Real-time control of exhaust flow

A flow control system for controlling exhaust flow can measure effluent escaping from the exhaust hood at a given flow rate. An interferometric detector can measure fluctuations in fluid properties external to and/or in the vicinity of the exhaust hood. The flow control system may vary a flow rate of the exhaust hood and/or control exhaust hood structures responsive to the measurements to contain the effluent while minimizing the exhaust of air from the occupied space.

FIELD

The present disclosure relates generally to flow-volume control devices. More specifically, the present invention relates to flow control devices that may be used for balancing fluid flow in a context where suspended particles are entrained in the fluid and their precipitation must be avoided, in free-flowing parts of a flow system, except during filtration.

BACKGROUND

Exhaust hoods are used to remove air contaminants close to the source of generation located in a conditioned space. For example, one type of exhaust hoods, kitchen range hoods, creates suction zones directly above ranges, fryers, or other sources of air contamination. Exhaust hoods tend to waste energy because they must draw some air out of a conditioned space in order to insure that all the contaminants are removed. As a result, a perennial problem with exhaust hoods is minimizing the amount of conditioned air required to achieve total capture and containment of the contaminant stream.

Referring toFIG. 1, a typical prior art exhaust hood90is located over a range15. The exhaust hood90has a recess55with at least one vent65(covered by a filter60) and an exhaust duct30leading to an exhaust system (not shown) that draws off contaminated air45. The vent65is an opening in a barrier35defining a plenum37and a wall of the canopy recess55. The exhaust system usually consists of external ductwork and one or more fans that pull air and contaminants out of a building and discharge them to a treatment facility or into the atmosphere. The recess55of the exhaust hood90plays an important role in capturing the contaminant because heat, as well as particulate and vapor contamination, are usually produced by the contaminant-producing processes. The heat causes its own thermal convection-driven flow or plume10which must be captured by the hood within its recess55while the contaminant is steadily drawn out of the hood. The recess creates a buffer zone to help insure that transient, or fluctuating, surges in the convection plume do not escape the steady exhaust flow through the vent. The convection-driven flow or plume10may form a vortical flow pattern20due to its momentum and confinement in the hood recess. The Coanda effect causes the thermal plume10to cling to the back wall. The exhaust rate in all practical applications is such that room air5is drawn off along with the contaminants.

Referring now also toFIG. 2, exhaust hoods90, such as illustrated inFIG. 1, vary in length and can be manufactured to be very long as illustrated inFIG. 2. Here multiple vents65can be seen from a straight-on view from the vantage of a worker80. The length can present a problem because the perimeter along which capture and containment must be achieved is longer near the ends than in the middle. In the middle, there is only one perimeter, the one along the forward edge indicated at70inFIG. 1. At the ends, this perimeter includes the side edge as well which is indicated at75inFIG. 1. The additional perimeter length that must be accommodated at the ends may be called an “end effect.” In other words, the hood cannot be approximated as a two-dimensional configuration because of its finite length. As a result of the increased perimeter at the ends, more air must be exhausted in the vicinity of the ends of the hood than in the middle because the perimeter at the ends consists of both the forward edge70of the hood adjacent the worker and end edges75, which are perpendicular to the forward edge70.

If the minimum exhaust rate for the entire hood is to be achieved, then less air should be exhausted near the middle section than near the ends. Otherwise, an excess rate of air exhaust will occur near the middle section to insure the rate at the ends is sufficient. Thus, as a result of the end effects and the requirement of full capture and containment, more air must be drawn through the middle section than necessary. In addition, a higher volume of effluent may be generated at some parts of a hood than at others. This variability leads to the same result: some parts of the hood may require a greater exhaust rate than others.

Referring toFIG. 3, a similar problem occurs when multiple hoods are connected to a single exhaust system. For example, the hoods may be connected to a common exhaust duct191. Each hood must be balanced against the others so that each exhausts at the minimum rate that ensures full capture and containment of the contaminants. Again, ducts carrying grease aerosol should not have dampers because of the hazard caused by grease precipitation.

The particular embodiments are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention. The description, taken with the drawings, makes it apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

DETAILED DESCRIPTION

The following U.S. 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,” which entered the U.S. national stage on Jun. 11, 2003; U.S. Pat. No. 6,851,421, entitled “Exhaust Hood with Air Curtain,” and U.S. patent application Ser. No. 10/638,754, entitled “Zone Control of Space Conditioning Systems with Varied Uses,” filed Aug. 11, 2003.

Referring toFIG. 4, a kitchen hood125has a canopy145positioned over a heat/contaminant source175(such as a grill) to capture a thermal convection plume170produced by the heat/contaminant source175. The canopy145defines a recess140, having an access155. An exhaust fan (not shown) draws a flue stream105through an exhaust plenum or duct180. Negative pressure in the exhaust duct180in turn draws gases residing in the recess140through a vent130. In the vent130is a mechanical grease filter115, set in a boundary wall that defines part of the recess140. The filter reduces the mass of suspended grease particles in the resulting flue stream. The grease filter115may be an impingement filter or one based on cyclone type separation principles. The thermal convection plume170carries pollutants and air upwardly into the canopy recess140by buoyancy forces combined with forced convection resulting from the suction created by the exhaust fan. A combined effluent stream comprising the thermal convection plume170and conditioned air drawn from the space165in which the hood125is located, flows into the vortex135. This flow is extracted from the canopy recess140steadily forming the effluent stream110, which becomes the flue stream105.

The kitchen hood125may have multiple vents130, each connected to the exhaust plenum180. Alternatively, multiple exhaust plenums180may be connected to a single exhaust duct header (not shown but as indicated at191inFIG. 3) supplied by a single fan (not shown) as will be appreciated by those skilled in the relevant art. The exhaust rate through the exhaust plenum180or exhaust duct header determines the rate of extraction of effluent and indoor air from the space165by the hood125. The determination of the optimal flow rate involves a tradeoff between energy conservation and a requirement called capture and containment. Capture and containment is the state where no pollutant from the thermal plume170or the buffered volume in vortex135escapes into the conditioned space.

Full capture and containment requires the exhaust of at least some air165from the space in which the hood125is located. To conserve energy, the exhaust rate should be set at the lowest possible rate that still provides full capture and containment. This setting must account for the variability of the thermal plume170, which varies with the cooking load, stage of cooking (e.g., rendering of fat which causes dripping and attendant smoke), and random variation (e.g., random dripping from fatty foods) or steam generation. Thus, not only does the exhaust load vary along the canopy145(in the direction into the plane of the drawing), as discussed in the background section, it also varies with time. The prior art approach has been one of setting the flow rate according to the peak expected load. This approach insures that the bulk exhaust rate is high enough to provide full capture and containment by the hood, or hood portion, requiring the greatest volume of exhaust to achieve it (capture and containment), at the times of maximum instantaneous load.

