WO2021024196A1

WO2021024196A1 - Forced ventilation installation with relays permitting on-demand ventilation of multiple working faces

Info

Publication number: WO2021024196A1
Application number: PCT/IB2020/057392
Authority: WO
Inventors: Christopher Norris
Original assignee: Etudes Et Constructions Electromecaniques
Priority date: 2019-08-05
Filing date: 2020-08-05
Publication date: 2021-02-11
Also published as: FR3099785A1; FR3099785B1

Abstract

The invention relates to a forced ventilation installation (1) with relays to provide ventilation of multiple underground working faces, based on the interposition of a plenum (3) between one or more primary lines (2) supplying outside air to the plenum (3) by means of one or more primary fan units (Vp) and multiple secondary lines (4) that leave the plenum (3) and each draw air from the plenum (3) to supply it to a respective working face by means of a secondary fan unit (Vs) mounted on the secondary line (4), the primary fan unit(s) (Vp) and the secondary fan unit(s) (Vs) being controlled in terms of flow rate so as to obtain the desired volume flow rates of air at the ends of the secondary lines (4).

Description

Relay forced ventilation installation allowing ventilation on demand from several fronts

The present invention relates to the field of ventilation of tunnels or other underground structures, and relates in particular to a forced ventilation system with relays making it possible to provide ventilation on demand from several fronts.

To ventilate a tunnel, especially during excavation, it is common to take air outside and route it along the tunnel via a ventilation line going to the front of the tunnel. 'attack and at the beginning of which is placed a fan, called primary fan, through which outside air is sucked.

In the case of a particularly long tunnel and / or of small section, it is necessary to resort to the use of one or more secondary fans, called relay fans, which are interposed between two successive sections of the ventilation line, which is in this case split into a series of line sections. This is called a relay forced ventilation installation.

It is sometimes necessary to ensure with a single access tunnel the ventilation of several fronts of attack of tunnels which communicate with each other at the level of a main chamber, for example in the case of two tunnels which are parallel one to the other and leave from the main chamber where the access tunnel arrives.

The conventional ventilation solution described above, according to which each leading front is ventilated by a ventilation line with its respective primary fan, has the advantage of allowing a different volume flow for each leading front, which makes it possible to take into account any differences in working conditions among the attacking fronts.

However, it will easily be understood that with this conventional ventilation solution, the number of ventilation lines and primary ventilation units increases with the number of leading fronts to be ventilated, and that the dimensions of the access tunnel quickly impose a limit to the number of ventilation lines that can be installed, and therefore to the number of fronts on the site.

The present invention therefore aims to propose a solution which makes it possible to ensure the ventilation of several leading fronts with optionally volume flow rates different from each other and adjustable independently from one another, and which is compact enough for installation in a site with a single access tunnel.

The solution according to the present invention is based on the interposition of a plenum, or air distribution chamber, between one or more primary lines supplying outside air to the plenum using one or more primary fan units and several secondary lines starting from the plenum and each taking air in the plenum to bring it to a respective leading edge by a secondary fan unit mounted on the secondary line, the primary fan unit (s) and the secondary fan units being controlled to achieve the desired air volume flow rates for the branch lines.

The plenum thus serves as a reservoir of fresh outside air in which each secondary fan unit draws, independently of the other secondary fan units, the amount of air it needs to ensure adequate ventilation of the leading front to which it is associated. . This air reserve is continuously adapted, through the primary fan units, in order to meet the fresh air needs of the sum of the withdrawals from the secondary fan units.

