ASHRAE+62.1-2022+(1) - Page 041
Extracted Content
Exception to A2.1: Because system ventilation efficiency ( Ev ) is determined by the minimum value of the
zone ventilation efficiency ( Evz ) in accordance with Equation A-9, calculation of Evz is not required for any ventilation zone that has an Evz value that is equal to or larger than that of the ventilation zone for which a calculation has been made.
Informative Note: The value of Evz for a ventilation zone will be equal to or larger than that for another ventilation zone if all of the following are true relative to the other ventilation zone:
a. Floor area per occupant ( Az/Pz ) is no lower. b. Minimum zone discharge airflow rate per unit area ( Vdz/Az ) is no lower. c. Primary air fraction ( Ep ) is no lower. d. Zone air distribution effectiveness ( Ez ) is no lower. e. Area outdoor air rate ( Ra ) is no higher. f. People outdoor air rate ( Rp ) is no higher.
A3. SYMBOLS
Az zone floor area: net occupiable floor area of the ventilation zone, ft [2] (m [2] ).
D occupant diversity: ratio of the system population to the sum of the zone populations.
Ep primary air fraction: fraction of primary air in the discharge air to the ventilation zone.
Er secondary recirculation fraction: in systems with secondary recirculation of return air, the fraction of secondary recirculated air to the zone that is representative of average system return air rather than air directly recirculated from the zone.
E v system ventilation efficiency: efficiency with which the system distributes air from the outdoor air intake to the breathing zone in the ventilation-critical zone, which requires the largest fraction of outdoor air in the primary airstream.
Evz zone ventilation efficiency: efficiency with which the system distributes air from the outdoor air intake to the breathing zone in any particular ventilation zone.
Ez zone air distribution effectiveness: a measure of the effectiveness of supply air distribution to the breathing zone. Ez is determined in accordance with Section 6.2.1.2 or Normative Appendix C.
Fa supply air fraction: fraction of supply air to the ventilation zone that includes sources of air from outside the zone.
Fb mixed-air fraction: fraction of supply air to the ventilation zone from fully mixed primary air.
Fc outdoor air fraction: fraction of outdoor air to the ventilation zone that includes sources of air from outside the zone.
Ps system population: simultaneous number of occupants in the area served by the ventilation system.
Pz zone population: see Section 6.2.1.1.
Ra area outdoor air rate: see Section 6.2.1.1.
Rp people outdoor air rate: see Section 6.2.1.1.
Vbz breathing zone outdoor airflow: see Section 6.2.1.1.
Vdz zone discharge airflow: expected discharge (supply) airflow to the zone that includes primary airflow and secondary recirculated airflow, cfm (L/s).
Vot outdoor air intake flow: see Sections 6.2.2, 6.2.3, and 6.2.4.4.
Vou uncorrected outdoor air intake: see Section 6.2.4.1.
Voz zone outdoor airflow: see Section 6.2.1.3.
Vps system primary airflow: total primary airflow supplied to all zones served by the system from the airhandling unit at which the outdoor air intake is located.
Vpz zone primary airflow: zone primary airflow to the ventilation zone, including outdoor air and recirculated air.
Xs average outdoor air fraction: at the primary air handler, the fraction of outdoor air intake flow in the system primary airflow.
Zpz primary outdoor air fraction: outdoor air fraction required in the primary air supplied to the ventilation zone prior to the introduction of any secondary recirculation air.
ANSI/ASHRAE Standard 62.1-2022 39