Again, the load can vary along the length of a long hood or from hood to hood and the balancing problem is analogous in balancing from hood portion to hood portion as it is for balancing from hood to hood.

In the present system, a flow control system is employed to permit modulation of the exhaust from one hood125to another or from one vent130to another along a single long hood125. In addition, the potential exists to provide this flow control system, to be discussed herein, with real-time control. Thus, according to the inventive system, the exhaust rate may be controlled to achieve the lowest local (“local” referring generically to the respective hood portion or each respective hood linked to a common exhaust) exhaust rate required for the current local, instantaneous load. This is achieved by controlling the local exhaust rate by an active flow control device120linked to a real-time control (discussed in greater detail much later in the present specification).

Referring now also toFIGS. 5A, 5B, and 6, to balance flow across a single hood canopy145(FIG. 6), or across multiple hoods connected to a single exhaust system (seeFIG. 7), a flow control device120selectively blocks a portion of an exhaust vent130in a boundary wall190of the hood canopy145. The flow control device120has a flat plate112partially covering the vent130defining an aperture185. The flat plate112is selectively moved across the vent130which makes the aperture185variable-sized. The flat plate112may be moved by a linear actuator119such as a linear motor with a driver118and stator117. The flat plate112may be guided by linear bearings113. Note that the shape of the flow control device120is generally flat so that its impact on the shape of the canopy recess140is minimal. Thus, the flow control device120does not interfere with the vortical flow pattern135. Where canopy145is of great length (again, “length” referring to the dimension perpendicular to the plane of theFIG. 5Adrawing and best illustrated byFIG. 6), where multiple vents130are linked to a common exhaust duct205, the respective flow control devices120may be set to provide a larger aperture185for the vents131close to the ends of the canopy145and to provide a smaller aperture185for the vents132near the middle of the canopy145. Alternatively, if the type of cooking appliance or load varies along the length of the hood, the flow control devices120may be set accordingly.

Referring now also toFIG. 7, in multiple hoods230linked to a common exhaust header220the flow control device120may be set to restrict flow more in those canopies145protecting lower loads and to restrict flow less in canopies145protecting higher loads. Further, real-time control, which is discussed later in the present specification, may be used to control each flow control device120according to an instantaneous load sensed by a smoke, temperature, image, and/or other sensor system as described below.

Referring toFIG. 8, the canopy recess140acts as a buffer to dampen the effects of temporal variability in the load. The thermal plume170rises at a rate that is faster than the mean rate of exhaust. In wall-type hoods as illustrated, the flow circulates within the canopy recess140dissipating its energy in a turbulent cascade whilst the plume170and room air165, drawn by negative pressure created by the exhaust fan (not shown), are tapped from the canopy recess140as indicated figuratively by the arrow245. The shape of the canopy recess140augments the vortical pattern by guiding it in a circular path as illustrated at135. The vortical pattern may not be present in all hoods, but all hoods have some capacity to buffer temporal variability in the load whether a stable vortex is formed or not. More complex flow patterns may arise in other hoods, depending on the load, the hood shape and other variables.

Referring now toFIGS. 9A, 9B, and 10, another type of flow control device provides variable control of the flow rate through certain types of filters305. Referring momentarily toFIG. 9Ain particular, in certain types of filters305, the raw effluent stream enters as indicated at246and leaves at the ends of the filters as indicated at307. Examples of this type of filter are described in U.S. Pat. No. 4,872,892, which is hereby incorporated by reference in its entirety as if fully set forth herein. Focusing now onFIG. 9B, the exit flows307are selectively blocked by movable plates300thereby providing a variable exit passage325. In the embodiment of9B, the plates300translate as indicated by arrows308. In the embodiment ofFIG. 10, movable plates330are pivotably mounted by hinges335and pivoted to provide variable exit passages340.

Referring now toFIGS. 11 and 12, another embodiment of a flow control device employs scroll shutters360that unroll from spools385inside a covered compartment365. Each shutter360selectively blocks a vent370on the canopy recess side thereby providing a variable aperture350with respect to each vent370. Each vent370may be separated by a partition portion380from one or two adjacent vents370. Suitable guides and drive mechanisms are available from the field of movable shutters and may be employed in the present embodiment.

Referring toFIGS. 13 and 14, a flow control device, such as described in U.S. Provisional Application No. 60/226,953, may be employed in a duct leading from the respective vents420of a single hood or from groups of vents in one or more hoods all linked to a common exhaust (not shown in this drawing). In the embodiment ofFIGS. 13 and 14, a single hood is shown. A wall425of the recess has three vents420each leading to a respective plenum430. Each plenum is connected to a duct containing a flow control device410having smooth walls, as described in the above referenced U.S. provisional application. Each flow control device410then leads to a common plenum400from which effluent is drawn through a common exhaust415. By regulating each flow control device410separately, the flow through the respective vents420can be optimized as discussed above. A similar configuration may be used to balance respective hoods connected to a common exhaust.

Referring toFIG. 15, another type of flow control device510selectively blocks flow through a vent505(in a wall525of a canopy) using a vertical-blind type mechanism. Louvers515of the flow control device510pivot in a manner analogous to window blinds. The louvers515may be oriented with their pivot axes parallel to the tangent of the vortex135formed within a canopy recess500. In this orientation, the louvers515generate less resistance to the vortical flow. To vary the flow through the flow control device510, the louvers515are pivoted about their axes in concert to vary the net flow area through the vent505in the canopy wall525. Referring toFIG. 16, in flow control device530, which is similar to that ofFIG. 15, louvers535are located over only a portion of the vent505, since the flow may not need to be cut off 100%. Alternatively, the louvers535may be as inFIG. 15, but not close 100%.

Referring toFIG. 17, the structure of an impingement filter545is varied to modulate flow therethrough. The drawing shows a split view of a single filter in two configurations. On the left side of the drawing, the concave-back plates550and concave forward plates555are close together narrowing the flow passage between the inlets570and the outlets580. In the right side of the drawing, the separation distance is increased thereby providing a larger flow passage with correspondingly less resistant to flow therethrough. The separation distance may be varied progressively or step-wise, depending on design choice, by any suitable mechanism.

In the example shown, adjustable standoffs are used to separate the plates550and555. For example, the adjustable standoffs could be screws560with idle clips565that hold one end of the screws560at a fixed position along each screw's length and threaded holes566that traverse the lengths of the screws560when the screws are turned. The separation device may be automatic or manual, as required.

