How to size a UV system

How to Size a UV System: A Step-by-Step Guide with Real Calculations :

Sizing a UV disinfection system isn’t just about matching numbers – it’s about ensuring water safety, compliance, and system efficiency.

In this guide, you’ll learn exactly how to calculate:

• The correct UV dose
• The flow rate
• The UV transmittance (UVT) needed

with a real-world calculation example at the end.

Why Sizing Matters

UV disinfection is a proven technology in water and wastewater treatment. But its effectiveness depends on proper sizing. If undersized, pathogens survive. If oversized, you’re wasting power and money.

Expert Insight:

“Over 70% of UV system performance issues come from incorrect sizing or poor maintenance.” – Alfaa UV Engineering Team

Step 1: Calculate the Required UV Dose (mJ/cm²)

What is UV Dose?

UV dose is the amount of UV light energy delivered to microorganisms. It’s measured in mJ/cm² (millijoules per square centimeter).

Typical UV Dose Requirements:

Formula:
UV Dose = UV Intensity (mW/cm²) × Exposure Time (sec)

Step 2: Determine Your Flow Rate

Flow rate tells us how much water passes through the system per second.

Common Units:

• m³/hr (cubic meters per hour)
• LPM (liters per minute)

Example Conversion:

If your plant processes 500 m³/day:
→ 500 / 24 = ~20.8 m³/hr
→ 20,800 L/hr

Step 3: Measure UVT (UV Transmittance)

What is UVT?

UVT is the percentage of UV light that can pass through water. The cleaner the water, the higher the UVT.

Use a UVT meter to measure UVT at 254 nm wavelength.

Example: Sizing a UV System for 500 m³/day Plant

Let’s say you have a plant processing 500 m³/day of treated drinking water.

• Flow Rate: 20.8 m³/hr
• Target UV Dose: 40 mJ/cm²
• Measured UVT: 92%

Based on these numbers, you can now work with UV manufacturers to select a system with:

• Reactor size that accommodates ~21 m³/hr
• UV lamps with sufficient intensity
• A reactor chamber designed for the measured UVT

✅ You’ve now successfully sized your system to meet disinfection standards.

FAQs

Final Thoughts

Sizing a UV system isn’t a guessing game. By understanding your UV dose, flow rate, and UVT, you make a system that’s safe, sustainable, and long-lasting.

Need help?

Reach out to the experts at Alfaa UV for custom solutions backed by over 20 years of experience.