DESIGN OF SPRINKLER SYSTEM

A LECTURE

DELIVERED DURING THE

PSPE LUZON CONVENTION

ON OCTOBER 17-18, BAGUIO CITY

BY

JESSIE M. MARIANODESIGN OF SPRINKLER SYSTEM

HYDRAULIC CALCULATION Purpose of Hydraulic Calculations in fire extinguishing systems are:

a. To find the amount of water in GPM (CMH) and the pressure in PSI (Pa) that is required to meet a given standard or specification, at a given point of supply.

b. To find the type and capacity of supply required to meet demand.

c. To enable the system to be designed so that each head will discharge the amount of water required, and within the variation permitted, by the standards or specifications applicable.

Reasons for Hydraulic Calculation in fire extinguishing systems are:

a. To enable the system to be designed so that it will meet the standard or specification. No economical pipe sizing schedule can be drawn enable uniform discharge from head at the same level and certainly not from different levels.

b. To enable the system to be designed to fulfill the discharge outlet requirements with a minimum of devices, piping and water supply from the standpoints of both pressure and volume, thus effecting the maximum economy in pump, tank, city and / or other supply capacities.

SYNOPSIS OF CALCULATION METHOD. For time saving and convenience the calculations start at the heads farthest from the supply, and picking up additional heads discharge, and thus finally back to the point of supply.

Sprinkler or Nozzle Orifice Demand in Volume ( GPM or CMH) ) and in Pressure ( PSI or Pa). This is the starting point for each straight-thru or trunk calculation and for each branch calculation, the starting volume being determined by standards or specification. After the first head, the orifice pressure is determined by the calculation total of all pressures at the junction of the individual head with its pipe. From this pressure the sprinkler volume is obtained. (Relation between Orifice Volume and Orifice Pressure for Sprinklers, Nozzles and Hose Nozzles is found in Table-1A thru 1D)

Table-1A

Table-1B

Table -1C

Table 1D

Friction Pressure Demand in PSI (Pa) is the fiction loss in piping between the farthest (pressure wise) head and point of supply. (For the various pipes, fittings, valves, etc, the unit friction losses are found in Table-2)

Table-2

Static ( Elevation ) Pressure Demand is the pressure in PSI (Pa) corresponding to the vertical distance in feet between elevation of highest head, and elevation of point of supply ( such as bottom of gravity tank or bottom of pump suction reservoir, elevation of point where city flow test was made, etc. ) Static Pressure is calculated between discharge heads that are at different levels, between heads and junction or reference points where pressure adjustments must be made, and between heads the level of point of supply. Static Pressure has no relation to size or length of piping.

Velocity Pressure Demand is the Velocity Pressure in PSI (Pa) caused by velocity of water in pipes. This is so relatively insignificant and tedious to figure that it is practically always ignored; it is not to be calculated unless specifications require it.

Supply Flow (GPM ) and Supply Pressure ( PSI ) are determined to meet the Total Demand at a point horizontally and vertically common to both Supply and Demand at any time within any 24-hour period of a year.

SUPPLY in Flow and Pressure is equal or greater than the Minimum Required Demand consisting Flow (Total Heads x Required GPM per Head) and Total Pressure (Orifice, Friction, Static and Velocity)Uniform Practice. In an effort to arrive at a uniform practice in hydraulic calculations for fire protection systems, a recommended standard method and standard forms were introduced in the 1957 revision of NFPA-15, STANDARDS FOR WATER SPRAY SYSTEMS FOR FIRE PROTECTION. This standard method embraced the principles and practice set up and used by Automatic Sprinkler Corporation of America since 1930 and published in AUTOMATIC HYDRAULIC DATE in Nov. 1944.

This section of AUTOMATIC SPRINKLER HYDRAULIC DATA explains and illustrates, by examples, the standardized method as we interpret and practice it.

Fractions of GPM and PSI. In sprinkler branch lines, take volumes to the nearest 0.1GPM. In all cross mains, feet mains and supply mains, and Fire-Fog Systems throughout, take volumes to the nearest GPM, as, 15.4 = 15 GPM and 15.5 = 16 GPM. All pressure, friction, orifice and static are taken to nearest 0.1 PSI.

CORRELATION WITH NFPA 15. The following outline follows the paragraph headings of Section A23.20 of NFPA-15, Water Spray Systems, July 1957 Edition

CALCULATION FORM. The four forms used are listed below and explained in detail pages. See example 1 for forms for Title sheet, Hydraulic Calculation Sheet, Graph Sheet and Summary of Hydraulic Calculations.

Title Sheet is filled out of the beginning of each System calculation. It is provided to conserve space on the hydraulic calculation sheet itself and to provide reviewers with a brief summary of calculation method and basis for design.

