JP2782482B2 - Differential pressure control system for rooms with fume hood - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Industrial applications] (Cross-reference of related applications) Name: Device for controlling ventilation of laboratory fume hood Inventor: Osman Ahmed, Steve Bradley, Steve Fritche and Steve Jacob Application No .: Japanese Patent Application No. 3-324235 Name: Device for finding the position of a movable structure along a track Inventor: David Egbers and Steve Jacob Application Number: Japanese Patent Application No. 3-324236 Name: Method and apparatus for determining the uncovered size of an opening to be covered by a plurality of movable doors Inventor: Osman Ahmed, Steve Bradley, and Steve Fritche Application No .: Japanese Patent Application No. 3-318117 Name: Laboratory fume hood control device with improved safety considerations Inventor: Osman Ahmed Application No .: Japanese Patent Application No. 3-318118 The present invention generally relates to ventilation control of a laboratory fume hood, and is particularly disposed inside. The present invention relates to a system for controlling the pressure difference in a room having one or more laboratory fume hoods.

[0002]

BACKGROUND OF THE INVENTION Fume hoods are used in a variety of laboratory environments that provide workplaces where potentially hazardous chemicals are used, and these hoods allow workers to access the interior of the enclosure for experiments and the like. Where possible, it has an enclosure with a movable door at the front that can be opened in various amounts. Typically, the enclosure is connected to an exhaust system that removes harmful fumes so that personnel are not exposed to harmful fumes while working in the hood. Fume hood controllers, which control the flow of air through the enclosure, have become increasingly sophisticated in recent years and now maintain precisely the desired flow characteristics and as a function of the desired average surface velocity of the fume hood opening, Fumes can be exhausted efficiently.

[0003] Average surface velocity is generally defined as the flow rate of air entering the fume hood per square foot of open area of the fume hood, the size of the open area being provided in front of the enclosure or fume hood. It depends on the location of one or more movable doors and, for most types of enclosures, on the amount of bypass opening provided when one or more doors are closed.

[0004] Fume hoods are typically evacuated by an exhaust system that generally includes a blower that can be driven at a variable speed to increase or decrease the flow of air from the fume hood to compensate for the varying size of the opening or open surface. You. Alternatively, one blower is connected to an exhaust manifold connected to each duct of a plurality of fume hoods, and a damper is provided in each duct to control the flow rate from each duct to maintain a desired average surface velocity. The flow rate may be modulated.

The doors of such fume hoods can be opened by raising them vertically to a position often referred to as a sash position, and some fume hoods are typically slidable along two sets of trucks. It has a plurality of doors mounted. In addition, some doors have multiple trucks mounted in a vertically movable frame assembly and are movable both horizontally and vertically.

[0006] The amount of air drawn through each of the fume hoods is at least partially a function of the uncovered area of the opening, and if a relatively constant average surface velocity is maintained, the greater the opening of the fume hoods. The area results in more air being drawn into and exhausted from the fume hood. It should be understood that in many facilities the total number of fume hoods present in a laboratory room (room) can be so large that a significant amount of air is removed from the laboratory room during operation. Also, since the HVAC (heating, ventilation and air conditioning control) system supplies air to each laboratory room, the supply to the laboratory room depends on whether the fume hood is frequently opened or other changes occur. The amount of air that needs to vary considerably.

[0007]

Since most of the work performed in many laboratories involves potentially hazardous chemicals, the differential pressure within the laboratory is reduced to a lower pressure than the corridors or adjoining rooms outside the laboratory. It is often desirable to maintain If the laboratory has several fume hoods that exhaust air from the room, the amount of air supplied to the laboratory will inevitably be larger than a similarly sized room without a fume hood, and the fume hood will open frequently. When having a sash door, it becomes more difficult to maintain the desired differential pressure in the laboratory.

Accordingly, one of the main objects of the present invention is to provide an improved control of the differential pressure between a laboratory room having a number of fume hoods disposed therein and a standard space which is preferably adjacent to the laboratory. It is to provide a system.

Another object of the present invention is to significantly improve control of HVAC equipment by integrating a fume hood controller into a heating, ventilation and air conditioning control (HVAC) facility for a laboratory room having a fume hood disposed therein. Accordingly, it is an object of the present invention to provide a system capable of maintaining a differential pressure of a chamber with respect to a pressure of a standard space such as a corridor or an adjacent area at a desired level.

Another one of the main objects of the present invention is to provide the HV with current accurate information on the air flow from each fume hood.
It is an object of the present invention to provide an improved system for controlling the pressure in a laboratory chamber achieved by feeding the AC system.

More specifically, it is an object of the present invention to provide an improved system for controlling the differential pressure in a room having multiple fume hoods relative to the pressure in a standard space such as a hallway, wherein the room has a room controller. Providing a signal indicating the amount of air being exhausted by each fume hood from each fume hood controller to the room controller, thereby providing an improved system for controlling the amount of air supplied to and exhausted from the room. is there.

[0012] These and other objects will become apparent from the following detailed description of the invention which refers to the accompanying drawings.

