METHOD AND APPARATUS FOR PROVIDING SUBSTANTIALLY CONSTANT AIR FLOW THROUGH THE DOOR OPENING OF A FUME CUPBOARD

Description

[0001] The present invention relates to a method and apparatus for providing substantially constant air flow through the door opening of a fume cupboard for laboratory applications and the like, independant of the size of the cupboard door opening.

[0002] Handling substances hazardous to health, such as liquids and gases, in different laboratory environments, for research and educational purposes and the like often takes place in fume cupboards, correct ventilation of the cupboard then being of the greatest importance. Accordingly, there are special standards for the air flow through such cupboards.

[0003] In GB-A-2 129 544 a fume cupboard is disclosed, wherein the opening of the door controls an exhaust air fan. The drawback with this device is that a constant flow is no longer achieved when the pressure in the suction duct is altered. For a proper functioning of this device a constant back pressure is assumed. In contrast thereto, according to the invention the flow is measured continously, which is the relevant parameter which makes possible the maintenance of the correct flow velocity of the fume cupboard opening independently of the prevailing pressure.

[0004] SE-B-429 013 discloses a device which allows for the setting of valves in the exhaust air and supply air ducts, respectively, in order to obtain a balance. According to the invention, however, the amounts of air are measured, which is the relevant parameter.

[0005] US-A-4 160 407 discloses a ventilation system, wherein pressure sensors regulate valves in the ducts, while the fans are running at constant speed.

[0006] The prior art has two important disadvantages. In an installation where there is a plurality of fume cupboards, the exhaust and supply air systems must be dimensioned for the maximum air flow from all the cupboards. This generally means heavy over-dimensioning of the systems. In practice it has been found that in installations with a large number of cupboards the total combined air flow from the cupboards attains at most about 50%-60% of the theoretical maximum flow, corresponding to the sum of all maximum flows from all cupboards. Another disadvantage with the apparatus of the known art is caused by the exhaust air flow from the cupboard being regulated to its maximum value as soon as the door to the cupboard is opened slightly. This gives rise to an airflow velocity through the cupboard which is too great when its door has only been opened slightly. This can cause the formation of turbulence, which sucks out gases and other substances from the cupboard, which can be dangeroeus, e.g. persons in front of the cupboard can inhale such gases. This is illustrated in Figure 1, schematically illustrating a fume cupboard 2 with an outlet 4 for exhaust air. In the Figure, the air flow moving towards the door opening and through the cupboard is illustrated with arrows, and if the air flow velocity is too great turbulence of the type illustrated at 6 will occur. This turbulence 6 can suck out substances hazardous to health from the fume cupboard, and can be inhaled by the person 8 standing in front of the cupboard door.

[0007] The object of the present invention is to mitigate these defiencies in the previously known art and to provide a method of achieving an apparatus for generating a desired, substantially constant air flow velocity through the door to a fume cupboard, irrespective of the size of the aperture the door has been opened to, while the need for over-dimensioning discussed above of the supply and exhaust air systems is eliminated, with accompanying saving in cost.

[0008] This object is achieved by a method and apparatus of the kind mentioned in the introduction and having the characterising features disclosed in claims 1 and 2.

[0009] In accordance with a preferred development of the invention, the total exhaust air quantity from one or more fume cupboards in a room is measured and the amount of supply air to the room is controlled in response to this amount. In this way an excess pressure or a sub-pressure can easily be set in the room, which is often desirable. In high-risk laboratories, e.g. laboratories for AIDS, it is desirable to have a sub-pressure to lessen the risk of injurious substances or organism leaving the laboratory room. On the other hand, in clean room laboratories an excess pressure is desirable to avoid contaminants migrating into such a laboratory. A further advantage with this embodiment of the invention is that the apparatus can readily be extended with more fume cupboards up to the limit of the capacities of the supply and exhaust air systems without any special setting of the apparatus being required, since there is local control of each room unit.

[0010] Another advantage of the invention is that it can be readily applied to any existing fume cupboard or cupboards.

