Abstract:
A system, method and apparatus is provided for monitoring and adjusting the quality of indoor air. A sensor array senses an air sample from the indoor air and analyzes the air sample to obtain signatures representative of contaminants in the air sample. When the level or type of contaminant poses a threat or hazard to the occupants, the present invention takes corrective actions which may include introducing additional fresh air. The corrective actions taken are intended to promote overall health of personnel, prevent personnel from being overexposed to hazardous contaminants and minimize the cost of operating the HVAC system. The identification of the contaminants is performed by comparing the signatures provided by the sensor array with a database of known signatures. Upon identification, the system takes corrective actions based on the level of contaminant present. The present invention is capable of learning the identity of previously unknown contaminants, which increases its ability to identify contaminants in the future. Indoor air quality is assured by monitoring the contaminants not only in the indoor air, but also in the outdoor air and the air which is to be recirculated. The present invention is easily adaptable to new and existing HVAC systems. In sum, the present invention is able to monitor and adjust the quality of indoor air in real time by sensing the level and type of contaminants present in indoor air, outdoor and recirculated air, providing an intelligent decision about the quality of the air, and minimizing the cost of operating an HVAC system.

Description:
CONTRACTUAL ORIGIN OF THE INVENTION 
     This invention was made with United States Government support under Contract No. DE-AC07-94ID13223, now Contract No. DE-AC07-99ID13727 awarded by the United States Department of Energy. The United States Government has certain rights in the invention. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to methods, systems and apparatus for monitoring and adjusting indoor air quality. More specifically, the present invention relates to methods and apparatus for monitoring and adjusting indoor air quality by sensing and removing indoor air contaminants. 
     2. Present State of the Art 
     Heating, Ventilation, and Air Conditioning (HVAC) systems can be designed to control the temperature and humidity of indoor air by combining fresh outside air with recirculated inside air. This process is tempered by air heating and cooling costs. The quality of the indoor air is usually determined by the temperature and humidity of the air. Typically, the ratio of outside air to inside air is fixed and adjustments to the ratio are usually made manually when there is concern about the quality of the indoor air. 
     HVAC systems relying on the manual adjustment of the ratio between outside air and recirculated indoor air are not economically optimized and have the potential to subject personnel to unknown hazardous contaminants. For example, when the indoor air quality is very good, the HVAC system draws and conditions more outside air than is needed, which increases cost because the excess outside air has to be heated and conditioned. When air quality is poor, not enough outside air is drawn into the system resulting in health risks to personnel, which in turn leads to increased costs due to overexposed personnel, loss of productivity, and increased facility maintenance. 
     More advanced HVAC system have the added ability to sense particulates, Volatile Organic Compounds (VOC), and carbon dioxide but do not address hazards from exposure to a wide range of contaminants. The ability to sense particulates and carbon dioxide has improved the efficiency of HVAC systems, but not all problems have been solved. In fact, numerous instances of workplace problems related to the quality of indoor air have been recorded. The recirculation of indoor air can permit odors and toxic gases to concentrate over time and ultimately leads to unhealthy indoor air. The sources of these contaminants can include: facility infrastructure such as carpet, paints, and furniture; electrical equipment such as photocopiers, video monitors and ovens; cleaning equipment and supplies; mechanical equipment fuels, lubricants and combustion byproducts; the use of tobacco and perfumes by personnel; and natural microbes such as those found in drains, vents and crawl spaces. 
     Most of the recorded incidents related to poor indoor air equality were attributed to air contaminated with volatile organic compounds (VOC) from paints, adhesives and polishes along with nitrogen containing compounds such as nitric acid, nitrogen dioxide, and ammonia. These incidents occur because most HVAC systems are maintained by manually altering the indoor airflow and recycling rates based on personal observations and experience with odors, hazes, and weather conditions. However, none of these systems provide a mechanism to recognize when non-visible or non-odorous contaminants are present. If the control of any of these rates is controlled automatically, it is typically based on some combination of humidity, temperature, smoke and carbon dioxide. Routine monitoring and control of regulated contaminants specified in the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) Standard 62—and its revisions is rare. Further, these systems do not take into account the status or quality of the outside air being introduced into the system. 
     The Clean Air Act of 1970 required the Environmental Protection Agency (EPA) to establish National Ambient Air Quality Standards (NAAQS) for the six most significant air pollutants in the outdoor environment: sulfur dioxide, nitrogen dioxide, carbon monoxide, ozone, lead, and particulate matter with a diameter less than or equal to 10 micrometers. Of these pollutants, sulfur dioxide, nitrogen dioxide, carbon monoxide and ozone are colorless at very low concentrations and significantly and adversely affect human health. Current HVAC systems usually presume the outside air to be free of contaminants and do not monitor or make adjustments for these or other contaminants. 
