While the current EBD method is the best available option to determine correct building dimensions in the model, a different method was suggested by EPA in the 2011 Memo: Model Clearinghouse Review of EBD for AERMOD. Attachment B to the 2011 Memo includes an assessment of the Alcoa Davenport Works EBD Study. In this evaluation EPA compared wind tunnel observations with AERMOD derived concentrations. However, this evaluation has important shortcomings. First, to carry out this comparison between wind tunnel and AERMOD concentrations, it is necessary to collect velocity profiles that include longitudinal and vertical turbulent intensity measurements upwind of the stack. These data were not available for the EPA evaluation of the Alcoa Davenport Works EBD Study. Second, the wind tunnel model operating conditions were converted to full scale conditions by using exact similarity. However, exact similarity is not used to specify model operating conditions since only momentum ratios are matched but not buoyancy ones. Whereas EPA did not provide important details on how this study was performed, this paper outlines how to properly carry out this new method where AERMOD is used to determine equivalent building dimensions. The viability of this new method was also evaluated and discussed.

1. www.cppwind.comwww.cppwind.com
Evaluating AERMOD and Wind
Tunnel Derived Equivalent
Building Dimensions
Guideline on Air Quality Models: The New Path
A&WMA’s 6th Specialty Conference - Chapel Hill, NC
Abstract #25
April 13, 2016
Sergio A. Guerra, Ph.D. – CPP Inc.
Ron Petersen, Ph.D., CCM – CPP Inc.

2. www.cppwind.comwww.cppwind.com
Outline
• Background
• Classic EBD Method
– Wind Tunnel-Derived EBD
• Experimental Method
– AERMOD-Derived EBD
• Evaluation of WT and AERMOD Derived EBD
• Conclusions

3. www.cppwind.comwww.cppwind.com
Building Downwash

4. www.cppwind.comwww.cppwind.com
Building Profile Input Program
(BPIP)
Figure created in BREEZE ® Downwash Analyst
BREEZE is a registered Trademark of Trinity Consultants, Inc.

5. www.cppwind.comwww.cppwind.com
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

6. www.cppwind.comwww.cppwind.com
BPIP Diagnostic Tool
http://bit.do/cppwind-BPIPDiagnostic
Likely Overprediction Factor for each Flow Vector
Source 1

7. www.cppwind.comwww.cppwind.com
ComplianceCompliance
CPP’s EBDCPP’s EBD
BPIP Diagnostic
ToolBuilding Geometry
Meteorological Data
Terrain Data
AERMET
AERMAP
Operating Parameters
AERMOD
OtherInputs
Building
Inputs
BPIP Diagnostic Tool

8. www.cppwind.comwww.cppwind.com
• 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
• Determined using wind tunnel modeling
What is EBD?

9. www.cppwind.comwww.cppwind.com
Classic Approach
Wind Tunnel-Derived EBD

10. www.cppwind.comwww.cppwind.com
Measure Ground-level
Concentrations
Data taken until good fit and max
obtained
Automated Max GL Concentration Mapper

11. www.cppwind.comwww.cppwind.com
Measure Ground-level Concentrations
With Site Structures Present
Tracer
from stack
Max ground-level concentrations measured versus x

12. www.cppwind.comwww.cppwind.com
Measure Ground-level Concentrations w/
Various EBD in Place of Site Structures
Tracer
from stack
Max ground-level concentrations measured versus x

13. www.cppwind.comwww.cppwind.com
Selecting and Equivalent Building

14. www.cppwind.comwww.cppwind.com
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
• After 2011 EPA Clearinghouse Memo
– Chevron 1 (Study Approved), Region 4, 2012
– Chevron 2 (Study Approved), Region 4, 2013
– Confidential Project (In process), Region 4, 2015
– Confidential Project, Region 10, 2016

15. www.cppwind.comwww.cppwind.com
Experimental Method
AERMOD-Derived EBD Approach

16. www.cppwind.comwww.cppwind.com
AERMOD-Derived EBD
• Step 1: Wind Tunnel Study to Establish
Maximum Ground-Level Profile Mapping with
the No Site Structures Present Case

17. www.cppwind.comwww.cppwind.com
AERMOD-Derived EBD
• Step 2: Adjust AERMOD Inputs for the No Site
Structures Present Case

18. www.cppwind.comwww.cppwind.com
AERMOD-Derived EBD
• Step 3: Wind Tunnel Study to Establish Max.
Ground-Level Profile Mapping with Site
Structures Present

19. www.cppwind.comwww.cppwind.com
AERMOD-Derived EBD
• Step 4: AERMOD-Derived EBD

20. www.cppwind.comwww.cppwind.com
Comparison between
Wind Tunnel and AERMOD-Derived
EBDs

21. www.cppwind.comwww.cppwind.com
Comparison of WT-derived and
AERMOD-derived EBD profiles

22. www.cppwind.comwww.cppwind.com
Conclusion
• Adjustments to key parameters in the *.sfc
and *.pfl meteorological files can be used to
get better agreement between WT and
AERMOD MGL concentrations for the no site
structures present case
• After these adjustments the AERMOD-EBD do
not match the Wind Tunnel-EBD

23. www.cppwind.comwww.cppwind.com
Conclusion
• Discrepancy suggests that AERMOD is not
suitable to evaluate EBDs derived from WT
observations
• Wind Tunnel-derived EBD are still the
preferred method to replace BPIP-generated
ones

24. www.cppwind.comwww.cppwind.com
Ron Petersen, PhD, CCM Sergio A. Guerra, PhD
rpetersen@cppwind.com sguerra@cppwind.com
Mobile: +1 970 690 1344 Mobile: + 612 584 9595
CPP, Inc.
2400 Midpoint Drive, Suite 190
Fort Collins, CO 80525
+ 970 221 3371
www.cppwind.com @CPPWindExperts
Thanks!