Sensor Technology Tackles Air Quality Challenges in the Industrial Realm
As we better understand the dangers of poor indoor air quality, engineers are looking to sensor technologies for detection and monitoring.
Scientific devices that can sense physical phenomena—sensors—are nothing new. We are approaching the 400th anniversary of the glass-tube thermometer, for example. Given a timeline that goes back centuries, the introduction of semiconductor-based sensors is quite new, however, and engineers aren’t anywhere near exhausting what is possible with them.
Semiconductor sensors quickly permeated our world, in part because they can be easily integrated with microcontrollers and managed by software. Photodetectors commonly measure the amount of daylight in order to activate lamps; motion sensors activate doors; audio sensors identify specific vocal sounds to initiate a query on the internet.
The current trend is to combine multiple types of semiconductor sensors to create systems able to detect, evaluate and respond to multiple simultaneous conditions. New vehicles use various combinations of visual and range-finding sensors to keep themselves on the road and avoid collisions. Aerial drones rely on a suite of directional, positioning, air pressure, and range-finding sensors to navigate safely.
The scientific principles used in that first glass tube thermometer created nearly 400 years ago have been known for two millennia. People have always been interested in their environment conditions.
In the modern era, semiconductor manufacturers have been creating, perfecting, and learning how to use a wide variety of sensors that can gauge characteristics such as temperature and humidity, and not only detect and measure the presence of gasses and particulates, but also identify specific volatile organic compounds (VOC).
These sensors, too, are being combined in new ways. As we accumulate data showing that air quality can have more significant consequences than previously understood, the ability to monitor the environments we create for ourselves, most notably office buildings, factories, and large campuses.
Indoor Air Quality
Poor indoor air quality (IAQ) can range from a lack of sufficient fresh air to the presence of compounds and chemicals that are hazardous to human health. It can be a problem anywhere, from individual residences to corporate offices, but potential problems are more acute in factories, laboratories, and other industrial facilities that rely on the use of hazardous substances.
Indoor air quality problems and solutions are well-documented, and while various US government agencies have jurisdiction over outdoor air quality, none have regulatory power over IAQ.
Elevated risk creates an obligation among industrial facility operators to conduct rigorous environmental monitoring integrated with heating, ventilation, and air conditioning (HVAC) systems.
Industrial ventilation systems require rigorous monitoring with sensors to keep the air healthy. Adobe Stock image (licensed)
HVAC systems alone may not be sufficient to ensure healthy IAQ for enterprises that deal with hazardous materials, however. In these cases, the use of additional filtration and gas-phase air cleaning (FAC) systems are very strongly recommended.
Effective monitoring starts with high-quality sensors. A common example is the carbon dioxide sensor (CO2). CO2 is a naturally occurring compound, but elevated levels can be indicative of poor ventilation, and when CO2 builds up within a building it can become harmful to human health and cause a range of issues including respiratory diseases, heart disease and cognitive deficits
Beyond this, other sensors can detect substances like Nitrogen Dioxide (NO2) and Ozone (O3). Temperature, humidity, pressure, and flow sensors are also fundamental in helping create a safer environment via IAQ monitoring.
The Imperative for IAQ
As previously stated, no US government agencies have regulatory power over IAQ. That said, the Occupational Safety and Health Administration (OSHA), the Environmental Protection Agency (EPA), the National Institute for Occupational Safety and Health (NIOSH), and the Centers for Disease Control (CDC) all have mandates to provide guidance and advice on IAQ.
Danger levels, symptoms, and sources of VOCs and other airborne substances. Image used courtesy of Mouser Electronics. (Click on image to enlarge)
The EPA notes that complaints about IAQ in general are rising. The CDC reports “increasing health problems such as cough, eye irritation, headache, and allergic reactions, and, in some rare cases,life-threatening conditions. Legionnaires disease and carbon monoxide poisoning and a couple of examples along those lines.
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) is a source of IAQ best practices and standards, including ANSI/ASHRAE Standard 62.1-2022, which covers design and maintenance of ventilation systems, along with minimum standards of indoor air quality.
ASHRAE recommends FACs especially in industrial facilities as being more effective at removing contaminants than source control or ventilation.
“The technologies of enhanced particulate FAC are well developed, with a history of over half a century of application in industrial process control, cleanrooms, health care and pharmaceuticals, and special usage buildings such as museums and laboratories,” ASHRAE states in its IAQ Guide.
Monitoring is Key
In the era of the IIoT and Factory 4.0, everything within a facility is a component of a networked whole, and that of course includes HVAC and FAC systems. Like almost everything else within an automated factory, these systems not only monitor external conditions but must be monitored themselves. All of it relies on sensors.
Semiconductor manufacturers continue to improve sensors for volatile organic compounds (VOC), particulate matter, gasses, relative humidity, and temperature. Furthermore, such sensors are compact in size, have exceptionally low power consumption, and boast a long life span.
There are sensors available that can monitor not only CO2 but also compounds such as NO2, an emission from combustion engines, and O3, which is generated from certain chemical reactions.
Volatile Organic Compounds
A common metric for IAQ is total volatile organic compounds (TVOC). TVOCs are components of petroleum fuels, hydraulic fluids, paint thinners, dry cleaning agents, and other products, according to the EPA. TVOC can be determined by using photoionization detectors (PIDs), which are based on photoionization sensors.
A PID uses a specially designed ultraviolet (UV) lamp to break down VOCs in the air into positive and negative ions to produce an electric current, which is the signal output of the detector. The higher the concentration of the component, the more ions are produced, and the stronger the current. The PID will only respond to components that have ionization energies similar to or lower than the energy of the photons produced by the PID lamp.
Air pressure sensors can be used to detect whether an indoor environment is properly enclosed or sealed, but they can also be used to monitor the monitoring equipment, for example, to determine when smart air filters need to be replaced. They are also integrated into barometers, a different type of pressure sensor, to monitor weather conditions.
Pressure sensors for a variety of keep air quality monitoring tasks. Adobe Stock image (licensed)
Pressure sensors are also easily integrated with temperature sensors. This combination of sensors can not only measure air quality directly, but also are useful for measuring the inputs and outputs of compressors in HVAC systems. Measuring the temperature differential is key to assuring HVAC cooling systems are operating correctly.
Combining Sensor Clusters
HVAC and FAC are complex, especially in industrial settings, and there are many additional operating parameters that need to be considered that could all make use of advanced sensor technology. Fan speeds, power consumption, and exhaust flow rates are only a few examples.
While sensors are used to detect direct qualities of IAQ or to monitor the performance of the systems used to ensure IAQ, there are many other ways to use them. ASHRAE recommends considering the use of room occupancy sensors, for example. In many cases, there will be no need to incur operational expenses to protect empty rooms with HVAC and FAC systems operating at full capacity—or at all.
Connectivity is Key
Networking is intrinsic to IIoT and Factory 4.0 applications. Modern sensor solutions are all built to be used in conjunction with any number of communications protocols, wired or wireless, including Zigbee, IEEE 802.15.4, WirelessHART, Ethernet, Bluetooth, Wi-Fi, LTE, and 5G, among others.
Mouser provides access to a wide variety of sensors from most of the leading sensor manufacturers, including Renesas, STMicroelectronics, Maxim Semiconductor, Amphenol, and more.
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