Humidification system maintenance guidelines

Properly designed, specified, installed, and maintained, humidification systems operate trouble-free for years. When operational issues occur, review the humidifier's troubleshooting guide, but also consider that other HVAC issues, such as temperature or airflow, affect humidifier performance. Consider the following humidifier maintenance guidelines:

Follow manufacturer's recommended maintenance schedule
The best prevention against field issues is regular inspection and maintenance. Maintenance requirements vary depending on humidifier type (e.g., cleanable boiling chambers vs. disposable) and water type (hard, naturally soft, softened, or demineralized water). All systems should be inspected after the first three months of duty to determine future inspection and maintenance requirements.

Verify that operating and design parameters match
Operating a humidification system within parameters for which it was designed also will keep systems running smoothly. For example, if a system was designed to meet a 35-percent-relative humidity (RH) requirement in a humidified space, but building occupants are operating systems at 55 percent, available absorption distance in a duct can become inadequate, resulting in duct wetness. It is important to communicate system expectations to building occupants.

Understand how supply water affects maintenance requirements
All humidifiers convert water to vapor, and supply water type has the most impact on maintenance requirements.

Untreated tap water includes minerals -- such as magnesium, calcium, and iron -- that make water "hard." These minerals clog boiling chambers, wetted media pads, and atomizing nozzles. Adiabatic (unheated water) systems using untreated water disperse minerals into air causing white dust fallout, which can contaminate furnishings and processes as well as cause inhalation hazards. Using softened water can mitigate many of these issues. Systems using properly processed demineralized water, such as deionized or reverse-osmosis filtered water, have virtually no supply water maintenance issues.

If using treated water, test water regularly to ensure proper quality. If using deionized water, change deionizing beds in a timely manner to ensure that chlorides, which corrode stainless steel, aren't introduced into the system.

Power and controls maintenance
Start with an easy maintenance task and check and tighten electrical connections such as contactors, fuses, and sensors.

Verify signal compatibility and properly placed sensors. For example, a signal going to a humidifier from a transmitter, humidistat, or building-automation system must be compatible with a signal a humidifier is set to receive. A controller will not understand a modulating humidistat sending a 4- to 20-mA signal if it is not wired or programmed to receive that signal.

Signal inputs typically can be changed at a controller board and/or through a controller's software. A control manual will have specific instructions. All control components should be wired per an appropriate wiring diagram.

A high-limit humidistat normally should be installed in a supply duct about 12 to 15 ft downstream of where a dispersion assembly delivers steam. If it is installed too close to the dispersion assembly it either will quit operating because it is wet or shut off the humidifier because it will accurately read that duct RH is very high (high-limit humidistats are adjustable and usually are set to switch open between 80- and 90-percent RH).

Dispersion assembly maintenance
Steam dispersion assemblies operate trouble-free if designed and installed correctly. They disperse distilled water so there are no issues with clogging, there are no moving parts, and they are constructed mostly of welded metal, often stainless steel. Adiabatic (unheated water) humidifiers can clog if water is untreated. Ultrasonic humidifiers have disks that need replacing periodically.

How clean affects performance
Steam generators with cleanable stainless steel tanks operate at peak performance when clean. Mineral accumulation insulates heaters, reducing output and potentially causing heater failure. Use a manufacturer-recommended cleaning solution for stainless steel tanks. Use softened or demineralized water to reduce mineral accumulation. Or, consider using a steam generator that has a replaceable plastic cylinder, requiring no cleaning. When mineral accumulation reaches a predefined level, the humidifier's controller will typically present a "change cylinder" message.