SE429013B - Method of controlling, regulating and indicating the ventilation air in ventilated spaces such as an exhaust hood and arrangement for carrying out the method - Google Patents

Abstract

The invention concerns a method and an arrangement for controlling, regulating and indicating the flow of ventilation air in ventilated rooms, such as an exhaust hood 2 at laboratory work stations and the like. At each exhaust hood 2, a first position pickup 15 is arranged to put out information as to how open or closed the shutters 3 of the exhaust hood 2 are. A second position pickup 13 is arranged to put out information on the degree of opening of the shutter 3. The information, in the form of electric or pneumatic signals, is taken to a control unit in which the signals are processed and some of them displayed on an indicator 18, others detected by a limit value circuit 29. The signal quantities thus shown on the indicator 18 are proportional to the air flow speed in the shutter opening of the exhaust hood and when this signal falls below a limit value previously set at the limit value circuit 29, i.e., when the air flow speed in the shutter opening falls below a lowest tolerable value, an optical and/or acoustical alarm is given off by an alarm unit 29, 30, 19, 21. <IMAGE>

Description

8004561-0 in ventilated spaces, you are confronted with two problems.

The first is purely ergonomic and ventilation-technical, namely how the workplace is to be designed, the second is the increased operating costs that come with increasing the ventilated work surface per laboratory technician. These cost increases are accentuated by energy price developments in recent years. In addition, environmental and ventilation technical problems will convert large amounts of air into limited building volumes.

It is previously known, i.a. by U.S. Pat. No. 1,155,289, to control the air flow in the fume cupboard by connecting to the fume cupboard sliding door a mechanical linkage system which, proportionally to the position of the door, acts on a throttle valve in the fume cupboard's exhaust air duct.

With this device a constant air velocity is obtained in the fume cupboard opening regardless of the position of the door, but the device cannot take into account the air consumption of the adjacent fume cupboard included in the workplace.

In addition, the location of the throttle valve in the fume cupboard resp. its immediate proximity associated with major disadvantages as the special air control device causes difficult sound attenuation problems.

Object of the invention and most important features By limiting the amount of air available to each laboratory technician and at the same time providing the opportunity for a flexible utilization of the air, efficient management of the amount of air and thus energy and building volume can be obtained. An uncompromising precondition for this is that continuous information reaches the laboratory technician about the ventilation standard prevailing in each fume cupboard through a well-developed indication system. The object of the present invention is thus to provide completely ventilated spaces, for example at a laboratory workplace with fume cupboards, where the laboratory technician, regardless of how adjacent fume cupboards are connected, is continuously informed of the correct air velocity in each individual fume cupboard opening, and that a relatively small amount of air is disposed of. group of fume cupboards and this amount of air can be controlled to the fume cupboard where it is most needed to obtain adequate ventilation. One way of achieving this is that the exhaust air flow is regulated partly individually for each fume cupboard and partly jointly for each group, that essentially all the amount of exhaust air within a group of fume cupboards can be supplied or distributed on one or a few fume cupboards within the group and that the air speed is indicated and / or at a minimum adjustable air speed an alarm is triggered.

A device for carrying out the method is described in more detail in claim Ä.

Description of the drawings The invention will be described below with reference to exemplary embodiments shown in the drawings.

Figure 1 shows schematically and partly in section a laboratory workplace comprising three fume cupboards.

Figure 2 shows a block diagram of the electronic control unit for a fume cupboard. 8001661 * 0 Figure 3 schematically shows a wiring diagram of the control unit according to figure 2.

Figure 4 shows a block diagram of an alternative embodiment of the control unit, in which circuits for I control of dampers are included.

Figure 5 shows a vertical section through a fume hood, seen from the side, and Figure 6 schematically shows a signal diagram for computerized control and regulation of the ventilation air in a number of fume cupboards.

Description of exemplary embodiments Figure 1 shows a possible construction of a laboratory workplace 1, which comprises a number of fume cupboards 2, for example three. In the following, the additional terms a, b, c, etc. refer to resp. fume cupboard part. Each fume cupboard 2 is provided with a vertically displaceable door 3, with which the fume cupboard opening can be closed. Connected to the upper part of each fume cupboard is an exhaust air pipe U communicating with the interior of the fume cupboard, in which an exhaust air damper 5 is arranged, which can be made to open or close via control means 6.