Referring toFIGS. 18, 19, and 20, in a configuration of a grease filter of a type similar to those described in U.S. Pat. No. 4,872,892, modulation of the flow of exhaust through a vent of a range hood is afforded. In this embodiment, a filter is formed substantially as described in the above patent. That is, air flows into slots620along a face of the filter as indicated at632(all similar slots—only one is labeled) and exits through the ends of tubular sections610as indicated by the outward-facing-flow symbol633. While travelling through each chamber tubular section615, the flow swirls helically due to the tangential entry of the flow at each slot620. The aperture of the slots620is varied by bending a flexible wall630of each slot by a gang pull-rod635. When the gang pull-rod is moved as illustrated inFIG. 19, the flexible walls630bend narrowing the slots620and restricting the flow.FIG. 20is a split view showing two configurations of the filter. The open configuration ofFIG. 18is illustrated on the left side ofFIG. 20and the narrowed configuration ofFIG. 19is illustrated on the right side ofFIG. 20. The aperture620may be varied progressively or in steps.

Note that while in the embodiment ofFIGS. 18-20the flow area of the inlet slots620is varied by bending a wall that forms the tubular chambers615, it is possible to accomplish a similar result by using a separate blocking plate with a hinge. That is, the wall630may be a separate element pivotably attached to the rest of the modules.

Referring toFIGS. 21A, 21B, and 21C, based on a filter design similar to that of U.S. Pat. No. 4,872,892, flow entering the filter is selectively blocked by a movable shutter plate660. Each tubular chamber650receives air through a respective slot-shaped flow aperture655and delivers it through ends649of each of the plurality of modules648as indicated by the arrows646and647, respectively. When the shutter plate660is in a relatively open position as shown inFIG. 21A, each flow aperture655is relatively large in area. When the shutter plate660is in a relatively closed position as shown inFIG. 21B, the flow aperture655is relatively small in area. Thus, the shutter plate660position may be used to control the pressure drop across the filter and consequently the flow rate across the filter.

All of the filters that are able to control flow may be used for hood balancing. If each filter is controlled independently, the flow rate through each vent of one or more hoods can be controlled independently. Each filter may be controlled in each hood of a system to flow-balance longer hoods and to balance hoods against each other. Alternatively, a single filter of a hood with multiple vents can be controlled leaving the other filters uncontrolled. This may allow the balancing of the entire hood against other hoods. In a longer hood, this solution may be less desirable because it would vary the exhaust rate across the length of the hood, which may produce inefficiencies as discussed above.

Referring toFIGS. 22A, 22B, and 22C, based on a more conventional type of filter cartridge known as an impingement filter652(also discussed above), a shutter plate653is moved to vary the size of flow apertures657. Effluent flows from the inlet flow apertures657to respective outlets658. The selective variation of the flow apertures657varies the pressure drop through the flow apertures657. Note that although in this embodiment, a shutter plate653is used to selectively block the aperture657, it is clearly possible to use a shutter plate to selectively block the outlets658or both to achieve the same effect.

The shutter plate ofFIGS. 21A-Cand22A-C are illustrated as having rectangular openings. Referring toFIGS. 23A and 23B, it is possible to employ other shapes to good effect. For example, in the embodiment ofFIG. 23A, a shutter plate680has openings675with a curved border such that access to the middle section of the filter is blocked more than the ends. In the embodiment ofFIG. 23B, the opposite is true. In the latter embodiment, a shutter plate681has openings676with a curved border such that access to the end sections is blocked more than the middle section. Either embodiment may be used with either type of filter cartridge or others not described herein, but the embodiment ofFIG. 23Bmay be more favorable in a filter such as described in U.S. Pat. No. 4,872,892 because it favors a longer travel path of the air along the flow modules providing greater grease separation in the process.

Referring toFIGS. 24A and 24B, a canopy717has a recess715bounded, in part, by a flexible accordion wall710, a filter720, and a water tank730. The filter720is partly immersed in a pool of water or other liquid735, held by the tank730. The exposed face of the filter is limited by the immersion of part of the filter720in the pool of water735and thus the flow area is reduced. As a result, the flow area may be modulated by varying how deeply the filter720is immersed. By varying this flow area, the pressure drop between the recess715and a plenum725may be selectively varied to vary the exhaust flow. To vary the depth of immersion, the filter720may be translated. The flexible accordion wall710flexes to follow the filter720. The flexible accordion wall710may be made of steel or some other material. The filter may be held by a suitable engagement device (not shown) at the distal end of the flexible accordion wall710. Cleaning solution may be used in the tank730. During shutdown of the exhaust system, the filter720may be immersed more completely in the cleaning solution to clean the filter720.

Referring now also toFIG. 24C, seal plates723prevent effluent gases from bypassing the filter720by going around it. The seal plates may extend from the top of the accordion wall710to the level of the liquid735.

In another embodiment, a recess745is bounded in part by a fixed wall section740to which a filter750is connected at a distal end thereof, as shown inFIGS. 25A and 25B. Seal plates (not shown) may be provided as in the embodiment ofFIGS. 24A-24C. The filter750is immersed partly in a tank755filled with water or a cleaning solution or some other liquid760. The pressure drop between a suction-side plenum765and the recess745across the filter750is governed by the level of the liquid760in the tank755, which in turn controls the flow area available through the filter. InFIG. 25A, the flow area is greater than the illustration ofFIG. 25Bbecause the liquid760level is higher inFIG. 25B.

Referring now toFIGS. 26 and 27, a recess788of an exhaust hood789is defined in part by a pivoting wall782that pivots at one end790and is connected by a flexible wall781at another end. The pivoting wall782also defines in part a suction side plenum775whose flow passage is reduced in flow area by the change in the angle of pivot of the pivoting wall782. The flow through the filter785in each controlled vent786may be modulated by means of an independent apparatus as shown. Thus, for balancing flow through a single hood, two or more sets (“sets” may be single in number) of vents may lead into separately controlled plenums775.

Referring toFIGS. 28A and 28B, a hood canopy, having a recess815, has a plenum810that receives exhaust air through a filter820. The pressure drop through the plenum810is modulated by varying the configuration of an obstruction805. The obstruction may, for example, be an inflatable bladder. The obstruction may be made of steel with an accordion type bellow integral thereto to permit its volume to vary. Alternatively, it may be of polymeric material or other suitable construction. The obstruction805is shown with a substantially pillow shape, but it is understood that it could have any shape. A shape that presents a face that is substantially parallel to the exit face of the filter820would be better than one that is at a substantial angle as shown so as not to favor one portion of the filter over another. Referring toFIG. 29, in a variation of the embodiments ofFIGS. 28A and 28B, wall of the plenum812has a face808and accordion ribbing807to permit the face808to be pushed into the plenum812to vary the flow channel area and thereby the pressure drop through the plenum. The same effect would be accomplished with an obstruction as inFIGS. 28A and 28B. That is, the face angled as face808could be formed in the obstruction805.

