Zone -> System Outdoor Air
Plain English:
403.3.1.1.1: For each zone, size OA from occupancy type and air-distribution effectiveness.
403.3.1.1.1.1 (Vbz): Vbz = Rp·Pz + Ra·Az (Rp/Ra from table; Pz = people; Az = net occupiable area).
403.3.1.1.1.2 (Ez): Pick Ez by config: ceiling cool 1.0; ceiling warm/ceiling return 0.8; floor warm/ceiling return 0.7; displacement (low-velocity cool, stratified) 1.2 when criteria are met.
403.3.1.1.1.3 (Voz): Voz = Vbz / Ez.
403.3.1.1.2 (System OA): Sum/correct zones by system type.
403.3.1.1.2.1 (Single-zone): Vot = ΣVoz.
403.3.1.1.2.2 (100% OA): Vot = ΣVoz.
403.3.1.1.2.3 (Multi-zone recirc): Zp/Ev/D method:
.2.3.1 (Zp): Zp = Voz / Vpz (Vpz = occupied-min primary airflow).
.2.3.2 (Ev): From table using Max(Zp).
.2.3.3 (Vou): Vou = D · ΣVoz, with D = Ps/ΣPz.
.2.3.4 (Vot): Vot = Vou / Ev.
403.3.1.2 (Exhaust): Provide table exhaust; transfer air OK where footnotes allow.
403.3.1.3 (DCV): May modulate by occupancy but not below Ra during occupancy.
403.3.1.4 (VAV controls): Must maintain OA across turndown-fixed damper alone isn't compliant.
Calculation Check: Step-by-Step (mirror on M-601)
Table -> Vbz: choose Rp, Ra; set Pz, Az -> Vbz.
Delivery -> Voz: pick Ez -> Voz = Vbz/Ez.
System:
Single-zone/100% OA -> Vot = ΣVoz.
Multi-zone: set Vpz -> Zp -> Ev; find Ps, D; Vou = D·ΣVoz; Vot = Vou/Ev.
Coordination Check: Frequent Redlines
Vbz shown but Ez not applied (no Voz).
VAV minimums in math != BAS setpoints.
Wrong Ps or missing D in Vou.
Claiming Ez = 1.0 for warm ceiling supply without <=15 degrees F ΔT and 150 fpm throw to 4.5 ft.
Calling "100% OA" in calcs but scheduling a mixed-air AHU/RTU.
Code Path: Where to Show It (sheet map)
M-601 (zones): Occupancy, Rp/Ra, Pz/Az, Vbz, Ez, Voz, Vpz, Zp.
AHU/RTU block: Max(Zp), Ev, D, Vou, Vot; DCV logic; VAV occupied minimums.
M-002 / M-603: OA tracking across turndown, Ra floor, sensors/alarms.
M-101+: Diffuser types/temps that justify Ez; tag exhaust/recirc limits.
Check: Outdoor Air Calculations and Controls
Show the outdoor air intake rate on the system schedule and confirm it meets the required minimum across all zones and operating modes.
For VAV systems, show the minimum primary air at minimum ventilation mode and the outdoor air control response to zone occupancy changes.
Show the occupancy sensor or scheduling system that controls outdoor air damper position and document the setpoints.
Review Risk:
Multiple-zone outdoor air efficiency calculations done at design peak but not verified at part-load conditions are a common compliance gap - the system must meet the minimum rate across the full range of operating conditions.
VAV systems that meet outdoor air at design but fall below the minimum at reduced primary airflow are a common submittal rejection - confirm minimum OA at minimum zone airflow.
Outdoor air controls described in the sequence but not tied to the damper schedule or control diagram will generate a controls coordination comment.
Field Tip:
Lay out diffusers to earn Ez >= 1.0 (or displacement 1.2 when criteria apply). If you can't defend it, reviewers default to 0.8.
Freeze VAV occupied minimums in schedules and sequences-your Zp/Ev math depends on them.
For swing-use rooms, base Pz on the highest concurrent load or attach approved stats.
Using transfer air to meet exhaust? Show the path, door relief, and that the Ra floor still holds.
Masterbuild QA Lens
ASHRAE 62.1 references in the code require tracking which addenda version the jurisdiction adopted. Confirm the standard version cited on M-001 matches the jurisdiction adoption table. When using the ventilation rate procedure, show the calculation inputs - occupant type, area, number of occupants - on the calculation sheet, not just the final cfm result.
Drawing / Submittal Check
For IMC 403 Part 3 (403.3-403.3.4 - multiple-zone recirculating systems and system controls): the drawings must show the outdoor air intake rate, the system outdoor air efficiency calculation (if using the multiple-zone procedure), and the occupancy sensor or scheduling system that controls outdoor air. For VAV systems, show the minimum primary air at minimum ventilation mode and the outdoor air control response to zone occupancy changes.
Common Review Risk
Multiple-zone recirculating system outdoor air efficiency calculations are frequently done at design conditions but not at part-load conditions. The system may meet the required outdoor air rate at peak occupancy but fall below the minimum at low occupancy or at reduced primary airflow. Confirm the outdoor air controls maintain the minimum rate across the full range of operating conditions, not just at design.
When To Escalate
Escalate when the multiple-zone recirculating system outdoor air efficiency calculation produces a required system outdoor air rate that the mechanical system cannot deliver without a complete AHU replacement. This situation is common on renovation projects where the existing AHU was sized for a less-demanding ventilation standard. The cost of the AHU upgrade must be in the project budget.
Load Assumption Check
Ventilation rates in Section 403 Part 3 are occupancy-based and area-based. Confirm that the occupant density assumption on the load calculation matches the occupancy type used in the ventilation rate table - a mismatch here changes both OA CFM and cooling load.
Ventilation Coordination
For 403 Part 3 (multiple-zone systems): the outdoor air coordination check is confirming that the system outdoor air rate accounts for all zones simultaneously - including zones at minimum occupancy and zones at maximum occupancy. The system outdoor air efficiency calculation must be done at the worst-case zone combination, not at the average.