses (0.4%/km)Waste heat (only 35-45% efficient)

Erdem and Sevilgen, 2005


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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


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Urban Wind PowerP ~ rU3

Humidity (humid air is less dense)Wind speed (10% DU 30% DP)Turbulence undesirable


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Energy Use Impacts Climate through the Urban Energy Balance

Solar radiation

Evaporative cooling

Long-wave radiation (LW)Waste heat (Qf)

Sensible heat (S)

Thermal storage (G)


• Magnitude depends upon scale of interest– City scale ~ 10’s W/m2 – Urban core ~ 100’s W/m2 – Downtown building scale ~ 1000’s W/m2

Length Scale of Analysis (m)

Qf (

W/m

2 )

100 1,000 10,00010

100

1,000


94°50'0"W95°0'0"W95°10'0"W95°20'0"W95°30'0"W95°40'0"W

30°0'0"N

29°50'0"N

29°40'0"N

29°30'0"N

Legend

comlh83_Qf16

SUM_LH16

0.000869 - 1.492313

1.492314 - 5.166143

5.166144 - 13.409781

13.409782 - 24.080339

24.080340 - 161.762334

COMMERCIAL W/m2 (Latent Heat)

COMMERCIAL W/m2 (Sensible Heat)RESIDENTIAL W/m2 (Sensible Heat)

-

Legend

resish83_Qf16

SUM_SH16

0.000781 - 1.410216

1.410217 - 3.599473

3.599474 - 6.588114

6.588115 - 11.070102

11.070103 - 21.772551

Legend

comsh83_Qf16

SUM_SH16

0.000425 - 2.018308

2.018309 - 7.211411

7.211412 - 18.877115

18.877116 - 36.533123

36.533124 - 233.170697

COMMERCIAL G/m2 (Moisture) Legend

comlh83_mf16

SUM_LH16

0.000000 - 0.000657

0.000658 - 0.002276

0.002277 - 0.005907

0.005908 - 0.010608

0.010609 - 0.071261

Building Sector Waste HeatHouston Texas, USA, AUGUST – WEEK DAY (1600 LST), 200m grids

Heiple and Sailor, 2008


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Vertical Distribution of Waste Heat from Energy Use

Waste heat (Qf)


Kimura and Takahashi, Atmos. Env., 1991

Tokyo, Japan

~ 100 W/m2 within 4km2 cells DTQf ~ 2 to 3 o C


Kikegawa et al., Appl. Energy, 2003

Tokyo, (Ootemachi)

(Temp @ 100m)

Simple 1-D Canopy model coupled with a simple BEM submodel.

MM: No Qf

Case-1: Qf rooftopCase-2: Qf at 3mCase-3: Qf subsurface

DTQf ~ 2 to 3 o C


• City-wide Qf exceeded 60 W/m2 in summer and 90 W/m2 in winter

• Case 1: With Qf

• Case 2: No Qf

• 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 day2 to 3 o C during night

19

23

27

31

35

8/10/020:00

8/10/0212:00

8/11/020:00

8/11/0212:00

Te

mp

era

ture

°C obs BL base BL Qf

19

23

27

31

35

8/10/020:00

8/10/0212:00

8/11/020:00

8/11/0212:00

Local time

Te

mp

era

ture

°C obs GS base GS Qf

(a)

(b)

19

23

27

31

35

8/10/020:00

8/10/0212:00

8/11/020:00

8/11/0212:00

Te

mp

era

ture

°C obs BL base BL Qf

19

23

27

31

35

8/10/020:00

8/10/0212:00

8/11/020:00

8/11/0212:00

Local time

Te

mp

era

ture

°C obs GS base GS Qf

(a)

(b)

Summer

Winter

Fan and Sailor, Atmos. Env. 2004

Philadelphia, PA USA


Strategies for Sustainable Urban Development

Energy

Air

Water

Carbon

High albedo surfaces

TransportationVegetation

Pervious surfaces

Building energy efficiency

Green roofs

Urban form

Building-integrated renewable energy

Bioswales

Ecodistricts



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

110 deg F (43 C)

150 deg F (65 C)


Atmos. Chem.ki

Transport/diffusion

Mixing depth

Fluxes/emissions:Heat, moisture, and pollutants

Deposition


UHI Mitigation Impacts Mixing…

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Student Union,Univ. Central Florida.

J. Sonne, FSEC

Temperature

Heat Flux

Green roof is warmer by ~20 oF at night

Green roof is ~30-40 o F cooler during a summer day.

Green Roofs


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Roof Design andSensible Fluxes

Scherba et al., Building and Environment 2011

Daily peak, summer

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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

LW SW

LW SW

High albedo

Low Albedo

SW

LW

40-70%

~ 0 %

Window glass


Building Efficiency Technologies


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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”

Emmanuel and Fernando, 2007.


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.

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[email protected]

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