[0011] According to still another advantageous embodiment of the apparatus in accordance with the invention the measuring device for the door opening includes an IR transmitter and receiver, as well as a reflector, the transmitter and receiver being fixedly disposed relative the cupboard, with the reflector attached to the door thereof, or vice versa. The reflector is then adapted for reflecting light sent from the transmitter to the receiver, the intensity of the reflected light decreasing with increasing distance between transmitter and receiver, on the one hand, and the reflector, on the other hand, there also being a photocell arranged to generate an electrical output signal varying in response to the intensity of the received light. In this way there is obtained simply and reliably a control signed varying continuously with the size of the door opening.

[0012] Since the reflective power of the reflector is sensitive to dirtying of its reflectign surface, i.e. the intensity of the reflected light decreases as the reflector gets dirty, a still further embodiment of the invention provides for the reflector to move inside a protective tube when the door moves.

[0013] Regulation of the exhaust air amount from minimum to maximum when the door is raised should take place within 3 - 5 secs, and in order to obtain a sufficiently rapid resetting of the regulators when the door opening is altered, yet another advantageous embodiment of the apparatus in accordance with the invention provides for the regulator to be pneumatically controlled, and an electropneumatic converter is arranged to convert the output signal from the measuring device for the door opening to a pneumatic signal for controlling the regulator.

[0014] According to an even further advantageous embodiment of the apparatus in accordance with the invention, suitable alarms can be arranged to be triggerd, e.g. the size of the air supply to a fume cupboard is incorrect for some reason, or the exhaust air fan unit capacity is exceeded as a result of too many fume cupboards being put into operation simultaneously, or if a cupboard door is left open after work has finished for the day.

[0015] An embodiment of the apparatus in accordance with the invention, selected as an example, will now be described in more detail and with reference to Figures 2 - 5. Figure 1 illustrates the turbulence formation that can occur in fume cupboards when the air flow velocity through the cupboard is too high, Figure 2 illustrates a fume cupboard provided with a measuring device for sensing the door opening such as to generate a corresponding control signal, Figure 3 illustrates more closely the implementation of the measuring device, Figure 4 illustrates an embodiment with the reflector arranged in a protective tube, and Figure 5 is a general depiction of an apparatus in accordance with the invention installed in a unit of four rooms.

[0016] In Figure 2 there is illustrated a fume cupboard 10 with a raisable and lowerable front window or door 12, and from the upper part of the cupboard 10 there is an exhaust air duct 14 provided with a damper.

[0017] Adjacent the working surface 16 of the cupboard 10 there is a photocell 18 with and IR transmitter and receiver fixedly mounted.

[0018] A reflector 20 is disposed at the lower edge of the door 12, the photocell 18 and the reflector 20 being adapted such that light from the transmitter 22 is reflected towards the receiver 24 of the photocell 18, see Figure 3.

[0019] The intensity of the received IR signal decreases as the distance between the photocell 18 and the reflector 20 increases, the photocell sending an output signal which is proportional to the intensity of the received IR light. In this way there is obtained an electrical output signal from the photocell 18 which is proportional to the distance between the photocell and the reflector, i.e. proportional to the opening of the door 12. The measuring device provided thus can suitable be implemented such that the photocell 18 sens an electrical output signal varying continuously from 0 to 10 V when the opening of the door 12 varies from 400 - 0 mm.

[0020] In practice the cupboard door is not often closed completely, and there is a minimum opening, e.g. 5 cm, which ensures basic ventilation. In such an embodiment, the door opening may vary from 50 - 450 mm, and constant air flow velocity through the door opening is ensured by the apparatus in accordance with the invention.

[0021] The reflector 20 is subjected to dirtying, thus causing its reflective power and consequently the reflected signal to decrease. For the apparatus to function correctly, it must therefore be ensured that the reflector 20 is kept clean all the time. For this reason, the reflector is suitably arranged in a protective tube 26, parallell to the side edge of the door 12, a longitudinal slot 28 being made in its side facing towards the door 12, a holder arm 30 for the reflector 20 being disposed in the slot for movement along it, see Figure 4. The ouput signal from the photocell 18 is converted in an electropneumatic converter 32 to a pneumatic signal for controlling an exhaust air regulator 34 on the exhaust air duct 14 of the cupboard 10, see Figure 2. Pneumatic control of the regulator 34 is necessary to obtain sufficiently rapid setting of the exhaust air flow when the door 12 is pulled up or down. The setting time from maximum to minimum air flow, or vice versa, should be about 3 - 5 secs. Flow variators can be used as regulators, and they are sold by the Applicant with the denotation EM(JP)(BC). The damper blade 36 is suitably made from an acid-resistant material.