Hydraulic Calculation Sheet contains all the items of Section A23.20 of NFPA 15, but the arrangement is altered slightly for convenience in use and checking and to provide a means for more positive identification. The calculation Q = K p may be made on this sheet in lieu of the graphical method on Graph Sheet. As will be seen in the example, this form lends itself to practically every needGraph Sheet, the regular N graph sheet used in this, is used for the several purposes, both to save calculation time and to provide means for a graphic summary of demand vs. supply. It can also be used to balance the volume-pressure of any one line, unit or system against that of another.

Summary of Hydraulic Calculations gives the reviewer the essence of the entire calculation on one sheet, including minimum and calculated demand, and actual supply.

INFORMATIN TO BE GIVEN ON DRAWING. Refer to the section on IDENTIFICATION on Title Sheet, which outlines the procedure for identifying heads, junction points, branch lines and units on plans and calculations. The first entry on the calculation sheet should identify the starting point of the calculation, and this reference point should be clearly marked on the plan.

Elevation of the highest sprinkler or other discharge outlet, and elevation relation between this highest sprinkler or other and every other sprinkler, hose nozzle or other discharge outlet, and with relation to the point of supply, such as pump reservoir bottom, pump center line, bottom of gravity tank, or point at which static and residual pressure were measured on a city water flow test. These must be clearly shown on plan, so that the static pressure may calculated between the water supply or supplies and every sprinkler, spray nozzle, hose nozzle or other discharge outlet. Slope of roof must be given so that the static difference between top sprinkler and all other sprinklers can be computed.

Kind and Size of Heads. If all heads shown on a drawing are the same kind and size, one covering descriptive note may be used. If all heads expert a minor number are the same kind and size, the covering note should make the necessary description, adding except as indicated. On FIRE-FOG System using more than one kind of nozzle each nozzle will be individually marked.

Discharge Characteristics of Heads. Instead of indicating on the plans and hydraulic calculation sheets a discharge constant K for Automatic heads and using the discharge formula to calculate q flow for each increment added, we pick up the discharge directly from Orifice Discharge Table 1A through 1E for Automatic Spray Sprinklers. VELOCITY PRESSURE. In accordance with the option allowed in first paragraph of this Subsection of the Standard, we omit consideration of velocity pressure figures from our calculations because we do not feel that the extra work of this more complicated procedure is justified by the negligible difference in results. This is the practice generally. FITTINGS. Loss through standard screwed fittings, in equivalent feet of steel pipe, is taken from Table 2, which was made up from Figure 12 of Section A23.20 of the NFPA 15 Standard.

Automatic practice regarding pressure loss due to fittings is not strict conformance with the standard, but we feel that it is more consistent and as accurate and our calculations are being accepted on this basis. Automatic s practice is as follows:

1. The fitting is included with the pipe on the discharge side of the fitting ( that is, the pipe the water is flowing into ), at the size of the outlet. See Fig - 1 for Screwed Fittings in Steel Pipe and Fig - 3 for Flanged Fittings in Headers and Socket Fittings in Underground Piping.

2. Fittings Loss (equivalent feet) is calculated wherever there is a change in direction of flow, excepting only as follow:

a. The tee or ell (in the line) into which the sprinkler or nozzle is screwed, these fittings losses having been included in the discharge characteristics (orifice pressure) for the head. See Fig 2A. b. In the case of a nozzle on the end of a swing joint, omit the tee in the line into which the swing joint is screwed. The ells between the nozzle and the line tee are calculated. See Fig -2b.

PIPE FRICTION CHART. Figure 11 of NFPA-15 is based on the Williams Hazen formula at C-120. Friction Tables 3A thru 3G below are more convenient to use. In accordance with NFPA Standards, friction tables for steel pipe are based on Williams-Hazen C-120; for Enameline underground pipe, cement lined and asbestos cement pipe, C-140, and for unlined cast iron pipe C-100.

FRICTION LOSS IN BLACK STEEL PIPE (SCHEDULE 40)

EXPRESSED IN PSI PER LINEAL FOOT

Table 3AFRICTION LOSS IN BLACK STEEL PIPE (SCHEDULE 40)

EXPRESSED IN PSI PER LINEAL FOOT

Table 3BFRICTION LOSS IN BLACK STEEL PIPE (SCHEDULE 40)

EXPRESSED IN PSI PER LINEAL FOOT

Table 3C

FRICTION LOSS IN BLACK STEEL PIPE (SCHEDULE 40)

EXPRESSED IN PSI PER LINEAL FOOT

Table 3D

FRICTION LOSS IN BLACK STEEL PIPE (SCHEDULE 40)