In order to be able to adjust the air flow rate from each fume cupboard 2, throttle flanges 7 are arranged in each exhaust air pipe 4. Between the damper 5 and the throttle flange there may possibly be a muffler. The exhaust air pipes M from several fume cupboards belonging to the same workplace radiate together in a collecting space 8, which is connected to an exhaust air duct 9 via two connecting pipes 10a and 10b, in which a main damper 11a and 11b are each arranged. The dampers 11 are actuated by control means 12 to assume open or closed position resp. intermediate positions between these. For detection of the current 3 gaps .___..._....___. 8004561-0 position, position sensors 13 are arranged at the fume cupboards 3, which are connected to resp. front hatch 3 via a wire shelter or similar. The position sensors 13 can for instance consist of multi-turn potentiometers, electric angle sensors, or pneumatic equivalents, which emit signals proportional to the positions 3a-30 of the doors in the vertical direction and thus proportional to the fume cupboard opening. At the front door 3 of each fume cupboard 2 or with parts cooperating therewith, a position sensor 15 is arranged, which closes or opens a circuit depending on whether the door 3 is in its lower end position or if the door is open. In the lower end position of the door, an air gap 16 remains, which allows a small predetermined amount of air to pass to the interior of the fume cupboard. This basic air supply is intended to provide a limited ventilation in the fume cupboard and which is made possible via a by-pass line or the like in the exhaust air duct.

On the front side of the fume hood 2 is arranged an instrument: panel 17, comprising a rotary coil instrument 18, indicator lamps 19, a switch 20, with which the electronic control unit can be disconnected and an acoustic and / or optical alarm device 21.

The entire laboratory workplace 1 is suitably arranged in a room (not shown), from which the ventilation air is sucked into the fume cupboards and further out through the exhaust air pipes U, the connecting pipes 10 and the exhaust air duct 9. To avoid the inconvenience with negative pressure in the room, there is a supply air system. 22 with exhaust devices (not shown) connected to their respective sockets 23, in which a supply air damper 2H is arranged, which is regulated by means of control devices SH in parallel with the exhaust air dampers 11. In this way, a ventilation system cooperating for the premises is achieved, which in the example shown here refers to a workplace with three fume cupboards. It is of course possible to arrange a plurality of workplaces in one and the same room, whereby each workplace may comprise a larger or smaller number of fume cupboards.

In order to avoid the disadvantages which arise with large air flows in the fume cupboard opening, as shown in Figure 5, supply air devices 50 can be arranged for the fume cupboard itself, preferably located at the upper horizontal edge of the fume cupboard opening. The supply air device 50 is provided with obliquely upwardly directed nozzles 51, which prevent downward air vortices from forming, which can transport some of the toxic gases present in the cabinet to the lower edge of the front cover 3. The air supplied through the fresh air devices 50 is regulated to each fume cupboard by means of dampers 52, control means 53 and a quoting unit 55. The damper 52 can either be varied continuously depending on pre-set distribution requirements and parameters included in the plant, but it is also possible to manually regulate air flow.

For controlling the control means 6, 12 and m33 shown in figure 1, an electronic control unit is provided.

