Abstract:
An exhaust system includes a ventilated ceiling component with multiple surfaces and recesses. Each recess has an exhaust intake, the recesses being distributed over an area of a ceiling that has a perimeter adjacent the recesses. The perimeter has a jet register located below the exhaust intake and configured to generate jets, a first of the jets being directed toward and located below at least one of the exhaust intakes and a second of the jets being directed substantially vertically downward. The perimeter further has a displacement ventilation register.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/988,487 filed Nov. 18, 2010, which is a U.S. national stage entry under 35 U.S.C. §371 of International Application No. PCT/US2009/041148 filed Apr. 20, 2009, which claims the benefit of U.S. Provisional Application No. 61/046,257 filed Apr. 18, 2008, the contents of which are incorporated herein by reference in their entireties. 
     
    
     BACKGROUND 
       [0002]    Exhaust devices, such as exhaust hoods and ventilated ceilings, are used to remove pollutants from occupied spaces with sources of pollutants. Examples include factories, kitchens, workshops, and food courts which contain industrial processes, kitchens appliances, tools, and portable cooking appliances, respectively. Preferably, exhaust hoods remove pollutants by drawing them from a collection area near the source and may also provide a containment function, usually by ensuring that the velocity of exhaust is sufficient near the source to overcome any local buoyancy or draft effects to ensure that all pollutants are prevented from escaping to the general occupied space. By managing transients in this way, an effective capture zone is provided. 
         [0003]    In exhaust systems, an exhaust blower creates a negative pressure zone to draw pollutants and air directly away from the pollutant source. In kitchen applications, the exhaust generally draws pollutants, including room-air, through a filter and out of the kitchen through a duct system. A variable speed fan may be used to adjust the exhaust flow rate to match the extant requirements for capture and containment. That is, depending on the rate by which the effluent is created and the buildup of effluent near the pollutant source, the speed of exhaust blower may be manually set to minimize the flow rate at the lowest point which achieves capture and containment. 
         [0004]    The exhaust rate required to achieve full capture and containment is governed by the highest transient load pulses that occur. This requires the exhaust rate to be higher than the average volume of effluent (which is inevitably mixed with entrained air). Such transients can be caused by gusts in the surrounding space and/or turbulence caused by plug flow (the warm plume of effluent rising due to buoyancy). Thus, for full capture and containment, the effluent must be removed through the exhaust blower operating at a high enough speed to capture all transients, including the rare pulses in exhaust load. Providing a high exhaust rate—a brute force approach—is associated with energy loss since conditioned air must be drawn out of the space in which the exhaust hood is located. Further, high volume operation increases the cost of operating the exhaust blower and raises the noise level of the ventilation system. 
         [0005]    Also known are “make up” air systems, some of which have been proposed to be combined with exhaust hoods in a manner in which make-up air is propelled toward the exhaust intake of a hood. This “short circuit” system involves an output blower that supplies and directs one, or a combination of, conditioned and unconditioned air toward the exhaust hood and blower assembly. Such “short circuit” systems have not proven to reduce the volume of conditioned air needed to achieve full capture and containment under a given load condition. 
         [0006]    Another solution in the prior art is described in U.S. Pat. No. 4,475,534 titled “Ventilating System for Kitchen.” In this patent, the inventor describes an air outlet in the front end of the hood that discharges a relatively low velocity stream of air downwardly. According to the description, the relatively low velocity air stream forms a curtain of air to prevent conditioned air from being drawn into the hood. In the invention, the air outlet in the front end of the hood assists with separating a portion of the conditioned air away from the hood. Other sources of air directed towards the hood create a venturi effect, as described in the short circuit systems above. As diagramed in the figures of the patent, the exhaust blower must “suck up” air from numerous air sources, as well as the effluent-laden air. Also the use of a relatively low velocity air stream necessitates a larger volume of air flow from the air outlet to overcome the viscous effects that the surrounding air will have on the flow. 