The present invention thus relates to a forced ventilation installation with relays to ensure the ventilation of several underground attack fronts, in particular of tunnels, communicating with each other at the level of a main chamber in which arrives an access tunnel, the 'ventilation system being characterized in that it comprises:

at least one line, called primary, extending along the access tunnel,
for each primary line, a primary fan unit with adjustable flow rate in real time, to suck outside air into said primary line,
a plenum located in the main chamber and with which at least one primary line is in fluid communication so as to be filled with outside air supplied by the primary fan unit (s),
several so-called secondary lines extending from the plenum and being in fluid communication with the latter, each secondary line extending to an associated leading edge to which it must provide a target air volume flow,
for each secondary line, a secondary fan unit with adjustable flow rate in real time, to suck air from the plenum,
secondary control means configured to control the flow rate of each secondary fan unit so as to achieve the target air volume flow rate at the end of the respective secondary line, and
primary control means configured to control the flow rate of the or each primary fan unit by taking into account the flow rate (s) of the secondary fan units, so as to ensure an air supply to the plenum which is sufficient.

The flow control of the fan units can be a control of the speeds of the fan units. In general, any means for controlling the flow rate can be used, such as for example means for controlling the pitch angle of the fan units, in the case where the latter have a variable pitch angle.

The secondary lines may in general be more numerous than the primary lines. However, it is also possible to provide the same number of secondary lines as of primary lines, in which case the invention makes it possible to install two medium-sized primary fan units instead of a large-sized primary fan unit and a fan unit. primary size, for example, and the sum of the installed and absorbed powers will be more advantageous in the first case.

Each fan unit can be formed by one or more fans (stages).

The plenum may be formed by a rigid box, for example made of metal, preferably formed by a plurality of individual segments assembled to each other in a sealed manner so as to form an interior space suitable for receiving exterior air. It will be understood that the use of such individual segments allows for easier placement of the plenum in the main chamber, since these individual segments are more easily routed there via the access tunnel.

The present invention is however not limited to a particular structure for the plenum, and one could thus, for example, envisage a plenum formed by several rigid boxes connected by flexible ducts.

Conventionally, a nominal air volume flow rate required for each leading edge can be determined in advance, and depends on the load of emissions from the thermal equipment on the site to be diluted, the number of people present or the minimum speed. return air.

In practice, the plenum will be advantageously sized to be a buffer capable of containing enough air so that each secondary fan unit can draw the required quantity of air from it, on the basis of the most unfavorable forecasts.

During operation, the target value for the air volume flow rate at the leading front will constantly change depending on the work phases in progress, the number of gear allocated, etc.

Preferably, the ventilation installation according to the present invention comprises means for measuring the volume flow of air at the end of each secondary line and the secondary control means are configured for a flow control of each secondary fan unit on the basis of the respective air volume flow rate measured by said measuring means, whereby the flow rate of each secondary fan unit is controlled to obtain the respective target air volume flow rate at the front regardless of any flow losses caused by air leaks. the secondary line.

As indicated above, according to the present invention, the primary control means are configured to provide a flow control which takes into account the flow rate (s) of the secondary fan units so as to ensure a sufficient supply of air to the plenum.

This taking into account of the flow rate (s) of the secondary fan units could be direct, by calculating in real time the speed to be given to the primary fan unit (s) in order to obtain, at the plenum inlet, a volume flow rate of air which is at less equal to the sum of the target air volume flow rates for the branch lines, taking into account the circuit parameters (resistance to air flow, leakage rate as a function of static pressure, etc.) of the or primary lines.

Preferably, this taking into account of the speed (s) of the secondary fan units will be indirect (slaved) and the parameter used to control the primary fan unit (s) will be an air pressure inside the plenum, downstream. of all the pipes leading to the secondary fans, which air pressure will be a function of the flow (s) of the secondary fan units since it will change according to the quantities of air taken from the plenum by the secondary fan units, upstream of this measuring point.

Thus, according to a particular preferred embodiment of the present invention, the ventilation installation comprises means for measuring an air pressure in the plenum and the primary control means are configured to control the flow rate of the or each primary fan unit on the basis of the air pressure measured by said measuring means.

The air pressure will advantageously be measured in the plenum downstream of the air samples from the secondary fans. Other measures could be taken which would take priority over this first in order to avoid, for example, negative pressure in the ducts of primary fan units, a condition which could exist when the speed in said ducts is too high.

