ASCE 7-16: Changes To Wind Calculations For Rooftop Solar
ASCE 7-16: Changes to WindCalculations for Rooftop SolarJoe Cain, P.E.Chair, SEIA Codes &Standards Working GroupDavid Banks, PhD, P.EngPrincipalCermak Peterka Petersen (CPP)
ASCE 7-16: Changes to Wind CalculationsAgenda Current Practice General changes toASCE 7-16 Solar-specificchanges to ASCE Mitigations inSEAOC PV2 updateSeptember 13, 2016
Calculation of Wind Pressure: ASCE 7-10 and ICC-ES AC 428 September 13, 2016Determine design wind speed and calculatedesign wind pressures using ASCE 7-10ICC Evaluation Services Acceptance CriteriaAC 428: Acceptance Criteria for ModularFraming Systems Used To SupportPhotovoltaic (PV) PanelsAC 428 is required to obtain an ICC-ESEvaluation Report; it is also useful asvoluntary guidanceAC 428 allows internal pressure set equal tozero (within constraints) in Components &Cladding methodIn future ASCE 7-16, there will be acalculation method specific to “flushmounted” PV systems on sloping “pitched”roofs 2016 Solar Energy Industries Association
ICC Acceptance Criteria AC 428 Components & Claddingmethod Internal pressure shall be setequal to zero Physical constraints areneeded for method to be valid Pressure equalization isdependent on gaps betweenmodulesSeptember 13, 2016 2016 Solar Energy Industries Association 4
ASCE 7-10 with ICC-ES AC 428 CriteriaDon’t forget to consider: Roof edge zones, whichare changing in ASCE 7-16 Fire setbacks, which arechanging (for the better) in2018 IFC & IRCPhysical constraints of AC 428 wind method: Required 10 inch minimum distance from roof edge or ridge Height above roof between 2 inches and 10 inches Minimum gap of 0.25 inch between adjacent rows of panels In earlier version of AC 428, minimum gap was 0.75 inchSeptember 13, 2016 2016 Solar Energy Industries Association 5
ASCE 7-16 Wind Speed Maps Revised (again) Risk Category II MeanRecurrenceInterval (MRI)700 years) ASCE 7-16wind speedmaps showcontour lines inWestern statesSeptember 13, 2016 2016 Solar Energy Industries Association 6
Compare ASCE 7-10 and ASCE 7-16 MapsASCE 7-10 Risk Category IISeptember 13, 2016ASCE 7-16 Risk Category II 2016 Solar Energy Industries Association 7
Compare ASCE 7-10 and ASCE 7-16 MapsASCE 7-10 Risk Category IISeptember 13, 2016ASCE 7-16 Risk Category II 2016 Solar Energy Industries Association 8
Development of Corner & Edge Roof ZonesSeptember 30, 2016 2016 Solar Energy Industries Association 9
Development of Corner & Edge Roof ZonesSeptember 30, 2016 2016 Solar Energy Industries Association 10
Development of Corner & Edge Roof ZonesASCE 7-10 Roof ZonesSeptember 30, 2016ASCE 7-16 Roof Zones 2016 Solar Energy Industries Association 11
C&C Roof Zones: ASCE 7-10 to 7-16ASCE 7-10 Figure 30.4-2CASCE 7-16 Figure 30.43-2D
Roof GCp Coefficients: ASCE 7-10 to 7-16ASCE 7-16Figure30.43-2DASCE 7-10 Figure 30.4-2C
Overhang Coefficients: ASCE 7-10 to 7-16ASCE 7-16Figure30.43-2DASCE 7-10 Figure 30.4-2C
University of Western Ontario: Stenabaugh Experiments wereconducted in UWOboundary layerwind tunnel Two primary areasof investigation Height of PVsystem above roof Pressureequalization fromvarious gapsbetween PV panelsSeptember 13, 2016 2016 Solar Energy Industries Association 15
University of Western Ontario - StenabaughSeptember 13, 2016 2016 Solar Energy Industries Association 16
University of Western Ontario - StenabaughSeptember 13, 2016 2016 Solar Energy Industries Association 17
ASCE 7-16 with “Associated Criteria”Physical constraints ofASCE 7-16 method: Required minimumdistance from roofedge or ridge 2h2 Height above roofbetween 2 inchesand 10 inches Minimum gap of0.25 inch betweenall panelsSeptember 13, 2016 2016 Solar Energy Industries Association 18
