/ Field knowledge · IMC 403.3.1.1
Vbz is not Voz. Divide by Ez.
IMC 403.3.1.1: Vbz is not Voz. Divide by Ez. A mixed-air RTU is not a 100% OA system. A fixed OA damper is not VAV outdoor-air control.
Educational 2024 IMC 403.3.1.1. Confirm adopted edition. Distinct from Table lookup on ventilation and from DCV / VAV controls. This is not a sealed outdoor-air design.
- Vbz = Rp·Pz + Ra·Az (Rp/Ra from Table 403.3.1.1; Pz = people; Az = net occupiable area).
- Ez by configuration: 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.
- Voz = Vbz / Ez.
- Single-zone or 100% OA: Vot = ΣVoz.
- Multi-zone recirc uses Zp / Ev / D: Zp = Voz / Vpz; Ev from table using Max(Zp); Vou = D · ΣVoz with D = Ps/ΣPz; Vot = Vou / Ev. Show that math on M-601 — this page does not compute Ev.
- 403.3.1.3 DCV may modulate by occupancy but not below Ra during occupancy.
- 403.3.1.4 VAV must maintain OA across turndown — a fixed damper alone is not compliant.
Do not claim Ez = 1.0 for warm ceiling supply without the Daily Code Talk redline checks (ΔT and throw). Do not show Vbz without Ez. Do not call the system 100% OA in the calcs while scheduling a mixed-air AHU/RTU. VAV minimums in the math must match BAS setpoints.
Vbz on the schedule, no Voz
Part-load OA on VAV is the common rejection: design peak looks fine; minimum primary airflow does not. Confirm minimum OA at minimum zone airflow.
Source: DCT 403 Part 3 · tool: Ez → Voz · table: 403.3.1.1 · DCV: controls.
What to send
The zone schedule (Rp, Ra, Pz, Az, Ez) and whether the AHU is mixed-air or 100% OA.
If Vbz is on the schedule and Ez is not
Send M-601. Masterbuild will say whether 403.3.1.1 even has a Voz — or the RTU is mixed-air pretending to be 100% OA.
Send Project Background+1 (786) 398-6940 · osmany.portal@masterbuildconsulting.com
Masterbuild provides engineering services under a written scope. Nothing on this page is project-specific engineering advice, a code interpretation for your project, or a representation about permit approval. Confirm the adopted edition. Ez and Voz values below are 2024 IMC 403.3.1.1 education from Daily Code Talk — not a sealed outdoor-air design. This page is not a fee quote.