[0022] In Figure 5 there is shown an apparatus in accordance with the invention installed in a unit of four rooms, each of which contains four fume cupboards 10. An exhaust air regulator 34 is arranged in the exhaust air duct 14 from each of the cupboards 10. The exhaust air is extracted from each room via a common plenum duct 38, in which a volume meter 40 is disposed. This meter suitably comprises a so-called volume measuring flange. The plenum ducts 38 merge into a common main plenum duct 42, provided with an exhaust air fan unit 44.

[0023] For the supply of air there is an air supply fan unit 46, disposed for feeding an air supply plenum duct 48, common to the whole unit, from which supply air ducts 50 lead to each of the rooms. In each of these ducts 50 there is a volume meter 52 and a regulator 54. The volume meters 52 are suitably volume measuring flanges of the same kind as in the exhaust plenum ducts and the regulators 54 are the same kind as the regulators in the exhaust air ducts 14 of the fume cupboards 10. Supply of air to each of the rooms suitably takes place using a supply air means 56 disposed in the ceiling of the rrspective room, and adapted such that a draught-free supply of air with a variable flow is obtained within the desired working volume. It is advantageous that the air supply takes place obliquely from above, since the bodily extension of persons working at the cupboards is less from above then seen from one side, thus reducing the risk of turbulence in the air supplied.

[0024] As illustrated by dashed lines in Figure 5, the volume meter 52 and regulator 54 in the duct 50 to each room are controlled from the volume meter 40 in the appropriate plenum duct 38. By controlling the air supply such as to respond to the exhaust air flow in this way, a desired air flow velocity through the cupboards 10 is maintained the whole time. Air velocities of the order of magnitude of 0,4 - 0,7 m/s are suitable in the door opening. By this regulation of the supply air amount in response to the exhaust air flow an excess pressure or sub-pressure is readily provided in the individual rooms, which is desirable in many applications as discussed above. In the exhaust air main plenum duct 42 there is a pressure transducer 58 for controlling the associated fan 44, and in the supply air plenum duct 48 there is a pressure transducer 60 for controlling the fan 46 so that the pressures in the ducts 42 and 48 are kept constant at a desired value.

[0025] Since there is an individual regulation of each room, further fume cupboards can be added without any further rearrangement of the apparatus being required.

[0026] The apparatus in accordance with the invention is furthermore suitably implemented such that the exhaust air regulator opens to a maximum if the control signal fails. The described embodiment example is implemented with respect to regulation so that increasing exhaust air flow is provided for a decreasing control pressure signal.

[0027] For the purpose of providing emergency ventilation when needed, the photocell can also be disconnected by a switch simultaneously as the exhaust air flow increases to its maximum value.

[0028] The fans 44 on the exhaust air side are suitably surface treated to withstand corrosive gases. The fan blades can therefore be epoxi anodised.

[0029] The apparatus in accordance with the invention can with advantage be provided with different alarms, such as an alarm triggered on detection of a too small amount of air in the fume cupboard, or when the fan unit capacity is exceeded, i.e. too many cupboards open at the same time, or when cupboard doors have been left open after work is finsished for the day. The alarm can be both visual and acoustic. When an alarm acknowledgement has been made, the acoustic alarm can be disconnected, although the visual alarm indication continues to be illuminated until the fault is remedied, this indication then being extinguished by a further alarm acknowledgement.

