Technical Article
Viking Residential Sprinklers: Application and Basic
Hydraulics
Scott Martorano, CFPS
Senior Manager Technical Services
May, 2010
Worldwide Fire Protection
www.vikinggroupinc.com
Viking Residential Sprinklers
Application and Basic
Hydraulics
TABLE OF CONTENTS
INTRODUCTION
3
UL 1626 RESIDENTIAL SPRINKLERS FOR FIRE PROTECTION SERVICE
4
UL 1626 MINIMUM FLOWS
4
THE HYDRAULICS OF RESIDENTIAL SPRINKLER SELECTION
5
DETERMINING FLOW (GPM) REQUIRED TO DELIVER THE REQUIRED DENSITY
5
HYDRAULIC FORMULAS
6
NFPA STANDARDS - DESIGN CRITERIA FOR RESIDENTIAL SPRINKLERS
7
PIPE AND FRICTION LOSS
9
EXAMPLES
10
CONCLUSION
10
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Viking Residential Sprinklers
Application and Basic
Hydraulics
INTRODUCTION
The last decade has seen tremendous growth in residential construction in the U.S. All indications are
that the percentage of newly constructed residential occupancies being protected with automatic sprinklers
will continue to grow and mature within the sprinkler industry. This is due in a large part to newly enacted
building codes and the efforts of groups such as the Home Fire Sprinkler Coalition, NFSA, AFSA and NFPA
providing education to home builders and helping local fire authorities get sprinkler ordinances instituted
within their communities. In response to the growth over the last decade and the minimum discharge density
changes implemented by UL and incorporated into NFPA standards, numerous new Viking residential
sprinklers have come to market to answer the needs of the industry.
Residential sprinkler installation is quickly becoming mandatory in many areas that are adopting the most
recent additions of recognized building codes. For example:
-
The 2011 International Building Code requires sprinkler protection of all residential occupancies.
-
The 2011 International Fire Code requires sprinkler protection of all residential occupancies.
-
NFPA 101 2006 Life Safety Code requires sprinkler protection for new single family dwelling units.
-
NFPA 5000 2006 Building and Construction Code requires sprinkler protection for all new single
family dwelling units.
More than ever it is extremely important to gain an understanding of the fundamental residential sprinkler
technology and the technical characteristics which will allow you to successfully install residential sprinklers.
Residential sprinklers are fundamentally different from standard and quick response sprinklers in that the
residential sprinkler is installed to provide for an increased level of life safety for the building occupants.
Because of this, residential sprinklers are tested to a separate UL standard which has a unique fire test
procedure, verifies the sprinklers’ thermal sensitivity and evaluates the water distribution characteristics. This
UL document is called UL 1626 Residential Sprinklers for Fire Protection Service.
The hydraulic design in NFPA 13D and 13R utilizes the same fundamental concept as a commercial
sprinkler system designed in accordance with NFPA 13. The available water supply will be the primary factor
in the selection of much of the equipment used on the project. The water supply will be evaluated to
determine the available water pressure and volume (GPM).
The only difference is instead of selecting the hydraulically most demanding rectangular area the
hydraulically most demanding 2 (13D) or 4 (13R) sprinklers will be selected for the calculation. The goal of
residential sprinkler systems since their inception has been to allow the highest quality residential sprinkler
system to be installed at a cost that does not deter the end user. Due to the much smaller design area and the
very low flows required for residential sprinklers the water supply requirements will be substantially less than
those required for commercial systems and the pipe sizes used will be much smaller as well.
Residential sprinkler are installed as a life safety device. The objective of residential sprinkler systems is
to prevent a room “flashover” for at least ten minutes, which allows the occupant’s time to evacuate. NFPA
13D requires that the water supply for these occupancies be available for at least 10 minutes. The small
water supply combined with the smaller pipe size, fittings, etc, combine to require extremely competitive
bidding for sprinkler contactors. Designing the most efficient piping network hydraulically allows the contractor
to successfully bid and profit from the installation.
The technical information below is designed to provide a basic understanding of the UL standard and the
information needed to properly design, layout and apply Viking residential sprinklers. Factory Mutual (FM)
does publish a testing standard for residential sprinklers called FM 2030 Approval Standard for Residential
Automatic Sprinklers and was extensively involved in the development of the fast response technology which
enabled the development of residential sprinklers, however, to a large part has not been involved in the
testing and approval for the residential sprinklers that are currently available.
