Formula used
Vbz = Rp × Pz + Ra × Az
Voz = Vbz ÷ Ez
Vou = D × Σ(Rp × Pz) + Σ(Ra × Az)
Ev = limited value of 1 + Xs − critical Zp
Vot = Vou ÷ Ev
The multiple-zone system method is a practical screening implementation. Verify every final equation, coefficient, exception, and table against the selected standard edition.
How to use this calculator
- Select project units, programme, ventilation method, and standard edition.
- Add every occupied zone and enter user-verified person and area rates.
- Enter primary airflow, provided outdoor air, exhaust, transfer air, and distribution effectiveness.
- Complete system, natural ventilation, filtration, monitoring, CO₂, and existing-building sections.
- Submit the form and review zone shortfalls, system efficiency, warnings, and recommendations.
- Export CSV or JSON, copy the summary, or print the report as PDF.
Example data
| Zone | Area | Population | Rp | Ra | Ez | Primary airflow | Provided outdoor air |
|---|---|---|---|---|---|---|---|
| Open Office | 2,200 ft² | 20 | 5 cfm/person | 0.06 cfm/ft² | 1.0 | 3,500 cfm | 700 cfm |
| Conference Room | 500 ft² | 10 | 5 cfm/person | 0.06 cfm/ft² | 1.0 | 1,000 cfm | 250 cfm |
These values demonstrate calculator operation only. They are not a substitute for edition-specific standard tables or project requirements.
Frequently asked questions
1. Does this calculator certify compliance?
No. It provides an organised engineering screening calculation. A qualified professional must verify final compliance.
2. Why are ventilation rates entered manually?
Rates and exceptions vary by standard edition, occupancy type, project programme, and adopted code. Manual rates keep the calculation edition-aware.
3. What is breathing-zone outdoor airflow?
It combines an occupant-related outdoor-air component and a floor-area-related component before distribution effectiveness is applied.
4. What is zone air-distribution effectiveness?
It adjusts breathing-zone airflow for supply and return arrangement, temperature mode, and air-distribution performance.
5. What is the critical zone?
It is the zone with the largest required outdoor-air fraction relative to its primary airflow in this screening calculation.
6. Can air cleaning replace outdoor air?
Not automatically. Substitution is allowed only where the selected method, standard edition, and authority explicitly permit it.
7. Is CO₂ a complete indoor-air-quality measurement?
No. It can indicate ventilation conditions but does not capture particles, gases, moisture, odours, or all contaminant sources.
8. How should measured airflow uncertainty be used?
The calculator reduces measured outdoor air by the entered uncertainty percentage to create a conservative comparison value.
9. What if a zone has no occupants?
The area component can still create an outdoor-air requirement. Verify the occupancy category and unoccupied operating schedule.
10. Why does the natural ventilation module use custom limits?
Opening percentages, depth limits, climate restrictions, and control requirements vary. Enter the limits required by your selected reference.
11. What records should be retained?
Retain calculations, drawings, schedules, test reports, balancing data, sensor specifications, commissioning records, and final reviewer approvals.