Calculator
Formula used
- derating = UVTfactor × aging × fouling × temperature
- Target dose is multiplied by your safety factor.
- This calculator uses a simplified average-intensity model for planning and comparison.
How to use this calculator
- Enter your recirculating flow rate and the chamber volume.
- Fill in chamber diameter and length from product specs.
- Enter lamp electrical power and an estimated UV efficiency.
- Add UVT and factors for aging, fouling, and temperature.
- Select a target dose that matches your garden application.
- Press Calculate to see dose, limits, and status.
- Export CSV for logs or PDF for maintenance records.
Example data table
| Case | Flow (L/min) | Volume (L) | Diameter (cm) | Lamp (W) | UV eff (%) | UVT (%) | Target (mJ/cm2) | Delivered (mJ/cm2) | Status |
|---|---|---|---|---|---|---|---|---|---|
| Hydroponics loop | 25 | 12 | 6 | 30 | 33 | 90 | 48 (40 × 1.2) | ≈ 62 | Meets |
| High turbidity water | 25 | 12 | 6 | 30 | 33 | 70 | 72 (60 × 1.2) | ≈ 28 | Below |
| Lower flow upgrade | 12 | 12 | 6 | 30 | 33 | 70 | 72 (60 × 1.2) | ≈ 58 | Below |
What this tool helps you decide
Dose targets for garden water systems
UV dose is measured in mJ/cm2. For algae control and water polishing, many garden loops plan 30–40 mJ/cm2. For broader bacteria reduction, 40–60 mJ/cm2 is a common benchmark. Higher targets near 90–100 mJ/cm2 increase resilience when disease pressure rises. For sensitive crops, consider higher dose during warm, humid periods.
Water clarity and UV transmittance
UV transmittance (UVT) at 254 nm indicates how much UV passes through water. Because absorption compounds compound across the chamber path, a drop from 90% to 70% UVT can sharply reduce delivered dose. Filtration, settled tanks, and avoiding iron staining help improve UVT. Measure UVT after filters to capture actual operating conditions.
Derating factors for real installations
Output declines with lamp age and sleeve fouling. Use aging and fouling factors to represent your maintenance plan, then add a temperature factor if lamp output changes in cold water. The calculator multiplies these with UVT to form a combined derating term that reduces average intensity and dose. Record lamp hours and sleeve cleaning dates to keep factors realistic.
Reading max flow and required power
Max flow estimates the highest flow your lamp can treat at the selected target dose after applying your safety factor. If your operating flow exceeds that value, reduce flow, add filtration, or increase UV power. Required electrical power is a planning value for comparing equipment sizes. Log changes in your system.
Example dataset for quick validation
Use these sample values to sanity-check new setups or maintenance changes:
- Flow 25 L/min, volume 12 L, diameter 6 cm, lamp 30 W, UV efficiency 33%.
- UVT 90%, aging 0.90, fouling 0.85, temperature 1.00, safety 1.20.
- Typical outcome: meets 48 mJ/cm2 target with margin.
- If UVT falls to 70%, outcome often shifts below target dose.
FAQs
1) What does UV dose mean in practice?
Dose is the product of UV intensity and exposure time. Higher dose generally increases inactivation. In gardens, dose choice depends on water clarity, reuse loops, and whether you are targeting algae, bacteria, or harder organisms.
2) Why is UVT so important?
UVT indicates how much UV light can travel through water. Lower UVT reduces intensity reaching microbes. Improving filtration, reducing color, and keeping sleeves clean usually increases UVT performance more than changing settings alone.
3) How do I pick a safety factor?
Use 1.1–1.3 for stable, well-filtered recirculation with routine maintenance. Use 1.4–2.0 when water quality varies, sleeves foul quickly, or you need extra assurance. Higher factors reduce allowable flow for the same lamp.
4) What if the result says “Below target dose”?
Reduce flow, increase lamp power, improve upstream filtration, or clean the quartz sleeve. Also verify your volume and UV efficiency inputs. A small error in chamber volume or UVT can significantly change the predicted dose.
5) Is chamber length used in the calculations?
Length is recorded for documentation and vendor comparison. The simplified model focuses on volume, cross-sectional area, and derating factors. For final design, confirm hydraulic mixing, lamp geometry, and dose distribution from manufacturer data.
6) How often should I replace lamps and clean sleeves?
Replacement is commonly scheduled by operating hours and performance checks. Use the aging and fouling factors to represent your maintenance plan. If dose margins shrink over time, shorten cleaning intervals or replace the lamp sooner.
7) Can I use this for drinking water?
This tool is intended for garden and recirculating systems planning. Drinking-water applications often require validated dose delivery, sensors, alarms, and regulated design standards. Use certified equipment and follow local requirements for potable systems.