Improvements for control of exhaust systems

[0001] The present invention generally relates to mechanisms for minimizing the extraction of conditioned air from occupied spaces, such as mass catering kitchens.

BACKGROUND [0002] DE 42 03 916 C1 discloses an exhaust hood having a suction blower, filter system, air deflectors, an additional blower with an outlet nozzle located at the bottom of the hood to produce a horizontal wall air stream directed towards the suction or filter surface and means in the nozzle area outlet, due to which the wall air stream becomes a helical stream.

[0003] EP 0 401 583 A1 discloses an exhaust hood having a suction blower, filter system, air deflectors and a blow-out nozzle system at the front lower edge of the hood that directs the blown air as a wall jet towards the filter located at the rear of the hood at substantially horizontal method, the wall stream being limited towards the top side by the bottom side of the hood, which is approximately horizontal.

[0004] DE 31 44 777 discloses an exhaust hood comprising a suction device for fresh air, provided on its front side with an air outlet that is directed horizontally or upwards or houses respective deflector plates.

[0005] Extraction hoods are used to remove air pollutants near the source of their formation, located in an air-conditioned space. For example, one type of extraction hoods, hoods for kitchen ovens, produces suction zones directly above furnaces, fryers or other sources of air pollution. Extraction hoods tend to waste energy because they need to draw some air from the conditioned space to ensure that all debris is removed. As a result, a constant problem associated with extraction hoods is to minimize the amount of conditioned air required to achieve complete capture and containment.

[0006] Referring to Fig. 1A, a typical known extraction hood 45 is located above the kitchen stove 40 or other cooking appliance. The extraction hood 45 has a cavity 25 with at least one ventilation opening 20 (covered by a filter, also designated by reference number 20) and an exhaust chamber 20 and a channel 10 leading to an exhaust system (not shown) which draws vapors 35. An exhaust system usually consists of an external duct and one or more fans that extract air and pollutants from the building and throw them into the treatment equipment or into the atmosphere. The recess 25 of the extractor hood 45 plays an important role in capturing contaminants because heat as well as solid contaminants and vapors are usually generated in the contamination generating process. Heat causes convection driven by its own flow or streak 35, necessary to be captured by the hood inside cavity 25, while dirt is constantly being drawn out of the hood. The cavity forms a buffer zone to help ensure that transient or pulsating, violent waves in the convection streak do not leave a predefined outlet flow through the vent.

[0007] It is desirable to extract as little air as possible from the conditioned space. There are various problems that complicate the simple regulation of the exhaust flow rate so that only the amount of air that is needed is extracted to ensure that all vapors are captured and drawn out by the hood. One problem is the unpredictable transverse air currents in an air-conditioned area. Workers can use local cooling fans or leave the outer door open. Rapid movement of personnel during periods of intensive work can also generate air movement. These air currents can move the exhaust streak 35 sideways causing a part of it to leave the hood suction zone, allowing some of the vapors to escape into the occupied space.

[0008] Another problem is changes in volume production, temperature and the corresponding convective forces, and phase change in vapors. Generally, exhaust hoods operate at extraction rates corresponding to the worst case scenario. However, this means that they are overly extensive for most conditions. There is a continuing need for mechanisms to minimize pullout while maintaining vapor capture and containment.

[0009] One measure to reduce the effect of transverse air currents is to use side shields 30 as shown in Fig. 1B. The side covers 30, which are ordinary metal plates, can be attached to the ends of the extraction hood 46, as shown, allowing employees to access the kitchen appliance 40 from the front edge 36 of the appliance 40 without colliding with the covers 30. The covers 30 reduce the sensitivity of the vapor trail to transverse air currents by simply blocking the transverse air currents. Although only one is shown, there is a default assumption of the cover 30 on the opposite side of the eaves 46, perpendicular to the projection line of sight.

[0010] Figs. 1A and 1B show hoods ("with rear shelf") that are usually placed on the wall. Another type of hood is shown in Fig. 2, which is referred to as extraction hood 60. This type of hood may have extraction openings in the mirror image, as indicated by reference number 21 (with filters also designated by reference number 20), or may have an asymmetrical configuration. The hood in the form of a hood 60 of the extraction type allows workers 5 access from many sides to the device 41, such as one or more furnaces. The extraction hood is particularly susceptible to lateral air currents due to its open design.

