Networked fume hood monitoring system

A system for monitoring the operation of laboratory fume hoods includes a local area network for transferring data representing alarm conditions, and other special functions, to a building supervisory control system. The system has a calibrating capability which is adapted to build a database of the operating parameters of the fume hood which can be used to detect any degradation of the operation of the fume hood.

The present invention generally relates to the control of the ventilation 
of laboratory fume hoods, and more particularly to a networked monitoring 
system for providing safety warnings related to such laboratory fume 
hoods. 
Research and development work involving chemicals in a laboratory 
environment requires the use of fume hoods to confine the chemical fumes 
and thereby protect the individuals who are working in the laboratory. The 
fume hoods generally comprise an enclosure having a front opening and one 
or more movable doors adapted to cover the opening, but which can be 
opened to permit an individual to gain access to the interior of the 
enclosure for the purpose of performing experiments or other work. The 
enclosure is typically connected to a forced air exhaust system driven by 
a blower and the air from the fume hood is constantly being removed 
through the exhaust duct which carries any noxious fumes away so that an 
individual should not be exposed to the fumes while performing work in the 
hood. 
Fume hood controllers which control the flow of air through the enclosure 
have become quite sophisticated in recent years and now are able to 
accurately maintain the desired flow characteristics to exhaust the fumes 
from the enclosure as a function of the desired average face velocity of 
the opening of the fume hood, regardless of the size of the uncovered 
opening. It should be understood that the volume of air that is required 
to maintain an average face velocity would necessarily have to increase as 
the opening is uncovered by moving the sash doors that are provided. 
Fume hood controllers which accomplish this sophisticated operational 
control as well as other functions are disclosed in U.S. Pat. Nos. 
5,090,303, 5,092,227, 5,115,728 and 5,090,304, all of which are assigned 
to the same assignee as the present invention. Fume hood controllers of 
the type disclosed in the aforementioned patents provide sophisticated 
control to maintain the face velocity relatively constant and do so by a 
combination of factors including a measurement of the position of the sash 
doors of the fume hood and a calculation of the uncovered area of the 
opening that results from the movement of the sash doors. The controller 
also controls the volume of air that is exhausted through the exhaust duct 
by either controlling the speed of a blower motor or by controlling the 
position of a damper located in the exhaust duct, either of which are 
effective to modulate the volume of air that is exhausted from the fume 
hood. 
Such sophisticated controls are designed to provide the proper amount of 
flow to insure safety of the individuals who may be in the laboratory near 
the fume hoods, while also reducing to a minimum the amount of air that is 
expelled from the fume hoods and therefore the room. The less the amount 
of air removed from the room, the less air is necessary to replace the 
removed air. Obviously, if the fume hood is being operated during the 
winter and the replacement air has to be heated, substantial energy and 
therefore cost is required to heat the replacement air. Similarly, such 
energy considerations apply in cooling replacement air in the summer. 
It is estimated that there are hundreds of thousands of fume hoods in 
existence in the United States at the present time and many of these fume 
hoods are installed without such sophisticated controllers. Many of these 
fume hoods are constant volume installations which remove a sufficient 
amount of air to maintain a safe condition regardless of whether the fume 
hood is opened or closed. While safety considerations are thereby 
satisfied when the fume hood is operating properly, more energy is 
expended in such an installation which results in increased operating 
costs. Because safety considerations are paramount, there is a need for 
monitoring systems which monitor the operation of the fume hoods even if 
they are constant volume type of installations. 
Accordingly, it is a primary object of the present invention to provide an 
improved monitoring system for laboratory fume hoods. 
Another object of the present invention is to provide such an improved 
monitoring system that is networked to a building supervisory control 
system so that a building superintendent will be immediately alerted in 
the event of a potentially dangerous condition having occurred in the 
operation of a fume hood. 
Another object of the present invention is to provide such an improved 
monitoring system that provides a group of special functions based on the 
operation of the fume hood. 
