Note: Descriptions are shown in the official language in which they were submitted.
-1- ~ 205514
1 A METHOD AND APPARATUS FOR DETERMINING
2 THE UNCOVERED
SIZE OF AN OPENING
ADAPTED
3 TO BE COVERED BY MULTIPLE MOVEABLE DOORS
_
4
6 Cross Reference
to Related Canadian
Applications
7
8 1. Title: Apparatus for Determining the Position of a
9 Moveable Structure Along a Track
Inventors: David Egbers and Steve Jacob
11 Serial No.: 2,055,258
12 Filed: November 12, 1991
13
14 2. Title: A System for Controlling the Differential
Pressure of a Room Having Laboratory Fume Hoods
16 Inventors: Osman Ahmed and Steve Bradley
17 Serial No.: 2,055,101
18 Filed: November 7, 1991
19
3. Title: Apparatus for Controlling the Ventilation of
21 Laboratory Fume Hoods
22 Inventors: Osman Ahmed, Steve Bradley, Steve Fritsche and
23 Steve Jacob
24 Serial No.: 2,055,126
Filed: November 7, 1991
26
27 4. Title: Laboratory Fume Hood Control Apparatus Having
28 Improved Safety Considerations
29 Inventors: Osman Ahmed
Serial No.: 2,055,100
31 Filed: November 7, 1991
32
33
34
The present invention relates generally to the
36 control of th e ventilation of laboratory fume hoods, and
more
37 particularly to a method and apparatus for calculating the
38 area of an opening
of a fume hood
that is not
covered by one
39 or more sash doors.
Fume hoods are utilized in various laboratory
41 environments for providing a work place where potentially
42 dangerous chemicals are used, with the hoods comprising an
43 enclosure having moveable doors at the front portion
44
2Q55~~~~
-2-
1 thereof which can be opened in various amounts to permit a
2 person to gain access to the interior of the enclosure for
3 the purpose of conducting experiments and the like. The
4 enclosure is typically connected to an exhaust system for
removing any noxious fumes so that the person will not be
6 exposed to them while performing work in the hood.
7 Fume hood controllers which control the flow of
8 air through the enclosure have become more sophisticated in
9 recent years, and are now able to more accurately maintain
the desired flow characteristics to efficiently exhaust the
11 fumes from the enclosure as a function of the desired
12 average face velocity of the opening of the fume hood. The
13 average face velocity is generally defined as the flow of
14 air into the fume hood per square foot of open face area of
the fume hood, with the size of the open face area being
16 dependent upon the position of one or more moveable doors
17 that are provided on the front of the enclosure or fume
18 hood, and in most types of enclosures, the amount of bypass
19 opening that is provided when the door or doors are closed.
The fume hoods are exhausted by an exhaust system
21 that includes a blower that is capable of being driven at
22 variable speeds to increase or decrease the flow of air
23 from the fume hood to compensate for the varying size of
24 the opening or face. Alternatively, there may be a single
blower connected to the exhaust manifold that is in turn
26 connected to the individual ducts of multiple fume hoods,
27 and dampers may be provided in the individual ducts to
28 control the flow from the individual ducts to thereby
29 modulate the flow to maintain the desired average face
velocity.
31 The doors of such fume hoods can be opened by
32 raising them vertically, often referred to as the sash
33 position, or some fume hoods have a number of doors that
34 are mounted for sliding movement in typically two sets of
vertical tracks. There are even doors that can be moved
36 horizontally and vertically, with the tracks being mounted
37 in a frame assembly that is vertically movable.
38 Prior art fume hood controllers have included
29551~'~
-3-
1 sensing means for measuring the position of a vertically
2 moveable sash door and then producing a signal proportional
3 to the sensed position to thereby vary the speed of the
4 blowers or the position of the dampers. While sensing
means for determining the position of a single vertically
6 moveable sash door are known and are relatively simple to
7 implement, a more difficult situation exists when several
8 sash doors are present in the fume hood.
9 Accordingly, it is a primary object of the pres-
ent invention to provide an improved fume hood controller
11 which is adapted to determine the uncovered area of the
12 opening of the fume hood, even when the fume hood is of the
13 type which has several sash doors.
14 It is another object of the present invention to
provide such an improved fume hood controller that is
16 easily adaptable for use in controlling most commercially
17 available fume hoods, and accurately calculates the effec-
18 tive area of uncovered opening to the fume hood, taking
19 into consideration the number of sash doors, the sizes of
the sash doors, any bypass area, in addition to other
21 structural features, such as the upper lip height.
22 A related object of the present invention is to
23 provide an improved fume hood controller which includes a
24 computing means and is adapted to accurately calculate the
uncovered area of the opening of a fume hood which has a
26 plurality of sash doors, and which can be easily configured
27 for most commercial fume hoods by simply inputting various
28 structural dimensions for the fume hood.
29 Still another object of the present invention is
to provide an improved fume hood controller which provides
31 extremely rapid response to changes in the position of one
32 or more sash doors by virtue of its capability of calculat-
33 ing the uncovered area of the opening of the fume hood
34 every few hundred milliseconds.
These and other objects will become apparent upon
36 reading the following detailed description of the present
37 invention, while referring to the attached drawings, in
38 which:
2g551~~
-4-
1 FIGURE 1 is a schematic block diagram of appa-
2 ratus of the present invention shown integrated with a room
3 controller of a heating, ventilating and air conditioning
4 monitoring and control system of a building:
FIG. 2 is a block diagram of a fume hood control-
6 ler, shown connected to an operator panel, the latter being
7 shown in front elevation:
8 FIG. 3 is a diagrammatic elevation of the front
9 of a representative fume hood having vertically operable
sash doors;
11 FIG. 4 is a diagrammatic elevation of the front
12 of a representative fume hood having horizontally operable
13 sash doors;
14 FIG. 5 is a cross section taken generally along
the line 5-5 of FIG. 4;
16 FIG. 6 is a diagrammatic elevation of the front
17 of a representative combination sash fume hood having
18 horizontally and vertically operable sash doors:
19 FIG. 7 is an electrical schematic diagram of a
plurality of door sash position indicating switching means;
21 FIG. 8 is a cross section of the door sash posi-
22 tion switching means;
23 FIG. 9 is a schematic diagram of electrical cir-
24 cuitry for determining the position of sash doors of a fume
2 5 hood
26 FIG. 10 is a block diagram illustrating the rela-
27 tive positions of FIGS. 10a, lOb, lOc, lOd and l0e to one
28 another, and which together comprise a schematic diagram of
29 the electrical circuitry for the fume hood controller means
embodying the present invention:
31 FIGS. 10a, lOb, lOc, 10d and 10e, which if con-
32 nected together, comprise the schematic diagram of the
33 electrical circuitry for the fume hood controller means
34 embodying the present invention;
FIG. 11 is a flow chart of the general operation
36 of the fume hood controller;
37 FIG. 12 is a flow chart of a portion of the
3~3 operation of the fume hood controller, particularly
~a5514'~
-5-
1 illustrating the operation of the feed forward control
2 scheme, which may be employed;
3 FIG. 13 is a flow chart of a portion of the
4 operation of the fume hood controller, particularly
illustrating the operation of the proportional gain,
6 integral gain and derivative gain control schemes;
7 FIG. 14 is a flow chart of a portion of the
8 operation of the fume hood controller, particularly
9 illustrating the operation of the calibration of the feed
forward control scheme;
11 FIG. 15 is a flow chart of a portion of the
12 operation of the fume hood controller embodying the present
13 invention, particularly illustrating the operation of the
14 calculation of the uncovered opening for a number of hori-
zontally moveable sash doors; and,
16 FIG. 16 is a flow chart of a portion of the
17 operation of the fume hood controller embodying the present
18 invention, particularly illustrating the operation of the
19 calculation of the uncovered opening for a number of hori-
zontally and vertically moveable sash doors.
