AU635695B1 - Laboratory fume hood control apparatus having improved safety considerations - Google Patents

Description

1- 635695

AUSTRALIA

PATENTS ACT 1990 rOM0 PT.F.RTP P R rTR T r A TTC nW FOR A STANDARD PATENT O R I G I NA L 9 a.

4 1 b "1 arne of Applicant: to* 4 it Actual Inventor: A~ddress for Service: too.-Invention Title: LANDIS GYR POWERS, INC.

Osman Ahmed.

SHELSTON WATERS Clarence Street SYDNEY NSW 2000 "LABORATORY FUME HOOD CONTROL APPARATUS HAVING IMPR'OVED SAFETY CONS IDERATIONS" S i The following statement is a full description of this invention, includingj the best method of performing it known to us:la LABORATORY FUME HOOD CONTROL APPARATUS jAVING IMPROVED SAFETY CONSIDERATIONS Cross Reference to Related Applications a. S a Ia a 13 14 S:.o 15 16 17 S 18 1. Title: Inventors: Serial No.: 2. Title: Inventors: Serial No.: 3. Title: Inventors: Serial No.: 4. Title: Inventors: Serial No.: Apparatus for Determining the Position of a Moveable Structure Along a Track David Egbers and Steve Jacob 591,102 A System for Controlling the Differential Pressure of a Room Having Laboratory Fume Hoods Osman Ahmed, Steve Bradley 589,931 A Method and Apparatus for Determining the Uncovered Size of an Opening Adapted to be Covered by Multiple Moveable Doors Osman Ahmed, Steve Bradley and Steve Fritsche 590,194 Apparatus for Controlling the Ventilation of Laboratory Fume Hoods Osman Ahmed, Steve Bradley, Steve Fritsche and Steve Jacob 590,195 I a a a a 24 The present invention relates generally to the control of the ventilation of laboratory fume hoods, and 26 more particularly to an improved method and apparatus for 27 controlling the ventilation of fumes from one or more fume 28 hoods that are typically located in a laboratory 29 environment.

Fume hoods are utilized in various laboratory 31 environments for providing a work place where potentially dangerous chemicals are used, with the hoods comprising an -2- 1 enclosure having moveable doors at the front portion 2 thereof which can be opened in various amounts to permit a 3 person to gain access to the interior of the enclosure for 4 the purpose of conducting experiments and the like. The enclosure is typically connected to an exhaust system for 6 removing any noxious fumes so that the person will not be 7 exposed to them while performing work in the hood.

8 Fume hood controllers which control the flow of 9 air through the enclosure have become more sophisticated in recent years, and are now able to more accurately maintain 11 the desired flow characteristics to efficiently exhaust the 12 fumes from the enclosure as a function of the desired 13 average face velocity of the opening of the fume hood 14 required to effectively exhaust the fume hood. The average 15 face velocity is generally defined as the flow of air into 16 the fume hood per square foot of open face area of the fume 4 17 hood, with the size of the open face area being dependent 18 upon the position of one or more moveable doors that are 19 provided on the front of the enclosure or fume hood, and in most types of enclosures, the amount of bypass opening that 21 is provided when the door or doors are closed. 22 The fume hoods are exhausted by an exhaust system 4 423 that includes one or more blowers that are capable of being 24 driven at variable speeds to increase or decrease the flow of air from the fume hood to compensate for the varying 26 size of the opening or face. Alternatively, there may be 27 a single blower connected to the exhaust manifold that is, 28 in turn connected to the individual ducts of multiple fume St"29 hoods, and dampers may be provided in the individual ducts to control the flow from the individual ducts to thereby 31 modulate the flow to maintain the desired average face 32 velocity. There may also be a combination of both of the S33 above described systems.

34 The doors of such fume hods can be opened by raising them vertically, often referre.d to as the sash 36 position, or some fume hoods have a number of doors that 37 are mounted for sliding movement in typically two sets of 38 tracks. There are even doors that can be moved -3- 1 2 3 4 6 7 8 9 11 12 13 14 16 17 18 19 21 22 23 24 26 27 28 29 31 32 33 34 36 37 38 horizontally and vertically, with the tracks being mounted in a frame assembly that is vertically moveable.

Prior art fume hood controllers have included sensing means for measuring the position of the doors and then using a signal proportional to the sensed position to thereby vary the speed uf the blowers or the position of the dampers. While such control has represented an improvement in the control of fume hoods, there are circumstances that arise that require further adjustment of the exhausting of such hoods that such a controller cannot perform. Significant improvements are disclosed in the above referenced cross related applications, and particularly Apparatus for Controlling the Ventilation of laboratory Fume Hoods by Ahmed et al., Serial No. 52370.

It is desirable for some fume hoods to have a filtering means typically located in the upper portion of the fume hood enclosure between the working area and the exhaust duct for the purpose of retaining noxious fumes and effluents. The filter medium for such filtering means often can become loaded with residue or the like which over time will tend to restrict the flow of air through-the filter medium. The resistance to flow through the medium and out of the exhaust duct will result in inefficiency of operation of the fume hood, and can also create a potentially hazardous condition. The inability of a fume hood to efficiently expel air will also increase the energy requirements during operation of the fume hood.

Accordingly, it is a primary object of the present invention to provide an improved apparatus for controlling the ventilation of laboratory fume hoods which apparatus has desirable safety features as well as maintaining good energy efficiency.

Another object of the present invention is to provide such an improved apparatus which is adapted to determine if a filter medium is loaded beyond a predetermined amount and provide a signal that is indicative of such a condition.

Still another obiect of the present invention is -4- 1 to provide such an improved apparatus which provides a 2 visual or audible indication in response to the loading 3 signal being generated.

4 Yet another object of the present invention is to provide such an improved apparatus which has emergency 6 switches near each fume hood, with the switch controlling 7 the fume hood when actuated so that the fume hood can 8 operate in an emergency mode, but also provide an 9 indication to a central building console of a building supervisory and control system for heating ventilating and 11 air conditioning apparatus.

12 Another object of the present invention is to 13 provide an improved apparatus which has additional 14 desirable safety features, including the feature of 15 controlling the differential pressure within the room to a 16 level that is slightly less than the pressure within a 17 reference space sut as a corridor, adjacent room or the 18 like, in the event of an emergency chemical spill or the 19 like within a fume hood which results in the fume hood increasing its exhaust flow to an emergency level. This is 21 highly desirable so that any persons within the room can 22 open an outwardly opening external door to the room to 23 escape from the room. Also, the slight difference in the e* 24 differential pressure will not normally result in an inwardly opening door being forced open.

