Calculator inputs
Example data table
| Scenario | Daily demand (L/day) | Peak factor | Operating hours (h/day) | Margin (%) | Recovery (%) | Autonomy (h) | Loop flow (L/min) | Permeate (L/h) | Storage (L) | Loop ID (mm) |
|---|---|---|---|---|---|---|---|---|---|---|
| Sample project | 5,000 | 1.80 | 10 | 15 | 70 | 4 | 30 | 575.00 | 1,500 | 23.03 |
Formulas used
- Average demand flow (L/h): Qavg = DailyDemand / 24
- Peak demand flow (L/h): Qpeak = Qavg × PeakFactor
- Permeate production (L/h): Qperm = (DailyDemand / OperatingHours) × (1 + Margin/100)
- RO feed (L/h): Qfeed = Qperm / (Recovery/100)
- Concentrate (L/h): Qconc = Qfeed − Qperm
- Storage volume (L): Vtank = Qpeak × AutonomyHours
- Pipe internal diameter (m): D = √(4Q / (πv)), where Q is loop flow in m³/s and v is design velocity in m/s.
How to use this calculator
- Enter the total daily purified water demand in liters per day.
- Choose a peak factor to represent short-term high usage periods.
- Set operating hours based on staffing, utilities, and control strategy.
- Apply a margin to account for membrane aging and future expansion.
- Select recovery based on feed quality and scaling control approach.
- Set storage autonomy to buffer peak consumption and short outages.
- If you have a loop, enter loop flow and a practical design velocity.
- Click Calculate to show results above the form instantly.
- Use the CSV/PDF buttons to export the latest results.
1) Defining demand and peak behavior
Start with a verified daily demand total from fixtures, processes, and cleaning. The calculator converts that value to an average hourly flow, then applies a peak factor to represent clustered usage. For offices and light process areas, a peak factor of 1.3–2.0 is common. Higher peaks increase storage needs and may justify longer production hours.
2) Production capacity and operating window
Production is sized from daily demand divided by operating hours, then increased by a design margin. A 10–20% margin is frequently used to cover membrane fouling, filter loading, and near-term growth. If the system only runs 8–12 hours per day, required permeate flow rises sharply, so confirm utility availability and maintenance windows early.
3) Recovery and the feed/concentrate balance
Recovery links permeate to the upstream feed rate: higher recovery reduces feed flow but increases scaling risk. Many facilities begin feasibility checks in the 60–80% recovery range, then refine with water analysis and antiscalant strategy. The calculator reports estimated feed and concentrate flows to support drain sizing and pretreatment discussions.
4) Storage autonomy for reliability
Storage volume is based on peak flow multiplied by autonomy hours. Typical autonomy targets range from 2–6 hours, depending on criticality and production continuity. Larger storage improves resilience during short outages, but it also requires careful sanitary design, circulation, and level control. Use the storage result as an initial tank selection benchmark.
5) Distribution loop sizing and velocity
If a recirculation loop is used, the calculator estimates an internal pipe diameter from loop flow and a chosen design velocity using Q = vA. Many designs aim around 0.8–1.5 m/s to maintain turnover without excessive pressure loss. The suggested nominal size is a guide; finalize with material, pressure rating, and hygienic fittings.
FAQs
1) What does “permeate production” represent?
It is the hourly purified water output needed to meet your daily demand within the operating hours, including the design margin. Use it as a target capacity for the treatment package.
2) How should I select the peak factor?
Base it on usage patterns. Batch processes, shift changes, or simultaneous washing can drive peaks. If you lack data, start with 1.5–2.0 and adjust after observing real consumption.
3) Why does higher recovery create a warning note?
Higher recovery concentrates salts and can increase scaling or fouling risk on membranes. Final recovery should be confirmed using a feed-water analysis, temperature, and the selected pretreatment and dosing approach.
4) Is the storage volume a final tank size?
No. It is a planning estimate for buffering peak demand during the autonomy period. Add allowance for usable working volume, instrument dead bands, and operational reserves when selecting a tank.
5) What loop flow should I enter?
Use a recirculation flow that maintains turnover and quality for your piping volume. Many systems target multiple turnovers per hour. If you are unsure, start with 20–60 L/min for small loops and refine later.
6) Why is the nominal pipe size labeled as a guide?
Nominal sizes vary by material and wall thickness, so internal diameter changes. The calculator provides an estimated internal diameter and a nearest common nominal size to help you start layout and budgeting.
7) What should I verify before procurement?
Confirm feed-water chemistry, required quality standards, sanitization method, redundancy, and manufacturer flux curves at your temperature. Then validate pressure losses, pump duty, controls, and tank hygiene details with the vendor.