Ultrasonic humidification is ultra-efficient

Engineered Systems, April, 2003 by Joanna R. Turpin

Low energy requirements, free cooling potential, and good retrofit suitability are just three appealing traits of this technology. As for caveats, water purity and adiabatic interaction within the system as a whole are two issues to keep in mind. Read on to see if and how an upcoming project might benefit from the efficiencies and economies that ultrasonic can offer.

Humidification is an important part of many different kinds of building environments. Proper humidity levels are required for certain types of industrial processes, as well as for cleanroom spaces and even for occupant comfort in office buildings. If the right amount of humidity is absent from these spaces, then the quality of a product or process may be in jeopardy, or occupants may complain of discomfort.

Just as there are many different kinds of spaces requiring proper humidity, there are many different ways in which humidification can be provided to a building. Each type of system has advantages and disadvantages, and as can be imagined, the costs to operate each type of system vary tremendously.

Ultrasonic humidification, which is an adiabatic type of system, is just one type of method available. These systems are known for using very little energy, and experts state that they also provide high-quality moisture and close control of an environment while requiring little maintenance. However, other factors such as first cost and water quality also have to be considered when figuring out how an ultrasonic humidifier will affect a building's total operating costs.

SOME HIGHER COSTS

Larry Cluchey, P.E., an independent consulting engineer in Grand Rapids, MI, who mainly focuses on solving humidity control problems, is a definite supporter of ultrasonic humidification systems.

"When I look at an application, I try to look at ultrasonic first to see if it's a right fit. If it's not, then I'll look at other systems. I tend to use ultrasonic on the smaller applications, say 150 lb/hour and down, just because it becomes a cost issue. The first cost gets a little high when you get into the bigger systems."

Indeed, the first cost of an ultrasonic humidification system is often much higher than other types of systems, particularly steam systems. Estimates usually show the first cost of an ultrasonic system (including water treatment) to be anywhere from two to four times higher than other types of systems.

That's why until recently, ultrasonic humidifiers were mainly considered for applications that could take advantage of their energy efficiency-- only 7% of the electric usage of electric steam generators -- to offset their high initial costs. However, over the last five years, the cost of ultrasonic humidifiers has come down considerably.

"Now that ultrasonic humidifiers are more cost effective, building owners are using them in applications where reduced maintenance, a healthy mist, or simplicity of installation is required," said David White, P.E., senior vice president of engineering, Humidifirst, Boynton Beach, FL. "Our typical clients include the baking industry, health care, fruit ripening rooms, printing rooms, laboratories, office buildings, and industrial manufacturing. We even have ultrasonic humidifiers in electronic rooms at the South Pole."

In addition to the higher first cost, ultrasonic humidifiers require ultra-pure water. White notes that smaller systems (30 lb or less) can use deionized (DI) water canisters, which clean the water to approximately 2.5 ppm. Larger ducted systems require an RO system, which can add approximately one-third or more to the cost of the humidifiers.

"Ultrasonic systems are a little less forgiving with regard to water treatment," stated James Mooney, P.E., president of Enginuity, LLC, an engineering-focused D-B mechanical services contracting firm in Mechanicsburg, PA. "If the water is not treated correctly through the use of DI canisters or RO, it can cause problems."

LOWER ENERGY COSTS

Where ultrasonic humidifiers really shine is in their low energy use. As White noted, ultrasonic humidification is the only way to make a steam size droplet (approximately 1 micron) without having to boil the water.

"Consider a typical 200 lb/hour humidifier," he said. "The electric steam humidifier will have an electric load of approximately 64 kW versus 5 kW for the ultrasonic humidifier. For a simple comparison, these systems, if operated at 3,000 hours per year would have an annual operating cost of $16,944 and $1,304 respectively. That is a 93% reduction of electrical usage.

Gluchey has devoted a lot of his time to studying how much it costs to generate each type of humidification. In fact, he has written an entire software program that performs the calculations based on humidification type. In his study, he determined that based on $0.065/kWh it costs about $0.17 to generate 100 lb of moisture using ultrasonics. Using the same cost per kW, electric steam (which Cluchey said people tend to buy first and hate later) costs $3.68 to generate 100 lb.