21 Detailed Description
22 It should be generally understood that a fume
23 hood controller controls the flow of air through the fume
24 hood in a manner whereby the effective size of the total
opening to the fume hood, including the portion of the
26 opening that is not covered by one or more sash doors will
27 have a relatively constant average face velocity of air
28 moving into the fume hood. This means that regardless of
29 the area of the uncovered opening, an average volume of air
per unit of surface area of the uncovered portion will be
31 moved into the fume hood. This protects the persons in the
32 laboratory from being exposed to noxious fumes or the like
33 because air is always flowing into the fume hood, and out
34 of the exhaust duct, and the flow is preferably controlled
at a predetermined rate of approximately 75 to 150 cubic
36 feet per minute per square feet of effective surface area
37 of the uncovered opening. In other words, if the sash door
2~5514~
' -6-
1 or doors are moved to the maximum open position whereby an
2 operator has the maximum access to the inside of the fume
3 hood for conducting experiments or the like, then the flow
4 of air will most likely have to be increased to maintain
the average face velocity at the predetermined desired
6 level.
7 Broadly stated, the present invention is directed
8 to an improved fume hood controlling apparatus that is
9 adapted to provide many desirable operational advantages
for persons who use the fume hoods to perform experiments
11 or other work, and also for the operator of the facility in
12 which the fume hoods are located. The apparatus embodying
13 the present invention provides extremely rapid and effec-
14 tive control of the average face velocity of the fume hood,
and achieves and maintains the desired average face
16 velocity within a few seconds after one or more doors which
17 cover the front opening of the fume hood have been moved.
18 This is achieved, at least in part, by the rapid calcula-
19 tion of the uncovered area of the opening of the fume hood,
i.e., that area not covered by sash doors, frames, lips and
21 the like, which calculation is repeated several times per
22 second. The fume hood controller apparatus of the present
23 invention includes a computing means, together with asso-
24 ciated memory, which can be configured for horizontally
and/or vertically moveable sash doors by inputting the
26 necessary dimensions of the sash doors and other structural
27 features, such as the upper lip height, frame widths and
28 the like, as will be described.
29 Turning now to the drawings, and particularly
FIG. 1, a block diagram is shown of several fume hood
31 controllers 20 embodying the present invention inter-
32 connected with a room controller 22, an exhaust controller
33 24 and a main control console 26. The fume hood con-
34 trollers 20 are interconnected with the room controller 22
and with the exhaust controller 24 and the main control
36 console 26 in a local area network illustrated by line 28
37 which may be a multiconductor cable or the like. The room
38 controller the exhaust controller 24 and the main control
. . 2x55147
-7-
1 console 26 are typically part of the building main HVAC
2 system in which the laboratory rooms containing the fume
3 hoods are located. The fume hood controllers 20 are pro-
4 vided with power through line 30, which is at the proper
voltage via a transformer 32 or the like.
6 The room controller 22 preferably is of the type
7 which is at least capable of providing a variable air
8 volume to the room, and may be a Landis & Gyr Powers System
9 600 SCU controller. The room controller 22 is capable of
communicating over the LAN lines 28. The room controller
11 preferably is a System 600 SCU controller and is a commer-
12 cially available controller for which extensive documenta-
13 tion exists. The User Reference Manual, Part No. 125-1753
14 for the System 600 SCU controller is specifically incor-
porated by reference herein.
16 The room controller 22 receives signals via lines
17 81 from each of the fume hood controllers 20 that provides
18 an analog input signal indicating the volume of air that is
19 being exhausted by each of the fume hood controllers 20 and
a comparable signal from the exhaust flow sensor that
21 provides an indication of the volume of air that is being
22 exhausted through the main exhaust system apart from the
23 fume hood exhausts. These signals coupled with signals
24 that are supplied by a differential pressure sensor 29
which indicates the pressure within the room relative to
26 the reference space enable the room controller to control
27 the supply of air that is necessary to maintain the dif-
28 ferential pressure within the room at a slightly lower
29 pressure than the reference space, i.e., preferably within
the range of about 0.05 to about 0.1 inches of water, which
31 results in the desirable lower pressure of the room rela-
32 tive to the reference space. However, it is not so low
33 that it prevents persons inside the laboratory room from
34 opening the doors to escape in the event of an emergency,
particularly if the doors open outwardly from the room.
36 Also, in the event the doors open inwardly, the differen-
37 tial pressure will not be so great that it will pull the
38 door open due to excessive force being applied dug to such
2~5~14?
_8_
1 pressure.
2 The sensor 29 is preferably positioned in a suit-
3 able hole or opening in the wall between the room and the
4 reference space and measures the pressure on one side rela-
y tive to the other. Alternatively, a velocity sensor may be
6 provided which measures the velocity of air moving through
7 the opening which is directly proportional to the pressure
8 difference between the two spaces. Of course, a lower
9 pressure in the room relative to the reference space would
mean that air would be moving into the room which is also
11 capable of being detected. Referring to FIG. 2, a fume
12 hood controller 20 is illustrated with its input and output
13 connector ports being identified, and the fume hood con-
14 troller 20 is connected to an operator panel 34. It should
be understood that each fume hood will have a fume hood
16 controller 20 and that an operator panel will be provided
17 with each fume hood controller. The operator panel 34 is
18 provided for each of the fume hoods and it is intercon-
19 nected with the fume hood controller 20 by a line 36 which
preferably comprises a multi-conductor cable having eight
21 conductors. The operator panel has a connector 38, such as
22 a 6 wire RJ11 type telephone jack for example, into which
23 a lap top personal computer or the like may be connected
24 for the purpose of inputting information relating to the
configuration or operation of the fume hood during initial
26 installation, or to change certain operating parameters if
27 necessary. The operator panel 34 is preferably mounted to
28 the fume hood in a convenient location adapted to be easily
29 observed by a person who is working with the fume hood.