         [0007]    In U.S. Pat. No. 4,346,692 titled “Make-Up Air Device for Range Hood,” the inventor describes a typical short circuit system that relies on a venturi effect to remove a substantial portion of the effluent. The patent also illustrates the use of diverter vanes or louvers to direct the air source in a downwardly direction. Besides the problems associated with such short circuit systems described above, the invention also utilizes vanes to direct the air flow of the output blower. The use of vanes with relatively large openings, through which the air is propelled, requires a relatively large air volume flow to create a substantial air velocity output. This large, air volume flow must be sucked up by the exhaust blower, which increases the rate by which conditioned air leaves the room. The large, air volume flow also creates large scale turbulence, which can increase the rate by which the effluent disperses to other parts of the room. 
         [0008]    Currently, in workplaces where fumes, dust, or chemical vapors present a hazard, local exhaust ventilation devices are used to prevent workers from inhaling contaminated air. Generally, an exterior exhaust hood, for example, a receiving hood, is disposed above the emission source to remove airborne contaminants. However, theoretical capture efficiency of such a receiving hood holds only in still air, the capture efficiency decreases due to crosswind in the surrounding environment, no matter how weak the crosswind is. To control the adverse effect of crosswind, a fume hood having a back panel, two side panels, and a hood sash in the front has been designed to replace a receiving hood. However, the side panels and hood sash of a fume hood limit the size of operation space for operators&#39; upper limbs. Therefore, how to eliminate the adverse effect of crosswind, and meanwhile retain the freedom of operators&#39; upper limbs, becomes a key topic to a receiving hood. 
         [0009]    In order to accomplish the key topic, U.S. Pat. No. 4,788,905, published on Dec. 6, 1988, disclosed a combination cooking, heating and ventilating system. The system contains an open fire grill surrounded by an unperforated griddle, both of which are surrounded by an eating counter. A fan is positioned below the cooking grill and griddle which forces the air upward between the eating counter and the griddle in the shape of an air curtain for removing hot smoking air from the cooking area. However, due to the limited size, the fan is not applicable in a large-scale worktable. Further, generally speaking, there is not necessarily enough space to accommodate the fan device below the worktable. 
         [0010]    U.S. Pat. No. 5,042,456, published on Aug. 27, 1991, disclosed an air canopy ventilation system. The system comprises a surface having two substantially parallel spaced apart side panels surmounted at their respective upper edges by a canopy. A vent means having a plurality of outlets extends between the side panels and substantially the whole length of the front edge of the surface. A fan means connected to the vent means is adapted to drive a flow of air through the vent means upwardly to form a curtain of air over the front of the system, thereby entraining within the area fumes and odors. The upwardly flowing air, fumes and odors are removed by an exhaust means. Though the system can solve the problem of the lateral diffusion of the smoke and the influence of the crosswind, the air flow perpendicular to the side panel affects the efficiencies of the upward air curtain and canopy. Meanwhile, the structure of the system having the side panel and back panel limits the size of the operation space in which the operator can operate. 
         [0011]    Further, U.S. Pat. No. 6,450,879, published on Sep. 17, 2002, disclosed an air curtain generator includes a casing with a fan received therein so as to blow an air curtain from opening of the casing, and the air curtain separates the workers and the source where generates contaminated air. However, the air curtain only isolates the smoke from laterally diffusing towards the operator, but does not isolate the smoke from diffusing towards the side without the air curtain generator. Additionally, the inventor of the present invention disclosed an air curtain generator in U.S. Pat. No. 6,752,144 published on Jun. 22, 2004, and the present invention is a continued invention along the lines of this patent. 
         [0012]    In U.S. Pat. No. 6,851,421, an exhaust hood has a vertical curtain jet which helps to prevent the escape of pollutants in the vicinity of the source. U.S. Pat. Nos. 4,811,724 and 5,220,910 describe a canopy type exhaust hood with a horizontal jet to enhance capture. In one the latter, general ventilation air is provided on a side face of the canopy hood. U.S. Pat. No. 5,063,834 describes a system in which a ceiling-level ventilation zone is created to remove unducted fumes from exhaust hoods. U.S. Pat. No. 4,903,894 describes displacement ventilation techniques in which ventilation air is brought into a conditioned space at low velocity and without mixing to capture impurities and convey them toward a removal zone near the ceiling. U.S. Pat. No. 5,312,296 describes an exhaust hood that is located near the ceiling with an exhaust intake jutting from the ceiling level. Ventilation air enters the occupied space via a horizontal jet that runs along the ceiling level and a displacement ventilation registers that distributes air at low (non-mixing) velocities. 