Preferably, the primary control means are configured for flow control based on the air pressure measured by said measuring means, so that the flow rate of the or each primary fan unit is controlled so that the air pressure is measured by said measuring means. air pressure in the plenum is within a target pressure range.

In other words, the target pressure range is delimited by a low limit, below which the primary fan unit (s) are instructed to increase the plenum fill rate, and a high limit, above from which the primary fan unit (s) are ordered to decrease the plenum filling rate. Such a definition of the target pressure range makes it possible to maintain acceptable pressure conditions in the various components of the ventilation circuits (fans, ducts, plenum) and to distribute the total load of each line, between the outside air intake and its supply to the attacking front in the least energy-consuming way. The target range is determined in advance but it remains fixed regardless of the flow rate of the withdrawals. It is determined on the basis of the lowest possible pressure achievable given the inertia of the system, which extends over several kilometers.

As indicated above, according to the present invention the value of the target air volume flow rate for each secondary line can be modified, in particular directly by an operator.

It is understood that in the case where this value is increased for a secondary line, the flow rate of the secondary fan unit will be caused to increase accordingly, preferably by following an acceleration ramp, the quantity of air which it takes in the plenum will also increase and therefore the air pressure in the plenum will decrease. This decrease in air pressure will be measured and supplied to the primary control means which will then increase the flow rate of the primary fan unit (s) accordingly. Conversely, if the value of the target air volume flow rate is decreased, the air pressure in the plenum will increase and the primary control means will decrease the flow rate of the primary fan unit (s).

Preferably, the secondary control means are configured to, when the air pressure measured by the measuring means is below a lower limit of the target pressure range, prohibit or interrupt any increase in the flow of the secondary fan units until that the measured air pressure returns to the target pressure range, and, when said air pressure is greater than an upper limit of the target pressure range, prohibit or interrupt any reduction in the flow of the secondary fan units until '' that the measured air pressure returns to the target pressure range.

Such a configuration of the secondary control means makes it possible to obtain an overall operation of the installation which is reliable, robust, safe and fully automatic, including during a modification of a target air volume flow for a secondary line. , without risk of underpressure or overpressure in the plenum.

Thus, for example, if the acceleration ramp of a secondary fan unit whose target air volume flow rate to be produced has just been increased is too high and the secondary fan unit draws a quantity of air too quickly in the plenum too high to be immediately compensated by an increase in the speed of the primary fan unit (s), the acceleration of the secondary fan unit in question will be stopped while the speed of the unit (s) increases. primary fans results in an increase in the volume flow of the inlet air into the plenum and the air pressure in the latter until it returns to the target pressure range, the fan unit acceleration ramp in question can then resume.

The plenum can be fitted with an additional supply line, also referred to as an auxiliary line, which does not have a secondary fan unit and which owes its flow to the pressure difference between the inside of the plenum and the outlet of the auxiliary line. The connection with the plenum will preferably be located downstream of the pressure measurement position of said measurement means (main pressure tap described above). This allows the pressure at its inlet to be as stable as possible.

The auxiliary line will preferably be equipped with an air regulation damper for the regulation of the flow supplied independently of the constant pressure upstream. The presence of such an auxiliary line implies an additional flow to be supplied by the primary fan unit (s) but does not require any modification of the control principle described above.

This auxiliary line can be used to supply fresh air to the main chamber. In the case of an ATEX site (risk of explosive gases), it opens into, and therefore can be used to supply, a chamber which constitutes an overpressure safety zone in which all the underground electrical equipment is placed and which is separated from the main chamber by a sealed wall.

Preferably, the primary control means comprise a first programmable controller located outside the access tunnel and the secondary control means comprise a second programmable controller located, if necessary, in the security zone.

To better illustrate the object of the present invention, two particular embodiments will be described below, by way of illustration and not limitation, with reference to the accompanying drawings.