The fume hood controller operator panel 34 in-
31 eludes a liquid crystal display 40 which when selectively
32 activated provides the visual indication of various aspects
33 of the operation of the fume hood, including three digits
34 42 which provide the average face velocity. The display 40
illustrates other conditions such as low face velocity,
36 high face velocity and emergency condition and an indi-
37 cation of controller failure. The operator panel may have
~8 an alarm 44 and an emergency purge switch 46 ~~hirh an
20~~14~'
-g-
1 operator can press to purge the fume hood in the event of
2 an accident. The operator panel has two auxiliary switches
3 48 which can be used for various customer needs, including
4 day/night modes of operation. It is contemplated that
night time mode of operation would have a different and
6 preferably reduced average face velocity, presumably
7 because no one would be working in the area and such a
8 lower average face velocity would conserve energy. An
9 alarm silence switch 50 is also preferably provided to
extinguish an alarm.
11 Fume hoods come in many different styles, sizes
12 and configurations, including those which have a single
13 sash door or a number of sash doors, with the sash doors
14 being moveable vertically, horizontally or in both direc-
tions. Additionally, various fume hoods have different
16 amounts of by-pass flow, i.e., the amount of flow permit-
17 ting opening that exists even when all of the sash doors
18 are as completely closed as their design permits. Other
19 design considerations involve whether there is some kind of
filtering means included in the fume hood for confining
21 fumes within the hood during operation. While many of
22 these design considerations must be taken into account in
23 providing efficient and effective control of the fume
24 hoods, the apparatus of the present invention can be
configured to account for virtually all of the above
26 described design variables, and effective and extremely
27 fast control of the fume hood ventilation is provided.
28 Referring to FIG. 3, there is shown a fume hood,
29 indicated generally at 60, which has a vertically operated
sash door 62 which can be moved to gain access to the fume
31 hood and which can be moved to the substantially closed
32 position as shown. Fume hoods are generally designed so
33 that even when a door sash such as door sash 62 is com-
34 pletely closed, there is still some amount of opening into
the fume hood through which air can pass. This opening is
36 generally referred to as the bypass area and it can be
37 determined so that its effect can be taken into considera-
38 tion in controlling the flow of air into the fume hood.
2055147
-10-
1 Some types of fume hoods have a bypass opening that is
2 located above the door sash while others are below the
3 same. In some fume hoods, the first amount of movement of
4 a sash door will increase the opening at the bottom of the
door shown in FIG. 3, for example, but as the door is
6 raised, it will merely cut off the bypass opening so that
7 the effective size of the total opening of the fume hood is
8 maintained relatively constant for perhaps the first one-
9 fourth amount of movement of the sash door 62 through its
course of travel.
11 Other types of fume hoods may include several
12 horizontally moveable sash doors 66 such as shown in FIGS.
13 4 and 5, with the doors being movable in upper and lower
14 pairs of adjacent tracks 68. When the doors are positioned
as shown in FIGS. 4 and 5, the fume hood opening is com-
16 pletely closed and an operator may move the doors in the
17 horizontal direction to gain access to the fume hood. Both
18 of the fumes hoods 60 and 64 have an exhaust duct 70 which
19 generally extends to an exhaust system which may be that of
the HVAC apparatus previously described. The fume hood 64
21 also includes a filtering structure shown diagrammatically
22 at 72 which filtering structure is intended to keep noxious
23 fumes and other contaminants from exiting the fume hood
24 into the exhaust system. Referring to FIG. 6, there is
shown a combination fume hood which has horizontally mov-
26 able doors 76 which are similar to the doors 66, with the
27 fume hood 74 having a frame structure 78 which carries the
28 doors 76 in suitable tracks and the frame structure 78 is
29 also vertically movable in the opening of the fume hood.
The illustration of FIG. 6 has portions removed as shown by
31 the break lines 73 which is intended to illustrate that the
32 height of the fume hood may be greater than is otherwise
33 shown so that the frame structure 78 may be raised suffi-
34 ciently to permit adequate access to the interior of the
fume hood by a person. There is generally a by-pass area
36 which is identified as the vertical area 75, and there is
37 typically a top lip portion 77 which may be approximately
38 2 inches wide. This dimension is preferably defined so
2Q551~'~
1 that its effect on the calculation of the open face area
2 can be taken into consideration.
3 While not specifically illustrated, other combin-
4 ations are also possible, including multiple sets of ver-
y tically moveable sash doors positioned adjacent one another
6 along the width of the fume hood opening, with two or more
7 sash doors being vertically moveable in adjacent tracks,
8 much the same as residential casement windows.
9 In accordance with an important aspect of the
present invention, the fume hood controller 20 is adapted
11 to operate the fume hoods of various sizes and configura-
12 tions as has been described, and it is also adapted to be
13 incorporated into a laboratory room where several fume
14 hoods may be located and which may have exhaust ducts which
merge into a common exhaust manifold which may be a part of
16 the building HVAC system. A fume hood may be a single
17 self-contained installation and may have its own separate
18 exhaust duct. In the event that a single fume hood is
19 installed, it is typical that such an installation would
have a variable speed motor driven blower associated with
21 the exhaust duct whereby the speed of the motor and blower
22 can be variably controlled to thereby adjust the flow of
23 air through the fume hood. Alternatively, and most
24 typically for multiple fume hoods in a single area, the
exhaust ducts of each fume hood are merged into one or more
26 larger exhaust manifolds and a single large blower may be
27 provided in the manifold system. In such types of instal-
28 lations, control of each fume hood is achieved by means of
29 separate dampers located in the exhaust duct of each fume
hood, so that variation in the flow can be controlled by
31 appropriately positioning the damper associated with each
32 fume hood.
33 The fume hood controller is adapted to control
34 virtually any of the various kinds and styles of fume hoods
that are commercially available, and to this end, it has a
36 number of input and output ports (lines, connectors or
37 connections, all considered to be equivalent for the
38 purposes of describing the present invention) that can be
.. 2055147
-12-
1 connected to various sensors that may be used with the
2 controller. As shown in FIG. 2, it has digital output or
3 DO ports which interface with a digital signal/analog
4 pressure transducer with an exhaust damper as previously
described, but it also has an analog voltage output port
6 for controlling a variable speed fan drive if it is to be
7 installed in that manner. There are five sash position
8 sensor ports for use in sensing the position of both
9 horizontally and vertically moveable sashes and there is
l0 also an analog input port provided for connection to an
11 exhaust air flow sensor 49. A digital input port for the
12 emergency switch is provided and digital output ports for
13 outputting an alarm horn signal as well as an auxiliary
14 signal is provided. An analog voltage output port is also
provided for providing a volume of flow signal to the room
16 controller 22. In certain applications where the exhaust
17 air flow sensor is not provided, a wall velocity sensor
18 indicative of face velocity may be utilized and an input
19 port for such a signal is provided, but the use of such
sensors is generally considered to be less accurate and is
21 not the preferred embodiment. With these various input and
22 output ports, virtually any type of fume hood can be con-
23 trolled in an effective and efficient manner.