In the embodiments ofFIGS. 28A, 28B, and 29separate plenums810/812may be provided for each modulated vent814/811. Alternatively, however, because the flow obstructor805/808may be made local to a respective vent814/811, all vents may share a common plenum810/812for a single hood while still providing the ability to balance a single long hood. That is, a separate and independently controllable flow obstructor805/808may be made respective to each vent814/811to control each vent independently of the others.

Referring toFIGS. 30 and 31, a hood of substantially standard construction has a suction side plenum835which draws air through a filter820. An aperture832leads to an exhaust collar800. The aperture832is selectively blocked by a smooth obstruction830whose distance from the aperture832determines the flow area for exhaust flow through the aperture. In an embodiment, the flow obstruction830is in the shape of a sphere. Referring toFIGS. 32A and 32B, an alternative shape for a flow obstruction840is a water-drop shape. For rectangular flow apertures, other shapes may be used. Preferably, the shape of the flow obstruction is smooth so as not to generate stable and quasi-stable or periodic flow structures that result in undue precipitation of aerosols.

Referring toFIGS. 33 and 34, in a rectangular exhaust collar850fed from a suction side plenum860of an exhaust hood, flexible smooth flow obstructor plates855are provided. By varying the shape and area of a flow channel857, the pressure drop across the flow channel857is modulated providing the ability to balance suction side plenums860selectively. The shapes of the obstructor plates855may be varied by translating tongue segments856accordingly. The final actuator used to vary the shape and size of the flow channel857may be any suitable device. Note that one side only may be translated rather than both as indicated.

Referring toFIGS. 35 and 36, an exhaust hood has a suction side plenum divided into an upper part536A and a lower part536B. The upper part536A and lower part536B are connected by a series of duct sections547/548that may be selectively covered with blanks546to vary the flow through each respective vent567. In the example situation shown inFIG. 35, two of the middle-most blanks are set to block flow through ducts547and permit free flow through ducts548. By selectively blocking some ducts547and permitting flow through other ducts548, the relative flow through the vents567is altered. For example, the flow through vent567′ would be reduced relative to the flow through adjacent vents567because of the presence of the blanks546. Since no obstructions are added to a flow path, no mechanism is introduced that would cause undue precipitation.

Note that while in the embodiment ofFIGS. 35 and 36, the blanks546are fixed in place, it would be possible to arrange for the blanks546to be selectively moved into place to provide real-time modulation of flow. Thus, in this embodiment, a movable blank546would either be in place blocking flow through a respective duct section547or it would be out of the way permitting free flow through the respective duct section548. Also, while in the embodiment described above, it was presumed that the configuration of the plenum536B was such that flow through the middle vent567′ would be appreciably reduced relative to that through the other vents567, the latter plenum may be sufficiently generously sized such that the only effect of reducing the aggregate flow area by blocking ducts547may be to reduce the total flow for the entire hood without redistributing the flow along the hood. Thus, this design may be used to balance multiple hoods or single hoods, as may all the previous embodiments. The advantage of using this technique rather than a single flow control, however, is that it does not create any obstruction around which fumes and air must flow. Thus, it avoids the attending precipitation problems.

Referring toFIG. 37, a cylindrical grease filter module581has an inlet588through which raw effluent and air are drawn and an outlet592from which the cleansed air is extracted. A guide vane582causes an incoming stream584to be directed into a helical flow590so that grease and other airborne particulates precipitate on the interior walls of module581. The exit flow586is directed at approximately a right angle to the incoming stream584. Functionally, the cylindrical grease filter module is similar to that of the filters described in U.S. Pat. No. 4,872,892. However, the cylindrical walls of module581may provide lower resistance and improved cyclonic flow therewithin.

Referring toFIGS. 38 and 39, a filter cartridge583is formed from multiple cylindrical grease filter modules581. Each cylindrical grease filter module has a lever tab604which is tied to a rotator bar602which is used to rotate the cylindrical grease filter modules581in concert. By rotating the cylindrical grease filter modules581, the exposed area of the inlet588of each cylindrical grease filter module581is selectively altered. When the cylindrical grease filter modules581are in the positions shown inFIG. 38the flow through the filter cartridge583is restricted more than when they are in the positions shown inFIG. 39. This is because the inlets588are increasingly blocked by partitions606as the cylindrical grease filter modules581rotate clockwise. Note that in an alternative embodiment, the cylindrical grease filter modules581may be set immediately adjacent to each other and the blocking function of the partition plate formed by the external surfaces of adjacent cylindrical grease filter modules581. In this way, the partition plates606may be avoided.

Referring toFIGS. 40 and 41, various sensor mechanisms may be used to provide real time control of the flow rate through one or more hoods. For example, a controller950may receive input signals from one or more input devices including one or more video cameras961, infrared video cameras962, opacity sensors963, temperature sensors964, audio transducers965(e.g., microphones), manual switches966, flow rate sensors967, motion sensors968, and proximity sensors969. Based on one or more of these inputs signals the controller may control the setting of one or more output controllers970connected to any of the flow control devices described previously or described later in the present specification. Video or IR cameras may be located at any desired position, examples being indicated at920and935and as discussed later in connection withFIG. 42. Opacity and temperature sensors may be located at any positions, two examples being indicated at925/930.

The technology in image processing is more than adequate to detect a change in a volume of smoke or heat resulting from an increased cooking load. Optical and/or infrared images may be captured and a cooking load indicator derived therefrom. For example, an IR image processing algorithm that simply indicates the percentage of the field of view that is above a temperature threshold may thereby indicate escape of a thermal plume from a hood; i.e., a loss of capture and containment due to the thermal plume rising in front of the external edge of the hood. As such a loss of containment is approached, the hot buffer zone tends to grow from deep within the recess until it breaches the capture zone. This growth of the buffer zone can be indicated in precisely the same way: by imaging a predefined field of view and recognizing the size and/or shape of the hot zone (the latter being defined as a zone in which the imaged temperature exceeds a predefined threshold). This is discussed further below.

