CA2116134C - Method and apparatus for controlling a fume hood - Google Patents
Method and apparatus for controlling a fume hoodInfo
- Publication number
- CA2116134C CA2116134C CA002116134A CA2116134A CA2116134C CA 2116134 C CA2116134 C CA 2116134C CA 002116134 A CA002116134 A CA 002116134A CA 2116134 A CA2116134 A CA 2116134A CA 2116134 C CA2116134 C CA 2116134C
- Authority
- CA
- Canada
- Prior art keywords
- hood
- detecting
- controller
- containment
- face
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B08—CLEANING
- B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
- B08B15/00—Preventing escape of dirt or fumes from the area where they are produced; Collecting or removing dirt or fumes from that area
- B08B15/02—Preventing escape of dirt or fumes from the area where they are produced; Collecting or removing dirt or fumes from that area using chambers or hoods covering the area
- B08B15/023—Fume cabinets or cupboards, e.g. for laboratories
Abstract
This invention relates to a fume hood controlling method and apparatus which reduces the amount of replacement air required to operate a fume hood (10) by permitting the fume hood to operate at a relatively low face velocity in the absence of a containment affecting condition, but which is capable of detecting the occurrence of a containment affecting condition, such as the presence or movement (34) of a user within a selected area of the face of the fume hood, and of increasing face velocity to a selected level in response to such detection. When the detected condition no longer exists, the control automatically returns the fume hood to the lower face velocity, preferably with a time delay. Maximum replacement air volume and minimum replacement air volume may also be controlled in response to such detection.
Description
r~~ 9~ro4~za ~~rr~s9zro7o~~
.~. .a. t.~ . t ~D ~-F~'~HO13 AND ~1PPAF~"rtTS FOR GOI~TTP,~LLTNG
~ FUME HpOD
Field of tine Tnvention:
this invention relates ~to laboratory fume hood controllers end more spec~.fically to methods and apparatus for varying a fume hood's face velocity in response to variations in o;ne pr mora hood containment affecting conditions.
~ackground of the Invention:
p laboratory fume hood-is a ventilated enclosure where harmful materials can be handled safely. ~'he hood captures contaminants and prevents them from escaping into the laboratory by using an exhaust blower to draw air and contaminants an and around ~he'hood's work era away from the operator so that inhalation of and contact with the contaminants are minimised. Access to the interior of the hood is ~hrough'.~n opening which is closed with a sash which typically slides up and down to vary the opening ~.nto the hood .
'1~0 93/04324 PCT/US92/0705.
., , . ~ ... _.. ,~ .~ z~ ._ The velocity of the air flow through the hood opening is called the f ace velocity. The more hazardous the material being handled, the higher the recommended f ace velocity, and guidelines have been established relating face velocity to texicity.
Typical face velocities for laboratory fume hoods are s0 to 150 feet per minute (fpm), depending upon the application.
When an operator is working in the hood, the sash is opened to allow free access to the materials inside. The sash may be opened partially or fully, depending on the operations to be performed in the hood. While fume hood and sash sues vary, the opening provided by a fully opened sash is on the order of ten square feet. Thus the maximum air flow which the blower mush provide is typically on the order of 600 to 1500 cubic feet per minute (cfm).
The sash is closed when the hood is not being used by an operator. Tt is common to store hazardous materials inside the hood when the hood is not in use, and a positive airflow must therefore be maintained to exhaust contaminants from such materials even when the hood is not in use and the sash is closed. As the hazard level of the mater~.als being handled and the resulting minimum face vel~city increases. maintaining a safe.face -velocity'becomes more difficult.
w~ 9moa~~a ~criu~9as~~os7 a t i ~ f 1 ) i n .. .~. a. ,.%
An important consideration in the design of a fume hood system is the cost of running the system.
There are three major areas of costs: the capital expenditure of installing the hood, the cost of power to operate the hood exhaust blower, and the cost of heating, cooling, and delivering the "make-up air,~~ which replaces the air exhausted from the room by the fume hood. ~'or a hood operating continuously with an opening of 10 square feet and a f act velocity of 100 fpm, the cost of heating and cooling the make-~up air could, for example, run as high as fifteen hundred dol7.ars per year in the northeastern United Mates. WThere chemical work is done, large numbers df fume hoods may be required.
For example, the Massachusetts s Institute of Technology has approximately 550 fume hoods, most of which are in operation 24 he>urs a day.
capital or investment costs is an important ~aCtor an the design ~f fume hood systems. This elates to the capital cost o~ the supply and exhaust fans, duct-work, boiler and cha.llers, and other equipment related to the movement and conditioning of the outside air brought into and exhausted from the building through the fume hoods.
The laze, capacity arid cost of this equipment is integrally related to the peak capacity of air 'volume~to be exhausted from the hoods. This total volume is in turn directly related to the face " , ,.., '. :' ". . . , , ~. ." . .
VSr~ 93/04324 .:, y ~. ; y, , : , ~, P~'i'/LJS92/0705 ~i velocities of those hoods. For example, a 20%
reduction in the face velocity for which. the building hoods are designed, from 1~0 FPM to 8o FPM
allows for a 20g reduction in the required capacity of the system air handling equipment.
Consequently, there are strong economic reasons for using the lowest face velocity which still produces acceptable fume hood capture and containment. P2uch research has been performed recently on the factors affecting this minimum acceptable face vel~cz,ty. For example, with a fume hood having no equipment in the first ~" back from the sash, uniform face velocity distribution across the face of the ho~d, and no high cross drafts, the face v~locit~ can be set to 60 FPM and excellent containment will occur. I~owever, spip age will occur at 60 FPM if people walk past the hood, someone waves their arms near the opening or supply air diffusers blow air past the corners in front of the hood. All these disturbances create cross drafts and challenges to the fume hood containment which can pull fumes out of the hood. Tncreasing the face velocity to 100 or 125 FPM significantly reduces the spillage caused by these factars. Above 1.5.~ FPM, the air flow into the hood can became turbulent creating eddy currents and local low ~~
pressure'areas which can also create spillage.
WO 931Oa132~1 PC'f/LJS92/07057 . ~ ., y l ° Because of the above factors, many laboratories operate their hoods at 100 to 125 FPM. Others allow the face velocities to drop to 70 to ~0 FPM when the laboratories are unoccupied and operators are not near the hood where they might create crossdrafts from their motions. A very few companies operate their hoods at 60 FPM, but only with strict operating guidelines in order to prevent disturbance of the fume hood's containment.
Tn order to save energy and reduce the peak air capacity in laboratories, fLlme hood control systems are presently used that maintain a constant face velocity independent of the sash opening. Ea~ly ~e~~ions of these systems ~~~raced by changing _ volume in a two or three st~,p operation based on the sash heig:~,t or the amount of: sash opening. Much better and more recent syst~ms,provide can~inuous control caf the air vol~xne based on sash position and are referred to as variable air volume systems. An~
e~ampl~ of one of these systems is described in U.S.
Pa°ten~s 4,528,98 and 4,706.55. These systems work weld., but aye dependent on the operator lowering the sash. When 'the c~pers.tor dines lower the sash, the exhaust, and typically also the room supply air volume; are reduced proportionately which generates i the energx savings. If many hoods are used an a ~.
v~uildi:ng'wi~h these controls, both the average and typical peak total a~.r volumes will be reduced due W~ 93/0434 G.) '~ ,-~ ~ ~ '~ ~ ~'Cl'/IJS9~/0705~
to the diversity in the hood's operation. Tn other words, it is unlikely that all the hoods will be fully open at any one time. A problem for the building designer, however, is in estimating how much diversity will actually occur in the building.
Consequently, many designers take a worst case view and don't size the buildings capacity below ar much below the 100% capacity assumption of all the hoods full open at the same time. This is done because the designer is concerned that the users will not lower the sash when leaving the hood area. This is unfortunate because studies have shown that operators spend only a small fraction of their time in front of the hood.
Tn an attempt to bypass the operator problem of not closing sashes some fume hood manufacturers have introduced devices such as ;>hown in U.S. Patent 4,774,~7~ that detect the presence of the operator in front of the hood and raise the sash to some preset position. When the operator moves away from the hood, the sash is automatically closed.
Typically, a two state or variable air volume control system is also used to vary the air volumes to maintain a constant face velocity at the two different sash positions.
These sash operator systems have not as of yet _~
.received~widespread acceptance among researchers for several reasons. Firstly, the rapid movement of the wo ~~ioa3za ~orius9zio7as~
r ~- ..L .
- 7 _ sash up and down can occur even when a person just walks past the hood, producing a disturbing f else reaction of the hood. Also, many researchers like to operate the sash at various heights, and this is made more difficult by the two position operators.
Further, many hoods have wires, tubes and small hoses going into the hood near the bottam of the sash opening. Uncontrolled movement of the sash might hit these wares and hoses and potentially tap over delicate glassware to which the tubes and hoses are connected. This in turn could create a serious and potentially dangerous accident. Lastly, many hoods have horizontally rnov'.ng sashes which make at difficult to implement a sysctem to move the sashes iz~ oxder to increase or decrease the amount of hood opening.
For all of the above reasons, a better approach is needed for reducing both energy usage and peak estimated replacement volume while not creating a potential hazard and not adversely affecting the researcher's work.
Summary of the Invention din object of this invention is to provide an improved methad and apparatus for controlling a fume hood, which controller (a) substantially reduces the replacement azr utilized by the system, regardless of 'sash position, (b) permits fume hood systems to be designed for lower peak volume flow without g _ permitting or creating any danger of a breakdown in toxic fume containment or any danger of damage to ongoing experiments or equipment, and (c) permits researchers complete flexibility in selecting sash positions.
The present invention provides a controller for use with a fume hood having face velocity control means, the controller comprising means for detecting changes in at least one containment affecting ~o condition; and change means responsive to the detecting means detecting a selected change in containment affecting condition for causing the control means to make a corresponding change in the face velocity of the fume hood to a preselected velocity for the changed containment condition, the change means including incrementing means responsive to a detection by the means for detecting of a selected increase in a selected containment affecting condition for causing the control means to increase 2o the face velocity of the fume hood to a selected increased level, and decrementing means responsive to detection by the means for detecting of a selected reduction in a containment affecting condition for causing the control means to reduce the face velocity of the fume hood to a selected decreased level.
In another aspect of the present invention, there is provided a method for controlling a fume hood having face velocity control means comprising the steps of detecting changes in at least one contain-3o ment affecting condition; and causing the control means to make a corresponding change in the face velocity of the fume hood in response to a detected change in containment affecting condition to a - 8a -preselected velocity for the changed containment condition, the change causing step including the steps of causing the control means to increase the face velocity of the fume hood to a selected increased level in response to the detection during the detecting step of the occurrence of a selected containment affecting condition, and causing the control means to reduce the face velocity of the fume hood to a selected decreased level in response to the ~o detection of a selected reduction in a containment affecting condition.
