Performance of a Four-Ton Rooftop Unit with Low GWP R410A Alternatives (ST-16-C064)

The HVAC&R industry continues to evaluate low global warming potential (GWP) alternatives to R410A.  This paper reports performance of a 4 RT commercial rooftop heat pump with R410A as a baseline along with potential alternatives DR-55, DR-5A (R454B), and R32.  An adjustable frequency drive (AFD) was installed to allow the same capacity to be achieved with each refrigerant, matching compressor capacity to heat exchanger capacity.  Adjustable thermal expansion valves (TXVs) were installed to achieve the same compressor suction superheats in each case. 

Measurements of performance at the AHRI Standard 210/240 rating points were made with each refrigerant.  In addition, tests were run under outdoor temperatures ranging from 65F to 125F (18C to 52C).  A simple thermodynamic cycle model that matches average saturation temperatures in the evaporator and condenser along with a common compressor isentropic efficiency indicates that the capacity with DR-55 should be 2.5% lower than with R410A and should have an efficiency 1% higher.  Actual performance with DR-55 matched the capacity of R410A at the same compressor speed (60 Hz) with an efficiency 4% higher.  Similarly positive results were obtained with DR-5A.  With R32, the compressor speed needed to be reduced to 53 Hz to match the baseline capacity.  Efficiency was 3% higher than baseline.  As expected, R32 produced compressor discharge temperatures (CDTs) that were elevated by 20F and increased to 40F at the higher ambient conditions over R410A while DR-55 and DR-5A CDTs were only 10F above the baseline.  

The results here demonstrate that DR-55 and DR-5A are "design compatible" alternatives to R410A.  That is, they can be used in existing equipment designs with very little modification.