130313 co2 levels in spaces

Sharing our Guidance

CO2 Levels in Spaces

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CO2 Levels in Spaces

Basics:

•ASHRAE 62.1-2010 defines the rate at which oxygen is consumed and carbon dioxide is produced as dependent on physical activity.

•CO2 levels are a measure of human body emissions and other odors in a space that would be deemed undesirable by other people in the space.

•Extremely high levels of CO2 have been found to cause adverse health effects

•CO2 levels are used to measure the amount of outside air needed in a space.

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CO2 Levels in SpacesCarbon Dioxide and Physical Activity

• A simple equation gives the outdoor airflow rate needed to maintain the steady-stat CO2 concentration below a given limit.

V0=N/(CS-C0)

whereV0 = outdoor airflow rate per person as defined by ASHRAE 62.1

N = CO2 generation rate per person

CS = CO2 concentration in the space

C0 = CO2 concentration in outdoor air

• These values can be found in ASHRAE Standard 62.1-2010, Ventilation for Acceptable Indoor Air Quality, Appendix C

• Occupied spaces with CO2 levels of 350 to 1,000 ppm indicate areas of good air exchange.

• CO2 concentrations in acceptable outdoor air typically range from 300 to 500 ppm.

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CO2 Levels in SpacesCarbon Dioxide Effects on Health

• The levels of CO2 in the air and potential health problems are:250 - 350 ppm – background (normal) outdoor air level350- 1,000 ppm - typical level found in occupied spaces with good air exchange.1,000 – 2,000 ppm - level associated with complaints of drowsiness and poor air.2,000 – 5,000 ppm – level associated with headaches, sleepiness, and stagnant, stale, stuffy air. Poor concentration, loss of attention, increased heart rate and slight nausea may also be present.>5,000 ppm – this indicates unusual air conditions where high levels of other gases could also be present. Toxicity or oxygen deprivation could occur. This is the permissible exposure limit for daily workplace exposures.>40,000 ppm - this level is immediately harmful due to oxygen deprivation.

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CO2 Levels in SpacesCO2 Sensors and Controls

• Low CO2 levels do not indicate good air quality while high CO2 levels do not mean that air is harmful. So CO2 sensors should be presented and sold as sensors of CO2 levels that provide information useful in determining ventilation rates to control CO2 levels.• It is important to determine CO2 sensor placement based on the

anticipated loads in the space • Sensors in every zone• Sensors in return air ductwork – used in applications where several

rooms have the same occupancy loads and space usage

• CO2 control strategies• On/Off – open-closed damper strategy based on CO2 setpoint• Proportional – control begins when indoor CO2 levels exceed outdoor

CO2 levels by a defined difference (i.e. 100 ppm)• Proportional Integral Derivative (PID) – used in low occupancy density

applications. Control is based on actual occupancy predicted by the CO2 level rate of rise.

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Building Envelope COMchecksCONCLUSION . . .

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