A VENTILATION SYSTEM

Abstract: A ventilation system particularly for use with a fume cupboard of the kind used in laboratories or similar situations including velocity sensors for providing signals to a control system which operates a damper system for selectively regulating the supply of external air to an exhaust duct for maintaining a predetermined air velocity in the fume cupboard. Preferably the sash of the fume cupboard includes drive means for enabling automatic closure of the sash in the event of extended periods of non-use.

Description: TITLE: A VENTILATION SYSTEM TECHNICAL FIELD The present invention relates to ventilation systems including ventilation systems associated with fume cupboards. The invention has been developed primarily for use with a fume cupboard for chemical laboratories and the like, and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to this particular field of use, and may also be applicable to enclosed spaces receiving conditioned air for maintaining predetermined conditions. BACKGROUND ART A fume cupboard provides a partially enclosed work place for minimising the dispersion of fumes to protect operators, other personnel and the local room air. This is generally achieved by extracting the fumes through associated exhaust ducting. Furthermore, fume cupboards also include selectively movable sashes for providing access to the partially enclosed workplaces. Strict and detailed specifications are set by the Standards Associations of most countries with respect to the minimum safe capture velocity or inflow velocity in the partially enclosed workplace which allows for sufficient removal of the fumes. Prior fume cupboards have utilised auxiliary passages to supply a varying external air flow to a main exhaust duct which extends from the fume cupboard. The flow of air in the auxiliary passage dilutes the fumes in the main exhaust duct and has been controlled according to the position of the sash. Opening the sash further restricts the amount of external air entering the exhaust duct thereby increasing the amount of air removed from the fume cupboard. The position of the sash has been indicated by such means as a multi-turn potentiometer mechanically turned by movement of the sash. This and other arrangements do not take into account ambient conditions to which the fume cupboard is subjected. Furthermore, such electro-mechanical systems have proved to be cumbersome and prone to wear. Additionally, should the sash of such a prior fume cupboard be left in the fully open position, due to operator error or otherwise, little or no external air is admitted through the auxiliary duct, and thus the exhaust system extracts air from the surrounding room. This results in an unnecessary expenditure of energy, both by the extraction system and any air temperature control system used in the laboratory. DISCLOSURE OF THE INVENTION It is an object of the present invention to overcome or substantially ameliorate at least one of these disadvantages of the prior art. According to the invention there is provided a fume cupboard including: a housing defining both a work compartment and a opening for providing access to said compartment; an exhaust duct extending from said compartment; an extraction fan co-operable with said duct to extract air from said compartment; a movable sash operable for closing predetermined portions of said opening; at least one velocity sensor for providing a signal indicative of the air velocity in said compartment; at least one auxiliary duct communicating with said exhaust duct between said compartment and said extraction fan for providing said exhaust duct with external air; and, at least one damper means responsive to said signal for selectively admitting external air to said exhaust duct to maintain a predetermined air velocity in said compartment. Preferably the damper means include two plates respectively rotatably mounted in the exhaust duct between the fume cupboard and the auxiliary passage and in the auxiliary passage. Preferably also, the sash is propelled by drive means to both close predetermined portions of the opening and to substantially close the opening after a predetermined time interval from the last use of the fume cupboard. BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a front view of the housing of a fume cupboard according to the invention. Figure 2 is a partially cut-away front view of the exhaust duct extending from the fume cupboard of Figure 1. Figure 3 is a partially cut-away side view of the exhaust duct showing an alternative embodiment of the damper means. MODES FOR CARRYING OUT THE INVENTION Referring to Figure 1 and Figure 2 a fume cupboard 1 includes a housing 2 which defines both a work compartment 3 and an opening 4 for providing access to the compartment. An exhaust duct 5 extends from compartment 3 and a centrifugal fan 6, driven by an electric motor 7, is co-operable with the exhaust duct for extracting air from the compartment 3 and expelling it through outlet 8. The motor 7 is connected to a constant voltage supply for providing a substantially constant speed of rotation of fan 6. Velocity sensors 9 and 10 are mounted to the housing 2 respectively adjacent the upper and lower edges of opening 4. These sensors supply electrical signals indicative of the sensed air velocity to a control unit 12 via standard electrical cables (not shown) . Velocity sensors such as a model from the AWM series, produced by Honeywell, are suitable for this application, however similar sensors may also be used. The position of the sensor within the compartment is selected according to the flow patterns therein. This