24 From the foregoing discussion, it should be
appreciated that if the desired average face velocity is
26 desired to be maintained and the sash position is changed,
27 the size of the opening can be dramatically changed which
28 may then require a dramatic change in the volume of air to
29 maintain the average face velocity. While it is known to
control a variable air volume blower as a function of the
31 sash position, the fume hood controller apparatus of the
32 present invention improves on that known method by incor-
33 porating additional control schemes which dramatically
34 improve the capabilities of the control system in terms of
maintaining relatively constant average face velocity in a
36 manner whereby reactions to perturbations in the system are
37 quickly made.
38 To determine the position of the sash doors, a
M ~0551~7
-13-
1 sash position sensor is provided adjacent each movable sash
2 door and it is generally illustrated in FIGS. 7, 8 and 9.
3 Referring to FIG. 8, the door sash position indicator
4 comprises an elongated switch mechanism 80 of relatively
simple mechanical design which preferably consists of a
6 relatively thin polyester base layer 82 upon which is
7 printed a strip of electrically resistive ink 84 of a known
8 constant resistance per unit length. Another polyester
9 base layer 86 is provided and it has a strip of elec-
trically conductive ink 88 printed on it. The two base
11 layers 82 and 86 are adhesively bonded to one another by
12 two beads of adhesive 90 located on opposite sides of the
13 strip. The base layers are preferably approximately five-
14 thousandths of an inch thick and the beads are approxi-
mately two-thousandths of an inch thick, with the beads
16 providing a spaced area between the conductive and resis-
17 tive layers 88 and 84. The switching mechanism 80 is
18 preferably applied to the fume hood by a layer of adhesive
19 92.
The polyester material is sufficiently flexible
21 to enable one layer to be moved toward the other so that
22 contact is made in response to a preferably spring biased
23 actuator 94 carried by the appropriate sash door to which
24 the strip is placed adjacent to so that when the sash door
is moved, the actuator 94 moves along the switching
26 mechanism 80 and provides contact between the resistive and
27 conductive layers which are then sensed by electrical
28 circuitry to be described which provides a voltage output
29 that is indicative of the position of the actuator 94 along
the length of the switching means. Stated in other words,
31 the actuator 94 is carried by the door and therefore
32 provides an electrical voltage that is indicative of the
33 position of the sash door.
34 The actuator 94 is preferably spring biased
toward the switching mechanism 80 so that as the door is
36 moved, sufficient pressure is applied to the switching
37 means to bring the two base layers together so that the
38 resistive and conductive layers make electrical contact
zo~5~ ~ ~
-14-
1 with one another and if this is done, the voltage level is
2 provided. By having the switching means 80 of sufficient
3 length so that the full extent of the travel of the sash
4 door is provided as shown in FIG. 3, then an accurate
determination of the sash position can be made.
6 It should be understood that the illustration of
7 the switching mechanism 80 in FIGS. 3 and 5 is intended to
8 be diagrammatic, in that the switching mechanism is
9 preferably actually located within the sash frame itself
and accordingly would not be visible as shown. The width
11 and thickness dimensions of the switching mechanism are so
12 small that interference with the operation of the sash door
13 is virtually no problem. The actuator 94 can also be
14 placed in a small hole that may be drilled in the sash door
or it may be attached externally at one end thereof so that
16 it can be in position to operate the switch 80. In the
17 vertical moveable sash doors shown in FIGS. 3 and 6, a
18 switching mechanism 80 is preferably provided in one or the
19 other of the sides of the sash frame, whereas in the fume
hoods having horizontally movable doors, it is preferred
21 that the switching mechanism 80 be placed in the top of the
22 tracks 68 so that the weight of the movable doors do not
23 operate the switching mechanism 80 or otherwise damage the
24 same.
Turning to FIG. 9, the preferred electrical
26 circuitry which generates the position indicating voltage
27 is illustrated, and this circuitry is adapted to provide
28 two separate voltages indicating the position of two sash
29 doors in a single track. With respect to the cross-section
shown in FIG. 5, there are two horizontal tracks, each of
31 which carries two sash doors and a switching mechanism 80
32 is provided for each of the tracks as is a circuit as shown
33 in FIG. 9, thereby providing a distinct voltage for each of
34 the four sash doors as shown.
The switching means is preferably applied to the
36 fume hood with a layer of adhesive 92 and the actuator 94
37 is adapted to bear upon the switching means at locations
38 along the length thereof. Referring to FIG. 7, a
2455~~~
-15-
1 diagrammatic illustration of a pair of switching means is
2 illustrated such as may occur with respect to the two
3 tracks shown in FIG. 5. A switching mechanism 80 is
4 provided with each track and the four arrows illustrated
represent the point of contact created by the actuators 94
6 which result in a signal being applied on each of the ends
7 of each switching means, with the magnitude of the signal
8 representing a voltage that is proportional to the distance
9 between the end and the nearest arrow. Thus, a single
switching mechanism 80 is adapted to provide position
li indicating signals for two doors located in each track.
12 The circuitry that is used to accomplish the voltage
13 generation is shown in FIG. 9 and includes one of these
14 circuits for each track. The resistive element is shown at
84 and the conductive element 88 is also illustrated being
16 connected to ground with two arrows being illustrated, and
17 represented the point of contact between the resistive and
18 conductive elements caused by each of the actuators 94
19 associated with the two separate doors. The circuitry
includes an operational amplifier 100 which has its output
21 connected to the base of a PNP transistor 102, the emitter
22 of which is connected to a source of positive voltage
23 through resistor 104 into the negative input of the opera-
24 tional amplifier, the positive input of which is also con-
nected to a source of positive voltage of preferably
26 approximately five volts. The collector of the transistor
27 102 is connected to one end of the resistive element 84 and
28 has an output line 106 on which the voltage is produced
29 that is indicative of the position of the door.
The circuit operates to provide a constant cur-
31 rent directed into the resistive element 84 and this cur-
32 rent results in a voltage on line 106 that is proportional
33 to the resistance value between the collector and ground
34 which changes as the nearest point of contact along the
resistance changes. The operational amplifier operates to
36 attempt to drive the negative input to equal the voltage
37 level on the positive input and this results in the current
38 applied at the output of the operational amplifier varying
2055~4~
-16-
1 in direct proportion to the effective length of the resis-
t tance strip 84. The lower portion of the circuitry
3 operates the same way as that which has been described and
4 it similarly produces a voltage on an output line 108 that
is proportional to the distance between the connected end
6 of the resistance element 84 and the point of contact that
7 is made by the actuator 94 associated with the other sash
8 door in the track.
