WO2018100181A1

WO2018100181A1 - Multi-phase fire inerting gas system

Info

Publication number: WO2018100181A1
Application number: PCT/EP2017/081229
Authority: WO
Inventors: Torbjørn LAURSEN
Original assignee: Fire Eater A/S
Priority date: 2016-12-01
Filing date: 2017-12-01
Publication date: 2018-06-07
Also published as: EP3548148A1

Abstract

A system and method for inerting a fire at an indoor location is provided. The system comprises a first container containing a first inerting gas void of oxygen or having a first concentration of oxygen and a first conduit extending at least between the first container and the indoor location. The system further comprises a second inerting gas having a second concentration of oxygen above zero. The system is configured to deliver an amount of the first inerting gas along the first conduit from the first container into the indoor location at a first mass flow rate for a first period of time, and subsequently deliver an amount of the second inerting gas into the indoor location at a second flow rate for a second period of time.

Description

MULTI-PHASE FIRE INERTING GAS SYSTEM FIELD OF THE INVENTION

The present invention relates to the field of fire inerting. More particularly, it relates to the field of indoor fire inerting gas systems. BACKGROUND OF THE INVENTION

In the field of indoor fire inerting gas systems, an inerting system is often installed to inert a fire in a specific room. In the procedure of inerting the fire, an amount of inert gas is discharged into the room to reduce the percentage of oxygen in the air of the room. The reduced level of oxygen serves to inert the fire in the room. Certain types of inerting gasses allow people to breathe and function in the room even though the oxygen level in the room is low enough to inert the fire. The inerting gasses themselves commonly do not contain oxygen but in conjunction with the remaining atmospheric air in the room, they may allow a person in the room to breathe.

The desired percentage of oxygen in a room may be reached by initially discharging an amount of inert gas corresponding to a certain percentage of the volume of the room. In a substantially airtight room, the oxygen level usually does not change significantly after the initial gas discharge, depending slightly on the oxygen consumption of the fire and number of people in the room. Accordingly, the desired level of oxygen may be substantially sustained after the initial discharge. In contrast, in a room with an air flow in or out of the room due to, e.g., an open window or door, the oxygen level will not be sustained at the desired level after the initial gas discharge due to the flow of air. In such cases it is therefore advantageous to provide an extended discharge of gas. The airflow in or out of the room renders it difficult, if not impossible, to predict the oxygen level in the room from the amount of gas discharged in the room. This poses a challenge in sustaining the desired level of oxygen low enough to inert the fire in the room and high enough to allow people in the room to breathe and sustain life.

SUMMARY OF THE INVENTION

In a first aspect, the invention provides a method for inerting a fire at an indoor location, the method comprising the steps of: providing a first container containing a first inerting gas void of oxygen or having a first concentration of oxygen;

providing a second inerting gas having a second concentration of oxygen above zero; delivering an amount of the first inerting gas along a first conduit from the first container into the indoor location at a first mass flow rate for a first period of time; and subsequently

delivering an amount of the second inerting gas into the indoor location at a second flow rate for a second period of time, wherein the second mass flow rate is equal to or smaller than the first flow rate, and wherein, in case the first inerting gas comprises oxygen, the second concentration of oxygen is higher than the first concentration of oxygen.

In a second aspect, the invention provides a system for inerting a fire at an indoor location, the system comprising a first container containing a first inerting gas void of oxygen or having a first concentration of oxygen, a first conduit extending at least between the first container and the indoor location, and a second inerting gas having a second concentration of oxygen above zero, the system being configured to: deliver an amount of the first inerting gas along the first conduit from the first container into the indoor location at a first mass flow rate for a first period of time; and subsequently

- deliver an amount of the second inerting gas into the indoor location at a second flow rate for a second period of time.

Thanks to the difference in oxygen content between the first inerting gas and the second inerting gas, the method as described above allows for effective fire inerting during the first period of time as well as during the second period of time, while simultaneously enabling an oxygen concentration at the indoor location high enough for people to breath.

In the present context, a concentration in percent by volume is referred to as a concentration in percent. Moreover, a concentration denoted as 9-13% is to be understood as a

concentration being 9-13 percent by volume.

