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What are the applications for CO2 sensors in HVAC system?

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171 views asked Oct 24, 2015 by Devan Talebi

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CO2 is a natural part of the atmosphere. A CO2 air sample is expressed as parts per million (ppm)-The number of CO2 molecules, per million molecules of air. CO2 concentrations in outdoor air typically range from 300 to 500 ppm.

One factor to provide indoor air quality is to maintain the carbon dioxide in acceptable level in space. As CO2 levels rise, the quantity of volatile organic compounds (VOCs), odors and micro-organisms in the air rise too. That’s the reason the HVAC engineers use carbon dioxide level transmitters (CO2 sensors) to regulate airflow in office buildings.

In addition to air quality, a carbon dioxide can also effect on human health. Studies have shown the high CO2 concentrations affect our ability to concentrate on tasks. If we find ourselves sleepy in the office or the classroom, it may be a buildup of CO2.

To control the level of the CO2, the ventilation system needs to provide more fresh air (outside air) for the space and remove the equal amount of air from the space by exhaust system.  This process is called Demand Control Ventilation (DCV).

Carbon dioxide transmitters used in LEED certified and on-demand HVACR systems to conserve energy. Rather than continuously supplying conditioned air, a carbon dioxide transmitter with relay can turn on the heat, fans, or air conditioners when people enter the room, and turn them off when they leave. Studies have shown that CO2 - based air control can result in up to 50% energy savings.


Effects of CO2 on humans:

• Normal Outdoor level:      300-500 ppm

• Acceptable Levels:       Less than 60O ppm

• Complaints of Stiffness and odors:      6DO - 1000 ppm

• ASHRAE And OSHA Standards:     1000 ppm

• General drowsiness:   1000 - 250O ppm

• Adverse Health Effects Expected:     2500- 5000 ppm

• Slightly intoxicating, Breathing and pulse rate increase, nausea:     30,000 ppm

• Above plus headaches and sight impairment:     50.000 ppm

• Unconscious, further exposure death:    100,000 ppm






answered Oct 26, 2015 by Devan Talebi

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