9 Referring to the composite electrical schematic
diagram of the circuitry of the fume hood controller, if
11 the separate drawings FIGS. 10a, lOb, lOc, 10d and l0e are
12 placed adjacent one another in the manner shown in FIG. 10,
13 the total electrical schematic diagram of the fume hood
14 controller 20 is illustrated. The operation of the cir-
cuitry of FIGS. l0a through l0e will not be described in
16 detail. The circuitry is driven by a microprocessor and
17 the important algorithms that carry out the control func-
18 tions of the controller will be hereinafter described.
19 Referring to FIG. lOc, the circuitry includes a Motorola MC
68HC11 microprocessor 120 which is clocked at 8 MHz by a
21 crystal 122. The microprocessor 120 has a databus 124 that
22 is connected to a tri-state buffer 126 (FIG. lOd) which in
23 turn is connected to an electrically programmable read only
24 memory 128 that is also connected to the databus 124. The
EPROM 128 has address lines AO through A7 connected to the
26 tri-state buffer 126 and also has address lines A8 through
27 A14 connected to the microprocessor 120.
28 The circuitry includes a 3 to 8-bit multiplexer
29 130, a data latch 132 (see FIG. lOd), a digital-to-analog
converter 134, which is adapted to provide the analog out-
31 puts indicative of the volume of air being exhausted by the
32 fume hood, which information is provided to room controller
33 22 as has been previously described with respect to FIG. 2.
34 Referring to FIG. lOb, an RS232 driver 136 is provided for
transmitting and receiving information through the hand
36 held terminal. The circuitry illustrated in FIG. 9 is also
37 shown in the overall schematic diagrams and is in FIGS. 10a
38 and lOb. The other components are well known and therefore
205514'
-17-
1 need not be otherwise described.
2 As previously mentioned, the apparatus of the
3 present invention utilizes a flow sensor preferably located
4 in the exhaust duct 70 to measure the air volume that is
being drawn through the fume hood. The volume flow rate
6 may be calculated by measuring the differential pressure
7 across a multi-point pitot tube or the like. The preferred
8 embodiment utilizes a differential pressure sensor for
9 measuring the flow through the exhaust duct and the appa-
ratus of the present invention utilizes control schemes to
11 either maintain the flow through the hood at a predeter-
12 mined average face velocity, or at a minimum velocity in
13 the event the fume hood is closed or has a very small
14 bypass area.
The fume hood controller of the present invention
16 can be configured for almost all known types of fume hoods,
17 including fume hoods having horizontally movable sash
18 doors, vertically movable sash doors or a combination of
19 the two. As can be seen from the illustrations of FIGS. 2
and 10, the fume hood controller is adapted to control an
21 exhaust damper or a variable speed fan drive, the con-
22 troller being adapted to output signals that are compatible
23 with either type of control. The controller is also
24 adapted to receive information defining the physical and
operating characteristics of the fume hood and other ini-
26 tializing information. This can be input into the fume
27 hood controller by means of the hand held terminal which is
28 preferably a lap top computer that can be connected to the
29 operator panel 34. It should be appreciated that the
day/night operation may be provided, but is not the pre-
31 ferred embodiment of the system; if it is provided, the
32 information relating to such day/night operation should be
33 included.
34 Operational information:
1. Time of day:
36 2. Set day and night values for the average
37 face velocity (SVEL), feet per minute or
38 meters per second;
205514fi
-18-
1 3. Set day and night values for the minimum
2 flow, (MINFLO), in cubic feet per minute;
3 4. Set day and night values for high velocity
4 limit (HVEL), F/m or M/sec;
5. Set day and night values for low velocity
6 limit (LVEL), F/m or M/sec;
7 6. Set day and night values for intermediate
8 high velocity limit (MVEL), F/m or M/sec;
9 7. Set day and night values for intermediate
low velocity limit (IVEL), F/m or M/sec;
11 8. Set the proportional gain factor (KP),
12 analog output per error in percent;
13 9. Set the integral gain factor (KI), analog
14 output multiplied by time in minutes per
error in percent;
16 10. Set derivative gain factor (KD), analog
17 output multiplied by time in minutes per
18 error in percent:
19 11. Set feed forward gain factor (KF) if a
variable speed drive is used as the control
21 equipment instead of a damper, analog output
22 per CFM:
23 12. Set time in seconds (DELTIME) the user
24 prefers to have the full exhaust flow in
case the emergency button is activated:
26 13. Set a preset percent of last exhaust flow
27 (SAFLOQ) the user wishes to have once the
28 emergency switch is activated and DELTIME is
29 expired.
The above information is used to control the mode
31 of operation and to control the limits of flow during the
32 day or night modes of operation. The controller includes
33 programmed instructions to calculate the steps in para-
34 graphs 3 through 7 in the event such information is not
provided by the user. To this end, once the day and night
36 values for the average face velocity are set, the con-
37 troller 20 will calculate high velocity limit at 120% of
'~8 the ~-.~~~~ ~ fare velocity, the low ~~~Zc~city limit at 80%
.. ~o~~~~~
-19-
1 and the intermediate limit at 90%. It should be understood
2 that these percentage values may be adjusted, as desired.
3 Other information that should be input include the follow-
4 ing information which relates to the physical construction
of the fume hood. It should be understood that some of the
6 infonaation may not be required for only vertically or
7 horizontally moveable sash doors, but all of the informa-
8 tion may be required for a combination of the same. The
9 information required includes vertical segments, which is
defined to be a height and width dimension that may be
11 covered by one or more sash doors. If more than one sash
12 door is provided for each segment, those doors are intended
13 to be vertically moveable sash doors, analogous to a double
14 sash residential window. The information to be provided
includes the following:
16 14. Input the number of vertical segments;
17 15. Input the height of each segment, in inches;
18 16. Input the width of each segment, in inches;
19 17. Input the number of tracks per segment;
18. Input the number of horizontal sashes per
21 track;
22 19. Input the maximum sash height, in inches:
23 20. Input the sash width, in inches;
24 21. Input the location of the sash sensor from
left edge of sash, in inches;
26 22. Input the by-pass area per segment, in
27 square inches;
28 23. Input the minimum face area per segment, in
29 square inches;
24. Input the top lip height above the
31 horizontal sash, in inches:
32 The fume hood controller 20 is programmed to
33 control the flow of air through the fume hood by carrying
34 out a series of instructions, an overview of which is
contained in the flow chart of FIG. li. After start-up and
36 outputting information to the display and determining the
37 time of day, the controller 20 reads the initial sash
38 positions of all doors (block 150), and this information is
2Q55.~4~
-20-
1 then used to compute the open face area (block 152). If
2 not previously done, the operator can set the average face
3 velocity set point (block 154) and this information is then
4 used together with the open face area to compute the ex-
haust flow set point (SFLOW) (block 156) that is necessary
6 to provide the predetermined average face velocity given
7 the open area of the fume hood that has been previously
8 measured and calculated. The computed fume hood exhaust
9 set point is then compared (block 158) with a preset or
required minimum flow, and if computed set point is less
11 than the minimum flow, the controller sets the set point
12 flow at the preset minimum flow (block 160). If it is more
13 than the minimum flow, then it is retained (block 162) and
14 it is provided to both of the control loops.