[0011] In addition to minimizing the extraction rate while providing interception and containment, there are many opportunities in the kitchens of mass caterers to recover otherwise lost energy spent on air conditioning, such as the use of air transfer from a restaurant area for kitchen ventilation, where exhaust flow rates and intensities Ventilation flow of outside air are high. In such systems, air conditioning or space heating, ventilation and air conditioning systems (HVAC) are responsible for the consumption of large amounts of energy. A large part of the energy consumed can be saved thanks to the use of advanced control systems that have been available for years. In large buildings, the cost of advanced control systems can be justified by energy savings, but in smaller systems it is more difficult to justify capital investments. One thing is that advanced controls are expensive and in smaller systems the costs of advanced controls do not spread favorably, leading to long payback periods for incremental quality gains. Thus, complex control systems are usually economically unjustified in systems that do not consume large amounts of energy. It happens that food preparation / serving facilities are large energy consumers, but due to the low success rate of new restaurants, investors justify capital expenditure based on very short payback periods.

[0012] Less advanced control systems tend to consume energy there and when it is not required. Thus they waste energy. But less advanced control systems force further losses by not providing adequate control, including discomfort, unhealthy air, and loss of supervision, benefits, and other charges that may result. Better control systems minimize energy consumption and maintain ideal conditions by incorporating more information and using that information with better results.

[0013] Among the high energy consuming food preparation / serving facilities, such as restaurants, there are other mass catering establishments such as hotels, conference centers and food supply facilities. Much of the energy in such facilities is lost due to poor control and wastage of recoverable energy. There are many publications discussing how to optimize the performance of HVAC systems in such food preparation / dining establishments. Proposals include systems that use traditional control techniques such as proportional, integral, differential (PID) feedback loops to accurately control various air conditioning systems in combination with energy saving suggestions by carefully calculating the required extraction rates, accurately dimensioning equipment, and ensuring air transfer from zones that extracts air, such as bathrooms and kitchens, to help meet ventilation requirements with smaller amounts of make-up air, and various special tactics for recovering lost energy using energy recovery devices and systems.

[0014] Although extensive discussion of these energy conservation methods has been made in the literature, they have only had a small impact on commonly accepted practices due to the relatively long payback period of their implementation. Most installed systems lag far behind the latest developments.

[0015] There are other barriers to the broad adoption of improved control strategies in addition to economies of scale that work against smaller systems. For example, there is an incomprehensible skepticism about paying for something when benefits cannot be clearly quantified. For example, how can a buyer of a completely new building with an expensive energy system know what the energy savings are? What benchmark should you compare performance with? The benefits are rarely perceptible or perhaps even uncertain. What about the complexity of the system that conflicts with the idea of ​​building operator control? A highly automated system can give users the feeling that they cannot or do not know how to make the right settings. Complex control systems may also run the risk of reaching unintended target states due to software errors. There is certainly a constant need to reduce costs and improve the performance of control systems. The characters described below present solutions to these and other problems related to HVAC systems, especially in the area of ​​ventilation of mass catering kitchens.

[0016] The invention provides a fume hood according to claim 1. Further embodiments of the invention are described in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS [0017] The figures of Figs. 3A, 3B, 4, 5 and 10-19 as such are not an embodiment of the invention, but are intended to describe aspects of the invention.

[0018] Fig. 1A shows a side view of a known hood with a rear shelf.

[0019] Fig. 1B is a side view of a known hood with a rear shelf with side skirts.

[0020] Fig. 2 is a side view of a known extraction hood with an island device.

[0021] Fig. 3A is a side view of an extraction hood with adjustable side covers that does not form part of the present invention.

[0022] Fig. 3B is a schematic diagram of a control system for the embodiments of Fig. 3A as well as for other embodiments that does not form part of the present invention.

[0023] Fig. 4 is a side view of the hood with a rear shelf with a fire gap and movable side covers and a movable rear cover which is not part of the present invention.

[0024] Fig. 5 is a side view of an extraction hood with adjustable side covers that does not form part of the present invention.

[0025] Fig. 6 shows a schematic representation of the combination of horizontal and vertical streams to be produced at the edge of the eaves, according to the inventive embodiment.

[0026] Fig. 7A shows a schematic representation of a chamber configured to produce vertical and horizontal streams with oblique horizontal streams at the ends of the chamber, according to the inventive embodiment.

[0027] Fig. 7B is a top view of a typical eaves, showing the central location of the outlet.

[0028] Figs. 8A and 8B illustrate the position of the chamber of Fig. 7 installed in a wall-mounted hood (with back shelf) as well as the combination of horizontal and vertical jets with side skirts, according to at least one inventive embodiment.