A block diagram of this control unit is shown in Figure 2, consisting of an equivalent circuit 25, an amplifier 26, a sensor 13, an indicator 18, a limit level circuit 29, an alarm circuit 30 and an optical and / or an acoustic alarm sensor 19 resp. 21. The said blocks consist mainly of electronic components such as semiconductors, in the form of integrated circuits, resistors, potentiometers and capacitors. The first block, the equivalent circuit 25, comprises five fixed resistors 3la-3le connected in such a way that the air flow through the exhaust air pipes Ä and the connecting pipes 10 is imitated. The intention is to create an input voltage to an operational amplifier 34 in each operating case, i.e. a potential on the branch line 33, which is proportional to the air flow available for the current fume cupboard 8004561-0. The resistors 31a and 51b are dimensioned so that proportionality to the exhaust air flow in the connecting pipes 10a, 10b is obtained. over the resistors šlc, d, e, (which are @ ~ the resistors 3la, b) i.e. a potential appears on the branch line 33, which is partly dependent on the supplied current via Bla, b, and partly on which combination of Blo, d, e is present. In order to be able to mimic the air flow paths at a workplace, at each occasion, switches 32 c, d, e, are further arranged to each correspond to the function of resp. exhaust air dampers 5a, B, the same applies to switches 32a, b and the main dampers 11a a b. Thus, for example, the switch 32a conducts current when the main damper 11a is in the open position, i.e. then air can pass through the connecting pipe l0a. The resistor 3la, in the equivalent circuit 25, will in this case be traversed by a current in proportion to the air flow in the connecting pipe 10a. The magnitude of the current determines the resulting potential at the branch conductor 35. Switches 32c-e also affect the potential at the branch conductor 35 (the arrows in the diagram indicate the working direction when activated). For example, is the switch 320 closed, i.e. if the control unit's "own" control cabinet Ba is closed and the damper 5a is closed, the branch conductor 35 is connected to earth, the potential at the branch conductor 53 and thus the output signal from the equivalent circuit 25 being equal to zero. however, if the door 3 on the fume hood 2a is opened, the switch 32c is also opened, whereby the resistor 31c will be passed through by a current and the branch conductor 33 obtains a potential other than zero. If one or both of the other fume cupboard doors 3 are opened, i.e. if the position sensors 15 detect that the doors have been opened, the switches 32d, 32e close. If, for example, the two doors Bb, c are open, the switches 32d, 32e are closed and the resistors Bld, 3le are connected to earth, whereby electric currents, proportional to the air flows passing the dampers 5 in the exhaust air pipes Ä, begin to flow through the resistors 3lc- e. The resulting potential at the branch conductor 33 becomes relatively lower, which reflects that the available air flow is distributed over three fume cupboards. If, on the other hand, the main damper 11b in the connecting pipe 10b is opened, the available air flow again increases. When the main damper 11b is opened, the switch 32b is also actuated so that it closes. In this case, a current will also flow through the resistor 3lb, which current is also further distributed on the resistors 3lc-e. The potential at the branch conductor 33 then increases again.

This resulting signal voltage is applied to the amplifier 26, where the signal is amplified, for example 10 times, in an operational amplifier 3Ä. The gain is tuned in by means of the potentiometer 35 which is connected between the output of the operational amplifier 3A and the negative input.

In order to filter out short-term disturbances in the system, a capacitor 36 is connected to the operational amplifier, which capacitor thus limits the bandwidth of the operational amplifier. The output voltage from the operational amplifier 33, which is also proportional to the air flow available to the fume hood, is applied to the component chain 35b, 13, 18 and 35e, all substantially resistive elements as follows. In series with the BÄ output of the operational amplifier, an additional potentiometer 35b is connected, by means of which tuning of the base air area, i.e. the air gap of the front door 3 opening degree, can be adjusted. The electrical signal thus processed in the amplifier 26 is applied to the position sensor I3, e.g. a potentiometer, but may in another arrangement be an angle sensor or the like. The position sensor 13 is mechanically actuated by the "own" fuse box door 3. The smaller the opening area of the fume cupboard, the less resistance the position sensor 13 has.

The signal is then applied to an indicator 18, which may, for example, consist of a rotary coil instrument 18 for the range 0-1 mA. The indicator 18 is then arranged to show a reading proportional to the current through the position sensor and thereby also proportional to the air flow velocity in the door opening of the fume cupboard 2a. A limit level circuit 29, comprising i.a. a comparator circuit 38 is connected with its input via a switch 39 to a small resistor 35e in series with the indicator 18 and its main function is to emit a signal when the potential across the resistor 35e drops below a certain predetermined level, which is set by means of the potentiometer 35d . Thus, since the potential above 35e is also proportional to the air flow rate in the "own" cabinet door opening, the limit level circuit 29 will emit a signal at its output when the air flow rate drops below a certain predetermined limit level, which may be 0.5 m / sec The signal is applied to an alarm circuit 30 comprising an oscillator RO, which then begins to operate (swing) and emits a pulsating output signal. The output signal is suitably applied to an indicator lamp 19, which is caused to flash or to an acoustic alarm sensor 21 which begins to sound.

