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Humans are the main indoor source of carbon dioxide (CO 2) in most buildings. Indoor CO 2 levels are an indicator of the adequacy of outdoor air ventilation relative to indoor occupant density and metabolic activity. Indoor CO 2 levels above 500 ppm can lead to higher blood pressure and heart rate, and increased peripheral blood circulation. [85]
As the sensor reads the increasing amount of carbon dioxide levels in a space, the ventilation increases to dilute the levels. When the space is unoccupied, the sensor reads normal levels, and continues to supply the unoccupied airflow rate. This rate is determined by the building owner standards, along with the designer and ASHRAE Standard 62. ...
Ventilation guidelines are based on the minimum ventilation rate required to maintain acceptable levels of effluents. Carbon dioxide is used as a reference point, as it is the gas of highest emission at a relatively constant value of 0.005 L/s. The mass balance equation is: Q = G/(C i − C a) Q = ventilation rate (L/s) G = CO 2 generation rate
ANSI/ASHRAE Standard 55: Thermal Environmental Conditions for Human Occupancy is an American National Standard published by ASHRAE that establishes the ranges of indoor environmental conditions to achieve acceptable thermal comfort for occupants of buildings. It was first published in 1966, and since 2004 has been updated every three to six years.
Another set of standards, for indoor air in employment settings, is administered by the U.S. Occupational Safety and Health Administration. [7] A distinction may be made between mandatory and aspirational air quality standards. For example, U.S. state governments must work toward achieving NAAQS, but are not forced to meet them.
Indoor PM 2.5 exposure levels have been consistently reported to be in the range of hundreds to thousands of micrograms per cubic meter (μg/m 3). Similarly, CO exposure levels have been measured to be as high as hundreds to greater than 1000 milligrams per cubic meter (mg/m 3 ).
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Air changes per hour is a measurement intended to communicate the air change effectiveness of a space’s ventilation system. Discussion around the ASHRAE standard 62, Ventilation for Acceptable Indoor Air Quality led to the development of a more direct method of measuring air change effectiveness with the use of a tracer gas. [1]