Abstract:
The disclosure first relates to a room comprising an inner space delimited by an upper wall, a lower wall and side walls, the room being provided with a ventilator, the ventilator including:
       an extractor operably extracting air from the inner space towards the outside of the room, arranged on one side wall; and   air intakes on the other side walls.       
 
     The disclosure also relates to a method for ventilating a room including an inner space delimited by an upper wall, a lower wall and side walls, the method including the extraction of air from the inner space to the outside of the room by an air extractor arranged on one side wall, and the entry of air via air intakes arranged on the other side walls. The disclosure further relates to an air intake adapted to perform the method above.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a National Phase Entry of International Application No. PCT/IB2011/050303, filed on Jan. 24, 2011, which claims priority to French Patent Application Serial No. 1050480, filed on Jan. 25, 2010, both of which are incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a method for ventilating a heavily cluttered room, as well as a room provided with ventilation means performing ventilation according to this method. The invention also relates to air intakes suitable for implementing the method. The invention can be applied in the context of natural gas liquefaction, which requires ventilation of heavily cluttered rooms (called LNG modules), including under particularly rigorous climate and environmental conditions (arctic region). 
       BACKGROUND 
       [0003]    A room containing a significant number of hazardous contaminant sources and that is heavily cluttered (by equipment, pipes, structures, etc.) must be ventilated in order to evacuate said contaminants. This ventilation, associated with other devices, contributes to improving safety conditions for personnel and equipment. However, when wintry outside conditions, call arctic conditions, exist, it may be very difficult to ventilate the room, as it is directly impacted by rain, snow, frost, ice and wind. Furthermore, the personnel and the equipment must also be protected from these different phenomena. 
         [0004]    In order to ventilate a room under wintry outside climate conditions, it is known to use natural ventilation, which uses both the dynamics of the outside wind and the variation of the density of the air inside the room (natural draught) to renew the air in the room. However, this solution, which appears simple, is in reality difficult to implement, given the outside climate conditions. In fact, outside a well-defined wind speed range, the air flows inside the building are unacceptably disrupted. Furthermore, since the effectiveness of natural ventilation also depends on the clutter in said room, the dilution effect contributed by the natural ventilation on the contaminants is mediocre for heavily cluttered rooms. Additionally, pressure losses are significant when the clutter of the room is heterogeneous (for example, heightwise), and it is impossible to capture contaminants in the area close to a piece of equipment, opposite the airflow striking that equipment (vacuum and aeraulic turbulence zone). As a result, natural ventilation does not make it possible to provide controlled security in all situations. 
         [0005]    A second solution, mechanical ventilation, is also known. Mechanical ventilation uses fans to provide (and possibly heat) the air blown into the room and then remove it. However, this solution requires providing a technical room dedicated to the aerothermodynamic equipment, the surface area of which typically represents between 50 and 70% of the area of the room to be ventilated for a LNG module. Furthermore, this solution requires the presence of air transport sheaths in the room to be ventilated. These air transport sheaths are generally very large and extremely restrictive for positioning the equipment in the room, in particular when the room is heavily cluttered. As a result, mechanical ventilation is difficult to implement and is costly in terms of investment (land, machines, etc.) and operation (heating a large volume of air). 
         [0006]    There is therefore a real need to develop a method for ventilating a room, and in particular a heavily cluttered room, that can operate correctly under wintry conditions, that is more reliable, simpler, and less expensive to implement and use than the existing methods. 
       SUMMARY 
       [0007]    The invention first relates to a room comprising an inner space delimited by an upper wall, a lower wall and side walls, the room being provided with a ventilation means, the ventilation means including:
       a means for extracting air from the inner space towards the outside of the room, arranged on one side wall; and   air intakes on the other side walls.
 
According to one embodiment, the ventilation means also comprises one or more fans in the inner space, the fans preferably being located near a side wall facing the side wall provided with the air extracting means, and the fans more particularly preferably comprising:
   one or more fans situated close to the lower wall and oriented so as to move air toward the upper wall; and   one or more fans situated close to the upper wall and oriented so as to move air toward the side wall provided with the air extracting means.       
 