Claims

1. Method for providing substantially constant airflow velocity through the door opening of a fume cupboard for laboratory applications and the like, independent of the size of the cupboard door opening (12), whereby the size of said cupboard door opening is sensed, and the exhaust air flow from the cupboard (10) is controlled in response to the sensed door opening, characterized in that the total exhaust air amount from one or more fume cupboards (10) in a room is measured and the amount of air supplied to the room is measured and controlled in response to the measured exhaust air amount.

2. Apparatus for providing substantially constant air flow velocity through the door opening (12), of a fume cupboard (10), for laboratory applications and the like, independent of the size of the cupboard door opening, whereby a measuring device (18,20,22,24) is disposed for delivering a signal varying continuously with the size of the door opening, and whereby a regulator (34) is arranged in the exhaust air duct from the fume cupboard (10), said regulator (34) being controlled by said signal varying continuously with the size of the door opening, characterized in that a volume measuring means (40) is arranged for measuring the total exhaust air amount from one or more fume cupboards in a room, said measuring means controlling a corresponding volume measuring means (52) and a regulator (54) in the supply air duct for regulating the flow of supply air to the room in response of the measured total exhaust air flow.

3. Apparatus as claimed in claim 2, characterized in that the volume measuring means (40) for the exhaust air is adapted to control the volume measuring means (52) and regulator (54) in the supply air duct, so that a sub-pressure or excess pressure is generated in the room.

4. Apparatus as claimed in any one of claims 2 or 3, characterized in that the measuring means for the door opening (14) includes an IR transmitter (22) and an IR receiver (24), and a reflector (20), the transmitter and receiver being fixedly mounted to the cupboard (10), and the reflector being fixedly mounted on the door, or vice versa, said reflector being adapted to reflect light sent from the transmitter to the receiver, the intensity of the reflected light decreasing with increasing distance between transmitter and receiver, on the one hand, and the reflector, on the other hand, and in that a photocell (18) is arranged for generating an electric output signal varying in response to the intensity of the received light.

5. Apparatus as claimed in claim 4, the reflector (20) being fixed to the door (12) such as to accompany it in its movement, characterized in that the reflector (20) is adapted for being moved inside a protective tube (26) when the door moves.

6. Apparatus as claimed in any one of claims 2 - 5, characterized in that the regulators (34) are pneumatically controlled and in that an electropneumatic converter (32) is adapted to convert the output signal from the measuring means to a pneumatic signal for controlling the associated exhaust regulator.

7. Apparatus as claimed in any one of claims 2 - 6, characterized in that main plenum duct for exhaust air (42) and plenum duct for supply air (48) are provided with pressure transducers (58,60) adapted to control their respective associated fans (46,44) for maintaining the correct constant pressure in the ducts.

8. Apparatus as claimed in any one of claims 2 - 7, characterized in that an alarm is arranged to be started in the case of incorrect magnitude of the air supply to a fume cupboard (10), should the capacity of the exhaust air fan unit be exceeded as a result of putting too many fume cupboards into operation simultaneously, or if a door (12) is left open after termination of work for the day.

Ansprüche

1. Verfahren zum Erzeugen einer im wesentlichen konstanten Luftstromgeschwindigkeit durch die Türöffnung eines Rauchabzugskastens für Laboranwendungen oder dergl., unabhängig von der Größe der Türöffnung (12) des Abzugskastens, wobei die Größe der Türöffnung des Abzugskastens erfaßt und der vom Abzugskasten (10) abgeführte Abluftstrom in Abhängigkeit von der erfaßten Türöffnung gesteuert wird, dadurch gekennzeichnet, daß die gesamte Abluftmenge, die von einem oder mehreren Rauchabzugskästen (10) eines Raumes abgeführt wird, gemessen wird und die dem Raum zugeführte Luftmenge gemessen und in Abhängigkeit von der gemessenen Abluftmenge gesteuert wird.

