AU2488101A

AU2488101A - Process for optimising a water spray extinguishing system and water spray extinguishing system for carrying out the process

Info

Publication number: AU2488101A
Application number: AU24881/01A
Authority: AU
Inventors: Bruno Covelli; Markus Muller
Original assignee: Siemens Building Technologies AG
Current assignee: Siemens Building Technologies AG
Priority date: 2000-04-08
Filing date: 2001-03-06
Publication date: 2001-10-11
Also published as: DE50009029D1; ATE285274T1; CN1196507C; SG104265A1; EP1142611A1; EP1142611B1; CN1317350A; HK1040205B; HK1040205A1

Abstract

The optimisation method regulates the pressure used for driving the water from the water feed device (4) to the spay jets (2) along the water spray pipeline system (1), for ensuring the required water droplet size. The water may be distributed to the spray jets via a propulsion gas, with calculation of the gas pressure for determining the droplet size in dependence on the size of the detected fire and the positioning of the spray jets relative to the fire.

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): SIEMENS BUILDING TECHNOLOGIES AG Invention Title: PROCESS FOR OPTIMISING A WATER SPRAY EXTINGUISHING SYSTEM AND WATER SPRAY EXTINGUISHING SYSTEM FOR CARRYING OUT THE PROCESS The following statement is a full description of this invention, including the best method of performing it known to me/us: Process for optimising a water spray extinguishing system and water spray extinguishing system for carrying out the process Description The present invention relates to a process for optimising a water spray extinguishing system which comprises a water storage device, a line system with nozzles which is connected to the latter and a propellant for delivering the water to the nozzles.

Conventional water spray extinguishing systems, which are also known as water mist extinguishing systems in the literature, spray drops of water out of the nozzles, and the propellant which is used is either a pressurised gas, preferably nitrogen, or a pump. Both high- and low-pressure systems are prevalent on the market. A gas pressure accumulator is provided when compressed gas is used.

The manufacturers of extinguishing systems of this kind favour the compressed gas S• variant, at least where high-pressure systems are concerned, because in this case the intrinsic energy of the pressurised gas is utilised and there is no requirement for any 'mechanical, susceptible pumps. High-pressure cylinders at a pressure of approximately 200 bar are preferably used for the gas pressure accumulator in order to save space. The disadvantage of this lies in the possibility of a massive water hammer with pressure peaks exceeding 200 bar loading the line system and, in particular, the water tanks upon starting the extinguishing or flooding operation. However the pressure at the nozzles simultaneously drops quickly during flooding, which has an influence on the extinguishing action.

As shown by practical experience and theoretical knowledge, certain extinguishing parameters, in particular the nozzle pressure and, linked with this, the diameter and speed of the drops, have a substantial influence on the extinguishing action. It is therefore essential, with regard to the extinguishing action, to know the interrelationships between the extinguishing parameters and then select them accordingly.

In a process described in EP-A-0 661 081 for optimising the extinguishing agent consumption and/or extinguishing time the extinguishing parameters are determined by means of methods relating to thermodynamics and fluid mechanics. Here the development of the fire gas flow and the behaviour of drops of water emerging from a nozzle in this fire gas flow are firstly established and the properties of the drops of water which are required for the extinguishing operation are calculated from the interrelationships between drop speed, drop size and drop evaporation. Finally, the equipment parameters pressure, water throughput and pipeline dimensions are adapted so as to produce the desired drops of water.

The object of the invention is to indicate a process of the type initially mentioned which enables the extinguishing action to be optimised through simple regulation of the drop size.

This object is achieved according to the invention in thatthe pressure propelling the water is selected such that the nozzle pressure necessary for the required drop size is obtained.

A first preferred embodiment of the process according to the invention is characterised in that a pressurised gas is used as propellant and the nozzle pressure is set by throttling the propelling compressed gas.

A second preferred embodiment of the process according to the invention is characterised in that the drop size which is to be set at the nozzles is calculated from the size of a given fire and the arrangement of the nozzles in relation to the fire, from which drop size the •nozzle pressure is calculated, and that the line diameter and throttling of the propelling compressed gas are calculated from the nozzle pressure.

In the process according to the invention the required nozzle pressure is therefore firstly S* 20 calculated and this nozzle pressure is then set by throttling the propelling compressed gas. Because of the phenomenon of the critical flow of compressible media, the action of throttling the propelling compressed gas maintains the delivery pressure constant for as long as possible during extinguishing. According to this phenomenon, the speed in the throttle member cannot be greater than the speed of sound and is therefore independent 25 of the propelling pressure difference, as long as this does not fall below a certain minimum value.

Further advantages of the process according to the invention lie in the fact that a o dangerous water hammer in the line system is prevented, that the water-carrying lines and the water tanks need not exhibit any high-pressure quality, and that the drop spectrum and the drop speed at the nozzles can be calculated for optimum extinguishing action.

The invention also relates to a water spray extinguishing system with a water storage device and a line system with nozzles which is connected to the latter and with a propellant for delivering the water through the line system to the nozzles. The extinguishing system according to the invention is characterised in that a throttle is provided to reduce the pressure of the propellant.

A first preferred embodiment of the extinguishing system according to the invention is characterised in that the propellant is formed by a gas which is stored in a gas pressure accumulator connected to the water storage device via a pressure line, and that the throttle is arranged in this pressure line.

A second preferred embodiment of the extinguishing system according to the invention is characterised in that the gas pressure accumulator contains a number of cylinders in which the propellant is stored under a high pressure, and that the gas cylinders are connected to the pressure line containing the throttle via controlled valves.

