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System Design <br /> 3-6.1.1.3 Designing For Large Ducts <br /> Large Ducts (Perimeters Greater than 100 Inches) <br /> For ducts larger than 100 in. (2540 mm) perimeter, the total perimeter of the duct must be divided <br /> by 50. If the ansWer contains a decimal (or fraction), it must be rounded-up to the nearest whole <br /> number. That will provide the number of nozzles necessary for proper protection of the duct. The <br /> diagonal dimension (nozzle to corner of duct) of each module must not exceed 11.78 inches (297 <br /> mm). If this diagonal dimension is exceeded, additional module divisions must be added until the <br /> diagonal dimension is not exceeded. A nozzle must then be centered in each "module" (refer to <br /> Figure 3-31). <br /> EXAMPLE <br /> You have a duct with a perimeter of 156 in. (3962 mm). <br /> Take the perimeter: 156 and divide it by the maximum allowable perimeter of a single nozzle: 50. <br /> 156/50 = 3.12 <br /> Round the 3.12 up to the ne�highest integer: 4. Four nozzles are required to protect this duct. <br /> Az + B2 = C2 Where A is length, B is width and C is diagonal. <br /> Each "section" of the duct is 18L x 15W. <br /> 182 + 152 = C2 <br /> 324 + 225 = 549 <br /> The square root of 549 is 23.43 inches (23.43= 549); therefore, the diagonal of each module is 23.43 <br /> inches. One-half of 23.43 is 11.71, which is the measurement from the nozzle to the corner of the <br /> duct. Our maximum allowable diagonal is 11.78 inches, as stated above. <br /> NOZZLE TO CORNER: 11.73 in.(298 mm) <br /> MAXIMUM ALLOWABLE is 11.78 in. (299 mm) <br /> 15 15 15 15 <br /> .% i i <br /> i <br /> i <br /> � <br /> i ! i . <br /> � i X i X � X 18 <br /> i i � <br /> i i � <br /> i <br /> i i i <br /> LARGE DUCT: 18 X 60 in.(457 mm x 1524 mm) <br /> TOTAL: 156 PERIMETER INCHES <br /> Figure 3-31. Modular Protection of Large Ducts <br /> �� �� °�!� ?� <br /> P/N 60-9127100-000 3-37 April 2009 <br />