On these drawings:

is a schematic plan of the ventilation installation according to a first particular embodiment of the present invention.

is a schematic top view of a plenum according to the first embodiment.

is a perspective view of a model of a plenum according to a second embodiment of the present invention.

is another plan view of the installation of Figure 1.

is another schematic top view of the plenum in Figure 2.

is a perspective view of the plenum in Figure 5.

If we firstly refer to Figures 1 and 4, it can be seen that there is shown schematically a ventilation installation 1 according to a first embodiment of the present invention, implemented on an ATEX site. with a main chamber Cp from which extend two parallel tunnels T each comprising two leading fronts, on either side of the main chamber Cp. A single access tunnel Ta connects the outside to a first end of the main chamber Cp, and at the other end of the main chamber Cp is a safety zone in overpressure Zs, separated from the latter by a partition double metal wall PM (visible in Figure 4). This configuration of the site is in itself classic.

In this embodiment, the ventilation installation 1 comprises two primary lines 2 each having a first end which is located on the outside and is equipped with a primary fan unit Vp sucking in the outside air to deliver it into the respective primary line 2. The other end of each primary line 2 is in fluid communication with a plenum 3.

Secondary lines 4 extend from plenum 3, each in a T tunnel to a respective attack front. One end of each secondary line 4 is in fluid communication with plenum 3 and the other end of each secondary line 4 is located at the respective leading edge.

A secondary Vs fan unit is mounted on each secondary line 4, here at the end region of secondary line 4 which is connected to plenum 3.

Each secondary fan unit Vs is equipped with an isolation damper of the normally open type, which closes when the secondary fan unit Vs stops in order to isolate the associated secondary line 4 and avoid an unwanted flow rate at cause of the pressure in the plenum 3.

Finally, an auxiliary line 5 extends from the plenum 3, at the end thereof opposite to that where the primary lines 2 arrive, until it emerges in the safety zone Zs.

The auxiliary line 5 is provided with an RR air regulation register (visible in Figure 4) arranged to obtain at the end of the auxiliary line 5 a given target air volume flow rate. No piloting of the air regulation damper is foreseen, the air volume flow rate at the end of auxiliary line 5 will only depend on the pressure differential between zone Zm of plenum 3 into which the auxiliary line 5 emerges and zone safety Zs. The pressure setpoint in the safety zone Zs will normally be fixed in advance, and said target air volume flow rate can therefore be obtained by maintaining the pressure in said zone Zm of the plenum at the appropriate constant value.

An aeraulic circuit is thus defined going from the outside of the site to the various attack fronts and to the Zs safety zone.

The primary 2, secondary 4 and auxiliary 5 lines can for example be flexible or rigid sheaths. The primary 2 and secondary 4 lines can also be formed, for example, by a single section of sheath, over their entire length, or be formed by several sections of sheath which can be assembled to each other in a sealed manner or be at a distance. from each other, possibly with the presence of relay fans at the start of each section, with or without force-feeding of these, as is well known in the art.

The primary Vp and secondary Vs fan units are flow controllable in real time, the motors of which are for example controlled by variable speed drives, again as is well known per se in the art.

The operations of the primary fan units Vp are in particular controlled by primary control means comprising here a programmable controller located near the primary fan units Vp, outside the access tunnel. The operations of the secondary fan units Vs are for their part controlled by secondary control means comprising here a programmable controller which is located in the safety zone Zs and has a man-machine interface allowing operators to enter a target value for the target air volume flow rate of each leading edge, independent of other leading edges. Provision could also be made for the primary fan units Vp and the secondary fan units Vs to be controlled by a single controller.

Communications between the different elements of the ventilation system are provided by fiber optic cabling, but other means of communication are possible, such as Ethernet, WiFi, etc.

