Conference Year

2016

Keywords

alternative refrigerants, rooftop unit, component performance

Abstract

Growing concerns about the impact on the environment of the refrigerants used in HVAC&R equipment are driving development and evaluation of alternative refrigerants with lower global warming potentials (GWPs). A new refrigerant blend, labeled DR-55, has been developed to be a design-compatible alternative to R410A. The composition was selected to closely match the capacity of R410A. DR-55 has the same GWP as R32 while having a lower burning velocity than R32 and DR-5A. Additional benefits include slightly higher thermodynamic efficiency than R410A, significantly lower compressor discharge temperature than R32, and slightly lower sensitivity to ambient temperature than R410A (ie, better capacity and efficiency at high ambient temperatures). The characteristics of DR-55 have been introduced by Kujak and Schultz (2015) and Kujak and Schultz (2016a). DR-55, DR-5A, and R32, along with R410A as baseline, have been tested in a 4-RT commercial unitary rooftop unit (RTU) in both heating and cooling modes. Overall unit performance has been reported by Schultz, et al (2015a,b) and by Kujak and Schultz (2016b). DR-55 and DR-5A were observed to have performance characteristics very similar and even superior to expectations based on their thermodynamic properties. This paper will report the performance of DR-55, DR-5A, and R32 in comparison to R410A at the component level in the rooftop unit tests. Analysis of refrigerant-side pressure drop and heat transfer performance in the evaporator and condenser will be presented. The lower mass flow rates associated with the alternate refrigerants (wider domes) compared with R410A produced lower effective temperature glides in the evaporator and resulted in higher pressures entering the compressor. This benefit was offset partially by slightly higher condensing saturation temperatures than R410A. Compressor performance in terms of volumetric and isentropic efficiencies was observed to be relatively insensitive to the refrigerant present. Samples of DR-55 refrigerant were obtained before and after simulated leak/recharge events. Measurement of the compositions indicates that there was essentially no fractionation of the DR-55 (glide of ~2°Fd) while the unit was running under steady-state conditions and no shift in composition despite the repeated leak/recharge events.  Kujak and Schultz, 2015, “Performance Comparison of Optimized R410A Replacements”, Proceedings of the 24th International Congress of Refrigeration ICR2015, Yokohama, Japan, Aug 16-22, 2015. Kujak and Schultz, 2016a, “Optimizing the Flammability and Performance of Next Generation Low GWP R410A Replacements”, conference paper to be presented at the 2016 ASHRAE Winter Conference, Orlando, Jan 24-27, 2016. Kujak and Schultz, 2016b, “Performance of a 4 Ton Rooftop Unit with Low GWP R410A Alternatives”, conference paper to be presented at the 2016 ASHRAE Annual Meeting, St. Louis, Jun 25-29, 2016. Schultz, Perez-Blanco, and Kujak, 2015a, “Test Report #56 – Soft-Optimized System Test of R410A, DR-55, R32, and DR-5A in a 4-Ton Unitary Rooftop Heat Pump, Cooling Mode Performance”, submitted to AHRI’s Low GWP Alternative Refrigerants Evaluation Program. Schultz, Perez-Blanco, and Kujak, 2015b, “Test Report #57 – Soft-Optimized System Test of R410A, DR-55, R32, and DR-5A in a 4-Ton Unitary Rooftop Heat Pump, Heating Mode Performance”, submitted to AHRI’s Low GWP Alternative Refrigerants Evaluation Program.

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