26 These and other objects will become apparent upon 27 reading the following detailed description of the present, 28 invention, while referring to the attached drawings, in 29 which: FIGURE 1 is a schematic block diagram of 31 apparatus of the present invention shown integrated with a 32 room controller of a heating, ventilating and air 33 conditioning monitoring and control system of a building; 34 FIG. 2 is a block diaqram of a fume hood controller, shown connected to an operator panel, the 36 latter being shown in front elevation; 37 FIG. 3 is a diagrammatic elevation of the front 38 of a representative fume hood having vertically operable 1 sash doors; 2 FIG. 4 is a diagrammatic elevation of the front 3 of a representative fume hood having horizontally operable 4 sash doors; FIG. 5 is a cross section taken generally along 6 the line 5-5 of FIG. 4; 7 FIG. 6 is a diagrammatic elevation of the front 8 of a representative combination sash fume hood having 9 horizontally and vertically operable sash doors; FIG. 7 is an electrical schematic diagram of a 11 plurality of door sash position indicating switching means; 12 FIG. 8 is a cross section of the door sash 13 position switching means; 14 FIG. 9 is a schematic diagram of electrical 15 circuitry for determining the position of sash doors of a 16 fume hood; 17 FIG. 10 is a block diagram illustrating the 18 relative positions of FIGS. 10a, 10b, 10c, 10d and 10e to 19 one another, and which together comprise a schematic diagram of the electrical circuitry for the fume hood 21 controller means embodying the present invention; 22 FIGS. 10a, 10b, 10c, 10d and 10e, which if 23 connected together, comprise the schematic diagram of the 0t' 24 electrical circuitry for the fume hood controller means embodying the present invention; 26 FIG. 11 is a flow chart of the general operation 27 of the fume hood controller of the present invention; 28 FIG. 12 is a flow chart of a portion of the 29 operation of the fume hood controller of the present invention, particularly illustrating the operation of the 31 feed forward control scheme, which is included in one of 32 the preferred embodiments of the present invention; 33 FIG. 13 is a flow chart of a portion of the 34 operation of the fume. hood controller of the present invention, particularly illustrating the operation of the 36 proportional gain, integral gain and derivative gain 37 control scheme, which embodies the present invention; and, 38 FIG. 14 is a flow chart of a portion of the -6- 1 operation of the fume hood controller of the present 2 invention, particularly illustrating the operation of the 3 calibration of the feed forward control scheme.

4 Detailed Description It should be generally understood that a fume 6 hood controller controls the flow of air through the fume 7 hood in a manner whereby the effective size of the total 8 opening to the fume hood, including the portion of the 9 opening that is not covered by one or more sash doors will have a relatively constant average face velocity of air 11 moving into the fume hood. This means that regardless of 12 the area of the uncovered opening, an average volume of air 13 per unit of surface area of the uncovered portion will be 14 moved into the fume hood. This protects the persons in the laboratory from being exposed to noxious fumes or the like 16 because air is always flowing into the fume hood, and out 17 of the exhaust duct, and the flow is preferably controlled S" 18 at a predetermined rate of approximately 75 to 125 cubic 19 feet per minute per square feet of effective surface area of the uncovered opening. In other words, if the sash-door 21 or doors are moved to the maximum open position whereby an 22 operator has the maximum access to the inside of the fume 23 hood for conducting experiments or the like, then the flow 24 of air will most likely have to be increased to maintain the average face velocity at the predetermined desired 26 level.

27 Since the total number of fume hoods that are 28 present in laboratory rooms can be quite large in many 29 installations, it should be appreciated that a substantial volume of air may be removed from the laboratory room 31 during operation. Also, since the HVAC system supplies air 32 to the laboratory zoom, there may be a substantial change 33 in the volume of air required to be supplied to a room 34 depending upon whether the fume hoods are frequently being opened, or other changes occur.

36 Because much of the work that is performed in 37 many laboratories involves chemicals which may be -7- 1 dangerous, it is often desirable to maintain the 2 differential pressure within the laboratory at a lower 3 pressure than the hallways outside of the laboratory or 4 adjacent rooms. If the laboratory has several fume hoods which are exhausting air from the room, the amount of air 6 supplied to the laboratory will necessarily be greater than 7 a comparably sized room without fume hoods, and there may 8 be increased difficulty in maintaining the desired 9 differential pressure within the laboratory if the fume hoods have their sash doors frequently opened.

11 If the differential pressure in a laboratory 12 room is maintained at a reduced level relative to the 13 reference space, noxious fumes which may escape from a fume 14 hood due to an accident or other cause will not permeate beyond the room. The system involves a room controller and 4.16 an exhaust controller which are part of the heating, 17 ventilating and air conditioning apparatus of the building.

18 The room controller is of the type which can receive 19 electrical signals from the fume hood controllers, which signals are proportional to the volume of air that is being 21 exhausted throtuh the fume hoods. Since each fume hood. can 22 be exhausting an amount of air that can vary considerably 23 depending upon its initial setting of the desired average 24 face velocity and the amount by which the sash doors are opened, it is very advantageous that the volume indicating S• 26 signals be communicated from each of the fume hood 27 controllers to the room controller so that it can modulate.

28 the volume of air that is being supplied to the room which 29 assists it in maintaining the differential pressure at the desired level with relatively quick response times.

31 Broadly stated, the present invention is directed 32 to an improved fume hood controlling apparatus that is S33 adapted to provide desirable operational safety features I 34 for persons who use the fume hoods to perform experiments or other work, and also for the operator of the facility in 36 which the fume hoods are located. More particularly, the 37 apparatus of the present invention, in one of its preferred 38 embodiments is iur use with fume hoods of the type which -8- 1 include a filtering means located between the fume hood 2 enclosure and the exhaust duct and the apparatus is adapted 3 to determine if a f ilter nediun is loaded beyond a 4 predetermined amount and provide a loading signal that is indicative of such a condition. The apparatus also 6 provides a visual or audible indiication in response to the 7 loading signal being generated. The apparatus also has 8 emergency switches near each fume hood, with the switch 9 controlling the fume hood when actuated so that the fume hood can operate in an emergency mode, and also provides an 11 indication to a central building console of a building 12 supervisory and control system for heating ventilating and 13 air conditioning apparatus.

14 In another embodiment, the system has additional desirable safety features, including the feature of *16 controlling the differential pressure within the room to a 17 level that is slightly less than the pressure within a 18 reference space such as a corridor, adjacent room or the 19 like, in the event of an emergency chemical spill or the like within a fume hood which results in the fume hood 21 increasing its exhaust flow to an emergency level. Th is is 22 highly desirable so that any persons within the room can 23 open an outwardly opening external door to the room to 24 escape from the room. Also, the slight difference in~ the differential pressure will not normally result in an 26 inwardly opening door being forced open. To this end, the 27 system utilizes emergency switches adjacent each fume hood' 28 and also an emergency switch that is preferably located *29 outside of the room containing the fume hoods.