       SUMMARY 
       [0013]    According to an embodiment, an exhaust device has a housing having an aspect ratio of at least ten. The housing has surfaces defining at least one recess having an exhaust intake. The housing has a perimeter adjacent the at least one recess having a jet register located below the exhaust intake and configured to generate jets, a first of the jets being directed toward the exhaust intake and located below it and a second of the jets being directed substantially vertically downward. The lower edges of a portion of the housing contains the exhaust intake and portions of the housing containing the jet register being substantially vertically aligned. The surfaces defining each of the at least one recess forms a piecewise arcuate continuous surface with a light source located adjacent the jet register. The exhaust intake defines a linear horizontal intake area, at least one portion of which is covered by a removable blank. The jet register has directable nozzles forming the first of the jets that are aimed at the exhaust intake areas not covered by the removable blank. Note that the nozzles can be replaced by discharge vents with movable vanes or sliding damper elements. The first of the jets terminates at or immediately short of the exhaust intake. The second of the jets terminates above approximately 1.8 meters above a floor level. A fume source is located below the housing with an edge of the fume source being positioned to form at least a 20 degree angle from the vertical with the jet register such that all of the fume source lies below the at least one recess. A control system is configured to control at least the volume flow rate of the second of the jets responsively to real time measured draft conditions in a space in which the housing is located. The control system may be configured to control the first of the jets responsively to real time measured draft conditions in a space in which the housing is located. A general ventilation register may be located adjacent the jet register, the general ventilation register directing ventilation air downwardly at non-mixing velocities. The jet register may be configured to surround the housing perimeter. The first and second of the jets may be supplied from a common plenum. The first and second of the jets may be supplied from separate plenums which are supplied by air sources at separately controlled flow rates. 
         [0014]    According to another embodiment, an exhaust device has a housing having an aspect ratio of at least ten. The housing may have surfaces defining at least one recess having an exhaust intake. The housing may have a perimeter adjacent the at least one recess having a jet register located below the exhaust intake and configured to generate jets with a first of the jets being directed toward the exhaust intake and located below it and a second of the jets being directed substantially vertically downward. Preferably, lower edges of a portion of the housing contain the exhaust intake and portion of the housing containing the jet register are substantially vertically aligned. Preferably, the surfaces defining each of the at least one recess form a piecewise arcuate continuous surface with a light source located adjacent the jet register. Preferably, the exhaust intake defines a linear horizontal intake area, at least one portion of which is covered by a removable blank. The jet register may have directable nozzles forming the first of the jets that are aimed at the exhaust intake areas not covered by the removable blank. The first of the jets terminates at or immediately short of the exhaust intake. Preferably, the second of the jets terminates above approximately 1.8 meters above a floor level. Preferably, a fume source is located below the housing with an edge of the fume source being positioned to form at least a 20 degree angle from the vertical with the jet register such that all of the fume source lies below the at least one recess. Preferably, a control system is configured to control at least the volume flow rate of the second of the jets responsively to real time measured draft conditions in a space in which the housing is located. 
