Control of exhaust systems

Abstract

Exhaust capture and containment are enhanced by means of automatic or manual side skirts, a sensitive breach detector based on interference effects, a combination of vertical and horizontal edge jets, and/or corner jets that are directed to the center diagonally from corners. Associated control functions are described.

Claims

1. An exhaust system for selectively increasing capture and containment of an exhaust hood, comprising: the exhaust hood having a roof and a plurality of side walls depending from the roof and defining a recess with an opening surrounded by bottom edges of the side walls, the opening being configured to permit fumes from a fume-generating process to rise into the recess of the exhaust hood; a plurality of movable side skirts attached to the exhaust hood such that each movable side skirt of the plurality of movable side skirts may be placed in a retracted position and an extended position, each movable side skirt of the plurality of movable skirts having a planar shape with a plurality of edges and each edge of the plurality having a respective length, wherein the extended position is effective to reduce an exposure of an area between the fume-generating process and the exhaust hood, the retracted position is effective to increase the exposure of the area between the fume-generating process and the exhaust hood, the plurality of movable side skirts includes at least two side skirts positioned adjacent to each other along the plurality of side walls of the exhaust hood, the at least two side skirts which are positioned adjacent to each other are spaced apart from each other by a gap that provides a view of the fume-generating process when the at least two side skirts are in the extended position, and the planar shape of each of the plurality of movable side skirts is substantially parallel to at least one side wall of the plurality of side walls, each of the plurality of movable side skirts is positioned adjacent to a respective one side wall of the plurality of side walls, the length of a longest edge of each movable side skirt of the plurality of movable side skirts is shorter than a longest edge of said respective one side wall of the plurality of side walls such that each movable side skirt of the plurality of movable side skirts is retractable completely into the recess of the exhaust hood when in the retracted position.

2. The exhaust system of claim 1, wherein the movable side skirts are manually movable.

3. The exhaust system of claim 1, wherein the fume-generating process includes a cooking appliance.

4. The exhaust system of claim 1, further comprising: an actuator connected to move the movable side skirts from the retracted position to the extended position; and a controller with a fume load detector connected to control said actuator and configured to control whether the movable side skirts are placed in the retracted position or remain the extended position responsively to a fume load.

5. The exhaust system of claim 4, further comprising: a camera connected to control said actuator and configured to control whether the movable side skirts are placed in the retracted position or the extended position responsively to a scene detected by said camera.

6. The exhaust system of claim 1, further comprising: an actuator connected to move the movable side skirts from the retracted position to the extended position; and a controller with a proximity sensor with a field of view connected to control said actuator and configured to lower the movable side skirts to the extended position when the proximity sensor indicates an absence of a person within the field of view of the proximity sensor after a lapse of a certain time.

7. An exhaust system, comprising: an exhaust hood having a plurality of side walls that define a recess configured to capture fumes from and located above an appliance; a plurality of movable side skirts configured to be raised or lowered by a motor drive mounted to at least some side walls of the plurality of side walls; and a controller configured to control the motor drive which controls a vertical position of the movable side skirts, wherein at least one movable side skirt of the plurality of movable side skirts is a trapezoidal shaped plate with four edges surrounding the plate, the plate is slidably mounted to one of the plurality of side walls of the exhaust hood, with at least a portion of the plate inside the recess, all of the four edges are not in contact with any other movable side skirt of the plurality of movable side skirts, each trapezoidal shaped plate has a size that permits a respective movable side skirt to be completely retracted into the recess of the exhaust hood such that an entirety of the respective movable side skirt is inside of the recess, the four edges include two opposed parallel edges and two opposed non-parallel edges, and a shorter one of the two opposed parallel edges is positioned closer to the appliance than a longer one of the two opposed parallel edges.

8. The exhaust system of claim 7, further comprising a proximity sensor located in a position to indicate whether access to a side of an appliance is required and to raise and lower the movable side skirts in response to a need for accessing the appliance.

9. The exhaust system of claim 8, wherein the controller raises and lowers the movable side skirt automatically in response to a signal from the proximity sensor.

10. The exhaust system of claim 7, wherein the movable side skirts are located on one side or opposite sides of the exhaust hood.

11. The exhaust system of claim 7, further comprising one or more proximity sensors connected to the controller and configured to raise and lower the movable side skirts.

