Healthy ventilation is an important component of good indoor air quality. Measuring indoor carbon dioxide (CO2) levels is a clear and simple way to evaluate if an area is adequately ventilated.
Carbon dioxide (CO2) monitors are useful for assessing a building’s ventilation, but their readings can mean different things in different buildings. A new online resource from NIST could help building professionals understand whether CO2 levels indicate poor or adequate ventilation in their particular space. Image Credit: Girts-Ragelis/Shutterstock
This greenhouse gas permeates more than merely the atmosphere. CO2 can also be present in the buildings where people live, work, and shop since it is a component of the air that is exhaled.
Good ventilation will help to keep CO2 and other impurities at bay as they can amass if there is insufficient ventilation. But how is it possible to know what category the ventilation falls into?
A new online tool created by National Institute of Standards and Technology (NIST) researchers provides an answer. The free application computes target CO2 levels depending on the user’s desired ventilation rate as well as details about the building and its inhabitants.
With NIST’s new tool, building professionals can use CO2 readings to regularly evaluate ventilation, detecting potentially unfavorable conditions that could lead to the accumulation of harmful contaminants.
Recent research published in the journal Indoor Air describes the concept of utilizing CO2 to appropriately evaluate ventilation and the tool dubbed Quick Indoor CO2 (QICO2).
By measuring CO2, you can verify that you are achieving the ventilation rate that your space was designed for, but you need to consider all the factors that impact CO2 levels.
Andrew Persily, Study Author, National Institute of Standards and Technology
While the direct influence of indoor CO2 on health is unknown, its concentration can be used to gauge a building's ventilation rate, which, if appropriate, can lower the concentration of many critical indoor toxins.
While many toxins tend to be difficult to detect, CO2, despite being invisible to human senses, can be easily tracked using commonly accessible CO2 sensors.
During the COVID-19 epidemic, federal and industry specialists advocated boosting ventilation as well as utilizing alternative measures such as masks and air filters, which do not catch CO2 but can trap infectious particles. However, monitoring is just half the fight when it comes to ensuring appropriate ventilation.
Persily added, “With the pandemic, many restaurants and other kinds of businesses started putting CO2 monitors on the wall. But what do those numbers they are showing mean?”
One prominent indicator of poor indoor air quality is a CO2 level of 1,000 parts per million (ppm) or above. But this generalization could be false. From building to building, several important aspects affect indoor CO2, therefore, while 1,000 ppm or less might indicate proper ventilation in some locations, it could not be acceptable in others.
“Finding the CO2 level that corresponds to one’s desired ventilation rate is a matter of collecting the relevant information and doing some math,” further stated Persily.
The quantity of CO2 inside a space is directly influenced by the number of people, as well as by their age, weight, and level of physical activity. The size and temperature of a structure, as well as the external CO2 levels, all have significant impacts.
Persily compiled the mathematical correlations between these elements and indoor CO2 levels and combined them in QICO2.
The software acts as a calculator for CO2 emissions. The user has the option of manually entering the necessary data or selecting from a list of predefined scenarios that describe classrooms, homes, and commercial structures, many of which are covered by a ventilation standard published by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE).
Then QICO2 does the necessary calculations to generate CO2 levels that customers can compare their actual readings to and, if necessary, adjust their ventilation system.
Building experts run the risk of overlooking poor indoor air quality by failing to monitor ventilation or judging it based on arbitrary CO2 measurements.
Persily stated, “The danger is that you may miss something that really matters. And you might think things are bad when they really aren’t, or perhaps even worse, you might think the air is fine when it is not.”
Using QICO2, which is available free of charge on NIST’s website, building professionals are able to evaluate their current approach to judging ventilation by monitoring it more often and more meaningfully to help maintain clean indoor air.
Journal Reference:
Persily, A. (2022) Development and application of an indoor carbon dioxide metric. Indoor Air. doi:10.1111/ina.13059.