         [0015]    According to an embodiment, an exhaust device has a housing having an aspect ratio of at least ten. The housing has surfaces defining at least one recess having an exhaust intake. The housing has a perimeter adjacent the at least one recess having a jet register located below the exhaust intake and configured to generate jets, a first of the jets being directed toward the exhaust intake and located below it and a second of the jets being directed substantially vertically downward. The lower edges of a portion of the housing contains the exhaust intake and portions of the housing containing the jet register being substantially vertically aligned. The surfaces defining each of the at least one recess forms a piecewise arcuate continuous surface with a light source located adjacent the jet register. The first of the jets terminates at or immediately short of the exhaust intake. The second of the jets terminates above approximately 1.8 meters above a floor level. A fume source is located below the housing with an edge of the fume source being positioned to form at least a 20 degree angle from the vertical with the jet register such that all of the fume source lies below the at least one recess. The control system may be configured to control the first of the jets responsively to real time measured draft conditions in a space in which the housing is located. A general ventilation register may be located adjacent the jet register, the general ventilation register directing ventilation air downwardly at non-mixing velocities. The jet register may be configured to surround the housing perimeter. The first and second of the jets may be supplied from a common plenum. The first and second of the jets may be supplied from separate plenums which are supplied by air sources at separately controlled flow rates. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]    The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate exemplary embodiments of the invention, and, together with the general description given above and the detailed description given below, serve to explain the features of the invention. 
           [0017]      FIG. 1  illustrates a side/section view of a lighting ventilation device (LVD) and fume source in a conditioned space. 
           [0018]      FIGS. 2A and 2B  illustrate the LVD of  FIG. 1  in section and bottom views. 
           [0019]      FIG. 3  illustrate another embodiment of an LVD. 
           [0020]      FIGS. 4A and 4B  illustrate a portion of a horizontal and vertical jet register according to an embodiment. 
           [0021]      FIG. 4C  illustrates a portion of a horizontal and vertical jet register according to another embodiment. 
           [0022]      FIG. 4D  illustrates a section view of an LVD in which the horizontal jet originates from a position that is not below the intake, in which there is no light fixture and in which the jet register is configured in accord with the embodiment of  FIG. 4C , all of which are features that may be combined or substituted for any and all of the corresponding features of the other embodiments. 
           [0023]      FIG. 5  illustrates features of a control system. 
           [0024]      FIG. 6  illustrates an LVD with vertical and horizontal jets surrounding it on multiple sides. 
           [0025]      FIGS. 7A, 7B, and 7C  illustrate an aimable horizontal jet nozzle. 
           [0026]      FIG. 8  shows various combinations of elements ventilation elements combined in kitchen ventilation system. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0027]    The efficiency of exhaust systems that employ ventilated ceiling systems, where the exhaust intake is located at the ceiling level, is particularly challenging. The capture efficiency of the system must be assured to prevent the spreading of impurities throughout the conditioned space. It has been shown that the efficiency of the exhaust system can be improved with a horizontal jet near the ceiling surface. The air jet is projected horizontally across the ceiling, which helps to direct heat and air impurities towards the exhaust intake. Preferably, such jets have a volume flow rate that is only about 10% of the total supply air flow rate. In the ventilated ceiling, the jet may improve the total effectiveness of the ventilation system. With the horizontal jet, the average contaminant level in the occupied zone was shown to be 40% lower than one without and the estimated energy saving potential can be as high as 23%. 
         [0028]    A ventilated ceiling may have features similar to the devices shown in U.S. Pat. No. D407,473, filed Apr. 1, 1999 and shown and described in U.S. Pat. No. 5,312,296, filed Jan. 30, 1991, both of which are hereby incorporated herein. In an embodiment, the ventilation device of U.S. Pat. No. 5,312,296 is modified by including a vertical curtain jet register between the non-mixing ventilation register  17  and the horizontal jet register  15 . The vertical curtain jet register in this embodiment has a velocity, thickness and breadth as to form a continuous curtain jet that terminates at about the height of the head of a worker, or approximately 1.8 m above the floor when located in an interior space. In another embodiment, the device is modified by lifting the intake plenum  18  and dropping the ventilation registers such that a configuration similar to that of  FIG. 1  is formed. Preferably, in this embodiment, a recess as indicated at  108  in  FIG. 1  may be defined. The recess  108  may have one or more arching surfaces as indicated in  FIG. 1  at  109 . 