[0029] Figs. 9A-9C show different ways of flowing a series of horizontal streams around a corner so as to avoid end effects according to the inventive (inventive) form. [0030] Fig. 9D illustrates a method of forming an opening in a chamber that redirects a small stream without separate attachment by bending the wall of the chamber.

[0031] Fig. 10 shows an extraction hood with vertical jets which is not part of the present invention and a configuration providing a vertical flow system that creates a problem of end effects.

[0032] Figures 11A and 11B show configurations of a fume hood which is not part of the present invention and which reduce or eliminate the problem of the end effects of the configuration of figure 10.

[0033] Fig. 12 shows a configuration of the extraction hood that is not part of the present invention and which reduces the problem of the final effect of the configuration of Fig. 10 due to the support of the extractor using columns at the corners shaped to eliminate impact at the ends.

[0034] Fig. 13A illustrates the configuration of a hood with a sensor that is not part of the present invention and which uses initial puncture control to minimize flow volume while providing capture and containment.

[0035] Fig. 13B illustrates an interferometric puncture sensor for use in the embodiment of Fig. 13A and in other applications that do not form part of the present invention.

[0036] Fig. 13C shows an interferometer using a directional connector and optical fibers instead of a beam splitter and mirrors, which is not part of the present invention.

[0037] Fig. 13D illustrates some mechanical measurement issues that depend on the structure of turbulence, which is not part of the present invention.

[0038] Fig. 14 shows a combination of make-up air outlet module and hood with a control mechanism for distributing the flow between the mixing outlet flow in the room and the outlet bypass flow which is not part of the present invention.

[0039] Fig. 15 shows the combination of make-up air outlet module and hood with a control mechanism for distributing the flow between the mixing outlet flow in the room and direct outflow to the hood extraction zone from outside air, air passed from another conditioned space or a mixture thereof, which combination does not form part of the present invention.

[0040] Figs. 16A-16C show drop down covers that do not form part of the invention and which can be tilted by hand and fall into place after some time.

DESCRIPTION OF THE FORM [0041] The following United States patent applications are hereby listed: Patent Application No. 10/344 505, titled "Device and Method for Controlling / Balancing Fluid Flow-Volume Rate in Flow Channels", registered on 8/11/2003; Patent Application No. 10/168 815, titled "Exhaust Hood with Air Curtain to Enhance Capture and Containment", registered on 5/5/2003 and Application No. 10 / 638,754, titled "Zone Control of Space Conditioning Systems with Varied Uses", registered on 8/11/2003

[0042] Fig. 3A shows a side view of a extraction hood 61 with adjustable side covers 105. Vapors 35 rise from the kitchen appliance 41 to the hood suction zone 61. Vapors are drawn in, along with ambient air, from the air-conditioned space 36 occupied by the hood 61, through the exhaust ventilation openings and grease filters marked with reference number 21 by the exhaust fan (not shown in this drawing) connected for extraction through the exhaust channel 11. The exhaust stream 15 is then withdrawn from the occupied space.

[0043] On one or more sides of the extraction hood 61 there are movable covers 105 that can be raised or lowered by means of a manual or motor drive 135. The manual or motor drive 135 rotates the shaft 115 which winds and unwinds a pair of wires carrying 130 to raise and lower side shields 105. Side shields 61 and spool 125, as well as bearings 120 and wires 130 can be hidden inside the housing 116 with the underside 117 open. In a preferred embodiment, the manual or motor drive 135 is a drive motor controlled by controller 121 that controls the position of side skirts 105.

[0044] Although the above and other embodiments of the invention described below have been discussed for use in the kitchen, it will readily be apparent to those skilled in the art that the same devices and features can be used in other contexts. For example, industrial buildings such as factories often accommodate large numbers of extractor hoods that extract vapors in a manner very similar to that found in a mass catering kitchen environment. In the light of this description, it should become clear how minor adjustments, such as raising or lowering the hood, adjusting the proportions when using conventional design criteria, and other such changes may be used to adapt the invention to other applications. The inventor / inventors of the present application consider / consider them perfectly within the scope of the following claims, unless this is expressly excluded.

