R O T R O N I C H U M I D I T Y F U N F A C T S

Ventilation Systems

Humidity in ventilation systemsVentilating is the process of chang-ing or replacing air in any space toprovide high indoor air quality. Inorder to maintain an office buildingwithin the comfort zone, or to main-tain any application specific climateconditions, humidity plays a key role.

Various equipment can beadded into air handling units toeither remove or add moisture.

The most common way todehumidify air in an air handlingunit is to regulate the cooling coilbelow the dew point and removehumidity by condensation. In mostcases it is necessary to reheat theair afterwards via a heating coil.

To increase humidity, a contacthumidifier can be used where theair passes through or over a wet

surface where it picks up additionalwater vapor to be introduced to theenvironment. A similar process isused with an air washer unit wherewater nozzles spray water aerosolinto the air stream. Water can alsobe added by an ultrasonic humidi-fier where a piezo-electric trans-ducer creates a high frequencymechanical oscillation in a body ofwater. An extremely fine mist isemitted which is quickly absorbedinto the air flow.

Each of these methods requirefrequent cleaning. Also, the passingair not only absorbs humidity butalso loses some heat energy (adia-batic cooling). Therefore, an addi-

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tional heating coil after the humidi-fier is usually required.

Direct steam injection is themost common form of humidifica-tion. These types of devices requirevery little maintenance because thesteam supply acts as a cleaningagent. However, the steam produc-tion and distribution is expensiveand is only cost effective for largerbuildings.

For accurate control of humid-ity, the distance between thehumidifier and the measurementprobe must be long enough toensure full mixing of the air andwater vapor.

Clockwise fromabove: Classroomwithout air condi-tioning . . . Large airhandling unit . . .evaporative cooler.

Facts & Figures The Beverly Briley building inNashville, Tennessee currently has thelargest installed air handling unit in theworld. It is capable of delivering 9,970cubic metres per minute.

The first air conditioner was inventedby Willis Carrier in 1902. He worked at apublishing company and needed a wayto keep his paper from expanding andink from running.

The revered summer break from schoolwas a necessity before the invention ofair conditioning. The schedule persiststoday even with the availability of mod-ern air handling units.

2135 Engineers Road, Hauppauge, NY 11788 Tel. 631-427-3898 Fax. 631-427-3902 info@rotronic-usa.com

Why the need to measure humidity?Controlling the temperature andthe humidity levels in a buildingusing an air handling unit will have an impact on the following: The humidity level plays animportant role in the felt temperature also known asheat index. Generally, the temperature feels colder whenthe humidity level is lower andvice versa.

Humidity level below 30%rh, thatare particularly common duringthe heating period, promoteitchy and cracked skin, irritatedeyes and chapped lips. Dry airalso dries the shield of mucus inairways that protects againstbacteria, viruses and airbornepollutants increasing the risk ofinfections.

On the contrary, high humiditylevels directly affect the amountof allergens in the indoor envi-ronment. In particular, highhumidity causes both dust mitepopulations and mold coloniesto grow.

An ideal humidity level for placeswhere people live and work isbetween 45 and 50% RH.

Dry air can cause wooden furni-ture to crack and paper to stick in printers.

R O T R O N I C H U M I D I T Y F U N F A C T S

Moist air can cause mildew onsurfaces and, with time andextreme levels, even concretewill start to dissolve.

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ORK) [CC BY-SA 3.0 (HTTP://CREATIVECOMMONS.ORG/LICENSES/BY-SA/3.0)],

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Evaporative Cooler Air Exchange