Steam Humidifier Product

Overview

A steam humidifier raises the moisture content of building air by boiling water and injecting the vapor into a duct or directly into a space. Steam is the preferred humidification method where hygiene matters — hospitals, museums, data centers, cleanrooms — because the water is sterilized by boiling and, unlike spray or evaporative systems, no aerosol of liquid water (a potential Legionella vector) ever enters the airstream. The electrode type described here is the most common electric design: it passes mains current directly through ordinary tap water between submerged plates, using the water's own conductivity as the heating resistance. Output runs from about 5 to 100 kg of steam per hour per unit, at roughly 0.75 kW per kg/h.

The machine consists of a replaceable Steam Cylinder, a Fill Water System and Drain System, the duct-mounted Steam Dispersion Assembly assembly connected by a Steam Hose, a Humidity Controller, and a Power Section, all in a wall-hung Cabinet.

The electrode principle

Inside the polypropylene Cylinder Shell, three plate Boiling Electrode assemblies (one per phase) hang into the water. Because tap water conducts — typically 125 to 1,250 µS/cm — current flows directly through it, dissipating heat exactly where boiling should happen, with no heating element to scale up or burn out. Output control is elegant: steam production is proportional to the wetted electrode area, so the controller modulates output simply by managing water level. To produce more steam it opens the Fill Solenoid Valve and raises the level; to produce less it lets boiling lower the level, or runs the Drain Pump briefly. A High-Level Sensing Electrode near the top signals full, and the Current Transformer reading tells the controller the actual boil rate, since electrode current is directly proportional to output.

The same conductivity that makes the principle work also concentrates minerals. As pure water leaves as steam, dissolved calcium and magnesium stay behind, raising conductivity and precipitating as scale. The controller manages this with periodic blowdown — pumping out a portion of the concentrated water and refilling with fresh — guided by the Conductivity Sensing Circuit measurement, so the cylinder chemistry stays in its working band across very different water supplies. Scale that does form collects on the sacrificial electrodes and in the Scale Collection Screen basket. After 500–2,500 hours, depending on hardness, the cylinder is simply unplugged from its Cylinder Base socket and replaced — the design treats the entire boiling vessel as a consumable, trading a recurring cartridge cost for near-zero maintenance labor. This is the key practical difference from resistive-element humidifiers, which run on demineralized water and use cleanable tanks.

Water connections

Fill water passes an Inlet Strainer and the solenoid Fill Solenoid Valve, then falls through the Fill Cup (Air Gap) — an open air gap required by plumbing codes to make backflow into the potable supply physically impossible — before running to the cylinder through the Fill Tubing. On the way out, blowdown water leaves near boiling, so a Drain Tempering Device fitting mixes in cold fill water to keep the drain stream under the 60 °C limit most codes set for building drains. A Drain Valve provides a gravity path for end-of-season emptying, and a Base Drip Tray under the wet compartment catches any leakage before it reaches the electrical side.

Steam distribution

Steam leaves the cylinder at essentially atmospheric pressure and travels through the 22–45 mm Steam Hose — run with continuous rise or fall, never a sag where condensate could pool and spit — to the Dispersion Tube spanning the duct. Calibrated Steam Nozzle orifices along the tube release steam evenly across the airstream; many draw from the tube's center-line so condensate running along the wall cannot be ejected. The Condensate Return Line line drains what condenses back to the cylinder or to waste. The critical application parameter is absorption distance: the 0.3–1.5 m of duct the steam needs to become invisible vapor before it reaches any elbow, filter, or coil that wet air would soak. Multi-tube panels shorten this distance for tight plenums, and Tube Insulation cuts condensate losses substantially.

Control and protection

The Control Board runs a PI loop on the Humidity Transmitter signal against a setpoint of typically 30–60% RH, modulating output 20–100%. Two interlocks are standard and code-driven: a High-Limit Humidistat humidistat downstream of the dispersion tube stops production before the duct air saturates, and an Airflow Proving Switch proves the fan is running so steam is never injected into a dead duct. The Power Contactor switches the full electrode current under board command, with Line Fuse protection on each phase, and the unit reports status and cylinder life to the building-management system over Modbus or BACnet.