Taking New Refrigerants to the Peak
But how can those new refrigerants operate at peak performance? Engineers at the recent Purdue University Refrigeration Conference here reported that they are still tinkering with such a task.
Retooling R-22 Units to Use R-410AOne report demonstrated the need for significant retooling of equipment that long used R-22 in order to operate successfully with R-410A.
Engineers at the National Institute of Standards and Technology (NIST) noted “an increased degradation of performance for fluids [such as 410A] having a low critical temperature. [They] will tend to have a higher volumetric capacity and a lower COP.”
Because of this, “R-410A in particular would benefit from heat exchangers’ optimization because of its small change in saturation temperature for a given pressure drop, and a postulated improved compressor efficiency due to the low pressure ratio.”
And what of R-407C, which is supposed to operate in more traditionally configured R-22 equipment? Accord-ing to a study from Matsushita Refrigeration Co., of Osaka, Japan, “We were able to vary the [R-407] refrigerant composition [from 23% R-32, 25% R-125, and 52% R-134a, to 6/14/80%], and thus to control the system capacity.”
The study reported on the development of a refrigerant composition control system, “which improves the system performance in capacity saved operation just like [an] inverter system under lower air conditioning load by using a constant-speed system, thereby realizing remarkable improvements in the annual SEER.”
Other methods of making new alternatives work well were reported by Centre d’energetique Ecole des Mines de Paris. A team of engineers noted, “Both 410A and 404A present low critical temperatures. Consequently, the refrigerating capacity and the energy efficiency of the system decrease substantially when condensing temperature rises.”
The Role of SubcoolingThe researchers turned to subcooling. In one approach, they used what they called the “superfeed” method for screw or scroll compressor systems.
“At the condenser outlet, the refrigerant flow is divided in two. The main flow passes in a heat exchanger located in the ‘superfeed’ capacity at the intermediate pressure of the two-stage cycle. Then the secondary flow is expanded in this capacity and the evaporated refrigerant is sucked at the intermediate pressure of the compressor.”
A second method “is to subcool the refrigerant flowing out of the condenser using an auxiliary refrigerating cycle. This method is known to yield energy savings, and to increase significantly the main system refrigerating capacity, while necessary modifications are simple and inexpensive compared to new system purchases.”
Three Refrigerants, One CompressorThermal Technology Centre of the National Research Council Canada in Ottawa, ON, Canada, wanted to find out what would happen in terms of efficiencies if R-22, -407C, and -410A were used with one compressor.
“Previous studies have used different types and sizes of compressors to directly compare the capacity and performance differences of these refrigerants. The objective of this investigation is a comparison of these three refrigerants using the same compressor operating at different speeds, [supplying the same cooling capacity] to provide a more accurate indication of the system differences of the long-term replacements.”
Among their findings:
- R-407C had a heating capacity 5% higher than R-22 at the high-temperature test condition, and 12% higher than R-22 at the low-temperature test condition.
- The heating capacity of R-410A ranged from 1% to 3% lower than R-22.
- The heat pump cooling energy efficiency ratio of R-407C ranged from 5.7% to 11% lower than R-22.
- The EER of R-410A range from 21.4% to 4.3% higher than R-22.
- Compared to the other two refrigerants, the EER of R-410A also decreased much more rapidly at the high and extreme operating temperature test conditions. “This is due to the lower critical temperature of R-410A,” the report said.
Publication date: 08/28/2000