Still another object of the present invention lies in the provision for 
such a monitoring system which is relatively inexpensive in terms of its 
initial cost and installation, but which is effective to provide reliable 
information relating to the operation of the fume hood. 
Another object of the present invention is to provide such an improved 
monitoring system which is effective to detect flow of air in the fume 
hood or in the exhaust duct connected to the fume hood, which is then 
processed to provide a face velocity value which can trigger alarm signals 
when the face velocity is outside of a predetermined bandwidth. 
Yet another object of the present invention is to provide an improved 
monitoring system that also has the capability of determining the face 
velocity at a plurality of spaced locations in the opening of the fume 
hood, sending the data on a network to the building supervisory control 
system or other location, and then recording the data in a memory device 
to thereby build a database of operation of the fume hoods over time.

DETAILED DESCRIPTION 
Broadly stated, a monitoring system for laboratory fume hoods implements a 
communication capability for networking the monitored information to a 
central location. In the preferred embodiment, the central location 
comprises a building supervisory control system which controls a plurality 
of special functions. The monitoring system includes hardware to measure 
predetermined parameters related to the fume hood and, based on the 
measured predetermined parameters related to the fume hood, notify the 
central location to activate one of a plurality of special functions. 
The hardware which measures the predetermined parameters also determines, 
based on the measured predetermined parameters related to the fume hood, 
whether an emergency condition in the fume hood exists. The measured 
predetermined parameters related to the fume hood include, but are not 
limited to, the minimum and maximum face velocity of the fume hood. In the 
preferred embodiment, the special functions include, but are not limited 
to, turning on/off lights throughout the building based on a determined 
emergency condition in the fume hood, activating an alarm for the entire 
building based on a determined emergency condition in the fume hood and 
providing notification to a superintendent as to whether the fume hood is 
or is not in use. 
The system of the present invention is also adapted to monitor the flow of 
air through an exhaust duct to which the fume hood is connected or to 
detect the differential pressure between the inside of the fume hood and 
the outside thereof or measure a representative sample of the flow of air 
from the room into the fume hood. This can be accomplished by means of a 
differential pressure sensor or a through-the-wall sensor which produces a 
signal that is indicative of the face velocity of the fume hood during 
operation. The system then calculates the face velocity and by means of a 
processing means, calculates a bandwidth of values which represents a safe 
operating range for the fume hood. 
While the preferred embodiment for the communication link is a two wire 
connection from the fume hood monitoring system to the building 
supervisory control system or other central location, other types of 
communication links are also within the scope of the present invention and 
may include multiple wire communication links, i.e., in excess of two 
wires, a fiber optic communication link, a coaxial connection, and even 
wireless communication, such as an RF transmission link or an infrared 
radiation communication link. 
The monitoring system preferably has a single enclosure display module 
which provides a numerical indication of the face velocity of the hood, an 
audible alarm, a relay providing a set of contacts to indicate an alarm to 
a supervisory control system as well as an alarm light. The display module 
also preferably has an audible alarm silencing pushbutton which enables an 
individual to turn off the alarm. This event is also preferably applied to 
the network for communication to the building supervisory control system 
in the form of an acknowledgement signal. Such an acknowledgement signal 
indicates that someone is present in the laboratory and is aware of the 
alarm condition at the local level. 
The system is also adapted to provide a plurality of face velocity signals 
in a face velocity traverse operation which is typically done 4 times a 
year. The readings are taken at various spaced apart locations within the 
fume hood opening, preferably at least nine locations, and these values 
are then communicated on the local area network to a memory device where a 
database of fume hood performance is accumulated over time. The database 
provides a baseline for operation and enables individuals to detect 
degradation of the operation of particular fume hoods, so that maintenance 
can be performed. 
Turning now to the drawings, and particularly FIG. 1, there is shown an 
overall schematic block diagram of a building supervisory control system, 
indicated generally at 10, which preferably has a central control console 
(not shown) with a computer which is typically manned by an operator and 
controls the building heating, ventilating and air conditioning equipment 
and sometimes fire alarm, security and other special functions that may be 
provided in the building. 