A third preferred embodiment of the extinguishing system according to the invention is characterised in that the propellant flowing through the pressure line is expanded and reaches the critical flow state upon passing through the throttle when the valves are open, in which state the pressure assumes an approximately constant value after the throttle.

A fourth preferred embodiment of the extinguishing system according to the invention is characterised in that the pressure in the gas pressure accumulator is above 100 bar, 20 preferably being 200 bar, and that the pressure in the pressure line after the throttle is below 100 bar, preferably being between 10 and 40 bar.

The invention is explained in detail in the following on the basis of an embodiment which is represented in the single drawing; this embodiment is a schematic representation of an extinguishing system according to the invention, in which the propellant which is used for S. 25 the extinguishing water is a pressurised gas, for example nitrogen.

As represented, the extinguishing system consists of a line system 1 with nozzles 2, which are provided for discharging extinguishing water in the form of droplets or spray mists.

ooo* The extinguishing water is stored in tanks. 3 of a water storage device 4, to which the line system 1 is connected. The extinguishing system also comprises a propellant for delivering the water from the storage device 4 to the nozzles 2. As represented, this propellant is a gas pressure accumulator The gas pressure accumulator 5 consists of a number of high-pressure gas cylinders 6, in which, for example, nitrogen is stored under a pressure of 200 bar. The high-pressure gas cylinders 6 are connected via valves 7 to a pressure line 8 leading to the water storage device 4. The pressure line 8 opens into the individual water tanks 3 and, under the action of high-pressure gas, forces the water out of the tanks 3 into the line system 1 and thus to the nozzles 2. The pressure line 8 is acted upon by high-pressure gas by opening the valves 7, this being initiated in the case of a fire by a corresponding signal from a fire alarm 9 or a central extinguishing unit 10, which is controlled by the fire alarm 9 in the latter case. It is of course also possible to manually initiate the extinguishing operation.

In the region of the gas pressure accumulator 5 the pressure line 8 contains an orifice plate or throttle 11, through which the delivery pressure in the pressure line 8 and therefore also in the line system 1 is throttled to an optimum nozzle pressure lying, for example, in the range from approximately 10 to 40 bar.

It is possible, through the arrangement of the throttle 11, to utilise the phenomenon of the critical flow of compressible media through nozzles to maintain the delivery pressure as constant as possible during extinguishing. The delivery pressure only changes slowly and guarantees optimum nozzle pressure during the decisive extinguishing or flooding phase.

The pressure reduction effected by the throttle 11 prevents any dangerous water hammer from occurring upon opening the valves 7 in the line system 1 and at the nozzles 2. It is S° 20 also possible to use materials which do not have to exhibit any high-pressure quality for the line system 1 and the water tanks 3.

The throttle 11 is designed when installing the extinguishing system so as to obtain the optimum pressure at the nozzles 2. This design takes place as follows: In a first step the number and arrangement of required nozzles 2 are determined from the dimensions of 25 the space provided for the extinguishing system and from a given fire, after which the development of the fire gas flow, in particular the rate of ascent and temperature of the fire gases, is determined on the basis of a fire model in accordance with the rate of burning, the manner of burning, the area of the fire and the room height. The behaviour of water drops after being discharged from the nozzles 2 is then described by means of these values and the speed and evaporation of the drops established as a function of the room height, from which the drep size and drop speed values which are optimum for extinguishing are determined.

The dimensions of the lines (line system 1) and the setting of the throttle 11 are then calculated in a second step from the optimum drop size and drop speed values now obtained.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

For the purposes of this specification it will be clearly understood that the word "comprising" means "including but not limited to", and that the word "comprises" has a corresponding meaning.

Claims

1. Process for optimising a water spray extinguishing system which comprises a water storage device a line system with nozzles which is connected to the latter and a propellant for delivering the water to the nozzles characterised in that the pressure propelling the water is selected such that the nozzle pressure necessary for the required drop size is obtained.

2. Process according to Claim 1, characterised in that a pressurised gas is used as propellant and the nozzle pressure is set by throttling the propelling compressed gas.

3. Process according to Claim 2, characterised in that the drop size which is to be set at the nozzles is calculated from the size of a given fire and the arrangement of the nozzles in relation to the fire, from which drop size the nozzle pressure is calculated, and that the line diameter and throttling of the propelling compressed gas are calculated from the nozzle pressure.

4. Water spray extinguishing system with a water storage device and a line system with nozzles which is connected to the latter and with a propellant for delivering the water through the line system to the nozzles characterised in that a throttle (11) is provided to reduce the pressure of the propellant.

5. Extinguishing system according to Claim 4, characterised in that the propellant is formed by a gas which is stored in a gas pressure accumulator connected to the water storage device via a pressure line and that the throttle (11) is arranged in this pressure line 9

6. Extinguishing system according to Claim 5, characterised in that the gas pressure *9*e accumulator contains a number of cylinders in which the propellant is stored ~under a high pressure, and that the gas cylinders are connected to the pressure line containing the throttle (11) via controlled valves 25

7. Extinguishing system according to Claim 6, characterised in that the propellant 0. ~flowing through the pressure line is expanded and reaches the critical flow state upon passing through the throttle (11) when the valves are open, in which state the pressure assumes an approximately constant value after the throttle (11).

8. Extinguishing system according to any one of Claims 5 to 7, characterised in that the pressure in the gas pressure accumulator is above 100 bar, preferably being 200 bar, and that the pressure in the pressure line after the throttle (11) is below 100 bar, preferably being between 10 and 40 bar. Dated this 6th day of March 2001 SIEMENS BUILDING TECHNOLOGIES AG By their Patent Attorneys GRIFFITH HACK Fellows Institute of Patent and Trade Mark Attorneys of Australia ee 6* ***00 S S* S* 05.5