The movement of a worker, the image of the food being cooked, the presence of smoke at particular locations (such as escape of containment at the edge of the hood), the temperature of air near the hood or within the canopy recess, the proximity of a worker, etc. may all be combined to form a classification input-vector from which a condition (e.g., percentage of full-load) classification may be derived. Algorithmic, rule-based methods may be used. Bayesian networks or neural network techniques may be used. Alternatively, just one sensory indicator of load may be used to determine the current load. For example, a gas flow rate sensor for a gas grill could provide the single input signal. Many possibilities are available with current sensor, machine-classification, and control technologies.

Referring toFIG. 42, various camera angles may be employed in a load-classifier that employs optical or IR images. For example, a camera982is positioned to image a side view of a canopy972, range984, and a work area between and to adjacent them. Referring also toFIGS. 43A-43C and 44, when camera982is an IR-based camera, this side view can image a hot zone whose size and shape are dependent on effluent load (which includes heat) and exhaust rate.FIG. 45is a Schlerian image, but the shape of the hot plume in the figure is essentially the same as that provided by a thermal camera. As the exhaust rate falls below that necessary to provide capture and containment, a hot zone image provided by the camera982would expand progressively as illustrated in the series ofFIGS. 43A-43C. The hot zone changes from one associated with adequate capture and containment990, to one on the verge of breaching992, to one where capture and containment has been lost994. The changes in the images, the rate of change of images, and the history of changes in the images may be employed in a control system as described to insure that capture and containment is maintained.

Referring now toFIG. 44, other camera angle views such as provided by camera980may provide more information about the particular location of the exhaust rate deficit along the canopy edge. Illustrated inFIG. 44is an oblique view of a canopy and plume1002showing a spillover1001over an edge988near an end of the canopy972. This image may be used to provide an adjustment to exhaust flow rate favoring the portion of the canopy972close to an end thereof, as illustrated. The ability to detect spillover and its position along the edge988may be obtained by positioning a camera986looking downwardly so that it captures the entire front edge988. By taking multiple images, such as provided by cameras974,976,978,980,982, and986, it is possible to compare the shape of the three dimensional plume to determine an imminent spill. Thermal plumes have a characteristic waist1005that results from the increase in velocity and the draw of cooler air as they rise. This waist begins to bulge at the top as capture competency is lost. Again, the spillover can be detected as a three-dimensional model based on temperature or opacity.

The model or two-dimensional image(s) may be graded or thresholded. The image resolution need not be high since the structures are highly repeatable and their variability quite distinct. Thus, a relatively inexpensive imaging device may be employed with a small number of pixels. The classification process must include unrecognized classes and be capable of indicating the same. For example, if the view of a camera is occasionally obstructed, the imaging and classification process should be capable of recognizing the absence of an expected image and responding to it. Images that change suddenly or do not belong to a recognized plume shape may be classified as a bad image. A response to a bad image may be ignoring the bad image or ramping the exhaust rate to a design maximum until a recognized image is acquired again. Fiducial marks or particular features of the exhaust or cooking equipment may be employed to help determine if the camera view is obstructed. The lack of such features or fiducials in the image may indicate the loss of the image.

Activity can be indicated by live camera images, IR and optical. For example, the presence of an operator near the working area of a cooking appliance may be used as a signal indicating that the cooking load is increased. The particular activities in which the operator is engaged are likely to be highly repeatable events and readily classifiable by video classification methods as a result. For example, a particular stage of cooking may be characterized by the laying out of many pieces of meat on a hot grill. The movement of a worker's arms over the hot grill placing the meat is an activity that may be readily classified since it has distinct characteristics that distinguish it from other background activities such as cleaning or walking around the grill. Classifying the event of placing the meat on a grill may trigger a timer to anticipate when the load reaches a maximum.

Neural networks may be trained to classify the conditions in a kitchen using neural network techniques. The inputs from multiple devices may be combined to form a vector. The following are possible vectors.

a) Thresholded image is an image reduced to 1-bit map such that all temperatures (radiative) or light levels above a threshold are one color and all temperatures or light levels another color. Process image to identify contiguous domains and form an area-number histogram by counting the number of domains falling within each of series of size ranges. The histogram values define a vector. The contiguous domains can be further processed to define feature points and their relationship mapped to a vector in a manner similar to optical character recognition techniques.

b) Thresholded image may be calibrated to provide high sensitivity to smoke or the range of radiative temperatures associated with a thermal plume characteristic of the cooking appliance. The image processing may be tuned to recognize and distinguish shapes characteristic of thermal plumes for the cooking processes being monitored. The output vector in this case would be a characterization of the particular plume state.

c) Camera may simply band-pass a color, luminosity, or radiative temperature range and cumulate the total of the image corresponding to that passed signal. This would be scalar. This could be done for a quad tree where the total band-passed image area for each quadrant of the image is passed as a component vector, and this could be done down to multiple levels of a quad tree.

d) Spot temperatures of food and empty areas on a grill or other appliance may be used to predict the load. These may be derived from a single IR image and processed to report the total area, average temperature, or other lump parameters predictive of the load.

a) Opacity may be monitored between two points to detect when a plume is swelling. For example, an opacity sensor may be positioned near the inside of the edge988of the canopy972and the opacity at that point indicated.

b) The opacity near multiple points may be monitored and provided as a single vector from which it is possible to deduce the scale of turbulence induced by the thermal plume. (The opacity would be expected to vary over time at different locations along the edge in response to three-dimensional turbulent gusts giving rise to temporal and spatial variability in opacity that can be resolved using multiple opacity signals spaced apart and monitored synchronously.)

a) A simple frequency profile may be resolved into a histogram whose values correspond to the sound power in each of a series of ranges of audio frequency. The ranges need not be adjacent; they can amount to discrete band pass filters. Depending on the particular cooking process, the sound of frying, grilling meat, operator activity, etc. can make characteristic profiles.

b) A sound-signature classifier may be employed to add the temporal component to the sound classification. Depending on the type of load being monitored, certain audio signatures may be present and recognized using technology as employed in voice recognition. For example, the sound of a switch being turned on, the sounds of a spatula being used on a grill, etc. are discrete audio events that have temporal signatures that are characteristic to them.

a) Sensors placed at various locations may each provide components of a vector.

b) Sensors may be arrayed to provide a signal indicative of a spatial temperature profile which can be characterized by a more compact set of numbers than simply the whole series of temperatures. For example, the sharpest increases of temperature along respective dimensions may be reported to indicate the location of respective boundaries of the thermal plume1002.

a) The presence of food or other workpieces whose presence is predictive of load, may be sensed. The proximity sensor may be provided as a single signal or multiple signals may be provided from multiple sensors. Alternatively, the distance of the object may be sensed using a proximity sensor. For example, something that grows while it is heated could indicate a stage of a varying load.

b) The presence of an operator and the duration of the operator's presence may be used to signal the load.

a) The movement of a worker, tools, and/or workpieces may be predictive of the load.

