Sensors for Improving IAQ

Improving Indoor Air Quality: The Role of Sensor Nodes in Monitoring and Enhancing Health and Productivity

Alex Pluemer for Mouser Electronics

Air Quality Indexes (AQI) have become a regular feature of weather reports worldwide as climate change continues to heat the planet and incite wildfires in hotter, drier climates. AQIs report the amount of particulate matter (such as ash and automobile exhausts) and other pollutants in the air, informing people when those pollutants reach dangerous levels of concentration for human exposure. AQIs are commonly used to describe the quality of the air outside—but what about indoor air quality?

Unhealthy outdoor air quality conditions can often be detected without technology (for example, smoke in the air or a strong odor), but poor indoor air quality isn’t as easily detectable. If you spend most of your day inside your home, a school, or an office building, the quality of the air indoors is more likely to affect your health than the air outside.

While polluted air from the outside can impact indoor air quality, several common indoor air pollutants can be detected and quantified only through air quality monitoring technology. Contaminants such as carbon monoxide (CO), secondhand smoke, and airborne mold or bacteria can be detected in the air indoors and lead to serious health ramifications through repeated exposure. The health and safety of employees and students are the primary responsibilities of any corporation or institution, and monitoring indoor air quality is an essential part of maintaining a safe and healthy indoor environment. This can also lead to greater productivity and better workplace morale.

Sensor nodes like Sensirion’s SEN5x can help monitor interior air quality and augment existing heating, ventilation, and air conditioning (HVAC) and air purification systems by measuring airborne pollutants in real time, providing end users with accurate, reliable measurements without requiring extensive reconfiguration. In this article, we will examine some of the most common indoor pollutants and how devices like the SEN5x can help end users keep their facilities healthy and productive.

Measuring Air Quality

As noted, the most common airborne pollutants are particulates—microscopic particles of solid matter, often resulting from combustion—that we often inhale without awareness. When the air outside is highly saturated with particulates, people may be advised to stay indoors with the windows closed or wear respiratory masks if they must be outdoors for extended periods. Many homes, schools, and office buildings implement air filtration systems to sift out particulate matter from the air. Still, small amounts of particulate are always present (outside of a clean room environment).  

Interior air quality is often compromised by other airborne pollutants, such as gases, that can cause serious health problems if they're not appropriately monitored. High levels of CO in the air can result in severe illness, unconsciousness, or even death. CO-related illnesses and deaths are commonly associated with using heating equipment or other appliances that burn fossil fuels; incomplete combustion creates an invisible, odorless gas that can build up in buildings and structures without adequate ventilation.   

Carbon dioxide (CO2) levels in the air must also be monitored. Although the adverse effects of CO2 exposure typically aren't as severe as those associated with CO, they can have long-lasting ramifications. People in CO2-rich environments are often drowsier than normal and can experience headaches and nausea. Currently, 38 U.S. states and the District of Columbia require CO/CO2 detectors in all private residences via regulation or legislation, but only five require them in school buildings. CO poisoning usually occurs in minimal, enclosed environments, so CO monitors often aren't required in larger office buildings or manufacturing facilities. Measuring CO2 levels is one way that facilities managers evaluate their HVAC systems' performance, so effective CO2 detection and monitoring can have a wide-reaching impact on interior air quality.

Mold and mold spores are other common airborne pollutants, typically resulting from humidity—and they aren't always easy to find. Homeowners and facility managers can take preventative measures against mold growing in those hard-to-reach spaces by monitoring interior humidity and condensation levels. Excess moisture can also cultivate certain airborne bacteria that can harm humans, another reason to closely monitor indoor humidity levels.

Volatile organic compounds (VOCs) are present in outdoor air almost anywhere where people live or work, but they are typically more highly concentrated indoors. VOCs are gases emitted from chemicals or other liquid or solid substances. They are present in a variety of goods, from cleaning supplies and paint to office equipment and furniture materials. Lowering the risk of VOC exposure is usually a matter of adequately storing hazardous materials and improving overall airflow and ventilation. Still, even low concentrations of certain VOCs (such as formaldehyde) in the air can be unhealthy.

Carcinogens like radon and asbestos can be detected in structures built with materials that have since been widely prohibited for safety reasons. Although the adverse health effects of prolonged exposure to these materials might not be as immediate as those from CO exposure, they can be just as severe and even deadly. Both radon and asbestos exposure have been determined to increase the chances of developing lung cancer.

Air Quality Monitoring Technology

Air quality monitors aren’t one-size-fits-all; they're available in different form factors and with various features and functionality. Depending on the installation location and environment, it may be beneficial to have a smaller AQ monitor. However, you may be sacrificing functionality in the process. Additionally, most AQ sensors can detect only some airborne pollutants, requiring a combination of sensors to detect everything.