The system 10 has a local area network (LAN) indicated generally by line 12 
that extends to field panels 14 that are typically located throughout the 
building for interconnecting the system 10 to the HVAC equipment, such as 
dampers and the like, that are located in the building. Since the present 
invention monitors laboratory fume hoods, the building quite likely has 
one or more laboratory rooms having fume hoods installed in the rooms. 
There are a number of fume hood monitors 16 shown in FIG. 1 which are 
connected to the field panel via the local area network line 18 which 
extends from the monitoring system of the present invention to the field 
panel. By virtue of the local area network lines 12, the monitoring system 
is also connected to and in communication with the building and 
supervisory control system 10. 
One embodiment of the monitoring system of the present invention is shown 
in FIG. 2 and includes a processor 20 that is powered by a 24 volt a.c. 
source 22 via line 24 and the processor has the LAN connection 18 to the 
field panel 14 in the manner previously described in connection with FIG. 
1. The processor 20 is also connected to a wall velocity sensor 26 via 
line 28 and receives a signal that is representative of the face velocity 
in the form of an analog voltage signal that is applied to the processor 
20 which converts it to a digital signal for processing. The wall velocity 
sensor 26 identified in FIG. 2 is preferably a through the wall sensor, 
but can be a differential pressure sensor. The processor 20 is also 
connected to a display module 32 via line 34 and the display module is 
adapted to display the face velocity as well as other conditions to be 
described. Provision is also made for providing an alarm relay signal 
shown at 36 which is connected to the processor via line 38 and this alarm 
relay may be used to operate an auxiliary central or local alarm. 
The wall velocity sensor 26 is preferably a through-the-wall sensor, but 
can be a differential pressure sensor as previously stated, which is 
installed on the fume hood at a location as shown in FIG. 4, with the 
through-the-wall velocity sensor or differential pressure sensor requiring 
an opening in the wall of the fume hood and means for measuring the flow 
or pressure of the outside relative to the inside of the fume hood. Of 
course, it should be understood that the location of the sensor 26 may be 
at the location shown or at some other location on the hood. Such an 
indication is representative of the face velocity of the fume hood when it 
is in a steady state condition. When flow rates change rapidly, such as if 
the sash door is opened, then the through-the-wall sensor or differential 
pressure sensor is not particularly accurate until it has reached a steady 
state condition. 
Through-the-wall sensors of the type that are preferred, are also known as 
anemometers, and generally comprise a pair of temperature dependent 
resistive elements or thermistors, one of which is generally heated to a 
predetermined value above the ambient temperature. The heated element is 
thereby cooled by air flow at a rate that is proportional to the flow 
rate, and the power required to maintain the heated element at the 
elevated temperature provides an electrical signal that is representative 
of the flow rate. Such anemometer sensors are available from Fenwall, 
Alpha Thermistors, TSI, Kurz and Sierra. Differential pressure 
transmitters in the range of 0.0015 and 0.0030 inches of water may also be 
used and are available from Air Monitor and MKS. 
With the embodiment of FIG. 2, the processor 20 monitors the signal from 
the sensor 26 and after calibration is able to determine upper and lower 
limits which establish a bandwidth defining a safe operating range. The 
lower face velocity is preferably approximately 60 feet per minute (fpm) 
and the limit is preferably approximately 500 fpm. In the preferred 
embodiment, the 60 fpm value is user selectable. As long as the face 
velocity is within these limits, then it is considered to be safe. If the 
face velocity falls below 60 fpm or exceeds 500 fpm, then the processor 20 
will issue an alarm signal on lines 34 and 38 which will cause an audio 
alarm and also a visual alarm to occur. It should be apparent that both an 
audio and visual alarm is not absolutely necessary, but is preferred. 