     In addition to the contaminants and pollutants found in outside air, many other contaminants can be the cause of harmful indoor air. Currently, general indoor air quality is not regulated, but many agencies have proposed standards which may serve as guidelines. Standards have been proposed by the U.S. Department of Labor&#39;s Occupational Safety and Health Administration (OSHA), the World Health Organization (WHO), and ASHRAE. The pollutants and contaminants these standards propose regulating include: carbon dioxide, carbon monoxide, formaldehyde, nitrogen dioxide, ozone, radon and progeny, sulfur dioxide, and a number of VOCs. In addition to these contaminants, many other chemicals are regulated by OSHA in work environments to control long and short-term exposures. 
     As noted above, HVAC manufacturers typically purchase sensors to monitor temperature, smoke, humidity and carbon dioxide. Providing additional sensors to monitor all potentially harmful contaminants is rare and expensive because of the cost of providing sensors for each contaminant. The addition of charcoal filters, water scrubbers, and reductant/oxidant scrubbers as a means of ensuring good indoor air is also impractical because they have a limited capacity that is exhausted rapidly during continuous operation. In other words, it is impractical to provide a sensor or filter for each contaminant and pollutant. There remains a need, however, to sense poor indoor air quality and make adjustments to the indoor air such that human health is preserved and economic costs are lowered. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     The present invention has been developed in response to the present state of the art, and in particular, in response to these and other problems and needs that have not been fully or completely solved by currently available HVAC systems for monitoring and adjusting the quality of indoor air. Thus, it is an overall object of the present invention to provide a method, system and apparatus for reliably monitoring and adjusting the quality of indoor air. 
     It is therefore an object of one embodiment of the present invention to monitor abnormal conditions indicative of unhealthy air. 
     It is another object of one embodiment of the present invention to monitor and adjust the quality of indoor air. 
     It is a further object of one embodiment of the present invention to minimize heating and cooling costs. 
     It is an additional object of one embodiment of the present invention to protect humans from over exposure to hazardous air pollutants. 
     It is another object of one embodiment of the present invention to identify contaminants and pollutants in the indoor air. 
     It is a further object of one embodiment of the present invention to infer the identity of contaminants and pollutants in the indoor air. 
     Yet another object of one embodiment of the present invention is to determine when alternative air supplies or mitigation processes should be used to provide healthy indoor air. 
     In summary, the foregoing and other objects are achieved by providing a method and apparatus for monitoring and adjusting the quality of indoor air. In one embodiment of the present invention a sensor array is provided which is capable of sensing a variety of contaminants. Each contaminant or mixture of contaminants may cause the individual sensors in the sensor array to produce a particular sensor signature or output. Further, each contaminant also causes the sensors to produce an array signature. Both the sensor signatures and the array signatures can be indicative of particular contaminants. 
     In this manner, personnel can be protected from over exposure to toxic substances and the costs associated with heating, cooling, and humidifying the air can be minimized. Another embodiment also monitors the outside air to ensure that harmful contaminants are not introduced from the outside air. 
     The signatures are sent to a processing unit which compares the signatures to a database or library of known signatures. Based on this comparison, the contaminant is identified or the identity of the contaminant is inferred. Once identified, the system evaluates the level of hazard presented by the contaminant and takes corrective action to remove the contaminant from the indoor air. An exemplary corrective action is to adjust the ratio of outside air mixed with recycled inside air to reduce the concentration of the contaminant to an acceptable level. 
     The combination of sensors and the database of signatures enables the present invention to monitor a number of contaminants beyond the contaminants that the sensors can monitor individually. Effectively, the sensor array can be represented by an n-dimensional space. The signatures of various contaminants are mapped within this n-dimensional space. The signatures of known contaminants are stored in a database and the signatures of sensed contaminants are compared to that database. The n-dimensions permit the identity of unknown contaminants to be inferred if the signature of the unknown contaminant is spatially near the signature of a known contaminant. 
     By adding more dimensions to the sensor array, which is done by adding additional senors, the accuracy of identifying the contaminant is increased. In an n-dimensional database, the interpolation between database points, which represent contaminants, is easily done and quite accurate because the points are not far apart spatially. Also, the n-dimensions of the database allows for more separation between the clusters of points, which results in better accuracy and the possibility of storing data on more contaminants. The present invention is also capable of learning to identify new contaminants and the database of known contaminants and pollutants can continually be updated and increased. 