More specifically, means for measuring the air volume flow are provided at the end of each secondary line 4 and configured to indicate to the secondary control means a measured air volume flow rate. The secondary control means are configured for a flow control of each secondary fan unit Vs, and thus they adjust the flow rate of each secondary fan unit Vs by increasing or decreasing it, preferably according to acceleration or reduction ramps. slowdown, until the measured air volume flow rate equals the target air volume flow rate.

Furthermore, the primary control means are configured for a flow control of the primary fan units Vp, on the basis of a measurement of an air pressure inside the plenum 3.

In the present embodiment, where a safety zone Zs is present, the register of the auxiliary line 5 must be adjusted so that the required flow rate in the safety zone Zs is ensured when the measured control pressure is in the range predetermined pressure. Flow measurement means are therefore also provided in the conduit of the auxiliary line 5, which make it possible to control this value. The primary control means are configured to increase or decrease the speed of the primary fan units Vp in order to increase or decrease the static pressure in said zone of the plenum 3 so that it is within the predetermined pressure range, taking into account the air taken from the plenum 3 by the secondary fan units Vs, and in particular variations in the quantity of air taken due to changes in the target air volume flow rate at the end of secondary line 4.

The secondary control means are also configured to take into account the air pressure measured in the plenum 3, in particular to prevent the air pressure in the plenum 3 from going outside the target pressure range in which the performances ventilation on branch lines 4 and auxiliary line 5 are acceptable. Thus, said air pressure measuring means supplies the measured air pressure also to the secondary control means which are configured to prohibit or interrupt any acceleration of the speed of the secondary fan units Vs until the pressure of measured air will return to the target pressure range if the air pressure has fallen below a low limit, and to prohibit or stop any reduction in the speed of the secondary fan units until the air pressure measured returns to the target pressure range if the air pressure has exceeded a high limit.

When the ventilation system 1 starts up, an automated protocol will control the operation of the primary fan units Vp at low speed until a start pressure is reached, which authorizes the start of the secondary fan units Vs. The aim is to avoid swelling the line sheaths too brutally and running the risk of damaging them.

The ventilation installation 1 may also operate in an emergency mode, triggered by a "power off" protocol initiated in the event that methane, for example, is detected in the ATEX zone. According to this protocol, the power supply to the standard electrical circuit in the tunnel will be cut off. The emergency lighting circuit will be the only power source, and the compressed air circuit will remain active. Power to the Vp primary fan units outside the tunnel will also remain available. In addition, an air pressure sensor remains operational.

In the event of an emergency mode, the primary fan units Vp will be instructed to accelerate to their maximum speed, in order to supply as much fresh air to plenum 3 as possible, so that a maximum of fresh air is distributed to the attacking fronts.

To prevent the air pressure in plenum 3 from exceeding the maximum allowable air pressure, continue to measure the air pressure in plenum 3 by the air pressure sensor mentioned above and the speed of Primary fan units Vp is limited in the event that the air pressure exceeds a safety threshold, until the air pressure falls below said safety threshold.

Regarding the secondary fan units, their power supply will be cut. The isolation dampers will then open automatically, since they are connected to the compressed air circuit and the pneumatic actuators are of the "normally open" type when its solenoid valve is no longer supplied. The air pressure accumulated in plenum 3 will be released through the open dampers, towards the attack fronts, and towards the safety zone Zs. The distribution of the air will not be regulated but will find a natural balance among the different branches.

The result is a ventilation system whose operation is fully automatic, reliable and robust, while allowing different air volume flows at each leading edge.

The means for measuring air volume flow and the means for measuring air pressure mentioned above may be any appropriate means, where appropriate ATEX approved if located in the ATEX zone, like any type of flowmeter. or pressure sensor, which are well known per se.

Referring now to Figures 2, 5 and 6, it can be seen that there is shown schematically a plenum 3 composed of nineteen individual segments 30 assembled end to end so as to form a parallelepipedal box defining a internal volume suitable for being filled with outside air via the primary lines 2.