[0013]

In order to achieve the above object, a system according to the present invention comprises a system for controlling a pressure difference between a room such as a laboratory and a standard space such as a corridor to a predetermined level. Wherein both the room and the standard space are arranged in a building having a building heating, ventilation and air conditioning system, and a plurality of fume hoods are arranged in the room, and the fume hood at least partially opens as it moves. At least one movable fume hood sash door, each fume hood has an exhaust duct connected to an exhaust system for exhausting air and fumes from the chamber, and each fume hood is provided with an associated exhaust duct. Means for measuring the flow of air through the exhaust duct to generate an actual flow signal indicative of the actual flow of air through the exhaust duct, each fume hood having a desired surface passing through the uncovered portion of the opening. A heating, ventilation and air conditioning system for a building, comprising a fume hood and a fume hood controller for controlling a flow rate modulation means attached to an exhaust duct attached to the fume hood to maintain the temperature. Room control means for at least controlling the amount of air supplied to the room from the fume hood controller means, so that a signal indicating the actual flow rate output from each fume hood controller means is communicated to the room control means. Interconnect means interconnecting each with the room control means, wherein the room control means comprises:
Receive and add the signal communicated from each fume hood controller means, determine the amount of air exhausted from the room by the fume hood, change the amount of air supplied to the room using the flow rate modulation means, from the room The amount of air to be exhausted is set to a flow rate necessary to maintain the predetermined level of differential pressure.

[0014]

In general, the fume hood controller controls the flow of air through the fume hood and determines the effective size of the full opening to the fume hood, including the openings not covered by one or more sash doors. It should be understood that this is to provide a relatively constant average surface velocity of the air traveling into the hood. This means that, regardless of the area of the uncovered opening, the average amount of air per unit surface area of the uncovered part,
It means moving into the fume hood. As a result,
Since air constantly flows into the fume hood and out of the exhaust duct, workers in the laboratory are protected from exposure to harmful fumes, etc.
Preferably, the predetermined speed is controlled at approximately 75-125 cubic feet per minute per square foot of effective surface area of the uncovered opening. In other words, if one or more sash doors are moved to the maximum open position and the operator gains maximum access to the interior of the fume hood to perform an experiment or the like, the air is maintained to maintain the average surface velocity at a predetermined desired level. Flow must be increased.

Generally speaking, for example, a laboratory or the like 1
The present invention provides a system for maintaining the pressure of a room containing one or more fume hoods at a predetermined level relative to the pressure of a standard space in a building, which may be pressure, such as an adjacent hallway or an adjacent room. In order to contain harmful fumes and prevent them from spreading across the laboratory room, it is often highly desirable to maintain the differential pressure in the laboratory room at a low level compared to the standard space. The system includes a room controller that is part of a building heating, ventilation and air conditioning system. The room controllers are capable of receiving from each fume hood controller an electrical signal proportional to the amount of air being exhausted through each fume hood. Since each fume hood can exhaust the amount of air that can vary greatly according to the initial setting of the desired average surface speed and the opening of the sash door, an air amount instruction signal is transmitted from each fume hood controller to the room controller. It would be very advantageous to modulate the amount of air supplied to the chamber to help maintain the differential pressure to the desired level with a relatively quick response time.

[0016]

1, there is shown a block diagram of several fume hood controllers 20 interconnected with a room controller 22, an exhaust controller 24 and a main control console 26. FIG. The fume hood controller 20 is a room controller 22 and an exhaust controller 2
4 and a main control console 26, interconnected by a local area network (LAN) indicated by line 28, which may be formed by multi-conductor cables or the like. The room controller 22, the exhaust controller 24 and the main control console 26 are typically part of the main HVAC system of the building in which the laboratory room including the fume hood is located. The fume hood controller 20 is powered through a line 30 at an appropriate voltage, such as through a transformer 32.

The room controller 22 is preferably one capable of giving at least a variable amount of air to the room.
It can be an ndis & Gyr Powers system 600 SCU controller. Room controller 22 is LAN line 2
8 can be communicated. However, when the response time is important, the room controller preferably receives the fume hood exhaust flow rate information from the fume hood controller directly as an analog signal via a dedicated line. In this case, a LAN that may be blocked to transmit other information from the fume hood controller to the room controller is bypassed. Room controller is system 600SC
Preferably, a U-controller is a commercially available controller for which extensive documentation exists. In particular, the User Reference Manual for the System 600 SCU Controller, Part No. 125-1753, is hereby incorporated by reference.

The room controller 22 receives via line 81 a signal from each fume hood controller 20 that provides an analog input signal indicating the amount of air being exhausted by each fume hood, and exhausts the fume hood. And a comparison signal from an exhaust flow sensor which gives an indication of the amount of air being exhausted through another main exhaust system. By combining these signals with a signal provided by a differential pressure sensor 29 indicating the pressure in the room relative to the standard space, the room controller can reduce the differential pressure in the room to slightly less than the standard space, preferably about 0. 0
The control of the air supply needed to maintain a low pressure in the range of 1 to about 0.05 inches of water can be controlled, resulting in the desired low chamber pressure compared to a standard space. However, the pressure in the room is not low enough to prevent personnel in the laboratory room from opening and exiting the door in an emergency, especially if the door opens outside the room. In the case of an inwardly-opening door, the pressure difference is not so large that the door is forcibly pulled open by an excessive force applied by the pressure difference.

The differential pressure sensor 29 is preferably located in a suitable hole or opening in the wall between the laboratory chamber and the standard space and measures the pressure on one side relative to the pressure on the other side. Alternatively, a speed sensor may be provided that measures the speed of the air passing through the opening, a value that is directly proportional to the pressure difference between the two spaces. Of course, a differential pressure in the room that is lower than that in the standard space means that the air flowing into the room can be detected.