In the present context, an indoor location is to be understood as any indoor location such as, e.g., a room of a building, a room or cargo compartment of a ship or plane, a construction or traffic tunnel or a garage. The first period of time may be initiated by detection of a fire and/or signs of a fire such as, e.g., elevated temperatures, presence of flue gas, or other indicators of fire. In this case, during the first period of time, it is desirable to relatively quickly bring down the oxygen content from the common atmospheric concentration of oxygen at around 21% to a target concentration of oxygen at the indoor location in order to inert the fire.

In embodiments, the method comprises the steps of: determining the size of the indoor location;

predetermining the amount of first inerting gas delivered during the first period of time based on the size of the indoor location; and

- upon detection of a fire at the indoor location, delivering the predetermined amount of first inerting gas along a first conduit from the first container into the indoor location at a first mass flow rate for a first period of time.

In one embodiment, the method comprises the step of installing the system to deliver inerting gas into the indoor location. In embodiments, the system is configured to deliver a predetermined amount of first inerting gas along the first conduit from the first container into the indoor location at a first mass flow rate for a first period of time, the predetermined amount of first inerting gas being determined based on the size of the indoor location.

In embodiments, the system comprises an interface for receiving input relating to the size of the indoor location and/or the predetermined amount of first inerting gas. This allows the system to be readily configured to deliver the predetermined amount of first inerting gas based on the size of the indoor location.

In present context, the term 'size' may be understood as volume or area.

The predetermined amount of delivered first inerting gas based on the size of the indoor location allows for estimation of the concentrations of, e.g., oxygen obtained after delivery of the first inerting gas. Such prediction allows for predetermining the amount of delivered first inerting gas to achieve a breathable yet fire inerting concentration of oxygen at the indoor location.

In embodiments, the first mass flow rate is predetermined to be much larger, preferably at least 10 times larger, than a reference flow, the reference flow defining an expected flow rate in and out of the indoor at conditions without activation of the fire inerting system. Accordingly, the flow in and out of the indoor location during delivery of the first inerting gas will be largely dominated by the first mass flow rate. Accordingly, the relatively high first mass flow rate according to present embodiment allows for a more accurate estimation of the concentration of, e.g., oxygen after delivery of the first inerting gas. The definition of the reference flow could be based on, e.g., the size of the indoor location, the number of size of passages to and from the indoor location, and/or the type or age of the structure enclosing the indoor location.

In embodiments, the amount of first inerting gas delivered during the first period of time is predetermined based at least in part on a desired target concentration at the indoor location, the target concentration of oxygen being preferentially around 8-14%, possibly 10-12%.

The target concentration of oxygen is preferentially around 8-14%, possibly 10-12%, and thereby low enough to inert the fire and still high enough to allow people to breathe in appropriate circumstances. The target concentration of oxygen may be combined with a target concentration of carbon dioxide of 2-5% being higher than the usual concentration of carbon dioxide in atmospheric air of around 0.05%. Also, at initiation of the first period of time, the air expelled from the indoor location by the first inerting gas delivered into the indoor location does likely not contain any inerting gas. However, eventually part of the air expelled by the first inerting gas will contain inerting gas and accordingly, to reach the target concentration of oxygen, the first concentration of oxygen is preferentially well below the target concentration of oxygen, preferentially void of oxygen. This allows for bringing down the concentration of oxygen at the indoor location. Similarly, the concentration of carbon dioxide of the first inerting gas is preferentially well above the target concentration of carbon dioxide.

In embodiments, the carbon dioxide concentration of the first inerting gas is higher than the carbon dioxide concentration of the second inerting gas.

During the second period of time, the main objective is no longer necessarily to reduce the concentration of oxygen and/or increase the concentration of carbon dioxide at the indoor location. Indeed, if the concentration of oxygen at the indoor location is continuously reduced, at some point the concentration of oxygen may become too low for effective breathing. In contrast, the objective during the second period of time is to sustain the target concentration of oxygen and possibly also carbon dioxide while compensating for air flows caused by, e.g., open windows and/or doors, ventilation and/or other air paths. By having the second concentration of oxygen being higher than that of the first inerting gas, the second inerting gas may be able to sustain a concentration of oxygen at the indoor location which is both breathable and fire inerting. Similarly, by having a carbon dioxide concentration of the first inerting gas higher than the carbon dioxide concentration of the second inerting gas, the second inerting gas may be able to sustain a breathable concentration of carbon dioxide at the indoor location. In summary, embodiments of the invention enables both relatively quick reduction of the concentration of oxygen at the indoor location during the first period of time, as well as a sustained target concentration of oxygen during the second period of time, even in case of air flowing to and/or from the indoor location.