         [0029]    Referring now to  FIG. 1 , which shows a preferred embodiment of a lighting-ventilation device (LVD)  10 . A general ventilation register  132  receives air from a plenum  134  which may be supplied through a collar  104  shared with another plenum  136  or through a separate collar (not shown). The register  132  is preferably configured such that ventilation air, cooler than the ambient below the register, is provided at non-mixing velocities as is typical for displacement ventilation applications. The general ventilation register  132  may or may not be present. It may be on one side of the device  10 , as shown, or on two or three sides, or it may completely encircle the LVD  10 . 
         [0030]    An additional combined vertical and horizontal jet register  138  emits air so as to form substantially vertical and substantially horizontal jets as indicated by arrows  122  and  120 , respectively. The vertical and horizontal jets may be supplied via a plenum  136  (supplied through a collar  104 ) and may encircle, flank on two or three sides, or border on a single side, the LVD  10 . The vertical and horizontal jets may be supplied by ventilation air, ambient air, or conditioned room air. Each may also be supplied from different ones of these sources of air. Preferably, the velocity of the horizontal jet  120  is such that it terminates approximately at the point where it would otherwise reach an exhaust intake  114 , which preferably has a removable filter  113 . Exhausted fumes and air are removed via plenums  106  and exhaust collars  102  which attach to suitable ductwork. Notwithstanding the name, “horizontal,” the angle of the horizontal jet  120  may be aimed toward the center of the exhaust intake  114  or at some intermediate angle between such angle and the horizontal. 
         [0031]    Unlike the device of U.S. Pat. No. 5,312,296, in the embodiment of  FIG. 1 , the intakes are relatively lowered and the origin of the horizontal jet register is lowered such as to form a low profile configuration with two recesses  108 . This configuration has the benefit of placing the horizontal jet below the intake while retaining the low profile and pleasing appearance of a ventilated ceiling as illustrated U.S. Pat. No. D407,473. It also creates a shallow recess  108 . Preferably diffusers or windows  111  are located in a surface  109  the recess  108  with lamps  110 , for example fluorescent lamps located behind them such as to form a continuous that a smooth surface  109 . Lights and diffusers  140  and  141  may also be located at a center between recesses  108 . Note that in an alternative embodiment, only one of the horizontal  120  and vertical  122  jets are provided in combination with the configuration illustrated having the recess and the intake  114  located above the point where the jet register  138 . 
         [0032]    Preferably, the vertical and horizontal jets  122 ,  120  originate from approximately the same location (register  138 ) which coincides with a perimeter of the LVD  10 . They do not need to be supplied from the same source of air nor do they need to originate from a common register structure. It is preferable, however that they both are positioned to form a 20° angle from the vertical and whose vertex is at the outermost edge of the pollution-generating part  121  of an appliance  100 . Thus, lower appliances must be located more inwardly and higher appliances can be located more outwardly. This minimum angle may be reduced if the exhaust flow is increased or the jet flow rates are increased. 
         [0033]    Preferably the horizontal jet has a velocity of 6 to 10 m/s and a volume flow rate per linear meter of 21 to 35 cm/hr per linear meter of the LVD  10  perimeter for a typical kitchen application. These approximately coincide with the throw conditions identified above. Preferably, the total volume rate of the vertical jets to the total volume rate of the horizontal jets is preferably about 0.25 to 0.35. These are not necessarily required values, but are representative for kitchen applications. A preferred aspect ratio of the exhaust device (e.g., W/Y indicated in  FIG. 3 ) is greater than ten. 
         [0034]      FIGS. 2A and 2B  illustrate the LVD in section  2 A and plan view (as viewed from underneath)  2 B. Blanks  118  are fitted to portions of the intake lengths to prevent air and fumes from being drawn into portions  139  of the LVD. The blanks  118  may replace removable filter cartridges (not shown, but for example, impact-type grease filters or as shown in U.S. Pat. No. 4,872,892, filed Sep. 16, 1988). The blanks  118  permit the exhaust to be drawn in positions overlying the pollution sources. Preferably, they are used only over areas with no pollutions sources and permit an overhang of the open intakes  114  over each pollution source of at least 20 degrees as discussed above with reference to the overhang angle of  FIG. 1 . 