DRAFT ASCE 7-16 Section 29.4.4 Basic form of Equation29.4-7 is very familiar Velocity pressure qhtimes pressurecoefficient GCp Velocity pressureincludes the square ofwind speed New coefficients gE andga are solar-specific for“flush mounts” installedparallel to roofSeptember 13, 2016 2016 Solar Energy Industries Association 19
Zone 1: ASCE 7-16 GCp Pressure CoefficientsSeptember 13, 2016 2016 Solar Energy Industries Association 20
Zone 1: Wind Pressure Equalization FactorSeptember 13, 2016 2016 Solar Energy Industries Association 21
Zone 1: Add ASCE 7-16 CA Wind SpeedsSeptember 13, 2016 2016 Solar Energy Industries Association 22
Zone 1: Closer to Roof, with PV2-2016 EqualizationSeptember 13, 2016 2016 Solar Energy Industries Association 23
Gable 27o - 45o: ASCE 7-16 GCp Pressure CoefficientsSeptember 13, 2016 2016 Solar Energy Industries Association 24
Gable 27o - 45o: With Pressure Equalization FactorSeptember 13, 2016 2016 Solar Energy Industries Association 25
Gable 27o - 45o: Add ASCE 7-16 CA Wind SpeedsSeptember 13, 2016 2016 Solar Energy Industries Association 26
Gable 27o - 45o: Qualify for SEAOC PV2 EqualizationSeptember 13, 2016 2016 Solar Energy Industries Association 27
DRAFT Update to SEAOC PV2 Wind Paper Original SEAOC PV 2 wind paper waspublished in October 2012 Dr. David Banks of CPP Wind isprimary author of PV2 update PV2 paper is updated to allrequirements of ASCE 7-16 Updated PV2 is expected to bepublished by the end of 2016 ASCE 7-16 intended to be referencedin the 2018 IBC, and in effect byJanuary 1, 2020 in most statesSeptember 13, 2016 2016 Solar Energy Industries Association 28
ASCE 7-16: Exploring the Edge Factor, gE Edge Factor gE (“gammaE”) is a direct, linearmultiplier to the windpressure The value of gE is either1.5 or 1.0 In ASCE 7-16, panelswithin 1.5 Lp from end ofrow are exposed Result is three rows orfewer are 100% edgeSeptember 13, 2016 2016 Solar Energy Industries Association 29
Mitigation for gE in (DRAFT) SEAOC PV2 UpdateFlush mount onlySeptember 13, 2016 2016 Solar Energy Industries Association 30
ASCE 7-16: PV Pressure Equalization Factor, ga EqualizationFactor ga is adirect multiplier towind pressure Wind pressure isreduced for gapsbetween panels John Wolfe publiccomment wasdisapproved bythe ASCE WindSubcommitteeSeptember 13, 2016 2016 Solar Energy Industries Association 31
Mitigation for ga in DRAFT SEAOC PV2 Update SEAOC PV2 update will includemore options for pressureequalization Options are height of PVsystem above roof and gapsbetween modules This alternative method rewardsdesigns that consideroptimization for wind Wind pressures can be reducedby 25 percent from worst-casebasis of ASCE 7-16September 13, 2016 2016 Solar Energy Industries Association 32
Recommendations Communicate with AHJ’s about SEAOC PV2 Wind paper Consider early adoption of 2h as minimum roof edgesetback Ensure fire setbacks are observed if they apply to yourproject, based on local code adoption and local policy Consider panel height above the roof in the optimal rangeof 4 inches – 5 inches Consider using gap of 3/4 inch between panelsSeptember 12, 2016 2016 Solar Energy Industries Association 33
Questions?ContactsCodes & Standards:Joe Cain, P.E.Chair, SEIA Codes & StandardsWorking GroupE-mail: JoeCainPE@gmail.comPhone: 1-408-605-3934David Banks, PhD, P.EngPrincipal, CPP WindE-mail: dbanks@cppwind.comPhone: 1-970-498-2350September 12, 2016 2016 Solar Energy Industries Association 34
AC 428: Acceptance Criteria for Modular Framing Systems Used To Support Photovoltaic (PV) Panels AC 428 is required to obtain an ICC-ES Evaluation Report; it is also useful as voluntary guidance AC 428 allows internal pressure set equal to zero (within constraints) in Components &am
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