12. The exhaust system claim 7, further comprising a rear skirt located between a wall and the exhaust hood.

13. The exhaust system of claim 7, further comprising a video camera linked to the controller, the movable side skirts being raised and lowered by the controller responsively to a scene change imaged by the video camera indicating whether a scene is stationary or not.

14. The exhaust system of claim 7, further comprising a shaft inside of the recess; at least two spools of wires wrapped around the shaft, wherein the plate is suspended from the shaft by the wires of the at least two spools, and the plate is movable up and down in response to rotation of the shaft and spooling and unspooling of the wires.

15. The exhaust system of claim 7, wherein the controller is configured to trade off side skirt elevation against exhaust flow rate such that when the side skirts are raised the exhaust flow rate is increased.

16. The exhaust system of claim 15, wherein the controller is configured to control elevation of the side skirts in response to a time of day.

17. The exhaust system of claim 7, wherein the controller is configured to control elevation of the side skirts in response to a time of day.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A is a side view illustration of a prior art backshelf hood.

(2) FIG. 1B is a side view illustration of a prior art backshelf hood with side skirts.

(3) FIG. 2 is a side view illustration of a prior art canopy style hood with an island appliance.

(4) FIG. 3A is a side view illustration of a canopy style hood with adjustable side skirts according to a first inventive embodiment.

(5) FIG. 3B is a schematic illustration of a control system for the embodiment of FIG. 3A as well as other embodiments.

(6) FIG. 4 is a side view illustration of a backshelf hood with a fire gap and movable side skirts and a movable back skirt.

(7) FIG. 5 is a side view illustration of a canopy style hood with adjustable side skirts according to a second inventive embodiment.

(8) FIG. 6 is a figurative representation of a combination of horizontal and vertical jets to be generated at the edge of a hood according to an inventive embodiment.

(9) FIG. 7A is a figurative illustration of a plenum configured to generate the vertical and horizontal jets with diagonal horizontal jets at ends of the plenum according to an inventive embodiment.

(10) FIG. 7B is a plan view of a typical hood showing a central location of the exhaust vent.

(11) FIGS. 8A and 8B illustrate the position of the plenum of FIG. 7 as would be installed in a wall-type (backshelf) hood as well as a combination of the horizontal and vertical jets with side skirts according to at least one inventive embodiment.

(12) FIG. 8C illustrates a wall-type (backshelf) hood with a combination of horizontal and vertical jets, according to an embodiment of the disclosed subject matter.

(13) FIGS. 9A-9C illustrate various ways of wrapping a series of horizontal jets around a corner to avoid end effects according to inventive embodiment(s).

(14) FIG. 9D illustrates a way of creating a hole in a plenum that redirects a small jet without a separate fixture by warping the wall of the plenum.

(15) FIG. 10 illustrates a canopy-style hood with vertical jets and a configuration that provides a vertical flow pattern that is subject to an end effects problem.

(16) FIGS. 11A and 11B illustrate configurations of a canopy hood that reduce or eliminate the end effect problem of the configuration of FIG. 10.

(17) FIG. 12 illustrates a configuration of a canopy hood that reduces the end effect problem of the configuration of FIG. 10 by supporting the canopy using columns at the corners that are shaped to eliminate interactions at the ends of the straight portions of the hood.

(18) FIG. 13A illustrates a hood configuration with a sensor that uses incipient breach control to minimize flow volume while providing capture and containment.

(19) FIG. 13B illustrates an interferometric breach detector for use with the embodiment of FIG. 13A and other applications.

(20) FIG. 13C illustrates an interferometer using a directional coupler and optical waveguides instead of beam splitter and mirrors.

(21) FIG. 13D illustrates some mechanical issues concerning measurements that depend on the structure of turbulence.

(22) FIG. 14 illustrates a combination make-up air discharge register and hood combination with a control mechanism for apportioning flow between room-mixing discharge and short-circuit discharge flows.

(23) FIG. 15 illustrates a combination make-up air discharge register and hood combination with a control mechanism for apportioning flow between room-mixing discharge and a direct discharge into the exhaust zone of the hood from either outdoor air, transfer air from another conditioned space, or a mixture thereof.

