Desiccant Dehumidifiers and Humidity Control

Desiccants and Desiccant Dehumidification

Desiccant materials have a high affinity for water vapor. Typically their moisture content is a function of the relative humidity of the surrounding air. Exposed to low relative humidities desiccant materials come to equilibrium at low moisture contents and exposure to high relative humidities results in equilibrium at high moisture contents. Virtually all materials exhibit desiccant type behavior but the term desiccant is reserved for materials for which this behavior can be exploited to produce some predictable and useful result

Two major categories of desiccants are absorbents and adsorbents. Absorbents go through a chemical change as they attract and retain water vapor. Lithium Chloride is probably the most common absorbent type desiccant. The LiCl and water combination results in a liquid solution after each LiCl molecule has absorbed three water molecules. LiCl continues to absorb water even after a solution has formed. Adsorbent materials hold water molecules in pores at their surface, no chemical change results. Absorbents generally can attract and hold greater quantities of water per pound of desiccant material however the issue of handling a liquid becomes a primary consideration.

A desiccant dehumidifier is a device that employs a desiccant material to produce a dehumidification affect. The process involves exposing the desiccant material to a high relative humidity air stream, allowing it to attract and retain some of the water vapor and then exposing the same desiccants to a lower relative humidity air stream which has the affect of drawing the retained moisture from the desiccant. The first air stream is the air that is being dehumidified while the second air stream is used only to regenerate the desiccant material so that it is ready to begin another cycle. Note that the first air streams water vapor content is reduced while the second air stream's water vapor content is increased. Typically the low relative humidity air stream is air taken from any available source and heated to reduce it's relative humidity. Hence desiccant dehumidifiers consume heat energy to produce a dehumidifying affect.

In general a desiccant dehumidifier is comprised of four major components. The component that holds the desiccant of which there are several types, a fan to move the air to be dehumidified (process air) through the desiccant holder, a fan to move the low humidity air for drying the desiccant through the desiccant holder and a heater to heat the air that will be used to dry the desiccant (regeneration air).

Some desiccant dehumidifiers use a cyclical type of operation where the desiccant is packed into a container through which the air to be dehumidified is passed. When the desiccant in the container reaches a certain level of moisture content a low humidity air stream is then passed through the container until the desiccant is dry enough to be used for dehumidifying again (regenerated). When two containers are used one can be dehumidifying while the other is being regenerated and vise versa. These types of machines produce varying levels of dehumidification due to the rising moisture content of the desiccant during the dehumidifying stage.

There are also non-cyclical types of desiccant dehumidifiers where the desiccant is contained by some type of rotating bed or extended surface wheel. Both process and regeneration air streams are passing through separate sections of the desiccant bed or wheel. The bed rotates slowly (usually less than 20 revolutions per hour). Since the moisture is being moved from the process to the regeneration air streams it is important that these air streams not be allowed to mix or the dehumidification accomplished may be compromised. The effectiveness of the sealing method can have an impact on energy efficiency and on the ability of the machine to produce low humidity air. That is leakage from the regeneration air stream to the dehumidified process air stream will raise the humidity level of the delivered process air

References on Desiccant Dehumidification:

ASHRAE Handbooks
ASHRAE Handbooks are a series of five reference books for the HVAC and Refrigeration industry. Each year a new edition of one of the five is published. There is information on desiccants and desiccant dehumidifiers in several of these, especially in the Fundamentals and Systems Handbooks. The handbook layouts change occationally so it is best to check the index for "desiccants", "dehumidifiers", "humidity control" and other related terms

The Dehumidification Handbook
The Cargocaire Division of Munters Corporation produced this reference in 1982 and issued a Second Edition in 1990. It covers nearly all aspects of the subject from psychrometrics to system design. Contact Cargocaire for availability

Publications from Manufacturers
Check with the manufacturers of desiccant equipment for publications explaining their technology

Desiccant Dehumidifier Manufacturers

APPIDI TECHNOLOGIES PVT TLD, SURVEY NO: 123, JEEDIMETLA VILLAGE, QUTBULLAPUR ROAD, HYDERBAD-500055 INDIA
phones: 0091 40 23090494 / 23098864
fax: 0091 40 23090495
e-mail:
hyd2_golden1@sancharnet.in
Web site::www.appidi.com

Bry-Air, Inc., Sunbury, OH, USA
phone: 740 965-2974
fax: 740 965-5470
e-mail: bryair7@aol.com
Web site: www.bry-air.com

Munters Corporation, 79 Monroe St., P.O. Box 640, Amesbury, MA 01913
phone: 978 241-1100
fax: 978 241-1215
e-mail: dhinfo@munters.com
Web site::www.munters.us

Concepts and Designs, Inc., 2100 Park Drive, PO Box 288 Owatonna, MN 55060
phone: 507-451-2198
fax: 507-451-1177
e-mail: sales@cdihvac.com.com
Web site::http://www.cdihvac.com

DehuTech AB, Enhagsslingan 23, 187 40 TABY, Sweden
phone: 0046 8 792 04 08
fax: 0046 8 792 55 59
e-mail: info@dehutech.com
Web site: www.dehutech.co

DryCool Division, Munters Corporation, 16900 Jordan, Selma, TX, USA 78154
phone: 210-651-5018
fax: 210-651-9085
e-mail: dcinfo@munters.com
Web site::www.muntersamerica.com

Dri-Eaz Products, Inc., 15180 Josh Wilson Road, Burlington, WA 98233
phone: (360) 757-7776 or (800) 932-3030
fax: (360) 757-7950
e-mail: info@dri-eaz.com - will be directed to the appropriate department
Web site: www.dri-eaz.com