         [0012]    According to one embodiment, the side wall provided with the air extracting means comprises two end portions situated close to respective adjacent side walls, and a central portion between the two end portions, the air extracting means being distributed on the side wall so that the air extraction capacity per surface unit in the central portion is greater than the air extraction capacity per surface unit in the end portions. According to one embodiment, the room has no heating means for the inner space. According to one embodiment, the room is a natural gas liquefaction module. 
         [0013]    The invention also relates to a method for ventilating a room comprising an inner space delimited by an upper wall, a lower wall and side walls, the method including the extraction of air from the inner space to the outside of the room by an air extraction means arranged on one side wall, and the entry of air via air intakes arranged on the other side walls. According to one embodiment, the method also includes moving air in the inner space using one or more fans positioned in the inner space, the air movement preferably being done close to a side wall facing the side wall provided with the air extraction means, and the air movement more particularly preferably comprising:
       moving air from bottom to top close to the lower wall and the side wall facing the side wall provided with the air extraction means;   moving air toward the side wall provided with the air extraction means close to the upper wall and the side wall facing the side wall provided with the air extraction means.       
 
         [0016]    According to one embodiment, the ratio of the air flow extracted on the surface of the side wall provided with the air extraction means is less than or equal to 0.5 m/s, preferably less than or equal to 0.3 m/s, still more preferably less than or equal to 0.2 m/s. According to one embodiment of the method, the room is a natural gas liquefaction module. 
         [0017]    The invention further relates to an air intake comprising:
       an air injection grid adapted to be positioned in an opening formed in a wall;   an enclosure adapted to be fastened on one side of the wall and communicating with the air injection grid;   an air entry conduit adapted to be fastened to the wall and communicating with the enclosure by a protective grid, the air entry conduit having a section smaller than the section of the enclosure along a plane perpendicular to the air injection grid.
 
According to one embodiment, the section of the air injection grid available for the passage of air on the enclosure side is larger than the section of the air injection grid available for the passage of air on the side opposite the enclosure and/or the air injection grid is provided with a heating means. According to one embodiment, the air entry conduit is provided with baffles and possibly drains, the baffles preferably being provided with heating means, and the baffles preferably having a surface oriented toward the enclosure and a surface oriented opposite the enclosure, the surface oriented toward the enclosure being less rough than the surface oriented opposite the enclosure. According to one embodiment of the room according to the invention, the air intakes are as described above.
       
 
         [0021]    The present invention makes it possible to overcome the drawbacks of the state of the art. It more particularly provides a method for ventilating a room, and in particular a heavily cluttered room, that can operate correctly under wintry conditions, which is more reliable, simpler and less expensive to implement and operate than the existing methods. This is accomplished owing to a ventilation means operating only for air extraction (from the inside to the outside of the room), the air entry in the room being ensured by passive devices (air intakes), i.e. without mechanical air blowing (from outside the room to the inside thereof). 
         [0022]    According to certain particular embodiments, the invention also has one or preferably more of the advantageous features listed below.
       The dilution of the contaminants is controlled irrespective of the outside conditions, and even at a high level of clutter, and thus the security of the facility is ensured.   The invention makes it possible to achieve surface area savings in technical rooms and energy consumption savings relative to traditional mechanical ventilation.   The work of the personnel is made easier because the invention allows a laminar state of the flow of air in the room.   The invention makes it possible to dispense with any general heating of the inner space of the room. In fact, the speed of the air being low, the sensation of cold for personnel remains moderate. More specifically, a low airflow rate means a low convection exchange between the occupant and the air of the room, and therefore a feeling of comfort and “warmth” relative to the outside. It is therefore possible to provide only localized (extra) heating for certain maintenance operations requiring specific comfort. The energy savings achieved by doing away with general heating of the room are considerable.   The invention provides an improved air intake relative to the air intakes of the state of the art. The air intake according to the invention makes it possible to greatly limit the risks of taking in ice or of snow blockage. The air intake according to the invention is advantageously used in the context of the ventilation method according to the invention, but it can also be used in the context of another ventilation method.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  diagrammatically illustrates a room according to one embodiment of the invention, in horizontal cross-section. 
           [0029]      FIG. 2  diagrammatically illustrates a room according to one embodiment of the invention, in vertical cross-section. 
           [0030]      FIG. 3  diagrammatically illustrates the side wall  3  of the room of  FIGS. 1 and 2 . 
           [0031]      FIG. 4  diagrammatically shows one embodiment of an air intake according to the invention, in cross-section. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    The invention will now be described in more detail and non-limitingly in the following description. 
         [0033]    Room According to the Invention and Ventilation Method According to the Invention 
         [0034]    In reference to  FIGS. 1 to 3 , the room to be ventilated according to the invention comprises an upper wall  6  (roof), a lower wall  7  (floor), and side walls  2   a ,  2   b ,  3 ,  4 . In general, the room is parallelepiped, and there are then four side walls  2   a ,  2   b ,  3 ,  4 . An inner space  5  is defined by the set of walls  2   a ,  2   b ,  3 ,  4 ,  6 ,  7 . The inner space  5  generally contains industrial equipment. 
         [0035]    According to one preferred embodiment, the room is a natural gas liquefaction module, i.e. a hangar containing part of the equipment necessary to produce liquefied natural gas from raw natural gas. However, the invention can also be applied to other fields, for example in the oil, mining, chemical, pharmaceutical, or other industries. 
         [0036]    According to the invention, the room is ventilated by a ventilation means that comprises:
       a means for extracting air  1 ; and   air intakes.
 
