Oak-Ridge-alternative-studyUSA: The lower GWP refrigerant R444B has come out tops in a study of alternatives in R22 split air conditioners in high ambients.

The tests carried out by Oak Ridge National Laboratory (ORNL) on four lower GWP refrigerants found that, while none could match the baseline R22, R444B showed the least drop in capacity and performance. (This story has been updated (Nov 3, 2015), with latest figures here.) 

A key technical barrier to an HFC phase-down agreement is concern over the performance of the most commonly proposed low-GWP refrigerants at high ambients. Of particular concern is the performance degradation that lower-GWP refrigerants might experience at higher temperatures.

At least four test programmes are currently being conducted. The United Nations Environment Programme (UNEP) and the United Nations Industrial Development Organization (UNIDO) are running two separate programmes: PRAHA (Promoting Low-GWP Alternative Refrigerants in the Air Conditioning Industry for High-Ambient Conditions) and EGYPRA (Egyptian Programme for Promoting Low-GWP Refrigerants’ Alternatives ).

PRAHA was developed in association with several high-ambient-temperature nations and is evaluating purpose-built prototypes, while EGYPRA is based in Egypt and is also testing purpose-built prototypes.

Possibly best known is AREP, an industry-wide effort on alternative refrigerants run by AHRI. Though not primarily focused on high-ambient-temperature testing, the programme is conducting is focusing on high-ambient temperature conditions in its latest phase ll tests.

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The indoor air enthalpy tunnel connected to the data acquisition system

A further series of high ambient tests is being conducted by the US Department of Energy (DOE), in cooperation with Oak Ridge National Laboratory (ORNL). Equipment manufacturer Carrier, international refrigerant suppliers, and technical experts from various countries are also participating.

ORNL’s objective is to assess whether it is possible to achieve similar or better energy efficiency and cooling capacity in mini-split air conditioners with low-GWP refrigerants compared to current baseline refrigerants such as R22 and R410A.

This interim report describes tests carried out so far of four alternative refrigerants compared to R22. Tests still to be completed include comparisons of the performance of five R410A alternatives as well as testing propane against R22.

The R22 tests involve refrigerants from Chemours, Honeywell and Arkema. The Chemour’s gas is development blend DR-3, an A2L gas with a GWP under 150 and a 7K glide. The Honeywell refrigerants under test are N-20B, an HFO blend, and R-444B, developed by Honeywell as Solstice L20 with a GWP under 350 composed of 41.5% R32, 10% R152a and 48.5% R1234ze(E). The remaining refrigerant is Arkema’s ARM-20B, which is thought to have a GWP of around 250.

ORNL also tested DR-93, a Chemours non-flammable refrigerant with a higher GWP (1258) than the five primary alternatives but whose results were thought to provide useful insights.

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Test results at moderate ambient temperatures

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Test results at high ambient temperatures

The Carrier R22 unit had a cooling capacity of 5.25kW with a COP of 2.78, equivalent to an EER of 9.5.

Each of the alternative refrigerants was found to deliver lower performance than R22, both in terms of COP and cooling capacity, but this was expected in a unit designed for R22 and soft optimised. Efficiency and capacity results would be expected to improve in units manufactured and optimised for the specific refrigerant.

The ORNL test plan involved relatively few optimisations, but these included refrigerant charge optimisation, lubricant change, and capillary tube/flow control changes. Additional performance improvements would be expected through more thorough engineering design, including compressor and heat exchanger optimisation.

At the highest ambient-temperature test condition (“extreme” 55°C outdoor temperature), two alternative refrigerants demonstrated only modest performance degradation relative to R22. The highest performing refrigerant, R444B, had a COP 6.9% lower and a cooling capacity 3.7% lower than the baseline refrigerant.

In addition to the result of tests on the performance of propane in the R22 units, the final ORNL report paper will also include tests of five refrigerants as alternatives to R410A. These are the single component HFC refrigerant R32,  Arkema’s ARM-71A, Chemours’ DR-55, Honeywell’s L-41 (R-447A) and Mexichem’s HPR-2A.

Related stories:

R410A subs perform well at high ambients – October 8, 2015
USA: Further tests of low GWP alternatives to R410A in air conditioners have again shown good results at high ambients. 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…