Referring to FIG. 2, the fume hood controller 20 clearly shows the functions of its input and output connector ports, and the fume hood controller 20 is connected to an operator panel 34. It should be understood that each fume hood has a fume hood controller 20 and an operator panel is provided for each fume hood controller 20. That is, an operator panel 34 is provided for each fume hood and interconnected with the fume hood controller 20 by a line 36, which preferably comprises a multi-conductor cable having eight conductors. The operator panel 34 is, for example, a 6-wire RJ
It has a connector 38 such as an 11-inch telephone jack, and a laptop personal computer or the like is connected to the connector 38 in order to input information about the configuration and operation of the fume hood at the time of initial setting or to change some operation parameters if necessary. Connectable. The operator panel 34
Is preferably attached to the fume hood at a convenient location that is easy to observe by workers working in the fume hood.

The operator panel 34 of the fume hood controller includes a liquid crystal display 40, which is selectively energized to provide visual indication of various aspects of the fume hood, including a three digit 42 for providing an average surface velocity. Display 4
0 also indicates other conditions such as low surface speed, high surface speed, emergency status, and indication of controller failure. The operator panel 34 may also have an alarm 44 and an emergency purge switch 46 that can be pressed by an operator to purge the fume hood in the event of an accident. The operator panel also has two auxiliary switches 48 that can be used for various customer needs, including day / night modes of operation. In the night time mode of operation, it is conceivable to have a different, preferably lower, average surface velocity than the day time mode. Nobody is working indoors late at night, and such a low average surface speed is expected to save energy. Preferably, an alarm silence switch 50 is also provided to turn off the alarm.

The fume hood can be of many different styles, sizes and shapes, including those having one or multiple sash doors, and those in which the sash doors can move vertically, horizontally or in both directions. Also, the various fume hoods have different bypass flow rates, i.e. different flow rates through the openings that are also present when all sash doors are closed as completely as possible by design. Other design factors also include whether there is any type of filtering means in the fume hood that traps the fumes during operation. While many of these design factors must be taken into account to provide efficient and effective control of the fume hood, the device can be configured to take into account almost all of the design variables described above, and the effectiveness of the ventilation of the fume hood can be improved. And very quick control is obtained.

Referring to FIG. 3, there is shown a fume hood, generally designated 60, wherein the fume hood 60 is movable to provide access to the fume hood and is in a substantially closed position as shown. And has a vertically operated sash door 62 that is movable to The fume hood is generally designed so that even when a door sash, such as door sash 62, is completely closed, there is a certain amount of opening through which air can pass through the fume hood. This opening is commonly referred to as a bypass region, and can be determined such that its effect can be taken into account when controlling the flow of air into the fume hood. Some fume hoods have a bypass opening located above the door sash, while others are located below. Also, in some fume hoods, the initial displacement of the sash door increases, for example, the opening at the bottom of the door shown in FIG. 3, but as it rises, the door blocks the bypass opening, and the total opening of the fume hood increases. The effective size is kept relatively constant during the first approximately one-quarter travel of the sash door 62 along the travel path.

Another type of fume hood includes several horizontally movable sash doors 66 as shown in FIGS.
Each door may be movable along. When the door is located as shown in FIGS. 4 and 5, the opening of the fume hood is completely closed and the worker can move the door horizontally to gain access into the fume hood. Fume hood 6
Both 0 and 64 have an exhaust duct 70 that typically extends to the exhaust system, which may be for an HVAC device as described above. The fume hood 64 includes a filter filtration structure, indicated generally at 72, which prevents harmful fumes and other contaminants from exiting the fume hood into the exhaust system.
Referring to FIG. 6, there is shown a combined fume hood 74 having a horizontally movable door 76 similar to the door 66, the fume hood 74 having a frame structure 78 supporting the door 76 along a suitable truck. And the frame structure 78 is vertically movable within the fume hood opening.

In FIG. 6, there is an omission, indicated by dashed line 73, which is used to raise the frame structure 78 sufficiently to allow personnel to properly access the interior of the fume hood. It is intended to indicate that the height of the hood can be greater than shown. Generally, there is a bypass region, shown as vertical region 75,
There is also typically a top lip 77 that can be about 2 inches wide. This dimension is preferably determined such that its influence on the calculation of the open surface area can be taken into account.

Although not specifically shown, two or more sash doors, such as two or more sash doors that are vertically movable along adjacent tracks, similar to a fenestration window for a house, are mutually connected along the width of the fume hood opening. Other combinations are also possible, including a plurality of vertically movable sash doors located adjacent to each other.

The fume hood controller 20 operates the fume hoods of various sizes and configurations as described above, and may have several fume hoods located therein, and may be a common part that may be part of the building HVAC system. It is installed in a laboratory room that may have an exhaust duct that joins the exhaust manifold. The fume hood can be one independent or have its own separate exhaust duct. If one fume hood is installed, such equipment has a blower driven by a variable speed motor and attached to an exhaust duct, and the motor and blower are arranged to regulate the flow of air through the fume hood. Generally, the speed can be variably controlled. Alternatively, in the most common case where there is more than one fume hood in one area, the exhaust duct of each fume hood is merged with one or more larger exhaust manifolds and one large blower is provided in the manifold system Sometimes. In such equipment, since the control of each fume hood is performed by a separate damper disposed in each fume hood, it is possible to control the flow change by appropriately positioning the damper attached to each fume hood. .