More specifically, this invention provides a controller for use with a fume hood having a face velocity control. The face velocity control may control face velocity directly or may control it indirectly by controlling flow volume or some other conditions affecting face velocity. The controller has a detector for detecting at least one containment affecting condition, which condition may be (a) the 2o presence or proximity of a person within a predetermined area of the fume hood, (b) movement within a predetermined area of the fume hood, either by a person or as a result of air drafts or other conditions, and/or (c) the presence of equipment or material within a predetermined distance from the front of the hood. Appropriate detectors are provided for each condition to be detected. In response to the detector detecting a selected change in containment affecting conditions, the face velocity control makes so a corresponding change in the face velocity of the fume hood to a preselected velocity which is appropriate for the changed containment condition.
- 8b -The change may be an increase in the face velocity of the fume hood to a '1~0 93/14324 ~G I'/~....IS92/~7057 :'.~ _. .;. ~ .
_ g _ level sufficient to assure containment of fumes in the hood with the containment affecting condition present, or the change may be a reduction in the face velocity of the fume hood to a selected decreased level in response to the de~tec~tion of a selected reduction in containment affecting condition. The incrementing preferably occurs substantially instahtaneously on the detection of a containment affecting condition, while a reduction in f ace velocst~ is delayed for a selected time period when a selected reduc~tiora in containment affecting c~nd:ition is detected. Containment affecting conditions may include a person being within a selected area of the f ace of the hood, the detection of movement within a selected area of the f ace of the hood, which movement may be of a person ~r may be air motion or turbulence either inside or outside the hood, may be a tracer fluid ejected in .
the hood, with the escape of such tracer fluid being measured, or may be the detection of apparatus within a predetermined distance from the front of the hood.
The f ace velocity control may control volume thxough the fume hood with a change being.a change in flow volume. The system may include a means fob e~tablx'shi~g a maximum flow volume and/or a means g~r'establishing a minimum flow volume with the maximum flow volume and/or the minimum flow volume W~ 93/04324 P(,"Y'/US92/0705, ", , _ r_ i:~ _~. ;) being changed in response to a change in containment affecting condition. Tin offset in the controlled flow volume may also be effected in response to a change in containment affecting condition. Where the fume hood has an opening which.may be covered to varying extents by at least one moveable sash, a selected vo~.ume is normally maintained relative to the sash position. The selected volume maintained may be changed in response to the detection of a change in containment affecting condition. For some embodiments, the selected volume maintained is a constant volume regardless of sash position.
For some embodiments, a first face velocity is caused in response to a detection of a containment affecting condition, and a second lower face velocity is caused in response to the absence of a detection. Where there may be varying degrees of containment. and the detection detects.the degree of containment affecting condition, the change in face velocity may be to a f ace velocity appropriate for the detected degree of containment affecting condition. ~'he changes in face velocity may be discrete or may be substantially continuous based on the degree of detected containment affecting dondition.
The~~f~ace velocity con~txol may include a speed -, contr~51 for a blower exhausting the fume hood, or may directly change the flow from the fume hood.
WO 93/04:324 F~'/~JS9z1o7o57 ~.. z. .a.
° 11 the foregoing other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawings.
In the ~rawinqs FIG. 1 is a side-view representation of a prior art fume hood system.
FIG. 2 is a semi-block diagram of a fume hood system in accordance with a first embodiment of the invention.
FTG. 3 and FIG. 4 are block diagrams of a passive and of an active motion detection system, respectively, which may be utxl~.zed in practicing the teachings of this invention.
FIG. 5 is a block diagram of an alternative embodiment of the invention illustrating another sensing concept.
FIG. 6A illustrates a typical detection zone for a proximity or motion detector and also illustrates the detection of another detection containment condition.
FIG. 6B is a front perspective view of a fume hood illustrating additional containment affecting condition detection elements.
FI_G~.,7 is a block diagram of a sash position sensing'circuit which may be utilized in conjunction with various embodiments of this invention.
9~Y~ 93/04324 PCT/US92/0705", rv ~ '~' d~
FTGS. S, 9, 10 and 11 are diagrams illustrating the relationship between air flow and sash position for various embodiments of the invention.
~°I~, 12 xs a schematic diagram of a cixcuit for controlling minimum and maximum air flows.
FTG, 1~ is a semi--block schematic diagram of a flow c~ntroller whack. may be utilized in conjunction with various embodiments of the invention to control minimum and maximum air flows.
FIG. 14 zs a ~e~i-block diagram of still another embodiment of the invention.
Detailed Description:
FIG. 1 shows a prior part system used primarily to maintain a constant face velocity. Air fl~w sensor 27 i.s placed in an ~pening in the fume hood so that it can dxrec~ly sense the velocity of ai.r entBring the hood. Sensor 27 could be placed in the sash opening Qr in a separate opening in the side of hood enclosure 10o as shown by opening 26 in ~'IG.
1, gn this system, the sensor may be used to control either the speed of blower 14 or to' c~ntrol a damp~~ ~:n the exheust ducting 15 to control the air flow. U:S. Patent No> 4.241.257 describes a similar device that measures the pressure drop between the inside and outs~.de of the hood as a methc~c~,of sensing a quantity related ~:n some way to .dace ~relocity.
V'1'~ 93/04324 P~T/1,1~92/07057 ~" w .x. ~ ~ ~9 systems of the type shown in FIO. 1 have several problems relating to the maintenance of a constant f ace velocity such as speed of response, stability, susceptibility to cantamination of the air flow sensor, etc. One potential problem which relates to the present invention is that the f ace velocity of a hood controlled by these devices is affected by the user standing close to the front of, the hood.
I~owever, unlike the present invent~.on, these systems reduce the face velocity when the user stands near the opening of the hood, which is directly opposite of the desired result. The present invention increases the average face velocity to generate better fume hood capture and contair~en~.
prior art devices also work slowly, so that even if they could produce the intended result. it would be too late to protect the user. Due both to the time delay and. the wrong control action of these systems, the disturbance of a person walking past the hood could create a significantly worse reaction than a hood with no such control system. The present invention uses different sensing and control er~u,ipment to immediately detect the disturbance and respond rapidly in the correct manner to provide better fume 'hood operation.
Th_e~Ypresent invention also differs from prior art systems that detect the presence o~ a user and raise the sash while trying to maintain a constant WO 93/04324 PC°f/US92/0705.
~.r t. ; ~S ~ ,~
. .a.
face velocity for two different sash positions. The goal of such prior art systems is to maintain a constant f ace velocity, ~r if no volume controller is used, then the volume may actually be fired. The present invention also trys to sense the user, but unlike the prior art, it changes face velocity to change the hood volume anal save energy; it does not disturb or move the hood sash or sashes.
Consequently, the present invention is universally applicable to all hoods even those that do not have a movable sash or such hoods as canopy hoods. also, this system, when used in combination with a constant face velocity control system such as that described in U.~. Patent Nos. 4,52~,~9~ and 4,706,553, can achieve greater energy savings then when such systems are used alone due to the decrease in average face velocity that the present invention achieves, Referring to FTG. Z, a first embodiment of the present invention is shown as it would be applied to a conventional fume Y~ood with a damper 30 or similar air throttling or resistance type flow control element. This damper controls the flow out of fume hood In and is actuated by actuator 31. Flow controller 3~ controls actuator 31 and may consist ' of a ~_on~tant volume controller to maintain a given volume flow independent of sash position, a two sta,~e (or mufti-state) volume controller that ~V~ 93/04324 1P~'f/6JS92/07a57 s~ r ,5 ~ c.
N .i 1 t.~
changes the volume of the hood based on the sash height or open area of the sash, or a variable volume control system which maintains a constant f ace velocity based on sash position. U.S. Patent l3os. 4,741.5'1; 4.58.898; and 4,706,553 describe various types of variable volume control systems which could be used for flow controller block 32.
All of these flow controllers work.to maintain a given setpoint value of face velocity. In the constant volume systems, this can be interpreted directly as a setpoint of volume, whereas in the variable volume systems the fume hood volume will vary for a given face velocity setpoint. In many cases, with the variable volume systems, there will also be a minimum and maximum exhaust volume limit placed on the fume hood control.
Transducer 35 and person/motion detector circuit 34 work together to detect the presence and movement of the user/researcher in front of the hood. The transducer may also detect significant air motion or turbulence in front of or near the hood. When air motion or user proximity/movement is detected, it activates f ace velocity setpoint change circuit ~3.
This circuit acts an flow controller 32 in one of many possible ways, but generally acts to increase its f~'~e velocity and/or volume flow setpoint.
Alternatively, it may act to modify the minimum and maximum exhaust volume limits of the flow controller through the volume clamps circuit 39.
WU 93/~4324 I'~'111~92/~7Q57 -, ~:a ~
~ 3 '~~
ri Transducer 85 and detector circuit 34 may be implemented with a variety of technologies such as is used in security or intrusion alarm systems. For example, transducer 35 could be implemented by using a passive far-infrared (typically 8-14 um) motion sensor. an active ultrasonic motion sensor, an active microwave motion sensor, an active near-infrared (typically 880-940 nm) or visible light proximity sensor, or a combination thereof.
Based on the type of transducer used, a compatible detector circuit 34 would be employed.
FIG. 3 illustrates an implementation using a passive gyro-electric infrared motion sensor and detector circuit. The pyra~electric detector 41 detects changes in heat patterns caused by the movement of a person relative to their background radiation, in a detection zone. The optical system 40, for example a mirror or fresnel lens, focuses the infrared energy, in for example the 8-1.4 um spectrum, onto the detector, after a variable gain stage 42 which controls the sensitivity of detection, the amplified signal is filtered in signal processing circuit 43 with a band pass filter which attenuates unwanted signals and increases the 8~N (signal to noise) ratio of the frequency of interest;, which is generally in the .3-3 Hz range.
-----~t~hen the signal is of a desired amplitude, comparator 44 triggers a timer 45. The timer Wf.~ 93/O~f324 P~CfJU~92f07057 IFv changes the state of relay (46), and thus of its output, f or some preset time period. The output from relay 46 is applied to control change circuit 33 (FTG.
The timer will restart its timing period if the comparator triggers a second time within the preset time period. This preset time period. or turn off ..
delay time, is used to keep the detector on even if the researcher is still far a few minutes while he is working in front of the hood, and also to prevent the nuisance and potential danger of the system . increasing and decreasing the f ace velocity based on how still the researcher is while the researcher is still in front ~f the hood. Alternatively, a smaller turn off delay could be used if the passive system were combined with some sort of active proximity or presence detector.
With the use of variable voltage control 47 the circuit could detect different zones. For example the variable voltage output would indicate the detection of the researcher in the lab relative to a detection zone an front of the fume hood. The variable voltage would tell the face velocity setpoint change block 33 of FTG. 2 to inorea~e the face yeloci~y a little when the researcher is present ;in the room and to increase the face ue1'ocity'even more if the researcher is in front of the hood.