The display module 32 is shown in FIG. 5 and preferably has a three digit 
LCD display indicated at 40 as well as a "low face velocity" readout, a 
"high face velocity" readout, an "user alarm" readout and a "general 
failure" readout. In addition to displaying the face velocity numerically, 
an alarm condition produced by either a high or low face velocity results 
in one of these indicators to be illuminated. The display module 32 also 
has an alarm horn indicated at 42 and an alarm silence pushbutton 44 
located on the display. If the horn is being sounded and an operator is 
present and knows what is occurring, the operator can push the button 44 
to expel the alarm. By operating the pushbutton 44, an alarm 
acknowledgement signal is thereby sent to the processor 20 which 
communicates that data to the field panel and to the supervisory control 
system 10 so that an acknowledgement of the alarm condition is provided. 
The processor 20 preferably communicates information on the local area 
network lines 18 which includes an address identifying the particular fume 
hood that is sending the information, data indicating an alarm condition 
if that event has occurred, as well as the face velocity in a digital 
signal representing feet per minute. It also will provide the alarm 
acknowledgement signal as well as a signal indicating the value of the 
voltage of the velocity sensor or differential pressure sensor itself. 
The processor 20 is adapted to be able to calibrate the wall velocity 
sensor or the differential pressure sensor if it is used, and depending 
upon the particular fume hood, a one volt signal may be representative of 
60 fpm or it may be 100 fpm. In any event, the calibration is 
straightforward and can be relatively easily accomplished by one of 
ordinary skill in the art. 
Another embodiment of the present invention is shown in FIG. 3 and it has 
similar components such as the processor 20, line 24, the analog signal on 
line 30, the 24 volt a.c. source 22, the field panel 14 and LAN connection 
18 as well as the alarm silence and display 32, the alarm relay 36 and 
lines 38 and 34. However, there is no through-the-wall sensor 26 or fume 
hood differential pressure sensor in this embodiment, but rather a duct 
flow sensor 50 that is connected to the processor via line 52 and a sash 
sensor 54 that is connected to the processor via line 56. 
Referring to FIG. 4, the duct flow sensor 50 is located in an exhaust duct 
52 of the illustrated fume hood, indicated generally at 53, and the duct 
flow sensor 50 provides a differential pressure measurement that can be 
used to calculate the volume of air of the fume hood. The range of the 
sensor 50 is preferably about 0.5 to 1.0 inch water column. More 
particularly, the duct velocity is the square root of the differential 
pressure measurement multiplied by a scaling constant and this duct 
velocity is then multiplied by the duct area to calculate the air volume 
through the fume hood. Using the sash sensor inputs, an open face area can 
be calculated, and by using the following equation, a face velocity can be 
derived: face velocity = air volume/face area. If the sash sensors are not 
used, then a flow sensor can be used by itself to monitor the flow through 
the fume hood. Without the sash sensors, a face velocity cannot be 
displayed but alarms can be triggered for flow rates that are too high or 
too low. 
The differential pressure measurement is typically an inches of water 
column reading with an output of preferably 0 to 20 milliamps and it is 
applied to the processor 20. The processor 20 shown in this embodiment 
also preferably provides a safe operating bandwidth and also issues an 
alarm signal if the face velocity falls below the 60 foot per minute value 
or exceeds the 500 foot per minute value. 
If an alarm condition occurs, a relay within the display module 32 closes, 
and the supervisory control system 10 is notified of the alarm condition. 
When an alarm condition occurs, the supervisory control system 10 also 
receives, via the local area network communication link 18, the duct 
velocity signal itself, the address of the fume hood and also an 
application number. In this manner, personnel at the supervisory control 
system 10 are alerted to potentially dangerous situations automatically. 
Referring to the composite electrical schematic diagram of the circuitry of 
the fume hood monitoring system, if the separate drawings FIGS. 6a, 6b, 
6c, 6d and 6e are placed adjacent one another in the manner shown in FIG. 