         [0035]    Referring to  FIG. 3 , as discussed above, a horizontal jet may be provided which is aimed nearly horizontally as indicated at  201 , slightly upwardly toward the center of the intake  210 , as indicated at  202 , or even more upwardly as indicated at  203  such that it flows along the recess  217  surface  215 . A combination of these jets may be employed. In the embodiment of  FIG. 3 , a light diffuser, lamp cover, or lens  214  is located adjacent horizontal jet to help keep it clean such that the horizontal jet does double duty by helping to trap fumes (guide pollution-containing plumes) and keep the light cover  214  clean. A vertical jet  218  may also be provided.  FIG. 3  also illustrates an embodiment with a recess  217  and which has the horizontal jet outlet located below the intake, but in which there is only one intake  210  connected to a common plenum  216  for each recess  217  on one side rather than two as in the prior embodiments. In an alternative embodiment, only one intake  210  and one recess  217  are provided in a configuration in which, preferably, a wall  237  bounds the intake side of the LVD  223 . 
         [0036]      FIGS. 4A and 4B  show a configuration for a common vertical and horizontal register fed from a plenum  250 .  FIG. 4A  shows a section view and  4 B shows a bottom view. A hole  238  generates the vertical jet  228 . A nozzle  231  generates the horizontal jet  230 . The nozzle  231  may be forged with the illustrated shape and an opening in a flat sheet of metal  240 , which forms the shell of the plenum  250 , at regular intervals. Examples of dimensions are shown. The opening  232  of the nozzle  231  may be 3.5 mm deep and 12 mm wide. The hole  238  may be 4.5 mm in diameter. The spacing between the jets/holes may be 30 mm. These dimensions are illustrative only.  FIG. 4C  shows in section another configuration of a jet register fed through a plenum  252  defined in a box-shaped extension  242 . A hole  236  generates the vertical jet  228 . Another hole  234  in the side of the box shaped extension  242  generates the horizontal jet  230 . The holes may be formed at regular intervals along the register. Examples of dimensions are shown. The opening  234  may be 6.5 mm in diameter. The hole  236  may be 4.5 mm in diameter. The spacing between the jets/holes may be 30 mm. These dimensions are illustrative only. 
         [0037]      FIG. 4D  illustrates a section view of an LVD  293  in which the horizontal jet  290  originates from a position that is not below the intake  292 , in which there is no light fixture and in which the jet register  296  is configured in accord with the embodiment of  FIG. 4C , all of which are features that may be combined or substituted for any and all of the corresponding features of the other embodiments. The LVD  293  contains a recess  294  defined within the jet register  296  which is substantially aligned with the bottom of the exhaust intake  292 . A vertical jet  291  emanates from the jet register  296 . 
         [0038]      FIG. 5  shows a control system that may be used in connection with the embodiments. Sensors (which may include associate signal conditioning and data processing elements)  310  may include one or more of: 
         [0039]    air velocity sensors indicating the average or maximum velocities (or some other statistic) responsive to the movement of air in the conditioned space, which air movement affects the stability of a rising plume, such as drafts, air movement induced by movement of personnel, etc. identified as ambient drafts  310   a;    
         [0040]    activity level sensors  310   b  responsive to the movement in the conditioned space that may cause air movement that can disrupt the plume including information extracted from event recognition in a video stream, activity from a proximity or infrared distance detector or range finder; 
         [0041]    time of day  310   c  from which the activity level may be inferred, such as in a production workspace such as a commercial kitchen; 
         [0042]    fume load  310   d  which may be indicated by means of a fuel usage indicator of a heat source such as a range or grill, a carbon dioxide detector, a temperature or moisture sensor or other composition sensor which may indicate the composition of a fume plume, a video stream-based event recognition device, for example one configured to recognize zero, light, medium, and heavy use of an appliance and the nature of the use; and 
         [0043]    temperatures  310   e  such as indoor, outdoor, and plume temperatures. 