CVO 93J04324 PCT/US92/a7057 - m -A complete active system that includes a Doppler motion detection is shown in FIG. 4. These systems can be combined ~rith a passive detector and are typically based on one of ~thre2 technologies:
infrared 800-900 nm, microwaves or ultras~nics. The active system detects the presence and or movement of a person. I~Iovement, which indicates where the researcher is and how fast he is moving, is detected by the Doppler effect for microwave and ultrasonics. Presence, which indicates if the researcher is present at a particular location, is detected by an infrared beam.
For the circuit of FTG. 4, transmitter 48 sends a pulse of appropriate frequency into the detection zone. Depending on the presence of personnel in the detection zone, the pulse is either returned to the receiver 49 within a selected clock interval or not. If the receiver receives the signal, preamplifier 57. boosts the signal sd that, assuming the signal is received within the interval of clocl~
50, sample and hold amplifier 5~ can sample the pu~,ses. with the signals of interest on them. The pulses are sampled in sync with the transmitted pulses of clock 50. Doppler/presence detector 53 detects the motion or presence from the sampled 'signal, the presence detector detecting presence of a signal end the Doppler detector detecting frequency shift. The signal is filtered and W~ 93/04324 PC'T/iUS92/07057 _ 19 _ processed in signal processing circuit 54 so that unwanted signals are attenuated, thus increasing the S/N ratio for the frequency of interest.
The block diagram of figure 4 illustrates two potential outputs, one indicating if the researcher is in the detection zone and the other detecting where in the zone the researcher is. In the first case, detecting if the researcher is iii the detection zone, the output of relay 57 tells the face velocity setpoint change block 33 of FIG. 2 to increase the f ace velocity by a present amount. The later case would change the f~~ce velocity by a certain percent relative to the distance of the researcher from the hood.
The presence of the researcher in the detection zone is indicated by the signal amplitude out of block 54 increasing until it rises above the threshold of the comparator 55. The comparator starts a timer 5~. The timer switches the state of the relay 57 for some preset time. As for the circuit of FIG. 3, the timer will reset back to zero if the comparator triggers a second time within the timer set period. The relay tells the face velocity setpoint change block 3~ (FIG. 2) to change the face velocity.
To indicate the position of the researcher relativevtb the fume hood, the signal coming out of block 54 would be converted to a variable voltage by r-~
WO 93/04324 ~CC°f/U~92/U7U57 ~~.:~~~34 - 2~ -clrcult rJ~s the voltage output telling the face velocity setpoint change block 33 (~I~. 2) the distance of the researcher from the fume hood. The face velocity may then be increased as the researcher moves closer to the fume hood and decreased as the researcher moves further from the fume hood.
The use of both a presence detector and a motion detector may prove useful to prevent the system from being adversely affected by people walking past the hood. If someone walks pa:>t the hood, the system must quickly activate the active mode. However , if the person does not stop in front of the hood, but continues walking, it would be wasteful to leave the hood in the active mode foy: more than perhaps ZO
seconds. This prevents a g,>erson fram walking around the room and activating all the hoods s~.multaneously. The presence detector is desirable for use in conjunction with the motion detector so that the active mode is only left on for greater than 10 seconds if a researcher remains standing in front of the hood.
F"1G. 5 illustrates another sensing concept to detect a person walking up to and, standing in front of the hood. This involves a floor mat type switch 36 which is activated by standing on a special mat placee3 5.n front of the hood. These devices are of the general type used to open doors, although W() 9~104~24 Pt.'f/1JS92/07057 generally modified in appearance and construction to fit in better for a laboratory application. For example a capacitive plate sensor or inductive plate sensor which would operate by stepping on a sheet of metal either on top of or embedded into the floor would provide a neater installation for this application which would be less affected by spilled chemicals, There are also many similar sensors such as piezoelectric or FSR (Force Sensing Resistor) which are very flat and can for example be laminated into. corrosion resistant plastic. Detectors of this type typically work on press>ure or on the capacitive or conductive affects of the human body. Except for the change in detector, fhe system of FIG. S has the same components and operates> in the same way as the system of FIG. 2.
then passive or active detectors such as those shown in Figs. 3 or 4 are used. the optics of the system will need to be adjusted to sense the proper area in front of the hood. Some field adjustability is desirable based on the different sizes of hoods and different lab casework layouts in which the hoods are applied. FIG. 6A shows a typical detector zone 50 for a detector 35 that is mounted on a hood l0 as shown in FIG. 6E. In some cases, two or more detecto_~s, may need to be used ar special optics may be4~required that can specifically shape the detecrtion field of a single detector. For example, W~ 93/04324 P~.'ff ~S92f0705 7 . s ~, 3 ~ri' s.. ..~~. ;fir .~ ~ ~~
it may prove useful to observe the hood area from a height of 3' ar 4' on up to ignore chairs, tables, equipment and other fixed or movable~objects. When, for instance, infrared detectors are used, special fresnel type lenses or specially shaped mirrors may be used. The size of the zone 50 would vary with application. For example, the zone might extend 1.°
to 4'from the front of the hood and beyond each side of the hood by from 0 to ~'.
ether means to implement sensor 35 and detector circuit ~4 would be through creating a light curtain or projecting a light beam around the desired detection zone, 50 of FTG. 6A. When an ope~rabor crosses and momentarily breaks the light beam, the detector circuit signals the presence of the operator. The circuit of FTG. 4 could be used to implement this type of detector circuit.
Tn addition to sensing the presence or motion of a user near the hood, there are, as was mentioned earlier, potentially other factors which might dictate the need for a higher f ace velocity, for ex~~ple, the presence of an: air velocity greater than 30 to 50 FPM such as from a nearby supply air diffuser. Additionally, the presence of apparatus in the first 6" or so of the hood back from the from Y~ the sash can also decrease hood containment, necessitating the need far a higher face velocity.
w~ ~3iod~x~ ~~°ous9xi~~os~
There are many finds and types of air velocity sensors that could be used to detect air motion, either in front of or at the corners or sides of the fume hood. tTnfortunately, many of these tend to be point sensors such as hot wire or thermistor--type thermal aneometers. ~ better system~wouid sense the presence of low air velocity over a wider area. one such approach would use long streamers; 51 (FIG. 6~) the length of each such streamer being roughly equal to the height of the sash openings. The streamers 5l would be placed at the front corners or edges of the hood where the hood is most affected by air currents. These streamers would be made of some 13~h~'m~terial easily maved by wand or other air curi~ez~ts striking the streamer. The motion of the streamers could then be detected by the motion detectors that were described earlier.
~lterna~ively; the motion could be detected directlx by ~ suitable motion detector 52 to which each streamer 51 is attached. As each streamer moves) its motion is transmitted to the corresponding detector 52, which senses the motion by for example movang the contact point on a variable resistor or b,~ sensing the variation in pressure, weight or twisting forge applied to a sensitive force measuring, device such as piezoelectric or strain _ ( -;
:gauge transducer. ' W~ 9~/0~1~24 a ~ .~ ~ ~ ~ t~ tp~ 11~~US921~D7~57 An even simpler approach is to use the pyro-electric or heat sensor mentioned earlier.
These devices can be made,sensitive to the motion of air that is at a different temperature than the background. For example, the conditioned supply air .coming out of a diffuser near a hood is typically 55~f'. versus the background room temperature of '70°F. depending on the turbulence of the airflow near the hood, this air motion would be detected by the pyro-electric sensor.
As mentioned earlier, one other factor affecting hood capture is the presence of apparatus in the first 6" of the hood work surf ace. This region 55 is shown in FIG. 6A. To sense this condition, a simple active or proximity sensor could be used to send a light or other type of beam from one side to the other side of the inside of the hood. Anything placed in the gone traversed by the beam would signal the system to increase the face ~relocity.
one implementation shown in FIG. 6A has an active transmitter and receiver unit 56. This unit bounces a light, ultrasonic, microwave or other appropriate wavelength beam 58 off reflector 57 and back to the transmitter/receiver unit 56. The circuit of ~'TG. 4 could again be used to implement the sensor and detectar~.~ircuits. Pressure sensitive '°floor mat"
type switches, og equivalent pressure sensing material strips, could also be used to detect the presence of apparatus in "buffer" gone 55.
rwo ~~io~3x~ ~~rus~x~o7os°~
IJ
mother method to determine if there are influences that are disturbing hood containment is to actually measure the containment of the hood in some way such as by releasing a harmless fluid, such as a tracer gas or vapor in the hood and measuring outside the hood to see if any is escaping. This measurement of the hood's containment could be used to help vary the f ace velocity to the optimum point or to provide a two step operation.
As mentioned earlier, one approach to detect air motion in, around or near the hood is to use an air velocity sensor that measures the air velocity near the hood to directly look fear high velocities that could affect containment. alternatively, an air velocity sensor either in the sidewall or someplace an front of the hood could be used to detect disturbances caused by a user standing in front of the hood or by air turbulence near the hood. The former could be sensed, for example, by observing an increase in the air velocity through the sensor when in fact no change in the actual face velocity (which would also be detected or probably computed by using exhaust volume and sash area measurements) occurred. In order to sense air turbulence, the variations or "noise" in the air velocity signal could b~,pbserved. A very noisy signal that was changiixg a lot would indicate the presence of air turbulence near the hood. In order not to be VVO 93/84324 ~.~ ~~ ~. ~ ~ ~ P~"f/Y1S92/07057 confused with changes in velocity caused by movement of the sash, the sash position or the effective area of the sash could be monitored if it was desired to separate out any air velocity changes caused by the movement of a sash.
Alternatively the actual exhaust volume of the hood could be measured or metered by appropriate means and this value could be divided by the sash position to generate a calculated face velocity.
Variations betweezx this term and the sidewall f ace velocity could be then compared, particularly on a transient basis, in order to detect disturbance causing c~nditions around or inside the hood.
The last sensor that might be utilized to vary or change f ace velocity is a sash, movement sensor.
Movement of the sash or sashes creates turbulence;
therefore, an increase in face velocity during and after the movement of the sash might help to increase the hood's cantainment of fumes during such an operation. The movement of the sash can be easily sensed by the use of a sash sensor such as thoVe described in U.S. Patents 4,528,898 and ~, 706, 553 cahere a spring--wound, multiturn pot assembllr is used to measure sash height . A
differentiator circuit such as that shown in FIG. 7 could b_e_~ased to detect even a small movement of the sash.v Iii this figure, sash sensor 62 produces a variable voltage signal that is differentiated by op W~ 93/04324 P(.'T/~J~92/07~57 _ 27 _ amp circuit 60. Comparator 61 compares the differentiated signal to a reference to generate a two-state output that could be used to switch a relay when the sash moves.
As mentioned earlier, the system utilized could involve many of the different sensors described above in combination. Also, the outputs of the different sensors might be utilized.as variable outputs or as two state or relay outputs in order to detect the magnitude of the disturbance or closeness of a person to the hood. This variable output might be used to create a variable face velocity with a magnitude depenr~ent on the magnitude of the disturbance.
~3lock 33 of FIG. 2 is the circuit which accepts the relay closure or signal fram the disturbance detector or detectors 34 in order to modify the face velocity or volume command of the flow controller ~l~ere are several ways in which the face vezocxty or volume could be changed in order to incxease containment when a disturbance occurs.