Referring now toFIGS. 46 and 47, a great variety of different kinds of actuators may be employed to operate the various flow control devices described above. Preferably, such designs are tolerant of grease deposition from the effluent. A couple of embodiments are shown to illustrate the range of possibilities, but by no means are these intended to represent an exhaustive range. The prior art relating to hermetic seals, motor and actuator seals, high temperature, high corrosion environments, etc. are rich with candidate devices that may be employed. InFIG. 46a lever formed by a first arm1017and a second arm1018connected through a top wall1019of a canopy. The top wall is corrugated to allow it to flex so that when an actuator1013pushes the first arm1017upwardly, the second arm1018moves downwardly actuating a blind mechanism1010. The embodiment ofFIG. 46thereby provides a hermetic seal between the linear actuator1013and the blind mechanism1010, which provides flow control. InFIG. 47, another actuator embodiment has a motor and cam1021that are mounted externally from the canopy recess1012which moves a blind mechanism1022through a seal1030with a bellows1026and pushrod1032. Again the sensitive mechanisms are isolated outside the canopy recess1012. Many such mechanisms may be employed and a comprehensive discussion of them is not necessary since many suitable mechanisms are described in the machine mechanism prior art.

Referring now toFIG. 48A, a scroll shaped module1130has an inlet1132through which air is admitted as indicated by arrows1120,1110and1115. The admitted air swirls as indicated by helical arrow1117and exits as indicated by arrow1125. The helical motion is caused by the fact that the inlet1132is at a tangent to the cylindrical space1131defined by the scroll shaped module1130. The inlet1132is a gap between an inside distal edge1136and an outside distal edge1137defined by the scroll shape of the scroll shaped module1130and can be increased or reduced in width by flexing the scroll shaped module1130.

Referring toFIG. 48B, a plurality of scroll shaped modules1130are connected to each other to form a filter cartridge1140. The outside distal edge1137of each module1130is connected to a middle portion1138of an adjacent module1130(except for a last module1130′). The modules1130may be supported in any of a number of ways so that when they are drawn apart (as indicated by arrows1171) as illustrated inFIG. 49, the inlet1132expands and the resistance to the inflow of air is reduced. When the modules1130are squeezed together, as illustrated inFIG. 50(the force being as indicated by arrows1172), the inlet1132contracts and resistance to the inflow of air increases. As a result, the bank of cartridges forms a combination filter and flow throttling device.

Referring toFIGS. 51 and 52, a support mechanism, which has a back plate1180and L-shaped lower braces1195, supports scroll-shaped modules1130through tongues1148on each module. The tongues1148fit into channels1147formed in the edges of back plate1180. A sliding L-shaped seal member1185is slidably attached to one of the L-shaped lower braces1195and is moved relative to the back plate1180and lower braces1195to squeeze and expand the scroll-shaped modules1130. A tongue of one of the L-shaped lower braces1195is elongated to serve as a seal when the entire device is placed in an exhaust vent.

Referring toFIGS. 53 and 54, a set of scroll shaped modules1270have exits1250in the center thereof Thus, functionally, modules1270are like the modules1130of the previous embodiments except that their outlets are toward the middle of the filter device1299rather than along the edges thereof. As in the previous embodiment, the air enters tangentially as indicated by arrows1265and swirls in a helical motion until it exits as indicated by arrows1255. Because the air does not need to exit at the sides, side panels1285may be incorporated in a support structure1225. A single opening1220may be formed in the back (downstream face) of the support structure for air to exit. A similar configuration1235to that described in connection with the embodiment ofFIG. 51may be used to compress and expand the modules1270.

FIG. 55is a side view illustration of a canopy style hood61with adjustable side skirts2105according to an inventive embodiment. Fumes2035rise from a cooking appliance2041into a suction zone of the hood2026. The fumes are drawn, along with air from the surrounding conditioned space2036the hood61occupies, through exhaust vents and grease filters connected to a plenum, the combination indicated at2021. Suction is provided by an exhaust fan (not shown in the present drawing) connected to draw through an exhaust duct collar2011. An exhaust stream2015is then forced away from the occupied space.

At one or more sides of the exhaust hood61are movable side skirts2105which may be raised or lowered in a direction2110by means of a manual or motor drive2135. The manual or motor drive2135rotates a shaft2115which spools or unspools a pair of support lines or straps2130to raise or lower the side skirts2105. The side skirts2105and shaft2115, as well as bearings2120and the straps2130, may be hidden inside a housing2116with an open bottom2117. In a preferred embodiment, the manual or motor drive2135is a motor drive controlled by a controller2121which controls the position of the side skirts2105.

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 similar to what is obtained 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.

FIG. 56is a schematic illustration of a control system for the embodiment ofFIG. 55as well as other embodiments. The controller2121may control the side skirts automatically in response to incipient breach, for example, as described in the U.S. Patent Application entitled “Device and Method for Controlling/Balancing Fluid Flow-Volume Rate in Flow Channels,” incorporated by reference above. To that end, an incipient breach sensor2122may 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.

Another sensor input that may be used to control the position of the side skirts2105is one that indicates a current load2124. For example, a temperature sensor within the hood61, 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 skirts2105may 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 sensor2122. Of course, any of the above sensors (or others discussed below) may be used in combination to provide greater control, as well as individually.

A draft sensor2123such 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 skirts2105are 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 hood61to give a general indication of cross-currents. When cross-currents appear, the side skirts2105may be lowered. Preferably the signals or the controller2121is 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 skirts2105.

The controller2121may also control the side skirts2105by time of day. For example, the skirts2105may be lowered during warm-up periods when a grill is being heated up in preparation for an expected lunchtime peak load. The controller2121may also control an exhaust fan2136to control an exhaust flow rate in addition to controlling the side skirts2105so that during periods when unhindered access to a fume source, such as a grill, is required, the side skirts2105may be raised and the exhaust flow may be increased to compensate for the loss of protection otherwise offered by the side skirts2105. The controller may be configured to execute an empirical algorithm that trades off the side skirt2105elevation against exhaust flow rate. Alternatively, side skirt2105elevation and exhaust rate may be controlled in a master-slave manner where one variable is established, such as the side skirt2105elevation in response to time of day, and exhaust rate is controlled in response to one or a mix of the other sensors2124,2123,2127, and/or2122.

