ASHRAE+62.1-2022+(1) - Page 029
Extracted Content
6.4.1 Prescriptive Compliance Path. Any zone designed for natural ventilation shall include a mechanical ventilation system designed in accordance with Section 6.2, Section 6.3, or both.
Exceptions to 6.4.1:
- Zones in buildings that have all of the following: a. Natural ventilation openings that comply with the requirements of Section 6.4.1. b. Controls that prevent the natural ventilation openings from being closed during periods of
expected occupancy, or natural ventilation openings that are permanently open. 2. Zones that are not served by heating or cooling equipment. 6.4.1.1 Ceiling Height. For ceilings that are parallel to the floor, the ceiling height ( H ) to be used in Sections 6.4.1.3 through 6.4.1.5 shall be the minimum ceiling height in the zone.
For zones wherein ceiling height increases as distance from the ventilation increases, the ceiling height shall be the average height of the ceiling determined over a distance not greater than 6 m (20 ft) from the openings.
6.4.1.2 Floor Area to Be Ventilated. The naturally ventilated area in zones or portions of zones shall extend from the openings to a distance determined by Sections 6.4.1.3, 6.4.1.4, or 6.4.1.5. Openings shall meet the requirements of Section 6.4.1.6. For zones where ceilings are not parallel to the floor, the ceiling height shall be determined in accordance with Section 6.4.1.1.
6.4.1.3 Single Side Opening. For zones with openings on only one side of the zone, the naturally ventilated area shall extend to a distance not greater that two times the height of the ceiling from the openings.
6.4.1.4 Double Side Opening. For zones with openings on two opposite sides of the zone, the naturally ventilated area shall extend between the openings separated by a distance not greater than five times the height of the ceiling.
6.4.1.5 Corner Openings. For zones with openings on two adjacent sides of a zone, the naturally ventilated area shall extend to a distance not greater than five times the height of the ceiling along a line drawn between the outside edges of the two openings that are the farthest apart. Floor area outside that line shall comply with Section 6.4.1.3 as a zone having openings on only one side of the zone.
Informative Note: “Floor area outside that line” refers to the remaining area of the zone that is not bounded by the walls that have the openings and the line drawn between the openings.
6.4.1.6 Location and Size of Openings. Zones or portions of zones to be naturally ventilated shall have a permanently open airflow path to openings directly connected to the outdoors. The minimum flow rate to the zone shall be determined in accordance with Section 6.2.1.1. This flow rate shall be used to determine the required openable area of openings, accounting only for buoyancy-driven flow. Wind-driven flow shall be used only where it can be demonstrated that the minimum flow rate is provided during all occupied hours. Openings shall be sized in accordance with Section 6.4.1.6.1 (Path A) or Section 6.4.1.6.2 (Path B).
Informative Note: Permanently open airflow path refers to pathways that would allow airflow unimpeded by partitions, walls, furnishings, etc.
6.4.1.6.1 Sizing Openings—Path A. Where the zone is ventilated using a single opening or multiple single openings located at the same elevation, the openable area as a percent of the net occupiable floor area shall be greater than or equal to the value indicated in Table 6-7. Where the zone is ventilated using two openings located at different elevations or multiple pairs of such openings, the openable area as a percent of the net occupiable floor area shall be greater than or equal to the value indicated in Table 6-8.
Where openings are obstructed by louvers or screens, the openable area shall be based on the net free area of the opening. Where interior zones, or portions of zones, without direct openings to the outdoors are ventilated through adjoining zones, the opening between zones shall be permanently unobstructed and have a free area of not less than twice the percent of occupiable floor area used to determine the opening size of adjacent exterior zones, or 25 ft [2 ] (2.3 m [2] ), whichever is greater.
Informative Note: Tables 6-7 and 6-8 are based solely on buoyancy-driven flow and have not been created to address thermal comfort.
6.4.1.6.2 Sizing Openings—Path B. The required openable area for a single zone shall be calculated using CIBSE AM10, Section 4.3.
6.4.2 Engineered System Compliance Path. For an engineered natural ventilation system, the designer shall
a. determine hourly environmental conditions, including outdoor air dry-bulb temperature; dew-point tem perature; outdoor concentration of contaminants, including PM2.5, PM10, and ozone where data are available; wind speed and direction; and internal heat gains during expected hours of natural ventilation operation.
ANSI/ASHRAE Standard 62.1-2022 27