FTG. ~ is a diagram indicating one way that dolume could be changed. In this example, the hood is operated with a standby face velocity of 70 FPM
which is shown by lines 131 and 105 which intersect at the~c~i.nt 149 of minimum flow, which point in . this dxample occurs at 20°s of open area. When a disturbance occurs, the face velocity is increased WO 93/0432~d P~T/U~92/07057 _ 2~ _ producing a flow-to-sash-position curve outlined in FIG. 8 by lines 130 and 104. Under some situations, it may be desirable to maintain the same minimum flow for both standby and active 4disturbance) modes. This is shown in FIG. 8 by the curve including lines 130, 134 and 105. In this example the minimum flow occurs at 28.6 of the full open sash at point 135. For operations Tong lines 130,, 131 and 134, f ace velocity will iincrease as sash opening decreases to maintain the desired constant flow volume.
Sim~.larly, it sometimes is advantageous to have a maximum limit for both si.andby and active modes.
FIG. 9 shows this with an ~xaa~n~le where the stanc'fby mode uses 70 FPP2 within bofih minimum and maximum limits. The standby mode is ind~.cated by lines 132, 107 and 120. Foiz~ts 110 azld 111 indicate the minimum and maximum limit intercepts, respectively.
The s.ctive mode at 100 FPM is indicated by lines 132, 106, and 120. The intercept points are 108 and 10~ for minimum and maximum limits, respectively.
different maximum limits may also be employed as shown ~~r the 100 FPM curve 132, 106, 137 and 136 where point 112 is the maximum intercept point.
,gain, for operators along lfines 120 or 136, face veloci~,yr will decrease as sash opening is increased to maintain constant volume flow.
6~V0 93/04324 1PC°I'/~IS92/07057 -- 2r~ -Another way of operating the system is to have the face velocity constant at some value such as 100 FPM, but a maximum clamp is engaged when a disturbance is detected. FIG. 10 illustrates this where lines 133, 113 and 121 would indicate a standby mode with a maximum clamp level.of, for example. 50%. Under the active mode, the clamp i.s rained 'to 70% as shown by lines 133_, 113. 114 and 123. Alternatively the maximum clamp may be eliminated altogether in t;he active mode ~s illustrated by extending line 114 to point 117 where 100 open occurs at 100°s flow.
Tn other cases, it may be useful to add or subtract an offset to the lhood's flow versus changes in the face velocity. FTG. l3 shows an example of this where lines 148 and 140 indicate a standby made and lines 1~8 and 141 indicate the active mode, offset 147 being the difference. A maximum clamp may also be added in the active mode as shown by line 124 with an intercept point of 145.
It is also passable to operate a fume hood system at a substantially constant volume through most positions of the sashes, with a trip switch or other element being utilized to reduce the volume for sash openings below a selected threshold. Thin resul~s,,in a stepped, varying face velocity curve with changes zn sash position, the step occurring at the threshold position. This stepped face velocity WfJ 93/04324 P~ f>US92/fl7057 .s r i ~ ; s'4 i ' 2.~ ~ z~ ~~
~n~~ A. ..~.
curve may have an offset superimposed thereon in accordance with the teachings of this invention based on detected Containment affecting conditions.
Another variatian would be to have multiple face velocity.levels or a variable f ace velocity based on conditions near the hood. Alternatively, a single face velocity could be used with multiple maximum clamps or again a variable maximum d amp based on hood conditions .or disturbances. FTC. 10 shows a situation where th~~e different maximum clamps are used. These might correspond, for example; to a staaadby mode where no one is near the hood, an active mode where someone is standimg qsaietly near the hood, and a turbulent made where rapid motion is detected near the hood. The maximum clamps indicated by lines 121, 123, and 122 would correspond, respectively, to these conditions.
A typical schematic block diagram which could implement block 33 of FIG. 2 for a single or multiple relay contact closure is shown in FIG. 12.
In this figure, the active or highest face velocity or flow volume setpoint is provided and adjusted by a trimpot 70 which is buffered by op amp 71 and is then attenuated by the faxed andJor variable resistor string 72, 73. 74, and 77. ~,elays 75 and 76 are_~~e output relay or relays of the disturbance de;tector~ circuitry of block 34. If only two states of ~p~rataon are desired, then only relay 75 and W~ 93/04324 Pd.'ft'/L1S92/~7~57 3d ~...~~~u~.;.' 3 ~ i fixed or variable resistor ~3 is used. For three states of operation, relay 76 and resister 74 can be added as shown. The output of this attenuation circuit can then be buffered as shown in op amp 78.
Additional relays and resistors could be added for even more states if desired.
Tf a true variable control is desired, then the output of op amp '~l could be multiplied by using an analog or digital signal multiplier circuit with a variable output signal from the disturbance detector block 34. The resultant output signal from this multiplier or the output from op amp 78 of FTG. 12 is then used as the face velocity setpoint or volume setpoint value for flow controller 32 of FIG. 2.
As was mentioned ~arlierp many different vol~ne or f ace velocity controllers may be used for block 32. Additionally, depending on the control approach desired, an additional circui block may be needed to provide maximum and/or minimum volume clamps.
This block is shown in FIG. 2 as block 39. This block may be implemented with fixed volume clamps or variable clamps that are controlled by the disturbance detector. The circuit of FTG. 12 can be used to implement these variable maximum or minimum damp setpoint circuits. If both clamps are desired ,, ; to be variable, then two of these circuits would be needed :f wo 93roa~2a fCT/US92/07057 FIG. 13 shows how these c lamps could be implemented in conjunction with block 32. The minimum and maximum volume clamp signals 86 and 87 respectively from block 39 of FIG. 2, being either fixed or variable signals, are then used as input signals to the actual volume clamp circuits in block 32. The actual minimum clamp circuit is implemented with op amp 82, its associated diode. and resistor 84. The actual maximum clamp circuit as implemented with op amp 83. its associated diode and resistor 85. These clamps work on a linear volume command output on line 88 from velocity or volume control block 80. The linear clamped signal is thus used to drive block 81 which in turn controls the volume moving through a damper, or air flow contral valve.
If a variable speed drive or inverter is used to control flow instead of a damper, FIG. 14 shows how the system can be implemented. Operation is the same as for FIG. 2, except damper 3~ and actuator 31 are replaced by block 14 which consists of a blower and blower speed controller. Far the blower system, block 81 (FIG. 13) would be used to control the :blower speed.
In both FIGS. 2 and 14, optional sash sensor, velocity sensors or volume sensors can be used in con~uncti9n with the flow controller block 32 to provide proper control of face velocity or flow.
U.~. patent Nos. 4,528,898 and 4,706,553 illustrate wc~ ~3io4~z~a pc.-t'i~s~z~o~os~
.~.~.i~J~~~
some typical applications and implementations of block 3z using these sensors.
While the invention has been shown and described above with reference to various embodiments, and specifio implementations have been shown and suggested for var~.ou~ elements of the system, it is apparent that the various sensor and control circuits shown are merely illustrat~.~re and that other devices and techniques might be utilized an particular applications. Thusa while the invention has been particularly shown and described above for the preferred embodiments. the foregoing other changes in form or detail may be made therein by one skilled in the art without departing from the sprit and scape of the invention.
6a;~.x zs ~z~AZt~n z~
.~. .a. t.~ . t ~D ~-F~'~HO13 AND ~1PPAF~"rtTS FOR GOI~TTP,~LLTNG
~ FUME HpOD
Field of tine Tnvention:
this invention relates ~to laboratory fume hood controllers end more spec~.fically to methods and apparatus for varying a fume hood's face velocity in response to variations in o;ne pr mora hood containment affecting conditions.
~ackground of the Invention:
p laboratory fume hood-is a ventilated enclosure where harmful materials can be handled safely. ~'he hood captures contaminants and prevents them from escaping into the laboratory by using an exhaust blower to draw air and contaminants an and around ~he'hood's work era away from the operator so that inhalation of and contact with the contaminants are minimised. Access to the interior of the hood is ~hrough'.~n opening which is closed with a sash which typically slides up and down to vary the opening ~.nto the hood .
'1~0 93/04324 PCT/US92/0705.
., , . ~ ... _.. ,~ .~ z~ ._ The velocity of the air flow through the hood opening is called the f ace velocity. The more hazardous the material being handled, the higher the recommended f ace velocity, and guidelines have been established relating face velocity to texicity.
Typical face velocities for laboratory fume hoods are s0 to 150 feet per minute (fpm), depending upon the application.
When an operator is working in the hood, the sash is opened to allow free access to the materials inside. The sash may be opened partially or fully, depending on the operations to be performed in the hood. While fume hood and sash sues vary, the opening provided by a fully opened sash is on the order of ten square feet. Thus the maximum air flow which the blower mush provide is typically on the order of 600 to 1500 cubic feet per minute (cfm).
The sash is closed when the hood is not being used by an operator. Tt is common to store hazardous materials inside the hood when the hood is not in use, and a positive airflow must therefore be maintained to exhaust contaminants from such materials even when the hood is not in use and the sash is closed. As the hazard level of the mater~.als being handled and the resulting minimum face vel~city increases. maintaining a safe.face -velocity'becomes more difficult.
w~ 9moa~~a ~criu~9as~~os7 a t i ~ f 1 ) i n .. .~. a. ,.%
An important consideration in the design of a fume hood system is the cost of running the system.
There are three major areas of costs: the capital expenditure of installing the hood, the cost of power to operate the hood exhaust blower, and the cost of heating, cooling, and delivering the "make-up air,~~ which replaces the air exhausted from the room by the fume hood. ~'or a hood operating continuously with an opening of 10 square feet and a f act velocity of 100 fpm, the cost of heating and cooling the make-~up air could, for example, run as high as fifteen hundred dol7.ars per year in the northeastern United Mates. WThere chemical work is done, large numbers df fume hoods may be required.
For example, the Massachusetts s Institute of Technology has approximately 550 fume hoods, most of which are in operation 24 he>urs a day.
capital or investment costs is an important ~aCtor an the design ~f fume hood systems. This elates to the capital cost o~ the supply and exhaust fans, duct-work, boiler and cha.llers, and other equipment related to the movement and conditioning of the outside air brought into and exhausted from the building through the fume hoods.
The laze, capacity arid cost of this equipment is integrally related to the peak capacity of air 'volume~to be exhausted from the hoods. This total volume is in turn directly related to the face " , ,.., '. :' ". . . , , ~. ." . .
VSr~ 93/04324 .:, y ~. ; y, , : , ~, P~'i'/LJS92/0705 ~i velocities of those hoods. For example, a 20%
reduction in the face velocity for which. the building hoods are designed, from 1~0 FPM to 8o FPM
allows for a 20g reduction in the required capacity of the system air handling equipment.