In general, the first concentration of oxygen and the concentration of carbon dioxide of the first inerting gas may depend on the flooding factor during the first period of time. Moreover, the flooding factor is a factor commonly known in the field and is a measure of the volume of the inerting gas delivered into the indoor location divided by the volume of the open space of the indoor location. As such, the higher the flooding factor, the closer the concentration of oxygen and/or carbon dioxide in the first inerting gas should be to the target

concentration(s).

In embodiments, the second period of time begins as the first period of time ends. In embodiments, a third period of time extends from the end of the first period of time to the beginning of the second period of time, wherein no inerting gas is delivered into the indoor location during the third period of time. In one embodiment, the third period of time has a predetermined third duration. In one embodiment, the predetermined third duration is predetermined based on the specifics of the indoor location such as, e.g., the volume and shape of the indoor location, and the air tightness of the indoor location. In one embodiment, the third period of time has a third duration determined based on sensor input. By virtue of the third period of time, the system is allowed to sustain the fire inerting target concentration of oxygen and possibly also the target concentration of carbon dioxide for a prolonged time without the need for additional fire inerting gas. Moreover, after the delivery of the first inerting gas, the concentration of oxygen and possibly also carbon dioxide may be sustained within target concentration intervals for a period of time without the need for delivery of the second inerting gas, whereby utilization of the second inerting gas may be optimised. In embodiments, the second flow rate is smaller than the first flow rate. This allows the delivered amount of second inerting gas to be reduced. In embodiments, the second period of time is longer than the first period of time. In this case, the amount of saved second inerting gas may be further reduced. As the concentration of oxygen during the second period of time need not necessarily be reduced, the second flow rate is allowed to be smaller than the first flow rate. In embodiments, the second concentration of oxygen is 9-14%, particularly 10-12%.

Accordingly, even if the second flow rate is well above the flow of atmospheric air into the indoor location, the concentration of oxygen at the indoor location does not drop below the limit for effective breathing. Also, the upper limit for the second concentration of oxygen may ensure that the concentration of oxygen at the indoor location remains at a fire inerting level. The second flow rate is thus allowed to be at a safe high level while enabling retainment of the target concentration of oxygen. Accordingly, the need for accurate measurement of the concentration at the indoor location is reduced. Further, a second flow rate providing second inerting gas in excess may further work to provide breathable air and/or expel flue gas from the indoor location, thereby reducing the risk of flue gas poisoning in case of fire at the indoor location.

In embodiments, the second flow rate is predetermined to be larger than the reference flow.

In embodiments, the second flow rate is predetermined at least in part based on the size of the indoor location. The combined effect of delivering the first inerting gas followed by the second inerting gas having second concentration of oxygen of 9-14%, particularly 10-12% allows for a quickly attained fire inerting and breathable concentration of oxygen by the first inerting gas, as well as sustaining the fire inerting and breathable concentration of oxygen with a relatively high second flow rate. Particularly, the fire inerting and breathable concentration of oxygen is allowed to be sustained during the second period of time even at indoor locations with a relatively large flow of air out of the indoor location (reference flow) as is the case for, e.g., old wooden buildings, and generally indoor locations with a high or unknown number of air passages to the outside. This is achieved by the ability of the system to define the second flow rate to be well above the reference flow. In embodiments, the first inerting gas has a concentration of carbon dioxide of 4-12% and/or the second inerting gas has a concentration of carbon dioxide of 2-5%. The carbon dioxide concentration of the first inerting gas is then tailored to facilitate a relatively quick increase of the concentration of carbon dioxide to attain breathable air in combination with the concentration of oxygen at the indoor location. The concentration of carbon dioxide in the second inerting gas is in the same range as the target concentration of carbon dioxide.

Accordingly, the second flow rate is allowed to be at a safe high level while enabling retainment of the concentration of carbon dioxide at the indoor location.

In embodiments, the extent of the first and/or second period of time is a predetermined value. This provides a simple way of controlling the extent of the first and/or second period of time. Further, because the second inerting gas is allowed to have breathable concentrations of oxygen and carbon dioxide, a prolonged second period of time does not increase the risk of the air at the indoor location becoming unbreathable. Conversely, a prolonged second period of time may provide breathable air and/or expel flue gas from the indoor location possibly even after the fire has been inerted.

