WEST LAFAYETTE, Ind. - Researchers at Purdue University have developed a technique that saves energy and reduces servicing time and costs by indicating when air conditioners are low on refrigerant. According to James Braun, professor of mechanical engineering, the new “virtual refrigerant charge sensor” is particularly practical for automotive air conditioners, which tend to leak refrigerant more than other types of units, and also for residential central air conditioning units.

Maintaining the proper refrigerant charge 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,” said Braun. “It’s also very time consuming and costly to have a technician check the refrigerant and charge it up to specification. To accurately learn how much charge is in the system, you have to remove all of the refrigerant and weigh it, a procedure that requires a vacuum pump and is quite time consuming.”

The new technique works by using sensors to monitor the temperature of refrigerant at various points along the tubing in an air conditioning unit. It is easy to use because the sensors are simply attached to the outside of the tubing, Braun said.

Researchers tested the system on various types of air conditioners running on R-22 and R-410A refrigerant. The research has been funded by the California Energy Commission through its Public Interest Energy Research (PIER) program.

Findings were detailed in a research paper presented during the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Annual Conference held in Louisville, Ky. The technique also was described in a paper published in the journal HVAC&R Research. The paper was written by Braun and former mechanical engineering doctoral student Haorong Li, who is now an assistant professor of architectural engineering at the University of Nebraska.

Another research project at Purdue is nearing completion and has involved a more extensive evaluation of the virtual refrigerant charge sensor. The project, also funded through California's PIER program, has been led by graduate student Woohyun Kim.

Purdue has applied for a patent on the technique. Li and Braun created a software algorithm that interprets temperature sensor data to estimate the amount of refrigerant in the system.

Braun said that automotive air conditioning units equipped with the virtual refrigerant charge sensor could activate a warning light on the vehicle’s dashboard. Technicians servicing residential air conditioners might simply plug a personal digital assistant into the unit to read the refrigerant charge information.

“The method could be commercialized if a company invested some time in the implementation side,” said Braun.

For more information, Braun can be reached at jbraun@purdue.edu.

Publication date: 07/27/2009