The air extracting means  1  consists of a plurality of fans  15  positioned on a side wall  3 , suitable for extracting air from the inner space  5  toward the outside of the room uniformly, i.e. with a laminar state airflow. In the context of this application, “air intakes” are “passive” devices allowing air to pass through a wall. In other words, the air intakes in the context of the present invention do not have a mechanical rotary machine (fan).
       
 
         [0039]    The invention provides that air intakes are formed in the side walls  2   a ,  2   b ,  4  separate from the side wall  3 , which comprises the air extracting means  1 . In other words, according to the invention, a single side wall comprises the air extracting means, while the other side walls have no active air movement means (i.e. active means for extracting air or injecting air) such as fans. The room is supplied with air, through the aforementioned air intakes, via an air vacuum in the room created by the air extracting means  1 , and does not involve the action of fans on either side of said air intakes. 
         [0040]    The air extracting means  1  according to the invention allows a laminar air movement in the entire inner space  5 , under the combined effect of the natural convection of the air and the forced convection caused by the vacuum existing at the side wall  3  provided with the air extracting means  1 . Given that the clutter of the room by the equipment generally varies heightwise (the lower portion of the room most often being more cluttered than the top portion of the room), and given that the possible contaminants may comprise light contaminants and heavy contaminants, it is advantageous to do the modeling by stratification, i.e. to vertically cut the inner space  5  into successive layers  10 ,  11 ,  12 , so as to determine the power and implantation of the fans making it possible to obtain satisfactory ventilation in each layer  10 ,  11 ,  12 . The inner space  5  is cut vertically into successive layers  10 ,  11 ,  12 , the power and implantation of the air extracting means  1  on the side wall  3  being adapted to the ventilation in each layer, the flow of air having a laminar state. In other words, the room has a wall (or barrier) supporting the fans to extract the air from several aeraulic layers, with different fan rates for each zone so as to have stratification of the layers of air and a laminar flow. 
         [0041]    Typically, the equivalent speed of the air in the room, which is defined as the ratio of the airflow rate extracted on the surface of the side wall  3  provided with the air extracting means  1 , is less than or equal to 0.5 m/s, preferably less than or equal to 0.3 m/s, still more preferably less than or equal to 0.2 m/s. This air speed must be as low as possible so as to minimize the turbulence (system effects) due to the presence of equipment in the room. Furthermore, the equivalent air speed in each layer  10 ,  11 ,  12  defined by a vertical cut of the room corresponds to the ratio of the airflow rate extracted from the stratified area divided by the surface projected on the side wall  3  provided with the air extracting means  1 . Thus, in a lower portion of the room (relative to the vertical direction), and for example in a lower half of the room, the equivalent air speed is preferably less than or equal to 0.3 m/s, more particularly preferably less than or equal to 0.2 m/s (or even less than or equal to 0.15 m/s). Due to these low speeds, the pressure losses are minimal in the room, even in the presence of heavy clutter, and the airflow is laminar in the entire inner space  5 . 
         [0042]    Preferably, the ventilation in the room is completed by one or more fans  8 ,  9  situated in the inner space  5 , so as on the one hand to eliminate dead areas in the inner space  5  (areas where the convection of the air is practically nonexistent) and on the other hand to orient the airflows correctly. Thus, these fans  8 ,  9  are preferably situated close to the side wall  4  facing (opposite) the side wall  3  provided with the air extracting means  1 . In one embodiment, the distance from the fans  8 ,  9  to the side wall  4  is smaller than or equal to 50%, for example smaller than or equal to 40%, or smaller than or equal to 30%, or smaller than or equal to 20%, the distance between said side wall  4  and the opposite side wall  3  provided with the air extracting means  1 . 
         [0043]    Particularly advantageously, one thus provides:
       one or more fans  9  situated close to the lower wall  7  and oriented so as to move the air from bottom to top;   one or more fans  8  situated close to the upper wall  6  and oriented so as to move the air toward the upper portion of the side wall  3  provided with the air extracting means  1 .
 