Consequently, there are strong economic reasons for using the lowest face velocity which still produces acceptable fume hood capture and containment. P2uch research has been performed recently on the factors affecting this minimum acceptable face vel~cz,ty. For example, with a fume hood having no equipment in the first ~" back from the sash, uniform face velocity distribution across the face of the ho~d, and no high cross drafts, the face v~locit~ can be set to 60 FPM and excellent containment will occur. I~owever, spip age will occur at 60 FPM if people walk past the hood, someone waves their arms near the opening or supply air diffusers blow air past the corners in front of the hood. All these disturbances create cross drafts and challenges to the fume hood containment which can pull fumes out of the hood. Tncreasing the face velocity to 100 or 125 FPM significantly reduces the spillage caused by these factars. Above 1.5.~ FPM, the air flow into the hood can became turbulent creating eddy currents and local low ~~
pressure'areas which can also create spillage.
WO 931Oa132~1 PC'f/LJS92/07057 . ~ ., y l ° Because of the above factors, many laboratories operate their hoods at 100 to 125 FPM. Others allow the face velocities to drop to 70 to ~0 FPM when the laboratories are unoccupied and operators are not near the hood where they might create crossdrafts from their motions. A very few companies operate their hoods at 60 FPM, but only with strict operating guidelines in order to prevent disturbance of the fume hood's containment.
Tn order to save energy and reduce the peak air capacity in laboratories, fLlme hood control systems are presently used that maintain a constant face velocity independent of the sash opening. Ea~ly ~e~~ions of these systems ~~~raced by changing _ volume in a two or three st~,p operation based on the sash heig:~,t or the amount of: sash opening. Much better and more recent syst~ms,provide can~inuous control caf the air vol~xne based on sash position and are referred to as variable air volume systems. An~
e~ampl~ of one of these systems is described in U.S.
Pa°ten~s 4,528,98 and 4,706.55. These systems work weld., but aye dependent on the operator lowering the sash. When 'the c~pers.tor dines lower the sash, the exhaust, and typically also the room supply air volume; are reduced proportionately which generates i the energx savings. If many hoods are used an a ~.
v~uildi:ng'wi~h these controls, both the average and typical peak total a~.r volumes will be reduced due W~ 93/0434 G.) '~ ,-~ ~ ~ '~ ~ ~'Cl'/IJS9~/0705~
to the diversity in the hood's operation. Tn other words, it is unlikely that all the hoods will be fully open at any one time. A problem for the building designer, however, is in estimating how much diversity will actually occur in the building.
Consequently, many designers take a worst case view and don't size the buildings capacity below ar much below the 100% capacity assumption of all the hoods full open at the same time. This is done because the designer is concerned that the users will not lower the sash when leaving the hood area. This is unfortunate because studies have shown that operators spend only a small fraction of their time in front of the hood.
Tn an attempt to bypass the operator problem of not closing sashes some fume hood manufacturers have introduced devices such as ;>hown in U.S. Patent 4,774,~7~ that detect the presence of the operator in front of the hood and raise the sash to some preset position. When the operator moves away from the hood, the sash is automatically closed.
Typically, a two state or variable air volume control system is also used to vary the air volumes to maintain a constant face velocity at the two different sash positions.
These sash operator systems have not as of yet _~
.received~widespread acceptance among researchers for several reasons. Firstly, the rapid movement of the wo ~~ioa3za ~orius9zio7as~
r ~- ..L .
- 7 _ sash up and down can occur even when a person just walks past the hood, producing a disturbing f else reaction of the hood. Also, many researchers like to operate the sash at various heights, and this is made more difficult by the two position operators.
Further, many hoods have wires, tubes and small hoses going into the hood near the bottam of the sash opening. Uncontrolled movement of the sash might hit these wares and hoses and potentially tap over delicate glassware to which the tubes and hoses are connected. This in turn could create a serious and potentially dangerous accident. Lastly, many hoods have horizontally rnov'.ng sashes which make at difficult to implement a sysctem to move the sashes iz~ oxder to increase or decrease the amount of hood opening.
For all of the above reasons, a better approach is needed for reducing both energy usage and peak estimated replacement volume while not creating a potential hazard and not adversely affecting the researcher's work.
Summary of the Invention din object of this invention is to provide an improved methad and apparatus for controlling a fume hood, which controller (a) substantially reduces the replacement azr utilized by the system, regardless of 'sash position, (b) permits fume hood systems to be designed for lower peak volume flow without g _ permitting or creating any danger of a breakdown in toxic fume containment or any danger of damage to ongoing experiments or equipment, and (c) permits researchers complete flexibility in selecting sash positions.
The present invention provides a controller for use with a fume hood having face velocity control means, the controller comprising means for detecting changes in at least one containment affecting ~o condition; and change means responsive to the detecting means detecting a selected change in containment affecting condition for causing the control means to make a corresponding change in the face velocity of the fume hood to a preselected velocity for the changed containment condition, the change means including incrementing means responsive to a detection by the means for detecting of a selected increase in a selected containment affecting condition for causing the control means to increase 2o the face velocity of the fume hood to a selected increased level, and decrementing means responsive to detection by the means for detecting of a selected reduction in a containment affecting condition for causing the control means to reduce the face velocity of the fume hood to a selected decreased level.
In another aspect of the present invention, there is provided a method for controlling a fume hood having face velocity control means comprising the steps of detecting changes in at least one contain-3o ment affecting condition; and causing the control means to make a corresponding change in the face velocity of the fume hood in response to a detected change in containment affecting condition to a - 8a -preselected velocity for the changed containment condition, the change causing step including the steps of causing the control means to increase the face velocity of the fume hood to a selected increased level in response to the detection during the detecting step of the occurrence of a selected containment affecting condition, and causing the control means to reduce the face velocity of the fume hood to a selected decreased level in response to the ~o detection of a selected reduction in a containment affecting condition.
More specifically, this invention provides a controller for use with a fume hood having a face velocity control. The face velocity control may control face velocity directly or may control it indirectly by controlling flow volume or some other conditions affecting face velocity. The controller has a detector for detecting at least one containment affecting condition, which condition may be (a) the 2o presence or proximity of a person within a predetermined area of the fume hood, (b) movement within a predetermined area of the fume hood, either by a person or as a result of air drafts or other conditions, and/or (c) the presence of equipment or material within a predetermined distance from the front of the hood. Appropriate detectors are provided for each condition to be detected. In response to the detector detecting a selected change in containment affecting conditions, the face velocity control makes so a corresponding change in the face velocity of the fume hood to a preselected velocity which is appropriate for the changed containment condition.
- 8b -The change may be an increase in the face velocity of the fume hood to a '1~0 93/14324 ~G I'/~....IS92/~7057 :'.~ _. .;. ~ .
_ g _ level sufficient to assure containment of fumes in the hood with the containment affecting condition present, or the change may be a reduction in the face velocity of the fume hood to a selected decreased level in response to the de~tec~tion of a selected reduction in containment affecting condition. The incrementing preferably occurs substantially instahtaneously on the detection of a containment affecting condition, while a reduction in f ace velocst~ is delayed for a selected time period when a selected reduc~tiora in containment affecting c~nd:ition is detected. Containment affecting conditions may include a person being within a selected area of the f ace of the hood, the detection of movement within a selected area of the f ace of the hood, which movement may be of a person ~r may be air motion or turbulence either inside or outside the hood, may be a tracer fluid ejected in .
the hood, with the escape of such tracer fluid being measured, or may be the detection of apparatus within a predetermined distance from the front of the hood.
The f ace velocity control may control volume thxough the fume hood with a change being.a change in flow volume. The system may include a means fob e~tablx'shi~g a maximum flow volume and/or a means g~r'establishing a minimum flow volume with the maximum flow volume and/or the minimum flow volume W~ 93/04324 P(,"Y'/US92/0705, ", , _ r_ i:~ _~. ;) being changed in response to a change in containment affecting condition. Tin offset in the controlled flow volume may also be effected in response to a change in containment affecting condition. Where the fume hood has an opening which.may be covered to varying extents by at least one moveable sash, a selected vo~.ume is normally maintained relative to the sash position. The selected volume maintained may be changed in response to the detection of a change in containment affecting condition. For some embodiments, the selected volume maintained is a constant volume regardless of sash position.
For some embodiments, a first face velocity is caused in response to a detection of a containment affecting condition, and a second lower face velocity is caused in response to the absence of a detection. Where there may be varying degrees of containment. and the detection detects.the degree of containment affecting condition, the change in face velocity may be to a f ace velocity appropriate for the detected degree of containment affecting condition. ~'he changes in face velocity may be discrete or may be substantially continuous based on the degree of detected containment affecting dondition.
The~~f~ace velocity con~txol may include a speed -, contr~51 for a blower exhausting the fume hood, or may directly change the flow from the fume hood.
WO 93/04:324 F~'/~JS9z1o7o57 ~.. z. .a.
° 11 the foregoing other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawings.
In the ~rawinqs FIG. 1 is a side-view representation of a prior art fume hood system.
FIG. 2 is a semi-block diagram of a fume hood system in accordance with a first embodiment of the invention.
FTG. 3 and FIG. 4 are block diagrams of a passive and of an active motion detection system, respectively, which may be utxl~.zed in practicing the teachings of this invention.
FIG. 5 is a block diagram of an alternative embodiment of the invention illustrating another sensing concept.
FIG. 6A illustrates a typical detection zone for a proximity or motion detector and also illustrates the detection of another detection containment condition.
FIG. 6B is a front perspective view of a fume hood illustrating additional containment affecting condition detection elements.
FI_G~.,7 is a block diagram of a sash position sensing'circuit which may be utilized in conjunction with various embodiments of this invention.
9~Y~ 93/04324 PCT/US92/0705", rv ~ '~' d~
FTGS. S, 9, 10 and 11 are diagrams illustrating the relationship between air flow and sash position for various embodiments of the invention.
~°I~, 12 xs a schematic diagram of a cixcuit for controlling minimum and maximum air flows.
FTG, 1~ is a semi--block schematic diagram of a flow c~ntroller whack. may be utilized in conjunction with various embodiments of the invention to control minimum and maximum air flows.
FIG. 14 zs a ~e~i-block diagram of still another embodiment of the invention.
Detailed Description:
FIG. 1 shows a prior part system used primarily to maintain a constant face velocity. Air fl~w sensor 27 i.s placed in an ~pening in the fume hood so that it can dxrec~ly sense the velocity of ai.r entBring the hood. Sensor 27 could be placed in the sash opening Qr in a separate opening in the side of hood enclosure 10o as shown by opening 26 in ~'IG.
1, gn this system, the sensor may be used to control either the speed of blower 14 or to' c~ntrol a damp~~ ~:n the exheust ducting 15 to control the air flow. U:S. Patent No> 4.241.257 describes a similar device that measures the pressure drop between the inside and outs~.de of the hood as a methc~c~,of sensing a quantity related ~:n some way to .dace ~relocity.
V'1'~ 93/04324 P~T/1,1~92/07057 ~" w .x. ~ ~ ~9 systems of the type shown in FIO. 1 have several problems relating to the maintenance of a constant f ace velocity such as speed of response, stability, susceptibility to cantamination of the air flow sensor, etc. One potential problem which relates to the present invention is that the f ace velocity of a hood controlled by these devices is affected by the user standing close to the front of, the hood.