2. Vorrichtung zur Erzeugung einer im wesentlichen konstanten Luftstromgeschwindigkeit durch die Türöffnung eines Rauchabzugskastens für Laboranwendungen oder dergl., unabhängig von der Größe der Türöffnung (12) des Abzugskastens, wobei eine Meßeinrichtung (18, 20, 22, 24) zur Abgabe eines sich stetig mit der Größe der Türöffnung ändernden Signals vorhanden ist und in dem vom Abzugskasten (10) wegführenden Luftabzugskanal ein Regulator (34) angeordnet ist, der durch das sich stetig mit der Größe der Türöffnung ändernde Signal gesteuert ist, dadurch gekennzeichnet, daß eine Volumenmeßeinrichtung (40) vorhanden ist, um die gesamte von einem oder mehreren Rauchabzugskästen eines Raumes abgeführte Abluftmenge zu messen, wobei die Volumenmeßeinrichtung (40) eine zugeordnete Volumenmeßeinrichtung (52) und einen Regulator (54), die sich im Zuluftkanal befinden, steuert, um den in den Raum geführten Zuluftstrom in Abhängigkeit von dem gemessenen gesamten Abluftstrom zu steuern.

3. Vorrichtung nach Anspruch 2, dadurch gekennzeichnet, daß die Volumenmeßeinrichtung (40) für die Abluft ausgebildet ist, die Volumenmeßeinrichtung (52) und den Regulator (54) im Zuluftkanal so zu steuern, daß im Raum ein Unter- oder Überdruck erzeugt wird.

4. Vorrichtung nach Anspruch 2 oder 3, dadurch gekennzeichnet, daß die Meßeinrichtung für die Türöffnung (12) einen IR-Sender (22), einen IR-Empfänger (24) und einen Reflektor (20) aufweist, daß der Sender und der Empfänger am Abzugskasten (10) und der Reflektor an der Tür befestigt ist oder umgekehrt, und daß der Reflektor ausgebildet ist, vom Sender ausgesandtes Licht zum Empfänger zu reflektieren, wobei die Intensität des reflektierten Lichts mit zunehmendem Abstand zwischen Sender und Empfänger einerseits und dem Reflektor andererseits abnimmt, und daß eine Fotozelle (18) angeordnet ist, um ein elektrisches Ausgangssignal zu erzeugen, das sich in Abhängigkeit von der Intensität des empfangenen Lichts ändert.

5. Vorrichtung nach Anspruch 4, wobei der Reflektor (20) so an der Tür (12) befestigt ist, daß er sie in ihren Bewegungen begleitet, dadurch gekennzeichnet, daß der Reflektor (20) ausgebildet ist, sich bei Bewegung der Tür im Inneren eines Schutzrohrs (26) zu bewegen.

6. Vorrichtung nach einem der Ansprüche 2 bis 5, dadurch gekennzeichnet, daß die Regulatoren (34) pneumatisch gesteuert sind und daß ein elektropneumatischer Wandler (32) ausgebildet ist, das Ausgangssignal der Meßeinrichtung in ein pneumatisches Signal zur Steuerung des zugeordneten Abluftregulators umzuwandeln.

7. Vorrichtung nach einem der Ansprüche 2 bis 6, dadurch gekennzeichnet, daß ein Hauptsammelkanal (42) für die Abluft und ein Verteilerkanal (48) für die Zuluft mit Drucksensoren (58, 60) versehen sind, die ausgebildet sind, ihre zugehörigen Gebläse (46, 44) zur Aufrechterhaltung des korrekten konstanten Drucks in den Kanälen zu steuern.

8. Vorrichtung nach einem der Ansprüche 2 bis 7, dadurch gekennzeichnet, daß eine Alarmeinrichtung ausgebildet ist, bei nicht korrekter Größe der Luftzufuhr zu einem Rauchabzugskasten (10) ausgelöst zu werden, wenn die Leistungsfähigkeit der Abluftgebläseeinheit überschritten sein sollte, weil zu viele Rauchabzugskästen gleichzeitig in Betrieb gesetzt wurden, oder wenn eine Tür (12) nach Beendigung des Arbeitstages offen gelassen wurde.