(24) FIGS. 16A-16C illustrate drop-down skirts that can be manually swung out of the way and permitted to drop into place after a time interval.

(25) FIG. 16D illustrates components of a system with drop-down skirts that can be manually swung out of the way and permitted to drop into place after a time interval.

(26) FIG. 17 illustrates a sensor configuration with a light guide having multiple sample gaps in a common light path.

(27) FIG. 18 shows a sensor configuration having multiple individual sample devices at a hood edge.

(28) FIG. 19 is a simplified process flow diagram for latching and releasing a skirt.

DETAILED DESCRIPTION

(29) The following US patent applications are hereby incorporated by reference as if set forth in their entireties herein: U.S. patent application Ser. No. 10/344,505, entitled “Device and Method for Controlling/Balancing Fluid Flow-Volume Rate in Flow Channels,” filed Aug. 11, 2003; U.S. patent application Ser. No. 10/168,815, entitled “Exhaust Hood with Air Curtain to Enhance Capture and Containment,” filed May 5, 2003; and U.S. patent application Ser. No. 10/638,754, entitled “Zone Control of Space Conditioning Systems with Varied Uses,” filed Aug. 11, 2003.

(30) FIG. 3A is a side view illustration of a canopy style hood 61 with adjustable side skirts 105 according to a first inventive embodiment. Fumes 35 rise from a cooking appliance 41 into a suction zone of the hood 61. The fumes are drawn, along with air from the surrounding conditioned space 36 the hood 61 occupies, through exhaust vents and grease filters indicated at 21 by an exhaust fan (not shown in the present drawing) connected to draw through an exhaust duct 11. An exhaust stream 15 is then forced away from the occupied space.

(31) At one or more sides of the exhaust hood 61 are movable side skirts 105 which may be raised or lowered by means of a manual or motor drive 135. The manual or motor drive 135 rotates a shaft 115 which spools and unspools a pair of support wires 130 to raise and lower the side skirts 105. The side skirts 61 and spool 125, as well as bearings 120 and the wires 130, may be hidden inside a housing 116 with an open bottom 117. In a preferred embodiment, the manual or motor drive 135 is a motor drive controlled by a controller 121 which controls the position of the side skirts 105.

(32) Although the above and other embodiments of the invention described below are discussed in terms of a kitchen application, it will be readily apparent to those of skill in the art that the same devices and features may be applied in other contexts. For example, industrial buildings such as factories frequently contain large numbers of exhaust hoods which exhaust fumes in a manner that are very similar to what obtains in a commercial kitchen environment. It should be apparent from the present specification how minor adjustments, such as raising or lowering the hood, adjusting proportions using conventional design criteria, and other such changes can be used to adapt the invention to other applications. The inventor(s) of the instant patent application consider these to be well within the scope of the claims below unless explicitly excluded.

(33) FIG. 3B is a schematic illustration of a control system for the embodiment of FIG. 3A as well as other embodiments. The controller 121 may control the side skirts automatically in response to incipient breach, for example, as described in the US patent application, “Device and Method for Controlling/Balancing Fluid Flow-Volume Rate in Flow Channels,” incorporated by reference above. To that end, an incipient breach sensor 122 may be mounted near a point where fumes may escape due to a failure of capture and containment. Examples of sensors that may be employed in that capacity are discussed below and include humidity, temperature, chemical, flow, and opacity sensors.

(34) Another sensor input that may be used to control the position of the side skirts 105 is one that indicates a current load 124. For example, a temperature sensor within the hood 61, a fuel flow indicator, or CO or CO2 monitor within the hood may indicate the load. When either of incipient breach or current load indicates a failure or threat to full capture and containment, the side skirts 105 may be lowered. This may be done in a progressive manner in proportion to the load. In the case of incipient breach, it may be done by means of an integral of the direct signal from the incipient breach sensor 122. Of course, any of the above sensors (or others discussed below) may be used in combination to provide greater control, as well as individually.

(35) A draft sensor 123 such as a velocimeter or low level pressure sensor or other changes that may indicate cross currents that can disrupt the flow of fumes into the hood. These are precisely the conditions that side skirts 105 are particularly adapted to control. Suitable transducers are known such as those used for making low level velocities and pressures. These may be located near the hood 61 to give a general indication of cross-currents. When cross-currents appear, the side skirts 105 may be lowered. Preferably the signals or the controller 121 is operative to provide a stable output control signal as by integrating the input signal or by other means for preventing rapid cycling, which would be unsuitable for the raising and lowering of the side skirts 105.

