auto layout technical note
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PIPENET
AUTOLAYOUT
A NEW TOOLFORTHESPRAY/SPRINKLER MODULE
TECHNICAL NOTE
S U N R I S E S Y S T E M S L I M I T E D , M A Y 2 0 0 8
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1 S U M M A R Y
This note describes a new tool for the PIPENET Spray/Sprinkler module. The tools
purpose is to automate part of the task of designing sprinkler systems for protecting
storage/process vessels, areas or other objects/locations from the effects of fire.
2 I N T R O D U C T I O N
Defining the layout of a sprinkler system for a large vessel or area can be laborious
even with the aid of a graphical tool such as PIPENET. Automating part of this
design process will not only save time and effort, it will also allow fire-protection
rules to be encapsulated within the software and thus help to ensure that the resulting
design is compliant with fire-authority standards. This note begins with a statement
of the problem and a discussion of an illustrative example, then goes on to give a
brief description of the prototype autolayout tool. Finally, some details concerning
the variations in spray and rundown density for vessel protection are discussed.
3 S TA TE M EN T O F PR OB LE M
Given the size and shape of a plant vessel or area, design a sprinkler system to
protect it from fire. The design must either comply with applicable fire-authority
standards, such as those laid down in NFPA 15, or else satisfy a user-defined areal
flowrate and spray distribution specification.
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4 F IR E- AU TH OR IT Y S TA ND AR DS
The autolayout tool is intended to handle a variety of fire authorities' standards
and protection scenarios. By way of illustration, the application of NFPA 15 to
the design of a vessel protection system is used as an example.
4.1 Example: NFPA 15 Applied To Vessel Protect ion
The following standards from NFPA 15 are applicable to the protection of plant
vessels (reproduced from NFPA 15 Standard for Water Spray Fixed Systems for
Fire Protection, 2007 Edition)
7.4 Exposure Protection.
7.4.1* General. A system for exposure protection shall operate as intended for the anticipated
duration of the exposure fire.
7.4.2* Vessels.
7.4.2.1 Water spray shall be applied to vessel surfaces (including top and bottom surfaces of
vertical vessels) at a net rate of not less than 0.25 gpm/ft2 [10.2 (L/min)/m2] of exposed
surface.
7.4.2.2* Where rundown is contemplated, the distance between nozzles at different levels or
elevations, protecting vertical or inclined surfaces, shall not exceed 12ft (3.7m) as measured
along the surface.
7.4.2.3* The horizontal distance between nozzles shall be such that spray patterns meet or
overlap at the protected surface.
7.4.2.4 Spherical or horizontal cylindrical surfaces below the vessel equator shall not be
considered wettable from rundown.
7.4.2.5 Where projections (manhole flanges, pipe flanges, support brackets, relief valves, etc.)
will obstruct water spray coverage, including rundown on vertical surfaces, additional nozzles
shall be installed around the projections to maintain the wetting pattern that otherwise would
be seriously interrupted.
7.4.2.6 All uninsulated vessel skirts and any uninsulated steel saddles greater than
12in. (305mm) high at the lowest point shall have water spray applied on one exposed
(uninsulated) side, at a net rate of not less than 0.25 gpm/ft2 [10.2 (L/min)/m2].
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4 .2 I nte rp ret at io n
For the purposes of this application, the following assumptions are made
a) For those surfaces which are not considered wettable from rundown, the
spray pattern must be such that there is no part of the surface which receives
less than the specified minimum areal flow directly from one or more
nozzles. Since this is unlikely to be achievable without overlapping spray
patterns, the average areal flow rate on such surfaces will generally need to
be greater than the specified minimum.
b) For those surfaces which are considered wettable from rundown, the system
must be such that there is no part of the surface which receives less than the
minimum flow directly from one or more nozzles, from rundown, or from a
combination of the two. Again, practical considerations imply that theaverage flow will need to be somewhat greater than the specified minimum.
c) With rundown, the water is depleted on its way down, ie the same litre of
water cannot be considered to contribute to the minimum required areal flow
for every square metre of surface that it runs down.
4 .3 Fu lf il li ng NF PA 1 5
In the context of the above standards, the proposal for the autolayout tool is
that, based on some design information provided by the user, it will generate a
sprinkler layout which is compliant with standards 7.4.2.1 to 7.4.2.4. Standard
7.4.1 can be handled by constraining the choice of pipe material, while 7.4.2.5
and 7.4.2.6 are addressed by allowing the user to change the design manually
once the basic layout has been generated.
