ASHRAE+62.1-2022+(1) - Page 027
Extracted Content
6.2.6.1.4 For DCV zones in the occupied standby mode, breathing zone outdoor airflow shall be permitted to be reduced to zero for the occupancy categories indicated “OS” in Table 6-1, provided that airflow is restored to Vbz whenever occupancy is detected.
6.2.6.1.5 Documentation. A written description of the equipment, methods, control sequences, set points, and the intended operational functions shall be provided. A table shall be provided that shows the minimum and maximum outdoor intake airflow for each system.
6.2.6.2 Ventilation Efficiency. Variations in the efficiency with which outdoor air is distributed to the occupants under different ventilation system airflows and temperatures shall be permitted as an optional basis of dynamic reset.
6.2.6.3 Outdoor Air Fraction. A higher fraction of outdoor air in the air supply due to intake of additional outdoor air for free cooling or exhaust air makeup shall be permitted as an optional basis of dynamic reset.
6.3 Indoor Air Quality Procedure. Breathing zone outdoor airflow ( Vbz ) shall be determined in accordance with Sections 6.3.1 through 6.3.5.
6.3.1 Design Compounds and PM2.5 Sources. The system design shall be based on the DCs and PM2.5 specified in Table 6-5. If there are additional outdoor sources identified from completing the process in Section 4.3, or if there are unusual sources, the compounds associated with those sources shall be determined and documented. The compounds from those additional sources shall be added to the DC list if a DL from a cognizant authority exists. For each DC and PM2.5, the emission rates from indoor sources from occupants, building materials, furnishings, equipment, and other sources and the outdoor concentrations shall be determined.
Informative Notes:
- Indoor emission rate information for some compounds is provided in Informative Appendix N.
- Outdoor concentrations can be determined from Section 4.
6.3.2 Design Compounds and PM2.5 Concentration. The concentration limits, referred to as design limits, shall be as specified in Table 6-5. Design ventilation shall be such that the calculated concentration of each DC, mixture of DCs, and PM2.5 does not exceed its limit. For any compounds added to the DC list in Table 6-5, data from cognizant authorities shall be used to determine if the compound causes the effects listed in Table 6-6, and compounds having one or more of the mixture effects shall be added to the mixture list for that effect. For each mixture, the mixed exposure sum ( Em ), as determined by Equation 6-12, shall be less than 1.0:
Em
= ------ C 1 - + -------- C 2 - + ------- Ci - DL DL2 DL i
(6-12)
where
Em = mixed exposure sum
Ci = mass-balance model calculated airborne peak concentration for the i- th DC
DL i = design limit for the i- th DC
Exceptions to 6.3.2:
- Benzene, phenol, and tetrachloroethylene shall not be included in the mixture calculation for upper respiratory tract irritation, eye irritation, and central nervous system depression. Outside the U.S., if the outdoor concentrations of carbon monoxide, PM2.5, or ozone exceed the DL, the DL shall be the applicable ambient air standards where the project is located or as accepted by the AHJ.
- Ammonia shall be included only for spaces that include nonhuman animals.
6.3.3 Design Approach. Zone and system outdoor airflow rates shall be the larger of those determined in accordance with Sections 6.3.3.1 and 6.3.3.2, based on emission rates, concentration limits, and other relevant design parameters.
6.3.3.1 Mass-Balance Analysis. Using a steady-state or dynamic mass-balance analysis, the minimum outdoor airflow rates required to achieve the concentration limits specified in Section 6.3.2 shall be determined for each DC, mixture of DCs, and PM2.5 within each zone served by the system.
Informative Note: In the completed building, measurement of the concentration of contaminants or contaminant mixtures of concern may be useful as a means of checking the accuracy of the design mass-balance analysis, but such measurement is not required for compliance.
ANSI/ASHRAE Standard 62.1-2022 25