COVID and Indoor Air Quality – Fighting Sensor “Drift” to Ensure Accurate Measurement

In our first installment in this series of posts, we introduced you to several of the complex challenges inherent with indoor air quality (IAQ) monitoring. These challenges are even harder to manage in the wake of COVID-19, and are more critical to address given the growing awareness that airborne transmission presents acute risks to people within indoor environments.

New vendor companies have rushed numerous IAQ solutions to market, and many of them tend to gloss over the complexities of genuine IAQ effectiveness. Nowhere is this tendency more likely than when dealing with the tendency of sensors to “drift” – that is, become inaccurate – over time.

In this post, we look at the issue of sensor drift and the overall accuracy of air quality sensors.

Sensor “Drift”

As a starting point, it’s important to keep in mind one simple truth: All air quality sensors drift. That is to say – every single sensor used to track and measure air quality will become increasingly more inaccurate over time.

What’s interesting is that almost every company that actually sells air quality sensors ignores this reality. If they do address it, they merely offer some vague reassurance about using software to overcome the “drift” that occurs.

Although it goes unacknowledged by most vendors, sensor drift is axiomatic. Need some proof? Field measured CO2 sensors average more than 40 percent drift, as measured by The Lawrence Berkley National Lab and The Iowa Energy Center. The other key parameters for air quality – total volatile organic compounds (TVOCs); airborne particulates; relative humidity; and carbon monoxide (CO) – are not as widely measured or studied. The few published papers on these other air quality parameters indicate that they also drift substantially over time.

Aircuity provides freshly calibrated sensors every 6 months for the life of the building. Our calibration lab updates more than 7,000 sensors annually. When sensors return to our calibration laboratory from a client’s building they go through an “As Received” check. This includes an inspection and calibration check (capturing drift), with data being archived for quality management. While there is not widely available data on TVOCs, particles, and relative humidity, through our calibration lab we know these sensors all drift substantially in only a few months. The Aircuity system solves sensor drift through 1) differential measurement (the topic of our next post); 2) 6-month sensor calibration; and 3) employing ruggedized lab-grade sensors.

This information is compelling – the data tell no lies, after all. But if you need more anecdotal or testimonial evidence, just talk to any building owner operating a laboratory. Lab folks are hyper-tuned to all environmental health and safety (EH&S) metrics – they have to be. Lab managers simply don’t trust the flimsy “puck” sensors, which are especially vulnerable to drift. Although they are marketed as “self-calibrating,” they simply don’t provide accurate air quality information.

What do EH&S leaders use to ensure the high-quality data they need to meet their compliance requirements?

Overwhelmingly, they use Aircuity.

We have been the trusted data driven ventilation provider in labs for more than 20 years. During that time, we have offered this same accurate, multi-parameter and patented approach to healthy ventilation and safe ventilation in offices, schools and other public settings. EH&S relies on our data analytics to ensure that their laboratories are operating safely and efficiently.

We are the tool lab folks use to fight sensor drift.

Fighting sensor drift may seem like a minor technical task, but failure creates a huge problem: inaccuracy in measurement. If a sensor is inaccurate, it’s virtually useless for building control. This can lead to false alarms, or worse – failure to identify real air quality issues. It can also cause disputes between landlords and tenants: if a landlord’s sensor is reading 40% high and a tenant’s sensor 40% low, stacking errors create an 80% or greater difference.

Differential measurement, the most powerful aspect of how Aircuity eliminates sensor drift, will be discussed in more detail in an upcoming post. Stay tuned!