position is dependant upon the physical dimensions of the compartment, and for example with large fume cupboards the sensors are respectively centrally located above and below the opening. An auxiliary air duct 14 communicates with the exhaust duct 5 between the compartment 3 and the extraction fan 6 for providing the exhaust duct with external air. Preferably the source of external air is distinct both from the laboratory air and that expelled through outlet 8. The damper means includes two plates 15 and 16 respectively rotatably mounted in the exhaust duct 5 between the fume cupboard and the auxiliary passage and in the auxiliary passage. Plates 15 and 16 are respectively driven by electric motors 17 and 18, each motor being selectively actuated by control unit 12 via suitable electrical conductors (not shown). Also, plates 15 and 16 move in an opposite sense to maintain a substantially constant cross-sectional area of ducting to supply air to the extraction fan. The positions of the plates can be continuously displayed by a pair of meters 31 and 32 located on the housing 2 above opening 4. The meters are responsive to signals from the control unit 12, which continuously updates the information displayed. Other conditions are able to be indicated on suitable displays for the operators information. For example a "power on" for the various components of the system, and various alarm indicators for alerting the operator of any potentially dangerous situations. The fume cupboard includes a movable sash 11 operable for closing predetermined portions of the opening 4. The sash preferably includes a sheet of transparent material whereby the contents of the compartment 3 can be perceived when the sash is in the closed position. Should the sash be propelled from a fully closed to a fully open position an increased volume of air will be required to be moved through the compartment 3 for the predetermined air velocity to be achieved. The velocity sensors 9 and 10 will initially signal a reduction in air velocity. The control unit 12 will respond by actuating motor 18 to rotate plate 16 to restrict the passage of external air through the auxiliary duct 14. Simultaneously, motor 17 will rotate plate 15 in an opposite sense for providing less restriction to the air flow in exhaust duct 5 resulting in an increase in volume of air moving through compartment 3. As the velocity sensors are providing the necessary feedback for the system, equilibrium will be achieved when the air velocity has reached the predetermined value. When moving the sash from a fully open to a fully closed position the plates will respond by moving in the opposite direction from that described above. The velocity sensors detect any ambient conditions in the air velocity or pressure resultant from changes in these conditions in the surrounding laboratory containing the fume cupboard. The control system accommodates these conditions by actuating an appropriate change in the position of the plates 15 and 16. In the event of such conditions dangerous fumes will continue to be removed through the exhaust system, and prevented from exiting through the sash opening and thus endangering the operators. Any wind gusts incident upon damper plates 15 or 16 from an external source are continuously accommodated by the control system, thereby preventing any fumes from being redirected back into the fume cupboard through the exhaust duct. Other ambient conditions, such as a substantial obstruction near the opening, (for example a person), causes the velocity sensors to detect the changed conditions and adjust the air flow in the respective ducts. This prevents the presence of excessively high air velocities at the opening 4 due to a large volume of air having to be passed through a restricted area. Should the extraction fan no longer perform its desired operation due to a failure or a blockage in the ducting system, velocity sensors 9 and 10 will correspondingly signal a failure in the maintenance of the predetermined airflow in compartment 3. A suitable alarm is then actuated for signalling such a fault to an operator. The sash 11 is propelled by a tubular motor 20 such as model 534B produced by Somfy. Following actuation of a manual switch 21 the motor 20, by winching suitable chords 29 and 30, will effect the movement of sash 11. It will be appreciated that a plurality of such switches can be conveniently located for actuating sash movement, such as a foot operable switch (not shown) being located at the base of the fume cupboard or a knee operable switch (not shown) located at the lower edge of the housing. Furthermore, a remote control switch (not shown) utilising infra-red radiation is able to actuate sash movement. The motor 20 is able to position the sash 11 in any location between a fully open position (as shown in Figure 1) and a fully closed position. The motor propels the sash either in a continuous motion or in discrete steps. An infra red transmitter 23 and sensor 24 are respectively located on opposing sides of the opening 4 to establish an infra red field across the opening. The output of sensor 24 is linked to control unit 12 via suitable conductors for allowing the detection of an interruption of the field by an operator or the like. In the event of such an interruption, the control unit resets an associated timer. Should the timer be allowed to progress to a predetermined value the control unit actuates motor 20 to effect the closing of sash 11. This feature allows for operator error resulting in the sash being left open, and prevents the unnecessary evacuation of heated or cooled air from the laboratory. Due to