[0045] Fig. 3B schematically illustrates the control system for the embodiments of Fig. 3A as well as for other embodiments. Controller 121 may automatically control the side guards in response to an initial puncture, e.g., as described in the US patent application "Device and Method for Controlling / Balancing Fluid Flow-Volume Rate in Flow Channels". To this end, a sensor

122 the initial puncture can be mounted close to the point where the vapors may escape due to capture and containment failures. Examples of sensors that can be used for this purpose are discussed below and include humidity, temperature, chemical, flow, and opacity sensors.

[0046] Another sensor input that can be used to control the position of side skirts 105 is the input 124 indicating the current load. For example, a temperature sensor inside the hood 61, a fuel flow indicator, or a CO or CO2 control indicator inside the hood can indicate load. When any or initial puncture or current load indicates a failure or threat for full interception and containment, side skirts 105 may be lowered. This can be done gradually, in proportion to the load. In the case of an initial breakdown, this can be done by using the integral of the direct signal from the initial breakdown sensor 122. Of course, any of the above sensors (or others discussed below) can be used in combination as well as individually to provide greater control.

[0047] A current sensor 123, such as a speedometer or low pressure sensor, or other changes may indicate transverse currents that may interrupt the flow of vapors into the interior of the hood. These are the conditions for which the side shields 105 are particularly suited to control. Suitable transducers are known, such as those used for transmitting low levels of speed and pressure. They can be placed near hood 61 for a general indication of transverse air currents. When transverse air currents arise, side shields 105 can be lowered. Preferably, the signals or controller 121 operates to provide a stable control output signal, such as by integrating the input signal, or by other means to prevent rapid cyclical operation, which would be inappropriate for raising and lowering side skirts 105.

[0048] The controller 121 may also control the side skirts 105 depending on the time of day. For example, the covers 105 can be lowered during warm-up periods when the grill is warming up, preparing it for the expected peak load at lunchtime. The controller 121 may also control the exhaust fan 136 to control the exhaust flow rate in addition to controlling the side skirts 105 so that, when periods of unrestricted access to a vapor source such as a grill are required, the side skirts 105 can be raised and the extraction flow increased to compensate for the loss of protection that the lateral covers 105 otherwise provide. The controller can be configured to perform an empirical algorithm that calculates the elevation of the side cover 105 depending on the exhaust flow rate. Alternatively, the lifting of the side cover 105 and the extraction current can be controlled in a "master - slave" system, in which one variable, e.g. raising the side cover 105 is determined in response to the time of day, and the extraction current is controlled in response to the signal of one or a combination of the other sensors 124, 123, 127 and / or 122.

[0049] Fig. 4 is a side view of the hood 46 with a rear shelf with a fire safety slot 76 and movable side skirts 70 and movable rear shield 75. The side skirts 70 can be placed on one or both sides and can be manually or automatically driven , as discussed previously with reference to Figs. 3A and 3B. The movable rear cover 75 is located behind the device 40 and is raised to block the movement of vapors due to transverse air currents. The back cover can easily be attached to hood 46 and lowered into position.

[0050] It should be noted that any of the guards discussed earlier and below can be configured based on a variety of known mechanical devices. For example, the cover can be hinged and can be turned to position.

It can have a number of segments so that it unfolds or unfolds, like some metal garage doors.

[0051] Fig. 5 is a side view of a hood type 62 with adjustable side skirts 210. The side skirts 210 can be moved manually or automatically. There can be two, one at each end of the eaves 62, or they can more or less reach adjacent sides of the eaves 62, such as to the back side 216. In certain situations where most of the required access to the devices can take place from the front side 217 of the hood 62, lowering the rear cover 218 may be feasible.

[0052] It should be noted that there is no need to discuss the location and type of drives to be used and the exact details of the manual and automatic guards, as they are within the knowledge of mechanical engineering. For the same reason, examples of relevant propulsion mechanisms are not repeated in the drawings.

[0053] Figure 5 also shows a suitable location for one or more proximity control sensors 230 that can be used in the present or other forms. Proximity sensors can be used to indicate whether access to the relevant side of the device 41 is required, in a way that does not differ from that used in the automatic door of a public building. One or more proximity sensors 230 can be used to raise and lower the side skirts.

