Engineers at Purdue University in West Lafayette, IN, have developed a technique that saves energy and servicing costs by indicating when air conditioners are low on refrigerant. The virtual refrigerant charge sensor is especially practical for automotive air conditioners, which leak refrigerant more than other types of units, and for household central air conditioning units, says James Braun, professor of mechanical engineering at Purdue. Maintaining the proper charge, or amount of refrigerant in a system, saves energy because air conditioners low on refrigerant must operate longer to achieve the same degree of cooling as properly charged units. “Not only does the energy efficiency go down, but you also reduce the lifetime of the unit because it has to work harder, causing parts to wear out faster,” Braun explains. However, checking refrigerant and charging it to specification is a costly and time-consuming process, requiring a technician to remove the refrigerant and weigh it using a vacuum pump. The new technology would eliminate periodic refrigerant checks by using sensors to monitor the temperature of refrigerant at various points along the tubing in an air-conditioning unit. Braun and colleagues created a software algorithm that interprets temperature-sensor data to estimate the amount of refrigerant in the system. Four sensors are attached to tubing running into and out of components called heat exchangers. In air conditioning and refrigeration systems, liquid refrigerant evaporates in a heat exchanger called an evaporator, cooling the air. The refrigerant vapor turns back into a liquid in another heat exchanger called a condenser. During these steps, the refrigerant undergoes dramatic temperature changes. Automotive air conditioning units equipped with the new refrigerant-charge system could activate a warning light on a car’s dashboard. Technicians servicing home air conditioners might simply plug a personal digital assistant into the unit to read the refrigerant-charge information, Braun explains. The researchers tested the system on various types of air conditioners running on conventional refrigerants, including R-22 and the more environmentally friendly R-410A, which replaces R-22 in new units. Their findings were published in HVAC&R Research. Purdue has applied for a patent on the technique. “The method could be commercialized if a company invested some time in the implementation side,” Braun says.

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Posted July 1st, 2009 under Tech Transfer

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