EXPRESSED IN PSI PER LINEAL FOOT

Table 3E

FRICTION LOSS IN BLACK STEEL PIPE-EXPRESSED IN PSI PER LINEAL FT. (SCHED.40 FOR 6-IN. AND SMALLER, SCHED.30 FOR 8-IN. AND LARGER

Table 3F

FRICTION LOSS IN BLACK STEEL PIPE-EXPRESSED IN PSI PER LINEAL FT. (SCHED.40 FOR 6-IN. AND SMALLER, SCHED.30 FOR 8-IN. AND LARGER

Table 3G

SAMPLE CALCULATIONS. Included is a typical example following the principles of the Standard, omitting velocity pressure consideration, except to show the calculation processes. The example should be studied individually as they will illustrate the general directions following.

TITLE SHEET is filled out for each individual system. Where there are two or more typical systems completely indentical so that no additional calculation is required, show a single system number in the space provided at upper right-hand corner of sheet, and beneath it write: Typical for System , , ,

It is of prime importance to study carefully every item in the Title sheet, because here is determined the kind of system to be installed, and the basis for all calculations on subsequent sheets. Any error in the beginning must be corrected thru out the calculations.

Title Block. Each space should be filed in carefully. After Building and Area protected, if building or area has a specific name or number, be sure to include it; if it has not use a descriptive note as to location, size, number of stories, occupancy, or other identifying data.

Item Protected space is to show the area covered by the system being calculated or, if protection is on equipment, the item or items specially protected. Combustible Material space should indicate the principal hazard definitely and exactly, e.g. Baled Cotton, Rubber Tire Storage; or Transformer Oil, Benzene, Aircraft fuel, etc. always describe Combustible Material separately regardless of how descriptive Item Protected may be.

Design Made. On next line, cross out the organization name that does not apply, and add the Standard Number. Name any other organization and specification if those shown do not apply.

Type Protection. In NFPA 15, carefully study paragraphs 12.11, 12.12, 12.13, 12.14, 12.20 and references. Check the type that is the object of the protection. For example, where the combustible is a material that can be extinguished by the system, check Extinguishment, check Control. If the system is designed to cool equipment such as tanks to reduce heat input, check Exposure Protection. In those cases where the system is designed to do more than one of those things, check those that apply.

Type system. In most cases the system will be automatic, but if it is manual only, check Manual. If an automatic sprinkler of deluge system is accompanied by inside and outside hose streams, check both automatic and manual.

Type Valve. Check type of valve used. In manually operated systems, the control valve is usually a gate valve, but in some cases it is a deluge valve which can be operated either by manual pull or remotely.

Discharge Heads. Beside the type of head used, write in the size or symbol number of the heads for the single system covered by the title sheet, including hose nozzles.

Head Spacing. Fill in the data called for, for the system covered by the little sheet. Note: In airplane hangars of the fire resistive construction, sprinkler spacing is extra-hazard, based on floor area, with no limitation as to the projected spacing along the sloping roof line; for other-than-fire-resistive construction, sprinkler spacing is extra-hazard, based on floor area, but projected spacing along the roof line must not exceed ordinary hazard. Extra spaces are provided in this column so that both roof and floor spacing may be indicated for Hangar jobs, as shown in Example 1.

Designed Coverage. This includes the next 6 captioned items, as follow

1. Density. This space is to be filled in if there is a specified or standard density for the occupancy; other-wise it may be left blank. The present trend for determining sprinkler spacing and discharge rates has been directed more and more specific densities for specific hazards. Design density of different occupancy classifications is presented in Table 4.2. Minimum GPM/Head. NFPA-NBFU-13 ( and NFPA-NBFU-409 for Aircraft Hangars) require that water deluge system calculations be made on the basis on not less than an average of 15 GPM per sprinkler, with a maximum variation of 15% up or down form this average discharge. For water deluge systems, write in: 15 GPM 15%. Some organization require a maximum variation of 10%. For systems where there is a specified density, write in the GPM that will provide that density on the spacing that applies to the System covered by the title sheet. NFPA-NBFU-409 Aircraft Hangars specifies a density of 0.17 GPM per SqFt for foam-water systems.

3. Minimum PSI at Head. Write in the PSI corresponding to the discharge shown in Minimum GPM/Head, above.

Table 4Design Density of Different Occupancy Classification

4. Number of Heads Discharging. Show the number of open heads in the system, if only a single system is to operate. If two or more systems of open heads are to operate simultaneously, insert in this space, See above, and at top of each title sheet write: FOR TOTAL EXPECTED DEMAND, SEE SHEET OF SYSTEM , which will refer to the end of the straight-through Trunk Calculation, usually Sheet 1 or 1-A of System 1. Following this practice will save complications and assure that reference will always be made to the true Expected Demand.