     Another embodiment of the present invention is that the system can decide which sources of air to use to assure healthy indoor air. The source could be another outside air inlet vent, mitigated recirculated indoor air, or a reservoir of purified air. If the source of air is unacceptable, the contaminants are first removed or reduced before the air is introduced into the system. This is accomplished by sensing the contaminants present in the air and then passing the air through a series of modules or filters which strip the contaminants from the air before the air is mixed and introduced into the system. In a preferred embodiment, the modules or filters are active only when contaminants are present in the outside air or the recirculated air. 
     One embodiment of the sensors array is capable of sensing a wide variety of contaminants including but not limited to carbon dioxide, carbon monoxide, sulfur dioxide, hydrogen sulfide, nitrogen oxides and a variety of volatile organics. In addition to these contaminants, the humidity, pressure and temperature of the air also monitored. In some cases, other specific sensors maybe added when the specific location has a historical record of other ambient contaminants. 
     Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the manner in which the above-recited and other advantages and objects of the invention are obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
     FIG. 1 is an example system that provides a suitable operating environment for the present invention; 
     FIG. 2 is an illustration of one embodiment of the present invention adapted to a heating, ventilation and air condition system; 
     FIG. 3 is an illustration of one embodiment of an indoor air quality management system; 
     FIG. 4 is a block diagram illustrating a process of deciding which source of air or mitigation processes is selected for sampled conditions and is a more detailed view of part of an indoor air quality management system; 
     FIG. 5 is an illustration of one embodiment of modules for monitoring and adjusting the outdoor air quality and the recirculated air quality; 
     FIG. 6 is a flow chart of one embodiment of a method for monitoring and adjusting indoor air quality; and 
     FIG. 7 is a flow chart of one embodiment of a method for identifying each contaminant in an air sample. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides system, apparatus and methods for monitoring and adjusting the quality of indoor air and is adaptable to new and existing HVAC systems. The quality of air is evaluated based on the quantity of contaminants present in the air. As used herein, contaminants includes but is not limited to pollutants, chemicals, particulates, smoke, bacteria, viruses, humidity, temperature as well as other substances or conditions which may or may not lead to poor air quality. Contaminant also refers to the substances listed in the indoor air quality standards proposed by OSHA, WHO, ASHRAE, and other organizations. 
     Embodiments within the scope of the present invention also include computer-readable media having computer-executable instructions or data structures stored thereon. Such computer-readable media can be any available media which can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EPROM, EEPROM, CDROM, or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired executable instructions or data structures and which can be accessed by a general purpose or special purpose computer. 
     When information is transferred or provided over a network or other communications connection to a computer, the computer properly views the connection as a computer-readable medium. Thus, such a connection is also properly termed a computer-readable medium. Combinations of the above should also be included within the scope of computer-readable media. Computer-executable instructions comprise, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing device to perform a certain function or group of functions. The computer-executable instructions and associated data structures represent an example of program code means for executing the steps of the invention disclosed herein. 
     FIG.  1  and the following discussion are intended to provide a brief, general description of a suitable computing environment in which the invention may be implemented. Although not required, the invention will be described in the general context of computer-executable instructions, such as program modules, being executed by a personal computer. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. 
     Moreover, those skilled in the art will appreciate that the invention may be practiced with other computer system configurations, including hand-held devices, multi-processor systems, microprocessor-based or programmable consumer electronics, network PCs, minicomputers, mainframe computers, and remote applications that include a LonWorks® type of communications system for indirect connection or for direct serial or parallel port connections to remote sensors, available from Echelon Corp of San Jose, Calif. The invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote memory storage devices. 
     With reference to FIG. 1, an exemplary system for implementing the invention includes a general purpose computing device in the form of a conventional computer  20 , including a processing unit  21 , a system memory  22 , and a system bus  23  that couples various system components including the system memory to the processing unit. The system bus  23  may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. The system memory includes read only memory (ROM)  24  and random access memory (RAM)  25 . A basic input/output system (BIOS)  26 , containing the basic routines that help to transfer information between elements within the computer  20 , such as during start-up, may be stored in ROM  24 . The computer  20  may also include a magnetic hard disk drive  27  for reading from and writing to a magnetic hard disk, not shown, a magnetic disk drive  28  for reading from or writing to a removable magnetic disk  29 , and an optical disk drive  30  for reading from or writing to removable optical disk  31  such as a CD-ROM or other optical media. The magnetic hard disk drive  27 , magnetic disk drive  28 , and optical disk drive  30  are connected to the system bus  23  by a hard disk drive interface  32 , a magnetic disk drive-interface  33 , and an optical drive interface  34 , respectively. The drives and their associated computer-readable media provide nonvolatile storage of computer readable instructions, data structures, program modules and other data for the computer  20 . Although the exemplary environment described herein employs a magnetic hard disk  27 , a removable magnetic disk  29  and a removable optical disk  31 , it should be appreciated by those skilled in the art that other types of computer readable media which can store data that is accessible by a computer, such as magnetic cassettes, flash memory cards, digital video disks, Bernoulli cartridges, random access memories (RAMs), read only memories (ROM), and the like, may also be used in the exemplary operating environment. 