Turning now to the drawings, and particularly 31 FIG. 1, a block diagram I.s shown of several fume hood 32 controllers 20 embodying the present invention intercon- 33 nected with a room controller 22, an exhaust controller 24 34 and a main czontrol conscile 26. The fume hood controllers 20 are interconnected with the roomi controller 22 and with 36 the exhau~t controller 24 and the main control console 26 37 in a local area network illustrated by line 28 which may be 38 a multiconductor cable or the like. The room controller, -9- 1 the exhaust controller 24 and the main control console 26 2 are typically part of the building main HVAC system in 3 which the laboratory rooms containing the fume hoods are 4 located. The fume hood controllers 20 are provided with power through line 30, which is at the proper voltage via 6 a transformer 32 or the like.

7 The room controller 22 preferably is of the type 8 which is at least capable of providing variable air volume 9 of air that is supplied to the room, and may be a Landis Gyr Powers System 600 SCU controller. The room controller 11 22 is capable of communicating over the LAN lines 28 and is 12 interconnected with the exhaust controller which is 13 preferably part of the same hardware as the room 14 controller, it is part of the System 600 SCJ 4115 controller. The System 600 SCU controller is a 16 commercially available controller for which extensive a17 documentation exists. The User Reference Manual, Part No.

a.

18 125-1753 for the System 600 SCJ controller is specifically 19 incorporated by reference herein.

The room controller 20 receives signals via lines 21 81 from each of the fume hood controllers 20 that provides 22 an analog input signal indicating the volume of air that is 23 being exhausted by each of the fume hood controllers 20 and 24 a comparablo signal from the exhaust controller 24 that provides an indication of the volume of air that is being 26 exhausted through the main exhaust system apart from the 27 fume hood exhausts. These signals coupled with signals' that are supplied by a differential pressure sensor 29 29 which indicates the pressure within the room relative to the reference space enable the room controller to control 31 the supply of air that is necessary to maintain the 32 differential pressure within the room at a slightly lower 33 pressure than the reference space, preferably within 34 the range of about 0.05 to about 0.1 inches of water, which vesults in the desirable lower pressure of the room 36 relative to the reference space. However, it is not so low 37 that it prevents persons inside the laboratory room from 38 opening the doors to escape in the event of an emergency, 1 particularly if the doors open outwardly from the room.

2 Also, in the event the doors open inwardly, the differ- 3 ential pressure will not be so great that it will pull the 4 door open due to excessive force being applied due to such pressure.

6 The sensor 29 is preferably positioned in a 7 suitable hole or opening in the wall between the room and 8 the reference space and measures the pressur~e on one side 9 relative to the other. Alternatively, a velocity sensor may be :?3rovided which measures the velocity of air moving 11 through the opening which is directly proportionial to the 12 pressure difference between the two spaces. Of course, a 13 lower differential pressure in the room relative to the 14 reference space would mean that air would be moving into the room which is also capable of being detected.

14016 Referring to FIG. 2, a fume hood controller 20 is *17 illustrated with its input and output connector ports being 18 identified, and the fume hood controller 20 is connected to 19 an operator panel 34. It should be understood that each fume hood will have a fume hood controller 20 and that an 21 operator panel will be provided with each fume hood 22 contraller. The operator panel 34 is provided for each of *23 the fume hoods and it is interconnected with the fume hood 24 controller 20 by a line 36 which preferably comprises a multi-conductor cable having six conductors. The operator 26 panel has a connector 38, such as a 6 wire RJ111 type 27 telephone jack for example, into which a lap top personal .28 computer or the like may be connected for the purpose of 29 inputting information relating to the configuration or operation of the fume hood during initial installation, or 31 to change certain operating parameters if necessary. The 32 operator panel 34 is preferably mounted to the fume hood in 33 a convenient location amdapted to be easily observed by a 34 person who is working with the fume hood.

The fume hood controller operator panel 34 36 includes a liquid crystal display 40 which when selectively 37 activated provides the visual indication of various aspects 38 of the operation of the fume hood, including three digits -11- 1 42 which provide the average faice velocity. The display 2 illustrates other condition.rs such as low face velocity, 3 high face velocity and emergency condition and an indi- 4 cation of controller failure.

The operator panel may have an alarm 44, and an 6 emergency purge switch 46 which an operator c press to 7 purge the fume hood in the event of an accident. In this 8 regard, the fume hood controller is programmed to prefer- 9 ably open the exhaust damper or control the blower so that it will exhaust the m~aximum amount of air that is possible 11 in the even the purge switch 46 is activated. Alterna- 12 tively, the amount of air can be preset to another value, 13 if desired, such as 75% of maximum.

*14 The operator panel has two au~iliary switches 48 which can be used for various customer needs,~ including 16 day/night modes of operation. It is contemplated that *17 night time mode of operation would have a different and 18 preferably reduced average face velocity, presumably 19 because no one would be working in the area and such a lower average face velocity would conserve energy. An 21 alarm silence switch 50 is also preferably provid~ad to 22 extinguish the alarm.

*23 Fume hoods come in many different styles, sizes "a *24 and configurations, inaluding those w)-ich have a sin~gle sash door or a number of sash doors, with the sash doors 26 bei.ng moveable vertically, horizontally or in both direc- 27 tions. Additionally, various fume hoods have different.

*28 amounts of by-pass flow, the amount of flow per- 'A 29 mitting opening that exists even when all of the sash doors are as completely closed as their design permits. Other 31 design considerations involve whether there is some kind of 32 filtering means included in the fume hood for confining 33 fumes within the aiood during operation. While many of 34 these design considerations must be taken into account in providing efficient and effective control of the flume 36 hoods, the apparatus of the prosent invention can be 37 configured to account for virtually all of thie above 38 described design variables, and effective and extremely -12- 1 fast control of the fume hood ventilation is provided.

2 Referring to FIG. 3, there is shown a fume hood, 3 indicated generally at 60, which has a ve~rtically operated 4 sash door 62 which can be moved to gain access to the fume hood and which can be moved to the substantially closed 6 position as shown. Fume hoods are gene. ally designed so 7 that even when a door sash such as dioor sash 62 is comn- 8 pletely closed, there is still some amount of opening into 9 the fume hood through which air can pass. This opening is generally referred to as the bypass area and it can be 11 determined so that its effect can be taken into considera- 12 tion in controlling the flow of air into the fume hood.

13 Some types of fume hoods have a bypass opening that is 14 located above the door sash while others are below the same. In some fume hoods, the first amount of movement of 16 a sash dour will increase the opening at the bottom of the 17 door shown in FIG. 3, for example, but as the door is wo 8 raised, .c will -merely cut off the bypass opening so that **19 the effective size of the total opening of the fume hood is maintained relativtely constant for perhaps the first one- 21 fourth amount of movement of the sash door 62 through -its 22 course of travel.

23 other types of fume hoods may include several 24 horizontally moveable sash doors 66 such as shown in FIGS.