The fume hood controller is capable of controlling virtually any of a variety of types and styles of fume hood on the market, and therefore has a number of input / output ports () that can be connected to various sensors used in the controller. Lines, connectors or connections, all of which are considered equivalent for the purposes of this description). As shown in FIG. 2, the fume hood controller has a digital output or DO port for interfacing with the digital signal / analog pressure conversion element provided in the exhaust damper as described above, and a variable speed fan drive is provided in an analog system. If so, it also has an analog voltage output port for controlling the drive. There are also five sash position sensor ports used to detect the position of the sash, which can be moved both horizontally and vertically, and an analog input port connected to an exhaust air flow sensor. Further, a digital input port for an emergency switch is provided, and each digital output port for outputting an alarm horn signal and an auxiliary signal is also provided.

As described above, according to the present invention, an analog voltage output port for providing a flow signal to the room controller 22 is also provided. This port is connected to the room controller 22 by individual lines 81 extending from each fume hood controller 20.

From the above description, if the desired average surface speed is to be maintained while changing the sash position, the size of the opening changes greatly. Therefore, a large change in the amount of air is required to maintain the average surface speed. It should be understood that it is necessary. Although it is known to control a variable air flow blower as a function of sash position, the fume hood controller uses a relatively constant average so that the control system's ability to respond quickly to changes in the system. The known method is improved by incorporating an additional control scheme which greatly improves in maintaining face velocity.

To determine the position of the sash door, a sash position sensor is provided adjacent to each movable sash door, which is schematically illustrated in FIGS. 7, 8 and 9. Referring to FIG. 8, the door sash position indicator preferably comprises a relatively thin polyester base layer 82, a relatively simple mechanical design of the elongated switching mechanism 8
0, and an electric resistance ink 84 having a known constant resistance per unit length is printed on the base layer 82 in a strip shape. Another polyester base layer 86 is provided, on which conductive ink 88 is also printed in a strip. The two base layers 82 and 86 are adhesively bonded to each other by two beads of adhesive 90 located on both sides of the strip. Both base layers are preferably approximately five thousandths of an inch thick, and both beads are approximately two thousandths
At inches thickness, these beads provide a space between conductive layer 88 and resistive layer 84. Switching mechanism 8
0 is preferably attached to the fume hood by a layer 92 of adhesive.

The polyester material is sufficiently flexible to allow one layer to move toward and contact the other layer in response to the actuator 94 supported by the corresponding sash doors with the strips arranged next to each other, so that the sash door can move. Then, the actuator 94 moves along the switching mechanism 80 to form a contact between the resistance layer and the conductive layer. This is detected by an electric circuit described later, and the actuator 94 along the length of the switching mechanism 80 is detected.
Is given. That is, the voltage indicating the position of the sash door is given by the actuator 94 being supported by the sash door.

Actuator 94 applies sufficient pressure to switching mechanism 80 as the sash door moves,
Preferably, the two base layers abut and the resistive and conductive layers make electrical contact with each other and are spring biased toward the switching mechanism 80 such that a voltage level is provided in response to the electrical contact. . By making the switching mechanism 80 long enough to cover the entire range of movement of the sash door as shown in FIG. 3, the sash position can be determined accurately. It should be noted that the switching mechanism 80 shown in FIGS. 3 and 5 is only an outline, and in practice, the switching mechanism 80 is preferably arranged in the sash frame itself, and cannot be seen from the outside as shown. Since the width and thickness dimensions of the switching mechanism 80 are small, interference with the operation of the sash door is practically not a problem. The actuator 94 may be placed in a small hole drilled in the sash door, or attached to the outside of one end of the sash door, so that the switching mechanism 80 is operated. In the vertically movable sash door shown in FIGS. 3 and 6, it is preferable to provide the switching mechanism 80 on one side or the other side of the sash frame, while in the fume hood having the horizontally movable door, the movable door Preferably, the switching mechanism 80 is located on top of the track 68 so that the weight of the switching mechanism 80 does not affect or damage the switching mechanism 80. In addition, the actuator 94 is arranged at one end of each door for the reason described in the above-mentioned cross-reference application entitled "Apparatus for Determining the Position of a Movable Structure Along a Track" by Exbers et al., No. 52496. preferable.

Referring to FIG. 9, there is shown a preferred electrical circuit for generating a position indicating voltage, the electrical circuit indicating the position of two sash doors within one track.
Suitable for giving two separate voltages. Referring to the cross-sectional view shown in FIG. 5, each of the two supports two sash doors.
There are three horizontal tracks, and for each track the same circuit as shown in FIG. 9 is provided, including the switching mechanism 80, to provide a separate voltage for each of the four sash doors shown.

The switching mechanism 80 is preferably attached to the fume hood with a layer of adhesive 92 and an actuator 94 abuts it at each location along the length of the switching mechanism 80. Referring to FIG. 7, 2 shown in FIG.
A schematic diagram of a pair of switching mechanisms 80, as used in one track, is shown. The switching mechanism 80 is provided on each track, and four arrows in the figure represent contact points formed by the actuators 94. As a result, a signal is given to each end of each switching mechanism, and the magnitude of this signal is reduced. It represents a voltage proportional to the distance between each end and the closest arrow. Thus, one switching mechanism 80 provides a position indicating signal for the two doors arranged on each track. The circuit used to implement the above voltage generation is shown in FIG. 9, where one circuit is provided for each track. Resistance element (layer)
Is shown at 84 and a conductive element (layer) 88 is shown connected at one end to ground and at the other end are two arrows pointing to the resistance formed by respective actuators 94 attached to two separate doors. It represents the point of contact between the element and the conductive element. The circuit shown includes an operational amplifier 100 having an output connected to the base of a PNP transistor 102, the emitter of which is connected directly to a positive voltage source via a resistor 104 to the operational amplifier 100. And the positive input of operational amplifier 100 is also connected to a positive voltage source, preferably of about 5 volts. The collector of transistor 102 is connected to one end of resistor element 84 and has an output line 106 at which a voltage indicative of the position of the door is generated.

