ASHRAE+62.1-2022+(1) - Page 015

Extracted Content

Informative Notes:

1. Examples of spaces that are potentially exempted by Exception 1 are shower rooms, swimming pool enclosures, kitchens, spa rooms, or semicooled warehouse spaces that contain stored contents that are not damaged by continuously high indoor air humidity or microbial growth.
2. This requirement reduces the risk of microbial growth in buildings and their interstitial spaces, because it limits the mass of indoor water vapor that can condense or be absorbed into mechanically cooled surfaces. The dew-point limit is explicitly extended to unoccupied hours because of the extensive public record of mold growth in schools, apartments, dormitories, and public buildings that are intermittently cooled during unoccupied hours when the outdoor air dew point is above 60°F (15°C).

5.13 Air Classification and Recirculation. Air shall be classified, and its recirculation shall be limited in accordance with the following subsections.

5.13.1 Classification. Air (return, transfer, or exhaust air) leaving each space or location shall be designated at an expected air-quality classification not less than that shown in Table 6-1, 6-2, or 6-3 or as approved by the AHJ. Air leaving spaces or locations that are not listed in Table 6-1, 6-2, or 6-3 shall be designated with the same classification as air from the most similar space or location listed in terms of occupant activities and building construction.

Exception to 5.13.1: Air from spaces where ETS is present. (Classification of air from spaces where ETS

is present is not addressed. Spaces that are expected to include ETS do not have a classification listed in Table 6-1.)

Informative Note: Classifications in Table 6-1, 6-2, or 6-3 are based on relative contaminant concentration using the following subjective criteria:

1. Class 1: Air with low contaminant concentration, low sensory-irritation intensity, and inoffensive odor.
2. Class 2: Air with moderate contaminant concentration, mild sensory-irritation intensity, or mildly offensive odors. (Class 2 air also includes air that is not necessarily harmful or objectionable but that is inappropriate for transfer or recirculation to spaces used for different purposes.)
3. Class 3: Air with significant contaminant concentration, significant sensory-irritation intensity, or offensive odor.
4. Class 4: Air with highly objectionable fumes or gases or with potentially dangerous particles, bioaerosols, or gases, at concentrations high enough to be considered as harmful.

5.13.2 Redesignation

5.13.2.1 Air Cleaning. If air leaving a space or location passes through an air-cleaning system, redesignation of the cleaned air to a cleaner classification shall be permitted per the following requirements:

a. Class 2 air where based on the subjective criteria in the informative note for Section 5.13.1 and where

approved by the AHJ. b. Class 3 and Class 4 air when all requirements of Sections 6.3.1 through 6.3.5 are followed.

5.13.2.2 Transfer. A mixture of air that has been transferred through or returned from spaces or locations with different air classes shall be redesignated with the highest classification among the air classes mixed.

Informative Note: For example, mixed return air to a common system serving both a Class 1 space and a Class 2 space is designated as Class 2 air.

5.13.2.3 Ancillary Spaces. Redesignation of Class 1 air to Class 2 air shall be permitted for Class 1 spaces that are ancillary to Class 2 spaces.

Informative Note: For example, an office within a restaurant might be designated as a space ancillary to a Class 2 space, thus enabling the office to receive Class 2 air.

5.13.3 Recirculation Limitations. When the Ventilation Rate Procedure (VRP) of Section 6 is used to determine ventilation airflow values, recirculation of air shall be limited in accordance with the requirements of this section.

5.13.3.1 Class 1 Air. Recirculation or transfer of Class 1 air to any space shall be permitted.

5.13.3.2 Class 2 Air

5.13.3.2.1 Recirculation of Class 2 air within the space of origin shall be permitted.

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