If there is a variable speed fan drive for the
16 fume controller, i.e., several fume hoods are not connected
17 to a common exhaust duct and controlled by a damper, then
18 the controller will run a feed-forward control loop (block
19 164) which provides a control signal that is sent to a
summing junction 166 which control signal represents an
21 open loop type of control action. In this control action,
22 a predicted value of the speed of the blower is generated
23 based upon the calculated opening of the fume hood, and the
24 average face velocity set point. The predicted value of
the speed of the blower generated will cause the blower
26 motor to rapidly change speed to maintain the average face
27 velocity. It should be understood that the feed forward
28 aspect of the control is only invoked when the sash
29 position has been changed and after it has been changed,
then a second control loop performs the dominant control
31 action for maintaining the average face velocity constant
32 in the event that a variable speed blower is used to
33 control the volume of air through the fume hood.
34 After the sash position has been changed and the
feed forward loop has established the new air volume, then
36 the control loop switches to a proportional integral
37 derivative control loop and this is accomplished by the set
38 flow signal being provided to block 168 which indicates
2fl~514'~
-21-
1 that the controller computes the error by determining the
2 absolute value of the difference between the set flow
3 signal and the flow signal as measured by the exhaust air
4 flow sensor in the exhaust duct. Any error that is com-
puted is applied to the control loop identified as the
6 proportional-integral-derivative control loop (PID) to
7 determine an error signal (block 170) and this error signal
8 is compared with the prior error signal from the previous
9 sample to determine if that error is less than a deadband
error (block 172). If it is, then the prior error signal
11 is maintained as shown by block 174, but if it is not, then
12 the new error signal is provided to output mode 176 and it
13 is applied to the summing junction 166. That summed error
14 is also compared with the last output signal and a deter-
urination is made if this is within a deadband range (block
16 180) which, if it is, results in the last or previous
17 output being retained (block 182). If it is outside of the
18 deadband, then a new output signal is provided to the
19 damper control or the blower (block 184). In the event
that the last output is the output as shown in block 182,
21 the controller then reads the measured flow (MFLOW) (block
22 186) and the sash positions are then read (block 188) and
23 the net open face area is recomputed (block 190) and a
24 determination made as to whether the new computed area less
the old computed area is less than a deadband (block 192)
26 and if it is, then the old area is maintained (block 194)
27 and the error is then computed again (block 168). If the
28 new area less the old area is not within the deadband, then
29 the controller computes a new exhaust flow set point as
shown in block 156.
31 One of the significant advantages of the present
32 invention is that the controller is adapted to execute the
33 control scheme in a repetitive and extremely rapid manner.
34 The exhaust sensor provides flow signal information that is
inputted to the microprocessor at a speed of approximately
36 one sample per 100 milliseconds and the control action
37 described in connection with FIG. 11 is completed appro-
38 ximately every 100 milliseconds. The sash door position
X055147
-22-
i signals are sampled by the microprocessor every 200 milli-
2 seconds. The result of such rapid repetitive sampling and
3 executing of the control actions results in extremely rapid
4 operation of the controller. It has been found that
movement of the sash will result in adjustment of the air
6 flow so that the average face velocity is achieved within
7 a time period of only approximately 3-4 seconds after the
8 sash door reposition has been stopped. This represents a
9 dramatic improvement over existing fume hood controllers.
In the event that the feed forward control loop
11 is utilized, the sequence of instructions that are carried
12 out to accomplish running of this loop is shown in the flow
13 chart of FIG. 12, which has the controller using the
14 exhaust flow set point (SFLOW) to compute the control
output to a fan drive (block 200), which is identified as
16 signal AO that is computed as an intercept point plus the
17 set flow multiplied by a slope value. The intercept is the
18 value which is a fixed output voltage to a fan drive and
19 the slope in the equation correlates exhaust flow rate and
output voltage to the fan drive. The controller then reads
21 the duct velocity (DV) (block 202), takes the last duct
22 velocity sample (block 204) and equates that as the duct
23 velocity value and starts the timing of the maximum and
24 minimum delay times (block 206) which the controller uses
to insure whether the duct velocity has reached steady
26 state or not. The controller determines whether the
27 maximum delay time has expired (block 208), and if it has,
28 provides the output signal at output 210. If the max delay
29 has not expired, the controller determines if the absolute
value of the difference between the last duct velocity
31 sample and the current duct velocity sample is less than or
32 equal to a dead band value (block 212). If it is not less
33 than the dead band value, the controller then sets the last
34 duct value as equal to the present duct value sample (block
214) and the controller then restarts the minimum delay
36 timing function (block 216). Once this is accomplished,
37 the controller again determines whether the max delay has
38 expired (block 208). If the absolute value of the
~~55~4~~
-23-
1 difference between the last duct velocity and the present
2 duct velocity sample is less than the dead band, the
3 controller determines whether the minimum delay time has
4 expired which, if it has as shown from block 218, the
output is provided at 210. If it has not, then it deter-
6 mines if the max delay has expired.
7 Turning to the proportional-integral-derivative
8 or PID control loop, the controller runs the PID loop by
9 carrying out the instructions shown in the flow chart of
FIG. 13. The controller uses the error that is computed by
11 block 168 (see FIG. 11) in three separate paths. With
12 respect to the upper path, the controller uses the pre-
13 selected proportional gain factor (block 220) and that
14 proportional gain factor is used together with the error to
calculate the proportional gain (block 222) and the propor-
16 tional gain is output to a summing junction 224.
17 The controller also uses the error signal and
18 calculates an integral term (block 226) with the integral
19 term being equal to the prior integral sum (ISUM) plus the
product of loop time and any error and this calculation is
21 compared to limits to provide limits on the term. The term
22 is then used together with the previously defined integral
23 gain constant (block 230) and the controller than calcu-
24 lates the integral gain (block 232) which is the integral
gain constant multiplied by the integration sum term. The
26 output is then applied to the summing junction 224.