The circuit operates to provide a constant current to the resistive element 84, which produces a voltage proportional to the resistance between the collector and ground, which varies as the closest contact point along the resistor changes. Occurs on output line 106. Operational amplifier 100 operates to drive the negative input to equal the voltage level of the positive input, so that the output of the operational amplifier is provided with a current that varies in direct proportion to the effective length of resistive element 84. The lower part of the circuit operates in the same manner as described above, and outputs a voltage proportional to the distance between the connection end of the resistive element 84 and the point of contact by the actuator 94 attached to the other sash door in the track on the output line 10.
8 occurs similarly.

Referring to the composite electrical schematic of the fume hood controller circuit, FIG.
When the respective drawings d and 10e are arranged side by side as shown in FIG. 10, an electric schematic diagram of the entire fume hood controller 20 is obtained. The operation of the circuits of FIGS. 10a to 10e will not be described in detail. The circuitry is driven by a microprocessor and the key algorithms that implement the control functions of the fume hood controller will be described later. FIG.
Referring to FIG. 3C, the circuit shown in FIG.
Motorola MC68 to which MHz clock input is applied
HC11 microprocessor 120 is included. Microprocessor 120 has a data bus 124 connected to a three-state buffer 126 (FIG. 10d), and buffer 126 is connected to an electrically programmable read-only memory (EPROM) 128 also connected to data bus 124. ing. EPROM 128 is a three-state buffer 12
6 and address lines A8-A14 connected to the microprocessor 120.

The circuit also includes a 3-to-8-bit multiplexer 130, a data latch 132 (see FIG. 10d), and a digital-to-analog converter 1 which provides an analog output indicating the amount of air being exhausted by the fume hood.
34, the information of which is provided to the room controller 22 described above with reference to FIG. Referring to FIG. 10b, R that transmits and receives information via a hand-held terminal
An S232 driver 136 is provided. The circuit shown in FIG. 9 is also shown as a comprehensive schematic in FIGS. 10a and 10b. The other components are well known and need not be described in particular.

As described above, the fume hood controller uses an air flow sensor which is preferably located in the exhaust duct 70 to measure the amount of air being drawn through the fume hood. Air flow may be calculated by measuring the differential pressure between both sides, such as a multi-point pitot tube.
The preferred embodiment uses a differential pressure sensor to measure the flow through the exhaust duct and the fume hood controller maintains the flow through the fume hood at a predetermined average surface velocity, or the fume hood is closed or very When a small bypass area is provided, a control method for maintaining the minimum speed is used.

The fume hood controller is applicable to almost any type of known fume hood, including a horizontally movable sash door, a vertically movable sash door, or a combination of both. As apparent from FIGS. 2 and 10, the fume hood controller controls the exhaust damper or the variable speed fan drive, and outputs a signal compatible with any type of control. The fume hood controller also receives information that determines the physical and operating characteristics of the fume hood and other initialization information. Such information can be input to the fume hood controller by a hand-held terminal, preferably a laptop computer connectable to the operator panel 34. The information to be provided to the controller includes the following, together with the dimensions of the information:
It should be noted that a day / night operation mode may be provided, but this is not a preferred embodiment of the present system.
Information on day / night operation should be included.

Operation information: Time; 2. Day and night setting of average surface velocity (SVEL), feet per minute or meters per second; 3. Minimum and daily flow rate setting (MINFLO), cubic feet per minute; 4. High speed limit (HVEL) day / night value setting, F / m or M / sec; 5. Low speed limit (LVEL) day / night value setting, F / m or M / sec; 6. Mid / high speed limit (MVEL) day / night value setting, F / m or M / sec; 7. Mid / low speed limit (IVEL) day / night setting, F / m or M / sec; 8. Proportional gain coefficient (KP) setting, analog output per error, percent; 9. setting of integral gain factor (KI), product of analog output per minute and minute time per error, percent; 10. setting of differential gain coefficient (KD), product of analog output and minute time per error, percent; The feedforward gain coefficient (K) when a variable speed drive is used instead of a damper as a control device
F) Setting, analog output per CFM.

12. Time when the user wants to continue full exhaust flow when the emergency switch is operated (DELTIME)
Set in seconds.

13. Emergency switch operated, DELT
When the IME expires, set a preset percentage (SAFLOQ) of the final exhaust flow that the user wants to keep.