FIG. 57is a side view illustration of a backshelf hood2168with a fire safety gap2166and movable side skirts2172and a movable back skirt2188. The side skirts2172may be one or both sides and may be manually moved or automatically driven as discussed above with reference toFIGS. 55 and 56. The movable back skirt2188is located behind the appliance2180and is raised to block the movement of fumes due to cross drafts. Alternatively, the back skirt may be attached to the hood2168and lowered into position. Note that the back skirt2188is shown in a partly extended position and may be extended variable amounts depending on the degree of shielding required.

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 be hinged and pivoted into position. It may have multiple segments such that it unfolds or unrolls, for example, as does a metal rolling garage door.

FIG. 58is a side view illustration of a canopy style hood62with adjustable side skirts2210according to another inventive embodiment. The side skirts2210may be manually or automatically movable. There may be two skirts or one skirt at either of two ends of the hood62. There may be more or less skirts on adjacent sides of the hood62, such as a back side2216. In some situations where most of the access required to the appliances can be accommodated on a front side2217of the hood62, it may be feasible to lower a rear skirt2218.

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.

Also shown inFIG. 58is a suitable location for one or more proximity control sensors2230that 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 appliance41is required, in a manner similar to that of an automatic door of a public building. One or more proximity sensors2230may be used to trigger the raising or lowering of the side skirts.

As taught in U.S. Pat. No. 6,851,421 for “Exhaust Hood with Air Curtain,” 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. 59is a figurative representation of a combination of horizontal2350and vertical2345jets to be generated at the edge2340and2355of 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 in 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 is the point at which individual jets coalesce into a single planar jet.

FIG. 60is a figurative illustration of a plenum2310configured to generate the vertical2325and horizontal2330jets with diagonal horizontal jets2315at ends of the plenum2310according to an inventive embodiment. Referring momentarily toFIG. 61, most hoods2307have an exhaust vent portion2306(such as the plenum, filter, vent combination indicated at2021inFIG. 55) within the hood recess that is centrally located. Even if the hood2307has a large aspect ratio, horizontal jets2309(2330inFIG. 60) are more effective at capturing exhaust if they are directed toward the center of the hood near the ends2308of the long sides2302. Thus, in a preferred configuration of the plenum2310, the ends2335of the plenum have an angled structure2320to project the horizontal jets diagonally inward as indicated at2315.

FIGS. 62A and 62Billustrate the position of the plenum2310ofFIG. 60as would be installed in a wall-type (backshelf) hood2370as well as a combination of the horizontal and vertical jets with side skirts2365according to another inventive embodiment. This illustration shows how the plenum2310ofFIG. 60may be mounted in a backshelf hood2370. In addition, the figure shows the combination of the vertical and horizontal jets and the side skirts2365. In such a combination, the velocity of the vertical and horizontal jets may be reduced when the side skirts2365are 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,” incorporated by reference above.FIG. 62Ashows the side skirts2365in a lowered position andFIG. 62Bshows the side skirts2365in a raised position. Note that the plenum2310may be made integral to the hood and also that a similar mounting may be provided for canopy style hoods.FIG. 62Balso shows an alternative plenum configuration2311with a straight return2385on one side which generates vertical2380and horizontal2395jets along a side of the hood2370. Although shown on one end only, the return leg2385may be used on both ends and is also applicable to canopy style hoods with a mirror-symmetrical arrangement around the wall (not shown).

FIGS. 63A-63Cillustrate 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 profiles2405,2410, and2415. Directional orifices may be created to direct flow inwardly at a corner without introducing a beveled portion2415A or curved portion2410A as indicated by arrows2420inFIG. 63A.FIG. 63Dillustrates a configuration for creating a directional orifice in a plenum2450to direct a small jet2451at an angle with respect to the wall of the plenum2450. This may done by warping the wall of the plenum2450as indicated or by other means as disclosed in the references incorporated herein.

FIG. 64Aillustrates a canopy-style hood2500with vertical jets2550and a configuration that provides a vortical flow pattern2545that 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,” incorporated by reference above, the vortical flow pattern2545works with the vertical jets2550to 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.

FIGS. 64B and 64Cillustrate configurations of a canopy hood that reduce or eliminate the end effect problem of the configuration ofFIG. 64A. Referring toFIGS. 64B and 64C, a round hood2570or one with rounded corners2576reduces the three-dimensional effects that can break down the stable vortex flow2545. In either shape, a toroidal vortex may be established in a curved recess2585or2590with the vertical jets following the rounded edge of the hood. Thus, the sectional view ofFIG. 64Awould roughly be representative of any arbitrary slice through the hoods2576,2570shown in plan view inFIGS. 64B and 64C.

The figures also illustrate filter banks2580and2595. It may be impractical to make the filter banks2580and2595rounded, but they may be piecewise rounded as shown. Thus filter-holding plenum portions2581may be rectangular and joined by angled plenum portions2582.

FIG. 64Dillustrates a configuration of a canopy hood5615that reduces the end effect problem of the configuration ofFIG. 64Aby supporting the canopy using columns5610at the corners. The columns5610are shaped so as to eliminate interactions at the ends of the straight portions5620of the hood5615. Vertical jets5650do not wrap around the hood5615and neither does the internal vortex (not illustrated) since there are separate vortices along each edge bounded by the columns5610.

FIG. 65Aillustrates 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 fumes5725rise from a source appliance5711, and there is a lack of sufficient exhaust flow or there is a cross-draft, part of the fumes may escape as indicated by arrow5720. A sensor located at5715or 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.

Various sensors may be used including optical, temperature, opacity, audio, and flow rate sensor in the present context. It is also proposed that chemical sensors such as carbon monoxide, carbon dioxide, and humidity may be used for breach detection. In addition, as shown inFIG. 65B, an interferometric sensor may also be employed to detect an associated change, or fluctuation, in index of refraction due to escape of fumes.

Referring toFIG. 65B, a coherent light source5825, such as a laser diode, emits a beam that is split by a beam splitter5830to form two beams that are incident on a photo-detector5835. A reference beam5831travels directly to the detector5835. A sample beam5842is guided by mirrors5840to a sample path5860that is open to the flow of ambient air or fumes. The reference beam5831and the sample beam5842interfere in the beam splitter, affecting the intensity of the light falling on the detector5835. The composition and temperature of the fumes creates fluctuations in the effective path length of the sample path5860due to a fluctuating field of varying index of refraction. This in turn causes the phase difference between the reference5831and sample5842beams to vary causing a variation in intensity at the detector5835.

The direct output of the detector5835may be passed through a bandpass filter5800, an integrator5805, and a slicer (threshold detector)5810to provide a suitable output signal. A bandpass filter may be useful to eliminate slowly varying components that could not be a result of fumes, such as when a person leans against the detector, as well as changes that are 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.