(36) The controller 121 may also control the side skirts 105 by time of day. For example, the skirts 105 may be lowered during warm-up periods when a grill is being heated up in preparation for an expected lunchtime peak load. The controller 121 may also control an exhaust fan 136 to control an exhaust flow rate in addition to controlling the side skirts 105 so that during periods when unhindered access to a fume source, such as a grill, is required, the side skirts 105 may be raised and the exhaust flow may be increased to compensate for the loss of protection otherwise offered by the side skirts 105. The controller may be configured to execute an empirical algorithm that trades off the side skirt 105 elevation against exhaust flow rate. Alternatively, side skirt 105 elevation and exhaust rate may be controlled in a master-slave manner where one variable is established, such as the side skirt 105 elevation in response to time of day, and exhaust rate is controlled in response to one or a mix of the other sensors 124, 123, 127, and/or 122.

(37) FIG. 4 is a side view illustration of a backshelf hood 46 with a fire safety gap 76 and movable side skirts 70 and a movable back skirt 75. The side skirts 70 may be one or both sides and may be manually moved or automatically driven as discussed above with reference to FIGS. 3A and 3B. The movable back skirt 75 is located behind the appliance 40 and is raised to block the movement of fumes due to cross drafts. The back skirt could as easily be attached to the hood 46 and lowered into position.

(38) Note that any of the skirts discussed above and below may be configured based on a variety of known mechanical devices. For example, a skirt may hinged and pivoted into position. It may be have multiple segments such that is unfolds or unrolls like some metal garage doors.

(39) FIG. 5 is a side view illustration of a canopy style hood 62 with adjustable side skirts 210 according to a another inventive embodiment. The side skirts 210 may be manually or automatically movable. There may be two, one at either of two ends of the hood 62 or there may be more or less on adjacent sides of the hood 62, such as a back side 216. In some situations where most of the access required to the appliances can be accommodated on a front side 217 of the hood 62, it may be feasible to lower a rear skirt 218.

(40) Note that it is unnecessary to discuss the location and type of drives to be used and the precise details of manual and automatic skirts because they are well within the ken of machine design. For the same reason, as here, examples of suitable drive mechanisms are not repeated in the drawings.

(41) Also shown in FIG. 5 is a suitable location for one or more proximity control sensors 230 that be used in the present or other embodiments. Proximity sensors may be used to give an indication of whether access to a corresponding side of the appliance 41 is required, in a manner not unlike that of an automatic door of a public building. One or more proximity sensors 230 may be used to raise and lower the side skirts.

(42) As taught in the patent application for “Exhaust Hood with Air Curtain to Enhance Capture and Containment,” incorporated by reference above, a virtual barrier may be generated to help block cross-drafts by means of a curtain jet located at an edge of the hood. FIG. 6 is a figurative representation of a combination of horizontal and vertical jets to be generated at the edge of a hood according to an inventive embodiment which has been shown by experiment to be advantageous in terms of minimizing the exhaust flow required to obtain full capture and containment. In a preferred configuration, the horizontal and vertical jets are made by forming holes in a plenum, for example holes of about 3-6 mm diameter with a regular spacing so that the individual jets coalesce some distance away from the openings to form a single planar jet. The initial velocities of the horizontal jets are preferably between 2 and 3.5 times the initial velocities of the vertical jets, the initial velocity in this case being the point at which individual jets coalesce into a single planar jet.

(43) FIG. 7A is a figurative illustration of a plenum 310 configured to generate the vertical 325 and horizontal 330 jets with diagonal horizontal jets 315 at ends of the plenum 310 according to an inventive embodiment. Referring momentarily to FIG. 7B, most hoods 307 have an exhaust vent 306 within the hood 307 recess that is centrally located so that even if the hood has a large aspect ratio, at the ends, horizontal jets 309 (330 in FIG. 7A) are more effective at capturing exhaust if they are directed toward the center of the hood near the ends 308 of the long sides 302. Thus, in a preferred, configuration of the plenum 310, the ends 325 of the plenum have an angled structure 320 to project the horizontal jets diagonally inwardly as indicated at 315.