6, the total electrical schematic diagram of the fume hood controller is 
illustrated. The circuitry is driven by a microprocessor 20 as shown in 
FIG. 6c which is preferably a Motorola MC68HCll which is preferably 
clocked at 8 MHz by a crystal 62. The microprocessor 20 has a databus 64 
that is connected to a tri-state buffer 66 (see FIG. 6d) which in turn is 
connected to an electrically programmable read only memory 68 that is also 
connected to the databus 64. The EPROM 68 has address lines A0 through A7 
connected to the tri-state buffer 66 and also has address lines A8 through 
A14 connected to the microprocessor 20. The circuitry includes a 
three-to-eight bit multiplexer 70, a data latch 72, and a 
digital-to-analog converter 74 which is adapted to provide the auxiliary 0 
to 10 volt analog output on line 30. 
In accordance with another important aspect of the present invention, the 
monitoring system of the present invention is also adapted to provide 
another feature for the fume hoods and that is to calibrate and perform 
maintenance of the fume hood and also to utilize the local area network to 
build a database of the operation of each fume hood for use in determining 
whether the fume hood is operating properly or is experiencing degradation 
in its operation. 
It is common practice to perform a face velocity traverse of the fume hood 
to indicate whether the fume hood is operating safely. Such a traverse is 
used on both constant volume and variable volume fume hoods and is 
typically performed at intervals of approximately three months. 
Referring to FIG. 7, a fume hood 80 is shown and it has an opening 82 that 
has a sash door 84 present but in a raised position. Within the uncovered 
portion of the opening is a sensor grid structure 86 that has a total of 9 
sensors 88 positioned in a matrixed arrangement. 
Velocity measurements are taken at preferably at least nine locations in 
the fume hood opening, with none of the probes being closer than 
approximately six inches from any edge of the opening. By taking nine 
simultaneous measurements, any unevenness in the flow can be detected and 
recorded. It is typical to average the velocity values over a period of 
time, for example, 10 to 15 seconds. The signals from each of the probes 
are applied on lines 90 which extend to a multiplexing switch 92 
controlled by the processor 20 via line 94 for sequentially applying the 
signals from each sensor 88 to the processor 20 through a serial port via 
line 96. Alternatively, a separate processor can be utilized to receive 
the velocity signals from the various sensors 88, which can then average 
them and then apply them to the processor 20. 
The processor 20 is then adapted to send these velocity signals to the 
supervisory control system 10 which preferably receives them and records 
them in memory to thereby provide a database over time indicating the 
performance of the fume hood. Inspection of the data over time may 
indicate a degradation of the fume hood operation, which can be used by 
maintenance personnel to make any necessary modifications or corrections. 
For example, a belt on a blower may be slipping or a filter may be loaded 
to the extent that air flow is impaired. The data may provide a history of 
performance and maintenance that may become important in a legal 
proceeding in the event that damage or injury occurs in the laboratory. 
From the foregoing, it should be appreciated that a superior monitoring 
system has been shown and described which has the capability of monitoring 
the face velocity and flow of the fume hoods during operation and can 
trigger alarm conditions in the event that the detected or monitored face 
velocity or flow goes outside of a predetermined safety bandwidth of 
values. The monitoring system has the advantage in that it is inexpensive 
in terms of its initial cost as well as installation, yet it has the 
capability of reporting relevant information relating to the operation of 
the fume hoods to a central location, such as a building supervisory 
control system. The monitoring system also has the ability to perform 
calibration and status checks of a plurality of points in the fume hood 
opening and this information can be sent on the local area network to a 
central repository where it can be recorded in memory and be used to 
provide a record of the operation of the fume hood which can be important 
in detecting degradation of the operation of the fume hood. 
While various embodiments of the present invention have been shown and 
described, it should be understood that various alternatives, 
substitutions and equivalents can be used, and the present invention 
should only be limited by the claims and equivalents thereof. 
Various features of the present invention are set forth in the following 
claims.