Density/Area Curves Concept

Density/Area Curves Concept 

The density/area curves have traditionally provided some flexibility in system pipe sizing. Under provisions of NFPA 13, meeting any point on the appropriate curve is acceptable. This permits the use of higher densities over smaller areas or lower densities over larger areas.  Higher densities with smaller areas will generally result in larger branch-line piping but lower main sizes and lower overall water supply requirements. For this reason, a high-density, small-area point is often selected as the most economical.

minimum orifice sizes were specified for spray sprinklers protecting general storage, rack storage, rubber tire storage, roll paper storage, and baled cotton storage. For design densities of 0.34 gpm/ft2 (13.9 mm/min) or less, standard response sprinklers with a nominal orifice co efficient of K = 8.0 (Km = 115) or larger must be used. For design densities exceeding 0.34 gpm/ft2 (13.9 mm/min), standard- response sprinklers with a nominal orifice coefficient of K = 11.2 (Km = 160) or larger and that are specifically listed for storage applications must be used.

WATER DISTRIBUTION AND SPRAY COOLING CHARACTERISTICS OF SPRINKLERS

 

At present, there is no method of predicting the actual amount of water that will be delivered to a specific unit of floor area under actual fire conditions, especially since spray patterns vary with water discharge pressures

Figure 16.1.6 demonstrates the variability of the spray pattern of a typical pendent spray sprinkler with a nominal orifice coefficient of K = 5.6 (Km = 80) when discharged under non fire conditions at selected pressures. A 7 psi (0.5 bar) operating pressure is considered minimum by NFPA 13 , At that minimum pressure, the extent of the spray pattern roughly approximates that of the maximum light hazard spacing permitted by NFPA 13, when the sprinkler is located 8 ft (2.4 m) above the floor. The spray pattern enlarges as the operating pressure is increased to about 70 psi (4.8 bar), then begins to contract at higher pressures, becoming more elliptical in shape at the upper end of the allowable pressure range.