The above information controls the mode of operation and is used to control the flow limit during the day or night mode of operation. The controller 20 includes programmed instructions for calculating each of the steps 3-7 if the relevant information is not provided by the user. Therefore, when the day / night value of the average surface speed is set, the controller 20 sets the high speed limit, which is 120% of the average surface speed, to 80%.
Is calculated, and a medium speed limit of 90% is calculated. It should be understood that these percentages can be adjusted as desired. Other information to enter includes the following information related to the physical structure of the fume hood: 13. Some of the following information may not be necessary for sash doors that can only move vertically or horizontally, but a combination of both requires all information: 14. Enter the number of segments in the vertical direction; 15. Enter the height of each section, inches; 16. Enter the width of each section, inches; 17. Enter the number of tracks for each section; 18. Enter the number of horizontal sashes per track; Enter the maximum sash height, inches; Enter sash width, inches; 21. Enter the position of the sash sensor from the left edge of the sash, in inches; 22. Enter bypass area per section, square inches; 23. Enter minimum surface area per section, square inches; Enter the top lip height above the horizontal sash, in inches; the fume hood controller 20 is programmed to control the flow of air through the fume hood by performing a series of commands, schematically shown in FIG. It is included in the flowchart. After starting, the information is output to the display and the time is obtained, and then the controller 20 reads the initial sash positions of all the doors (block 15).
0), then this information is used to calculate the open area (block 152). If not previously done, the operator can now set the average surface velocity set point (block 154), and this information is later taken together with the open surface area, given the previously measured and calculated fume hood open area. , Used to calculate the required exhaust flow set point (SFLOW) to provide a predetermined average surface velocity (block 1)
56). The calculated fume hood exhaust flow set point is then compared to a preset or required minimum flow (block 158), and if the calculated set point is less than the minimum flow, the controller presets the set point flow. The minimum flow rate is set (block 160). If the operation set point is larger than the minimum flow rate, it is kept as it is (block 16).
2), given to both control loops.

If the fume hood controller has a variable speed fan drive, that is, if some fume hoods are not connected to a common exhaust duct and are not controlled by a damper, the controller executes a feedforward control loop (block 164), which represents a control operation of the open-loop type, and provides a control signal sent to the addition junction 166. In this control operation, a predicted value of the blower speed is generated based on the calculated opening of the fume hood and the average surface speed set point. The predicted value of the generated blower speed causes the blower motor to change its speed quickly so as to maintain the average surface speed.
Note that the control of the feed forward mode is called only when the sash position is changed and after it is changed,
If a variable speed blower is used to control the amount of air passing through the fume hood, it should be understood that another control loop performs the dominant control action to keep the average surface velocity constant. It is.

After the sash position has changed and the feedforward loop has established a new air volume, the control loop switches to a proportional-integral-differential control loop, which provides a set flow signal to block 168. In block 168, the controller calculates the error by determining the absolute value of the difference between the set flow signal and the flow signal measured by the exhaust air flow sensor in the exhaust duct. The calculated error is provided to a control loop called a proportional-integral-differential control loop (PID) to determine an error signal (block 170), which is compared to a previous error signal from a previous sample, It is determined whether the error is less than a dead band (block 172). If smaller, the previous error signal is block 1
Maintained as shown at 74, but if not small, a new error signal is provided at output node 176 and further to summing junction 166. The error after addition is also compared to the previous output signal to determine if it is within the dead zone (block 180), and if so, the previous or previous output is retained (block 182). If not, a new output signal is provided to the damper controller or blower (block 184).

If the previous output is an output, as shown in block 182, the controller determines the measured flow rate (MFLO
W) (block 186), then the sash position is read (block 188), the net open surface area is recalculated (block 190), and the new calculated area minus the old calculated area is smaller than the dead zone. A determination is made (block 192), if so, the old area is maintained (block 194) and the error is calculated again (block 168). If the new area minus the old area is not within the dead zone, the controller computes a new exhaust flow set point as shown in block 156.

One of the important advantages of the fume hood controller
First, it is suitable for executing the control strategy very quickly in an iterative manner. An exhaust air flow sensor provides flow signal information, which is input to the microprocessor at a rate of about one sample every 100 milliseconds, and the control operations described in connection with FIG. 11 are completed approximately every 100 milliseconds. . The sash door position signal is sampled by the microprocessor every 200 milliseconds. This rapid repetitive sampling and execution of control actions results in a very quick action of the controller. Thus, it has been found that movement of the sash door results in adjustment of the air flow rate and achieves an average surface velocity within only about 3-4 seconds after the sash door is repositioned and stopped. This represents a significant improvement over existing fume hood controllers.

If a feed-forward control loop is used, the sequence of instructions used to execute this loop is shown in the flow chart of FIG. 12, where the controller uses the exhaust flow set point (SFLOW) to the fan drive. Is calculated (block 200). This control output is shown as signal AO and is calculated as the product of the set flow rate and the slope value plus the intercept point. The intercept point is the value of the fixed output voltage to the fan drive, and the slope in the equation correlates the exhaust flow rate with the output voltage to the fan drive. The controller then reads the duct speed (DV) (block 202) and retrieves the previous duct speed sample (block 204).
It sets the duct speed value and starts the maximum and minimum delay timing functions (block 206), which the controller uses to determine if the duct speed has reached a steady state. That is, the controller determines whether the maximum delay time has elapsed (block 20).
8) If the time has elapsed, give an output signal to the output 210. If the maximum delay has not elapsed, the controller determines whether the absolute value of the difference between the previous duct speed sample and the current duct speed sample is less than or equal to the deadband value (block 212). If not, the controller sets the previous duct value equal to the current duct value sample (block 214) and then restarts the minimum delay timing function (block 216). At the conclusion of this process, the controller again determines whether the maximum delay has elapsed (block 208). If the absolute value of the difference between the previous duct speed sample and the current duct speed sample is less than the dead zone value, the controller determines whether the minimum delay time has elapsed and, if so, as shown in block 218. , The output is provided to 210. If not, it is determined again whether the maximum delay time has elapsed.