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5 U SE OF TH E A UT OL AY OU T T OO L
Use of the prototype autolayout tool is described in the following sections.
5. 1 Too l Selec tion
Having selected pipe types and nozzle libraries, the user selects Autolayout from the
Tools menubar item:
If an existing node is selected when the tool it launched, it will offer to join the new
sub-network which is about to be generated to that node.
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5.2 Dimensions And Spray Requirements
In the first of two dialogue windows, the user specifies the shape and size of the
object to be protected, spray density and nozzle layout requirements (which can beselected to be compliant with a built-in fire-authority standard), pipe parameters and
component labels:
In this example the diameter and height of the vessel have been entered but all other
parameters have been left at their default values.
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5.3 Nozzle Conf igurat ion
In the second dialogue the user can adjust the nozzle configuration (within the
constraints imposed by the selected standard). Based on the information suppliedtogether with the parameters of each nozzle in the library, values such as pressure,
total flowrate and overlap are displayed for each nozzle type.
Having adjusted the nozzle configuration values interactively and selected the nozzle
type from the list, the user then clicks on the Finish button.
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5.4 The Generated Layout
The generated sub-network is drawn on the schematic grid ready for further editing.
Fittings are included on the pipes, and pipe-sizing can be performed in the usual way.
Note that the generation of this example involved seven mouse-clicks and the entry
of two numbers: a further two mouse-clicks were involved in having it joined to theexisting node automatically.
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5.5 Area Protect ion Example
The following screen-shots show the two dialogues and generated sub-network for an
area protection scenario:
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6 S PR AY D EN SI T Y C ON SI DE RA TI O NS
For surfaces which are not considered wettable from rundown, the choice of nozzle
configuration depends on whether the flowrate requirement is an average or a
minimum
average flow requirement: the total required flow defines the number of
nozzles, which are then distributed in a near-uniform arrangement such
that, overall, the surface receives the correct areal flow;
minimum flow requirement: the nozzles are distributed in a covering
arrangement, such that no part of the surface receives less than the minimum
areal flow directly from one or more nozzles.
The autolayout tool will allow for either option. Note that meeting the second of
these requirements is complicated by the fact that, even with uniform spray densitywithin the spray cone, the areal flow striking the vessel surface will vary with
angular distance from the centre of the cone. This is because, with increasing angular
distance from the centre of a nozzles spray pattern
the distance to the vessel surface increases, reducing the spray density in the
diverging cone;
the angle of incidence on the vessel surface increases, spreading the flow
over a larger area of vessel.
For surfaces which are considered wettable from rundown, there is an additional
factor causing the rundown density to vary the height over which rundown is
accumulated decreases with increasing horizontal distance from the centre of a
nozzle's spray pattern. The variation in rundown density is illustrated below
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Again, the choice of nozzle configuration depends on whether the flowrate
requirement is an average or a minimum.
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6.1 Calculation Of Rundown
The autolayout tool will calculate rundown as outlined in the following diagram,
which shows (in elevation view) the spray patterns from nozzles N1 and N2overlapping on the side of the vessel:
In the column from the top of the area protected by these nozzles to the point P, the
areal flowrate including rundown is given by
RP=1
hP
y=yP
y=yPhS
F1 xP , y F2 xP , y . dy
where Fn(x,y) is the areal flowrate at (x,y) from nozzle n.
By handling the variation of spray and rundown density rigorously, the autolayout
tool will allow the user to ensure that the minimum flowrate requirement is truly met
at all points around a vessel where this is a design requirement, and to do so in the
most economical way (minimizing total flowrate in order to keep supply piping and
pumping costs to a minimum, for example).
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7 C ON C L UD I NG RE M AR KS
The autolayout tool is not intended to produce a finished, certified design or
to provide a substitute for the user's expertise and engineering judgement it
is primarily a productivity aid.
The autolayout tool will be extended to handle a variety of vessel shapes and
other fire protection scenarios.
The autolayout tool will be extended to support a variety of fire protection
standards, with the user choosing which standard is applicable or else
specifying the spray density and other requirements directly.
The purpose of this note is to gauge opinion on the way in which the
autolayout tool is presented to the user, and to invite further comments and
suggestions. The information contained in this note is strictly confidential and is not to be
shared with third parties without the express agreement, in writing, of
Sunrise Systems Ltd.
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