In one embodiment, the distance from the fans  9  to the lower wall  7  is smaller than or equal to 50%, for example smaller than or equal to 40%, or smaller than or equal to 30%, of the distance between said lower wall  7  and the upper wall  6 ; and the distance from the fans  8  to the upper wall  6  is smaller than or equal to 50%, for example smaller than or equal to 40%, or smaller than or equal to 30%, of the distance between said upper wall  6  and the lower wall  7 . In this way, the dead areas located close to the side wall  4  facing the side wall  3 , provided with the air extracting means  1 , are eliminated.
       
 
         [0046]    The air extracting means  1  present on the side wall  3  can be fans  15  known in the field and preferably compliant with the regulatory provisions for explosion risk protection (ATEX fans). In particular, these fans  15  generally comprise a peripheral gap of 2 to 3 mm to avoid static electricity phenomena. Electric tracing may be provided to avoid frost in that peripheral gap. Furthermore, reinforcements of the side wall  3  supporting said fans  15  can be provided to take the normal vibratory modes of said fans  15  into account. 
         [0047]    The choice of the number, power and flow rate of the fans  15 , as well as their implantation on the side wall  3 , are made so as to obtain the aforementioned stratification as well as convection of the air in the entire inner space  5  with a slow speed, as a function of all of the parameters involved, and in particular: the dimensions and the clutter of the room, the geometry of the stratification area inside the room (layers  10 ,  11 ,  12 ), and the nature of the potential contaminants (and in particular their greater or lesser density). Furthermore, in order to avoid the appearance of lateral preferential convection phenomena at the walls  2   a  and  2   b , the central part of the side wall  3 , bearing the air extracting means  1 , is “loaded” with fans  15  so that the air extraction capacity is greater in the central part  13  of said side wall  3  than in the end portions  14   a ,  14   b .  FIG. 3  provides an example of the implantation of the fans  15  on the side wall  3 . 
         [0048]    The air intakes are implanted on the side walls  2   a ,  2   b ,  4  separate from the side wall  3  provided with the air extracting means  1  so as to allow a supply of air adapted to the desired convection in the inner space  5 . The air intakes can be distributed on all of the side walls  2   a ,  2   b ,  4  separate from the side wall  3 , provided with air extracting means  1 . Portions  16   a ,  16   b  on the side walls  2   a  and  2   b  are provided without air intakes close to the wall  3 , so as to avoid risks of contaminants returning from the outside into the room. Furthermore, the density of air intakes on the side walls  2   a ,  2   b ,  4  is generally greater close to the lower  7  and upper  6  walls than in a central portion of the side walls  2   a ,  2   b ,  4 , i.e. the air intakes will be located in the upper and lower portions of the side walls  2   a ,  2   b  and  4 . 
         [0049]    The air intakes can be traditional air intakes and for example comprise a set of inclined strips positioned in openings formed in the wall, adapted to reduce the air entry speed in case of outside wind. They can also comprise heating means to prevent snow or ice deposits, and comprise a protective cover. However, according to one preferred embodiment, the air intakes are as described below. 
         [0050]    Air Intake According to the Invention 
         [0051]    In reference to  FIG. 4 , an air intake according to the invention on a wall  20  (of a room or any other type of closed chamber) comprises three main parts, which are, in the direction of the airflow:
       an air entry conduit  21 ;   an enclosure  22 ; and   a grid  23  equipped with profiled fins.
 
