The HVAC&R industry continues to evaluate low global warming potential (GWP) alternatives to R410A. This paper reports the performance of a4 RT commercial rooftop heat pump with R410A as a baseline along with potential alternatives DR-55 (R452B), DR-5A (R454B), and R32. Anadjustable frequency drive (AFD) was used to allow the same capacity to be achieved with each refrigerant.

Measurements of performance at the AHRI Standard 210/240 rating points were made with each refrigerant. In addition, tests were run under outdoortemperatures ranging from 65°F to 125°F (18°C to 52°C). A simple thermodynamic cycle model that matches average saturation temperatures in theevaporator and condenser along with a common compressor isentropic efficiency indicates that the capacity with DR-55 should be 2.5% lower than withR410A and should have an efficiency 1% higher. Actual performance with DR-55 matched the capacity of R410A at the same compressor speed (60Hz) with an efficiency 4% higher. Similarly positive results were obtained with DR-5A. With R32, the compressor speed needed to be reduced to 55 Hz(−8.3%) to match the baseline capacity. Efficiency was 3% higher than baseline. As expected, R32 produced compressor discharge temperatures (CDTs)that were elevated by 20°Fd (11°Cd) and increased to 45°Fd (25°Cd) at the higher ambient conditions over R410A while DR-55 and DR-5ACDTs were only 10°Fd (6°Cd) above the baseline.

The results here demonstrate that DR-55 (R452B) and DR-5A (R454B) are "design compatible" alternatives to R410A. That is, they can be useddirectly in existing equipment designs with very little modification (other than those that might be needed to accommodate their "2L" mildly flammableclassification) while producing performance very similar to R410A.