Using Physical Modeling to Refine Downwash Inputs to AERMOD

www.cppwind.comwww.cppwind.com

Using Physical Modeling to

Refine Downwash Inputs to

AERMOD

Rocky Mountain States Section –

Air & Waste Management Association

Denver, CO

Sergio A. Guerra, PhD

Ron Petersen, PhD, CCM

April 13, 2017

Outline1. Building Downwash in AERMOD

2. Equivalent Building Dimensions Method

3. Potential Benefits

Using Physical Modeling to Refine Downwash Inputs to AERMOD2

3

Compliance?Compliance?

BPIPBuilding Geometry

Meteorological Data

Terrain Data

AERMET

AERMAP

Operating Parameters AERMOD

Other Inputs

Building

Inputs

Traditional AERMOD Modeling

ApproachCompliance may

require taller

stacks and/or

additional

emission controls

Using Physical Modeling to Refine Downwash Inputs to AERMOD

Building Downwash

4 Using Physical Modeling to Refine Downwash Inputs to AERMOD

Image from Lakes Environmental Software

Building Profile Input Program

(BPIP)

Figure created in BREEZE ® Downwash Analyst

BREEZE is a registered Trademark of Trinity Consultants, Inc.


6

PRIME

AERMOD’s Building Downwash Algorithm

• Used EPA wind tunnel data

base and past literature

• Developed analytical

equations for cavity height,

reattachment, streamline

angle, wind speed and

turbulence

• Developed for specific

building dimensions

• When buildings outside of

these dimensions, theory falls

apart


7

Overprediction due to Building

Downwash


8

AECOM Field Study at Mirant Power

Station (Shea et al., 2012)

Shea, D., O. Kostrova, A. MacNutt, R. Paine, D. Cramer, L. Labrie, “A Model Evaluation Study of AERMOD Using Wind Tunnel

and Ambient Measurements at Elevated Locations,” 100th Annual AWMA Conference, Pittsburgh, PA, June 2007.

• Model overpredicted by factor of

10 on residential tower

• Better agreement with EBD, but

still overpredicted by factor of 4

• Best agreement with no

buildings, still overpredicted by

factor of 2.

• In reality, plume is not affected

by building downwash.


What’s Causing These

Problems?


Petersen, R., Guerra, S., Bova, A., ”Critical Review of the Building Downwash Algorithms in

AERMOD”, Journal of the Air & Waste Management Association. Accepted author version:

http://www.tandfonline.com/doi/full/10.1080/10962247.2017.1279088

Long Buildings with Wind

at an Angle

Figure created in BREEZE® Downwash Analyst

BREEZE is a registered trademark of Trinity Consultants, Inc.


AERMOD Building Wake

AERMOD Overestimates Downwash

Hb = 20 m

Problem even worse for longer buildings

• Wake height

overestimated:

need higher plumes

to avoid downwash.

• Start of maximum

building downwash

farther downwind

than in reality


AERMOD/PRIME

Overestimates

Downwash

Reality

AERMOD Building DownwashHeight of Building Downwash Zone Overestimated in PRIME


Refinery Structures Upwind

- Horizontal Flow

Solid BPIP Structure Upwind

No Structures

Streamlines for Lattice Structures

Should be Horizontal


How to Minimize the Effect from

these Errors?


Solutions to Downwash Overpredictions

– Refine building dimensions with a wind tunnel study

– Equivalent Building Dimensions (EBDs) are the dimensions (height, width, length and location) that are input into AERMOD in place of BPIP dimensions to more accurately predict building wake effects

– Guerra, S., Petersen, R. “Using Physical Modeling to Refine Downwash Inputs to AERMOD”, EM Magazine, October 2016

http://www.cppwind.com/wp-content/uploads/2016/10/Using-Physical-Modeling-to-Refine-Downwash-Inputs-to-AERMOD_EMMag-Oct-16_PetersenGuerra.pdf


• Equivalent Building Dimensions (EBDs) are the dimensions (height, width, length and location) that are input into AERMOD in place of BPIP dimensions to more accurately predict building wake effects

• Guidance originally developed when ISC was the preferred model –

– EPA, 1994. Wind Tunnel Modeling Demonstration to Determine Equivalent Building Dimensions for the Cape Industries Facility, Wilmington, North Carolina. Joseph A. Tikvart Memorandum, dated July 25, 1994. U.S. Environmental Protection Agency, Research Triangle Park, NC