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Viking Residential Sprinklers
Application and Basic
Hydraulics
UL 1626 RESIDENTIAL SPRINKLERS FOR FIRE PROTECTION SERVICE
UL 1626 is not a design document. In fact many professionals involved with the design of residential
sprinkler systems may never actually have the opportunity to read this document. UL 1626 is a standard
published and used by Underwriters Laboratory to evaluate the performance of residential sprinklers.
Underwriters Laboratory (UL) is the most recognized independent testing agency for residential sprinklers.
The scope of UL 1626 is defined within the document as:
“These requirements cover residential sprinklers intended for installation on sprinkler systems for fire
protection service. Requirements for the installation and use of residential sprinklers for the Installation of
Sprinkler Systems, NFPA 13, and Installation of Sprinkler Systems in One- and Two-Family Dwellings and
Mobil Homes, NFPA 13D and Residential Occupancies up to and Including Four Stories in Height Sprinkler
Systems, NFPA 13R.”
The selection of residential sprinklers can and does in many cases boil down to the hydraulic
characteristics of the sprinklers. The terms flows and pressures are tossed around very often and it is very
important to understand the economic impact of the system hydraulics.
When residential sprinklers are UL listed, the requirements of UL 1626 must be met. In order to place the
UL listing on a product all the testing must be passed in accordance with that document. This means that all
manufacturers conform to the same testing and performance standard. This is what the industry demands
and requires. By having an independent laboratory test the products the industry removes the potential for
marketing spin on the fundamental performance of the sprinklers. This is why the UL listing is so important to
AHJs, engineers and end-users.
As part of UL 1626 the minimum rated sprinkler flows are described within the document.
UL 1626 Minimum Flows
Upright, pendent, recessed pendent, flush and concealed sprinklers:
Spacing ft (m)
Minimum Flow GPM (l/m)
Density
12 x 12 (3.7 x 3.7)
8 (30)
.055 gpm/ft2 (2.24 mm/min)
14 x 14 (4.3 x 4.3)
10 (37)
.051 gpm/ft2 (2.08 mm/min)
16 x 16 (4.9 x 4.9)
13 (49)
.050 gpm/ft2 (2.04 mm/min)
18 x 18 (5.5 x 5.5)
17 (62)
.052 gpm/ft2 (2.12 mm/min)
20 x 20 (6.1 x 6.1)
20 (76)
.050 gpm/ft2 (2.04 mm/min)
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Viking Residential Sprinklers
Application and Basic
Hydraulics
Sidewall Sprinklers:
Spacing ft (m)
Minimum Flow GPM (l/m)
Density
12 x 12 (3.7 x 3.7)
8 (30)
.055 gpm/ft2 (2.24 mm/min)
14 x 14 (4.3 x 4.3)
10 (37)
.051 gpm/ft2 (2.08 mm/min)
16 x 16 (4.9 x 4.9)
13 (49)
.050 gpm/ft2 (2.04 mm/min)
18 x 18 (5.5 x 5.5)
17 (62)
.052 gpm/ft2 (2.12 mm/min)
20 x 20 (6.1 x 6.1)
20 (76)
.050 gpm/ft2 (2.04 mm/min)
16 x 18 (4.9 x 5.5)
15 (55)
.052 gpm/ft2 (2.12 mm/min)
16 x 20 (4.9 x 6.1)
16 (61)
.050 gpm/ft2 (2.04 mm/min)
18 x 20 (5.5 x 6.1)
18 (69)
.050 gpm/ft2 (2.04 mm/min)
Sidewall sprinklers with listed spacing other than those in this table shall not have less than a flow correlating
to a 0.05 gpm/ft2 (2.04 mm/min) discharge density.
THE HYDRAULICS OF RESIDENTIAL SPRINKLER SELECTION
Sprinkler hydraulics can be confusing. For those who do not use it on a regular basis the terminology and
formulas can be intimidating and install a level of technical uncertainty. It is important to understand that the
principles of hydraulics are universal. The laws that govern the movement of water through a sprinkler orifice
are the same for manufacturers. With the basic information that is provided below and an understanding of
the UL requirements from 1626 a quick comparison and evaluation of the flows and pressures can be done
for any sprinkler. There are some fundamentals that are common to all residential sprinklers.
-
First, the minimum operating pressure shall be the UL listed pressure or 7 psi (0.5 bar). If the
sprinkler is UL listed for a higher pressure than 7 psi (0.5 bar), the higher pressure shall be used in
the calculations.