Referring to the proportional-integral-derivative or PID control loop, the controller executes the PID loop by executing the commands shown in the flowchart of FIG. The controller uses the error calculated in block 168 (see FIG. 11) in three separate paths.
In the upper path, the controller uses a preselected proportional gain factor (block 220), which is used with error to calculate a proportional (P) gain (block 222), and the calculated proportional gain is The signal is output to the addition junction 224.

The controller also computes an integral term using the error signal (block 226), which is equal to the product of the loop time and the error plus the previous integral sum (ISUM), resulting in the resulting computation. The value is compared to the limit to place a limit on the integral term. This integral term is then used with the previously defined integral gain constant (block 230), and the controller calculates the integral (I) gain therefrom (block 232). The obtained integral gain is obtained by multiplying the integral gain constant by the integral sum term. Thereafter, the output is provided to summing junction 224.

The input error is also used by the controller to calculate the derivative gain factor. To this end, the controller inputs the previously defined derivative gain coefficient at block 234 and uses this together with the error to differentiate (D).
The gain is calculated (block 236). This differential gain is obtained by multiplying the reciprocal of the time required to execute the PID loop by the differential gain coefficient, and multiplying the difference by subtracting the previous sample error from the current sample error. 224.

The control action performed by the controller 20 as shown in FIG. 13 provides three separate gain factors, which provide a very quick way of modifying the steady state of the air volume through the fume hood. Such PID
The formation of the output signal based on the control loop takes into account not only the magnitude of the error but also the result of the differential gain part of the control. It is proportional to speed. In other words, the differential gain makes it possible to grasp how fast the actual state is changing, and acts as a "prediction factor" for minimizing the error between the actual state and the desired state. The integral gain produces a correction signal that is a function of the error integrated over time, thus providing the necessary corrections to bring the actual state closer to the desired state on a continuous basis. With an appropriate combination of the proportional, integral, and derivative gains, the processing speed of the loop is increased, and a desired state can be reached without overshooting.

An important advantage of the PID control operation is that it compensates for variations that may occur in the laboratory where the fume hood is located, in a manner not available with other controllers. In a laboratory room with multiple fume hoods connected to a common exhaust manifold, moving the sash door with a separate fume hood connected to the common exhaust manifold typically causes pressure changes in the fume hood exhaust duct. I do. These pressure changes affect the average surface velocity of the fume hood that did not move the sash door. However, in the PID control operation, the air flow rate can be adjusted by determining a change in pressure using an exhaust duct sensor. To a lesser extent, the opening and closing of the laboratory's own doors can cause pressure changes in the laboratory, especially if the differential pressure in the laboratory room is maintained at a pressure lower than the standard space, for example, an outdoor corridor. .

It is also necessary to calibrate the feedforward control loop, and for this purpose the instructions shown in the flow chart of FIG. 14 are implemented. When performing initial calibration,
Preferably, for example, via a hand-held terminal that can be connected to the operator panel via connector 38. The controller then determines whether feedforward calibration is on (block 242), and if so, sets the analog output of the fan drive to a value of 20% of the maximum value;
This is set to the value AO1 (block 244). Thereafter, the controller sets the previous sample duct speed (LSDV) as the current duct speed (CDV) (block 2).
46) Start both the maximum and minimum timers (block 248). The controller determines the steady state duct speed as follows. First, the controller checks whether the maximum timer has expired. If not, the controller determines whether the absolute value of the difference between the previous sample duct speed minus the current duct speed is equal to or less than the dead zone (block 20) If so, the controller determines whether the minimum timer has expired (block 272). If not, the controller reads the current duct speed (block 274).
If the absolute value of the difference obtained by subtracting the current duct speed from the previous sample duct speed is larger than the dead zone, the previous sample duct speed is set as the current duct speed (block 276), and the minimum timer is restarted (block 276). 278), the current duct speed is read again (block 274). If either the maximum timer or the minimum timer has expired, the controller checks the previous analog output value to the fan drive (block 252) and the previous analog output value is 70% of the maximum output value.
It is inquired as to whether or not (block 254).
If it is not 70%, the analog output value to the fan drive is set to 70% of the maximum value AO2 (block 256).
A stable state duct speed corresponding to O1 is set. The controller then repeats the procedure for determining a steady state duct speed when the analog output is AO2 (block 258). If it is 70% of the maximum, the duct speed corresponds to the steady state speed of AO2 (block 258). Finally, the controller calculates both slope and intercept values (block 262).

As a result of the calibration process, 20% of the analog output value
And 70% duct flow is determined, and both slope and intercept can be determined from the measured flow so that the required fan speed can be accurately predicted by the feedforward control operation when the position of the sash door is changed.

[0057]

As will be appreciated from the foregoing detailed description, the improved system of the present invention described above is superior to the prior art in effectively maintaining the desired differential pressure in a room where multiple fume hoods are present. It should be understood that it has advantages.

Although various embodiments of the present invention have been illustrated and described,
It should be understood that various alternatives, substitutions and equivalents may be used, and the present invention is limited only by the following claims and equivalents thereof.

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

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of the system of the present invention including a building heating, ventilation and air conditioning monitoring and control unit and several fume hood controllers.

FIG. 2 is a block diagram of the fume hood controller, shown connected to an operator panel showing a front view.

FIG. 3 is a front schematic view of an exemplary fume hood having a vertically actuatable sash door.

FIG. 4 is a schematic front view of an exemplary fume hood having a horizontally actuatable sash door.

FIG. 5 is a sectional view taken substantially along the line 5-5 in FIG. 4;

FIG. 6 is a front schematic view of an exemplary combination sash fume hood having a sash door operable in both horizontal and vertical directions.

