b"Reference velocity pressure - NBC table C-2actor -NBC clause 4.1.7.3.(5)(b))Exposure fCLEAN ENERGY Topographic factor (NBC sentence 4.1.7.4.(1))Step 3: Calculate the tributary area of the array normalized by theThe pressure-gust coefficient values shown in Figure 1 Importance factor (normal, NBC table 4.1.7.3)building sizecover the range of solar panel tilt angles from 0 degrees to 35The equation represents it:degrees. These angles represent the practical range of incli-Step 3: Calculate the tributary area of the array normalized by the building sizenation for solar array installations on commercial buildings.The equation represents it: A N = 1000 xA It should be noted that the pressure-gust coefficients are for [max(L ,5)] 2 both positive and negative values. The wind tunnel data has b shown that the wind loading on the interior panels in the A= normalized tributary, array layout (sheltered panels) has different loading condi-N tions than the perimeter edge panels in large arrays. Parapets A = dimensional tributary area, for the array component underpresence worsens the wind loads on solar panels as they tend consideration, andA N= normalized tributary,to lift the vortices higher above the roof surface and push L b= normalized building length = min[0.4(hWL)0.5,h,Ws], where them inward from the edges. Similarly, the wind tunnel dataA = dimensional tributary area,for the array component under consideration, and L b= normalized building length = min[0.4(hW L )0.5,h,Ws], wherealso revealed that an increase in the panel chord length has W= width ofthe building on its longest side, andL also increased the wind load. Since the pressure-gust coeffi-W L= width of the building on its longest side, and W S= width ofthe building on its shortest side. cients are generally applicable to sheltered solar panels, they W S= width of the building on its shortest side.need to be adjusted for array edge conditions (E), parapet Thepressure-gustcoefficients(CgCp) ,inFigure1,are ndeveloped ients (CgCp) n , in Fi data. This data applies to all size ( p ) and chord length ( c ) as shown in Step 4. The pressure-gust coefficfrom wind tunnel testgure 1, are developedfrom wind tunnel test data. building heights. The concept of normalized area is used to This data applies to all building heights. The concept of normalized area is used to not over-not over-penalize the lower-rise buildings relative to the high- Step 5:Calculate the net design pressure penalize the lower-rise buildings relative to the higher-rise buildings. This effect is not currently er-rise buildings. This effect is not currently addressed in NBCCombining the inputs from Step 1 to 4, the net design pres-components and cladding figures.sure for solar is calculated as follows:addressed in NBC components and cladding figures.Step 4: Determine the net-gust pressure coefficient() net g C p ) netDepending on the edge factor, E, used for exposed and Step 4: Determine the net-pressure-gust coefficient (C non-exposed solar panels in Step 4, Step 5 calculates the The net pressure-gust coefficient for the applicable tributary isroof-mounted solar panels net design pressure. Figure 2 The net pressure-gust coefficient for the applicable tributary is calculated as follows: calculated as follo(ws:) net=provides the definition for exposed and non-exposed solarpanels on the rooftop. developments for the upcoming In the ongoing code Where Where:2020 NBC, a proposed code change (PCF 1143) has been = min (1.2,0.9 + h /h) (hbeing the height ofthe approved to introduce provisions for roof-mounted solar p pt pt panels in the next edition of the National Building Code.p= min (1.2,0.9 + h pt /h) (h ptbeing the height of the parapet above the roofs surface), parapet above the roofs surface), These provisions are based on material from the Structuralc= max (0.6 + 0.2L p ,0.8),p ,0.8), Commentaries(UsersGuideNBC2015:Part4of = max (0.6 + 0.2LcL=solar panel length (chord length) Division B). The approval of this proposed change will L p =solar panel length (chord length) pensure that the building structures design will include the E = edge factor,additional loads from the roof-mounted solar panels. It will E = edge factor,(C g C p ) n= normalized area-averaged pressure-gust (C g C p ) n= normalized area-averaged pressure-gust coefficients, as defined in Figure 1 coefficients, as defined in Figure 1 also facilitate Code enforcement in their design.The pressure-gust coefficients values shown in Figure 1 cover the range of solar panel tilt angles from 0 degrees to 35 degrees. These angles represent the practical range of inclination for solar Figure 2: Definition sketch of exposed and unexposed panels in a roof-mounted solar array (NBC User Guide)array installations on commercial buildings. It should be noted that the pressure-gust coefficients are for both positive and negative values. The wind tunnel data has shown that the wind loading d edge of adjacent 1 array or roof edgeon the interior panels in the array layout (sheltered panels) has different loading conditions than the perimeter edge panels in large arrays. Parapets' presence worsens the wind loads on solar dpanels as they tend to lift the vortices higher above the roof surface and push them inward from d 2 d 11 unexposed panels: E = 1.0the edges. Similarly, the wind tunnel data also revealed that increase the panel chord length has d exposed panels: E = 1.52 row of d 0.5h and d1 max(4h ,1.2m)12panels d max(4h ,1.2m)22d2d120lROOFINGBC l FALL 2020"