-
Second, the minimum discharge densities for residential sprinklers are defined with the installation
standards and within UL 1626. All manufactures must conform to the same requirements.
-
Finally, as stated above, the principles used to determine required flow, pressure and K factors in
hydraulic calculations are universal.
DETERMINING FLOW (GPM) REQUIRED TO DELIVER THE REQUIRED DENSITY
The term density refers to the volume or amount of water that will be discharged (flow) within a specific
area. In the case of residential sprinklers NFPA 13D and 13R require a minimum discharge density of .05
gpm/ft2 (2.04 mm/min). When residential sprinklers are used in a building being designed to NFPA 13 the
discharge density is required to be .1 gpm/ft2 (4.07 mm/min).
The UL listed flows and coverage areas are provided on the sprinkler technical datasheet. The
installer is required to use this information and interpolation is not allowed. You will not need to
manipulate the flows to ensure the proper densities unless the project is being designed to NFPA 13
which we will discuss later. However having a basic knowledge of how densities can be determined
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Viking Residential Sprinklers
Application and Basic
Hydraulics
Mathematically provides the installer with a greater understanding of why and how the installation rules are
developed.
Flow and coverage area determine the density. To determine what flow (GPM) is required in order to
deliver the required density, the area of coverage in square feet is multiplied by the required density for the
applicable installation standard. If a system is being designed in accordance with NFPA 13D or 13R for
example, if the area of coverage for the sprinkler which has been selected is 12 ft x 12 ft (3.7 m x 3.7 m) this
would be 144 ft2 (13.4 m2). The solution is to multiply 144 x .05 (for metric, multiply 13.4 x 2.04). The
theoretical required flow will be 7.2 GPM (27.3 l/min). However, we know that the UL requirements for
discharge density are different than the theoretical and for this spacing a minimum flow of 8 GPM (30 l/min) is
required. This means that the best flow possible for 12 ft x 12 ft (3.7 m x 3.7 m) spacing to meet the UL listing
is 8 GPM (30 l/min). In reality, the best flow in the industry that has been achieved for this spacing is the
VK435, which is UL listed at 9 GPM (34 l/min). Again for 13D and 13R systems this calculation is not used
because the information on the technical data sheet already states the flows needed to conform to the .05
gpm/ft2 (2.04 mm/min) requirement, but it will be used in systems designed to NFPA 13.
The goal of the sprinkler designer is to select the residential sprinkler that will provide the required flow at
the lowest starting pressure possible based on the UL listing or the minimum 7 psi (0.5 bar). Evaluating these
characteristic is accomplished using a simple algebraic formula to solve for flow, pressure or the K factor.
This formula is not limited to residential sprinklers and can be used with other types of sprinklers as well.
Within the formula if two of the variables are identified the third can be solved for. Because we are using
a formula and manipulating it with basic algebra does not make this difficult. Any basic calculator with a
square root function can be used. Mathematically the identifying symbol for square root can be shown with the
traditional (√) symbol or by using the 0.5 or ½ after the number, indicating the number to the 0.5 power for
example.
The ability to achieve the best flow and the minimum 7 psi (0.5 bar) or listed starting pressure is based on
the amount of water being discharged (flow) and K factor of the sprinkler. Flow, operating pressure and the K
factor are all related. Each one of these variables has a direct impact on the others. For instance, if the
amount of water being discharge through a sprinkler (flow) is increased the K factor doesn’t change but there
will be a corresponding increase in the operating pressure. Or if a different sprinkler is selected with a larger
K factor the flow does not change but there will be a decrease in the operating pressure.
HYDRAULIC FORMULAS
Q = Flow
P = Pressure
K = K factor
To solve for flow:
Q = K x P0.5
To solve for pressure:
P = (Q/K)2
To solve for the K factor:
K = Q/P0.5
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Viking Residential Sprinklers
Application and Basic
Hydraulics
Examples:
Q. If a sprinkler has a K factor of 3.1 (45 metric) and it is discharging 10 GPM (37.9 l/min). What is the
discharge pressure?
A. Using P= (Q/K)2
(10/3.1)2 = 10.4 psi
for metric (37.9/44.7)2= .72 bar
Q. I am flowing 20 GPM (75.7 l/min) and I have a discharge pressure of 7.3 psi (.5 bar). What K factor
sprinkler is this?