4 and 5, with the doors being movable in upper and lower 26 pairs of adjacent tracks 68. When the doors are positioned 27 as shown in FIGS. 4 and 5, the fume hood opening is' 28 completely closed and an operator may move the doors in the *29 horizontal direction to gain access to the fume hood. Both of the fuines'hoods 60 and 64 have an exhaust duct 70 which *31 generally extends to an exhaust system which may be that of 32 the MVAC apparatus previously described.

33 The fume hood 64 is of the type which includes a 34 filtering structure shown diagrammatically at 72 which kiltering structure is intended to keep noxious fumes and 36 other contaminarits from exiting the fume hood into the 37 exhaust system. The filtering structure includes a filter 38 medium which is adapted to entrap fumes and effluents and -1.3- 1 keep themn from being exhausted, and the filter medium may 2 become loaded over time as a result of residue accumulation 3 on the medium. When the residue builds up, a greater 4 resistance to air flow through the medium is experienced, which is potentially dangr~jus if air cannot be exhausted 6 from the fume hood. Also, more energy is required to 7 remove the air from the fume hood due to the increased 8 resistance to flow.

9 In accordance with an important aspect of the present invention, a differential pressure sensor, 11 generally indicated at 55, is provided and measures the 12 differential pressure of one side of the filtering 13 structure relative to the other. The sensor is adapted to 14 provide an analog input voltage to the fume hood controller 20 that is proportional to the degree of loading of the 16 f ilter medium. When the signal reaches a predetermined 17 level, the fume hood controller 20 detects the same and 18 provides ai warning indication on the operator panel 34, ,*19 which alerts anyone using the fume hood of such condition.

to.~ 20 Alternatively, the predetermined signal level may be 21 detected by the controller and it can be adapted to sbund 22 the alarm 44.

23 Referring to FIG. 6, there is shown a combination 24 fume hood which has horizontally movable doors 76 which are 64:925 similar to the doors 66, with the fume hood 74 having a 26 frame structure 78 which carries the doors 76 in suitable 27 tracks and the frame structure 78 is also vertically' 28 movable in the opening of the fume hood.

29 OtheL types of fume hoods may include several 17orizontally moveable sash doors 66 such as shown in FIGS.

*31 4 and 5, with the doors being movable in upper and lower 32 pairs of adjacent tracks 68. When the doors are positioned 33 as shown in FIGS. 4 and 5, the fume hood opening is 34 completely closed and an operator may move the doors in the horizontal direction to gain access to the fume hood. Both 36 of the fumes hoods 60 and 64 have an exhaust duct 70 which 37 generally extends to an exhaust system which may be that of *38 the HVAC apparatus previously described. The fume hood 64 -14- 1 also includes a filtering structure shown diagrammatically 2 at 72 which filtering structure is intended to keep noxious 3 fumes and other contaminanti from exiting the fume hood 4 into the exhaust system. Referring to FIG. 6, there is shown a combination fume hood which has horizontally 6 movable doors 76 which are similar to the doors 66, with 7 the fume hood 74 having a frame structure 78 which carries 8 the doors 76 in suitable tracks and the frame structure 78 9 is also vertically movable in the opening of the fume hood.

The illustration of FIG. 6 has portions removed 11 as shown by the break lines 73 which is intende to 12 illustrate that the height of the fume hood may be greater 13 than is otherwise shown so that the frame structure 78 may 14 be raised sufficiently to permit adequate access to the 15 interior of the fume hood by a person. There is generally 16 a by-pass area which is identified as the vertical area 17 and there is typically a top lip portion 77 which may be S. 18 approximately 2 inches wide. This dimension is preferably 19 defined so that its effect on the calculation of the open 20 face area can be taken into consideration. Similarly, the 21 dimension of the lower sash portion 79 of the frame is 22 similarly defined for the same reason.

23 While not specifically illustrated, other 24 combinations are also possible, including multiple sets of 25 vertically moveable sash doors positioned adjacent one 26 another along the width of the fume hood opening, with two 27 or more sash doors being vertically moveable in adjacent' 28 tracks, much the same as residential casement windows.

29 The fume hood controller 20 is adapted to operate the fume hoods of various sizes and configurations as has 31 been described, and it is also adapted to be incorporated 32 into a laboratory room where several fume hoods may be 33 located and which may have exhaust ducts which merge into 34 a common exhaust manifold which may be a part of the building HVAC system. A fume hood may be a single self- 36 contained installation and may have its own separate 37 exhaust duct. In the event that a single fume hood is 38 installed, it is typical that such an installation would 1 have a variable speed motor driven blower associated with 2 the exhaust duct whereby the speed of the motor and blower 3 can be variably controlled to thereby adjust the flow of 4 air through the fume hood.

Alternatively, and most typically for multiple 6 fume hoods in a single Irea, the exhaust ducts of each fume 7 hood are merged into one or more larger exhaust manifolds 8 and a single large blower may be provided in the manifold 9 system. In such types of installations, control of each fume hood is achieved by means of separate dampers located 11 in the exhaust duct of each fume hood, so that variation in 12 the flow can be controlled by appropriately positioning the 13 damper associated with each fume hood.

14 The fume hood controller is adapted to control 'ee 15 virtually any of the various kinds and styles of fume hoods "16 that are commercially available, and to this end, it has a 17 number of input and output ports (lines, connectors or 18 connections, all considered to be equivalent for the 19 purposes of describing the present invention) that can be connected to various sensors that may be used with -the 21 controller. As shown in FIG. 2, it has digital output or 22 DO ports which interface with a digital signal/analog 23 pressure transducer with an exhaust damper as previously 24 described, but it also has an analog voltage output port for controlling a variable speed fan drive if it is to be 26 installed in that manner. There are five sash position.

27 sensor ports for use in sensing the position of both 28 horizontally and vertically moveable sashes and there is 29 also an analog input port provided for connection to an eihaust air flow sensor 49.

31 A digital input port for a second emergency 32 switch 51 is provided and digital output ports for S33 outputting an alarm horn signal as well as an auxiliary 34 signal is provided. An analog output port is also provided for providing a volume of flow signal to the room 36 controller 22. This port is connected to the room 37 controller by the individual lines 81 which extend from 38 each of the fume hood controllers -16- 1 From the foregoing discussion, it should be 2 appreciated that if the average face velocity is desired to 3 be maintained and the sash position is changed, the size of 4 the opening can be dramatically changed which may tnen require a dramatic change in the volume of air to maintain 6 the average face velocity. While it is known to 'ontrol a 7 variable air volume blower as a function of the sash 8 position, the fume hood controller apparatus of the present 9 invention improves on that known method by incorporating additional control schemes which dramatically improve the 11 capabilities of the control system in terms of maintaining 12 relatively constant average face velocity in a manner 13 whereby reactions to perturbations in the system are 14 quickly made. Such improvements are illustrated, described 15 and claimed in the above referenced cross related 16 applications.