In embodiments, the method further comprises the step of providing a sensor for sensing at least one condition at the indoor location, wherein the extent(s) of the first and/or second period of time, and/or the first and/or second flow rate is determined based on at least one condition sensed by the sensor. In this case, the extent of the first and/or second period of time may be optimized according to the actual condition(s) sensed by the sensor.

Accordingly, more accurate control of the concentration of oxygen and/or carbon dioxide at the indoor location may be achieved providing improved fire inerting conditions and/or improved breathing conditions.

One condition may be a concentration of oxygen at the indoor location and/or one condition may be a temperature at the indoor location. Accordingly, the first period of time may, e.g., end when the target concentration of oxygen is reached. Further or alternatively, the first flow rate may be increased if the concentration of oxygen at the indoor location decreases slower than a predetermined rate. Further or alternatively, the second flow rate may be increased if the concentration of oxygen at the indoor location increases above a

predetermined value during the second period of time. Further or alternative, the first and/or second flow rate may depend on the sensed temperature. More specifically, if the

temperature increases faster than a predetermined rate possibly indicating increase of fire, the first and/or second flow rate may be increased to decrease the concentration of oxygen at the indoor location. One condition may be whether a door and/or a window leading to the indoor location is open or closed. In this case, the method allows for adjustment of the first and/or second flow rate(s) in response to a sensed open or closed door and/or window. Similarly, the first and/or second period of time may be adjusted.

In embodiments, the method comprises the steps of mixing the first inerting with a third gas, the third gas comprising or being compressed atmospheric air to form the second inerting gas. Accordingly, the second inerting gas is allowed to be formed at the indoor location from the first inerting gas and the third gas. The first inerting gas may be an already approved inerting gas for use in fire inerting systems and with the third gas being allowed to be compressed atmospheric air, the second inerting gas may be readily formed on site from possibly already approved components. Further, the compressed atmospheric air may be stored at the indoor location alleviating the need for a fresh air supply at the indoor location, which may be compromised in case of fire at the indoor location.

In embodiments, the system comprises a second container containing the second inerting gas, the second container being connected, via a valve, with the first conduit at a point in the first conduit downstream of the first container and upstream of the indoor location. In this case, the second inerting gas is readily available to the system with predetermined concentrations of oxygen and possibly also of carbon dioxide. This increases the reliability of the system and/or the simplicity and convenience of operating the system. Further, by connecting the second container via a valve, delivery of the second inerting gas into the indoor location may readily be adjusted and/or controlled.

In embodiments, the first conduit of the system comprises at least one pipe, the at least one pipe being rigid and hollow.

In embodiments, the system is configured to form at least part of the second inerting gas by mixing the first inerting gas with a third gas, the third gas comprising oxygen. This allows the third gas to have a relatively high concentration of oxygen, possibly at the level of atmospheric air. Accordingly, the second inerting gas may be formed by a mixture of the first inerting gas and the third gas having a concentration of oxygen, e.g., at the level of atmospheric air. This may reduce the number of containers needed for a functioning system. Further, in case the third gas consists of atmospheric air, this third gas may be obtained from an inlet remote from the fire. Alternatively or additionally, the atmospheric air may readily be captured in containers prior to usage for storage until needed in the system.

The first inerting gas may be an already approved inerting gas for use in fire inerting systems and with the third gas being allowed to be compressed atmospheric air, the second inerting gas may be readily formed on site from possibly already approved components. Further, the compressed atmospheric air may be stored at the indoor location alleviating the need for a fresh air supply at the indoor location, which may be compromised in case of fire at the indoor location.

The third gas may be contained in a third container being connected, via a valve, with the first conduit at a point in the first conduit downstream of the first container and upstream of the indoor location. In this case, the third gas is readily available with predetermined concentrations of oxygen and possibly also of carbon dioxide.

The third gas may comprise atmospheric air and/or have a concentration of oxygen of 16- 24%. Atmospheric air is commonly abundantly available and thus convenient to provide. Also, by mixing atmospheric air with the first inerting gas, the second inerting gas may readily achieve desired concentrations of oxygen and/or carbon dioxide.