I~owever, unlike the present invent~.on, these systems reduce the face velocity when the user stands near the opening of the hood, which is directly opposite of the desired result. The present invention increases the average face velocity to generate better fume hood capture and contair~en~.
prior art devices also work slowly, so that even if they could produce the intended result. it would be too late to protect the user. Due both to the time delay and. the wrong control action of these systems, the disturbance of a person walking past the hood could create a significantly worse reaction than a hood with no such control system. The present invention uses different sensing and control er~u,ipment to immediately detect the disturbance and respond rapidly in the correct manner to provide better fume 'hood operation.
Th_e~Ypresent invention also differs from prior art systems that detect the presence o~ a user and raise the sash while trying to maintain a constant WO 93/04324 PC°f/US92/0705.
~.r t. ; ~S ~ ,~
. .a.
face velocity for two different sash positions. The goal of such prior art systems is to maintain a constant f ace velocity, ~r if no volume controller is used, then the volume may actually be fired. The present invention also trys to sense the user, but unlike the prior art, it changes face velocity to change the hood volume anal save energy; it does not disturb or move the hood sash or sashes.
Consequently, the present invention is universally applicable to all hoods even those that do not have a movable sash or such hoods as canopy hoods. also, this system, when used in combination with a constant face velocity control system such as that described in U.~. Patent Nos. 4,52~,~9~ and 4,706,553, can achieve greater energy savings then when such systems are used alone due to the decrease in average face velocity that the present invention achieves, Referring to FTG. Z, a first embodiment of the present invention is shown as it would be applied to a conventional fume Y~ood with a damper 30 or similar air throttling or resistance type flow control element. This damper controls the flow out of fume hood In and is actuated by actuator 31. Flow controller 3~ controls actuator 31 and may consist ' of a ~_on~tant volume controller to maintain a given volume flow independent of sash position, a two sta,~e (or mufti-state) volume controller that ~V~ 93/04324 1P~'f/6JS92/07a57 s~ r ,5 ~ c.
N .i 1 t.~
changes the volume of the hood based on the sash height or open area of the sash, or a variable volume control system which maintains a constant f ace velocity based on sash position. U.S. Patent l3os. 4,741.5'1; 4.58.898; and 4,706,553 describe various types of variable volume control systems which could be used for flow controller block 32.
All of these flow controllers work.to maintain a given setpoint value of face velocity. In the constant volume systems, this can be interpreted directly as a setpoint of volume, whereas in the variable volume systems the fume hood volume will vary for a given face velocity setpoint. In many cases, with the variable volume systems, there will also be a minimum and maximum exhaust volume limit placed on the fume hood control.
Transducer 35 and person/motion detector circuit 34 work together to detect the presence and movement of the user/researcher in front of the hood. The transducer may also detect significant air motion or turbulence in front of or near the hood. When air motion or user proximity/movement is detected, it activates f ace velocity setpoint change circuit ~3.
This circuit acts an flow controller 32 in one of many possible ways, but generally acts to increase its f~'~e velocity and/or volume flow setpoint.
Alternatively, it may act to modify the minimum and maximum exhaust volume limits of the flow controller through the volume clamps circuit 39.
WU 93/~4324 I'~'111~92/~7Q57 -, ~:a ~
~ 3 '~~
ri Transducer 85 and detector circuit 34 may be implemented with a variety of technologies such as is used in security or intrusion alarm systems. For example, transducer 35 could be implemented by using a passive far-infrared (typically 8-14 um) motion sensor. an active ultrasonic motion sensor, an active microwave motion sensor, an active near-infrared (typically 880-940 nm) or visible light proximity sensor, or a combination thereof.
Based on the type of transducer used, a compatible detector circuit 34 would be employed.
FIG. 3 illustrates an implementation using a passive gyro-electric infrared motion sensor and detector circuit. The pyra~electric detector 41 detects changes in heat patterns caused by the movement of a person relative to their background radiation, in a detection zone. The optical system 40, for example a mirror or fresnel lens, focuses the infrared energy, in for example the 8-1.4 um spectrum, onto the detector, after a variable gain stage 42 which controls the sensitivity of detection, the amplified signal is filtered in signal processing circuit 43 with a band pass filter which attenuates unwanted signals and increases the 8~N (signal to noise) ratio of the frequency of interest;, which is generally in the .3-3 Hz range.
-----~t~hen the signal is of a desired amplitude, comparator 44 triggers a timer 45. The timer Wf.~ 93/O~f324 P~CfJU~92f07057 IFv changes the state of relay (46), and thus of its output, f or some preset time period. The output from relay 46 is applied to control change circuit 33 (FTG.
The timer will restart its timing period if the comparator triggers a second time within the preset time period. This preset time period. or turn off ..
delay time, is used to keep the detector on even if the researcher is still far a few minutes while he is working in front of the hood, and also to prevent the nuisance and potential danger of the system . increasing and decreasing the f ace velocity based on how still the researcher is while the researcher is still in front ~f the hood. Alternatively, a smaller turn off delay could be used if the passive system were combined with some sort of active proximity or presence detector.
With the use of variable voltage control 47 the circuit could detect different zones. For example the variable voltage output would indicate the detection of the researcher in the lab relative to a detection zone an front of the fume hood. The variable voltage would tell the face velocity setpoint change block 33 of FTG. 2 to inorea~e the face yeloci~y a little when the researcher is present ;in the room and to increase the face ue1'ocity'even more if the researcher is in front of the hood.
CVO 93J04324 PCT/US92/a7057 - m -A complete active system that includes a Doppler motion detection is shown in FIG. 4. These systems can be combined ~rith a passive detector and are typically based on one of ~thre2 technologies:
infrared 800-900 nm, microwaves or ultras~nics. The active system detects the presence and or movement of a person. I~Iovement, which indicates where the researcher is and how fast he is moving, is detected by the Doppler effect for microwave and ultrasonics. Presence, which indicates if the researcher is present at a particular location, is detected by an infrared beam.
For the circuit of FTG. 4, transmitter 48 sends a pulse of appropriate frequency into the detection zone. Depending on the presence of personnel in the detection zone, the pulse is either returned to the receiver 49 within a selected clock interval or not. If the receiver receives the signal, preamplifier 57. boosts the signal sd that, assuming the signal is received within the interval of clocl~
50, sample and hold amplifier 5~ can sample the pu~,ses. with the signals of interest on them. The pulses are sampled in sync with the transmitted pulses of clock 50. Doppler/presence detector 53 detects the motion or presence from the sampled 'signal, the presence detector detecting presence of a signal end the Doppler detector detecting frequency shift. The signal is filtered and W~ 93/04324 PC'T/iUS92/07057 _ 19 _ processed in signal processing circuit 54 so that unwanted signals are attenuated, thus increasing the S/N ratio for the frequency of interest.
The block diagram of figure 4 illustrates two potential outputs, one indicating if the researcher is in the detection zone and the other detecting where in the zone the researcher is. In the first case, detecting if the researcher is iii the detection zone, the output of relay 57 tells the face velocity setpoint change block 33 of FIG. 2 to increase the f ace velocity by a present amount. The later case would change the f~~ce velocity by a certain percent relative to the distance of the researcher from the hood.
The presence of the researcher in the detection zone is indicated by the signal amplitude out of block 54 increasing until it rises above the threshold of the comparator 55. The comparator starts a timer 5~. The timer switches the state of the relay 57 for some preset time. As for the circuit of FIG. 3, the timer will reset back to zero if the comparator triggers a second time within the timer set period. The relay tells the face velocity setpoint change block 3~ (FIG. 2) to change the face velocity.
To indicate the position of the researcher relativevtb the fume hood, the signal coming out of block 54 would be converted to a variable voltage by r-~
WO 93/04324 ~CC°f/U~92/U7U57 ~~.:~~~34 - 2~ -clrcult rJ~s the voltage output telling the face velocity setpoint change block 33 (~I~. 2) the distance of the researcher from the fume hood. The face velocity may then be increased as the researcher moves closer to the fume hood and decreased as the researcher moves further from the fume hood.
The use of both a presence detector and a motion detector may prove useful to prevent the system from being adversely affected by people walking past the hood. If someone walks pa:>t the hood, the system must quickly activate the active mode. However , if the person does not stop in front of the hood, but continues walking, it would be wasteful to leave the hood in the active mode foy: more than perhaps ZO
seconds. This prevents a g,>erson fram walking around the room and activating all the hoods s~.multaneously. The presence detector is desirable for use in conjunction with the motion detector so that the active mode is only left on for greater than 10 seconds if a researcher remains standing in front of the hood.
F"1G. 5 illustrates another sensing concept to detect a person walking up to and, standing in front of the hood. This involves a floor mat type switch 36 which is activated by standing on a special mat placee3 5.n front of the hood. These devices are of the general type used to open doors, although W() 9~104~24 Pt.'f/1JS92/07057 generally modified in appearance and construction to fit in better for a laboratory application. For example a capacitive plate sensor or inductive plate sensor which would operate by stepping on a sheet of metal either on top of or embedded into the floor would provide a neater installation for this application which would be less affected by spilled chemicals, There are also many similar sensors such as piezoelectric or FSR (Force Sensing Resistor) which are very flat and can for example be laminated into. corrosion resistant plastic. Detectors of this type typically work on press>ure or on the capacitive or conductive affects of the human body. Except for the change in detector, fhe system of FIG. S has the same components and operates> in the same way as the system of FIG. 2.
then passive or active detectors such as those shown in Figs. 3 or 4 are used. the optics of the system will need to be adjusted to sense the proper area in front of the hood. Some field adjustability is desirable based on the different sizes of hoods and different lab casework layouts in which the hoods are applied. FIG. 6A shows a typical detector zone 50 for a detector 35 that is mounted on a hood l0 as shown in FIG. 6E. In some cases, two or more detecto_~s, may need to be used ar special optics may be4~required that can specifically shape the detecrtion field of a single detector. For example, W~ 93/04324 P~.'ff ~S92f0705 7 . s ~, 3 ~ri' s.. ..~~. ;fir .~ ~ ~~
it may prove useful to observe the hood area from a height of 3' ar 4' on up to ignore chairs, tables, equipment and other fixed or movable~objects. When, for instance, infrared detectors are used, special fresnel type lenses or specially shaped mirrors may be used. The size of the zone 50 would vary with application. For example, the zone might extend 1.°
to 4'from the front of the hood and beyond each side of the hood by from 0 to ~'.
ether means to implement sensor 35 and detector circuit ~4 would be through creating a light curtain or projecting a light beam around the desired detection zone, 50 of FTG. 6A. When an ope~rabor crosses and momentarily breaks the light beam, the detector circuit signals the presence of the operator. The circuit of FTG. 4 could be used to implement this type of detector circuit.