– New guidance currently being developed with EPA

• Determined using wind tunnel modeling

EBD Method


BPIP Diagnostic Toolhttp://www.cppwind.com/what-we-

do/air-permitting/bpip-diagnostic-tool#/Likely Overprediction Factor for each Flow Vector

Source 1


18

ComplianceCompliance

CPP’s EBDCPP’s EBD

BPIP Diagnostic

ToolBuilding Geometry

Meteorological Data

Terrain Data

AERMET

AERMAP

Operating Parameters AERMODOther Inputs

Building

Inputs

BPIP Diagnostic Tool


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Summary of Approved Projects• Studies conducted and approved using original guidance for ISC

applications– Amoco Whiting Refinery, Region 5, 1990

– Public Service Electric & Gas, Region 2, 1993

– Cape Industries, Region 4, 1993

– Cambridge Electric Plant, Region 1, 1993

– District Energy, Region 5, 1993

– Hoechst Celanese Celco Plant, Region 3, 1994

– Pleasants Power, Region 3, 2002

• Studies conducted using original guidance for AERMOD/PRIME

applications – Hawaiian Electric (Approved), Region 9, 1998

– Mirant Power Station (Approved), Region 3, 2006

– Cheswick Power Plant (Approved), Region 3, 2006

– Radback Energy (Protocol Approved), Region IX, 2010

– Chevron 1 (Study Approved), Region 4, 2012

– Chevron 2 (Study Approved), Region 4, 2013

– On going confidential study in Region X

– On going confidential study in Region X



How to Use EBD for Regulatory Purposes?

� Step 1: Develop a protocol outlining the EBD study

� Step 2: Submit EBD protocol for approval to regulatory agency. Also need to

involve Model Clearinghouse

� Step 3: Perform wind tunnel testing

� Step 4: Use building geometry from EBD study in AERMOD to show compliance

� Step 5: Submit final report for agency review and approval

General EBD Methodology• Specify model operating

conditions

• Construct scale model

• Install model in wind tunnel and

measure concentrations

• Determine EBD


22

Measure Ground-level Concentrations

Data taken until good fit and max obtained Automated Max GL Concentration Mapper


23

Measure Ground-level Concentrations

With Site Structures Present

Tracer

from stack

Max ground-level concentrations measured versus x


24

Measure Ground-level Concentrations with

Various EBD in Place of Site Structures

Tracer

from stack



25

Measure Ground-level Concentrations with

no Structures

Tracer

from stack



26

Specify Wind Tunnel Determined EBD that

Matches Dispersion with Site Structures Present

Wind

Tunnel EBD

much

smaller

than actual

building

No building

works best

for this

case

Site Structures in Wind TunnelEBD in Wind Tunnel


27

Typical Result

Wind Tunnel EBD


28

Downwash Based on EBD and BPIP

Figures created in BREEZE® Downwash Analyst

BREEZE is a registered trademark of Trinity Consultants, Inc.



Potential Benefits from use of EBD


Past CPP Project

Stack S_XXX From Industrial Facility

Stack height = 27 m

Q = 2 g/s

Building height = 17 m

Building width/length > 200 m

5 years of meteorological data

AERMOD Results With Wind

Tunnel EBD

wide/Long/Short Buildings

Description

AERMOD Maximum

Predicted

Concentration

(µg/m3)

Compliance

BPIP Building Dimension Inputs 258.2 No

Wind Tunnel Determined Building Inputs (EBD) 54.9 Yes

PM10 24-hr Standard 150


AERMOD Results With Wind Tunnel EBD

Very wide/narrow building

Stack height: 47 m

Building height: 31 m

Property line in Red

Emission rate: 20 g/s

AERMOD RESULTS

Five years of met data Description

AERMOD Maximum

Predicted

Concentration

(µg/m3)

Compliance

BPIP Building

Dimension Inputs303.8 No

Wind Tunnel

Determined Building

Inputs (EBD)

79.9 Yes

NO2 1-hr Standard 188

Sergio A. Guerra, PhD Ron Petersen, PhD, [email protected] [email protected]

Mobile: + 612 584 9595 Mobile:+1 970 690 1344

CPP, Inc.

2400 Midpoint Drive, Suite 190

Fort Collins, CO 80525

+ 970 221 3371

www.cppwind.com @CPPWindExperts

Questions?


Engineering

Using Physical Modeling to Refine Downwash Inputs to AERMOD