| Scenario | Volume (m³) | Target ACH | Existing Clean Air (m³/h) | Purifier CADR (m³/h) | Recommended Units |
|---|---|---|---|---|---|
| Site office cabin | 112 | 6 | 200 | 450 | 2 |
| Enclosed cutting room | 180 | 8 | 150 | 600 | 3 |
| First-aid container | 60 | 7 | 80 | 350 | 1 |
- Volume = (Length × Width or Area) × Height × Room Count
- Required clean air flow (m³/h) = Target ACH × Total Volume (m³)
- Safety-adjusted target = Required flow × (1 + Safety %)
- Existing clean air = Outdoor flow + (Recirculation flow × Filter efficiency)
- Purifier clean air needed = max(0, Safety-adjusted target − Existing clean air)
- Recommended units = ceil(Purifier needed ÷ Per-unit CADR)
- Achieved ACH = Total clean air ÷ Total volume
- Cleanup time: C(t)/C0 = exp(−ACH × t), so t = −ln(remaining) ÷ ACH
- Select your unit system and enter room dimensions.
- Set a target ACH for the occupancy and dust level.
- Add any existing outdoor air and recirculation filtration.
- Enter the purifier CADR from the product specification.
- Calculate to get recommended unit count and cleanup time.
- Adjust safety factor if doors open frequently onsite.
- Export CSV or PDF for purchasing and reporting.
CADR sizing for temporary construction spaces
Clean Air Delivery Rate (CADR) is the effective clean airflow a purifier provides, usually stated in CFM or m³/h. This calculator converts CADR into a clean-air ACH target, so teams can compare different unit sizes using one consistent performance metric. For dusty tasks, select higher targets and keep equipment away from direct dust plumes to protect filters.
Linking ACH, volume, and required clean air
Required clean air is computed as ACH × room volume. For example, a 120 m³ site office targeting 6 ACH needs about 720 m³/h of total clean air before safety margin. If you work in imperial units, the same logic applies using CFM after conversion. Larger ceiling heights raise volume, so confirm dimensions, not only floor area.
Including ventilation and HVAC filtration
Many site cabins already have outdoor air or recirculating HVAC. The calculator treats outdoor airflow as fully “clean” and adds an equivalent clean-air credit for recirculation multiplied by filter efficiency. A 500 m³/h recirculation stream with 70% efficiency contributes 350 m³/h of clean air. If the filter is changed less often, reduce efficiency to keep sizing conservative.
Interpreting cleanup time for dust and aerosols
Cleanup time uses a first‑order mixing model: concentration falls exponentially with ACH. At 8 clean-air ACH, a 90% reduction typically occurs in about 17 minutes (because −ln(0.10)/8 ≈ 0.29 hours). Door openings, partitions, and “dead zones” can extend this time onsite. Use the time outputs to plan pre‑occupancy purge periods and shift changeovers.
Procurement decisions and operating cost
For procurement, compare required units, noise, and energy use together. If each unit draws 60 W and runs 10 hours daily, one purifier uses about 219 kWh per year; multiply by your electricity rate for annual cost. Include spare filters, measured airflow at the intended fan speed, and the placement plan to avoid short‑circuiting between inlet and outlet. Oversizing by a safety factor overall can reduce complaints during high‑dust activities, while still keeping budgets predictable.
CADR is the amount of clean air a purifier delivers. Higher CADR reduces airborne dust and fine aerosols faster, improving comfort in enclosed cabins, first-aid rooms, and meeting spaces where ventilation may be limited.
Size by volume. ACH is air changes per hour, so ceiling height matters. If you only use floor area, you may under-size high-ceiling spaces such as container stacks or temporary workshops.
Enter recirculation airflow and an estimated filter efficiency. The calculator credits clean air as recirc flow multiplied by efficiency, which approximates how much contaminant is removed each hour by the HVAC path.
Construction spaces have door openings, shifting partitions, and localized dust sources. A safety factor adds buffer capacity so the target ACH is still met during peak activity and when filters load with dust.
They are planning estimates based on a well-mixed room model. Real results vary with layout, obstructions, and air short‑circuiting. Use measurements if you need compliance-level verification.
Run units at higher speed during dusty tasks, then step down when activity ends. Place units to avoid blocked intakes, and replace filters on schedule. Proper placement often improves effective CADR without added power.
Note: This calculator assumes well-mixed air and steady operation. For critical applications, verify with measurements and site-specific HVAC data.