In embodiments, the system comprises a compressor and/or an ejector having an inlet at a location with atmospheric air, the location being remote from the indoor location, the compressor and/or ejector being connected, via a valve, with the first conduit at a part of the first conduit downstream of the first container and upstream of the indoor location. This may reduce the number of containers needed for a functioning system. The compressor may be electrically powered. The compressor may alternatively or additionally be powered by a flow of inerting gas as in a turbo. The ejector may be self-sustained by a flow of inerting gas. Present embodiments are particularly advantageous in cases where space is limited such as, e.g., in tunnels, clean room research facilities, airplanes, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described in further described with reference to the accompanying drawings, in which: Fig. 1 illustrates an embodiment of a system for inerting a fire according to the invention; Fig. 2 illustrates an embodiment of a system for inerting a fire according to the invention; Fig. 3 illustrates an embodiment of a system for inerting a fire according to the invention; Fig. 4 illustrates a concentration of oxygen over time at an indoor location according to an embodiment; and

Fig. 5 illustrates mass flow of inerting gas over time at an indoor location according to an embodiment.

DETAILED DESCRIPTION OF THE DRAWINGS

The fire inerting gas system 1 illustrated in Fig. 1 comprises a first container 3 containing a first inerting gas void of oxygen and having a first concentration of carbon dioxide of 4-12%. The system 1 is configured to deliver the first inerting gas into an indoor location 5, via a first conduit 7 and valve 8, in case a fire detector 9 detects a fire at the indoor location 5. As the fire detector 9 detects the fire, a first period of time is initiated. During the first period of time, the first inerting gas is delivered. The system 1 of Fig. 1 further comprises a second container 11 containing a second inerting gas. At the end of the first period of time, the second period of time commences in which an amount of the second inerting gas is delivered. The second inerting gas has a second concentration of oxygen of 10-12% being similar to a target concentration of oxygen at the indoor location 5. The second inerting gas further has a second concentration of carbon dioxide of 2-5%, similar to a target concentration of carbon dioxide concentration at the indoor location 5.

A first flow rate characterising delivery of the first inerting gas into the indoor location 5 is optimized for rapid reduction of the concentration of oxygen and increase of the

concentration of carbon dioxide to reach the target concentrations of 10-12% and 2-5%, respectively. This allows rapid achievement of fire inerting, as well as breathable, conditions at the indoor location 5. Subsequently, delivery of the second inerting gas during the second period of time works to sustain the target concentrations even in the case when an airflow exists to or from the indoor location 5. In one embodiment, a second flow rate characterizing delivery of the second inerting gas is smaller than the first flow rate. In one embodiment, the second flow rate is predetermined on the basis of expected air flows to and from the indoor location 5 in case of fire. In one embodiment, the second flow rate and the extent of the second period of time are determined based on sensor input for optimization according to the current condition sensed by the sensor. The condition may be a temperature and/or concentration of oxygen at the indoor location 5. The condition may also be whether or not a door and/or window (not shown) leading to the indoor location 5 is open. For instance, a sensor may be arranged to sense if any or all of the doors and windows (not shown) leading to the indoor location 5 are open, and increase the second flow rate depending on how many and what doors and/or windows are open. An open door or window may, e.g., be sensed by disconnection of an electric circuit.

In the embodiment of Fig. 2, the second inerting gas is formed by mixing part first inerting gas and part third gas in the form of atmospheric air in a 1 : 1 mixture. The atmospheric air is provided to the first conduit 7 via a mixing valve 15 from an inlet 13 arranged outdoors in open air, e.g., outside a building 17 containing the indoor location 5. Before reaching the mixing valve 15, the atmospheric air is compressed by an electrically driven compressor 18 for reaching the higher pressure of the first inerting gas.

In the embodiment of Fig. 3, the second inerting gas is also formed by mixing atmospheric air and the first inerting gas as described with reference to Fig. 2. However, in the embodiment of Fig. 3, the atmospheric air is mixed with the first inerting gas to form the second inerting gas by use of an ejector 19. The ejector 19 is arranged relatively close to the point where the second inerting gas is delivered into the indoor location 5. This is done to improve performance of the ejector 19. The ejector 19 may be configured to allow a 1 : 1 mixture of atmospheric air and first inerting gas to be formed as the second inerting gas.

