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Evaluation of AERMOD and Wind Tunnel Derived Equivalent Building Dimensions


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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.

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Evaluation of AERMOD and Wind Tunnel Derived Equivalent Building Dimensions

  1. 1. 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. 2. Outline • Background • Classic EBD Method – Wind Tunnel-Derived EBD • Experimental Method – AERMOD-Derived EBD • Evaluation of WT and AERMOD Derived EBD • Conclusions
  3. 3. Building Downwash
  4. 4. Building Profile Input Program (BPIP) Figure created in BREEZE ® Downwash Analyst BREEZE is a registered Trademark of Trinity Consultants, Inc.
  5. 5. 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. 6. BPIP Diagnostic Tool Likely Overprediction Factor for each Flow Vector Source 1
  7. 7. 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. 8. • 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. 9. Classic Approach Wind Tunnel-Derived EBD
  10. 10. Measure Ground-level Concentrations Data taken until good fit and max obtained Automated Max GL Concentration Mapper
  11. 11. Measure Ground-level Concentrations With Site Structures Present Tracer from stack Max ground-level concentrations measured versus x
  12. 12. Measure Ground-level Concentrations w/ Various EBD in Place of Site Structures Tracer from stack Max ground-level concentrations measured versus x
  13. 13. Selecting and Equivalent Building
  14. 14. 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. 15. Experimental Method AERMOD-Derived EBD Approach
  16. 16. AERMOD-Derived EBD • Step 1: Wind Tunnel Study to Establish Maximum Ground-Level Profile Mapping with the No Site Structures Present Case
  17. 17. AERMOD-Derived EBD • Step 2: Adjust AERMOD Inputs for the No Site Structures Present Case
  18. 18. AERMOD-Derived EBD • Step 3: Wind Tunnel Study to Establish Max. Ground-Level Profile Mapping with Site Structures Present
  19. 19. AERMOD-Derived EBD • Step 4: AERMOD-Derived EBD
  20. 20. Comparison between Wind Tunnel and AERMOD-Derived EBDs
  21. 21. Comparison of WT-derived and AERMOD-derived EBD profiles
  22. 22. 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. 23. 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. 24. Ron Petersen, PhD, CCM Sergio A. Guerra, PhD Mobile: +1 970 690 1344 Mobile: + 612 584 9595 CPP, Inc. 2400 Midpoint Drive, Suite 190 Fort Collins, CO 80525 + 970 221 3371 @CPPWindExperts Thanks!