     A number of program modules may be stored on the hard disk, magnetic disk  29 , optical disk  31 , ROM  24  or RAM  25 , including an operating system  35 , one or more application programs  36 , other program modules  37 , and program data  38 . A user may enter commands and information into the computer  20  through input devices such as a keyboard  40  and pointing device  42 . Other input devices (not shown) may include a microphone, joy stick, game pad, satellite dish, scanner, or the like. These and other input devices are often connected to the processing unit  21  through a serial port interface  46  that is coupled to system bus  23 , but may be connected by other interfaces, such as a parallel port, game port or a universal serial bus (USB). A monitor  47  or other type of display device is also connected to system bus  23  via an interface, such as video adapter  48 . In addition to the monitor, personal computers typically include other peripheral output devices (not shown), such as speakers and printers. 
     Computer  20  may operate in a networked environment using logical connections to one or more remote computers, such as a remote computer  49 . Remote computer  49  may be another personal computer, a server, a router, a network PC, a peer device or other common network node, and typically includes many or all of the elements described above relative to the computer  20 , although only a memory storage device  50  has been illustrated in FIG.  1 . The logical connections depicted in FIG. 1 include a local area network (LAN)  51  and a wide area network (WAN)  52  that are presented here by way of example and not limitation. Such networking environments are commonplace in offices enterprise-wide computer networks, intranets and the Internet. 
     When used in a LAN networking environment, the computer  20  is connected to the local network  51  through a network interface or adapter  53 . When used in a WAN networking environment, the computer  20  typically includes a modem  54  or other means for establishing communications over the wide area network  52 , such as the Internet. The modem  54 , which may be internal or external, is connected to the system bus  23  via the serial port interface  46 . In a networked environment, program modules depicted relative to the computer  20 , or portions thereof, may be stored in the remote memory storage device. It will be appreciated that the network connections shown are exemplary and other means of establishing a communications link between the computers may be used. 
     FIG. 2 is a block diagram of an exemplary system implementing one embodiment of the present invention. In FIG. 2, each zone  60  represents an area being heated, cooled, or conditioned using a HVAC system or other system. As used herein, zone may refer to an entire building, a floor of a building, part of a floor of a building, or any other area which has a heating, cooling or air conditioning system. Each zone  60  may be in the same building or in separate buildings. Both the outside air and the recirculated air are considered zones. A zone comprises any area from which an air sample is taken and there may be multiple sources of outside or makeup air to be selected. Indoor Air Quality Monitoring System (IAQMS)  80  may monitor multiple sources of inside air from different zones, multiple sources of outside air, and multiple sources of recirculating air. Multiple systems may also be used in a single facility, based on the size of the HVAC system and the level of monitoring needed or desired. 
     Each zone  60  has a supply air  64  and supply air  64  may come from multiple potential sources, including the outside air, a reservoir of clean air or recirculated air. Each zone  60  also has a central exhaust  78 . Central exhaust  78  further comprises an alternate exhaust  76 . Alternate exhaust  76  leads to a heat recovery unit  70  where the heat from the indoor air is transferred to outside air  72  which will be introduced into each zone  60  within the HVAC system. Central exhaust  78  also comprises recirculated air  68 , which is fed to recirculation valve  66 . At recirculation valve  66 , recirculated air  68  is combined with outdoor air  72  coming from heat recovery unit  70 . Recirculation valve  66  outputs supply air  64 , which is typically a mixture of outside air  72  and recirculated air  68 , to each zone  60 . 