[0054] As stated in the patent application for "Exhaust Hood with Air Curtain to Enhance Capture and Containment", a virtual barrier can be created to assist in blocking transverse air currents by means of a curtain jet located on the edge of the hood. FIG. 6 presents an ideological representation of the combination of horizontal and vertical streams that should be generated at the edge of the eaves according to the invention, which experience has shown is advantageous in terms of minimizing the exhaust flow required to achieve full capture and containment. In a preferred configuration, horizontal and vertical streams are produced by making holes in the chamber, e.g. holes with a diameter of about 3 - 6 mm spaced at regular intervals so that individual streams merge at a distance from the holes to form one flat stream. According to the invention, the initial velocities of the horizontal streams are between 2 and 3.5 times more than the initial velocities of the vertical streams, the initial velocity in this case being the point at which individual streams merge into one flat stream.

[0055] Fig. 7A illustrates a schematic representation of a chamber 310 configured to produce vertical streams 325 and horizontal streams 330, with oblique horizontal streams 315 at the ends of the chamber 310, according to the inventive embodiment. Referring temporarily to Fig. 7B, most of the hoods 307 have an exhaust vent 306 inside the hood recess 307, which is located in the middle so that even if the hood has a large span, at the ends horizontal jets 309 (330 in Fig. 7A) are more effective in capturing the emitted vapors if they are directed towards the center of the hood near the ends 308 of the long sides 302. Thus, in the preferred configuration of the chamber 310, the ends of the chamber 325 have an angular structure 320 to eject horizontal streams obliquely inward, as indicated by reference 315.

[0056] Figs. 8A and 8B show the location of the chamber 310 of Fig. 7A that could be installed in a wall ("rear shelf") hood eaves 370, as well as a combination of horizontal and vertical streams with compatible side skirts 365. This drawing shows how the chamber 210 of Fig. 7B can be mounted in the eaves 370 with a rear shelf. In addition, the figure shows a combination of vertical and horizontal jet and side shields 365. In this combination, the speed of the vertical and horizontal jets can be reduced when the side skirts 365 are lowered and increased when the side skirts are raised. It should be noted that although not shown in a separate drawing, the same control function as described in "Exhaust Hood with Air Curtain to Enhance Capture and Containment" can be used for only horizontal and only vertical streams. Fig. 8A shows side skirts 365 in a lowered position, and Fig. 8B shows side skirts 365 in the raised position. It should be noted that the 365 chamber can be made integral with the hood, and similar assembly can be done in the case of extraction hoods. Fig. 8A also shows an alternative configuration of the chamber 311 with a straight branch 385 facing backwards from one side, producing vertical streams 380 and horizontal streams 395 along one side of the hood 370. Rear branches 385, although shown at one end only, can be used at both ends, and can also be used on extraction hoods.

[0057] Figs. 9A-9C show different ways to "wrap" a series of horizontal streams around a corner so as to avoid end effects according to the inventive (inventive) form. These alternative arrangements can be obtained by shaping the appropriate chamber as shown by the appropriate profile 405, 410, 415. Directional holes can be made to direct the flow inward at the corner without introducing the bevelled portion 415A or the curvilinear portion 410A, as indicated by arrows 420. Fig. 9D illustrates how to make a directional opening in the chamber 450 to direct a small stream 451 at an angle to the chamber wall 450. This can be done by wrapping the chamber wall 450 as shown in the drawing or by other means as disclosed in the cited reference materials.

[0058] Fig. 10 shows a hood type 500 with vertical jets 550 and a configuration that provides a vortex flow system 545 in which there is a problem of end effects. The problem of the final effects is that where vortices meet in the corners, the vertical flow system is broken. As discussed in the "Exhaust Hood with Air Curtain to Enhance Capture and Containment" publication, the 545 vortex flow system works with air curtain 550 to help ensure that pulsating vapor loads can be stopped at low, medium extraction rates. However, the vortex must not bend at a right angle so that the acid-steady flow is interrupted at the corners of the hood.

[0059] Figures 11A and 11B show configurations of the extraction hood that reduce or eliminate the end-effect problem of Figure 10. Referring to Figures 11A and 11B, a round hood 570 or hood with rounded corners 576 reduces three-dimensional effects that can interrupt a steady flow vortex 545. In each of these shapes, a toroidal vortex can be induced in a curved recess 585 or 590 with vertical streams following along the rounded edge of the eaves. Thus, the cross-section of Fig. 10 it could be approximately representative of any cross-section through hoods 576, 570, shown in plan view in Figs. 11A and 11B.

[0060] The figures show filter assemblies 580 and 595. It may be impractical to make filter assemblies 580 and 595 rounded, but the individual filters may be rounded in pieces, as shown in the drawing.