(44) FIGS. 8A and 8B illustrate the position of the plenum 310 of FIG. 7A as would be installed in a wall-type (backshelf) hood 370 as well as a combination of the horizontal and vertical jets with side skirts 365 according to another inventive embodiment. This illustration shows how the plenum 310 of FIG. 7B may be mounted in a backshelf hood 370. In addition, the figure shows the combination of the vertical and horizontal jets and the side skirts 365. In such a combination, the velocity of the vertical and horizontal jets may be reduced when the side skirts 365 are lowered and increased when the side skirts are raised. Note that although not shown in an individual drawing, the same control feature may be applied to horizontal-only jets and vertical-only jets which are discussed in “Exhaust Hood with Air Curtain to Enhance Capture and Containment,” incorporated by reference above. FIG. 8A shows the side skirts 365 in a lowered position and FIG. 8B shows the side skirts 365 in a raised position. Note that the plenum 310 may be made integral to the hood and also that a similar mounting may be provided for canopy style hoods. FIG. 8B also shows an alternative plenum configuration 311 with a straight return 385 on one side which generates vertical 380 and horizontal 395 jets along a side of the hood 370. The return leg 385, although shown on one end only, may be used on both ends, for example, as shown in FIG. 8C, and is also applicable to canopy style hoods.

(45) FIGS. 9A-9C illustrate various ways of wrapping a series of horizontal jets around a corner to avoid end effects according to inventive embodiment(s). These alternative arrangements may be provided by shaping a suitable plenum as indicated by the respective profile 405, 410, 415. Directional orifices may be created to direct flow inwardly at a corner without introducing a beveled portion 415A or curved portion 410A as indicated by arrows 420. FIG. 9D illustrates a way of creating a directional orifice in a plenum 450 to direct a small jet 451 at an angle with respect to the wall of the plenum 450. This may done by warping the wall of the plenum 450 as indicated or by other means as disclosed in the references incorporated herein.

(46) FIG. 10 illustrates a canopy-style hood 500 with vertical jets 550 and a configuration that provides a vertical flow pattern 545 that is subject to an end effects problem. The end effects problem is that where the vortices meet in corners, the flow vertical flow pattern is disrupted. As discussed in “Exhaust Hood with Air Curtain to Enhance Capture and Containment,” incorporated by reference above, the vertical flow pattern 545 works with the air curtain 550 to help ensure that fluctuating fume loads can be contained by a low average exhaust rate. But the vortex cannot make sharp right-angle bends so the quasi-stable flow is disrupted at the corners of the hood.

(47) FIGS. 11A and 11B illustrate configurations of a canopy hood that reduce or eliminate the end effect problem of the configuration of FIG. 10. Referring to FIGS. 11A and 11B, a round hood 570 or one with rounded corners 576 reduces the three-dimensional effects that can break down the stable vortex flow 545. In either shape, a toroidal vortex may be established in a curved recess 585 or 590 with the vertical jets following the rounded edge of the hood. Thus the section view of FIG. 10 would be roughly representative of any arbitrary slice through the hoods 576, 570 shown in plan view in FIGS. 11A and 11 B.

(48) The figures also illustrate filter banks 580 and 595. It may be impractical to make the filter banks 580 and 595 rounded, but they may be piecewise rounded as shown.

(49) FIG. 12 illustrates a configuration of a canopy hood 615 that reduces the end effect problem of the configuration of FIG. 10 by supporting the canopy using columns 610 at the corners that are shaped to eliminate interactions at the ends of the straight portions 620 of the hood 615. Vertical jets 650 do not wrap around the hood 615 and neither does the internal vortex (not illustrated) since there are separate vortices along each edge bounded by the columns 610.

(50) FIG. 13A illustrates a hood configuration with a sensor that uses incipient breach control to minimize flow volume while providing capture and containment. Incipient breach control is discussed in “Device and Method for Controlling/Balancing Fluid Flow-Volume Rate in Flow Channels,” incorporated by reference above. Briefly, when fumes 725 rise from a source appliance 711, and there is a lack of sufficient exhaust flow or there is a cross-draft, part of the fumes may escape as indicated by arrow 720. A sensor located at 715 or nearby position may detect the temperature, density, or other detectable feature of the fumes to indicate the breach. The indication may be used by a controller to control exhaust flow as discussed in the above patent or others such as U.S. Pat. No. 6,170,480 entitled “Commercial Kitchen Exhaust System,” which is hereby incorporated by reference as if fully set forth herein in its entirety.

