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The Bromide Absorption Cycle

            The average person usually thinks of chlorofluorocarbons or hydrofluorocarbons when the word 'refrigerant' is used. Names like Freon, Suva, Forane, R-22, R-12, R-134A   ordinarily spring to mind. But ordinary water becomes an excellent refrigerant when it is combined with ammonia or a unique salt made of lithium and bromide.

            Two keys to the understanding of the lithium bromide absorption refrigeration cycle are:
            Similar to the ammonia absorption cycle, refrigerant vapor from the evaporator is absorbed by a solution mixture in the absorber. This solution is then pumped to the generator. In the generator, the refrigerant re-vaporizes using a heat source. The refrigerant-depleted solution then returns to the absorber.

            We will start this illustration at the evaporator. The evaporator chamber is is under a high vacuum of about 29.8 in.Hg. At this pressure, water boils at 35°F . The water is then pumped through spray heads into the evaporator. The high vacuum causes the water to vaporize. In order for the water to vaporize, it must draw heat from its surroundings. In this case, the water draws heat from the chilled water tubes in the evaporator bundle. It removes heat from the circulating chilled water. Water at about 40°F is evaporated off the chilled water tubes, thereby bringing the temperature of the circulated chilled water down from approximately 54°F being returned from the air handlers to the required 44°F chilled water supply temperature.

            Next, the water vapor flows to the absorber section. The absorber is filled with water vapor. Lithium bromide salt solution is pumped out from a spray head into the absorber. As the lithium bromide mist solution is sprayed out, it comes in contact with the water vapor. This water vapor is absorbed by the concentrated lithium bromide solution. The heat of vaporization and the heat of solution are removed using cooling water at this step. The lithium bromide/ water solution is then pumped to the concentrator.

            In the concentrator, heat is applied (using steam or hot water) to drive off the water and thereby re-concentrate the lithium bromide.    The water driven off by the heat input step is then condensed (using cooling tower water), collected, and then sent back to the evaporator to repeat the cycle.

            Most commercial absorption chillers use lithium bromide. Lithium bromide has a very high affinity for water, is relatively inexpensive and non-toxic. However, it can be highly corrosive and disposal is highly regulated.

            Compared with mechanical chillers, absorption chillers are relatively inefficient. However, absorption chillers can be cost-effective to operate if they are powered by low-grade heat, low-cost heat or are powered by a source of waste heat . Vapor compression chillers, by contrast, must be always be electric motor or gas, diesel propane engine-driven.

            Is an absorption chiller right for your building?   Absorption cooling may be worth considering if your building requires cooling, and if at least one of the following applies:
           In short, absorption cooling may fit when a source of free or low-cost heat is available, or if objections exist to using conventional refrigeration. Essentially, a low-cost heat source offsets the higher-cost electrical source which would power a conventional chiller.

            To evaluate the cost-effectiveness of a waste-heat absorption chiller in your commercial building by, first consider :
           Finally,   If you have a steam system of any kind, you should study the information provided at www.oit.doe.gov/bestpractices/steam/.  The web site is full of tips and information to improve productivity and increase profits by using BestPractices tools for your building.

www.Dr-Fix-It.Com: The Ammonia Absorption Cycle

Absorption Cooling An informative document on Absorption Cooling by American Yazaki.

Absorption Chiller System Go to: Products,  Commercial Products,  Absorption Chiller

 Refrigeration Specialties  Parker Products





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