| Scenario | Room (L×W×H) | ACH | Diffusers | Face Velocity | Estimated Total Flow | Estimated Diffuser Size |
|---|---|---|---|---|---|---|
| Propagation greenhouse zone | 30 ft × 20 ft × 10 ft | 6 | 4 | 500 ft/min | 600 CFM | Ø ~7.4 in (round) |
| Hydroponic grow room (metric) | 9 m × 6 m × 3 m | 8 | 6 | 2.5 m/s | 360 L/s | Ø ~174 mm (round) |
| Garden studio comfort zone | 18 ft × 14 ft × 9 ft | 4 | 2 | 450 ft/min | 151 CFM | ~7.8 in side (square) |
Examples are illustrative. Confirm diffuser selection with manufacturer data.
- Room Volume:
V = L × W × H - Total Airflow:
Imperial:
CFM = (ACH × V(ft^3)) ÷ 60
Metric:m^3/h = ACH × V(m^3), thenL/s = (m^3/h × 1000) ÷ 3600 - Per-Diffuser Airflow:
q = Total ÷ N - Required Free Area:
Imperial:
A(ft^2) = q(CFM) ÷ v(ft/min)
Metric:A(m^2) = q(m^3/s) ÷ v(m/s) - Convert Area to Size:
Round:
d = √(4A/π)
Square:s = √A - Pressure Indicator (rough):
dP ∝ K × v^2
- Pick your unit system to match your drawings and equipment.
- Enter greenhouse room dimensions to compute the air volume.
- Set ACH based on humidity, odor, and crop needs.
- Choose diffuser count and a conservative face velocity.
- Press Calculate to see airflow and size estimates.
- Use CSV/PDF exports for submittals and field notes.
Airflow planning for plant health
Greenhouse ventilation must balance temperature, humidity, and CO2 delivery. Using air changes per hour gives a fast target for total supply air, even when loads vary across benches. Higher ACH improves moisture removal after irrigation, while lower ACH reduces leaf chilling during cool nights. Pair the airflow target with zoning so sensitive crops receive steadier mixing. For seedling trays, prioritize gentle mixing above the canopy to avoid desiccation.
Choosing diffuser quantity and location
More diffusers usually lowers per-outlet flow and improves distribution. In long bays, spacing outlets along the centerline helps prevent stagnant corners. Near doors and glazing, aim supply to temper cold surfaces without blasting foliage. If the room has tall canopy zones, consider higher throw patterns to reach the occupied plant layer evenly. Avoid placing outlets directly over misting lines, where cold air can condense and drip.
Selecting a safe face velocity
Face velocity controls diffuser free area and strongly affects noise. For quiet garden studios, conservative velocities reduce hiss and drafts. For production zones, slightly higher velocities can support throw, but keep a margin for filter loading and fan speed changes. When results show very small openings, reduce velocity or add outlets. In ducted systems, include balancing dampers so each diffuser meets the calculated share.
Interpreting the sizing result
The calculated diameter or side is a geometric estimate of the required free area. Real products include blades, neck losses, and discharge patterns, so check manufacturer data for net free area and throw at your airflow. Use the pressure indicator trend to compare alternatives; lower resistance generally supports efficiency and quieter operation during seasonal setpoint changes.
Documentation and field use
Export the CSV for quick review of assumptions and results. The PDF summary works well for submittals, commissioning notes, and maintenance records. Recheck calculations after changing diffuser type, zoning, or ACH targets. If measured airflow differs from design, adjust diffuser count or velocity before increasing fan speed, which may raise noise and energy.
What ACH should I use for a greenhouse zone?
Use your humidity and odor goals to pick ACH. Start with 4 to 8 for general circulation, then adjust after measuring temperature and moisture uniformity across benches.
Why does diffuser count change the size result?
Total airflow is split across outlets. More diffusers reduce flow per diffuser, which reduces required free area and often produces quieter, easier-to-balance distribution.
Is the calculated diameter the same as a catalog neck size?
No. The calculator sizes free area geometrically. Manufacturer neck size and net free area differ due to blades and frames, so confirm against product data.
What face velocity is considered quiet?
Lower velocities are quieter. For comfort-oriented garden rooms, keep velocity conservative and increase diffuser count if the computed opening becomes too small.
How do I use the pressure indicator?
It is a simple comparison tool. If you raise velocity or K, the indicator rises, suggesting higher resistance and potentially more noise and fan energy.
When should I recalculate diffuser sizing?
Recalculate after changing room dimensions, ACH target, diffuser type, or diffuser count. Also update inputs after commissioning if measured airflow differs from design.