[0061] Fig. 12 illustrates a hood configuration 615 that reduces the problem of the final configuration of Fig. 10 by supporting the hood using columns 610 in corners shaped to eliminate interaction at the end portions of straight portions 620 of hood 615. The vertical jets 650 do not "wrap" around the eaves 615, nor do they occur in the case of an internal vortex (not shown), because there are separate vortices along each edge bounded by columns 610.

[0062] Fig. 13A illustrates the configuration of the hood with the sensor using the initial puncture control to minimize the flow volume while providing capture and containment. Initial puncture control is discussed in the publication "Device and Method for Controlling / Balancing Fluid FlowVolume Rate in Flow Channels". In short, when the vapor 725 rises from the source device 711 and there is insufficient exhaust flow or a transverse air current is present, some of the vapor can escape, as indicated by arrow 720. A sensor located at 715 or in a nearby location can detect temperature, density or other detectable feature of vapors to indicate a puncture. The indication can be used in the controller to control the exhaust flow, as discussed in the above patent or in others, such as in the US Patent No. 6170480 entitled "Commercial Kitchen Exhaust System".

[0063] Earlier applications discussed the optical sensor, temperature, opacity, acoustic and flow rate. In this application, we propose the use of chemical sensors such as carbon monoxide, carbon dioxide and humidity sensors for puncture detection. In addition, as shown in Figure 13B, an interferometer may also be used to detect the associated change or pulsation in the refractive index due to the escape of vapors.

[0064] Referring to Fig. 13B, a coherent light source 825, such as a laser diode, emits a beam which is separated in the beam splitter 830 to form two beams incident on the photodetector 835. The reference beam 831 runs directly to the detector 835. Sampling beam 842 is guided by mirrors 840 to a sampling path 860 open to the flow of ambient air or vapors. The reference and sampling beams, 831 and 842, interfere in the beam splitter, affecting the intensity of light incident on the detector 835. The composition and temperature of the vapor produces pulsations of the actual length of the sampling path 860 due to the pulsating field of the variable refractive index. This, in turn, causes a phase difference between the reference beam 831 and the sampling beam 860, causing a change in the intensity in the detector 835.

[0065] The direct output signal from the detector 835 can be passed through the bandpass filter 800, the integrator 805 and the limiting filter (threshold detector) 810 to provide the corresponding output signal. The reason the bandpass filter may be useful is to eliminate slowly changing components that may not be caused by vapors, such as a person leaning on the detector, as well as changes too fast to be characteristic of the turbulent flow field associated with a thermal streak or air current, such as engine vibration. The integrator ensures that the transient transients do not generate false signals, and the limiting filter provides a threshold level.

[0066] It should be understood that in the case of sampling paths 860 that are large, i.e. have many wavelengths, numerous rapid changes in the output signal of the detector 835 may occur as a result of temperature changes or under the influence of a gas mixture, due to a change in the speed of light by sampling 860. Therefore, an alternative way to detect changes is to count the number of detected fringes (e.g. using a monostable circuit to shape the edge of the pulse) and to generate a signal corresponding to the number of pulses. A large number of pulses indicates a correspondingly large change in the speed of light in the sampling path. Major changes are associated with turbulent mixing and the escape of heat and / or gases from the cooking process.

[0067] Referring to Fig. 13C, in an alternative detector embodiment, a directional connector 830A is used instead of the beam splitter, as in the previous embodiment. Instead of a beam splitter, 864 optical fiber is used to form the 860A sampling path. Light source 825 sends light toward the directional connector 830A, which separates into one component, going to the detector 835 and the other, passing through the sample path 860A and back to the directional connector 830A. The pulses of the returning light phase from the 860A sampling path cause changes in the light intensity incident on the 835 detector, as in the previous embodiment.

[0068] Preferably, the interferometric detector should allow gas to flow through the measuring beam without being overly viscous. If the sampling path is closed in a narrow channel, the viscous forces will dominate and the detector will respond slowly. This may be desirable. For example, you can avoid false data that arises when an unsteady flow of gas comes into contact with the sensor, but it does not occur for a sufficiently long time or there is not enough concentration of impurities to dissipate enough gas or heat in the sample gap. Also, if the sampling path is too long, the signal may weaken under the effect of averaging, where the average speed of light on the same path remains relatively constant, although at a given point the speed varies significantly due to changes in gas content or properties. These phenomena vary depending on the application and involve the performance of certain experiments. Different detectors can be used for different applications, e.g. in the case of an extractor hood for a grill or a steam table.

