Tests were carried out on a 14kW Trane Precedent rooftop unit

USA: Further tests of low GWP alternatives to R410A in air conditioners have again shown good results at high ambients.

The latest results, from phase ll of AHRI’s Low-GWP Alternative Refrigerants Evaluation Programme, compared the performance of R32 and Chemours’ development refrigerants DR-55 and DR-5A in soft optimisation tests against baseline R410A.

The three alternatives all offer considerable lower GWPs compared to R410A’s GWP of 2088. R32 has a GWP of 675, DR-5A slightly higher at 698 and DR-55 the lowest of the three at 466. All are A2L “mildly flammable” gases but Chemours has recently claimed that DR-55 has a lower burning velocity than the other two.

The latest tests were performed on a Trane Precedent 14 kW rooftop heat pump at Ingersoll Rand/Trane’s La Crosse Development Laboratory in La Crosse, Wisconsin.

The unit was run at the rating conditions specified in AHRI Standard 210/240 for both cooling and heating modes. In addition, the unit was run in cooling mode at ambient temperatures from 18°C to 52°C.

Cooling Post - humiDisk banner 300px x 250px - 20.07.2015The original factory-installed fixed TXVs for cooling and heating were both replaced with adjustable TXVs of the same size. Additionally, a variable frequency drive was installed to allow the compressor speed to be varied so that all refrigerants could be tested at the same capacity.

DR-55 and DR-5A were found to be near design-compatible alternatives to R410A in terms of capacity while providing improved efficiencies of ~4.5% at the A-rating conditions (26.7°C dry bulb/19.4°C wet bulb indoor and 35°C outdoor) and ~3% at the B-rating (27.8°C ambient) conditions.

Cyclic testing suggested DR-55 and DR-5A offer additional benefits over R410A during transient operation. Both showed less capacity loss (0% to +3%) and efficiency (+4% to +7%) compared with R410A at high ambient temperatures. Compressor discharge temperatures increased only modestly (-12.2 to -11.1ºC) up to 52°C ambient.

R32 required an 8.5% reduction in compressor speed to match R410A’s cooling capacity at the A-rating conditions. R32 produced an EER nearly 6% higher than R410A at the A conditions and ~4.5% better at the B conditions.

The single component refrigerant, currently being adopted by many Japanese air conditioning manufacturers, performed similar to DR-55 and DR-5A at high ambient temperatures with respect to capacity. However, R32’s efficiency appeared to drop off above 43°C ambient. As the test team expected, R32 exhibited a significantly increased compressor discharge temperature, starting 11°C above R410A at 18°C ambient, increasing to +15°C at 35°C ambient, and then increasing more rapidly to +24°C at 49°C ambient at which point the unit’s maximum discharge temperature limit of 121°C prevented operation.

The full report can be viewed and downloaded here.

Related stories:

DR-55 is 5% better as drop-in – September 16, 2015
USA: Chemours R410A replacement DR-55 is reported to have performed well in high ambient drop-in tests on a R410A rooftop air conditioner. Read more…

Is DR-55 best option to replace R410A? – September 2, 2015
USA: Chemours has unveiled further details of a new refrigerant blend to rival R32 in the search for a lower GWP alternative to R410A in air conditioning systems. Read more…

R32 passes high ambient test – September 16, 2015
SAUDI ARABIA: Tests in Saudi Arabia have indicated that, as well as having better performance, R32 might be compatible with existing R410A air conditioners in high ambients. Read more…

R32 performs well in drop-in test – August 18, 2015
USA: The lower GWP refrigerant R32 is said to have shown similar performance to R410A in drop-in tests on a single-package vertical heat pump. Read more…