The pros and cons of different humidifiers

System type dictates maintenance demands for peak equipment performance
Friday, June 23, 2017
By Dave Schwaller

In mechanical systems for buildings, benefits in some areas may come with trade-offs in other areas. For example, the lowest possible upfront cost might mean future costs for consumables. Conversely, a larger upfront investment might deliver payback in the form of maintenance-free operation for months or even years. Following that logic, it’s helpful to consider maintenance requirements when selecting a humidification system.

Every humidifier system requires some level of maintenance. The type of system chosen will directly affect the amount of time, effort, and expense that must be invested to keep the equipment running at peak performance. The following overviews describe maintenance scenarios by humidification system type, along with their benefits and tradeoffs.

Electrode humidifiers: Low upfront cost, fast/simple maintenance, more consumables

Electrode steam humidifiers are designed with replaceable steam cylinders, rather than cleanable tanks. All minerals in the fill water stay in the steam cylinder as water is boiled away. It could be thousands of hours before enough minerals build up in the steam cylinder to affect performance. Most electrode steam humidifiers display a message when the steam cylinder reaches the end of its life. All that’s required is a very brief shutdown ─ just long enough to swap in a new steam cylinder and discard the old one.

The benefits of an electrode steam humidifier are low upfront costs and time saved not cleaning a tank. The tradeoff is future costs for replacement steam cylinders ─ which will vary depending on water quality and frequency of use.

Heated tank humidifiers: Average upfront cost, longer maintenance interruptions, no consumables

Gas-fired, resistive electric and steam-to-steam humidifiers can deliver high performance and high capacities, even with tap water. Further, these systems can be programmed to skim and drain their tanks more frequently if the fill water is very hard. This minimizes minerals in the tank and means fewer and shorter shutdowns for cleaning.

The tradeoff is longer interruptions in steam output for routine tank maintenance, as steam cannot be produced when a tank is refilling with cold fill water. This could be an issue in applications where tight relative humidity control is critical.

Combined humidifier and water treatment systems: Higher upfront cost, little or no maintenance for the life of the humidification system, some consumables

Gas-fired, resistive electric and steam-to-steam humidifiers can deliver high performance and high capacities with little or no maintenance year after year ─ if water treatment is included in the system.

Softened fill water will eliminate much of the required maintenance, as soft-water scale is much easier to remove than hard-water scale. Better yet, it is possible to practically eliminate maintenance with reverse-osmosis or deionized supply water. These systems provide ultra-pure fill water, so the tank and heaters or heat exchangers could possibly look like new even after thousands of hours of operation.

Humidification systems that run year round and/or need tight relative humidity control benefit the most from reverse-osmosis or deionized water.

The tradeoff, in a building that does not already have a water treatment system, is the cost of a water treatment system. Also, water softeners require salt refills, while reverse-osmosis and deionization systems require occasional filter, membrane, and resin bed service.

The best of both worlds, of course, is a steam humidifier and a reverse-osmosis system in a single package. Such systems are commercially available and finding great success in applications where space is limited and single-point water, electrical, and drain connections are desired for both the water treatment system and the humidifier.

Pressurized steam-injection humidifiers: Upfront cost varies with building/application size, minimal maintenance, no consumables

Pressurized steam injection humidifiers typically cost less per application than steam-generating humidifiers, because they disperse boiler steam that is already being generated for heat or other building purposes. Costs vary by the length and quantity of dispersion tubes and the quantity and types of traps, fittings, and modulating valves. There are few items to inspect every few months, such as strainers, steam traps, valves, and seals, but these are not high-maintenance items and are easy to clean or replace.

While pressurized steam-injection humidifiers leverage the output of an existing boiler or central steam plant, the tradeoff is that boiler chemicals carried by the steam enter the airstream along with the steam. Buildings with processes or occupants requiring steam that is free of chemicals should not use boiler steam for humidification.

High-pressure atomization: Higher upfront cost, very low energy consumption, minimal maintenance, no consumables

High-pressure atomizing systems can deliver humidification and cooling for large or small loads with very tight control. Because they use heat in already in the air for evaporation, they are inexpensive to operate. Because these systems require pump stations or air compressors, control systems, and stainless steel piping, they have a higher upfront investment with a payoff of very little maintenance.

Most high-pressure atomizing systems require ultra-pure water to avoid covering surfaces with hard-water dust. Like steam humidification systems using treated water, the tradeoff is the additional cost of water treatment and water treatment system maintenance.

Wetted-media systems: Lower upfront cost, very low energy consumption, minimal maintenance, some consumables

Wetted-media systems are inexpensive to purchase, require very little maintenance, and do not require treated water. While wetted media systems are not capable of tight control, higher-end systems can monitor upstream and downstream conditions and automatically cycle though modes of operation to maximize water use and extend media life.

The tradeoff is that the media needs to be inspected periodically and replaced if sagging under the weight of hard-water scale or deteriorated from prolonged use.

Choose a system, choose maintenance levels

Each type of humidification system has its advantages, and all require some level of maintenance. Thinking through the complete lifecycle when purchasing a humidification system will ensure that both system performance and ongoing maintenance requirements are good fits.

Dave Schwaller has designed and applied evaporative cooling and humidification systems for both traditional and custom HVAC applications for more than 19 years. Dave has been a product development engineer for DriSteem’s gas-to-steam and steam-to-steam humidification product lines, and he has been a product manager for DriSteem’s evaporative cooling systems, water treatment systems, and new technologies. In his current role, Dave is a senior applications engineer on DriSteem’s inside sales team.

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