The walls of the individual segments 30 may be reinforced with ribs, in order to avoid vibrations produced by possible fluctuations in the air flow and the pressure inside the plenum 3.

Shutters 31 with actuator can be provided at each entrance where a primary line 2 arrives.

Each secondary fan unit Vs is connected by a series of duct sections 32 aligned and whose starting section communicates with an opening provided for this purpose in a wall of the corresponding segment 30. A shock absorber gasket 33 can be fitted in each starting section 32, and a shutter 34 is mounted at the end of the last section 32, after which the secondary Vs fan unit is connected.

Finally, a duct 35 extends from the end of the plenum 3 opposite to that where the inlets of the primary lines 2 are located.

An example of the sizing of the ventilation installation 1 is given below for a site whose access tunnel Ta has a length of 1900 m and whose main chamber Cp has a length of 180 m. The first T tunnel should have a length of 2705 m on one side of the main chamber Cp and a length of 1793 m on the other side, and the second tunnel T should have a length of 2727 m on each side of the chamber main Cp.

Each leading edge needs to receive a flow rate of 44 m ³ / s, which can be translated into a set point of 50 m ³ / s for the secondary fans Vs, taking into account the pressure drops and leaks along the secondary lines 4.

Consequently, the primary lines 2 must each theoretically be able to produce at the inlet of the plenum 3 a flow rate of 100 m ³ / s of fresh outside air.

Pipes with a coefficient of friction of 0.015 and leak rates of 5 mm ² / m ² are used for primary lines 2 and pipes with a coefficient of friction of 0.018 and leak rates of 15 mm ² / m ² were used for secondary 4 and auxiliary 5 lines.

The ventilation installation 1 can therefore be sized as follows:

two primary fan units Vp, each consisting of two fans mounted in series, with a diameter of 1800 mm and a power of 315 kW, for a total installed power of 1260 kW;
two flexible PVC ventilation tubes for primary lines 2, each with a diameter of 2400 mm and a length of 1900 m;
four secondary fan units Vs installed on four outlets of plenum 3 in the main chamber Cp, each consisting of two fans with a diameter of 1600 mm and a power of 200 kW, for a total capacity installed in the basement of 1600 kW;
four flexible ventilation tubes for branch lines 4, each with a diameter of 2200 and a maximum length of 2690 m; and
a metal plenum 34.7 m long, 6 m wide and 3 m high, for an internal volume of 588 m 3 and an internal working pressure ≤ 500 Pa, and the diameter of the ducts connected to plenum 3 is 2000 mm.

Under the above conditions, the target static pressure range in the area of plenum 3 in the vicinity of its outlet to auxiliary line 5 is 150 to 200 Pa.

A ventilation installation 1 has been described above for an ATEX site, in which it is necessary to ventilate a safety zone Zs under overpressure.

However, the present invention is not limited to this type of site and it is possible to omit the auxiliary line 5.

If we now refer to Figure 3, we can see that we have shown a plenum 3 'for a ventilation installation according to a second embodiment, whose auxiliary line supplies the main chamber, and not a zone safety Zs. There is therefore no emergency mode.

As with the first embodiment, the installation comprises several primary lines, three in the example shown, the plenum 3 ’and several secondary lines. Each primary line is equipped with a primary fan unit and each secondary line is equipped with a secondary fan unit.

The control of the primary and secondary fan units is similar to that described for the first embodiment.

It is therefore possible, for example, to provide a pressure control for the control of the primary fan units so that the air pressure measured in the plenum 3 'remains within a target pressure range making it possible to satisfy the ventilation needs at the various fronts in an acceptable manner attack, without overloading the primary fan units.

Additional pressure control in the primary lines can also be provided, which takes priority over the control measure in order to avoid negative pressure in the primary lines.