The air entry conduit  21  is preferably positioned parallel to the wall  20 . It comprises a beveled open end intended for the air entry, and another end that communicates with the enclosure  22 . Preferably, the air entry conduit  21  is oriented so that the open end is oriented downwardly. In this way, any accumulation of snow or water in the air entry conduit  21  is avoided.
       
 
         [0055]    Preferably, the air entry conduit  21  is provided with baffles  24 , which are intended on the one hand to create pressure losses so as to break the dynamics of the outside wind, and on the other hand to stop the snow carried into the airflow  28 . Preferably, there are no more than four baffles  24 . Typically, the baffles  24  are plates fastened, for example by welding, to the inner wall of the air entry conduit  21 , inclined (i.e. forming an angle smaller than 90° with said inner wall) and oriented toward the open end of the air entry conduit  21 . For example, the baffles  24  can form an angle of about 60° with the inner wall of the conduit and the baffle  24  closest to the open end of the conduit can form an angle of about 45° with the inner wall thereof. 
         [0056]    The baffles  24  (or a portion thereof) can be provided with a heating means  26  (for example electric resistances) making it possible to melt the snow accumulating on said baffles  24  (the water resulting from the melting snow being driven outside the air entry conduit  21  by gravity). Preferably, the baffles  24  have a different roughness on the surface oriented toward the enclosure (called upper surface) and on the surface oriented toward the open end of the conduit  21  (called lower surface). The lower surface is advantageously rougher than the upper surface (i.e. the asperities on the lower surface have a larger average height than the asperities on the upper surface), which makes it possible to effectively stop the snowflakes present in the air from entering the conduit  21 . For example, the baffles  24  can be made from 316L stainless steel having an absolute roughness of 1 to 1.5 μm (passivated descaled sheet metal) or approximately 8 μm (industrial weld sheet metal), and scratches can be added on the lower surface. 
         [0057]    It is advantageous to provide drains  25  on one or more baffles  24 , and especially on the baffle  24  closest to the open end of the air entry conduit  21 , so as on the one hand to make it possible to discharge the water resulting from melting snow in the air intake, and on the other hand to minimize the turbulence phenomena under the baffle  24  closest to the open end of the air entry conduit  21 . The width of the air entry conduit  21  must be large enough to avoid the effects of a local increase in the air speed in the conduit  21 . In fact, at the perpendicular of each baffle passage, the snow accumulation that is deposited on said baffles will reduce the section thereof, and therefore increase the air passage speeds. 
         [0058]    Between the air entry conduit  21  and the enclosure  22 , a protective grid  27  is provided to stop the snowflakes carried in the flow of air. For example, the protective grid  27  can be a 316L stainless steel plate perforated at 80% (“honeycomb” plate). Between the air entry conduit  21  and the enclosure  22  (or plenum), a protective grid  27  is provided to stop any snowflakes carried in the airflow. For example, the protective grid  27  may be a 316L stainless steel plate perforated at 80% of the “honeycomb” type. 
         [0059]    The enclosure  22  (or plenum) has a larger section than that of the air entry conduit  21  along a plane perpendicular to the wall  20 , and for example along the horizontal plane (which in the illustrated embodiment is the plane perpendicular to the average airflow direction in the air entry conduit  21 ). This enclosure  22  makes it possible to reduce the speed of the air before arrival on the profiled grid  23 , and therefore to break the dynamics due to the outside wind, thereby avoiding the freezing phenomena on the grid  23 . Preferably, the dimensions of the enclosure  22  are chosen so that the speed of the air is reduced to a value below or equal to 0.5 m/s in the enclosure  22 . Preferably, the enclosure  22  has an inclined upper wall so as to avoid an accumulation of snow thereon. 
         [0060]    The air injection grid  23  is positioned in an opening formed in the wall  20  and allows the air to pass through the wall  20 . Preferably, the air injection grid  23  comprises a convergent shape, so as to increase the speed of the air when it passes through the wall  20 . Thus, the section of the air injection grid  23  that is available for the passage of air on the enclosure  22  side (i.e. the side outside the room) is larger than the section of the air injection grid  23  that is available for the passage of air on the side opposite the enclosure  22  (i.e. the side inside the room). 