17 To determine the position of the sash doors, a 4*o 18 sash position sensor is provided adjacent each movable sash S19 door and it is generally illustrated in PFGS. 7, 8 and 9.

20 Referring to FIG. 8, the door sash position indicator.,com- 21 prises an elongated switching mechanism 80 of relatively 22 simple mechanical design which preferably consists of a 23 relatively thin polyester base layer 82 upon which is 24 printed a strip of electrically resistive ink 84 of a known :l 25 constant resistance per unit length. Another polyester 26 base layer 86 is provided and it has a strip of elec- 27 trically conductive ink 88 printed on it. The two base 28 layers 82 and 86 are adhesively bonded to one another by 29 two beads of adhesive 90 located on opposite sides of the 30 strip. The base layers are preferably approximately five- 31 thousandths of an inch thick and the beads are approxi- 32 mately two-thousandths of an inch thick, with the beads 33 providing a spaced area between the conductive and resis- 34 tive layers 88 and 84. The switching mechanism 80 is preferably applied to the fume hood by a layer of adhesive 36 92.

37 The polyester material is sufficiently flexible 38 to enable one layer to be moved toward the other so that -17- 1 contact is made in respon~se to a preferably spring biased 2 actuator 94 carried by the appropriate sash door to which 3 the strip is placed adjacent to so that when the sash door 4 is moved, the actuator 94 moves along the switching mechanism 80 and provides contact between the resistive and 6 conductive layers which are then sensed by electrical 7 circuitry to be described which provides a voltage output 8 that i~i irndicative of the position of the actuator 94 along 9 the lenigth of the switching mechanism. Stu±ted in other words, the actuator 94 is carried by the door and therefore 11 provides an electrical voltage that is indicative of the 12 position of the sash door.

13 The actuator 94 is preferably spring biased 14 toward the switching mechanism 80 so that as the door is 15 moved, sufficient pressure is applied to the switching 16 mechanism to bring the two base layers together so that the 17 resistive and conductive layers make electrical contact 18 with one another and if this is done, the voltage level is *19 provided. By having the switching mechai'sm 80 of sufficient length so that the full extent of the travel of 21 the sash door is provided as shown in FIG. 3, then an 22 accurate determination of the sash position can be made.

23 It should be understood that the illustration of 24 the switching mechanism 80 in FIGS. 3 and 5 is intended to be diagrammatic, in that the switching mechanism is 26 preferably actually located within the sash frame itself 27 and accordingly would not be visible as shown. The'width 28 and thickness dimensions of the switching mechanism 80 are 29 so small that interference with the operation of the sash 4*8 *30 door is virtually no problem. The actuator 94 can also be 31 placed in a small hole that may be drilled in the sash door 32 or it may be attacheu externally at one end thereof so that 33 it can be in position to operate the switching mechanism 34 80. In the vertical moveable sash doors shown in FIGS. 3 and 6, a switching mechanism 80 is preferably provided in 36 one or the other of the sides of the sash frame, whereas in 37 the fume hoods having horizontally movable doors, it is 38 preferred that the switching mechanism 80 be placed in the -18- 1 top of the tracks 68 so that the weight of the movable 2 doors do not operate the switching mechanism 80 or other- 3 wise damage the same. It is also preferred that the 4 actuator 94 be located at one end of each of the doors for reasons that are described in the cross-referenced appli- 6 cation entitled "A method and apparatus for determining the 7 uncovered size of an opening adapted to be covered by 8 multiple moveable doors" by Ahmed et al., Serial No. 52498.

9 Turning to FIG. 9, the preferred electrical circuitry which generates the position indicating voltage 11 is illustrated, and this circuitry is adapted to provide 12 two separate voltages indicating the position of two sash 13 doors in a single track. With respect to the cross-section 14 shown in FIG. 5, there are two horizontal tracks, each of which carries two sash doors and a switching mechanism 16 is provided for each of the tracks as is a circuit as shown *4 4 17 in FIG. 9, thereby providing a distinct voltage for each of 18 the four sash doors as shown.

19 The switching mechanism 80 is preferably applied °we 20 to the fume hood with a layer of adhesive 92 and the 21 actuator 94 is adapted to bear upon the switching mechanism 22 80 at locations along the length thereof. Referring to 23 FIG. 7, a diagrammatic illustration of a pair of switching 24 mechanism 80 is illustrated such as may occur with respect to the two tracks shown in FIG. 5. A switching mechanism 26 80 is provided with each track and the four arrows 27 illustrated represent the point of contact created by the 28 actuators 94 which result in a signal being applied on each 29 of the ends of each switching mechanism, with the magnitude of the signal representing a voltage that is proportional 31 to the distance between the end and the nearest arrow.

32 Thus, a single switching mechanism 80 is adapted to provide 33 position indicating signals for two doors located in each i 34 track. The circuitry that is used to accomplish the voltage generation is shown in FIG. 9 and includes one of 36 these circuits for each track. The resistive element is 37 shown at 84 and the conductive element 88 is also illus- 38 trated being connected to ground with two arrows being -19- 1 illustrated, and represented the point of contact between 2 the resistive and conductive elements caused by each of the 3 actuators 94 associated with the two separate doors. The 4 circuitry includes an operational amplifier 100 which has its output connected to the base of a PNP transistor 102, 6 the emitter of which is connected to a source of positive 7 voltage through resistor 104 into the negative input of the 8 operational amplifier, the positive input of which is also 9 connected to a source of positive voltage of preferably approximately five volts. The collector of the transistor 11 102 is connected to one ehu of the resistive element 84 and 12 has an output line 106 on wh.ch the voltage is produced 13 that is indicative of the position of the door.

14 The circuit operates to provide a constant current directed into the resistive element 84 and this cur- 16 rent results in a voltage on line 106 that is proportional 17 to the resistance value between the collector and ground 18 which changes as the nearest point of contact along the 19 resistance changes. The operational amplifier operates to 20 attempt to drive the negative input to equal the voltage 21 level on the positive input and this results in the current 22 applied at the output of the operational amplifier varying 23 in direct proportion to the ef2ective length of the *i,i 24 resistance strip 84. The lower portion the circuitry 25 operates the same way as that which has been described and 26 it similarly produces a voltage on an output line 108 that 27 is proportional to the distance between the connected end 28 of the resistance element 84 and the point of contact that 29 is made by the actuator 94 associated with the other sash ,1 30 door in the track.

31 Referring to the composite electrical schematic 32 diagram of the circuitry of the fume hood controller, if i 33 the separate drawings FIGS. 10a, 10b, 10c, 10d and 10e are 34 placed adjacent one another in the manner shown in FIG. the total electrical schematic diagram of the fume nood 36 controller 20 is illustrated. The operation of the 37 circuitry of FIGS. 10a through 10e will not be described in 38 detail. The circuitry is driven by a microprocessor and 1 the important algorithms that carry out the control 2 functions of the controller will be hereinafter described.