DryKor, Inc.
205 Carnes Drive
Fayetteville, GA 30214
phone: 678-817-0299
fax: 678-817-1355
e-mail: usa.marketing@drykor.com
Web site: www.drykor.com

Dryomatic, 4600 Wedgewood Blvd. Unit R, Frederick, Maryland 21703
Phone 301 668-8200
Fax 301 668-9922

e-mail:
 vanessa@dryomatic.com
Web Site: www.Dryomatic.com

Humidity Control Systems Ltd, The Green, Nettleham, Lincoln, LN2 2NR, England
phone: 0044 (0) 1522 753722
fax: 0044 (0) 1522 753822
e-mail: dst@hcsltd.wanadoo.co.uk
Web site: www.humiditycontrol.co.uk

Innovative Air Technologies, 8425 Hazelbrand Rd.,Covington, GA 30014
phone: (770)788-6744
fax:(770)788-6745
e-mail: innovativeair@msn.com
Web site: www.dehumidifiers.com

Kathabar Dehumidification Systems Inc., A Niagara Blower Company, P.O. Box 310, Somerville, NJ, USA 08876
phone: 732-356-6000
fax: 732-356-0643
e-mail: kathabar@kathabar.com
Web site: www.kathabar.com

Kathabar Systems Europe, P.O. Box 220, 2700 AE Zoetermeer, The Netherlands
phone: +31 79 3710760
fax: +31 79 3510434
e-mail: kathabar@imtech.nl
Web site: www.kathabar.imtech.nl

Miller-Picking Division, York International, P.O. Box 130, Johnstown, PA, USA 15907
phone: 814 479-4023
fax: 814 479-2469
e-mail:
Web site:

NovelAire Technologies, 10132 Mammoth Ave, Baton Rouge, La 70814
phone: 504/924-0427
fax: 504/930-0340
e-mail: novelair@eatel.net
Website:/www.novelaire.com

ProFlute, Vargmötesvägen 8, SE-186 30 VALLENTUNA, SWEDEN
phone: +46 (0)8 5118 7800
fax: +46 (0)8 5118 7700
e-mail: info@proflute.se
Website:http://www.proflute.se/

SEMCO Incorporated, 1800 East Pointe Drive, Columbia, Missouri 65201-3508
phone: (573) 443-1481
fax: (573) 886-5408
e-mail: aqpinfo@semcoinc.com
Website:www.semcoinc.com

Stulz Air Technology Systems, Inc.,DESICAiR Division 1572 Tilco Drive, Frederick, MD 21704
phone: 301 620-2033
fax: 301 662-5487
e-mail:
info@stulz-ats.com
Web site::www.stulz-ats.com

Cooling Based Dehumidifier Manufacturers

Dectron, Inc., 2697 Int'l Pkwy, #201, Virginia Beach, VA 23452
phone: 800 676-2566
fax: 804 468-9397
e-mail: info@dectron.com
Web Page URL: http://www.dectron.com/

Desert Aire Corp., 8300 W. Sleske Court, Milwaulee, WI 53223
phone: 414 357-7400
fax: 414 357-8501
e-mail: info@desert-aire.com
Web Page URL: www.desert-aire.com

DryAire Systems Corp., 6539 North Sidney Place, Glendale, WI 53209
phone: 414 351-4520
fax: 351-5065
e-mail: Web Page URL:

Dri-Eaz Products, Inc., 15180 Josh Wilson Road, Burlington, WA 98233
phone: (360) 757-7776 or (800) 932-3030
fax: (360) 757-7950
e-mail: info@dri-eaz.com - will be directed to the appropriate department
Web site: www.dri-eaz.com

Dumont Refrigeration Corp., Main Street, P.O. Box 149, Monmouth, ME 04259
phone: 207 933-4811
fax: 207 933-2649
e-mail: Web Page URL:

EBAC Dehumidifiers, 106 John Jefferson Road, Williamsburg, VA 23185
phone: 804 229-3038
fax: 804 229-3321
e-mail: pza@ichange.com
Web Page URL:

Heat Pipe Technology, 4340 N. E. 49th Avenue, Gainesville, FL 32609
phone: 352 367-0999
fax: 352 367-1688
e-mail: heatpipe@heatpipe.com
Web Page URL: www.heatpipe.com

Nautica Dehumidifiers, Inc., 9 East Carver Street, Huntington, NY 11743
phone: 516 424-8030
fax: 516-351-8249
e-mail: Sales@NauticaDehumid.com
Web Page URL: www.NauticaDehumid.com/

Other Humidity Control Information Sources

National Renewable Energy Laboratory - NREL
Advanced Desiccant Cooling and Dehumidification Program
www.nrel.gov/desiccantcool/

Gas Tecnology Institute
Desiccant Systems for Controlling Humidity
www.gri.org/desiccant/

U.S. Department of Energy
Office of Building Technology, State and Community Programs
www.eren.doe.gov/buildings/building_equipment/desiccant.html

Mississippi State University
The Global Center for Desiccant Technology
www.me.msstate.edu/GCDT

Oak Ridge National Laboratory
Desiccant Research and Development
www.ornl.gov/ORNL/BTC/desiccant.html

ASHRAE Technical Committee
TC 3.5, Desiccant and Sorption Technology
www.ashrae.org/techcomm/tc35.htm

American Gas Cooling Center
Building Energy Solutions Center
www.agcc.org/techdes.cfm
Desiccant Q & A Page

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