PSYCHROMETRICS for Engineers


		Desiccant Dehumidifiers and Humidity Control Desiccants and Desiccant Dehumidification Desiccant Dehumidifier Manufacturers Cooling Dehumidification Manufacturers Other Humidity Control Information Sources 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 MSP Technology, 223 Wall Street #140, Huntington, NY 11743 phone: 631 424-7542 fax: 631 980-7607 e-mail: MSPtechnology 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
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