3 Referring to FIG. loc, the circuitry includes a Motorola MC 4 68HCII idicroprocessor 120 which is clocked at 8 MHz by a crystal 122. The microprocessor 120 has a databus 124 that 6 is connected to a tni-state buffer 126 (FIG. 10d) which i~n 7 turn is connected to an electrically programmable read only 8 memory 128 that is also connected to the databus 124. The 9 EPROM 128 has address lines AO through Ai connected to the tri-state buffer 126 and also has address lines A8 thro~ugh 11 A14 connected to the microprocessor 120.

12 The circuitry includes a 3 to 8-bit multiplexer 13 130, a data latch 132 (see FIG. l0d), a digital-to-analog 14 converter 134, which is adapted to provide the analog 15 outputs indicative of the volume of air being exhausted by i V 16 the fume hood, which information is provided to room 17 controller 22 as has been previously described with respect 18 to FIG. 2. Referring to FIG. lob, an RS232 driver 136 is 19 provided for transmitting and receiving information through 20 t1he hand held terminal. The circuitry illustrated in FIG.

21 9 is also shown in the overall schematic diagrams and is in 22 FIGS. 10a and lob. The other components are well known and 23 therefore need not be otherwise described.

24 As previously mentioned, the apparatus utilizes the flow sensor 49 preferably located in the exhaust duct 26 70 to measure the air volume that is being drawn through 27 the fume hood. The volume flow rate may be calculated by 28 measuring the differential pressure across a multi-point 29 pitot tube or the like, hood. The volume may be measured 4 4*30 with an air valve, flow meter or by measuring the 31 differential pressure across an orifice plate or the like.

32 The preferred embodiment utilizes a differential pressure *33 sensor for measuring the flow through the exhaust duct and 34 the apparatus of the present invention utilizes control schemes to either maintain the flow through the hood at a 36 predete73ined average face velocity, or at a minimum 37 velocity in the event the fume hood is closed or has a very 38 small bypass area.

-21- 1 The fume hood controller can be configured for 2 almost all known types of fume hoods, including fume hoods 3 having horizontally movable sash doors, vertically movable 4 sash doors or a combination of the two. As can be seen from the illustrations of FIGS. 2 and 10, the fume hood 6 controller is adapted to control an exhaust damper or a 7 variable speed fan drive, the controller being adapted to 8 output signals that are compatible with either type of 9 control. The controller is also adapted to receive information defining the physical and operating 11 characteristics of the fume hood and other initializing 12 information. This can be input into the fume hood 13 controller by means of the hand held terminal which is 14 preferably a lap top computer that can be connected to the 15 operator panel 34. The information that should be provided 16 to the controller include the following, and the dimensions 17 for the information are also shown: 18 Operational information: 19 1. Time of day; 2. Set day and night values for the average 21 face velocity (SVEL), feet per minute or 22 meters per second; 23 3. Set day and night values for the minimum 24 flow, (MINFLO), in cubic feet per minute; 25 4. Set day and night values for high velocity 26 limit (HVEL), F/m or M/sec; 27 5. Set day and night values for low velocity 28 limit (LVEL), F/m or M/sec; 29 6. Set day and night values for intermediate high velocity limit (MVEL), F/m or M/sec; 31 7. Set day and night values for intermediate 32 low velocity limit (IVEL), F/m or M/sec; 33 8. Set the proportional gain factor (KP), 34 analog output per error in percent; 9. Set the integral gain factor analog 36 output multiplied by time in minutes per 37 error in percent; 38 10. Set derivative gain factor analog -22- 1 output multiplied by time in minutes per 2 error in percent; 3 11. Set feed forward gain factor (KF) if a 4 variable speed drive is used as the control equipment instead of a damper, analog output 6 per CFM; 7 The above information is used to control the mode 8 of operation and to control the limits of flow during the 9 day or night modes of operation. The controller includes programmed instructions to calculate the steps in 11 paragraphs 3 through 7 in the event such information is not 12 provided by the user. To this end, once the day and night 13 values for the average face velocity are set, the 14 controller 20 will calculate high velocity l'.mit at 120% of the average face velocity, the low velocity limit at 16 and the intermediate limit at 90%. It should be understood 0* 17 that these percentage values may bes adjusted, as desired.

18 Other information that should be input include the 19 following information which relates to the physical construction of the fume hood. It should be understood 21 that some of the information may not be required for only 22 vertically or horizontally moveable sash doors, but all of 23 the information may be required for a ccmbination of the 24 same: 12. Input the number of vertical segments; 26 13. Input the height of each segment, in inches; 27 14. Input the width of each segment, in inches? 28 15. Input the number of tracks per segment; 29 16. Input the number of horizontal sashes per track; 31 17. Input the maximum sash height, in inches; 32 18. Input the sash width, in inches; 33 19. Input the location of the sash sensor from 34 left edge of -ash, in inches; 20. Input the by-pass area per segment, in 36 square inches; 37 21. Input the minimum face area per segment, in 38 square inches; -23- 1 22. Input the top lip height above the 2 horizontal sash, in inches; 3 23. Input the bottom lip height below horizontal 4 sash, in inches.

The fume hood controller 20 is programmed to 6 control the flow of air through the fume hood by carrying 7 out a series of instructions, an overview of which is 8 contained in the flow chart of FIG. 11. After start-up and 9 outputting information to the display and determining the time of day, the controller 20 reads the initial sash 11 positions of all doors (block 150), and this information is 4:48 12 then used to compute the open face area (block 152). If 13 not previously done, the operator can set the average face 14 velocity set point (block 154) and this information is then used together with the open Lface area to compute the 16 exhaust flow set point (SFLO)W) (block 156) that is 17 necessary to provide the predetermined average face 18 velocity given the open area of the fume hood that has been 19 previously measured and calculated. The computed fume hood exhaust set point is then compared (block 158) wi 'th a 21 preset or required minimum flow, and if computed set Point 22 is less than the minimum flow, the controll sets the set 23 point flow at the preset minimum flow (block 160). If it 24 is more than the minimum flow, then it is retained (block 162) and it is provided to both of the control loops.

26 If there is a variable speed fan drive for the 27 fume controller, several fume hoods are not connected *28 to a common exhaust duct and controlled by a damper, then 29 the controller will rux a feed-forward control loop (block 164) which provides a control signal that is sent to a 31 summing junction 166 which control signal represents an 32 open loop type of control action. In this control action, 33 a predicted value of the speed of the blower is generated 34 based upon the calculated opening of the fume hood, and the average ta,e velocity set pa.tnt. The predicted value of 36 the speed of the blower generated will cause the blower *37 motor to rapidly change speed to maintain the average face 38 velocity. It should be understood that the feed forward -24- 1 aspect of the control is only invoked when the sash 2 position has been changed and after it has been changed, 3 then a second control loop performs the dominant control 4 action for maintaining the average face velocity constant in the event that a variable speed blower is used to 6 control the volume of air through the fume hood.