         [0044]    A controller  302  receives one or more sensor  310  signals and may control one or more outputs including drives  304 - 308  which control flow rates indicated by fan symbols  312 - 316 . The drives  304 - 308  may be damper drives or speed drives or any device for controlling volume flow rate. The drive signals may control the exhaust rate, vertical jet flow rate, horizontal jet flow rate, and/or displacement ventilation flow rate. Any of these may be controlled separately or together (e.g., a common drive signal or a mechanical coupling in the control and mechanical aspects) according to various mechanical embodiments (such as one in which a shared plenum provides air for both the vertical and horizontal jets). 
         [0045]    In an embodiment, the exhaust flow rate is preferably modulated responsively to the fume load and/or indicators of drafts or air movement in the conditioned space. The velocities of the vertical and/or horizontal jets may be modulated in response to such inputs as well. For example, when there is greater air movement in the conditioned space, such as caused by workers moving about, the exhaust velocity may be proportionately increased and the vertical jet speed may be increased proportionately as well. 
         [0046]      FIG. 6  shows a perspective illustration of a configuration in which the vertical  311  and horizontal  312  jets run along an entire perimeter of a LVD  10 .  FIGS. 7A, 7B, and 7C  illustrate an aimable horizontal jet nozzle  350 . The nozzle  350 , which may be a press-fitted plastic member. When a section of the LVD is fitted with blanks and therefore has zones without exhaust intakes, the aligned portions of horizontal and vertical jet registers may be tilted to direct certain ones  376  at a horizontal angle toward an adjacent intake section  370  and away from a section with a blank  372  as shown in  FIG. 7C . For long blank sections  372 , some of the horizontal jet outlets may be closed or plugged. The holes for the vertical jets  356  are also shown. Tilted positions  354  are shown. Any of the nozzles may also be substituted with a discharge vent with a movable vane and/or sliding damper blade. 
         [0047]    While the present invention has been disclosed with reference to certain embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it has the full scope defined by the language of the following claims, and equivalents thereof. 
         [0048]    Although the LVDs shown including lighting components, these are not essential to all embodiments and any of the embodiment may be modified by their removal. The LVD structures may be configured as modular components that can be assembled to form various shapes to cover pollution sources in various arrangements in a production space. Blanks that cover exhaust intakes may be provided as part of a kit and used to redefine the exhaust intake coverage as a production space is modified by the replacement, removal, or rearrangement of pollutions sources. Control adjustments discussed above may be done manually as well as automatically. The LVD embodiments may be surface mounted or recessed into a ceiling or false ceiling. General ventilation registers may be located at all sides of an LVD or only some sides. General ventilation registers may be located adjacent or remotely from the LVD. Note also that although the vertical and horizontal jets in the embodiments described are single point jets forming linear arrays, in alternative embodiments, the jets may be formed as slots to form vertical and horizontal curtains. 
         [0049]      FIG. 8  shows various combinations of elements ventilation elements combined in kitchen ventilation system. Multiple recesses such as indicated at  860  cover an entire ceiling area of a kitchen thereby protecting multiple appliances  816  which can be located anywhere in the kitchen. The region covered by the multiple recesses  860  can have any number sections producing horizontal  807  and vertical  808  jets and makeup air discharges  810 , such as indicated at  823 . Each recess may have an exhaust inlet  846  drawing fumes as indicated at  802  thereinto. The horizontal jets can be located at various locations throughout the multiple recesses to help direct fumes to the exhaust and away from other ceiling fixtures such as the lights  804 . The vertical jets  808  are preferably located to define the perimeter of the protected are. Alternatively the perimeter can be defined by a displacement ventilation register  830  or a wall (not shown). 
         [0050]    In the present and all systems, a ventilated ceiling is distinguished from conventional hoods by being very shallow relative to the height at which it is located. Here in this case, the depth  842  of the recess  860  may be more than five time the distance  840  from the source of fumes and the blind end of the recess  860 . 
         [0051]    Note that any of the embodiments described herein may be modified by eliminating the lighting component. So wherever the term “LVD” is used, the alternative lacking a light source is also a possible embodiment.