6.4 Step Four - Determine Layout of Water Supply
Determine the layout of the water supply, the underground piping that
will supply water to the residence. This includes determining the
length, type and size of pipe required and accounting for pressure
loss.
Pipe needs to be sized to minimize pressure loss through the service
line during maximum
fl
ow demand of the system. Determine the
elevation difference between the connection to the water supply
source and the grade of the residence.
Following are other considerations for calculating the pressure loss
through the service line.
6.4.1 Shut-off Valves
For system maintenance and safety, every system must have a control
valve to shutoff the water
fl
ow. Valves must be installed and operated
according to NFPA 13D and prevailing local codes.
A sign shall be af
fi
xed adjacent to the main shut-off valve that states
the following:
WARNING
The water system for this home supplies
fi
re
sprinklers that require certain
fl
ows and pressures to
fi
ght a
fi
re. Devices that restrict the
fl
ow or decrease the
pressure or automatically shut-off the water to the
fi
re sprinkler system, such as water softeners,
fi
ltration
systems and automatic shutoff valves shall not be added
to this system without a review of the
fi
re sprinkler
system by a
fi
re protection specialist.
DO NOT REMOVE THIS SIGN.
Fig. 6.1: Warning sign for main water shut-off
6.4.2 Water Meters
Pressure loss through the water meter must be taken into consider-
ation during design and installation. Some water meters have
associated
fl
ow limits that when exceeded may result in improper
system operation.
The designer/installer should verify that the installed water meter’s
pressure loss is within the speci
fi
cations that were used for the design
of the system and that the maximum
fl
ow rate, as recommended by
the water meter manufacturer, is not exceeded.
6.4.3 Pressure Reducing Valves
As required by typical plumbing codes, if the pressure entering the
residence is above 80 psi (6 bar), a pressure reducing valve (PRV) is
required to limit the pressure to a maximum of 80 psi (6 bar). When
using a PRV, the designer must take into consideration the pressure
loss through the PRV. Some PRVs have associated
fl
ow limits that
when exceeded may result in improper system operation.
If a PRV is used on a stand-alone sprinkler system, an automatic
means of pressure relief should be installed on the sprinkler side also.
6.4.4 Back
fl
ow Requirements
The designer/installer must con
fi
rm with the authority having
jurisdiction on back
fl
ow requirements.
6.4.5 Additional Flow-restricting Devices
Design and calculation of the system should account for any
fl
ow
restricting devices that may be added to the system in the future such
as water softeners,
fi
ltration systems and automatic shut-off valves.
6.4.6 Smoke Detectors and Water Flow Alarms
The NFPA 13D standard does not require a water
fl
ow alarm on a
piping system when the dwelling has smoke detectors throughout the
dwelling unit. The smoke detectors must be installed in accordance
with NFPA 72, National Fire Alarm Code.
6.5 Step Five - Determine Sprinkler Requirements
Performance requirements for sprinklers de
fi
ne the water
fl
ow,
operating pressure and coverage area speci
fi
cations. The coverage
area dictates the
fl
ow rate and pressure of the system. Typical
coverage area speci
fi
cations for sprinklers range from 12 x 12 ft to
20 x 20 ft (3.7 x 3.7 m to 6 x 6 m).
The local code and the listing of the sprinkler manufacturer de
fi
ne
proper spacing of the sprinklers. The minimum distance between
residential sprinklers to prevent cold soldering, which is the spray
from one operating sprinkler onto an adjacent sprinkler preventing its
proper activation, is typically 8 ft (2.4 m). The maximum sprinkler
spacing should be no farther than the listed coverage area.
To ensure proper coverage in each room, lay out the sprinklers, taking
into consideration all
fl
at and sloped ceilings, as well as proper
locations for sidewall heads. When locating the sprinklers, ensure
proper clearance from ceiling fans, lights, duct work, registers and
fi
replaces.
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