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CO2 Sensors vs. VOC Sensors for IAQ - What's the Difference?

Indoor Air Quality CO2 Sensors vs. VOC

Customers often ask about the difference between volatile organic compound (VOC) sensors and carbon dioxide (CO2) sensors. While both can be used to measure indoor air quality they are not interchangeable.

They measure very different things.

The challenge is that when searching for sensors to measure indoor air quality, both work, and both have their strengths and weaknesses. So the question becomes, when measuring IAQ, which sensor is right for you? 

Why measure Volatile Organic Compounds (VOCs)?

VOCs are molecules of hazardous chemicals in the air. Exposure to these chemicals can directly and negatively impact your health. Thus, the need for monitoring VOC's can be critical - especially indoors or in enclosed areas.

The EPA classifies a volatile organic compound (VOC's), as "any compound of carbon that participates in atmospheric photochemical reactions". By definition, this classification eliminates carbon monoxide, carbon dioxide, carbonates, ammonium and other gases since they do not chemically react with other molecules.

Common VOC's stem from a variety of household products such as

  • Paints
  • Cosmetics
  • Scented candles
  • Fragrances
  • New furniture
  • Cleaning products
  • Cooking sprays
  • Plastic products like children's toys
  • New carpet and drywall

In fact, any time you read the term "off-gassing" or notice a smell from a product brought into your home, chances are you are being exposed to VOCs.

Because these products are used in indoor air environments like homes, offices, or classrooms these VOC gases can build up and contaminate any fresh air. 

VOC's can cause eye and throat irritation, liver and kidney damage, cancer or severe ailments depending upon the VOC and amount of exposure. 

In order to combat the amount of VOC indoors several strategies may be used:

  • HEPA air filters
  • Avoiding purchasing products with high VOC levels
  • Purchasing used furniture
  • Hardwood or laminate floors
  • Changing to low VOC cleaning products

However, even these small acts towards reducing the gases can not always be enough. Since VOC exposure can lead to severe health effects, the only way to accurately monitor the level of VOCs in a room is with a VOC sensor.

Note that while some VOC indoor air quality meters claim to measure CO2, they do not. Instead they perform a rough calculation of the CO2 levels based on VOC measurements.

Volatile Organic Compound Sensors

VOC sensors are used to monitor VOCs by measuring the number of molecules in the air of gases like aromatic hydrocarbons. Because of their sensitivity to the molecules they are able to measure quantities that human senses cannot detect.

VOC sensors such as the IAQ-2000 or IAQ-0001 can specifically measure the concentration of these molecules, providing a warning when concentrations get too high and increased ventilation is needed.

This sensor shown is a sensitive, metal oxide semiconductor (MOS) that is able to detect a broad range of VOC's while correlating directly with CO2 levels in the room. This means that the sensor provides a total VOC concentration, not specific molecules or compounds.

Unlike CO2 sensors, a VOC sensor cannot indicate the specific rate of ventilation needed - only the total level of VOCs in the air. It can however indicate a general change in the concentration of contaminants.

In the case of VOC sensors, ventilation is regulated based on the actual presence of some pollutants sensed by the air quality sensor. This may or may not conflict with established ventilation codes. These sensors can also be used to sense periodic episodes of high pollution that might occur when special equipment is being used, or when potent chemicals from cleaners are released into the air.

VOC's that can be detected by using a sensor such as the IAQ-2000 include:

  • CO, CH4, LPG
  • Alcohols
  • Ketones
  • Organic acids
  • Amines
  • Aliphatic hydrocarbons
  • Aromatic hydrocarbons

Like a CO2 sensor, a VOC sensor can be used to save energy running a HVAC system. When VOC levels get too high, conditioned fresh air can be added into the system. If VOC levels are low, the indoor air is conditioned and recirculated. This insures that only the required amount of fresh air is used, thereby saving energy and lowering building operating costs.

Why measure Carbon Dioxide?

For many years, CO2 has become the "go-to" for measuring indoor air quality across homes, classrooms, or commercial buildings. CO2 sensor technologies are stable, they are not subject to short term drift, and output signals can be used to control the fresh air exchange of an HVAC system.

Carbon dioxide levels indoors give an indication of how many occupants are in an enclosed space. The more people, the more fresh air that is required for maintaining comfortable air quality. But just as importantly, high CO2 levels have been shown to be an indirect indicator of high levels dust, mold, germs, bacteria, VOCs and other contaminants that can impact human health. 

CO2 Sensors

CO2 levels of 1,000ppm (parts per million) or more are known to directly affect cognitive ability, ailments, asthma, productivity and even the ability to make strategic decisions. Aside from these health effects, in the case where occupants may be around tanks of compressed CO2, concentrations above 3% or 30,000ppm can be life-threatening.

Carbon Dioxide CO2 Sensor for Indoor Air Quality

Carbon Dioxide Sensors

A CO2 sensor like our K30 10,000ppm CO2 Sensor is designed to control the ventilation rate in occupied spaces. Since people are the principal source of CO2 in indoor air, an indoor CO2 measurement can be used to determine whether a room or building is occupied. In other words, higher levels of CO2 correspond to larger numbers of people inside, and therefore, the rate of air exchange required.

As a control, a CO2 sensor can also activate an alarm or mitigation strategy (activate filters or ventilation). Because carbon dioxide is an inert gas, it will not cause a VOC sensor to react. Both approaches can be applied to a demand-controlled ventilation strategy, but the results may be very different.

When you use a CO2 sensor, you can also save on energy, because ventilation is based on actual occupancy of the space rather than the design occupancy of the space. Energy is saved when pollutant loads are low and ventilation can be reduced, which may occur during or after occupied hours. Where a CO2 sensor would specifically reduce ventilation during unoccupied periods, a VOC sensor may actually maintain ventilation rates during unoccupied periods if there is a significant pollutant level in the building.

CO2 or VOC Sensors - Which is right for you?

CO2 sensors will remain the standard for monitoring indoor air quality environments. CO2 measurement technology is mature, it is easy to measure, and there is a known correlation between CO2 levels indoors and IAQ.

Because CO2 sensors are often an alternative measure for VOC sensing, it is important to recognize that a key difference is in the contaminants being  measured. While VOC sensors can provide indication of potentially harmful molecules, they do not give an overall measurement of indoor air quality. 

    Overall, the real delineation between CO2 vs. VOC sensors comes down to answering the following questions:

    • What are you looking to measure?
    • Do you need to regulate what you are measuring?
    • How would you like this data to be shown?

    For more information on CO2Meter.com sensing technologies or indoor air quality devices, please contact us at Sales@CO2Meter.com or (877) 678 - 4259


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