Referring toFIG. 65C, an alternative embodiment of a detector uses a directional coupler2630A instead of a beam splitter as in the previous embodiment. Instead of mirrors, a waveguide2664is used to form a sample path2660A. A light source2625sends light into the directional coupler2630A. Light is split by the coupler2630A with one component going to the detector2635and the other passing through the sample path2660A and back to the directional coupler2630A. Fluctuations in the phase of the return light from the sample path2660A cause variations in the intensity incident on the detector2635as in the previous embodiment.

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 to a narrow channel, viscous forces will dominate and the detector will be slow to respond. Also, from a practical standpoint, filtering of slowly varying electrical signals may be more difficult. If the sample path is too long the signal might be diminished due to an averaging effect. The effect of these considerations varies with the application. It may also 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 so as 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, while this may be desirable in some detector applications, such applications are likely removed from typical commercial kitchen applications. Referring toFIG. 65D, an eddy is figuratively shown at3900. The structure of the detector3912may provide a space3918(i.e., a sample gap3918) that is large relative to the smallest substantial turbulent scale as indicated at3905. Alternatively, the structure of the detector may be smaller than the smallest turbulent scale, but thin and short as indicated at3914in which case viscous forces may not impede greatly the variation of the constituent gases in the sample path3910due to turbulent convection. As is known in the art, the speed of flow for forced convection and the temperature differences for natural convection determine how small the smallest turbulent eddies are. High turbulent energy drives the momentum effects toward smaller scales before the turbulent energy is dissipated in viscous friction. Lower turbulent energy will result in larger minimum turbulent scales. Note that an interferometric detector may detect fluctuations even when the sample gap3918is smaller than the smallest turbulent eddies, though the effect registered may not be as rapid or the fluctuations as extreme due to the species or temperature diffusion transport required.

Note that another alternative for measuring fluctuations in temperature, species, and or flow is a hot film or hot wire anemometer. Such devices, as is known, can have extremely sensitive response times. As is also known, they respond to thermal diffusivity and heat transfer coefficient, which change with species, as well as temperature and velocity, all of which fluctuate in a fume driven or fume-filled turbulent flow field.

FIG. 66illustrates a combination make-up air discharge register/hood combination with a control mechanism for apportioning flow between room-mixing discharge and short-circuit discharge flows. A hood2787has a recess2774through which fumes2794flow to plenum2785, where they are exhausted by an exhaust fan2779, usually located on the top of a ventilated structure. A make-up air unit2745replaces the exhausted air by blowing air into a supply duct2780which vents to a combination plenum2789. Plenum2789feeds a mixed air supply register2786and a short-circuit supply register2776. The fresh air supplied by the make-up air unit2745is apportioned between the mixed air supply register2786and the short-circuit supply register2776by a damper2770whose position is determined by a motor2765controlled by a controller2769.

When air is principally fed to the short-circuit supply register2776, it helps to provide most of the air that is drawn into the hood2787along 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 controller2769into the occupied space through the mixed air supply register2786. When the outside air does not have an enthalpy that is useful for space-conditioning, the controller2769should cause the make-up air to be vented through the short-circuit supply register2776.

FIG. 67illustrates 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. The make-up air may come from outdoor air, air transferred from another conditioned space, or a mixture thereof. A blower2797brings 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. Sensors2775on the outside2790, sensors2791in the occupied space2795, sensors2777in the transfer air stream2798, and/or sensors2731in the other conditioned space2796may be provided to indicate the conditions of the source air streams. A mixing box2746may be used to provide an appropriate ratio of transfer air and fresh air. The ratio will depend on the exhaust requirements of the occupied space2795. Control of the damper2770is as discussed with reference toFIG. 66.

FIGS. 68A, 68B, and 70illustrate drop-down skirts that can be manually swung out of the way and permitted to drop into place after a lapse of a watchdog timer under control of a controller shown inFIG. 69.FIGS. 68A and 68Bare side views of a drop-down skirt917that pivots from a hinge906from a magnetically suspended position over a fume source931, such as a cooking device. The skirt(s)917is (are) shown in a raised position inFIG. 68Aand in a dropped position inFIG. 68B. A magnetic holder/release mechanism936, which may include an electromagnet or permanent magnet, holds the skirt panel917in position out of the way of an area above a fume source931. The skirts917may be released after being moved up and engaged by the magnetic holder/release mechanism936. After a period of time monitored by a controller960, the skirts917may be released from the magnetic holder/release mechanism936. The controller960may be connected to a timer971, a proximity sensor926, and the magnetic holder/release mechanism936. The proximity sensor926may 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 skirt917. When released by the magnetic holder/release mechanism936, the skirt917falls into the position ofFIG. 68Bto block drafts. Preferably, as shown in the front view ofFIG. 70, there are multiple skirts917separated by gaps916. A passing worker may scan the area behind the skirts917even though the skirts are down if the worker moves at least partly parallel to the plane of the skirts917. In an embodiment, the magnetic holder/release mechanism936may be combined with the controller960, the timer971, and the proximity sensor926in a unitary device.

Although the discussion with regard to the above embodiments 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. For example, the controller may recognize when a blob larger than a particular size appears or disappears within a brief interval in a scene or when a scene remains stationary for a given interval. An example of a control process is illustrated inFIG. 73. A controller detects the latching of the skirt as step5900and starts a watchdog timer at step5905. Control then loops through5910and5905as 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 step5920and control returns to step5900where 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 ofFIGS. 55-58, 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.

Referring toFIG. 71, multiple sample gaps, such as the two indicated at4915may be linked together in a common light path by a light guide4900and a single directional coupler4830or equivalent device. As in prior embodiments, a light source4835and detector4825are connected by a directional coupler4830with focusing optics4862and one or more linking light guides4905to provide any number of sample paths.FIG. 72shows a hood edge4920with multiple individual sample devices4871which conform to any of the descriptions above linked to a common controller4925. Although parallel connections are illustrated, serial connections of either fiber or conductor may be provided depending on the configuration.

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 device120may be set manually or periodically, but at intervals to provide the local load control without the benefit of real-time automatic control.

Features of the disclosed embodiments may be combined, rearranged, omitted, etc., within the scope of the invention to produce additional embodiments. Furthermore, certain features may sometimes be used to advantage without a corresponding use of other features.

It is, thus, apparent that there is provided, in accordance with the present disclosure, methods, systems, and devices for real-time control of exhaust flow. Many alternatives, modifications, and variations are enabled by the present disclosure. While specific embodiments have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles. Accordingly, Applicants intend to embrace all such alternatives, modifications, equivalents, and variations that are within the spirit and scope of the present invention.