The embodiment described above means that the air flow rate in the fume cupboard opening varies with the degree of opening of the door 3, i.e. the air flow rate is inversely proportional to the area of the fume cupboard opening.

In cases where it is desired to keep the air velocity in the fume cupboard opening constant, regardless of the degree of opening of the door, you can arrange continuously variable constant flow regulators or fan systems. Such regulators or fan systems are intended to place the main dampers 11a, b in such a working position that the air speed is always the same in the fume cupboard opening. The signal available in the system described above can not be used without further ado to cause the control means 12 to assume the desired setting without the signal, which is suitably drained between the indicator 18 and the limit level circuit 29 (see Figure U), aoo4sa1-o 10, a comparator circuit H2 is suitably supplied. A setpoint is also supplied to the comparator circuit H2, which indicates the desired air flow rate in the door opening of the fume cupboard. The actual value and setpoint are compared in the comparator circuit 42 and the resulting signal is then applied to a processing circuit H3, in which the signal is adapted to the electrical and mechanical characteristics of the damper controller H4 and the main damper 11a, b, so that the main damper 11a, b by means of the damper controller HU position in the connecting pipe ida, b that the desired air speed specified in the setpoint setting in the fume cupboard opening is achieved. When the capacity of the control means 12 and the main dampers 11a, b are fully utilized, the air flow rate in the fume cupboard door opening drops below the level set at the limit level circuit 29, which causes the alarm circuit 30 to be switched on and generate an acoustic and / or optical alarm. In doing so, the laboratory technician is made aware that the capacity limit has been reached and that an unduly low air flow rate prevails at the workplace.

Supply air dampers 2H are automatically controlled in the same way and in parallel with the control means 12 and the main dampers 11a, b to provide balance in the system.

Of course, it is also conceivable to use a micro or mini computer H5 instead of a control unit built up of discrete components. This is particularly advantageous as a larger number of workplaces are arranged in close proximity to each other. Fig. 6 schematically shows the signal diagram for a microcomputer, which is arranged for a group of, for example, three fume cupboards. This microcomputer replaces all the functions that the electronic control unit can perform.

An example of this is the collection of data by means of an input circuit 46 8004561-0 11 regarding position information from dampers, regulators and position sensors. Furthermore, the microcomputer performs calculation of for resp. fume cupboard opening current air speed and emits a signal to indicate the same. The microcomputer further compares the amount with the entered preset setpoint and provides an alarm indication if applicable.

In case the system is to keep the air flow rate in each door opening constant, the microcomputer calculates a control signal adapted to the curve for each actuator equipment. The program developed for the microcomputer also contains routines for cyclically updating information from all sensors. Routines are available for calculating the desired output signal and for updating all signals to the flow indicator, alarm devices and controller equipment. By using a micro- or mini-computer, routines for indicating abnormal operating situations can suitably also be included. An example of this can be when the damper or regulator is in a position that does not correspond to the applied signal or there is an interruption in the information from the sensor to the actuator. To facilitate the manual handling and programming of the mini- or microcomputer, a terminal 47, through which e.g. information can be fed, connected to it. Information entered via the terminal can refer to e.g. available air volumes, curve fitting and different alarm limits. Via a circuit 48, the computer communicates with e.g. the alarm and display units.

The invention is of course not limited to the above-related embodiments, but a number of alternative embodiments are possible within the scope of the claims. For example, the control unit may be wholly or partly made up of pneumatic components or combinations of electrical and pneumatic components and circuit blocks, which in their function are substantially equivalent to the control unit consisting of electronics.