     IAQMS  80  in one embodiment, monitors and adjusts the quality of the air present in each zone  60 . IAQMS  80 , described in more detail with reference to FIG. 3, has a plurality of air samplers including an outdoor air sampler  74 , a recirculated air sampler  69 , and a plurality of zone samplers  62 . IAQMS  80  may comprise additional air samplers depending on the quantity of outdoor and recirculated air sources. Outdoor air sampler  74  is an example of means for sampling and monitoring the quality of the outdoor air. Each zone sampler  62  is an example of means for sampling and monitoring the quality of the indoor air for each zone  60 . Recirculated air sampler  69  is an example of means for sampling and monitoring the quality of recirculated air  68  which is to be recycled and reintroduced to the system. One embodiment of each air sampler is a tube connecting sensor array  82  to the air to be sampled. The placement of each air sampler can vary. For example, the air samples can be physically located in the zones, or in the duct work of the system in order to cover remote applications. IAQMS  80  further comprises valve control  79 , which adjusts recirculation valve  66  such that the ratio of recirculated air  68  and outdoor air  72  varies. FIG. 2 is an example of an air delivery system which is connected to IAQMS  80 . 
     FIG. 3 is a block diagram of one embodiment of an IAQMS  80 . IAQMS  80  monitors the indoor air quality of each zone  60  using sensor array  82 . The embodiment illustrated in FIG. 3 comprises a single sensor array  82 . Other embodiments contemplate a separate sensor array  82  located in each zone  60 , a sensor array  82  to test outside air  72 , and a sensor array  82  to test recirculated air  68 . The information gathered by the sensor arrays would then be sent to IAQMS  80  for analysis. In the embodiment illustrated in FIG. 3, sensor array  82  is connected to a plurality of zone samplers  62 , outdoor air sampler  74  and recirculated air sampler  69 . Each zone sampler  62  provides sensor array  82  access to the indoor air located with the respective zone  60 . Outdoor air sampler  74  provides sensor array  82  access to the outdoor air and recirculated air sampler  69  provides sensor array  82  access to the recirculated air. In a preferred embodiment, sensor array  82  has access to only one air sampler at a time such that IAQMS  80  knows the location of the air that is being sampled or tested for contaminants. Sensor array  82  is an example of sensing means for evaluating an air sample. 
     Embodiments of sensor array  82  can include any number of sensors including one sensor. A preferred embodiment of sensor array  82  comprises sensors for carbon dioxide, carbon monoxide, hydrogen sulfide, nitrogen oxides, volatile organics, sulfur dioxide, relative humidity, pressure and temperature. A key advantage of these sensors is that the sensors selected for the IAQMS are readily available and inexpensive, as well as stable and rapid so that adjustments to the quality of the indoor air can be made in real time. Another key advantage of these sensors is that they embody varying transducer principles allowing the sensors to respond selectively to the contaminants of interest, yet broad-based to respond to other contaminants. This is significant to allow the IAQMS to respond to a wide variety of expected and unexpected contaminants while controlling the system to conserve energy and reduce costs. 
     In other words, the sensors selected for inclusion in sensor array  82  are chosen for reasons related to cost, availability, regulated contaminants, response time, and other reasons. Other sensors can be included in sensor array  82 , as regulations change or specific hazards become known in a particular environment. An example would be an ammonia sensor in a facility near a feed lot or sewage processing area. 
     ASHRAE specifies that an HVAC system use either minimum air flow/exchange rates or performance-based methods to achieve acceptable indoor air quality. A sensor that takes a significant amount of time to make a measurement is impractical and cannot satisfy either of these requirements. The number of sensors in sensor array  82 , however, can be expanded or decreased. IAQMS functions by recognizing when contaminants reach concentration levels determined to be harmful and therefore need to be reduced to acceptable levels. The need for the IAQMS is based on the consideration that low levels of most contaminants exist in most locations at levels that are not considered hazardous. 
     Because there are many different contaminants that may be hazardous, sensors array  82  can detect contaminants that may not be detected by the individual sensors. For example, even though an ozone specific sensor is not included in sensor array  82 , sensor array  82  is capable of detecting not only ozone, but a wide variety of contaminants. For example, the sensor used to detect nitrogen dioxide generates a positive voltage in proportion to the amount of nitrogen dioxide detected. This same sensor produces a negative voltage in proportion to the amount of ozone detected. This negative voltage is recognized as a trait of ozone and is an indication of a sensor response to a specific contaminant and concentration of the contaminant. Responses of the additional sensors to the same contaminant serve to confirm the presence and concentration of the contaminant. In combination as the sensor array, the indication of a response and the magnitude of the response for each sensor serves as an array signature which indicates the presence of a contaminant and the magnitude indicates the quantity or concentration of the contaminant. IAQMS  80  can infer that ozone is present and in a recognizable quantity due to the response of sensor array  82 . The aggregate response of sensor array  82  to this particular contaminant is an array signature. The response of a single sensor to a particular contaminant is a sensor signature. 