[0069] To control based on puncture detection, a variety of techniques can be used. Pure feedback control can be accomplished by slowly reducing the speed of the speed controlled exhaust fan until a breakthrough threshold indication is obtained. The threshold can be, for example, a set minimum frequency of pulses from the monostable configuration described earlier, persisting for a minimum time. In response to a puncture, the speed can be increased by a set amount and the speed reduction process repeated. A more sophisticated approach can be a prediction or model-based technique in which, in addition to puncture, other factors are used to model the vapor production process as described in this application and United States Patent Application No. 10/638 754. The feedback control technique may be in accordance with the outlined US Patent Application No. 6,170,480.

[0070] It may be advantageous for the gap to be longer than the scale of the length of temperature fluctuations (or components, because the vapors can be mixed with ambient air) to provide a clear signal characteristic if the gap substantially inhibits flow. Otherwise, the transfer of temperature and components through the sampling beam would be mainly influenced by molecular diffusion slowing down the changes, for example, if the sampling beam would only be exposed in a narrow opening. However, in some detector applications this may be desirable, but such applications are likely to be eliminated from typical applications in mass catering kitchens. Referring to Fig. 13D, the microscale vortex is schematically represented by reference numeral 900. The detector structure may provide a space 918 that is large relative to the substantially smallest turbulent microscale, as indicated by reference numeral 912. Alternatively, the detector structure may be smaller than the microscale, but thin and short, as indicated by reference number 914, in which case the viscous forces may not significantly inhibit changes in gas components by sampling 910 due to turbulent convection.

[0071] Fig. 14 shows the outlet module / hood 887 combination with the control mechanism 869 and 870 for distributing the flow between the room mixing outlet flow 886 and the bypass outlet flow 876. Hood 874 has a cavity through which vapors 894 flow and are drawn by the fan hood 879, usually located on top of a ventilated structure. The make-up air module 845 replaces the extracted air by blowing it into the supply channel 880, which flows into the combination chamber supplying the mixed air outlet 886 and bypass outlet 876. The fresh air supplied by the make-up air module 845 is divided between the outlet 886 supplying mixed air and bypass outlet 876 by means of a damper 870, the position of which is set by the engine 865, which in turn is controlled by the controller 869.

[0072] When air is mainly supplied to the bypass outlet 876, it helps to ensure that most of the air will be drawn into the hood 887 along with vapors and ejected. Some believe that bypass supply of supplementary air provides some benefits in terms of efficiency. When the outside air has a temperature within the comfort zone, or when its enthalpy is lower during the cooling season or higher during the heating season, most of the make-up air should be directed by the controller 869 to the occupied space through the mixed air outlet 886. When outdoor air lacks enthalpy useful for space conditioning, controller 869 may cause make-up air to be discharged through bypass 876.

[0073] Fig. 15 shows the combination of make-up air outlet module and hood with a control mechanism for distributing the flow between the mixing outlet flow in the room and direct outflow to the hood exhaust zone, from outside air, air passed from another conditioned space or a mixture thereof. The 897 blower pumps in the transferred air, which can be used to supply some demand for make-up air and ensure that positive enthalpy is involved in the heating or cooling load. The stale air transferred to the highly ventilated kitchen environment is balanced by the total volume of supplementary (fresh) air that must be supplied. Sensors 875 may be used outdoors, 830 in occupied space, 931 in the transfer air stream and / or in the space from which the intake air is transferred to indicate the conditions of the source air streams. A mix box 846 can be used to ensure the correct ratio of air transfer and fresh air. The proportion will depend on the exhaust requirements from the space occupied 896. Throttle control 870 is as discussed with reference to Fig. 14.

[0074] Figs. 16A-16D show falling guards that can be manually deflected and which can fall after the time set on the timer has elapsed. Figs. 16A and 16B are side views of a falling cover 915 that pivots on hinge 905 from the magnet suspended position shown in Fig. 16A to the lowered position shown in Fig. 16B. The magnetic gripping / releasing mechanism 935, which may include an electromagnet or permanent magnet, holds the cover plate 915 out of the area above the vapor source 930. Guards 915 can be released when lifted and captured by the magnetic gripping / releasing mechanism 935. time programmed in the 960 controller. The 960 controller can be combined with a time relay 970, a proximity sensor 925 and a magnetic gripping / releasing mechanism 935. The 925 proximity sensor can be a sensor that is used to activate automatic doors. If nothing is in range of the proximity sensor after a certain period of time, the controller can release the cover 915. When released by the magnetic gripping / releasing mechanism 935, the cover 915 falls into the position shown in Fig. 16B to block air currents. Preferably, as shown in the front view of Fig. 16C, there is a series of shields 915 separated by slots 916. A passing employee can view the area behind the shields 915 even when they are lowered, if the worker moves at least partially parallel to the plane of the shields 915. In one embodiment, the magnetic gripping / releasing mechanism 935 can be combined with the controller 960, time relay 970 and proximity sensor 925 in a unitary device.

