Ensuring ASHRAE 62.1 Compliance for CO2 Sensors in Demand-Controlled Ventilation (DCV)

Every building engineer who works with ventilation and indoor air quality (IAQ) knows ASHRAE 62.1. It’s the most commonly referenced standard for designing and maintaining ventilation systems to provide IAQ that’s acceptable to human occupants, with the goal of removing substances and pollutants in the air that can negatively impact occupant health and well-being.

However, what many may not have read too closely is a tiny section about halfway through that talks about using CO2 sensors for demand-controlled ventilation (DCV). 

There’s a lot more to the story than just a list of sensor requirements, but first, let’s start with some background about DCV — if you’re already familiar with DCV, feel free to skip to the next part!

What Is DCV?

DCV is a smart HVAC function that automatically adjusts ventilation rates in a given space to match changes in occupancy. In other words, the system will increase ventilation during peak occupancy hours to maintain optimal air quality, while decreasing ventilation when occupancy is low to optimize energy usage. This system is a win-win for both IAQ optimization and energy-saving goals, so it’s no surprise that more smart buildings are using this technology.

One of the ways that DCV gauges occupancy levels is by measuring the amount of CO2 in the air with a CO2 sensor. The more people that are in any given space, the more CO2 that is breathed out and fills the air. The sensor will measure these levels continuously and change HVAC settings as necessary to reach the optimal level of ventilation that promotes health and well-being while also preventing energy wastage.

As you can imagine, striking this balance requires a highly sensitive and accurate sensor to closely track CO2 levels in real time. That’s why, as part of its DCV requirements, ASHRAE also provides standards for those using CO2 sensors to guide their DCV systems.

What ASHRAE 62.1 Says About CO2 Sensors for DCV

If you crack open ANSI/ASHRAE Standard 62.1-2022, you’ll find a whole section about requirements for DCV parameters like ventilation rates and breathing zone outdoor airflow, as well as this paragraph about CO2 sensors:

“6.2.6.1.3 Where CO2 sensors are used for DCV, the CO2 sensors shall be certified by the manufacturer to be accurate within ±75 ppm at concentrations of both 600 and 1000 ppm when measured at sea level at 77°F (25°C). Sensors shall be factory calibrated and certified by the manufacturer to require calibration not more frequently than once every five years. Upon detection of sensor failure, the system shall provide a signal that resets the ventilation system to supply the required minimum quantity of outdoor air (Vbz) to the breathing zone for the design zone population (Pz).”

There’s a lot packed into this paragraph, but there are two key requirements to pay attention to when evaluating CO2 sensors:

Accuracy:

• At 600 ppm of CO2, the sensor reading has to be within ± 75 ppm of the actual level
• At 1000 ppm of CO2, the sensor reading has to be within ± 75 ppm of the actual level

Calibration:

• The sensor must be factory-calibrated
• The sensor shouldn’t require calibration sooner than every five years

These requirements may seem straightforward, but what might surprise many is that there are few sensors available that actually meet them. What’s more, it can be quite difficult to verify whether a sensor meets these requirements just by reading the specifications. Manufacturers often don’t present their technical details in a way that clearly aligns with ASHRAE 62.1 standards.

How Kaiterra's CO2 Sensors Meet ASHRAE 62.1 Requirements

At Kaiterra, we know how much of a headache it can be to do this math for yourself. That’s why we went ahead and completed all the calculations and cross-comparisons for you! So we can tell you that all Kaiterra monitors meet the requirements outlined in ANSI/ASHRAE Standard 62.1-2022 for CO2 sensors used in DCV. Here’s how:

Accuracy:

Our sensors provide a CO2 reading that is accurate within ± 40 ppm ± 3% max value in environments ranging from 0-50ºC and 0-80% relative humidity (RH). Using this formula, let’s crunch the numbers with specific ASHRAE 62.1 requirements:

• Using 600 ppm as the max value, we do the following calculation: ± 40 ppm ± 3% * 600 ppm = ± 58 ppm. This means that Kaiterra sensor readings are within ± 58 ppm of the actual CO2 level, which is less than the ASHRAE requirement of ± 75 ppm, so Kaiterra meets the accuracy requirement at 600 ppm.
• Using 1000 ppm as the max value, we do the following calculation: ± 40 ppm ± 3% * 1000 ppm = ± 70 ppm. This means that Kaiterra sensor readings are within ± 70 ppm of the actual CO2 level, which is also less than the ASHRAE requirement of ± 75 ppm, so Kaiterra meets the accuracy requirement at 1000 ppm.

Calibration:

All Kaiterra monitors are tested and calibrated in the factory to ensure the CO2 sensor meets our accuracy and quality requirements and demonstrates ASHRAE 62.1 compliance. Every monitor leaves the factory with a certificate that says the monitor does not need to be calibrated more frequently than every five years.

Here’s a quick recap:

Another advantage of choosing Kaiterra is that our monitors are BTL certified, which allows you to achieve robust BMS integration, sync up data with building automation systems, and optimize building performance all in one place. 

If you’re thinking about using CO2 sensors for DCV in your building, reach out to our team to see how we can help you meet ASHRAE 62.1 requirements while getting the most out of your air quality monitor!