7 After the sash position has been changed and the 8 feed forward loop has established the new air volume, then 9 the control loop switches to a proportional integral derivative control loop and this is accomplished by the set i1 flow signal being provided to block 168 which indicates 12 that the controller computes the error by determining the 13 absolute value of the difference between the set flow '.14 signal and the flow signal as measured by the exhaust air f low sensor in the exhaust duct. Any error that is 16 computed is applied to the control loop identified as the *17 proportional-,integral -derivative control loop (PID) to 18 determine an error signal (block 170) and this error signal 19 is compared with the prior error signal from the previous sample to determine if that error is less than a deadband 21 error (block 172). If it is, then the prior error signal off$#: 22 is maintained as shown by block 174, but if it is not, then 4 23 the new error signal is provided to output mode 176 and it 24 is applied to the summing junction 166. That summed error is also compared with the last output signal and a 26 determination is made if this is within a deadband range 27 (block 180) which, if it is, results in the last oi 28 previous output being retained (block 182). if it is 29 outside of the deadband, then a new output signal is provided to the damper control or the blower (block 184).

31 After the sash positiun has been changed and the 32 feed forward loop has established the new air volume, then 33 the control loop switches to a proportionaiL intagral 34 derivative control loop and this is accomplished by the set flow signal being provided to block 168 which indicates 36 that the controller computes the error by determining the 37 absolute value of the difference between the set flow 38 signal and the flow signal as measured by the exhaust air 1 f low sensor in the exhaust duct. Any error that is 2 computed is applied to the control loop identified as the 3 proportionrl-integral-derivative control loop (PID) to 4 determine an error signal (block 170) and this error signal is compared with the prior error signal f,om the previous 6 sample to determine if that error is less than a deadband 7 error (block 172). If it is, then the prior error signal 8 is maintained as shown by block 174, but if it is not, then 9 the new err.or signal is provided to output mode 176 and it is applied to the summing junction 166. That summed error 11 is also compared with the last output signal and a 12 determination is made if this is within a deadband range QVQ 13 (block 180) which, if it is, results in the last or 14 previous output being retained (block 182). If it is 15 outside of the deadband, then a new output signadl is **16 provided to the damper control or the blower (block 184).

'so 4 age 17 In the event that the last output is the output 18 as shown in block 182, the controller then reads the 19 measured flow (MFLOW) (block 186) and the sash positions are then read (block 188) and the net open face area is 21 recomputed (block 190) and a determination made As- to sees.22 whether the new computed area less the old computed area is 23 less than a deadband (block 192) and if it is, then the old so 24 area is maintained (block 194) and the error is then computed again (block 168). If the new area less the old 26 area is not within the deadband, then the controller 27 computes a new exh~aust flow set point as shown in bloc- *.28 156.

*29 one of the significant advantages of the fume hood controller is that it is adapted to execute the 31 control scheme in a repetitive and extremely rapid manner.

32 The exhaust sensor provides flow signal, information that is 33 inputted to the microprocessor at a speed of approximately 34 one sample per 100 milliseconds and the control action described in connection with FIG. 11 is completed 36 approximately every 100 milliseconds. The sash door 37 position signals are sampled by the microprocessor every 38 200 milliseconds. The result of such rapid repetitive -26- 41i4 SI

II

S

sampling and executing of the control actions results in extrealy rapid operation of the controller. It has been found that movement of the sash will result in adjustment of the air flow so that the average face velocity is achieved within a time period of only approximately 3-4 seconds after the sash door reposition has been stopped.

This represents a dramatic improvement over existing fume hood controllers.

In the event that the feed forward control loop is utilized, the sequence of instructions that are carried out to accomplish running of this loop is shown in the flow chart of FIG. 12, which has the controller using the exhaust flow set point (SFLOW) to compute the control output to a fan drive (block 200), which is identified as signal AO that is computed as an intercept point plus the set flow multiplied by a slope val,-s. The intercept is the value which is a fixed output vo: age to a fan drive and the slope in the equation correla, as exhaust flow rate and output voltage to the fan drive. The controller then reads the duct velocity (DV) (block 202), takes the last.:,duct velocity sample (block 204) and equates that as the duct velocity value and starts the timing of the maximum and minimum delay times (block 206) which the controller uses to insure whether the duct velocity has reached steady state or not. The controller determines whether the maximum delay time has expired (block 208), and if it has, provides the output signal at output 210. If the max delay has not expired, the controller determines if the absolute value of the difference between the last duct velocity sample and the current duct velocity sample is less than or equal to a dead band value (block 212). If it is not less than the dead band value, the controller then sets the last duct value as equal to the present duct value sample (block 214) and the controller then restarts the minimum delay timing function (block 216). Once this is accomplished, the controller again determines whether the max delay has expired (block 208). If the absolute value of the difference between the last duct velocity and tne present 4,ttiI 4 lil ft i .4 ir ft -27- 1. duct velocity sample is less than the dead band, the 2 controller determinei whether th'q minimum delay time has 3 expired which, if it has as shown from block 218, the 4 output is provided at 210. If it has not, then it determines if the max delay has expired.

6 Turning to the proportional -integral -derivative 7 or PID control loop, the controller runs the PID loop by 8 carrying out the instructions shown in the flow chart of 9 FIG. 13. The controller uses the error that is computed by block 168 (see FIG. 11) in three separate paths. With 11 respect to the upper path, the controller uses the 12 preselected proportional gain factor (block 220) and that 13 proportional gain factor is used together with the error to *14 calculate the proportional gain (block 222) and the proportional gain is output to a summing junction 224.

16 The controller also uses the error signal and taa17 calculates an integral term (block 226) with the integral 18 term being equal to the prior integral sum~ (ISUM) plus the 19 product of loop time and any error and this calculation is compared to limits to provide limits on the term. The term 21 is then used together with t%.e previously defined init6gral list.&22 gain constant (block 230) and the controller than *23 calculates the integral gain (block 232) which is the 24 integral gain constant multiplied by the integration sum I S 4 .25 term. The output is then applied to the summing junction 4 a 26 224.

27 The input error is also used by the controller toa~a28 calculate a derivative gain factor which is done by the 29 controller using the previously defined derivative gain factor from block 234 which is used together with the error 31 to calculate the derivative gain (block 236) which is the 32 reciprocal of the time in which it is required to execute 33 the PID loop multiplied by the derivative gain factor 34 multiplied by the current sample error minus the previous sample error with this result beilig provided to the summing 36 junction 224.

