Calculator Inputs
Example Data Table
| Parameter | Example Value |
|---|---|
| Emission Rate | 5 g/h |
| Target Concentration | 10 mg/m³ |
| Supply Concentration | 1 mg/m³ |
| Initial Concentration | 30 mg/m³ |
| Room Volume | 500 m³ |
| Current Airflow | 1,200 m³/h |
| Mixing Factor | 1.3 |
| Safety Factor | 1.15 |
| Capture Efficiency | 20% |
| Required Airflow Result | 663.56 m³/h |
| Current Steady Concentration | 5.33 mg/m³ |
| Purge Time at Current Airflow | 29.25 minutes |
Formula Used
1) Effective emission after capture:
Geff = G × (1 − η / 100)
2) Required dilution airflow:
Qreq = (Geff × K × SF) / (Ctarget − Csupply)
3) Steady concentration at current airflow:
Csteady = Csupply + (Geff × K) / Q
4) Air changes per hour:
ACH = (Q × 3600) / V
5) Purge time to reach a target:
t = −(V / Q) × ln[(Ctarget − Csupply) / (Cinitial − Csupply)]
6) ppm to mg/m³ conversion when needed:
C (mg/m³) = ppm × MW / 24.45
Here, G is emission rate, η is capture efficiency, K is mixing factor, SF is safety factor, Q is airflow, and V is room volume.
How to Use This Calculator
- Enter the contaminant emission rate and choose its unit.
- Set the target room concentration and supply concentration.
- Provide molecular weight if any concentration uses ppm.
- Enter the room volume and current ventilation airflow.
- Add mixing and safety factors to reflect real design conditions.
- Enter local capture efficiency to account for source control.
- Press the calculate button to show results above the form.
- Review required airflow, ACH, purge times, and the graph.
- Use the CSV or PDF buttons to export the results.
FAQs
1. What does this air dilution calculator estimate?
It estimates the ventilation airflow needed to dilute an airborne contaminant to a chosen target concentration. It also shows air changes per hour, steady-state concentration, extra airflow needed, and purge time.
2. When should I use a mixing factor above 1.0?
Use a higher mixing factor when room airflow is uneven or short-circuiting is likely. Poor air distribution means you need more dilution air than an ideal fully mixed room would require.
3. Why is capture efficiency included?
Local exhaust or enclosure may remove part of the emission before it enters the room. Capture efficiency reduces the effective emission rate and can greatly lower required general ventilation.
4. Can I enter concentrations in ppm?
Yes. When ppm is selected, the calculator converts it to mg/m³ using molecular weight and the standard 24.45 conversion basis. Enter a valid molecular weight for accurate results.
5. What is steady-state concentration?
It is the concentration expected after enough time has passed for emission and ventilation to balance. It helps show whether your current airflow can hold the contaminant below the chosen limit.
6. Why might purge time show as not achievable?
That usually means the chosen target is at or below the supply concentration, or the initial and target values do not satisfy the decay equation. In that case, ventilation alone cannot reach the target.
7. Is this suitable for final compliance design?
It is excellent for screening, comparison, and preliminary engineering checks. Final compliance decisions should still consider codes, toxicology limits, sensor data, room geometry, and professional review.
8. What does the graph show?
The graph plots predicted steady concentration against airflow. It helps you see how concentration drops as airflow rises, and where your current and required ventilation sit relative to the target.