Sprinklers system design Type of sprinklers -Wet pipe systems They are simple, with the only operating components being the automatic sprinklers. An automatic water supply provides water under pressure to the system piping. All of the piping is filled with water. water. Until sufficient heat is applied, causing one or more sprinklers to fuse (open), the automatic sprinklers prevent the water from being discharged. Operation - When an automatic sprinkler sprinkler is exposed to sufficient heat, the heat sensitive element (glass (glass bulb or fusible link) link ) releases, allowing water to flow from that . .
-Dry pipe systems Water is not present in the piping until the system operates. When one or more of the automatic sprinklers is exposed to sufficient heat, it opens, allowing the maintenance air to vent from that sprinkler. Each sprinkler operates individually. As the air pressure in the piping drops, the pressure differential across the dry pipe valve changes, allowing water to enter the piping system. Water flow from sprinklers needed to control the fire is delayed until the air is vented from the sprinklers. For this reason, dry pipe systems are usually not as effective as wet pipe systems in fire control during the initial stages of the fire.
-Deluge systems "Deluge" systems are systems that have open sprinklers, the heat sensing operating element is removed or specifically designed open sprinklers, so that all sprinklers connected to the water piping system are open. These systems are used for special hazards where rapid fire spread is a concern, as they provide a simultaneous application of water over the entire hazard. They are commonly seen as preventive measures to prevent egress of fire from an external source. Water is not present in the piping until the system operates. Because the sprinkler orifices are open, the piping is at atmospheric pressure. To prevent the water supply pressure from forcing water into the piping, a deluge valve is used in the water supply connection, which is a mechanically latched valve. It is a non-resetting valve, and stays open once tripped.
-Hybrid system “Preaction-system” A combination of previous types 2 subcategories of Hybrid system do exist
-single interlock that act like dry system except these systems require that a “preceding” fire detection event, typically the activation of a heat or smoke detector, takes place prior to the “action” of water introduction into the system’s piping by opening the pre-action valve.
-double interlock similar to deluge systems except that automatic sprinklers are used. Activation of either the fire detectors alone, or sprinklers alone, without the concurrent operation of the other, will not allow water to enter the piping
-Classification of Occupancies sprinkler design and installation are directly related to the classification of occupancy . We Have : *Light Hazard Occupancies -Low combustibility , Low rate of heat release. *Ordinary Hazard Occupancies -Ordinary Hazard (Group 1) “Low combustibility” -Ordinary Hazard (Group 2) “Moderate to high combustibility” *Extra Hazard Occupancies -Extra Hazard (Group 1) “High combustibility with great probability of rapidly developing fire . -Extra Hazard (Group 2) ”Moderate amount of flammable liquids exist” *Commodity Classification. 4 classes exist according to the type of materials which are in their turn classified into 3 groups .
System Hardwares sprinklers shall be permanently marked with a one- or two-character manufacturer symbol, followed by three or four numbers, in order to determine the characteristic of each one . Sprinklers have standardized discharge characteristics where The “K-factor” Is one of them which describe the size and shape of the sprinkler’s orifice .
Governing equation for sprinkler’s dicharge
P:pressure in PSI Q:Flow rate IN GPM
-Another characteristic that must be taken in consideration is :Temperature Automatic sprinklers shall have their frame arms, deflector, coating material, or liquid bulb colored in accordance with the requirements of Table 6.2.5.1”NFPA13”. Pipe and tubes above ground are also standardized
Please check NFPA 13 , 6.3.1.2 , 6.3.2, 6.3.3, 6.3.4. , and Table 6.3.6.1 , Table 6.3.1.1 for steel , copper and Chlorinated polyvinyl chloride pipes and tubes specifications. ASTM: International develops international standards for materials, products, systems and services used in construction, manufacturing and
FOAM WATER SPRINKLER
The Foam-Water Sprinklers are used to protect the risk where foam is required to be applied from overhead sprinklers and is to be followed with plain water in a standard sprinkler pattern. Foam Water Sprinklers protect the loading and unloading area in the event of a spill fire with low expansion foam systems. These are useful in otherwide applications including Air Craft Hangers.
