Definition
Water that sits without circulation in a tank, pipe or channel for extended periods; at 25–55°C it creates an ideal environment for bacteria (especially Legionella), biofilm and microorganism growth.
Detailed Explanation
Stagnant water is the most common source of hygiene breach in humidification systems. Typical locations: (1) Dead legs — branch lines unused for long periods; (2) Dead volume — 5–10 cm of undrained water at tank bottoms; (3) Low flow — laminar flow in pipes lets biofilm grow on the wall; (4) System downtime — weekends, holidays, off-season. Once water has been still for 6+ hours, bacterial growth becomes exponential; 1,000× multiplication in 24 hours is common.
Why It Matters
Four engineering remedies address stagnant water: (1) HYGIENIC PIPING — no dead legs, continuous loop design, maximum dead-leg length where a branch is unavoidable (pipe diameter × 6); (2) CONTINUOUS RECIRCULATION — 24/7 pump operation at minimum flow (Reynolds > 4,000 for turbulent flow); (3) AUTO DRAIN/PURGE — automatic discharge when the system is idle (triggered after 8 h); (4) PERIODIC FLUSHING — weekly or biweekly automatic chemical clean, or high-temperature (70°C+) recirculation. Together they practically eliminate stagnation.
Practical Example
A hotel restaurant in Antalya shuts off its kitchen adiabatic humidifier outside the 5-month summer season. The original passive system had no auto-drain. After 6 months, the first restart produced foul odour + brown water from the nozzles; the system was out of service for 4 weeks. NKT retrofit: an auto-purge cycle (8-hour recirculation check, drain + refresh if needed) + a full off-season drain protocol. Over the next 3 season openings, restart was trouble-free.
Engineering Note
Hygienic piping design rules: (1) Dead leg length < 6× pipe diameter (e.g. < 150 mm for DN25); (2) Branch take-off angle ≥ 45° (90° tees accumulate); (3) Drains at the lowest pocket; (4) Slope ≥ 1%; (5) Idle equipment is isolated + drained, not bypassed. PLC programming: drain-trigger criteria use water temperature + idle time + conductivity change. Modern Neptronic SKH/SKVF systems ship with these algorithms as standard.
NKT Application Link
For this application NKT – Nem Kontrol Teknolojileri supplies the Neptronic SKH high-pressure atomisation system and the Neptronic SKVF evaporative cooler. Unit-selection support is based on space conditions, humidification load and the feed-water analysis; technical service and spare parts are provided. Design and installation of water treatment, as well as engineering design, installation and commissioning, remain within the scope of the facility's designer, contractor and water-treatment specialist.