27 The input error is also used by the controller to
28 calculate a derivative gain factor which is done by the
29 controller using the previously defined derivative gain
factor from block 234 which is used together with the error
31 to calculate the derivative gain (block 236) which is the
32 reciprocal of the time in which it is required to execute
33 the PID loop multiplied by the derivative gain factor
34 multiplied by the current sample error minus the previous
sample error with this result being provided to the summing
36 junction 224.
37 The control action performed by the controller 20
38 as illustrated in FIG. 13 provides three separate gain
2~55~4?'
-24-
1 factors which provide steady state correction of the air
2 flow through the fume hood in a very fast acting manner.
3 The formation of the output signal from the PID control
4 loop takes into consideration not only the magnitude of the
error, but as a result of the derivative gain segment of
6 control, the rate of change of the error is considered and
7 the change in the value of the gain is proportional to the
8 rate of change. Thus, the derivative gain can see how fast
9 the actual condition is changing and works as an "antici-
pator" in order to minimize error between the actual and
11 desired condition. The integral gain develops a correction
12 signal that is a function of the error integrated over a
13 period of time, and therefore provides any necessary cor-
14 rection on a continuous basis to bring the actual condition
to the desired condition. The proper combinations of pro-
16 portional, integral and derivative gains will make the loop
17 faster and reach the desired conditions without any over-
18 shoot.
19 A significant advantage of the PID control action
is that it will compensate for perturbations that may be
21 experienced in the laboratory in which the fume hood may be
22 located in a manner in which other controllers do not. A
23 common occurrence in laboratory rooms which have a number
24 of fume hoods that are connected to a common exhaust
manifold, involves the change in the pressure in a fume
26 hood exhaust duct that was caused by the sash doors being
27 moved in another of the fume hoods that is connected to the
28 common exhaust manifold. Such pressure variations will
29 affect the average face velocity of those fume hoods which
had no change in their sash doors. However, the PID con-
31 trol action may adjust the air flow if the exhaust duct
32 sensor determines a change in the pressure. To a lesser
33 degree, there may be pressure variations produced in the
34 laboratory caused by opening of doors to the laboratory
itself, particularly if the differential pressure of the
36 laboratory room is maintained at a lesser pressure than a
37 reference space such as the corridor outside the room, for
38 example.
~fl5514~
-25-
1 It is necessary to calibrate the feed forward
2 control loop and to this end, the instructions illustrated
3 in the flow chart of FIG. 14 are carried out. When the
4 initial calibration is accomplished, it is preferably done
through the hand held terminal that may be connected to the
6 operator panel via connector 38, for example. The control-
? ler then determines if the feed forward calibration is on
8 (block 242) and if it is, then the controller sets the
9 analog output of the fan drive to a value of 20 percent of
the maximum value, which is identified as value A01 (block
11 244). The controller then sets the last sample duct
12 velocity (LSDV) as the current duct velocity (CDV) (block
13 246) and starts the maximum and minimum timers (block 248).
14 The controller ensures the steady state duct velocity in
the following way. First by checking whether the max timer
16 has expired, and then, if the max timer has not expired,
17 the controller determines if the absolute value of the last
18 sample duct velocity minus the current duct velocity is
19 less than or equal to a dead band (block 270), and if it
is, the controller determines if the min timer has expired
21 (block 272). If it has not, the controller reads the
22 current duct velocity (block 274). If the absolute value
23 of the last sample duct velocity minus the current duct
24 velocity is not less than or equal to a dead band (block
270), then the last sample duct velocity is set as the
26 current duct velocity (block 276) and the mintimer is
27 restarted (block 278) and the current duct velocity is
28 again read (block 274). In case either the max timer or
29 min timer has expired, the controller then checks the last
analog output value to the fan drive (252) and inquires
31 whether the last analog output value was 70 percent of the
32 maximum output value (block 254). If it is not, then it
33 sets the analog output value to the fan drive at 70 percent
34 of the max value A02 (block 256) and the steady state duct
velocity corresponding to A01. The controller then repeats
36 the procedure of ensuring steady state duct velocity when
37 analog output is A02 (block 258). If it is at the 70
38 percent of max value, then the duct velocity corresponds to
-26-
1 steady state velocity of A02 (block 258). Finally, the
2 controller (block 262) calculates the slope and intercept
3 values.
4 The result of the calibration process is to
determine the duct flow at 20% and at 70% of the analog
6 output values, and the measured flow enables the slope and
7 intercept values to be determined so that the feed forward
8 control action will accurately predict the necessary fan
9 speed when sash door positions are changed.
The apparatus of the present invention is adapted
11 to rapidly calculate on a periodic basis several times per
12 second, the uncovered or open area of a fume hood access
13 opening that is capable of being covered by one or more
14 sash doors as previously described. As is shown in FIG. 6,
the actuator 94 is preferably located at the righthand end
16 of each of the horizontally movable doors of which there
17 are four in number as illustrated. The position indicating
18 capability of the switching mechanism 80 provides a signal
19 having a voltage level for each of the four doors which is
indicative of the position of the particular sash door
21 along its associated track. While the actuators 94 are
22 shown at the righthand portion of the sash doors, it should
23 be understood that they may be alternatively located on the
24 lefthand portion, or they could be located at virtually any
location on each door, provided that the relationship
26 between the width of the door and the position of the
27 actuator is determined and is input into the fume hood con-
28 trolley. It should be appreciated that having the location
29 of the actuators 94 at a common position, such as the right
end, simplifies the calculation of the uncovered opening.
31 While the fume hood shown in FIG. 6 is of the
32 type which has four horizontally movable doors 76 that are
33 housed within a frame structure 78 that itself is vertical-
34 ly movable, the fume hood controller apparatus of the pres-
ent invention is adapted to be used with up to four movable
36 sash doors in a single direction, i.e., horizontally, and
37 a perpendicularly movable sash door frame. However, there
38 are five analog input ports in the controller for inputting
20~5~4~
-27-
1 position information regardless of whether it is horizontal
2 or vertical and the controller can be configured to accom-
3 modate any combination of horizontally and vertically mov-
4 able doors up to a total of five. To this end, it should
be appreciated that there are vertically movable double
6 sash doors in certain commercially available fume hoods,
7 which configuration is not specifically shown in the
8 drawings, with the double sash configuration being housed
9 in a single frame structure that itself may be horizontally
movable. The fume hood controller of the present invention
11 may treat the double sash door configuration in the ver-
12 tical direction much the same as it operates with the
13 horizontally movable sash doors that operate in two tracks
14 as shown in FIG. 6.
Turning now to FIG. 15, the flow chart for the
16 fume hood controller operation as it calculates the
17 uncovered portion of the opening of the fume hood as
18 illustrated for the embodiment of FIG. 6 with respect to
19 the four horizontally movable doors. The flow chart
operation would also be applicable for determining the
21 uncovered area for the embodiment of FIG. 4 as well. The
22 initial step is to read each sash door position (block
23 300). The next step is to sort the sash doors to determine
24 the sash door positions relative to the left edge of the
opening (block 302). It should be understood that the
26 determination could be made from the right edge just as
27 easily, but the left edge has conveniently been chosen.