the large volume of air which can be removed, this represents the saving of substantial amounts of energy. Referring to Figure 3 where corresponding features are denoted by corresponding reference numerals, a single plate 25 is located at the junction of the auxiliary air duct 14 and the exhaust duct 5. This arrangement provides for a similar effect as that shown in Figure 2 while only requiring the use of the single plate 25. The plate is hingedly mounted for rotation between fully restricting air flow from the auxiliary duct to a position where it fully restricts air flow from the fume cupboard into exhaust duct 5. The plate is driven by electric motor 26, which in turn is actuated by the control unit 12. The control unit is able to supply all the information it collects to an external source via a connector 35, and can further respond to instructions received from such a source. This facilitates the central control of a plurality of such fume cupboards for example in a large laboratory. Safety conditions are able to be monitored from a central location for providing suitable warning to all operators. In this embodiment connector 35 is a DIN96. This enables the cupboard to be connected to a microprocessor system, or the like, for allowing a plurality of such cupboards to be centrally connected and controlled. Although the invention has been described with reference to a specific example, it will be appreciated by those sJ.illed in the art that the invention may be embodied in many other forms. For example, a ventilation system for a room including doors and other openings, where the associated ducting directs the supply of conditioned air to the room. Velocity sensors appropriately positioned are able to supply a signal indicative of the air velocity to a damper system within the ducting for maintaining a substantially constant predetermined air velocity in the room.

Claims: CLAIMS : - 1. A fume cupboard including: a housing defining both a work compartment and an opening for providing access to said compartment; a exhaust duct extending from said compartment; an extraction fan co-operable with said duct to extract air from said compartment; a movable sash operable for closing predetermined portions of said opening; at least one velocity sensor for providing a signal indicative of the air velocity in said compartment; at least one auxiliary duct communicating with said exhaust duct between said compartment and said extraction fan for providing said exhaust duct with external air; and, at least one damper means responsive to said signal for selectively admitting said external air into said exhaust duct to maintain a predetermined air velocity in said compartment. 2. A fume cupboard according to claim 1 wherein said damper means includes two plates respectively rotatably mounted in the exhaust duct between the fume cupboard and the auxiliary passage and in the auxiliary passage. 3. A fume cupboard according to claim 2 wherein said plates move in an opposite sense for providing a substantially constant cross-sectional area of ducting for supplying air to said extraction fan. 4. A fume cupboard according to claim 1 wherein said damper means includes a plate mounted at the junction of said auxiliary duct and said exhaust duct which moves to close one duct while opening the other. 5. A fume cupboard according to claim 3 wherein said sash is propelled by drive means. 6. A fume cupboard according to claim 5 wherein said drive means effects the movement of the sash to a closed position after a predetermined time interval from the last use of the fume cupboard. 7. A fume cupboard according to claim 6 wherein said sash is selectively operable for movement between an open and closed position. 8. A fume cupboard according to claim 7 wherein said movement is in discrete steps. 9. A fume cupboard according to claim 3 wherein said damper means is driven by at least one motor. 10. A fume cupboard according to claim 9 including a control unit for receiving said signal from at least one said velocity sensor and for actuating at least one said motor. 11. A fume cupboard according to claim 1 wherein said sash includes a sheet of transparent material whereby the contents of the compartment can be perceived when the sash is in said closed position. 12. A fume cupboard according to claim 1 including at least one meter for displaying a reading indicative of the position of said at least one damper. 13. A fume cupboard according to claim 1 wherein said predetermined air velocity is selectively variable. 14. A fume cupboard according to claim 8 including an infra red transmitter and receiver for providing a second signal when the fume cupboard is in use. 15. A fume cupboard according to claim 14 wherein said second signal resets a timer progressing to said predetermined time interval. 16. A fume cupboard according to claim 5 wherein said sash movement is actuatable by one or a combination of either hand, knee or foot controls. 17. A ventilation system for a chamber having at least one opening provided with a selectively operable closing means, ducting connected to supply or remove air from said chamber, fan means co-operable with said ducting to effect said removal or supply; at least one velocity sensor disposed to provide a signal indicative of air velocity within said chamber; and at least one damper means responsive to said signal to control the removal or supply of air and maintain a substantially constant predetermined air velocity.

Inventors: STASCH KARLHEINZ, STASCH, KARLHEINZ
Applicants: STASCH KARLHEINZ, STASCH, KARLHEINZ
Application year: 1990
Main classification: F24F7
IPC codes: B08B15