Definition

Steam reverting to liquid water on contact with a cold surface; in humidification ducts, an unwanted liquid-water droplet formation caused by insufficient absorption distance or a cold surface.

Detailed Explanation

Condensate is steam or humid air turning into liquid water on contact with a surface below its saturation temperature. In steam humidification it forms in two places: (1) in the steam line between the unit and the distributor: atmospheric steam is saturated at about 100 °C; when it loses heat it does not cool down, an amount equal to the heat lost condenses. The longer and less insulated the line, the more condensate. (2) Downstream of the distributor on duct walls, elbows, filters or cold surfaces: when an obstruction sits inside the absorption distance or the air approaches saturation.

Why It Matters

Condensate causes three main problems: (1) Hygiene: standing water in the duct is a medium for Legionella, Pseudomonas and other bacteria; critical in hospitals, pharma and food plants. (2) Corrosion: long-term corrosion of galvanized and carbon-steel ducts, dampers and coil faces. (3) Performance: condensed steam never reaches the space and the target humidity is missed. The remedy is the right distributor and placement, a clear absorption distance, an insulated and sloped steam line, and a trapped condensate drain.

Practical Example

When a long, uninsulated, sagging hose connects an SKE4 to a duct distributor, steam condenses in the hose in proportion to the heat lost and condensate collects at the sag. This water is carried to the distributor by the steam flow and drips into the duct, while less steam reaches the space. In a line built to the Neptronic manual, flexible hose stays within 5 m in total, the line is insulated, downward runs get at least 2% slope and upward runs at least 15%, and condensate traps are fitted at low points.

Engineering Note

Condensate management rules (Neptronic manuals): (1) Flexible hose is for short connections and stays within 5 m in total; longer runs use insulated rigid pipe, with length kept within the manufacturer's limit for the unit capacity. (2) At least 2% slope on downward runs and at least 15% on upward runs of the steam line; no sags or kinks. (3) Rigid copper pipe is insulated. (4) The distributor's condensate outlet is connected to drain through an S-type trap at least 51 mm higher than the system static pressure. (5) No obstruction is left within the absorption distance downstream of the distributor.

NKT Application Link

When supplying Neptronic humidifiers and distributors, NKT shares the manufacturer's installation manuals for the steam line, slope and condensate drainage with the design and installation team, and provides technical service and spare-parts support.