Fig. 4 illustrates an exemplary concentration of oxygen at an indoor location 5 during operation of a fire inerting gas system according to an embodiment of the invention, with the concentration of oxygen at the indoor location 5 on the vertical axis 21 and time on the horizontal axis 23. At time equal to zero 24, fire is detected by the fire detector 9 of the system. This initiates the first period of time in which an amount of the first inerting gas is delivered into the indoor location 5 at the first flow rate. During the first period of time the concentration of oxygen at the indoor location 5 is reduced from atmospheric level 26 until the end of the first period of time at time equal to T_one 27 in order to approach a target concentration of oxygen 25 at 11% according to present embodiment. T_one 27 also marks the beginning of the second period of time during which an amount of the second inerting gas is delivered into the indoor location 5 at the second flow rate. The average second mass flow rate 28 during the second period of time is smaller than the first average mass flow rate 30 during the first period of time. The delivery of the second inerting gas into the indoor location 5 works to stabilize the concentration of oxygen at or near the target concentration of oxygen 25. T_two 29 marks the end of the second period of time. At T_two 29, a flue gas detector (not shown) detects that the level of flue gas at the indoor location 5 is below a

predetermined target flue gas concentration. Exemplary first and second mass flow rates are illustrated in Fig. 5. The first and second mass flow rates of Fig. 5 may lead to the

concentration of oxygen at the indoor location 5 as illustrated in Fig. 4. In Fig. 5, the mass flow rate of inerting gas is on the vertical axis 31 and time is on the horizontal axis 33.

Claims

1. A method for inerting a fire at an indoor location, the method comprising the steps of: providing a first container containing a first inerting gas void of oxygen or having a first concentration of oxygen;

- providing a second inerting gas having a second concentration of oxygen above zero; delivering an amount of the first inerting gas along a first conduit from the first container into the indoor location at a first mass flow rate for a first period of time; and subsequently

2. A method for inerting a fire according to claim 1, wherein the second mass flow rate is smaller than the first flow rate.

3. A method for inerting a fire according to claim 1 or 2, wherein the second concentration of oxygen is 9-14%.

4. A method for inerting a fire according to claim 1 or 2, wherein the first inerting gas has a carbon dioxide concentration of 4-12% and/or the second inerting gas has a carbon dioxide concentration of 2-5%.

5. A method for inerting a fire according to any of the preceding claims, wherein the extent of the first and/or second period of time is a predetermined value.

6. A method for inerting a fire according to any of the preceding claims, wherein the method further comprises the step of providing a sensor for sensing at least one condition at the indoor location, and wherein the extent of the first and/or second period of time is determined based on at least one condition sensed by the sensor.

7. A method for inerting a fire according to claim 6, wherein one condition is a concentration of oxygen at the indoor location and/or one condition is a temperature at the indoor location.

8. A method according to claim 6 or 7, wherein one condition is whether a door and/or a window leading to the indoor location is open or closed.

9. A system for inerting a fire at an indoor location, the system comprising a first container containing a first inerting gas void of oxygen or having a first concentration of oxygen, a first conduit extending at least between the first container and the indoor location, and a second inerting gas having a second concentration of oxygen above zero, the system being configured to: deliver an amount of the first inerting gas along the first conduit from the first container into the indoor location at a first mass flow rate for a first period of time; and subsequently

deliver an amount of the second inerting gas into the indoor location at a second flow rate for a second period of time.

10. A system for inerting a fire according to claim 9, wherein the system comprises a second container containing the second inerting gas, the second container being connected, via a valve, with the first conduit at a point in the first conduit downstream of the first container and upstream of the indoor location.

11. A system for inerting a fire according to claim 9 or 10, wherein the system is configured to form at least part of the second inerting gas by mixing the first inerting gas with a third gas, the third gas comprising oxygen.

12. A system for inerting a fire according to claim 11, wherein the third gas is contained in a third container being connected, via a valve, with the first conduit at a point in the first conduit downstream of the first container and upstream of the indoor location.

13. A system for inerting a fire according to claim 11 or 12, wherein the third gas comprises atmospheric air and/or has a concentration of oxygen of 16-24%.

14. A system for inerting a fire a according to any of claims 9-13, wherein the system comprises a compressor and/or an ejector having an inlet at a location with atmospheric air, the location being remote from the indoor location, the compressor and/or ejector being connected, via a valve, with the first conduit at a part of the first conduit downstream of the first container and upstream of the indoor location.