A. Using K= Q/P0.5
20/7.30.5 = 7.4 K factor for metric 75.7/.50.5 = 107 metric
Q. The contactor is asking for a K 4.9 (70.6 metric) and the UL listing pressure at the required spacing
is 12 psi (.83 bar). What flow will I have from the sprinkler?
A. Using Q = K x P0.5 4.9 x 120.5 = 17 GPM for metric 70.6 x .830.5 = 64 l/min
NFPA STANDARDS – DESIGN CRITERIA FOR RESIDENTIAL SPRINKLERS
As mentioned earlier, residential sprinklers can be applied and installed under three NFPA standards,
NFPA 13, 13R and 13D. The original intent and goal of 13D and 13R was to provide sprinkler protection at a
minimal cost to eliminate a potential installation deterrent for owners and builders. Because of the significant
differences between the three types of occupancies covered by these standards and the need to optimize the
requirement of 13D and 13 R to reduce cost, substantial changes exist between the water supply and the
discharge density requirements.
NFPA 13D 2002 Installation of Sprinkler Systems in One-and Two-Family dwellings and
Manufactured Homes.
System Design Criteria - The number of design sprinklers under flat, smooth, horizontal ceilings shall
include all sprinklers within a compartment, up to a maximum of two sprinklers that requires the greatest
hydraulic demand.
Minimum Density - .05 gpm/ft2 (2.04 mm/min)
Water Supply - 7 to 10 minutes for a stored supply.
Hose Streams - Not required
The sprinklers are applied as listed.
NFPA 13R 2002 Installation of Sprinkler Systems Residential Occupancies up to and Including
Four Stories in Height.
System Design Criteria- The number of design sprinklers under flat, smooth, horizontal ceilings shall
include all sprinklers with a compartment, up to a maximum of four sprinklers that requires the greatest
hydraulic demand.
Minimum Density - .05 gpm/ft2 (2.04 mm/min)
Water Supply - 30 minutes
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Viking Residential Sprinklers
Application and Basic
Hydraulics
Hose Steams - Not Required
The sprinklers are applied as listed
NFPA 13 2002 Installation of Sprinkler Systems
System Design Criteria - The design area shall be the area that includes the four hydraulically most
demanding sprinklers.
Minimum density - for residential sprinkler installed in NFPA 13 occupancies the minimum required
discharge from each of the four most hydraulically most demanding sprinklers shall be the greater of the
following:
-
In accordance with minimum flow rates indicated on the individual listings.
-
Calculated based on delivering a minimum of 0.1 gpm/ft 2 (4.07 mm/min) over the design area in
accordance with the provisions of NFPA 13 2002 section 8.5.2.1.
NFPA 13 requires that the greater of either the individual listing or a calculation of the sprinkler delivering
0.1 gpm/ft2 (4.07 mm/min) in accordance with section 8.5.2.1 be used. Section 8.5.2.1 is the determination of
the protection area of coverage for sprinklers, commonly referred to as the S & L rules.
A degree of confusion exists within the industry regarding the conversion of the UL listed .05 gpm/ft2 to the
0.1 gpm/ft2 (2.04 mm/min to the 4.07 mm/min) requirement for NFPA 13 installations. Mistakenly, some
interpret this to mean that you simply take the area of coverage such as 20 x 20 or 400 ft 2 and multiply it by .1
(6.1 m x 6.1 m or 37.2 m2 and multiply it by 4.07) to get the required flow. This is NOT the case.
Example: The VK458 7.4 K (107 bar) Residential Pendent when the .1 (4.07) density and the S & L
rules would be used.
The UL listed flow for this sprinkler when being used for 20 x 20 (6.1 m x 6.1 m) coverage is 24 GPM at
10.5 psi (91 l/min at .7 bar).
If the actual coverage area is 20 x 16 (6.1 m x 4.9 m) for example, the area of coverage is 320 ft2 (29.7
To determine the require flow needed to deliver 0.1 gpm/ft2 multiply 320 x .1 = 32 GPM (4.07 mm/min
multiply 29.7 x 4.07 = 121 l/min).
m2).
32 GPM (121 l/min) is higher than the listed 24 GPM (91 l/min) so the 32 GPM (121 l/min) must be used.
Going back to our basic hydraulics formulas and P= (Q/K)2, we know that (32/7.4)2 = 18.7 psi (121/107)2 =
1.28 bar).