37 The control action performed by the controller 38 as illustrated in FIG. 13 provides three reparate gain -28- 1 factors which provide steady state correction of the air 2 flow through the fume hood in a very fast acting manner.

3 The formation of the output signal from the PID control 4 loop takes into consideration not only the magnitude of the error, but as a result of the derivative gain segment of 6 control, the rate of change of the error is considered and 7 the change in the value of the gain is proportional to the 8 rate of change. Thus, the derivative gain can see how fast 9 the actual condition is changing and works as an "anticipator" in order to minimize error between the actual 11 and desired condition. The integral gain develops a 12 correction signal tha\. is a function of the error !'ill1 integrated over a period of time, and therefore provides 14 any necessary correction on a continuous basis to bring the actual condition to the desired condition. The proper 16 combinations of proportional, integral and derivative gains a17 will make the loop faster and reach the desired conditions a18 without any overshoot.

4 419 A significant advantage of the PID control action is that it will compensate for perturbations that may be 21 experienced in the laboratory in which the fume hood may be 22 located in a manner in which other controllers do not. A 23 common occurrence in laboratory rooms which have a number 6 24 of fume hoods that are connected to a common exhaust 25 manifold, involves the change in the pressure in a fume fell#, 26 hood exhaui'=t duct that was caused by the'sash doors being 27 moved in another of the fume hoods that is connected to the, ,28 common exhaust manifold. Such pressure variations will 29 affect the average face velocity of those fume hoods which had no change in their sash doors. However, the PID 31 control action may adjust the air flow if the exhaust duct 32 sensor determines a change in the pressure. To a lesser 33 degree, there may be pressure variations produced in the 34 laboratory caused by opening of doors to the laboratory itself, particularly if the differential pressure of the 36 laboratory room is maintained at a lesser pressure than a 37 reference space such as the corridor outside the room, for n8 example.

-29- 1 It is necessary to calibrate the feed forward 2 control loop and to this end, the instructions illustrated 3 in the flow chart of FIG. 14 are carried out. When the 4 initial calibration is accomplished, it is preferably done through the hand held terminalJ that may be connected to the 6 operator panel via connector 38, for example. The 7 controller then determines if the feed forward calibration 8 is on (block 242) and if it is, then the controller sets 9 the analog output of the fan drive to a value of 20 percent of the maximum value, which is identified as value A01 11 (block. 244). The controller then sets the last sample duct 12 velocity (LSDV) as the current duct velocity (CDV) (block 13 246) and starts the maximum and minimum timers (block 248).

14 The controller ensures the steady state duct velocity in the following way. First by checking whether the max timer 16 has expired, and then, if the max timer has not expired, 17 the controller determines if the absolute value of the last 18 sample duct velocity minus the current duct velocity is 19 less than or equal to a dead band (block 270), and if it 20 is, the controller determines if the min timer has expired 21 (block 272). If it has not, the controller reads the 22 current duct velocity (block 274). If the absolute value 23 of the last sample duct velocity minus the current duct 24 velocity is not less than or equal to a dead band (block 270), then the last sample duct velocity is set as the 26 current duct velocity (block 276) and the mintimer is 27 restarted (block 278) and the current duct velocity is 28 again read (block 274). In case either the max timer or 29 min timer has expired, the controller then checks the last 30 analog output value to the fan drive (252) and inquires 31 whether the last analog output value was 70 percent of the i 32 maximum output value (block 254). If it is not, then it 33 sets the analog output value to the fan drive at 70 percent S34 of the max value A02 (block 256) and the steady state duct velocity corresponding to A01. The controller then repeats 36 the procedure of ensuring steady state duct velocity when 37 analog output is A02 (block 258). If it is at the 38 percent of max value, then the duct velocity corresponds to 1 steady state velocity of A02 (block 258). Finally, the 2 controller (block 262) calculates the slope and intercept 3 values.

4 The result of the calibration process is to determine the duct flow at 20% and at 70% of the analog 6 output values, and the measured flow enables the slope and 7 intercept values to be determined so that the feed forward 8 control action will accurately predict the necessary fan 9 speed when sash door positions are changed.

?rom the foregoing detailed description, it 11 should be appreciated that an improved system and apparatus 12 for controlling fume hoods and the room in which they are 13 contained has been shown and described. The many desirable 14 safety features insure increased safety for those present 15 in a room containing fume hoods. The apparatus detects ar' 16 excessive loading of a filter medium and provides an audio 17 and/or video indication of that condition. The system t 18 controls the air supply into the room, taking into 19 consideration the volume of air that is being exhausted by the fume hoods within it and the amount of air being 21 exhausted by the HVAC equipment for the room, and controls 22 the differential pressure of the room so that in the event 23 of an emergency, an unusual emergency fume hood exhaust 24 mode of operation can be instituted without trapping an individual in the room or causing external doors from' a 26 opening into the room, which may rapidly dissipate the .27 desired lower differential pressure within the room.

28 While various embodiments of the present 29 invention have been shown and described, it should be understood that various alternatives, substitutions and *31 equivalents can be used, and the present invention should 32 only be limited by-the claims and equivalents thereof.

33 Various features of the present invention are set 34 forth in the following claims.

Claims (1)

1. 4. to modulate the flow of air into the room whereby the differential pressure in the room is within the range of about 0.05 and 0.1 inches of water lower than a reference pressure outside of the room, so that any outwardly opening door can be opened by a person inside the room 4 and the differential pressure will not normally force any inwardly opening door open. Claim 11. A system as defined in claim 10 wherein said predetermined emergency flow rate is the maximum flow rate. Claim 12. A system as defined in claim 10 wherein said fume hood controller means operates to provide said predetermined emergency flow rate at a high flow rate for 36 a predetermined time and then reduce the flow rate thereafter. DATED this 19th day of January, 1993 LANIDIS GYR POWERS, INC. Attorney: LEON K. ALLEN Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS 04 4 4 4 4 I 4 4 4 1* -37- 1 LABORATORY FUME HOOD CONTROL APPARATUS 2 HAVING IMPROVED SAFETY CONSIDERATIONS 3 Abstract of the Disclosure 4 A fume hood controlling apparatus(20) that provides desirable operational safety features for persons who use 6 the fume hoods(60) and (64) to perform experiments or other work. The 7 apparatus is adapted for use with fume hoods that have a 8 filtering means(72) located between the fume hood enclosure and 9 the exhaust duct(70). The apparatus determines if a filter medium is loaded beyond a predetermined amount. The 11 apparatus also provides a visual or audible indication in 12 response to the detected loading. The apparatus also has 13 emergency switches near each fume hood, with the switch 14 controlling the fume hood when actuated so that the fume hood can operate in an emergency mode, and also provides an 16 indication to a central building console of a building 17 supervisory and control system for heating ventilating..and 18 air conditioning apparatus. S S q S *0