[0075] Although real-time control has been described in the embodiments previously described and elsewhere herein, it is known that some of the benefits of the invention can be obtained without real-time control. For example, flow control devices can be adjusted manually or periodically, but at intervals providing local control without the benefits of real-time control.

[0076] It should be noted that although in the above embodiments the discussion is mainly about air flow, it is clear that the principles of the invention may apply to any fluid. It should also be noted that instead of proximity sensors, the described release mechanisms can be triggered by video cameras connected to controllers, configured or learned to recognize events or scenes. The simplest controller configurations can be used, where a spot larger or smaller than a specific size appears or disappears within a short time in a given scene, or the scene remains unchanged for a given time. The controller detects blocking of the shields as step S900 and starts the timer in step S905. Then the control enters the loop through S910 and S915 as long as no scene changes are detected. Again, simple spot analysis is enough to determine changes in the scene. We assume here that the camera is set to observe the scene in front of the hood so that if the employee is present and working, scene changes will be constantly detected. If the scene changes are not detected until the time set on the time relay has elapsed (step S915), then the cover will be released in step S920 and the control returns to step S900, where the controller waits for the cover to lock. A similar control algorithm can be used to control the automatic lowering and lifting of the guards in the embodiments of Figs. 3A-5, discussed earlier. Instead of releasing the cover, the cover would remain extended to the cover position, and instead of waiting for the cover to lock, a scene change would be detected and the cover would be retracted automatically.

[0077] Referring to Figure 17, a number of sampling slots, such as the two designated 1815, can be joined together into a common light path by means of optical fiber 1802 and a single directional connector 1801, or an equivalent device. As in previous embodiments, the light source 1835 and detector 1825 are connected by a directional connector 1830 to a focusing optic 1862 and one or more guide optical fibers 1864 to form any number of sampling paths, such as roads 1815. Fig. 18 shows the edge of a 1920 hood with many single sampling devices 1871, corresponding to any of the above descriptions, connected to a common controller. Although parallel connections are shown, serial connections of either fibers or conductors can be used, depending on the configuration.

[0078] There is a whole range of control techniques that can be used in conjunction with the sensor configurations of Figures 13A-C, 17 and 18 operating using interference. The original signal from the sensor is a system of fringes resulting from the interference of the reference beam and the sampling beam. When the sampling beam properties change, e.g. due to a change in temperature, vapor content or mixture of ingredients resulting from cooking or another vapor-generating process, the associated speed of light running through the sampling path generally changes. The sampling path length can be chosen based on the predicted change due to the escape of fume vapors. The configuration can also be based on either the assumption that the properties will permeate to the sampling path or will be transferred to the sampling path directly by convection. These may be the issues of choosing the design variant. The signal and the way it is conditioned also depends on the choice of design variant. If a large sampling path is chosen, many interference bands can pass over the optical detector when a single portion of gas interacts with the detector; ie. when a portion of gas travels to the sampling path or spreads its fractions in that sampling path so that it changes the speed of light along the sampling path. If a puncture occurs, in most cases the flow will be a turbulent thermal convection streak containing a mixture of vapors and ambient air, causing a series of back and forth shifts in the band pattern when vapors and ambient air interact with the detector. Alternatively, the process may, if the transfer takes place via molecular diffusion or viscous flow as a result of the scale of the device, the vapor-air mixture may be averaged, generating a slower response and a single shift of the bands back and forth. Each fringe shift can generate many light and dark pulses, but again it depends on the scale of the device and the specific wavelength of the chosen light.

[0079] By experimenting with full containment and puncture conditions, a characteristic arrangement can be obtained and identified in the signal. In the case of the grill, thermal convection is strong and the vapor properties are such that continuous mixing with the surrounding air generates a pulse train as soon as the vapors escape from the hood. Thus, the simple frequency of the bands (e.g. by transforming into pulses and counting), as mentioned earlier, you can compare with the threshold level (background) to determine if a puncture occurred.