Solution: VK458 will be designed into this area flowing 32 GPM at 18.7 psi (121 l/min at 1.28 bar), not the
40 GPM (151 l/min) that would be calculated from a straight density calculation.
Example: The VK458 7.4 K (107 bar) Residential Pendent when the UL listed flow and pressure
would be used.
The UL listed flow for this sprinkler when being used for 20 x 20 (6.1 m x 6.1 m) coverage is 24 GPM at
10.5 psi (91 l/min at .7 bar).
If the actual coverage area is 10 x 20 (3.05 m x 6.1 m) for example, the area of coverage is 200 ft2 (18.6
To determine the required flow needed to deliver 0.1 gpm/ft2 multiply 200 x .1 = 20 GPM (4.07 mm/min
multiply 18.6 x 4.07 = 75.7 l/min).
m2).
The listed flow of 24 GPM (91 l/min) is higher than S & L calculation to 0.1 gpm/ft2 of 20 GPM (4.07
mm/min of 75.7 l/min), so the greater flow of 24 GPM at 10.5 psi (91 l/min at .7 bar) will be used.
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Viking Residential Sprinklers
Application and Basic
Hydraulics
PIPE & FRICTION LOSS
Selecting the proper pipe size is an essential part of any hydraulically calculated sprinkler system. There
are two basic methods allowed to accomplish this for one and two family dwellings. The International Building
Code (IBC) allows the systems to be hydraulically calculated in accordance with the procedures described
within NFPA 13D or the pipe sizes can be determined based upon available pressure as described within the
IBC and NFPA 13D. From a design point of view, selecting the smallest size pipe that can efficiently allow the
required flow of water reduces both material and installation cost. Most sprinkler systems today are
hydraulically calculated using computer software but there are some general rules of thumb that can be used
for estimating and evaluating the efficiency of the computer calculated system.
As we discussed earlier, the hydraulic calculations of the sprinkler system will be based in large part upon
the capabilities of the water supply. The amount of available water volume (flow) and residual pressure will be
the primary measure of what size piping will be used within the project. If the selection of a pipe size that
causes more friction loss than can be support by the water supply occurs, the system will likely be modified to
incorporate a larger pipe size.
Below is a chart in which you can manipulate the variables to gain an understanding of how they impact
friction loss. By double clicking on the Excel document below, the values in yellow can be manipulated and
the friction loss per foot and through 50 feet (15.2 m) of CPVC pipe will be identified on the bottom. Increasing
pipe size increases the cost of a project.
Residential
Sprinkler Hydraulic Comparison
Viking CPVC Size
Internal Diameter
3/4"
1"
1 1/4"
1 1/2"
2"
2 1/2"
3"
.874"
1.101"
1.394"
1.598"
2.003"
2.423"
2.950"
"General Rule of Thumb"
Pipe size will increase by one size when the friction
loss equal .25 to .3 psi per foot
Hazen Williams C-Factor Listed Plastic Pipe: 150
Enter Values Below
Listed Flow
Pipe Size
C-Factor
Friction Loss PSI/FT 0.268458
Friction loss through 50 ft of CPVC
42
1.101
150
13.42291
Double Click Above to Activate
By using this quick reference, you can see that theoretically it requires a flow between 42 and 46 GPM
(159 to 174 Lpm) through the equivalent (pipe & fittings) of 50 feet (15.2 m) of 1 inch (25 mm) plastic pipe,
before the design is at the point where it will become necessary to increase pipe size.
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Viking Residential Sprinklers
Application and Basic
Hydraulics
EXAMPLES
Example: VK438 14 x14 spacing 13 GPM @ 7 psi or (4.2 m x 4.2 m 49 Lpm @ .48 bar)
Two sprinklers flow – at least 26 GPM (98 Lpm)
Pressure – at least 12.65 psi (.87 bar)
Friction Loss through 50 ft CPVC – 5.33 psi (.36 bar)
Minimum flow and pressure 26 GPM @ 12.65 psi (98 Lpm @ .87 bar)
Of course this is theoretical, not an actual calculation and the flow and pressure requirements at the street
will be higher. But this can be used as a quick evaluation tool.
CONCLUSION
The ability to deliver water to an area of coverage is the bottom line for the sprinkler capabilities.
Providing the most economical system that can achieve the of life safety goals of the residential sprinklers
standards is the intent of the industry. Having a basic understanding of sprinkler system hydraulics will allow
the contractor to install the system in the most efficient and economical manner.
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