Tn addition to sensing the presence or motion of a user near the hood, there are, as was mentioned earlier, potentially other factors which might dictate the need for a higher f ace velocity, for ex~~ple, the presence of an: air velocity greater than 30 to 50 FPM such as from a nearby supply air diffuser. Additionally, the presence of apparatus in the first 6" or so of the hood back from the from Y~ the sash can also decrease hood containment, necessitating the need far a higher face velocity.
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There are many finds and types of air velocity sensors that could be used to detect air motion, either in front of or at the corners or sides of the fume hood. tTnfortunately, many of these tend to be point sensors such as hot wire or thermistor--type thermal aneometers. ~ better system~wouid sense the presence of low air velocity over a wider area. one such approach would use long streamers; 51 (FIG. 6~) the length of each such streamer being roughly equal to the height of the sash openings. The streamers 5l would be placed at the front corners or edges of the hood where the hood is most affected by air currents. These streamers would be made of some 13~h~'m~terial easily maved by wand or other air curi~ez~ts striking the streamer. The motion of the streamers could then be detected by the motion detectors that were described earlier.
~lterna~ively; the motion could be detected directlx by ~ suitable motion detector 52 to which each streamer 51 is attached. As each streamer moves) its motion is transmitted to the corresponding detector 52, which senses the motion by for example movang the contact point on a variable resistor or b,~ sensing the variation in pressure, weight or twisting forge applied to a sensitive force measuring, device such as piezoelectric or strain _ ( -;
:gauge transducer. ' W~ 9~/0~1~24 a ~ .~ ~ ~ ~ t~ tp~ 11~~US921~D7~57 An even simpler approach is to use the pyro-electric or heat sensor mentioned earlier.
These devices can be made,sensitive to the motion of air that is at a different temperature than the background. For example, the conditioned supply air .coming out of a diffuser near a hood is typically 55~f'. versus the background room temperature of '70°F. depending on the turbulence of the airflow near the hood, this air motion would be detected by the pyro-electric sensor.
As mentioned earlier, one other factor affecting hood capture is the presence of apparatus in the first 6" of the hood work surf ace. This region 55 is shown in FIG. 6A. To sense this condition, a simple active or proximity sensor could be used to send a light or other type of beam from one side to the other side of the inside of the hood. Anything placed in the gone traversed by the beam would signal the system to increase the face ~relocity.
one implementation shown in FIG. 6A has an active transmitter and receiver unit 56. This unit bounces a light, ultrasonic, microwave or other appropriate wavelength beam 58 off reflector 57 and back to the transmitter/receiver unit 56. The circuit of ~'TG. 4 could again be used to implement the sensor and detectar~.~ircuits. Pressure sensitive '°floor mat"
type switches, og equivalent pressure sensing material strips, could also be used to detect the presence of apparatus in "buffer" gone 55.
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mother method to determine if there are influences that are disturbing hood containment is to actually measure the containment of the hood in some way such as by releasing a harmless fluid, such as a tracer gas or vapor in the hood and measuring outside the hood to see if any is escaping. This measurement of the hood's containment could be used to help vary the f ace velocity to the optimum point or to provide a two step operation.
As mentioned earlier, one approach to detect air motion in, around or near the hood is to use an air velocity sensor that measures the air velocity near the hood to directly look fear high velocities that could affect containment. alternatively, an air velocity sensor either in the sidewall or someplace an front of the hood could be used to detect disturbances caused by a user standing in front of the hood or by air turbulence near the hood. The former could be sensed, for example, by observing an increase in the air velocity through the sensor when in fact no change in the actual face velocity (which would also be detected or probably computed by using exhaust volume and sash area measurements) occurred. In order to sense air turbulence, the variations or "noise" in the air velocity signal could b~,pbserved. A very noisy signal that was changiixg a lot would indicate the presence of air turbulence near the hood. In order not to be VVO 93/84324 ~.~ ~~ ~. ~ ~ ~ P~"f/Y1S92/07057 confused with changes in velocity caused by movement of the sash, the sash position or the effective area of the sash could be monitored if it was desired to separate out any air velocity changes caused by the movement of a sash.
Alternatively the actual exhaust volume of the hood could be measured or metered by appropriate means and this value could be divided by the sash position to generate a calculated face velocity.
Variations betweezx this term and the sidewall f ace velocity could be then compared, particularly on a transient basis, in order to detect disturbance causing c~nditions around or inside the hood.
The last sensor that might be utilized to vary or change f ace velocity is a sash, movement sensor.
Movement of the sash or sashes creates turbulence;
therefore, an increase in face velocity during and after the movement of the sash might help to increase the hood's cantainment of fumes during such an operation. The movement of the sash can be easily sensed by the use of a sash sensor such as thoVe described in U.S. Patents 4,528,898 and ~, 706, 553 cahere a spring--wound, multiturn pot assembllr is used to measure sash height . A
differentiator circuit such as that shown in FIG. 7 could b_e_~ased to detect even a small movement of the sash.v Iii this figure, sash sensor 62 produces a variable voltage signal that is differentiated by op W~ 93/04324 P(.'T/~J~92/07~57 _ 27 _ amp circuit 60. Comparator 61 compares the differentiated signal to a reference to generate a two-state output that could be used to switch a relay when the sash moves.
As mentioned earlier, the system utilized could involve many of the different sensors described above in combination. Also, the outputs of the different sensors might be utilized.as variable outputs or as two state or relay outputs in order to detect the magnitude of the disturbance or closeness of a person to the hood. This variable output might be used to create a variable face velocity with a magnitude depenr~ent on the magnitude of the disturbance.
~3lock 33 of FIG. 2 is the circuit which accepts the relay closure or signal fram the disturbance detector or detectors 34 in order to modify the face velocity or volume command of the flow controller ~l~ere are several ways in which the face vezocxty or volume could be changed in order to incxease containment when a disturbance occurs.
FTG. ~ is a diagram indicating one way that dolume could be changed. In this example, the hood is operated with a standby face velocity of 70 FPM
which is shown by lines 131 and 105 which intersect at the~c~i.nt 149 of minimum flow, which point in . this dxample occurs at 20°s of open area. When a disturbance occurs, the face velocity is increased WO 93/0432~d P~T/U~92/07057 _ 2~ _ producing a flow-to-sash-position curve outlined in FIG. 8 by lines 130 and 104. Under some situations, it may be desirable to maintain the same minimum flow for both standby and active 4disturbance) modes. This is shown in FIG. 8 by the curve including lines 130, 134 and 105. In this example the minimum flow occurs at 28.6 of the full open sash at point 135. For operations Tong lines 130,, 131 and 134, f ace velocity will iincrease as sash opening decreases to maintain the desired constant flow volume.
Sim~.larly, it sometimes is advantageous to have a maximum limit for both si.andby and active modes.
FIG. 9 shows this with an ~xaa~n~le where the stanc'fby mode uses 70 FPP2 within bofih minimum and maximum limits. The standby mode is ind~.cated by lines 132, 107 and 120. Foiz~ts 110 azld 111 indicate the minimum and maximum limit intercepts, respectively.
The s.ctive mode at 100 FPM is indicated by lines 132, 106, and 120. The intercept points are 108 and 10~ for minimum and maximum limits, respectively.
different maximum limits may also be employed as shown ~~r the 100 FPM curve 132, 106, 137 and 136 where point 112 is the maximum intercept point.
,gain, for operators along lfines 120 or 136, face veloci~,yr will decrease as sash opening is increased to maintain constant volume flow.
6~V0 93/04324 1PC°I'/~IS92/07057 -- 2r~ -Another way of operating the system is to have the face velocity constant at some value such as 100 FPM, but a maximum clamp is engaged when a disturbance is detected. FIG. 10 illustrates this where lines 133, 113 and 121 would indicate a standby mode with a maximum clamp level.of, for example. 50%. Under the active mode, the clamp i.s rained 'to 70% as shown by lines 133_, 113. 114 and 123. Alternatively the maximum clamp may be eliminated altogether in t;he active mode ~s illustrated by extending line 114 to point 117 where 100 open occurs at 100°s flow.
Tn other cases, it may be useful to add or subtract an offset to the lhood's flow versus changes in the face velocity. FTG. l3 shows an example of this where lines 148 and 140 indicate a standby made and lines 1~8 and 141 indicate the active mode, offset 147 being the difference. A maximum clamp may also be added in the active mode as shown by line 124 with an intercept point of 145.
It is also passable to operate a fume hood system at a substantially constant volume through most positions of the sashes, with a trip switch or other element being utilized to reduce the volume for sash openings below a selected threshold. Thin resul~s,,in a stepped, varying face velocity curve with changes zn sash position, the step occurring at the threshold position. This stepped face velocity WfJ 93/04324 P~ f>US92/fl7057 .s r i ~ ; s'4 i ' 2.~ ~ z~ ~~
~n~~ A. ..~.
curve may have an offset superimposed thereon in accordance with the teachings of this invention based on detected Containment affecting conditions.
Another variatian would be to have multiple face velocity.levels or a variable f ace velocity based on conditions near the hood. Alternatively, a single face velocity could be used with multiple maximum clamps or again a variable maximum d amp based on hood conditions .or disturbances. FTC. 10 shows a situation where th~~e different maximum clamps are used. These might correspond, for example; to a staaadby mode where no one is near the hood, an active mode where someone is standimg qsaietly near the hood, and a turbulent made where rapid motion is detected near the hood. The maximum clamps indicated by lines 121, 123, and 122 would correspond, respectively, to these conditions.
A typical schematic block diagram which could implement block 33 of FIG. 2 for a single or multiple relay contact closure is shown in FIG. 12.
In this figure, the active or highest face velocity or flow volume setpoint is provided and adjusted by a trimpot 70 which is buffered by op amp 71 and is then attenuated by the faxed andJor variable resistor string 72, 73. 74, and 77. ~,elays 75 and 76 are_~~e output relay or relays of the disturbance de;tector~ circuitry of block 34. If only two states of ~p~rataon are desired, then only relay 75 and W~ 93/04324 Pd.'ft'/L1S92/~7~57 3d ~...~~~u~.;.' 3 ~ i fixed or variable resistor ~3 is used. For three states of operation, relay 76 and resister 74 can be added as shown. The output of this attenuation circuit can then be buffered as shown in op amp 78.
Additional relays and resistors could be added for even more states if desired.
Tf a true variable control is desired, then the output of op amp '~l could be multiplied by using an analog or digital signal multiplier circuit with a variable output signal from the disturbance detector block 34. The resultant output signal from this multiplier or the output from op amp 78 of FTG. 12 is then used as the face velocity setpoint or volume setpoint value for flow controller 32 of FIG. 2.
As was mentioned ~arlierp many different vol~ne or f ace velocity controllers may be used for block 32. Additionally, depending on the control approach desired, an additional circui block may be needed to provide maximum and/or minimum volume clamps.