     The array signature of sensor array  82  is important because the sensors are designed for certain contaminants. As mentioned above, however, the sensors respond to other contaminants. By exposing sensor array  82  to various contaminants and observing the response of sensor array  82  to those contaminants, the ability of IAQMS  80  to identify contaminants is expanded beyond what contaminants the sensors can identify individually. Also, database  88  is created and expanded by exposing sensor array  82  to different contaminants and storing the array signature. 
     It is clearly difficult to identify a wide variety of contaminants using a single sensor because most sensors provide only a magnitude of response. When used in an array, the direction, shape, and magnitude of the response can be used to fingerprint as well as identify and locate the contaminant. The array signature, which is produced in part by these characteristics, is substantially more unique for a given contaminant. For example, if the sensors consisted of a carbon dioxide sensor, a volatile organic sensor and a sulfur dioxide sensor, then the response of these three sensors to various contaminants can be mapped to a three dimensional space. This is analogous to an array signature for the contaminant. Using a three dimensional space, contaminants that have an array signature spatially near the array signature of other known contaminants can be presumed hazardous and the identity of the contaminant can be inferred. A system having n sensors places the array signatures of various contaminants in an n dimensional space. The additional dimensions allows for more accurate identification of indoor air contaminants. By learning the array signature of additional contaminants, IAQMS  80  can learn to identify a wide variety of contaminants. 
     As described above, sensor array  82  can be implemented in a variety of ways. One embodiment has a single sensor array attached to tubes or conduits that have access to the air of various zones, the outdoor air and the recirculated air. When sensor array  82  is testing or sampling the air from a particular zone, only the air from that sampling point is exposed to sensor array  82 . Upon obtaining an air sample, data acquisition  84  performs signal preprocessing, analog/digital conversions, and system communication. Once the sensor signatures and the array signatures are obtained, they are sent to inference engine  86 . Inference engine  86  compares the sensor signatures and the array signatures received from sensor array  82  with known sensor signatures and known array signatures stored in signature database  88 . Inference engine  86  is an example of processor means for comparing sensor signatures and array signatures with known sensor signatures and known array signatures. 
     FIG. 4 is an illustration of inference engine  86  and its interaction as part of IAQMS  80 . Sensor array  82  produces an output, which is sent to data acquisition module  84 . Data acquisition module  84  functions to produce an array signature which is indicative of the contaminants in the air sampled by sensor array  82 . Data acquisition module  84  may employ compression and decompression techniques as well as analog/digital signal conversions. This information is then passed to inference engine  86 . In this embodiment, inference engine  86  receives the information through a newel neural net  130 . Next, the array signature is placed within the n-dimensional space by matrix  131 . Recognition module  132  compares the array signature in matrix  131  with the array signatures in database  88 . If this comparison is a new signature in step  133 , then the array signature is labeled or rejected in step  135 . If the comparison produces a known signature, then identity module  134  identifies the contaminant and HVAC control  90  then takes corrective actions, which may include adjusting the recirculation rate, selecting an alternative outside or makeup air source, adjusting the air flow rate, selecting a mitigation module, or issuing an alert or evacuation signal. If a new signature is indicated in step  133 , then the spatial proximity of the array signature of the unknown contaminant to other known contaminants is used to identify the hazard associated with the unknown contaminant in proximity module  136 . Proximity module  136  will infer the hazard of the unknown contaminant in identity module  134 . HVAC control  90  then takes corrective actions as previously indicated. 
     In FIG. 4, IAQMS  80  permits operator input  139 . Operator input  139  permits acceptable contaminant levels to be set, permits database  88  to be updated and allows unknown or new signatures to be identified in step  135  and entered into database  88 . The contaminant levels are connected with HVAC control  90 . In this manner, inference engine  86  is able to increase its ability to identify previously unknown contaminants as well as infer the hazard associated with those unknown contaminants and take corrective actions. 
     In one embodiment, signature database  88  contains the n dimensional array signatures for a wide variety of contaminants it is trained to identify. IAQMS  80  has the capability to learn to recognize the array signatures of previously unknown contaminants. In this manner, signature database  88  can be updated and IAQMS  80  is therefore capable of of learning and increasing its ability to identify contaminants and take corrective action. It then infers the level of hazard from the proximity in n-space to known contaminants in the database. Signature database  88  is a library of contaminant signatures. Some of the contaminants may or may not be related to unhealthy indoor air. 
     The signatures stored in signature database  88  may be stored in a compressed form or format using compression techniques well known in the art. The comparison between signatures provided by sensor array  82  and the signatures stored in signature database  88  may involve a compression/decompression technique well known in the art. Signature database  88  can take the form of a programmable EPROM, a CDROM or other form. As more contaminants are learned, signature database  88  can be updated with a new EPROM or CDROM. Signature database  88  is preferably stored in an EPROM for several reasons. First, EPROMs can be removed and replaced easily and inexpensively. Second, the physical location of the system may make the use of a keyboard and a monitor difficult. Thus an EPROM is a convenient manner of updating signature database  88 . 
