Designing A Sprinkler System @ Amazon.com
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An assortment of building occupancy examples are classified in Sec. A.5.2 of the NFPA 13 Appendix. The following are noted as light hazard occupancies: offices, churches, schools, museums, auditoriums, library seating areas, restaurant seating areas, and unused attics. The greatest or most complete or best possible sprinkler spacing (protection area) for these is brought up in Table 8.6.2.2.1(a) if frequent sprinklers are used. Usually, the greatest or most complete or best possible limit is 225 square feet for light hazard on a hydraulically calculated system. However, when exposed construction is combustible, with structural members spaced less than 3 ft. apart, the greatest or most complete or best possible coverage limit shrinks to 130 square feet. Ordinary hazard Group 1 occupancies include laundries, restaurant service areas, and automobile parking garages. Ordinary hazard Group 2 occupancies include the aforementioned arid cleaners, automobile repair and services areas, auditorium stages, woodworking plants, post offices, and stack room areas of libraries. Standard sprinklers protecting all standard hazard occupancies shall not cover an excess of 130 square feet per head (Table 8.6.2.2.1(b). Extra hazard occupancy examples include printing plants, paint and varnish dipping operations, plywood manufacturing, solvent cleaning, and plastics processing. Maximum sprinkler spacing for these occupancies is fixed to 100 square feet. However, where the required design density is less than 0.25 gpm/sf (and this goes for high-piled storage as well), a shelter area of up to 130 square feet per sprinkler is allowable (Table 8.6.2.2.1-c). It will have to be noted that mercantile insurance carriers and advisors develop their own creative writing of recognized artisti value containing more broad listings of occupancy examples and classifications than does the NFPA 13 standard, info which often times comes in handy when making an occupancy classification determination. Design Density Criteria The NFPA 13 Density / Area Curves are found in Fig. 11.2.3.1.1. When hydraulically calculating a light hazard sprinkler system, the design density employed is distinctively 0.10 gpm/sf over a 1500 square foot (the most hydraulically demanding) area of operation. To commence a calculation, the architect starts with the end-sprinkler and works “backwards” to the water supply source. Suppose that the sprinklers are spaced 14 ft. detached on branch-lines that are 12 ft. apart. Our square foot coverage then, is (12 x 14) 168 square feet. Q (in gpm) is determined by multiplying the density by the square foot coverage (.10 x 168), so we know that we’ll need 16.8 gallons per minute (Q) discharging out of the end sprinkler. The square root of the required end-head pressure is determined by “Q” disunited by “K”. If the design density is 0.10 and the K-factor of the sprinkler head is 5.5, we may see to it our end-head pressure by dividing 16.8 by 5.5, and squaring the sum to obtain a 9.33 psi figure. 9.33 psi is the required end-head pressure. To double-check, we may plainly plug in the numbers while performing the following equations to ascertain that they match: Q= K times the square root of the pressure, K= Q divided by the square root of the pressure, and the design density equals Q disunited by the square foot coverage. If our area of operation remains 1500 square feet, our design density will change to 0.15 for Ordinary hazard Group 1 occupancies and 0.20 for Ordinary hazard Group 2 occupancies. Everything changes when extended-coverage sprinklers are employed. Let’s suppose that we determine to extend our coverage to 324 square feet in a light hazard office, spacing sprinklers 18′ x 18′ apart. Now we will have to refer to the sprinkler manufacturer’s data sheets for direction. If we choose to install Tyco EC-11 pendent sprinklers, the selective information sheets dictate that our end-sprinkler must discharge a minimum of 33 gpm at 8.7 psi. This means that our design density (Q divided by the square foot coverage) is still 0.10 gpm/sf. The K-factor of this peculiar sprinkler is 11.2, which we may validate by the equation K= Q separated by the square root of the pressure. Extended-coverage sprinklers for general hazard occupancies work the same way. For example, we could use the Tyco EC-14 extended-coverage pendent sprinkler (K=14.0) in a (Ordinary hazard group 1) restaurant service area to protect an 18′ x 18′ area, but here the data sheet parameters require a 49 gpm minimum discharge at 12.3 psi for the end-sprinkler. In other words, Q= 49, K= 14.0, the square root of the pressure is 3.51, and the coverage is 324 square feet. All the equations match, including the required design density (0.15) which is received by dividing Q by the 324 sq. feet. Of course, the local water supply ought to still be competent to satisfy the resulting overall sprinkler scheme demand. In order for that to be accomplished, more spectacular scheme piping is installed to deliver the further and added gpm necessitated by the extended-coverage heads. Sprinkler discharge characteristics are outlined in cogent form in Table 6.2.3.1- these outline the differing K-factors for sprinkler identification. One other handy table to reference for sprinklers in NFPA 13 is Table 6.2.5.1, which deals with classifications and temperature ratings. To be utterly sure of code compliance with respect to sprinkler elevations, we refer to Sec. 8.6.4.1 in NFPA 13. The allowable distances cited beneath roofs, beams, or ceilings are always measured to the sprinkler deflector. It is adequate for the purpose for designers to consult info sheets for suitable distances beneath ceilings for specific sprinkler types, even though the safe bet is to call for a distance among 1″ and 12″ under the undersurface of the roof deck. The closer sprinklers are to the ceiling, the more immediate they will operate. But caution must be exercised because often times severe interferences to lateral water distribution may result from very close sprinkler placement to the ceiling. For all instances, the minimum of 1 inch (in the code) is to concede for the installation and remotion of upright sprinklers. When sprinklers are installed under pitched roofs, the most eminent sprinkler deflector (Sec. 8.6.4.1.3.1) may extend 3 ft. down from the most eminent peak.
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Design of Special Hazards and Fire Alarm Systems