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Mathematics and reality in the field of hydraulic calculations of gas fire extinguishing systems

9 April 2018

In this article, we will consider the possible options for the optimal construction of automatic gas fire extinguishing installations based on the results of hydraulic calculations of piping and other associated parameters of the protected object.

Issues of more effective use of extinguishing agent.

Chief engineer of the project “ASPT Spetsavtomatika”
V.P. Sokolov

A little history in the issue of the method of hydraulic calculation of pipelines and determination of the area of ​​the holes of the nozzle for gas extinguishing installations. In theory, the dynamic behavior of extinguishing agent in the lines on the design of the pipe layout and arrangement of the nozzles can be analyzed using mathematical equations and formulas, developed by scientists working in the field of science. A mathematical model of hydrodynamics of a process is constructed on the basis of higher mathematics. Mathematical analysis is performed with some simplifications in the physics of the occurring process, as well as by setting permissible calculation limits, using constant constants and limiting the values ​​of the specified parameters used in the calculations. These simplifications and limitations determine the calculation error, which can reach up to 14% of the complexity of the calculation.

At one time, we had to use this technique for practical calculations of gas fire extinguishing installations, although all calculations were carried out manually using a calculator. Depending on the complexity of the hydraulic calculation, it took quite a long time, sometimes up to a week. The calculation consisted in that, changing the values ​​of the initial data, it was necessary to recalculate the equations and formulas until the result obtained was in accordance with the optimal values ​​of all hydraulic calculation parameters.
The document, which produced the hydraulic calculation of the gas fire extinguishing system, was called: “Method of hydraulic calculation of pipelines of gas fire extinguishing installations”. This methodology was developed for us in accordance with contract No. 6719 / N-2.3. FGU VNIIPO EMERCOM of Russia. The methodology was developed on the basis of research work carried out in various organizations, as well as in FGU VNIIPO EMERCOM of Russia, in the field of gas fire extinguishing installations.

But time does not stand still, and today ASPT Spetsavtomatika has a universal computer program «Vector» for the hydraulic calculation of pipe layout with nozzles, calculate the mass of extinguishing agent to create a regulatory extinguishing concentration in the protected volume and timing of exit GOTV gas extinguishing modules.

Vector program, one of the few programs that allows you to solve accurately and optimally all sorts of complicated tasks in the field of hydraulic calculation of gas fire extinguishing systems in a short time.

To confirm the authenticity of the verification results of calculation performed hydrants-crystal-calculation on the program «Vector» and obtained positive-set Expert enclose № 40 / 20-2016 from 31.03.2016g. Russian Ministry for Emergency Situations of the Academy to use the application of hydraulic calculations «Vector» in gas fire plants, production ASPT Spetsavtomatika with the following fire extinguishing agents:

FK-5-1-12 (Novec 1230)
Hladon 125
Chladon 227aa
Hladon 318TS
CO2 (carbon dioxide)

The “Vector” program is a modern software product that tends to constantly update, develop and improve the software, allowing the user to conveniently and simply work with the program on the computer.

The program for hydraulic calculations “Vector” for a given scheme of installation of gas fire extinguishing, includes the following initial data, manually set by the designer:

Area of ​​the room, m2;
height of the room, m;
additional volume, subtracted from the main volume, m3;
minimum temperature in the room, deg. FROM;
height of the room above sea level, m;
maximum allowable overpressure in the room, kPa;
standard time of submission of GOTV, s;
area of ​​permanently open openings, m2;
parameter “P” taking into account the location of the openings;
type of GOTV;
normative fire extinguishing concentration of GOTV;
vapor density GOTV, kg / m3;
Increasing coefficient for fire according to SP 5.13130.2009;
type of GPT modules;
load factor of the module;
working (initial) filling pressure at a temperature of 20 ° C, MPa;
type of high pressure hose RVD;
switchgears RU (with centralized GPT);
standard (GOST) of the pipes used.

Let’s now take a closer look at some of the most significant raw data for the hydraulic calculation from the list listed above that significantly affect the calculation result.

One of these parameters is the total area of ​​permanently open openings in the protected space “ΣFn, m2”. This value affects the estimated amount of gas “Mp”, because through the open openings there is a leakage of gas. It means that these losses must be compensated, so that the amount of gas “Mp” obtained by calculating the gas would be enough to create a standard fire-extinguishing concentration of the substance in the protected volume. Obtaining a real value of the parameter “ΣFn, m2” in the protected space is always associated with a big problem. We are looking at the extract from the JV section. 5.13130.2009.

8.14. Requirements for protected rooms.

8.14.1 The parameter is not
Table 1
п / п No. Product name Constantly open openings, m2
1 Single door, no more than 0,021 *
2 Double-leaf door, no more than 0,039 *
3 Single-leaf wooden window, no more than 0,024 *
4 Double-leafed wooden window, not more than 0,036 *
5 Single-leaf Eurowindows, not more than 0,016 *
6 Double-leaf Eurowindows, not more than 0.024 *

The data in Table 1 are obtained by calculation and correspond to the accepted method of hydraulic calculation of gas fire extinguishing installations in OOO ASPT Spetsavtomatika.