It can also be noted that the present invention is not limited to a specific geometry for the plenum, since here the plenum 3 ’has a more complex geometry than the plenum 3, the box of which is parallelepiped. The plenum 3 'will also include, for each primary line and each secondary line, a series of sections 32' similar to the series of sections 32 of the first embodiment, but which may, if necessary, include elbows, etc., to hold account of the configuration of the various tunnels.

It is understood that the particular embodiments which have just been described have been given by way of indication and without limitation, and that modifications can be made without departing from the present invention.

Claims

Forced relay ventilation installation (1) to ensure the ventilation of several underground attack fronts, in particular tunnels (T), communicating with each other at the level of a main chamber (Cp) in which an access tunnel arrives ( Ta), the ventilation installation (1) being characterized in that it comprises:

at least one line (2), called primary, extending along the access tunnel (Ta),

for each primary line (2), a primary fan unit (Vp) with adjustable flow rate in real time, to suck outside air into said primary line (2),

a plenum (3; 3 ') located in the main chamber (Cp) and with which at least one primary line (2) is in fluid communication so as to be filled with outside air supplied by the primary fan unit (s) (Vp),

several so-called secondary lines (4) extending from the plenum (3; 3 ') and being in fluid communication with the latter, each secondary line (4) extending to an associated leading edge to which it must provide a target air volume flow rate,

for each secondary line (4), a secondary fan unit (Vs) with adjustable flow rate in real time, to suck air from the plenum (3; 3 '),

secondary control means configured to control the flow rate of each secondary fan unit (Vs) so as to achieve the target air volume flow rate at the end of the respective secondary line (4), and

primary control means configured to control the flow rate of the or each primary fan unit (Vp) taking into account the flow rate (s) of the secondary fan units (Vs), so as to ensure an air supply to the plenum (3; 3 ') which is sufficient.
Ventilation installation (1) according to Claim 1, characterized in that it comprises means for measuring the volume flow of air at the end of each secondary line (4) and the secondary control means are configured for servo-control. flow rate of each secondary fan unit (Vs) based on the respective air volume flow rate measured by said measuring means, whereby the flow rate of each secondary fan unit (Vs) is controlled to obtain the air volume flow rate respective target at the front regardless of any flow losses caused by secondary line leaks.
Ventilation installation (1) according to any one of Claims 1 and 2, characterized in that it comprises means for measuring an air pressure in the plenum (3; 3 ') and the control means primary are configured to control the flow rate of the or each primary fan unit (Vp) based on the air pressure measured by said measuring means.
Ventilation installation (1) according to claim 3, characterized in that the primary control means are configured for flow control on the basis of the air pressure measured by said measuring means, such that the flow of the or each primary fan unit (Vp) is controlled so that the air pressure in the plenum (3; 3 ') is within a target pressure range.
Ventilation installation (1) according to Claim 4 taken in dependence on Claim 2, characterized in that the secondary control means are configured for, when the air pressure measured by the measuring means is below a lower limit of the target pressure range, prohibit or interrupt any increase in the flow of the secondary fan units (Vs) until the measured air pressure returns to the target pressure range, and, when said air pressure is higher at an upper limit of the target pressure range, prohibit or interrupt any flow reduction until the measured air pressure returns to the target pressure range.
Ventilation installation (1) according to any one of the preceding claims, characterized in that the plenum (3) is equipped with an auxiliary line (5), free of secondary fan unit and which owes its flow to the difference pressure between the interior of the plenum (3) and the outlet of the auxiliary line (5), the connection with the plenum (3) preferably being located downstream of the pressure measurement position of said measuring means.
Ventilation installation (1) according to claim 6, characterized in that the auxiliary line (5) is equipped with an air regulation damper for regulating the flow rate supplied independently of the constant upstream pressure.
Ventilation installation (1) according to Claim 7, characterized in that the auxiliary line (5) opens into a chamber which constitutes an overpressure safety zone (Zs) in which all the underground electrical equipment is placed and which is separated of the main chamber (Cp) by a sealed wall.