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Using Physical Modeling to Refine Downwash Inputs to AERMOD

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Achieving compliance in dispersion modeling can be quite challenging because of the tight National Ambient Air Quality Standards (NAAQS). In addition, AERMOD’s limitations can, in many cases, produce higher than normal concentrations due to the inherent assumptions and simplifications in its formulation. In the case of downwash, the theory used to estimate these effects was developed for a limited set of building types. However, these formulations are commonly used indiscriminately for all types of buildings. This presentation will cover how the basics of wind tunnel modeling can overcome some of these limitations and be used to mitigate downwash induced overpredictions to achieve compliance.

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Using Physical Modeling to Refine Downwash Inputs to AERMOD

  1. 1. 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
  2. 2. Outline 1. Building Downwash in AERMOD 2. Equivalent Building Dimensions Method 3. Potential Benefits Using Physical Modeling to Refine Downwash Inputs to AERMOD2
  3. 3. 3 Compliance?Compliance? BPIPBuilding Geometry Meteorological Data Terrain Data AERMET AERMAP Operating Parameters AERMOD OtherInputs Building Inputs Traditional AERMOD Modeling Approach Compliance may require taller stacks and/or additional emission controls Using Physical Modeling to Refine Downwash Inputs to AERMOD
  4. 4. Building Downwash 4 Using Physical Modeling to Refine Downwash Inputs to AERMOD Image from Lakes Environmental Software
  5. 5. Building Profile Input Program (BPIP) Figure created in BREEZE ® Downwash Analyst BREEZE is a registered Trademark of Trinity Consultants, Inc. 5 Using Physical Modeling to Refine Downwash Inputs to AERMOD
  6. 6. 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 Using Physical Modeling to Refine Downwash Inputs to AERMOD
  7. 7. 7 Overprediction due to Building Downwash Using Physical Modeling to Refine Downwash Inputs to AERMOD
  8. 8. 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. Using Physical Modeling to Refine Downwash Inputs to AERMOD
  9. 9. What’s Causing These Problems? 9 Using Physical Modeling to Refine Downwash Inputs to AERMOD 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
  10. 10. Long Buildings with Wind at an Angle Figure created in BREEZE® Downwash Analyst BREEZE is a registered trademark of Trinity Consultants, Inc. 10 Using Physical Modeling to Refine Downwash Inputs to AERMOD
  11. 11. 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 11 Using Physical Modeling to Refine Downwash Inputs to AERMOD
  12. 12. AERMOD/PRIME Overestimates Downwash Reality AERMOD Building Downwash Height of Building Downwash Zone Overestimated in PRIME 12 Using Physical Modeling to Refine Downwash Inputs to AERMOD
  13. 13. Refinery Structures Upwind - Horizontal Flow Solid BPIP Structure Upwind No Structures Streamlines for Lattice Structures Should be Horizontal 13 Using Physical Modeling to Refine Downwash Inputs to AERMOD
  14. 14. How to Minimize the Effect from these Errors? 14 Using Physical Modeling to Refine Downwash Inputs to AERMOD
  15. 15. 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 15 Using Physical Modeling to Refine Downwash Inputs to AERMOD
  16. 16. • 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 16 Using Physical Modeling to Refine Downwash Inputs to AERMOD
  17. 17. BPIP Diagnostic Tool http://www.cppwind.com/what-we- do/air-permitting/bpip-diagnostic-tool#/ Likely Overprediction Factor for each Flow Vector Source 1 17 Using Physical Modeling to Refine Downwash Inputs to AERMOD
  18. 18. 18 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 Using Physical Modeling to Refine Downwash Inputs to AERMOD
  19. 19. 19 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 Using Physical Modeling to Refine Downwash Inputs to AERMOD
  20. 20. 20 Using Physical Modeling to Refine Downwash Inputs to AERMOD 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
  21. 21. General EBD Methodology • Specify model operating conditions • Construct scale model • Install model in wind tunnel and measure concentrations • Determine EBD 21 Using Physical Modeling to Refine Downwash Inputs to AERMOD
  22. 22. 22 Measure Ground-level Concentrations Data taken until good fit and max obtained Automated Max GL Concentration Mapper Using Physical Modeling to Refine Downwash Inputs to AERMOD
  23. 23. 23 Measure Ground-level Concentrations With Site Structures Present Tracer from stack Max ground-level concentrations measured versus x Using Physical Modeling to Refine Downwash Inputs to AERMOD
  24. 24. 24 Measure Ground-level Concentrations with Various EBD in Place of Site Structures Tracer from stack Max ground-level concentrations measured versus x Using Physical Modeling to Refine Downwash Inputs to AERMOD
  25. 25. 25 Measure Ground-level Concentrations with no Structures Tracer from stack Max ground-level concentrations measured versus x Using Physical Modeling to Refine Downwash Inputs to AERMOD
  26. 26. 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 Using Physical Modeling to Refine Downwash Inputs to AERMOD
  27. 27. 27 Typical Result Wind Tunnel EBD Using Physical Modeling to Refine Downwash Inputs to AERMOD
  28. 28. 28 Downwash Based on EBD and BPIP Figures created in BREEZE® Downwash Analyst BREEZE is a registered trademark of Trinity Consultants, Inc. Using Physical Modeling to Refine Downwash Inputs to AERMOD
  29. 29. 29 Using Physical Modeling to Refine Downwash Inputs to AERMOD Potential Benefits from use of EBD
  30. 30. 30 Using Physical Modeling to Refine Downwash Inputs to AERMOD 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
  31. 31. 31 Using Physical Modeling to Refine Downwash Inputs to AERMOD 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 Inputs 303.8 No Wind Tunnel Determined Building Inputs (EBD) 79.9 Yes NO2 1-hr Standard 188
  32. 32. Sergio A. Guerra, PhD Ron Petersen, PhD, CCM sguerra@cppwind.com rpetersen@cppwind.com 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? 32 Using Physical Modeling to Refine Downwash Inputs to AERMOD

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