     As mentioned earlier, many contaminants that are known to be hazardous have a known signature located in the n-dimensional space. If an unknown contaminant has an array signature that is spatially near the array signature of a known hazardous contaminant, then inference engine  86  presumes the contaminant to be hazardous and takes corrective action. For the safety of personnel exposed to the indoor air, it is important to understand that any array signature that is not within a normal range of array signatures is presumed to be hazardous. In other words, any off normal array signature is presumed harmful. 
     Corrective action is taken by having inference engine  86  issue commands to HVAC control  90 . These commands may include increasing the amount of outside air that is mixed with the recirculated air and introduced into the system. The corrective response is automatic and prevents people from being overexposed to undesirable levels determined to be hazardous by regulation, guidelines or personal preferences. As discussed above, there are no regulated requirements for indoor air quality. Various groups have proposed various standards and IAQMS  80  preferably takes corrective action before the contaminants or pollutants in the indoor air reach those levels. For example, corrective action may be taken when the contaminants or pollutants in the indoor reach  80  percent of the proposed ASHRAE standards. HVAC control  90  is an example of control means for adjusting the indoor air quality. HVAC control  90  implements corrective actions indicated by inference engine  86 . 
     Typically, one solution to removing contaminants in indoor air is to increase the amount of presumably fresh outdoor air. Outdoor air is not always fresh, however, and may introduce more contaminants that it removes. For this reason, sensor array  82  or IAQMS  80  also has an outdoor air sampler  74 , through which the outdoor air is sampled and sensed using sensor array  82 . If the outdoor air contains contaminants, those contaminants must be removed or mitigated before the outdoor air is introduced and mixed with the indoor air or an alternate outdoor air source can be selected. A similar process occurs with the air to be recirculated. IAQMS  80  has recirculated air sampler  69 , which permits sensor array  82  to sample the recirculated air. If the recirculated air contains an unacceptable level of contaminants, those contaminants must be removed or mitigated before the recirculated air is actually introduced into the system. IAQMS  80  may also increase the amount of indoor air recirculated if the recirculated air is less hazardous. 
     FIG. 5 illustrates how contaminants in the outside air or in the recirculated air may be removed or mitigated. Outdoor air intake  100  is illustrated in FIG. 5 as having or containing a plurality of mitigation modules  104 . In one embodiment, each mitigation module  104  has two flaps  106 . Sensor array  82  first samples the outdoor air via outdoor air sampler  74 . If IAQMS  80  determines that the outdoor air contains unacceptable contaminants, then IAQMS  80 , via HVAC control  90 , activates mitigation modules  104  in outdoor air intake  100 . 
     A similar process occurs for the recirculated air where sensor array  82  samples the recirculated air via recirculated air sampler  69 . If IAQMS  80  determines that the recirculated air contains unacceptable contaminants, then IAQMS  80 , via HVAC control  90 , activates mitigation modules  104  in recirculated air intake  101  to remove the contaminants in the recirculated air. 
     Mitigation module  104  is an apparatus which is able to strip contaminants from the air. In order to strip the contaminants from the outdoor air or the recirculated air, mitigation modules  104  are designed or positioned such that the air flow passes through mitigation module  104 . In the embodiment illustrated in FIG. 5, mitigation module  104  has two flaps  106  which extend out from mitigation module  104  such that the outdoor air is directed through mitigation module  104 . 
     Each mitigation module  104  is designed to strip certain contaminants from the air which passes through them. For example, the first mitigation module  104  may be designed to strip ammonia from the air. Another mitigation module  104  may be designed to strip volatile organic compounds from the air. In one embodiment, the only mitigation. modules activated are those indicated by the signatures of the contaminants present in the air as indicated by sensor array  82 . Some methods used to strip contaminants from the air are well known in the prior art, but opportunity exists to utilize novel or state-of-the-art techniques. Mitigation modules  104  are only activated when sensor array  82  indicates that contaminants are present. When contaminants are no longer present or are not at levels recognized as undesirable, flaps  106  are closed and the air flow no longer passes through mitigation modules  104 . 
     FIG. 6 is a flow diagram of a method of monitoring and adjusting the quality of indoor air. In step  110 , an air sample is taken. The air sample can be a sample of outdoor air, a sample of indoor air, a sample of recirculated air, or a sample air from a zone. In the embodiment illustrated in FIG. 2, only one air sample is taken at a time. In embodiments having a plurality of sensor arrays, the air sample is specific to the particular sensor array. 