         [0061]    The air injection grid  23  can be provided with a heating means so as to still further decrease the risks of freezing. This heating means can be electric resistances positioned in cavities placed on the path of the air and posing an obstacle thereto. The air injection grid  23  can be a commercially available grid distributed by Halton, as for example described in document SE 500838. 
       Example 
       [0062]    The following example illustrates the invention without limiting it. Modeling was done on a natural gas liquefaction module 50 m long, 36 m wide and 16 m high. The outside temperature is hypothetically −33° C. and the outside wind has a speed of 17 m/s. Fans in extraction mode are implanted on one of the walls perpendicular to the length direction of the module. Air intakes are positioned on the other walls. 
         [0063]    The inner space of the module is modeled in three zones: a (lower) zone 10 that is 2.80 meters high, heavily cluttered, capable of containing heavy contaminants; an (intermediate) zone 11 that is 4.25 m high, moderately cluttered, capable of containing middle-density contaminants; and an (upper) zone 12 that is 7.15 m high, capable of containing light contaminants. Modeling makes it possible to define an implantation of fans on the wall as well as secondary ventilation in zone 10 (vertical ventilation) and in zone 12 (horizontal ventilation) as shown in  FIG. 2  so as to correct the dead spaces. The assembly makes it possible to obtain a laminar state airflow with a low speed in the entire module. 
         [0064]    The characteristics used for the main ventilation (extraction ventilation) are summarized in table 1 below: 
         [0000]                                                                                                                                                                                      TABLE 1                   Characteristics of the Main Ventilation (air extraction)                Zone 10   Zone 11   Zone 12                        Airflow rate   69,120   m 3 /h   103,680   m 3 /h   172,800   m 3 /h       (without secondary       ventilation)       Airflow rate   45,723   m 3 /h   98,042   m 3 /h   202,008   m 3 /h       (with secondary       ventilation)       Average air speed   0.126   m/s   0.176   m/s   0.218   m/s       (with secondary       ventilation)            Number of fans   6   6   8       installed       Number of fans   5   5   7       running            Airflow rate per   9,145   m 3 /h   19,609   m 3 /h   28,858   m 3 /h       fan       Manometric height   650   Pa   650   Pa   650   Pa       Diameter of the   450   mm,   630   mm,   900   mm,            fan   6 blades, 26°   3 blades, 15°   4 blades, 23°            Power   3.4   kW   6.0   kW   8.5   kW       Motor   4.0   kW   7.5   kW   11   kW            Revolutions per   2,900        2,900        1,450            minute       Fan + motor mass   26 kg + 70 kg   53 kg + 106 kg   160 kg + 172 kg                    
All of the fans are of the helical Solyvent-Ventec Axipal BZI type. Standard EN 14986 is applicable (zone 1, T3). The flow rate (5%) and pressure (10%) reductions, due to the presence of increased peripheral gap, were taken into account to calculate the power.
 
         [0065]    The characteristics used for the secondary ventilation are summarized in table 2 below: 
         [0000]                                                                                                                                                                                        TABLE 2                   Characteristics of the Secondary Ventilation                    Zone 10   Zone 12                            Number of fans   6   6           installed           Number of fans   5   5           running                Airflow rate per   28,858   m 3 /h   9,145   m 3 /h           fan           Manometric height   810   Pa   90   Pa                (400 Pa dynamic)   (40 Pa dynamic)                Diameter of the   630   mm,   630   mm,                fan   4 blades, 33°   3 blades, 24°                Power   8   kW   0.32   kW           Motor   11   kW   1.0   kW                Revolutions per   3,000        950            minute           Fan + motor mass   60 kg + 172 kg   58 kg + 38 kg                        
All of the fans are of the helical Solyvent-Ventec Axipal BZI type with an elongated shroud. Standard EN 14986 is applicable (zone 1, T3). The fans are of the “jet fan” type.
 
         [0066]    Explosion simulations were done on the module of this example. Out of 64 simulations performed, the dilution of the gaseous contaminants obtained owing to the invention caused the likelihood of explosion to drop by a factor of 10 relative to a “traditional” fan of reference.