Revendications

1. Procédé destiné à procurer une vitesse d'écoulement d'air sensiblement constante à travers l'ouverture de porte d'une hotte d'aspiration pour des applications de laboratoire et équivalent, indépendamment de la taille de l'ouverture de porte (12), la taille de ladite ouverture de porte de hotte étant détectée, et l'écoulement d'air d'évacuation de la hotte (10) étant commandé en réponse à l'ouverture de porte détectée, caractérisé en ce que la valeur d'évacuation d'air totale d'une ou plusieurs hottes d'aspiration (10) dans une pièce est mesurée et la valeur d'air délivrée dans la pièce est mesurée et commandée en réponse à la quantité d'évacuation d'air mesurée.

2. Appareil destiné à procurer une vitesse d'écoulement d'air sensiblement constante à travers l'ouverture de porte (12) d'une hotte d'aspiration (10), pour des applications de laboratoire et équivalent, indépendamment de la taille de l'ouverture de porte de hotte, un dispositif de mesure (18, 20, 22, 24) étant disposé afin de délivrer un signal qui varie en continu avec la taille de l'ouverture de porte, et un régulateur (34) étant disposé dans la conduite d'air d'évacuation de la hotte d'aspiration (10), ledit régulateur (34) étant commandé par ledit signal qui varie en continu avec la taille de l'ouverture de porte, caractérisé en ce que des moyens de mesure de volume (40) sont prévus pour mesurer la valeur d'évacuation d'air totale d'une ou plusieurs hottes d'aspiration dans une pièce, lesdits moyens de mesure commandant des moyens de mesure de volume correspondants (52) et un régulateur (54) dans la conduite d'alimentation en air afin de réguler l'écoulement d'alimentation en air dans la pièce en réponse à l'écoulement d'air d'évacuation total mesuré.

3. Appareil selon la revendication 2, caractérisé en ce que les moyens de mesure de volume (40) pour l'évacuation d'air sont prévus pour commander les moyens de mesure de volume (52) et le régulateur (54) dans la conduite d'alimentation en air, de sorte qu'une dépression ou une surpression est générée dans la pièce.

4. Appareil selon l'une quelconque des revendications 2 ou 3, caractérisé en ce que le moyens de mesure de l'ouverture de porte (14) comprennent un émetteur infrarouge (22) et un récepteur infrarouge (24), et un réflecteur (20), l'émetteur et le récepteur étant montés de façon fixe sur la hotte (10), et le réflecteur étant monté de façon fixe sur la porte, et vice versa, ledit réflecteur étant prévu pour réfléchir la lumière envoyée par l'émetteur vers le récepteur, l'intensité de la lumière réfléchie diminuant avec la distance croissante entre l'émetteur et le récepteur, d'une part, et le réflecteur, d'autre part, et en ce qu'une photocellule (18) est prévue pour générer un signal de sortie électrique qui varie en réponse à l'intensité de la lumière reçue.

5. Appareil selon la revendication 4, le réflecteur (20) étant fixé sur la porte (12) de façon à l'accompagner dans son mouvement, caractérisé en ce que le réflecteur (20) est prévu pour être déplacé à l'intérieur d'un tube de protection (26) lorsque la porte se déplace.

6. Appareil selon l'une quelconque des revendications 2 à 5, caractérisé en ce que les régulateurs (34) sont commandés pneumatiquement et en ce qu'un convertisseur électro-pneumatique (32) est prévu pour convertir le signal de sortie des moyens de mesure en un signal pneumatique destiné à commander le régulateur d'évacuation associé.

7. Appareil selon l'une quelconque des revendications 2 à 6, caractérisé en ce que la conduite de raccordement principale pour l'évacuation d'air (42) et la conduite pour l'alimentation en air (48) sont pourvues de transducteurs de pression (58, 60) prévus pour commander leurs ventilateurs (46, 44) associés respectifs afin de maintenir la pression constante correcte dans les conduites.

8. Appareil selon l'une quelconque des revendications 2 à 7, caractérisé en ce qu'une alarme est prévue pour être mise en marche dans le cas d'une amplitude incorrecte de l'alimentation en air vers une hotte d'aspiration (10), si la capacité de l'unité de ventilateur d'évacuation d'air est dépassée du fait de la mise en mise en fonctionnement simultanée d'un trop grand nombre de hottes, ou si une porte (12) est laissée ouverte à la fin du travail de la journée.

Drawing