28 The apparatus then initializes the open area 304 as being
29 equal to zero and then the apparatus computes the distance
between the right edge of the sash door nearest the left
31 edge of the opening and the right edge of the next sash
32 door that is adjacent to it (block 306).
33 If the difference between the edges, as deter-
34 mined by the actuator location, is greater than the width
of the sash (block 308), then the net open area is set to
36 be equal to the net open area plus the difference minus the
37 sash door width (block 310) and this value is stored in
38 memory. If the difference is less than the sash door
~0~5147
-28-
1 width, then the program proceeds to repeat for the next two
2 pair of sash doors (block 312) as shown. In either event,
3 then the program similarly repeats for the next two pair of
4 sash doors. After the controller performs its repetitions
to calculate any open area between all of the sash doors,
6 then the controller checks the distance between the right
7 edge of the nearest sash door and the left track edge which
8 is comparable to the left opening (block 314) and if the
9 left difference is less than the sash door width (block
316) the controller then checks the distances between the
11 left edge of the furthest sash door and the right edge of
12 the track, i.e., the right opening 318. If the left dif-
13 ference is not less than the sash door width, then the net
14 open area is determined to be equal to the net open area
plus any left difference (block 320). The controller then
16 determines if the right difference is less than the sash
17 width (block 322) which, if it is, results in the net face
18 area being equal to the net open area plus the fixed area
19 (block 324) with the fixed area being the preprogrammed
bypass area, if any. If the right difference is not less
21 than the sash width, then the controller determines that
22 the net open area equals the net open area plus the right
23 difference (block 326). In this way, the net open area is
24 determined to be the addition between any open areas
between sash doors and between the rightward sash door and
26 the right edge of the opening and the difference between
27 the left edge of the leftmost sash door and the left edge
28 of the opening.
29 Turning now to FIG. 16, a flow chart of operation
of the apparatus for determining the uncovered area of the
31 opening for a fume hood which has multiple vertically
32 moveable sash doors is shown. The controller, when ini-
33 tially configured, requires the input of the width of each
34 segment, the number of such segments, the minimum face
area, i.e., the bypass area, plus any other residual open
36 area with the sash doors closed, and the number of sash
37 doors per segment (block 330). The controller then sets
38 the area equal to zero (block 332) and begins the
zo5~~~~
-29-
1 calculation for the first segment (block 334) and sets the
2 old height equal to zero (block 336). It then begins with
3 the first sash door (block 338) and reads the sash position
4 (block 340), inputs the slope and intercept (block 342)
from the prior calibration routine, and calculates the
6 height for that sash door and segment (block 344). The
7 apparatus then determines if it is sash door number 1,
8 which if it is, forwards the height of the segment (block
9 348), obtains the width of the segment (block 350) and
calculates the area by multiplying the height times the
11 width (block 358). If the sash door was not the number 1
12 sash, then the controller determines if the height of the
13 segment and sash was less than the old height, which if it
14 is, then the height of the segment is set as the height
(block 352) and the next sash door is made the subject of
16 inquiry (block 354) and the old height is retrieved (block
17 356) and the controller returns to block 338 to repeat the
18 calculations for the other segments and sash doors. After
19 the sash doors for a segment have been considered, and the
area of the segment determined (block 358), the controller
21 determines if the area for the segment is less than the
22 minimum flow area, and if it is, then the area is set to
23 the minimum flow area (block 362). If it is greater than
24 the minimum flow area, then the area for the segment is
determined to be equal to the bypass area plus the cal-
26 culated area for the segment (block 364). The area is then
27 calculated as the prior calculated area plus the area of
28 the segment under consideration (block 366), and the
29 controller then proceeds to consider the next segment
(block 368). After all segments have been considered, the
31 total area is obtained (block 370).
32 In accordance with an important aspect of the
33 present invention, the apparatus is also adapted to deter-
34 mine the uncovered area of a combination of vertically and
horizontally moveable sash doors, such as the fume hood
36 illustrated in FIG. 6, which has four horizontally moveable
37 sash doors that are contained in two sets of tracks, with
38 the sets of tracks being contained in a frame structure
20~~14'~
-30-
1 which is itself vertically moveable. As previously men-
2 tinned, there is an upper lip 77 having a front thickness
3 of about 2 inches, the exact dimension of which can vary
4 with the manufacturer's design, a lower portion 79 of the
frame 78, and a bypass area 75. As may be appreciated,
6 when the frame 78 is in its lowermost position, the entire
7 bypass area is "open" and air may be moved through it. As
8 the frame is raised, the portion of the sash doors 76 which
9 cover the opening will increasingly cover the bypass area
as shown. In the particular illustration of FIG. 6, the
11 horizontally moveable doors overlap and are completely
12 closed, but the frame is shown being slightly raised.
13 To determine the uncovered area of the combina-
14 tion sash door fume hood, the following specific steps are
performed. The net open area, i.e., the uncovered area, is
16 the sum of the vertical (hereinafter "V" in the equations)
17 area and the horizontal (hereinafter "H") area:
18 Net Open Area = V area + H area
19 with the horizontal area being determined as follows:
H area = H width * minimum of (panel Ht; Max of
21 (panel Ht + top lip Ht + min. face Ht -
22 sash Ht; 0)}
23 with the H width comprising the previously described opera-
24 tion being performed with respect to the horizontally mov-
able sash doors. The vertical area (V area) is determined
26 by the following equation:
27 V area = Max of (Sash Ht * V width; minimum face
28 area)
29 To complete the determination, the Net Face Area
is then equal to the sum of the Net Open Area and the Fixed
31 or bypass Area:
32 Net Face Area = Net Open Area + Fixed Area
33 From the foregoing detailed description, it
34 should be appreciated that a fume hood controller has been
shown and described that has superior capabilities in being
36 able to determine the effective uncovered area through
2~5514f~
-31-
1 which air may pass into most fume hoods that are commer-
2 cially available. Moreover, this capability exists even
3 when there are multiple sash doors, as well as combination
4 sash door configurations which have both horizontal and
vertical movement. With such capability, and the fact that
6 the fume hood controller calculates the open area several
7 times per second, the volume of air being drawn through the
8 fume hood can be very rapidly adjusted to maintain the
9 average face velocity at the desired value even when sash
door positions are changed.
11 While various embodiments of the present inven-
12 tion have been shown and described, it should be understood
13 that various alternatives, substitutions and equivalents
14 can be used, and the present invention should only be
limited by the claims and equivalents thereof.
16 Various features of the present invention are set
17 forth in the following claims.