This block is shown in FIG. 2 as block 39. This block may be implemented with fixed volume clamps or variable clamps that are controlled by the disturbance detector. The circuit of FTG. 12 can be used to implement these variable maximum or minimum damp setpoint circuits. If both clamps are desired ,, ; to be variable, then two of these circuits would be needed :f wo 93roa~2a fCT/US92/07057 FIG. 13 shows how these c lamps could be implemented in conjunction with block 32. The minimum and maximum volume clamp signals 86 and 87 respectively from block 39 of FIG. 2, being either fixed or variable signals, are then used as input signals to the actual volume clamp circuits in block 32. The actual minimum clamp circuit is implemented with op amp 82, its associated diode. and resistor 84. The actual maximum clamp circuit as implemented with op amp 83. its associated diode and resistor 85. These clamps work on a linear volume command output on line 88 from velocity or volume control block 80. The linear clamped signal is thus used to drive block 81 which in turn controls the volume moving through a damper, or air flow contral valve.
If a variable speed drive or inverter is used to control flow instead of a damper, FIG. 14 shows how the system can be implemented. Operation is the same as for FIG. 2, except damper 3~ and actuator 31 are replaced by block 14 which consists of a blower and blower speed controller. Far the blower system, block 81 (FIG. 13) would be used to control the :blower speed.
In both FIGS. 2 and 14, optional sash sensor, velocity sensors or volume sensors can be used in con~uncti9n with the flow controller block 32 to provide proper control of face velocity or flow.
U.~. patent Nos. 4,528,898 and 4,706,553 illustrate wc~ ~3io4~z~a pc.-t'i~s~z~o~os~
.~.~.i~J~~~
some typical applications and implementations of block 3z using these sensors.
While the invention has been shown and described above with reference to various embodiments, and specifio implementations have been shown and suggested for var~.ou~ elements of the system, it is apparent that the various sensor and control circuits shown are merely illustrat~.~re and that other devices and techniques might be utilized an particular applications. Thusa while the invention has been particularly shown and described above for the preferred embodiments. the foregoing other changes in form or detail may be made therein by one skilled in the art without departing from the sprit and scape of the invention.
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Claims (30)
1. A controller for use with a fume hood having face velocity control means, the controller comprising:
means for detecting changes in at least one containment affecting condition; and change means responsive to said detecting means detecting a selected change in containment affecting condition for causing said control means to make a corresponding change in the face velocity of the fume hood to a preselected velocity for the changed containment condition, the change means including incrementing means responsive to a detection by said means for detecting of a selected increase in a selected containment affecting condition for causing said control means to increase the face velocity of the fume hood to a selected increased level, and decrementing means responsive to detection by said means for detecting of a selected reduction in a containment affecting condition for causing said control means to reduce the face velocity of the fume hood to a selected decreased level.
means for detecting changes in at least one containment affecting condition; and change means responsive to said detecting means detecting a selected change in containment affecting condition for causing said control means to make a corresponding change in the face velocity of the fume hood to a preselected velocity for the changed containment condition, the change means including incrementing means responsive to a detection by said means for detecting of a selected increase in a selected containment affecting condition for causing said control means to increase the face velocity of the fume hood to a selected increased level, and decrementing means responsive to detection by said means for detecting of a selected reduction in a containment affecting condition for causing said control means to reduce the face velocity of the fume hood to a selected decreased level.
2. A controller as claimed in claim 1, wherein said incrementing means operates substantially instantaneously on a detection by said detecting means; and including means for delaying operations of said decrementing means for a selected time period when a selected reduction is detected.
3. A controller as claimed in claim 1, wherein said means for detection detects the presence of a person within a selected area of the face of the hood.
4. A controller as claimed in claim 1, wherein said means for detection detects movement within a selected area of the face of the hood.
5. A controller as claimed in claim 4, wherein the means for detecting movement detects movement of a person.
6. A controller as claimed in claim 5, wherein said means for detecting also detects the presence of a person within a selected area of the face of the hood.
7. A controller as claimed in claim 4, wherein the means for detecting movement includes means for detecting air motion or turbulence at least outside the hood.
8. A controller as claimed in claim 4, wherein the means for detecting movement includes means for detecting air motion or turbulence at least inside the hood.
9. A controller as claimed in claim 4, wherein the means for detecting movement includes means for detecting air motion or turbulence in a selected area relative to the hood, the means for detecting air motion including a strip of material extending in the area, and means for detecting motion of said strip.
10. A controller as claimed in claim 1, wherein said means for detecting includes means for detecting at least one of weight and pressure in a selected area relative to the fume hood face.
11. A controller as claimed in claim 1, wherein said means for detecting includes means for projecting a radiation beam into a selected area relative to the face of the fume hood, means for detecting radiation reflected from said area, and means responsive to the reflected radiation for detecting selected containment affecting conditions in said area.
12. A controller as claimed in claim 1, wherein the means for detecting includes means for ejecting a tracer fluid in the hood, and means for measuring the quantity of the tracer fluid escaping from the hood.
13. A controller as claimed in claim 1, wherein said means for detecting includes means for detecting the presence of apparatus inside the hood within a predetermined distance from the front of the hood.
14. A controller as claimed in claim 1, wherein the face of the fume hood may be covered by one or more sashes, and wherein said means for detecting includes means for detecting movement of at least one of said sashes.
15. A controller as claimed in claim 1, wherein said control means controls flow volume through the fume hood, and wherein said change means changes flow volume.
16. A controller as claimed in claim 15, including means for establishing a maximum flow volume, and means for changing the maximum flow volume in response to the means for detecting.
17. A controller as claimed in claim 15, including means for establishing a minimum flow volume, and means for changing the minimum flow volume in response to the means for detecting.
18. A controller as claimed in claim 15, including means responsive to the detecting means for effecting an offset in the controlled flow volume.
19. A controller as claimed in claim 15, wherein the fume hood has an opening which may be covered to varying extents by at least one movable sash; and wherein the control means normally maintains a selected volume relative to sash position, the selected volume being maintained being changed by the changing means.
20. A controller as claimed in claim 19, wherein the selected volume is a constant volume regardless of sash position.
21. A controller as claimed in claim 20, wherein said constant volume is constant at a first value for sash openings above a threshold value and at a second value for sash openings below the threshold.
22. A controller as claimed in claim 1, wherein the change means causes a first face velocity in response to a detection by said detecting means and a second lower face velocity in response to the absence of a detection.
23. A controller as claimed in claim 1, wherein there may be varying degrees of containment;
wherein the means for detecting detects the degree of detected containment affecting condition;
and wherein the change means includes means for changing the face velocity to a velocity appropriate for the detected degree of containment affecting condition.
wherein the means for detecting detects the degree of detected containment affecting condition;
and wherein the change means includes means for changing the face velocity to a velocity appropriate for the detected degree of containment affecting condition.
24. A controller as claimed in claim 23, wherein the means for changing the face velocity is operative to vary the face velocity substantially continuously based on the degree of detected condition.
25. A controller as claimed in claim 1, wherein the face velocity control means includes a speed control for a blower exhausting the fume hood.
26. A controller as claimed in claim 1, wherein the face velocity control means includes means for changing the flow out of the fume hood.
27. A method for controlling a fume hood having face velocity control means comprising the steps of:
detecting changes in at least one containment affecting condition; and causing said control means to make a corresponding change in the face velocity of the fume hood in response to a detected change in containment affecting condition to a preselected velocity for the changed containment condition, said change causing step including the steps of causing said control means to increase the face velocity of the fume hood to a selected increased level in response to the detection during said detecting step of the occurrence of a selected containment affecting condition, and causing said control means to reduce the face velocity of the fume hood to a selected decreased level in response to the detection of a selected reduction in a containment affecting condition.
detecting changes in at least one containment affecting condition; and causing said control means to make a corresponding change in the face velocity of the fume hood in response to a detected change in containment affecting condition to a preselected velocity for the changed containment condition, said change causing step including the steps of causing said control means to increase the face velocity of the fume hood to a selected increased level in response to the detection during said detecting step of the occurrence of a selected containment affecting condition, and causing said control means to reduce the face velocity of the fume hood to a selected decreased level in response to the detection of a selected reduction in a containment affecting condition.
28. A method as claimed in claim 27, wherein incrementing by the control means occurs substantially instantaneously while decrementing of the control means is delayed for a selected time period.
29. A method as claimed in claim 27, wherein said detecting step includes the step of detecting at least one of the presence of a person within a selected area of the face of the hood, movement of a person within said selected area, detecting air motion or turbulence within a selected area relative to the face of the hood, the presence of apparatus inside the hood within a predetermined distance from the front of the hood, and movement of at least one sash covering the face of the hood.
30. A method as claimed in claim 27, including the steps of establishing at least one of a maximum flow volume and minimum flow volume and changing at least one of the maximum flow volume and minimum flow volume in response to the detection of a containment affecting condition.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US749,279 | 1991-08-23 | ||
| US07/749,279 US5240455A (en) | 1991-08-23 | 1991-08-23 | Method and apparatus for controlling a fume hood |
| PCT/US1992/007057 WO1993004324A1 (en) | 1991-08-23 | 1992-08-17 | Method and apparatus for controlling a fume hood |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2116134A1 CA2116134A1 (en) | 1993-03-04 |
| CA2116134C true CA2116134C (en) | 1999-10-05 |
Family
ID=25013071
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002116134A Expired - Lifetime CA2116134C (en) | 1991-08-23 | 1992-08-17 | Method and apparatus for controlling a fume hood |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US5240455A (en) |
| EP (1) | EP0610224B1 (en) |
| JP (1) | JP2701981B2 (en) |
| AT (1) | ATE173187T1 (en) |
| CA (1) | CA2116134C (en) |
| DE (1) | DE69227592T2 (en) |
| DK (1) | DK0610224T3 (en) |
| WO (1) | WO1993004324A1 (en) |
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-
1991
- 1991-08-23 US US07/749,279 patent/US5240455A/en not_active Expired - Lifetime
-
1992
- 1992-08-17 EP EP92918817A patent/EP0610224B1/en not_active Expired - Lifetime
- 1992-08-17 WO PCT/US1992/007057 patent/WO1993004324A1/en active IP Right Grant
- 1992-08-17 DE DE69227592T patent/DE69227592T2/en not_active Expired - Lifetime
- 1992-08-17 DK DK92918817T patent/DK0610224T3/en active
- 1992-08-17 CA CA002116134A patent/CA2116134C/en not_active Expired - Lifetime
- 1992-08-17 AT AT92918817T patent/ATE173187T1/en not_active IP Right Cessation
- 1992-08-17 JP JP5504603A patent/JP2701981B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| DK0610224T3 (en) | 1999-07-26 |
| JPH07500899A (en) | 1995-01-26 |
| WO1993004324A1 (en) | 1993-03-04 |
| EP0610224B1 (en) | 1998-11-11 |
| ATE173187T1 (en) | 1998-11-15 |
| US5240455A (en) | 1993-08-31 |
| EP0610224A4 (en) | 1995-02-15 |
| EP0610224A1 (en) | 1994-08-17 |
| JP2701981B2 (en) | 1998-01-21 |
| DE69227592D1 (en) | 1998-12-17 |
| CA2116134A1 (en) | 1993-03-04 |
| DE69227592T2 (en) | 1999-04-29 |
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