Sensirion’s SEN5x environmental sensor nodes can monitor airborne particulates, VOCs, nitrogen oxides, and relative temperature and humidity. The SEN5x measures particulate matter in the air by emitting a laser reflected by particulates back to a photodiode on the device. The more light reflected toward the photodiode, the larger the particulate. This method provides much more accurate readings than devices that use a tapered oscillating element, which can accommodate only particulates of a certain size. Photodetection also provides more accurate measurements, typically within seconds of starting a sampling cycle.

By sampling the pollutants in the air at intervals of a second or less, SEN5x devices provide continuous, real-time AQ monitoring in a small 53mm×44mm×22mm form factor. SEN5x is a complete sensor node with multiple sensors in an enclosure that uses sheath flow technology to increase resistance to dust and other particulates, allowing it to function in harsher indoor environments like factories or production facilities. SEN5x nodes also include fans with tested airflow geometry to help maintain optimal functionality and extend the devices' lifetimes, which are expected to exceed ten years. The fan performs an auto-cleaning function to expel collected dust and particulates while the sensor is in measurement mode. The interval between cleaning cycles can be adjusted if the sensor node is located in a highly polluted area.

SEN5x nodes come with an I²C interface to enable easy integration into existing HVAC, air purification, and air quality monitoring systems, avoiding costly, time-consuming reconfigurations. They also employ pre-integrated, proprietary algorithms for temperature and humidity compensation and VOC index calculation to further promote seamless integration into existing systems and save developers the trouble of writing the code themselves. These algorithms include the Sensirion Temperature Acceleration Routine (STAR) engine, which provides end users with temperature readings up to three times faster and more reliably than the competition, per Sensirion. SEN5x nodes provide fully calibrated digital output upon installation and can restart at a maximum of 50ms, reducing the calibration and startup times associated with other AQ monitors.

SEN5x nodes typically only draw between 0.7mA and 70mA of supply current and max out at 100mA, potentially saving customers from having to rewire or reconfigure existing electrical setups. The devices also boast an average acoustic emission level of just 24dB, making them unintrusive and unlikely to disrupt even the quietest work environments.

Air Quality, Health, and Productivity

Although no federally or internationally recognized standards currently exist for healthy air quality, agencies like the U.S. Environmental Protection Agency (EPA) and the Centers for Disease Control (CDC) have helped create a set of recommended guidelines for safe exposure levels to the most common airborne pollutants. Airborne chemical pollutants like CO or CO2 are measured in parts per million (ppm). CO2 levels of 400ppm–650ppm are considered normal for indoor environments, whereas levels of 800ppm or above may start to cause adverse effects. High levels of CO2 in the air aren't just bad for your health—they can have severe ramifications for workplace productivity.

If you've ever been in a crowded, stuffy room, you may be familiar with the feeling: Your eyelids start to get heavy, the other voices in the room become background noise, and you drift off into a daydream. The meeting may have been boring, but you may have also felt the effects of CO2 overexposure. Studies have demonstrated that CO2 levels in the air directly correlate with workplace productivity and morale; that is, better ventilation equals happier, harder-working employees. Using this logic, casinos monitor CO2 levels to ensure their patrons aren't getting too tired—even pumping oxygen into the building to energize them.  

Other airborne pollutants are safe only in minuscule concentrations (like formaldehyde, with recommended exposure levels no greater than 0.2ppm) or are unsafe at any level (like radon or asbestos fibers). Particulate matter in the air is measured in micrograms per cubic meter (µg/m3). The EPA recommends that PM2.5 (pieces of particulate matter with a diameter no greater than 2.5 micrometers) levels stay below 12µg/m3 and PM10 (larger particulates with a diameter of greater than 10 micrometers) remain at or below 54µg/m3, as larger pieces of particulate matter are more manageable for human lungs to filter out of our air than smaller ones.

Keeping HVAC systems operating at optimal levels also helps prevent the transmission of airborne diseases like COVID-19 transmission, saving companies time and money lost to sick days and reduced productivity. AQ monitors that can detect airborne pathogens aren't widely commercially available, but monitoring airborne pollutants like CO2 can help improve overall airflow and ventilation and reduce the risk of disease transmission.

Conclusion

Maintaining healthy air quality is critical to cultivating a safe and healthy working or learning environment. Strong HVAC and air purification systems require sensors to inform facilities managers how well they're functioning and how they can be improved. Sensor nodes like the Sensirion SEN5x provide this information in real time with exceptional accuracy, giving end users the data they need to make environmental adjustments when necessary, all while easily integrating into pre-existing systems. Whether at home, school, office, or manufacturing facility, air quality monitoring is vital to health and well-being—and AQ sensor nodes like the SEN5x are integral to getting timely, reliable readings.