SPECIFICATION
Foam Water Sprinklers are open and air aspirating type. The pattern of coverage is similar to the conventional sprinkler head. The Foam Water Sprinkler has standard orifice with Kfactor of 42. Foam Water Sprinklers are designed to operate at a minimum of 2 bar pressure and maximum of 4.1 bar .The Foam Water Sprinkler with K-42 will deliver about 61 LPM at 2 bar pressure. The standard coverage per Foam Water Sprinkler is 9.3sq.m. (100 sq.ft.)
Pre-action and Deluge system Requirements -Pressure gauges must be installed above and below preaction valve and below deluge valve -Spacing of detection devices, including automatic sprinklers used as detectors, shall be in accordance with their listing and manufacturer's specifications. -Not more than 1000 automatic sprinklers shall be controlled by any one preaction valve.
The following types of sprinklers and arrangements shall be permitted for preaction systems: (1) Upright sprinklers (2) Pendent sprinklers and sidewall sprinklers installed on return bends, where the sprinklers, return bend, and branch line piping are in an area maintained at or above 40°F (4°C) (4) Horizontal sidewall sprinklers, installed so that water is not trapped The difference between an upright head and a pendent head is, an upright sprinkler is designed to be installed upright in the branchline piping of a sprinkler system. The pendent is designed to be in the pendent or 6 o clock position, with the deflector facing downward. We may use Anti-freeze agents according to the type of water supplied in the pipes “Potable or non-potable water “ check NFPA 13 Table 7.5.2.2 & Table 7.5.2.3
Hangers sprinkler specifications Group I -In group I hangers we use “Deluge Foam-Water Sprinklers” -The maximum distance between sprinklers either on branch lines or between branch lines shall be 3.7 m (12 ft). -System piping shall be hydraulically designed using the Hazen and Williams formula where the coefficient C shall be taken as 120 in the calculations. -The discharge devices shall have a minimum nominal 6.4-mm (¼-in.) orifice and shall be listed for use with the particular type of foam concentrate to be used in the system. - The discharge density from air-aspirating discharge devices using protein-type, uoroprote n-type, or
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e a m n mum o
.
mn m
(0.20 gal of foam solution per min per ft2) of floor area and a minimum of 6.5 L/min/m2 (0.16 gal of foam solution per min per ft2) of floor area for non non air-aspirating discharge devices.
Hangers sprinkler specifications Group IV -In Group IV hangers we use “Preaction system” - Sprinkler spacing shall be similar to group I - The design density from sprinkler systems shall be a minimum of 6.9 L/min/m2.
Hydraulic Calculation -Pipe sizes shall be no less than 1 in. (25.4 mm) nominal for ferrous piping and ¾ in. (19 mm) nominal for copper tubing or nonmetallic piping listed for fire sprinkler service. - The number of sprinklers per branch line, and number of branch lines per cross main shall otherwise be limited only by the available water supply. - Pipe friction losses shall be determined on the basis of the Hazen-Williams formula. The Hazen-Williams equation for calculating the pressure drop due to friction for a given pipe diameter and flow rate is as follow
The equation in metric units
*∆P = frictional pressire drop, kPa/m *Q = flow rate, m^3/h *D = pipe inside diameter, mm *C = Hazen-Williams C factor, dimensionaless.
Hydraulic Calculation example :”Tree system “
We begin with the furthest sprinkle -Assuming the density of discharge of the sprinkler is equal to :0.15 : 0.15 gpm/ft gpm/ft sqr sqr.. -The area of application < is equal to 1500 ft sqr . - Coverage / sprinkler = 130 ft sqr -Number of of sprinklers sprinklers on branch line = 1.2 x radical(design area)/distance between sprinklers 1.2 x radical(1500)/13 = 3.58 >>> 4 sprinklers on each branch. -We chose the type of sprinkler we want to use , we chose The nominal factor K <5.6> We calculate the flow rate of the furthest sprinkle Q= Coverage per sprinkler X density of discharge Q= 130 X 0.15 = 19.5 GPM -we calculate the length of the pipe between the last sprinkler on that branch and the previous one + the Hazen--Williams formula to calculate the fiction pressure /ft of equivalent length of fittings , then we use the Hazen pipe , using factor “C” , Diameter of the pipe , and the flow rate inside that pipe Then we multi l Pf b Pf b the total e uivalent len th of that i e . We calculate the pressure at the furthest discharging sprinkler using Pt= (Q/K) square We add Pt + Pf and we get the total pressure on the second sprinkler on the same branch
Steps continued in this table taken from NFPA 13 ,ANNEX A EXPLANATORY MATERIAL .
