Appliance Design - April 2009 - (Page 26) $0 Kathabar S.G. Wheel Subcool & Reheat COOLING TECHNOLOGIES Equipment Owning Cost 3 Year Utility Cost 3 Year Maintenance Cost Total 3 Year Cost of Ownership Kathabar $69,259 $17,542 $1,482 $88,283 S.G. Wheel $60,016 $54,984 $986 $115,986 Subcool & Reheat $38,273 $57,009 $782 $96,064 Estimated cost of a project comparing a liquid desiccant system to a dry desiccant system and a conventional cooling system. – removing moisture and preparing the material for reuse – is low when compared to chilling the air below its dewpoint. Regenerating the desiccant is the biggest cost factor. The reason it must be regenerated is that a desiccant is a hygroscopic substance that attracts and holds water molecules from the surrounding air. Desiccants have a low surface vapor pressure, says Meyers, and if the desiccant is cool and dry and its surface vapor pressure is low, it can attract mois- ture from the air, which has a high vapor pressure when it is moist. After the desiccant becomes wet and hot, its surface vapor pressure is high, and the material is saturated and will not absorb additional moisture. This is when it goes through the regeneration process. The material is subjected to heat to remove the moisture. Dry desiccant systems must be heated to about 300 DegF, while temepratures as low as 130 degF can be used on liquid desiccant systems. Our pumps for more efficiency! Give free rein to your ideas. Your requirements are our drive – and have been for more than 60 years. HANNING's sophisticated and customized pumps and drive systems in synchronous technology result from a close contact with our worldwide customers. If you wish highest efficiency and lowest ppm rates come to HANNING. Challenge us! HANNING ELEKTRO-WERKE GmbH & Co. KG · Holter Straße 90 D-33813 Oerlinghausen · Tel +49 (5202) 707-0 · Fax +49 (5202) 707-301 info@hew.hanning.com · www.hew.hanning.com This continual process of regeneration is a major source of energy consumption. Heating the desiccant is usually done with steam, hot water, direct and indirect gas heaters and burners, or through electric heaters. In addition, if a liquid desiccant is used, the side stream of desiccant solution must be cooled before reuse, which also uses energy. In all, factoring in the power to run the desiccant dehumidifier and regenerate the material, a typical liquid desiccant system will use 1,800 BTUs per pound of moisture. In comparison, dehumidifying with a vapor compression system takes about 970 BTUs per pound of moisture. To reduce energy consumption, liquid desiccant suppliers have developed various ways to use alternative energy sources to regenerate the desiccant and cool the desiccant solution after reactivation. Instead of using electricity for the energy to remove the moisture, waste heat can be used, and waste heat is a resource that almost every company has, says Harvey. Many companies, he says, have waste heat streams that reach the required temperature. If the waste heat falls short of the 170 DegF mark, a common temperature to regenerate liquid desiccant, a staged system can be used that will incorporate heaters to elevate the temperature up to the required level, says Brian Demers, an application engi- neer with Kathabar. To cool the desiccant, many buildings use water from coolant towers and other frequently occurring sources. The most common wasteheat sources are boiler systems. A secondary coil runs from the boiler and through the desiccant solution, which heats it to the reactivation level. Another method, while not commonly used, is the waste heat from a combined heat and power (CHP) system. A DOE analysis that studied CHP and desiccant systems, found that an 84,000 scfm liquid desiccant system could be reactivated with the waste heat from a 2 MW CHP reciprocating engine or a bank of microturbines. Desiccants used in a 5,000 scfm system could be regenerated by a 30 kW to 100 kW CHP engine or microturbine. In a similar scenario, such as the hybrid desiccant dehumidification system and natural-gas fired absorption chiller, the combustion of the natural gas used to power the chiller can be used to regenerate the desiccant. Solar energy is another power source that has been successfully used to regenerate liquid desiccants. Other applications used solar panels, which Demers says can easily heat water to 200 DegF. Another form of wasted energy comes in the form of exhaust air, which some suppliers are capturing and using to control both latent cooling AD04094Hann.indd 1 26 applianceDESIGN April 2009 3/16/09 10:14:50 AM www.applianceDESIGN.com http://www.hew.hanning.com http://www.hew.hanning.com http://www.appliancedesign.com
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