The total area of ​​permanently open openings in the protected room is calculated by the formula:

ΣFn = KB (ΣFd + ΣFo + ΣFinzh), m2 (3)

Where:

ΣFd is the total area of ​​permanently open openings of all doors (the door type according to Table 1 is multiplied by their number in the protected room);

ΣFo is the total area of ​​permanently open openings of all windows (the window type according to Table 1 is multiplied by their number in the protected room);

ΣFinzh – total area of ​​permanently open openings of engineering systems of fire automatics, etc. (if there are any permanently open openings in the wall, on the ceiling or in the floor, these areas are calculated separately and summed);

Кб – safety factor (constant value) is equal to – 1,1.

Let us now consider the location of the gas fire extinguishing modules on the protected site, the general requirements for the pipeline and nozzles in the light of obtaining reliability of the results when performing hydraulic calculations. We are looking at the copying of the section “8” from the joint venture. 5.13130.2009.

8.8 Vessels for gas extinguishing agent.

8.8.3 Vessels should be placed, possibly closer to the protected areas …

8.9 Pipelines.

8.9.9 The internal volume of the pipelines shall not exceed 80% of the volume of the liquid phase of the estimated quantity of GOTV at a temperature of 20 ° C.

Strict compliance with the requirements of paragraphs 8.8.3 and 8.9.9 is the key to obtaining the most accurate and close to the optimal values ​​of the result of hydraulic calculation.

Consider the effect of the length and diameter of the pipes of the collector, as well as the distribution pipeline, on the results of calculating the mass of the extinguishing agent and the standard release time. Consider, for example, an automated installation of (volumetric) gas fire extinguishing (AOGPT) with the supply of gas in several directions from the central fire-extinguishing station. At RIS-1, a graph of the functional dependence of the values ​​of “Vtr” from “Vzhg” is given in accordance with the requirement of clause 8.9.9 of the code of regulations of SP 5.13130.2009.

Calculations were made using the formula:

80% (4)

where: Vtr – internal volume of pipes of the axonometric diagram, л;

Vzhg – the volume of the liquid phase of the calculated amount of HOPV (chladone 227ea) at a temperature of 20 ° C and an operating pressure of 4.2 MPa, l.

The additional axis in the RIS-1 graph is “Mg, kg” – the calculated amount of GOTV (chladone 227aa) at 20 ° C and working pressure of 4.2 MPa in kilograms. The calculation was made using the formula:

Мг = k Vжг, kg (5)

where: Vжг – the volume of the liquid phase of the calculated quantity of GOTV (chladone 227еа) at a temperature of 20 ° С and working pressure of 4.2 MPa, l;

k – coefficient equal to – 1,85, kg / l.

The graph is constructed by interpolation over several calculated points. A graph is a section line between two zones. Conditionally, let’s name their zone above the graph and the zone under the graph.

At the beginning of the hydraulic calculation according to the “Vector” program, the mass of the extinguishing agent required to extinguish the protected room is calculated. Then, an axonometric diagram of the piping from the gas fire suppression module to the exhaust nozzles is drawn. Having the result of calculating the amount of the fire extinguishing agent and its value equal to the volume of the liquid phase of the GOTW in accordance with the plotted graph, we get the value “Vtr” the internal volume of the pipes of the axonometric diagram, which, according to paragraph 8.9.9, we have no right to exceed.

Two variants of calculation are possible. The first we do not exceed this value in 80% are in the zone under the graph and get a ready calculation. If this value is exceeded, the “Vector” program will indicate this error.

The way out of this situation:

– First, it is necessary to place the equipment as required by paragraph 8.9.3 (the vessels should be placed, possibly closer to the protected premises …);

– the second, if it is impossible to optimize the axonometric scheme, it is necessary to increase the amount of fire-extinguishing substance “Mg, kg” until, for example, point “B” (see FIG-1) is in the zone below the graph. In our example, this is instead of 555 kg. (Chladona 227aa) will have to produce 740kg of gas extinguishing in this direction. In some cases, using an automatic fire extinguishing station, which is located on the first floor, and the protected room is on the 10th floor and removed from it by 80 to 100 meters, the increase in the amount of gas can reach several times. It is very difficult to explain to the Customer.

By saving, the customer wants to have a centralized automatic gas fire-extinguishing station to extinguish all directions of the GPT, and the lengths and diameters of the axon-flow pipes in the building, as well as the amount of gas obtained, does not give advantages over modular fire fighting. You can take for example that part of the premises is extinguished by a centralized automatic fire-extinguishing station, and remote premises have a modular fire-extinguishing system.

The graph of the functional dependence of the values ​​of “Vtr” from “Vzhg” in accordance with the requirement of clause 8.9.9 of the code of regulations SP 5.13130.2009.

We have considered in this article the most important and sensitive parameters that affect the final results of hydraulic calculations performed in the “Vector” program. But this is not all the pitfalls that you have to meet. The real objects on which the gas fire extinguishing systems are realized represent a great variety of difficulties that have to be overcome by the developers. The more valuable is that the development of the possibilities of computer technology has allowed us to simplify our work in this area. With the advent of specialized programs such as “Vector”, the labor costs for hydraulic calculations have decreased tens of times and especially this is valuable when it is necessary to calculate several variants of the same hydraulic calculation for comparison.

The “Vector” program uses in its calculations only the equipment produced by “ASPT Spetsavtomatika” LLC, which is today one of the most reliable, technically perfect and optimal in terms of financial costs.

In our organization, free-of-charge training is provided on the “Vector” hydraulic calculation program, where you can get the most complete answers to all the questions that arise and also get any consultations in the field of fire protection.

Reliability and high quality is our top priority.