(51) Prior applications have discussed optical, temperature, opacity, audio, and flow rate sensors. In the present application we propose that chemical sensors such as carbon monoxide, carbon dioxide, and humidity may be used for breach detection. In addition, as shown in FIG. 13B, an interferometric device may also be employed to detect an associated change, or fluctuation, in index of refraction due to escape of fumes.

(52) Referring to FIG. 13B, a coherent light source 825 such as a laser diode emits a beam that is split by a beam splitter 830 to form two beams that are incident on a photo detector 835. A reference beam 831 travels directly to the detector 835. A sample beam 842 is guided by mirrors 840 to a sample path 860 that is open to the flow of ambient air or fumes. The reference and sample beams 831 and 842 interfere in the beam splitter, affecting the intensity of the light falling on the detector 835. The composition and temperature of the fumes creates fluctuations in the effective path length of the sample path 860 due to a fluctuating field of varying index of refraction. This in turn causes the phase difference between the reference 831 and sample 860 beams to vary causing a variation in intensity at the detector 835.

(53) The direct output of the detector 835 may be passed through a bandpass filter 800, an integrator 805, and a slicer (threshold detector) 810 to provide a suitable output signal. The reason a bandpass filter may be useful is to eliminate slowly varying components that could not be a result of fumes such as a person leaning against the detector, as well as changes too rapid to be characteristic of the turbulent flow field associated with a thermal plume or draft, such as motor vibrations. An integrator ensures that the momentary transients do not create false signals and the slicer provides a threshold level.

(54) It will be understood that for sample paths 860 that are large, i.e., many wavelengths long, many rapid changes in the detector 835 output may occur as the result of changes in the temperature or mix of gases due to the change in the speed of light through the path 860. Thus, an alternative way of detecting changes is to count the number of fringes detected (using for example a one-shot circuit to form pulse edges) and to generate a signal corresponding to the rate of pulses. A high rate of pulses indicates a correspondingly large change in the speed of light in the sample path. Large changes are associated with turbulent mixing and the escape of heat and/or gases from the cooking process.

(55) Referring to FIG. 13C, an alternative embodiment of a detector uses a directional coupler 830A instead of a beam splitter as in the previous embodiment. Rather than mirrors, a waveguide 864 is used to form a sample path 860A. A light source 825 sends light into the direction coupler 830A which is split with one component going to the detector 835 and the other passing through the sample path 860A and back to the direction coupler 830A. Fluctuations in phase of the return light from the sample path 860A cause variations in the intensity incident on the detector 835 as in the previous embodiment.

(56) Preferably, the interferometric detector should allow gases to pass through the measurement beam without being affected unduly by viscous forces. If the sample path is confined in a narrow channel, viscous forces will dominate and the detector will be slow to respond. This may be desirable. For example, it may avoid false positives resulting when a transient flow of gas contacts the sensor but does not remain present for a sufficiently long time or does not have sufficient concentration of contaminant to diffuse enough gas or heat into the sample gap. Also, if the sample path is too long the signal might be diminished due to an averaging effect, where the average of the speed of light in the same path remains relatively constant even though at a given point, the speed varies a great deal to the variation in the gas content or properties. These effects vary with the application and will involve some experimentation. Different detectors may be provided for different applications, for example, a hood for a grill versus one for a steam table.

(57) To control based on breach detection, a variety of techniques can be used. Pure feedback control may be accomplished by slowly lowering the speed of a variable speed exhaust fan until a threshold degree of breach is indicated. The threshold may be, for example, the specified minimum frequency of pulses from the one-shot configuration described above sustained over a minimum period of time. In response to the breach, the speed may be increased by a predefined amount and the process of lowering the speed repeated. A more refined approach may be a predictive or model-based technique in which other factors, besides breach, are used to model the fume generation process as described in the present application and in U.S. patent application Ser. No. 10/638,754 incorporated by reference above. The technique for feedback control may follow those outlined in U.S. Pat. No. 6,170,480 also incorporated by reference above.

