Six steps of humidification design—to meet your facility’s specific requirements

By Bob Nelson, DRI-STEEM Humidifier Company

Humidification systems are as variedas the buildings they serve.

Schools, hospitals, offices, cleanrooms,museums, printing plants, food process-ing plants—every facility has uniquehumidification requirements. But theyalso share common requirements;among them are low first cost, minimumenergy cost, high performance, and min-imum maintenance cost.

Properly designed, a humidification systemwill optimize indoor air quality, improvemanufacturing processes, and preserveexpensive equipment. Despite thesebenefits, only two percent of facilitiesactually contain humidification systems,partly because commercial humidifica-tion systems are not widely understood.

Six variables most affect the performanceof humidification systems: building con-struction, load, energy and water sources,placement and controls. The following sixsteps of humidification design will helpyou control these variables and aid youin the construction of an efficient, effec-tive humidification system.

Step 1: Evaluate building structureto avoid moisture loss, condensation

Just as buildings are protected againstunwanted heat loss—with insulation and double glazing—they can also beprotected against unwanted humidityloss in new and retrofitted buildings.Insulation for walls, as well as steel roofand wall supports, should be protectedwith a vapor barrier on the warm side to avoid saturation from condensed

water vapor. Double-glazed windows andhollow core steel doors also minimizecondensation.

Step 2: Calculate humidificationload for consistent humidity levels

A humidified building constantly losesmoisture, primarily due to air changes.As a general rule, humidification load isbased only on the amount of outside ormake-up air entering a building or space.Loads are calculated based on the differ-ence between desired conditions and en-tering conditions. Calculation methodsvary, depending on whether the buildinguses mechanical, natural or economizerventilation.

Step 3: Determine the most energy-efficient heat source

One of the most common and energy-efficient methods of humidification is todischarge steam from an in-plant boilerdirectly into a space or ducted air stream.Another way to use boiler steam is withan indirect steam-to-steam system toprevent the discharge of chemically-treated steam into an occupied or manu-facturing space. These and other isother-mal systems are ideal for commercial andindustrial applications, primarily due totheir high capacity, compact size, rapidresponse to control, and ability to achievesteam absorption within a short distance.

Another method, known as the adiabaticprocess, uses heat from the surroundingair to change water into vapor for humid-ification. Foggers, ultrasonic and peziodisk humidification are typical adiabaticsystems, and perform best when the sup-ply air is consistently warm and dry.

Step 4: Condition water source for optimum performance

Because water contains dissolved min-erals, suspended materials, and dissolvedorganic material in varying amounts, thewater used in a humidification system hasa direct effect on system performance.

Deionized water is purest and, along withwater treated by reverse osmosis, is oftenrecommended for hospitals, cleanroomsand other installations requiring very cleanhumidification steam.

The higher the mineral concentration inthe water supply, the more downtime re-quired for cleaning. Humidification systemsthat are continuously online should usedemineralized water (deionized or reverseosmosis). Systems using softened watercan operate several seasons without clean-ing (yearly inspections are recommended).

Step 5: Determine equipment placement to ensure proper absorption

Humidification systems include a vaporor steam generator and a dispersionassembly. While the steam generator maybe placed in numerous locations, place-ment of the dispersion assembly is cru-cial. Allow adequate absorption distanceso that dispersed steam is absorbed intothe airflow before it comes in contactwith duct elbows, fans, vanes, filters orany object that may cause condensationand dripping.

Step 6: Establish control systemparameters for best performance

As the final step to humidificationdesign, the control system will determineday-to-day operation. Three primaryfactors affect performance and comfortlevel, and should be determined in thedesign process. These include desiredrelative humidity set point, acceptableRH fluctuation and space temperature.

Carefully considering these six steps willhelp you design an efficient, cost-effec-tive humidification system that meetsthe specific requirements of the facility.

About the author:Bob Nelson is director of sales and marketing for DRI-STEEM Humidifier Company. He has 21 years of experience in the HVAC industry,including 15 years in humidification and sixyears in building design.