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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]
The 1989 ASHRAE standard (Standard 62–89) states that appropriate ventilation guidelines are 20 CFM (9.2 L/s) per person in an office building, and 15 CFM (7.1 L/s) per person for schools, while 2004 Standard 62.1-2004 has lower recommendations again (see tables below).
For standards relating to ventilation rates, in the United States refer to ASHRAE Standard 62.1-2010: Ventilation for Acceptable Indoor Air Quality. [16] These requirements are for "all spaces intended for human occupancy except those within single-family houses, multifamily structures of three stories or fewer above grade, vehicles, and aircraft."
ASHRAE was founded in 1894 at a meeting of engineers in New York City, formerly headquartered at 345 East 47th Street, and has held an annual meeting since 1895. [4] Until 1954 it was known as the American Society of Heating and Ventilating Engineers (ASHVE); in that year it changed its name to the American Society of Heating and Air-Conditioning Engineers (ASHAE). [5]
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. ...
In classrooms, the requirements in the ASHRAE standard 62.1, Ventilation for Acceptable Indoor Air Quality, would typically result in about 3 air changes per hour, depending on the occupant density. As the occupants are not the only source of pollutants, outdoor air ventilation may need to be higher when unusual or strong sources of pollution ...
In 1973, in response to the oil crisis and conservation concerns, ASHRAE Standards 62-73 and 62-81 reduced required ventilation from 10 cubic feet per minute (4.7 L/s) per person to 5 cubic feet per minute (2.4 L/s) per person, but this was found to be a contributing factor to sick building syndrome. [18]
ASHRAE regularly organizes two annual technical committees and publishes recognized standards for HVAC design, which are updated every four years. [56] Another popular society is AHRI, which provides regular information on new refrigeration technology, and publishes relevant standards and codes.