Claims (10)

800íi561- * G i 12 P A T E N T K R A V 1. l. Methods of controlling, regulating and indicating the ventilation air in ventilated spaces, such as fume cupboards * (2) connectable to at least one ventilation system, and provided with their own closing device, for example a door (3), which cooperates with control means ( 6, 12) in the ventilation system, whereby the air velocity through the spaces can be varied, and each door, (3) cooperates with a position sensor which, depending on the opening of the door (3), connects the space to the ventilation system's exhaust air duct (9), characterized by that the exhaust air flow is regulated partly individually for each fume cupboard (2) and partly jointly for each group, that essentially all exhaust air volume within a group of fume cupboards can be supplied or distributed on one or a few fume cupboards within the group and that the current air velocity in each fume cupboard is indicated and / or at a minimum adjustable air speed an alarm is triggered. 2. A method according to claim 1, characterized in that the group-connected pull-out cabinets (2) communicate via a common connection (10) with the exhaust air duct (9). 3. A method according to claim 1 or 2, characterized in that an analog circuit (25), which depending on the operating situation of and the number of 'in the group' included dampers, regulators / fans and the like emits a signal which in each situation is proportional to that of resp. fume hood per unit of time maximally evacuable air volume, which signal is supplied * a second position sensor (13) connected to each door (3) or the like, which in proportion to the opening area of the door (3) changes the signal in such a way that the indicator connected to the system ( 18), will show the flow rate of the air in the opening and / or be supplied with an alarm unit (29, 30), the alarm threshold of which corresponds to a lowest, adjustable air velocity. Device for controlling, regulating and indicating the ventilation air in ventilated spaces, such as fume cupboards (2) connectable to at least one ventilation system, and provided with their own closing device, for example a door (3), which cooperates with control means (6) in the ventilation system, whereby the air velocity through the spaces can be varied, and each door (3) cooperates with a position sensor which, depending on the opening of the door (3), connects the space to the ventilation system's exhaust air duct, characterized in that the fume cupboards (2) are provided with both individual as for the fume cupboards in a group common flow control by means of control means (6, 12), that control means (6, 12) belonging to the same group and the doors of the fume cupboards (3) are arranged to enable distribution together with a control unit (25, 26, 13) of substantially all the amount of exhaust air to some or some fume cupboards (2) within the group, and that the control unit (25, 26, 13) is arranged to, depending on the doors (3), ) and the position of the control means' (6, 12) indicate the air velocity prevailing in each fume cupboard opening and / or in the event of insufficient ventilation trigger an alarm unit (19, 29, 30). Device according to claim 4, characterized in that the fume cupboards (2) are arranged in groups with a common connection (10) to the exhaust air duct (9). Device according to Claim 4 or 5, characterized in that a first position sensor (15) is arranged at each fume cupboard (2a-c), intended to detect whether the door (3) is in the closed or open position, to each door (3) is connected to a second position sensor (l3) intended to sense the degree of opening of the door (3) and that one to resp. The control unit (25, 26) connected to the fume cupboard (2a-c) is arranged to supply, depending on the signals from the first and second position sensors (15 and 13) 8004561-.0 1 »to an indicator (18) and / or connected to said control unit. alarm unit (29, 30) a signal proportional to the air velocity in resp. fume cupboard opening. 7. Device according to claim 4, 5 or 6, characterized in that air flow regulators (24, arranged per se) are arranged in the supply and / or exhaust air ducts (23, 50, 4, 10) of the ventilation system. 52; 5, 11), for example dampers or fans, which by means of control means (54, 53, 6, 12) are continuously or stepwise variable, so that a substantially constant air velocity is obtained in the door opening, regardless of the degree of opening of the door (3), - the regulators (24) are controlled in parallel with the exhaust air regulators (II). 8. ' In a device according to claim 4,5 or 6, it is characterized in that the alarm unit (29, 30) is provided with means (35d) for selectable adjustment of the alarm limit value, so that when the air flow rate in the fume cupboard ( 2a-c) door opening below this limit, the alarm unit (29, 30) generates and emits an optical and / or an acoustic alarm. Device according to one or more of Claims 4 to 3, characterized by a quoting unit (55) arranged »to determine the relationship between external and internal air to the fume cupboard (2) and / or to the room surrounding the fume cupboard on the basis of pre-arranged distribution requirements' and parameters included in the device. Device according to one or more of Claims 4 to 9, characterized in that the control means (6, 12, 54) and the control unit (25, 26, 13, 55) are connected to an input circuit (46) of a microcomputer (45). ) arranged to recalculate the position information from said control means and control unit to for resp. fume hood opening current air speed and that the calculation result is visualized in an indicator (18) and / or compared with a preset setpoint for triggering an alarm.