     In step  112 , the individual sensor signatures and the array signature of the contaminants in the air sample are obtained. As described earlier, the array signature is represented in an n-dimensional space where n is either the number of sensors in the sensor array or the aggregate of responses from point and spectral sensors. These signatures are compared with a library or database of known signatures in step  114 . 
     In step  116 , contaminants for which the individual sensors were designed will easily be detected and identified. Contaminants that the system has learned or that have a signature stored in the database will also be identified, and the hazards of unknown contaminants will be inferred according to the spatial proximity to locations of array signatures known within the n-dimensional space in step  116 . In step  116 , the contaminants in the air sample are either identified or an inference as to their identity is made. The hazard or health risk associated with the contaminant is also identified and in step  118 , corrective action is taken using HVAC controls. 
     The corrective actions can include activating certain mitigation modules to strip particular contaminants from the incoming outdoor air, increasing the percentage of outdoor air that is introduced to the system, or reducing the percentage of outdoor air that is introduced to the system when the IAQMS indicates that indoor air quality is very good, or switch to an alternative air supply reservoir of good air. Other corrective actions include identifying the source or location of the contaminant, replacing the indoor air of a particular zone or increasing the temperature of the air. The corrective actions taken are intended to promote overall health of personnel, prevent personnel from being overexposed to hazardous contaminants and minimize the cost of operating the HVAC system. 
     FIG. 7 is illustrative of a method for identifying contaminants found in an air sample. In step  120 , a sensor array is used to evaluate an air sample from a zone. As mentioned previously, a zone includes the outdoor air, the recirculated air as well as other areas. In step  122 , the array signature for each contaminant is obtained by the system. The array signature is the aggregate response of all sensors in the sensor array to each contaminant. As noted above, a sensor array can comprise one sensor or a plurality of sensors. The aggregate response of the sensors within the sensor array can be mapped to an n-dimensional space, as discussed previously, where n is the number of sensors in the sensor array. Because the array signature is mapped to n dimensions, the spatial location of the array signature within the n dimensions permits the contaminant to be identified or inferred. 
     In step  124 , each contaminant in the air sample is inferred. The contaminants are identified by comparing each array signature with a database or library of known array signatures. The library of known array signatures is created by training the sensor array with many different contaminants and continually expanded as the array signatures of additional contaminants are recorded in the database or library. Note that the database is continually increasing as the array signature of additional contaminants is added to the database or library. Once the comparison of step  124  has been performed, step  126  identifies each contaminant based on the comparison. If a contaminant has an array signature that matches a stored array signature, then the contaminant is identified. If the n-dimensional location of the array signature is near a group of known array signatures, then the identity of the contaminant may be inferred. The method comprises an additional step of quantifying the amount of each contaminant in the air sample. This step is performed to evaluate the risk that the contaminant poses to personnel. After each contaminant has been identified, the system will take or issue corrective actions based on the analysis of the above described method. 
     The present invention has been described in terms of an HVAC system used to heat, cool and air condition a zone in a building, aircraft, ship, or similar occupied space. However, the ability of the sensor array to recognize a wide range of contaminants allows the present invention to function in other environments. For example, the sensor combination could be altered to recognize bio agents and chemicals used in warfare and terrorist activities. If a chemical agent were released in a public facility such as an airport, subway or hospital, the early detection of the chemical agent enables the population to be notified of evacuation procedures immediately as well as begin corrective action such as diluting the concentration of the chemical with additional forced air. The system could also be able to release a neutralizing agent or destroy the agent with pre-placed mitigation modules. 
     The present invention can also be used to monitor and control environments where produce or crops such as grain, fruits, vegetable, meats and dairy products are stored. For example, a series of sensor arrays could be placed in a potato cellar to sense the gases and heat produced by fermenting potatoes. Early detection of these contaminants permits the problem potatoes to be removed before substantial damage is done to the entire crop. In this example, the sensor arrays are used not only to sense the contaminants in the air but also indicate the location of the source of the contaminants. 
     Another application of the present invention is in a processing plant that makes semiconductors. Gases such as silane and arsenicals are used in the process, with silane being particularly dangerous. Altering the sensor array to detect these dangerous gases would enable fresh air to be sent to the contaminated area and the personnel could avoid injury. The present invention could also be used to monitor or indicate hazardous exposure conditions during industrial or mining activities, drug laboratories, confined animal feeding operations, global air monitoring, or arson investigation. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.