Oval-Tube Condenser Cut R-32 Charge 44.2 Percent in Split Heat Pump Tests
In the preprint, required charge fell 44.2 percent with R-32 and 13.7 percent with R-410A. Cooling capacity rose 4.3 to 4.8 percent, and R-32 posted the highest COP of the three refrigerants by 8.3 percent.
Swapping a conventional fin-and-tube condenser for a compact oval-tube design cut the refrigerant charge a residential split heat pump needed by 44.2 percent on R-32 and 13.7 percent on R-410A, according to a study now in the December issue of the International Journal of Refrigeration. Cooling capacity rose 4.3 and 4.8 percent for those two refrigerants.
The journal version sits behind Elsevier's paywall and its abstract could not be retrieved for this article. The figures here come from the authors' preprint abstract, posted to SSRN in March under the title "Experimental investigation of the heat pump performance based on an oval-tube heat exchanger." Bibliographic databases link the two records as one work, but numbers can change between a preprint and the published paper.
Charge, Capillary Length and Three Refrigerants
The team ran R-410A, R-290 and R-32 in the same heat pump across several refrigerant charges and capillary tube lengths. The authors describe the oval-tube heat exchanger as reducing condenser volume and mass while transferring heat better than fin-and-tube coils. With it, compressor power fell 2.4 percent on R-410A, 7.4 percent on R-290 and 12.9 percent on R-32. COP rose 1.3 percent for the R-410A and R-32 systems, and R-32 with the oval-tube unit beat the other refrigerants on COP by 8.3 percent.
The authors are A. Haggag, M.A. Said, Walid G. Alshaer, Shinsuke Mori and A.A. Hawwash. Haggag's ORCID record lists him as head of air conditioner development at the Elaraby Group R&D Center, and Mori's lists an associate professorship in chemical science and engineering at Tokyo Institute of Technology. Affiliations for the other three could not be confirmed.
Why This Matters to Contractors
ASHRAE 15.2 Addendum f sets R-32's m1 charge level at 4.0 pounds, the same figure it lists for R-454B, so a percentage cut matters most when it carries a system across that line. The abstract reports only percentages, without the absolute charge in pounds or the system's nominal capacity, and that is the number that would show whether a residential split moves under the threshold. A charge measured on one laboratory rig also leaves out the line-set length that adds refrigerant on an actual install.
Sources
- A. Haggag, M.A. Said, W.G. Alshaer, S. Mori and A.A. Hawwash, "Experimental investigation of R410A, R32, and R290 in a residential split heat pump integrated with an oval-tube heat exchanger," International Journal of Refrigeration, vol. 192, 107147, December 2026. doi.org
- A. Haggag et al., "Experimental investigation of the heat pump performance based on an oval-tube heat exchanger," SSRN preprint, 2026. doi.org
- Crossref metadata record for the preprint, including its abstract. api.crossref.org
- ASHRAE, Addendum f to ANSI/ASHRAE Standard 15.2-2022, approved July 31, 2024. ashrae.org