(58) It may be preferable for the gap to be longer than the length scale of the temperature (or species, since the fumes may be mixed with surrounding air) fluctuations to provide a distinct signature for the signal if the gap would substantially impede the flow. Otherwise, the transport of temperature and species through the sample beam would be governed primarily by molecular diffusion making the variations slow, for example, if the sample beam were only exposed in a narrow opening. However, in some applications of a detector this may be desirable, but such applications are likely removed from typical commercial kitchen application. Referring to FIG. 13D, a microscale eddy is figuratively shown at 900. The structure of the detector may provide a space 918 that is large relative to the smallest substantial turbulent microscale as indicated at 912. Alternatively, the structure of the detector may be smaller than the microscale, but thin and short as indicated at 914 in which case viscous forces may not impede greatly the variation of the constituent gases in the sample path 910 due to turbulent convection.

(59) FIG. 14 illustrates a combination make-up air discharge register/hood combination 887 with a control mechanism 869 and 870 for apportioning flow between room-mixing discharge 886 and short-circuit discharge 876 flows. A hood 874 has a recess through which fumes 894 flow and are exhausted by an exhaust fan 879, usually located on the top of a ventilated structure. A make-up air unit 845 replaces the exhausted air by blowing it into a supply duct 880 which vents to a combination plenum that feeds a mixed air supply register 886 and a short-circuit supply register 876. The fresh air supplied by the make-up air unit 845 is apportioned between the mixed air supply register 886 and a short-circuit supply register 876 by a damper 870 whose position is determined by a motor 865 which is in turn controlled by a controller 869.

(60) When air is principally fed to the short-circuit supply register 876, it helps to provide most of the air that is drawn into the hood 887 along with the fumes and exhausted. Short-circuit supply of make-up air is believed by some to offer certain efficiency advantages. When the outside air is at a temperature that is within the comfort zone, or when its enthalpy is lower in the cooling season or higher in the heating season, most of the make-up air should be directed by the controller 869 into the occupied space through the mixed air supply register 886. When the outside air does not have an enthalpy that is useful for space-conditioning, the controller 869 should cause the make-up air to be vented through the short-circuit supply register 876.

(61) FIG. 15 illustrates a combination make-up air discharge register and hood combination with a control mechanism for apportioning flow between room-mixing discharge and a direct discharge into the exhaust zone of the hood from either outdoor air, transfer air from another conditioned space, or a mixture thereof. A blower 897 brings in transfer air, which may be used to supply some of the make-up air requirement and provide a positive enthalpy contribution to the heating or cooling load. The staleness of transfer air brought into the heavily ventilated environment of a kitchen is offset by the total volume of make-up (fresh) air that is required to be delivered. Sensors on the outside 875, the occupied space 830, in the transfer air stream and/or the space from which transfer air is drawn 831 may be provided to indicate the conditions of the source air streams. A mixing box 846 may be used to provide an appropriate ratio of transfer air and fresh air. The ratio will depend on the exhaust requirements of the occupied space 896. Control of the damper 870 is as discussed with reference to FIG. 14.

(62) FIGS. 16A-16D illustrate drop-down skirts that can be manually swung out of the way and permitted to drop into place after the lapse of a watchdog timer. FIGS. 16A and 16B are side views of a drop-down skirt 915 that pivots from a hinge 905 from a magnetically suspended position shown in FIG. 16A to a dropped position shown in FIG. 16B. A magnetic holder/release mechanism 935, which may include an electromagnet or permanent magnet, holds the skirt panel 915 in position out of the way of an area above a fume source 930. The skirts 915 may be released after being moved up and engaged by the magnetic holder/release mechanism 935, after a period of time by a controller 960. The controller 960 may be connected to a timer 970, a proximity sensor 925, and the magnetic holder/release mechanism 935. The proximity sensor 925 may be one such as used to activate automatic doors. If nothing is within view of the proximity sensor after the lapse of a certain time, the controller may release the skirt 915. When released by the magnetic holder/release mechanism 935, the skirt 915 falls into the position of FIG. 16B to block drafts. Preferably, as shown in the front view of FIG. 16C, there are multiple skirts 915 separated by gaps 916. A passing worker may scan the area behind the skirts 915 even though they are down if the worker moves at least partly parallel to the plane of the skirts 915. In an embodiment, the magnetic holder/release mechanism 935 may combined with the controller 960, the timer 970, and the proximity sensor 925 in a unitary device.