FIG. 7 is an electrical schematic diagram of a plurality of door sash positions showing switching means.

FIG. 8 is a sectional view of a door sash position switching means.

FIG. 9 is a schematic diagram of an electric circuit for determining a position of a sash door of the fume hood.

FIG. 10 is a block diagram showing a relative positional relationship between FIGS. 11, 12, 13, 14 and 15, and also constitutes a schematic diagram of an electric circuit for fume hood controller means.

11 is connected to FIGS. 12, 13, 14 and 15;
FIG. 1 constitutes a schematic diagram of an electric circuit for a fume hood controller means.

FIG. 12 is connected to FIGS. 11, 13, 14 and 15;
FIG. 1 constitutes a schematic diagram of an electric circuit for a fume hood controller means.

FIG. 13 is linked to FIGS. 11, 12, 14 and 15;
FIG. 1 constitutes a schematic diagram of an electric circuit for a fume hood controller means.

FIG. 14 is linked to FIGS. 11, 12, 13 and 15;
FIG. 1 constitutes a schematic diagram of an electric circuit for a fume hood controller means.

FIG. 15 is linked to FIGS. 11, 12, 13 and 14;
FIG. 1 constitutes a schematic diagram of an electric circuit for a fume hood controller means.

FIG. 16 is a flowchart of the overall operation of the fume hood controller.

FIG. 17 is a flow chart of a part of the operation of the fume hood controller means of the present invention, particularly showing the operation of the feedforward control method included in one embodiment of the fume hood controller means.

FIG. 18 is a flow chart of a part of the operation of the fume hood controller means, particularly showing the operation of the proportional gain, integral gain and differential gain control methods.

FIG. 19 is a flow chart of a part of the operation of the fume hood controller means, specifically illustrating the operation of the feedforward control type calibration.

[Explanation of symbols]

Reference Signs List 20 fume hood controller 22 room controller (room control means) 24 exhaust controller 29 differential pressure sensor 49 fume hood air flow rate measurement means (exhaust air flow sensor) 60, 64, 74 fume hood 62, 66, 76 sash door 70 exhaust duct 81 mutual Connection means (conduction means, line)

────────────────────────────────────────────────── (5) References JP-A-60-164141 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G05D 7/06 F24F 7/007 G05D 16 / 20

Claims (5)

(57) [Claims] 1. A system for controlling a pressure difference between a room such as a laboratory and a standard space such as a corridor to a predetermined level, wherein both the room and the standard space are used for building heating, ventilation and ventilation. A fume hood disposed in a building having an air conditioner, wherein the fume hood has at least one movable fume hood sash door at least partially covering the opening as it moves; Has an exhaust duct connected to an exhaust device that exhausts air and fumes from the room, each fume hood measures the actual air flow through an attached exhaust duct and measures the actual air flow through the exhaust duct. Means for generating an actual flow signal indicating each of the fume hoods and associated exhaust ducts to maintain a desired surface velocity through the uncovered portion of the opening. In a differential pressure control system for a room having a fume hood controlling an amount modulation means by a fume hood controller means, a room control means for controlling at least an amount of air supplied to the room from the building heating, ventilation and air conditioning devices, As a signal indicating the actual flow rate output from each fume hood controller means is communicated to the room control means,
Interconnect means interconnecting each of said fume hood controller means with said room control means, said room control means receiving and adding signals communicated from each of said fume hood controller means, The amount of air exhausted from the chamber is determined, the amount of air supplied to the chamber is changed using the flow rate modulation means, and the amount of air exhausted from the chamber is required to maintain the predetermined level of differential pressure. A differential pressure control system for a chamber having a fume hood, characterized by a flow rate. 2. The system of claim 1, wherein said interconnecting means comprises conducting means extending from each of said fume hood controller means to said room control means. 3. The fume hood controller means for transmitting a voltage level proportional to the actual air flow through the exhaust duct of the fume hood to which the fume hood controller means is connected. Differential pressure control system for rooms with fume hood. 4. The system according to claim 1, wherein the flow rate measuring means is arranged to measure an air flow rate in an exhaust duct of the fume hood. 5. An apparatus for controlling a differential pressure in a room of a building having a heating, ventilation and air-conditioning and exhaust system for a building to a predetermined level with respect to a pressure of another space in a building such as a corridor. A plurality of fume hoods are disposed in the room, the fume hood having at least one movable fume hood sash door at least partially covering the opening as it moves, each fume hood exhausting air and fumes from the chamber. An exhaust duct coupled to the system, each fume hood having means for measuring the actual air flow through the associated exhaust duct and generating an actual flow signal indicative of the actual air flow through the exhaust duct. Each fume hood has flow rate modulation means attached to the fume hood and an associated exhaust duct so as to maintain a desired surface velocity through the uncovered portion of the opening by the fume hood controller means. A room pressure control device for a room having a fume hood, wherein the control unit controls at least an amount of air supplied to the room from the building heating, ventilation and air conditioning device; and an output from each of the fume hood controller means. As a signal indicating the actual flow rate to be communicated to the room control means,
Interconnect means for interconnecting each of the fume hood controller means with the room control means, the room control means receiving and adding signals communicated from each of the fume hood controller means, The amount of air exhausted from the chamber through the exhaust duct is adjusted to adjust the amount of air supplied to the chamber, and a flow rate sufficient to maintain the amount of air exhausted from the chamber at the predetermined level of differential pressure. A differential pressure control device for a chamber having a fume hood.