Humidification system installation guidelines

Ensure proper humidification system operation with these humidifier installation guidelines:

Accommodate equipment noise
Humidifier noise levels vary by technology, but in general, install humidifiers away from quiet or occupied areas.

Direct steam injection systems can be noisy at the control valve, where boiler steam passes through on its way to a dispersion assembly.

Non-pressurized steam generators produce noise when filling and draining. Some electric steam humidifiers produce noise when con­tactors cycle on and off. For very quiet areas, con­sider an electric unit with quiet solid state relay (SSR) control rather than contactors. When not dispersing into a duct or air handling unit (AHU), locate dispersion fan units in quiet areas remote from the steam generator.

Noise from adiabatic (unheated water) humidifiers varies by type. Residential bypass humidifiers generate minimal noise. Atomizing systems have water pumps and sometimes also air compressors that generate a fair amount of noise. With these systems it is usually possible to place the dispersion nozzles remotely from the pumping station, isolating noise to a mechanical room.

Allow equipment access
Create access to installed humidification equipment to allow convenient visual inspection and maintenance. Boiler-steam humidifiers contain devices (such as a control valve, a steam trap, and a strainer) that require periodic maintenance. While these devices can operate for long periods of time without attention, they should be accessible for inspection.

Non-pressurized steam humidifiers are either cleanable or have disposable cylinders. Location should allow for easy access with ample space for servicing.

Adiabatic humidifiers can require adjacent water treatment, so allow enough space for all system components. Locate residential bypass humidifiers where it's easy for homeowners to replace evaporative pads, and place controls so they are easily accessed by the homeowner.

Protect from water damage
Protect areas surrounding humidifiers from water damage. The potential for water damage is always pres­ent with any steam or water appliance, but a properly planned installation virtually eliminates this risk. Be aware of valuable equipment or stored materials that are either adjacent or on a lower level. Install drip pans under humidifiers to contain water leaks when necessary.

Use rigid pipe for steam
For runs over 10 ft, use stainless steel or copper tubing, or steel pipe to connect non-pressurized steam generators to dispersion assemblies, rather than using steam hose. Though initially more expensive, there are several advantages to using rigid interconnecting pipe, including:

  • Longer service life. Flexible hose will need replacing and may be more expensive in the long term.
  • Easy to install at a uniform slope for condensate drainage. Rigid pipe won't sag and create pockets, which can cause condensate to pool, resulting in spitting at the dispersion assembly.
  • Easy to insulate. Insulating rigid pipe reduces steam loss due to condensation and can yield considerable energy savings.

Design for proper condensate drainage
Non-pressurized steam systems generate condensate in dispersion tubes and in the piping that connects the steam generator to the dispersion assembly. This water must be drained to prevent it from being discharged into the duct. For reasons of energy econ­omy, whenever possible drain condensate back to the steam generator.

There are two ways to return condensate to a non-pressurized steam generator. One method is to pitch the dispersion assembly and steam piping to return condensate to the generator. When this is done, condensate flows counter to steam flow. This method works satisfactorily only when steam piping is adequately sized for humidifier capacity and when a given minimum recommended pitch can be maintained. Otherwise, the velocity of the steam will carry condensate into the duct. Usually, humid­ifier manufacturers recommend a maximum steam flow rate and a minimum pitch.

The other method, used with higher capacity sys­tems, involves returning condensate through a separate line. With this method, the dispersion assembly has a drain connected to a condensate return line, and both are pitched so that condensate returns to the humidifier. This installation requires an air vent in the return line.

When wasting condensate to an open drain, a P-trap is required to prevent steam from escaping into the room. The trap is usually constructed of metal tubing. Water column height in the P-trap must be sufficient to withstand the operating pressure inside the humidi­fier. Consult the manufacturer's recommenda­tions for P-trap heights.

If required, cool discharged water
Many non-pressurized steam humidifiers have periodic drain and flush cycles or automated skimming where a portion of water in the tank drains to remove precipitated minerals. This water is typically 212 °F (100 °C) which, according to many municipal codes, should not be discharged to a sani­tary system. In this situation, add a water tempering device to cool discharged water. Water tempering may be required for condensate sent to drain, as well. 

Install a duct high limit humidistat
This device is a must for most humidifier installations and is mounted in the duct downstream of the dispersion assembly. It is usually set at 90 percent relative humidity (RH). If duct RH rises above that setting, it will shut down the humidifier. Wetted media humidifiers cannot oversaturate airstreams and so a duct high-limit humidistat is not a requirement.

To ensure proper operation, the high-limit sensor must be located far enough downstream of the disperser to allow for full absorption and for humidity to equalize in the airstream. Otherwise, short cycling of the humidifier can occur, resulting in an unsatisfied humidification demand.

Most humidifiers can use an inexpensive on/off-type high-limit humidistat, except in variable air volume (VAV) systems. In this case, a modulating high-limit humidistat provides more satisfactory control.

Install an airflow proving switch
If duct air flow stops for any reason all humidifiers, except for wetted-media types, must be shut down immediately to prevent water damage. This can be accomplished by using a duct-mounted airflow prov­ing switch. Use a switch that is activated by the move­ment of a shaft, which has a vane or sail attached to it (often called a sail switch).

Another type is a diaphragm-operated switch, in which the static pressure inside the duct actuates the switch. The latter type isn't a good choice for VAV systems, because when the VAV box modulates the airflow, the duct static pressure remains high and allows the humidifier to continue to operate without suffi­cient volume of steam-absorbing airflow. A sail-switch is the best choice for VAV applications.

Place primary humidity control sensor in room center or in return air duct
Humidity sensor or transmitter loca­tion has a significant impact on humidifier perfor­mance. Placing a sensor in the center of a room or inside a return air duct will give the best all-around control.

Do not place a sensor near a supply duct, on a perimeter wall, in sunlight or near a heat-producing object. The humidity sensor should be located where it can measure an average space temperature and humidity.