(63) Although in the embodiments described above and elsewhere in the specification, real-time control is described, it is recognized that some of the benefits of the invention may be achieved without real-time control. For example, the flow control devices may be set manually or periodically, but at intervals to provide the local load control without the benefit of real-time automatic control.

(64) Note that although in the above embodiments, the discussion is primarily related to the flow of air, it is clear that principles of the invention are applicable to any fluid. Also note that instead of proximity sensors, the skirt release mechanisms described may be actuated by video cameras linked to controllers configured or trained to recognize events or scenes. The very simplest of controller configurations may be provided, where a blob larger than a particular size appears or disappears within a brief interval in a scene or a scene remains stationary for a given interval. A controller detects the latching of the skirt at step S900 and starts a watchdog timer at step S905. Control then loops through S910 and S915 as long as scene changes are detected. Again, simple blob analysis is sufficient to determine changes in a scene. Here we assume the camera is directed to view the scene in front of the hood so that if a worker is present and working, scene changes will continually be detected. If no scene changes are detected until the timer expires (step S915), then the skirt is released at step S920 and control returns to step S900 where the controller waits for the skirt to be latched. A similar control algorithm may be used to control the automatic lowering and raising of skirts in the embodiments of FIGS. 3A-5, discussed above. Instead of releasing the skirt, the skirt would be extended into a shielding position and instead of waiting for the skirt to be latched, a scene change would be detected and the skirt automatically retracted.

(65) Referring to FIG. 17, multiple sample gaps, such as the two indicated at 1815 may be linked together in a common light path by a light guide 1802 and a single directional coupler 1801 device or equivalent device. As in prior embodiments, a light source 1835 and detector 1825 are connected by a directional coupler 1830 with focusing optics 1862 and one or more linking light guides 1864 to provide any number of sample paths, such as paths 1815. FIG. 18 shows a hood edge 1920 with multiple individual sample devices 1871 which conform to any of the descriptions above linked to a common controller. Although parallel connections are illustrated, serial connections of either fiber or conductor may be provided depending on the configuration.

(66) There are a variety of control techniques that may be used in connection with the interference-based sensor configurations of FIGS. 13A-C, 17, and 18. The raw signal from the sensor is the fringe pattern resulting from the interference of a reference beam and a sample beam. As the properties of the sample beam change, for example due to temperature change, vapor content, or the mix of compounds resulting from cooking or other fume-generating process, the associated speed of light through the sample path generally changes. The length of the sample path length may be chosen based on the predicted variation due to escape of exhaust fumes. Also, the configuration may be based on whether the properties will diffuse into the sample path or be transported directly by convection into the sample path. These may be matters of design choice. The signal and how it is conditioned also depends on design choice. If the sample path is chosen to be large, many interference fringes may pass over the optical detector as a single bolus of gas interacts with the detector; i.e., as the bolus moves into, or diffuses fractions thereof into, the sample path such that it changes the speed of light in the sample path. If a breach occurs, under most circumstances, the flow would be a turbulent thermal convection plume containing a mix of fumes and air from the surrounding environment producing multiple back and forth shifts in fringe pattern as the fume and ambient air boluses interact with the detector. Alternatively the process may, if the transfer is by molecular diffusion or viscous flow due to the scale of the device, the mix of fumes and air may be averaged out producing a slower response and a single back and forth fringe shift. Each fringe shift may generate multiple light and dark pulses, but again this depends on the scale of the device and the particular wavelength of light chosen.

(67) By experimenting with the conditions of full containment and breach, one can obtain a characteristic pattern and identify it in the signal. For a grill, the thermal convection is vigorous and the properties of the fumes are such that continuous mixing with surrounding air causes a train of pulses to be generated whenever the fumes escape the hood. Thus, a simple frequency of the fringes (e.g., by converting to pulses and counting) as mentioned above may be compared to a threshold (background) level, to determine if a breach is occurring.