5. Number of Systems Operating. If the system covered by the title sheet is the only one figured as expected demand, insert 1. If two or more systems are to operate simultaneously, insert in this space, See above, and at top of each title sheet write: FOR TOTAL EXPECTED DEMAND, SEE SHEET , OF SYSTEM , as explained in a preceding paragraph.

In FIRE-FOG Systems and in Foam-water deluge systems for occupancies other than hangars, the expected operation will depend upon the hazardous material involved between equipment items protected, etc. Where a number of adjacent systems are involved, the engineer must carefully review the situation with respect to the water supply.

6. Hose Streams, GPM. If the expected demand is a single system plus one or more small or large hose streams, insert the GPM. If the expected demand is a single system plus one or more small or large hose streams, insert the GPM for hose stream(s) here. If two or more systems are to operate simultaneously, insert See Above, and make the notation at top of sheet referred to in Number of Heads Discharging, above.

Starting Point. Identify location of starting point clearly. Put yourself in the place of the person reviewing your calculation.

The lower half of the Title Sheet should be studied carefully, as it explains the sequence followed in the calculations, the identifying number for discharge outlet and letters for junctions, and the procedure for numbering the calculation sheet. Please note that the Trunk (straight-through) Calculations are intended to give an uninterrupted path from the far (or worst) head of the system straight to the supply point, and this can generally be accomplished on a single Sheet 1. If additional sheets are required for the straight through calculation, they are numbered 1, 1-A, 1-B, etc. If one sheet is sufficient for straight through, the Graphical Demand and Supply sheet is 1-A, the Summary is 1-B, etc. The subordinate or balancing Branch Calculations are numbered 2-3-4-etc. By following this numbering plan and numbering each system independently, it is easy to calculate all systems to a junction point and to rearrange the sets of sheets if the system first selected proves not to have the maximum demand.

HYDRAULIC CALCULATION SHEET. Preparatory to make the calculations one will have made the basic layout ( see example 1) and will have reviewed all systems to note which ones are typical (also which branch lines, loops, units, etc) so that calculation time is saved through re-using calculations by means of reference note. Determine which system will probably have the greatest demand; and the sprinkle or nozzle at the end of a branch line or loop, that on a straight-through calculation will produce the greatest total pressure (orifice + friction + static) demand. (See Example 1.)

After filling in the information called for at the top of the form and marking it Sheet 1, the first step is to write in the starting point, plan reference point, the of the head, the volume to be figured from this head and the starting pressure that is, the pressure which must be at this head to discharge the volume shown.

The calculation proceeds directly through the system from this starting point, calculating in the direction opposite to the water flow, following the path of the water back to the supply point, picking up the volume for each line and unit on the way. This can nearly always be performed on Sheet 1.

Branch calculation are made on separate sheets 2,3,4,etc; the sheet number and starting reference for each branch calculation are shown in the two right columns of the Trunk Calculation Sheet 1. At the junction with each successive unit or system, the volume for the unit or system is added into the Trunk Calculation; the added system has likewise been calculated to this point.

Calculation Procedure. The best way to explain calculation procedure is by a concrete example. Commencing with Problem 1, refer to the examples and their explanations and follow the calculations step by step from the starting discharge point to the supply point. The same general procedure is followed in FIRE-FOG and foam-deluge calculations as in sprinkler calculation.

Problem - 1 was designed for the beginner. All the elements of this simple problem are, for convenience, on one page. Mastery of this problem first will enable a quicker and better understanding of the more intricate phases of the Example Problem, should be accomplished before proceeding further.

Example: Problem - 1

Principle: -- At the same point (horizontally and vertically) the water supply must deliver the required GPM discharge at equal or grater than the demand pressure. Problem: -- A special hazard requires 1,000 SqFt of floor (20 x 50) to be deluged as follows:

a.) Minimum density, 0.30 GPM/SqFt of floor.

b.) Ten standard sprinklers 10CC, branch lines 10CC = 100 SqFt/Spk.

c.) 100 SqFt/Spk x 0.30 GPM/SqFt = minimum 30 GPM/Spk (Table 5)

d.) With 30 GPM/SqFt the sprinkler orifice pressure is 28.7 PSI (Table -1C)

e.) A 50,000 gallon gravity tank to be 1,500 away from deluge valve.

f.) Find the height (h) (from grade to bottom of gravity tank) required to supply the deluge system demand.

Table - 5

SUMMARY OF EXAMPLE PROBLEM PSI

Head Sprinkler orifce pressure28.7

Friction loss in piping16.1

Elevation (static) pressure8.7

TOTAL DEMAND AT GRADE-TANK RISER53.5

REQUIRED SUPPLY TANK h = 123.5'53.5