R404A – the low GWP options

With European legislation sounding the death knell for R404A and other countries around the world likely to follow suit with similar bans on high GWP gases, what are the alternatives?

With its GWP of 3922, the highest of all the most common HFCs, the days of R404A have been numbered for some time. While it will be no mean feat to replace a refrigerant which is estimated to account for 46% of worldwide F-gas usage, its replacement will go a long way to meeting European F-gas reduction targets.

We recently looked at R407A, R407F and R442A, all potential retrofit blends for R404A, but while they might serve as a short to medium-term solution, their GWPs of around 2,000 means they may not be a long-term answer.

Thankfully, there are a number of other even lower GWP options. Supermarkets, one of the biggest users of R404A, are exploring natural options, particularly CO2, hydrocarbons, or CO2 in tandem with lower GWP HFCs or HFOs in cascade systems.

The world’s refrigerant producers also have options in development, testing and on the point of availability. These can mainly be broken down into two types: medium GWP, non-flammable, non-toxic blends and low GWP, non-toxic blends carrying the A2L “mildly flammable” rating.

In the first group are two refrigerants – R449A and R448A. Both are classed as A1, non-flammable and non-toxic and in many ways the blends are similar.

R449A was developed by DuPont as DR33 and now carries the trade name Opteon XP40. A replacement for R404A and R507A, it is a blend of R32 (24.3%), R125 (24.7%), R1234yf (25.3%) and R134a (25.7%) with a GWP of 1397.

R448A is Honeywell’s option, sold under the trade name Solstice N40. It uses the same components as DuPont’s R449A with the addition of a small amount of R1234ze(E). Its composition is R32 (26%), R125 (26%), R1234yf (20%), R134a (21%) and 1234ze(E) (7%).

Due to their similar compositions, the two refrigerants are likely to be close matches in performance. Both have been undergoing tests with equipment manufacturers and are being added to the recently published ANSI/ASHRAE Standard 34-2013.

As well as being suitable for new equipment, with their pressures, temperatures, and performance being close to R404A, they could work as retrofits (with minor modifications, such as valve  adjustments).

Leading compressor manufacturer Emerson has tested Honeywell’s N40 (R448A) in a  supermarket simulation laboratory and found that it performed as well or better than R404A.  At the time of writing Emerson had not tested Honeywell’s DR33 but Rajan Rajendran, vice president of engineering services and sustainability at Emerson Climate Technologies, confirmed that they expected DR33 to be a very close match in performance.

Emerson’s results (below) from tests with R448A in a centralised DX system with cases and food simulators and air-cooled condensers 

The LT rack was equipped with Emerson Scroll compressors: ZF25, ZF34, ZFD41 (Digital)
MT rack equipped with scroll compressors: ZB95, ZBD76 (Digital) 

DuPont tests with R449A

DuPont carried out separate comparative tests using R449A and R404A on a 2.5m open frozen food display case (right) designed for R404A and fully loaded with food simulator.

The condensing unit was using a reciprocating compressor with POE 32 oil and a refrigerant charge of around 3.8 kg, adjusted based on liquid density.

Tests were carried out to ASHRAE Standard 72-2005 at two ambient temperatures: 28ºC and 35ºC.

Only minor adjustment were made to the expansion valve.

Average food simulator temp controlled at -16ºC, average evaporator temp -34ºC.

In the test results R449A showed 3-4% lower energy consumption with a similar pressure and compression ratio to R404A. There was a modest increase in discharge temperature and slightly lower mass flow rate

The results are below:

Low GWP options

Further up the environmental scale are two refrigerants with GWPs under 300. However, as previously mentioned, their A2L “mildly flammable” rating will currently limit their use to smaller charge systems. Also, in Europe, under the new F-gas rules they will not be able to be used in hermetically sealed systems from January 2022 when the GWP limit for that type of product will drop to 150.

Again, Honeywell and DuPont are the front runners with these gases, although other manufacturers are working on options.

Honeywell’s offering is L40 – a blend of 40% R32, 10% R152a, 20% R1234yf and 30% R1234ze(E) with a GWP of 285.

DuPont’s development blend is DR7. Possessing a slightly lower GWP of  around 250, DR7 is a simpler blend of 36% R32 and 64% R1234yf.

Emerson has tested both L40 and DR7 in reach-in types of equipment and compared them with the same units running on R404A.

The test was carried out to ASHRAE 72 in a steady state with no cycling or door openings. The only changes between tests were adjustment to the refrigerant charge amounts and the expansion valve settings.

The room ambient was 23.9⁰C (75⁰F) and reach-in air temperature -17.8⁰C  (0⁰F) with product simulators loaded.

Both blends refrigerants were found to be more efficient than R404A with DR7 showing higher capacity compared to L40.

Emerson notes that the unit was not designed or optimised for the new refrigerants.

DuPont has also carried out tests with DR7 and DR33 in a 1.5m³ double-door reach-in freezer unit designed for R404A. Average freezer compartment temperature was controlled at -17ºC and average evaporator temp was -28ºC. Tests were carried out at three ambient temperatures: 32ºC, 24ºC and 21ºC.

Again, as can be seen on the  right, the refrigerants returned impressive results in an un-optimised piece of equipment.