It’s one thing to announce new refrigerants, but it’s another to figure out how they will work in real-life situations. With the industry facing an apparent shift to low-GWP (global warming potential) refrigerants, the performance of those gases is being carefully studied.

At the most recent 15^th International Refrigeration and Air Conditioning Conference at Purdue University — one of three concurrent conferences, the others dealing with compressors and high-performance buildings — a number of researchers presented papers as part of an “Alternative Refrigerant Performance Comparison” program.

Chillers

A familiar hydrofluorocarbon (HFC) is R-32 because it is used in a blend with HFC-125 to create R-410A. Now, it is being looked at as a stand-alone refrigerant because it has a lower GWP than -410A.

In that context, a paper, “Energy Efficiency of a Chiller Using R-410A or R-32” was presented by Claudio Zilio on behalf of colleagues at Emerson Climate Technologies Inc. in Germany and the University of Padova in Italy.

The paper asserted that, “based on the proposed modeling work, R-32 system efficiency performance is acceptable as alternative to R-410A for water chillers.”

Additionally, researchers noted they would continue to examine hydrofluoroolefin (HFO) refrigerants in regards to chillers.

Refrigeration

Gustavo Pottker presented on behalf of engineers at Honeywell Intl. Inc. The topic, “Refrigerants with Low Environmental Impact for Refrigeration Applications,” considered two refrigerants: one, N-40, is nonflammable, and the other, HDR-110, is said to be mildly flammable.

The company also noted the GWP of HDR-110 is below 150, which will allow its use in certain applications under European Union f-gas regulations.

“N-40 may be used in current refrigeration systems based on preliminary findings, providing a great reduction of environmental impact,” Pottker stated, concluding his presentation. “This is mainly due to its reduction of GWP and significantly higher efficiencies. Both internal and external large-scale lab evaluations were consistent in showing N-40 has a superior energy efficiency compared to [HFC]-404A with improvements between 3 and 11 percent.

“Other options, such as HDR-110, provide further reduction of GWP and may be used in self-contained systems capable of working with mildly flammable refrigerants in the future. Experimental evaluations of HDR-110 conducted in a R-404A reach-in freezer showed lower energy consumption and a near match in capacity. However, more work is needed to fully explore potential applications of this refrigerant in such systems.”

HFO Aspect

A paper presented by Charles Janicki of Marquette University, speaking on behalf of the university and Rexnold, dealt with efforts to bring HFOs (one of which, 1234yf, is being used in automotive air conditioning) to stationary systems. Research is underway in conjunction with 1234yf and a room air conditioner designed to work with R-410A. The undergraduate students at Marquette reported the first step in the redesign process was “to develop a thermodynamic model of the existing RAC. The model was then modified to provide the same cooling capacity as the original unit using R-1234yf, and a replacement compressor was selected based on the model results.”

Researchers then broadened their reach, considering 1234yf and 1234ze. Regarding the latter, the report stated, “While the team was able to modify the RAC to operate with R-1234ze, and was able to predict the unit’s performance with reasonable accuracy, the modifications required a significantly larger compressor and capillary tubes; therefore, the project clearly illustrated that fitting within the space and weight constraints of window units presents a significant challenge to implementing R-1234ze in RACs.”

Elevated Ambient

And what of all those low-GWP refrigerants that might need to be used in high-ambient situations? That was one of the tasks tackled by Kenneth Schultz, lead engineer, technology validation group, Ingersoll Rand. He used a 15.5-kW air-cooled water chiller/heat pump for testing a number of refrigerants, some with R-410A-like pressures and some with R-22-like pressures.

Schultz found that: “R-32 offers potential for increased capacity and efficiency compared to R-410A with high-ambient characteristics similar to R-22. DR-5 offers characteristics very similar to R-410A with a somewhat elevated compressor discharge temperature that did not exceed the limit until reaching 122°F air temperature for the equipment tested. L-20 has characteristics very similar to R-22; compressor discharge temperatures are only slightly elevated, possibly being an issue in the equipment tested as air temperature approaches 122°.”

Evaporative Cooling

Alexis Nicolette-Baker, test engineer, Parker Hannifin Corp., presented a paper, “Experimental Performance Investigation of New Low-GWP Refrigerants for Use in Two-Phase Evaporative Cooling of Electronics,” on behalf of research conducted by herself and colleagues at Parker Hannifin Corp.

“The study investigated four potential refrigerants: R-1234yf, R-1234ze, N-13a (HDR-17), and N-13b (HDR-15). R-134a was used as benchmark.

“Each of these refrigerants was experimentally examined and compared to R-134a in a two-phase pumped-loop cooling system using a specifically designed test stand,” Nicolette-Baker said. “This test stand included a liquid pump, an evaporator with a heating component, and an air-cooled condenser.”

She continued: “The results indicated that R-134a had the best performance in terms of its required volume flow rate for a given heat load as well as its overall heat transfer coefficient and two-phase pressure drop at a given mass flow rate. While the former characteristic is important for pump sizing, the latter can have a significant impact on overall thermal resistance.

“With an average volume flow rate increase of 8 percent, N-13b exhibited the best performance in terms of flow rate when compared to R-134a. R-1234yf closely matched the heat transfer coefficient values of R-134a. R-1234yf also showed 39 percent higher two-phase pressure drop, which was better than the other candidates.”

Publication date: 10/6/2014

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