Dehumidifying Heat Pipes for Air Conditioning

Dehumidifying Heat Pipes for Air Conditioning
In order to make a room comfortable in hot, humid climates, an air conditioner must lower the indoor humidity level as well as the air temperature. If an air conditioner fails to lower the humidity adequately, the air will be cool, but will feel uncomfortably damp. Inappropriately sized air conditioners are prone to this problem. Large units quickly cool the air, but cycle off before they can properly dehumidify it.

One technology that addresses this problem is the dehumidifying heat pipe. It is a device that enables an air conditioner to dehumidify better and still efficiently cool the air. It does not need additional electricity to operate. The heat pipe is ideal for hot, humid environments.

A dehumidifying heat pipe resembles two heat exchangers, located on either side of the air conditioner's evaporator coil. Several tubes connect the two sections. A refrigerant (usually an HCFC) inside the tubes pre-cools the incoming supply air by absorbing the heat from it. This causes the refrigerant in the tube to evaporate. The air conditioner evaporator takes the pre-cooled cools it further, extracting up to 91% more water vapor than a conventional evaporator would. After the refrigerant in the tubes changes into a vapor, it flows to the condensing section at the other end of the system. There, it releases its heat into the air stream and returns to its liquid state again. It then flows by gravity to the evaporator end of the pipe to begin the cycle again.

The dehumidifying heat pipe is used mostly in commercial and industrial applications. To test the effectiveness of heat pipes, the Florida Solar Energy Center installed one of these systems in a 45,000 square foot (4,180.5 square meter) warehouse belonging to a large candy manufacturer in Albany, Georgia. Humidity in the facility had to be kept below 40% to properly store large quantities of Christmas candy. Before the addition of the dehumidifying heat pipe, an oversized air conditioner equipped with electric resistance re-heating coils was used to adequately dehumidify the warehouse. The system's operating cost was $140,000 per year. The study found that the dehumidifying heat pipes, along with other modifications to the cooling system, reduced the candy factory's air conditioning bill by 60%, and paid for itself in less than a year.

Most models of heat pumps and air-conditioners can be retrofitted with dehumidifying heat pipes. They can also be built into new heat pump or air-conditioner heat exchanger coils. Heat pipes save electricity in another way as well. They allow the cooling system to be reduced in size. They can also be used to help heat domestic hot water. To do so, a heat exchanger transfers the heat extracted by the pipes to a water tank.Thomas Register of Manufacturers online or at your local public library for names and addresses. --

The following articles provide additional information on using dehumidifying heat pipes.

"Cool Savings for Muggy Climates," V. Gilmore, Popular Science, (231:5) p. 30, November 1987.

Design and Technology of Heat Pipes for Cooling and Heat Exchange, C. Silverstein, Hemisphere Publishing Corporation, 1992. 550 pp. ISBN: 0891168591.

"," Environmental Building News, (7:6) June 1998.

"Heat Pipe Defeats Mold, Mildew; Saves Energy in Humid Houston," G. Schulz, , pp. 11-13, March 21, 1994.

"Heat-Pipe Heat Pump," C. Gilmore, , (231:6) p. 51, December 1987.

Heat Pipes (4th Ed.), P. Dunn, Elsevier Science, 1994. 358 pp. ISBN: 0080419038.; World Wide Web: . --

Heat Pipe Technology: Theory, Applications and Prospects, Proceedings of the 5th Heat Pipe Symposium, Melbourne, Australia, 17-20, November 1996, Elsevier Science, 1997. 464 pp. ISBN: 0-08-042842-8.

"HVAC Retrofit Job Using Heat Pipes Brings Utility Rebate to Fla. Center," , p. 73, April 13, 1992.

"Surrealism and the Real World of Heat Pipe Technology," P. Kelsey, , pp. 23, July 16, 1995.